NOAA Technical Memorandum NMFS NE 161
Demersal Fish and American Lobster Diets
in the Lower Hudson - Raritan Estuary
by Frank W. Steimle, Robert A. Pikanowski, Donald G. McMillan,
Christine A. Zetlin, and Stuart J. Wilk
National Marine Fisheries Serv., 74 Magruder Rd., Highlands, NJ 07732
Print
publication date November 2000;
web version posted April 30, 2002
Citation: Steimle FW, Pikanowski RA, McMillan DG, Zetlin CA, Wilk SJ. 2000. Demersal
Fish and American Lobster Diets
in the Lower Hudson - Raritan Estuary. US Dep Commer, NOAA Tech Memo NMFS NE 161; 106 p.
Download complete PDF/print version
Abstract
Characterizing the demersal fish food web in the Hudson-Raritan
Estuary is important for understanding specifically how this estuary
is used by fishery resources. Knowledge of fish food webs and essential
fish forage resources of the estuary can support habitat management decisions.
Little is known about diets of the community of fish and the American
lobster (Homarus americanus) that inhabit this estuary, although
it is a major estuarine complex in the Northeast that continues to support
fisheries. To gain insight into trophic and habitat functions in this
estuary, the diets of the most abundant demersal fish species and the
American lobster were examined. These predators were collected by trawl
in various parts of the Hudson-Raritan Estuary over six seasons, July
1996 through November 1997.The most widely preyed-upon taxa were crustaceans,
such as: small or juvenile decapods (e.g., sevenspine bay or sand
shrimp (Crangon septemspinosa), hermit crabs (Pagurus spp.),
juvenile Atlantic rock crabs (Cancer irroratus), lady crabs (Ovalipes
ocellatus), and mud crabs (Xanthidae)); the mysid Neomysis americana;
and several amphipod species. Clam siphons, primarily from the northern
quahog (Mercenaria mercenaria) and Atlantic surfclam (Spisula
solidissima), were commonly preyed upon by winter flounder (Pseudopleuronectes
americanus), as well as by scup (Stenotomus chrysops) and
spot (Leiostomus xanthurus) during some seasons. The diets of
common fish and the American lobster in the human-stressed Hudson-Raritan
Estuary are similar to those in other, less-stressed estuaries in the
Middle Atlantic Bight.
INTRODUCTION
The
Lower Hudson-Raritan Estuary (hereafter, the Estuary), located at the
mouths of the Hudson, Raritan, and Navesink-Shrewsbury Rivers (New Jersey
- New York), is the polyhaline part of a major, urban, estuarine complex
in the Northeast. The Estuary has supported diverse and productive commercial
and recreational fisheries (MacKenzie 1992). Many of these fisheries
are gone or operate at a reduced level because of low resource abundances,
harvest regulations, and/or habitat degradation.
The Estuary has been characterized as one of the most human-altered
on the East Coast (Wolfe et al. 1996). Although some sources of
habitat alteration or degradation in the Estuary (e.g., point-source
discharges and marsh filling) are being largely controlled through regulation,
other sources (e.g., nonpoint-source discharges and toxic substance
spills) continue with little effective control, and new activities have
the potential for adverse effects (Palermo et al.1998). Despite
these alterations, the Estuary is still used by a diversity of aquatic
species (Wilk et al.1998).
To conserve and restore the Estuary's fishery resources, there is a
need for community- or ecosystem-level information on the status and
function of the Estuary's various habitats and associated species to
provide advice for policy decisions on conflicting uses of the Estuary.
Characterizing fish and American lobster diets in the Estuary is critical
for understanding the value and habitat sources of various prey taxa
in the estuarine food web. Knowledge of food webs and key predator-prey
relationships is important for habitat-use policy development (Hartman
and Brandt 1995).
Although broadscale trophodynamic studies have been conducted in many
other Middle Atlantic Bight estuaries, e.g., Long Island Sound
(Richards 1963), central New Jersey (Festa 1979), Delaware Bay (de Sylva et
al.1962), and Chesapeake Bay (Homer and Boynton 1978), as well as
offshore in the New York Bight (e.g., Sedberry 1983; Bowman et
al.1987), the Hudson-Raritan Estuary has never had such an effort.
Only the middle Hudson River part of the Estuary (near Indian Point,
New York) has received attention for general dietary analysis (Gladden et
al.1988), although there have been focused dietary analyses of a
few species such as striped bass (Morone saxatilus) and juvenile
bluefish (Pomatomus saltatrix). Also, Stehlik et al.(in
preparation) examined the diets of several species of crabs within Raritan
Bay, which complements the present study. Little else has been reported
on the diets of the demersal fishery resource community of the Estuary,
except for some brief incidental or anecdotal observations (Hall 1894;
Merrill 1904; Breder 1922b; NJDEP 1975; Lynch et al.1977; Lawler,
Matusky & Skelly Engineers 1980; Conover et al.1985).
To address this information deficiency, we report on the results of
a seasonal study of the diets of common demersal fish species and the
American lobster (Homarus americanus) collected in various parts
of the Estuary. This study is roughly modeled on Festa's (1979) study
for a shallow, south New Jersey estuary, and is intended to complement
that effort, as well as the cursory dietary information in Able and Fahay
(1998). These results are also compared to a comprehensive summary of
most other dietary studies for the same predators in other Middle Atlantic
Bight estuarine or coastal areas. A brief summary of the life history
and habitat of major prey is also included because many of the habitat
issues that managers have to deal with involve potential perturbations
to the health and availability of common prey. This report is intended
to be a ready source of trophic and habitat-use information for subtidal
habitat management within this estuary.
METHODS
The
strata and blocks (areas) that were sampled to collect fish and American
lobster for stomach content analysis covered most of the Estuary (Figure 1), but were restricted to depths greater than 3.0 m because of survey
vessel operational factors. The habitat characteristics of these strata
are summarized in Table 1.
Six seasonal sampling periods were used to collect specimens for diet
analysis: 1) July 8-12, 1996; 2) October 7-10, 1996; 3) January 27-30,
1997; 4) April 22-29, 1997; 5) August 18-28, 1997; and 6) November 17-20,
1997. In addition, a special collection of scup (Stenotomus chrysops)
was made during June 9-11, 1997; data on scup from that collection are
included in the August 18-28, 1997, sampling period. For each sampling
period, approximately 40 blocks were randomly selected from about 200
possible blocks within the nine sampling strata.
Fish and American lobster samples were collected by a semiballoon otter
trawl that had a 8.5-m headrope, 10.4-m footrope, 10.2-cm stretch-mesh
nylon net, and a 3.5-cm stretch-mesh liner in the cod end. This trawl
was towed for 15 min at ~3.7 km/hr (2 knots). Hydrographic data (i.e.,
depth, salinity, temperature, and dissolved oxygen) were collected after
each successful tow using a "Hydrolab Surveyor 4" multisensor.
[Use of trade names is for information only, and does not represent endorsement
by NMFS.] Details of the overall trawl survey are available in Wilk et
al.(1998).
After the trawl was retrieved, the catch was sorted to species, weighed
(g), and measured (0.1 cm). Then, up to about 10-15 specimens of each
nonplanktivorous fish species were selected for analyses, as available.
If available, additional samples were also collected for each apparent
size class of a species. As feasible, the stomachs of large fish such
as skates, dogfishes, and adult striped bass were examined in the field,
or the eviscerated stomachs of such fish were placed individually in
labeled plastic bags and quickly frozen. Small specimens were also bagged
and frozen whole for later laboratory analysis.
To examine the diets in the field or laboratory, the contents of each
stomach were carefully emptied onto a gridded petri dish. The total stomach
bolus volume was visually estimated by a side-by-side comparison with
a set of variable-diameter, volume-calibrated (cm3) cylinders.
The bolus was separated and examined (by dissecting microscope, if necessary),
then the stomach items or prey were segregated into the lowest identifiable
taxon, counted, and measured for length (if possible), and finally, the
proportion of each prey taxon or other item to the total stomach volume
was estimated visually using the petri dish grid. Items or prey were
identified to the lowest level practical using numerous taxonomic references, e.g.,
Bigelow and Schroeder (1953), Gosner (1973), and Weiss (1995). The findings
of clam siphons in winter flounder (Pseudopleuronectes americanus)
and a few other predators prompted the collection of whole specimens
of larger bivalve mollusks which commonly occurred in the area in order
to examine their siphons for characteristics that could identify the
specific source of the siphons that were found in the stomachs. These
characteristics were used to develop a rough guide to siphons to improve
the level of prey species identification.
The young-of-the-year (YOY) stages of most fish species (either as
predator or prey) examined in the analyses were identified mostly using
Bigelow and Schroeder (1953), Fitz and Daiber (1963), and a prepublication
draft of Able and Fahay (1998). The transition lengths at 50% maturity,
used to segregate juvenile and adults of certain fish species as part
of the diet analysis, were based on O'Brien et al. (1993).
A literature review of target predator diets in the coastal Middle
Atlantic Bight, the area between Cape Cod and Cape Hatteras, was used
to create summary tables of the diet of each predator for comparison
with results of the present study. In these tables, prey were listed
by their relative overall importance using several ranking metrics, as
available from the document source: mean percent frequency of occurrence
(FO), mean percent contribution to total stomach content volume (TV),
mean percent contribution to total stomach content weight (TW), mean
percent contribution to total stomach content dry weight (TDW), mean
percent contribution to total number of individual items in the stomach
(TN), and an index of relative importance (IRI; FO x TV, or, FO x TW).
Those comparative data available as FO and TV are the same as those used
in the present study. The two "fresh condition" variables of
TV and TW are nearly equivalent (i.e., 1 g of prey as "fresh" weight
approximates 1 cm3 of prey as "fresh" volume) for
most prey such as crustaceans, polychaetes, fish, shell-less mollusk
meat, etc., but not for heavy-shelled prey (e.g., sand dollars
and mollusks in the shell) consumed whole (Steimle et al.1994).
Our results for diets focus on dominant prey used by predators found
in the Estuary. Dominant prey are generally defined as those contributing
five or more percent to total stomach content volume, but prey of fishery
management significance, such as juvenile fishery species, are also noted.
The results are also presented in the order of predator sample abundance.
For each predator, the results of this study are followed by the summary
of the results of other studies for comparative purposes. Because of
the relatively large number of predators considered in this predator-community-focused
report, this strategy of reporting by predator sample abundance keeps
relevant information together for each predator, and should be most convenient
to users of this report. Summaries focused on common prey, with a brief
review of their life history and habitat associations, are also presented.
RESULTS AND DISCUSSION
DIETS
Winter Flounder (Pseudopleuronectes americanus)
Hudson-Raritan Estuary Results
This species is a common, year-round inhabitant of the Estuary, and
was collected in a range of sizes (6.1-45.0 cm total length (TL), mean
of 20.0 cm) and strata, except in the central and coastal parts of Lower
Bay, Stratum 3 (Figure 2). The 710 winter
flounder which were examined ate 80 distinct, identifiable prey taxa,
although only about 20 benthic invertebrates occurred at a relatively
high FO. Endobenthic and epibenthic polychaetes (21+ species), amphipods
(14+ species), and mollusks (10+ species) dominated the diet. This flounder
also ate a range of food types, from plant detritus to algae to tunicates,
including planktonic copepods (e.g., Pseudodiaptomus coronatus),
suprabenthic mysids and the amphipod Gammarus lawrencianus, as
well as the epibenthic and endobenthic invertebrates. Typically, smaller
species, earlier life stages, and/or fragments of larger benthic species
were eaten. Some larger bivalve mollusks, e.g., northern quahogs
(Mercenaria mercenaria) and Atlantic surfclams (Spisula solidissima),
were important in the diet, but only their siphons were nipped or torn
off by this nearly toothless predator. The blue mussels (Mytilus edulis)
that were found in the diet, e.g., during April 1997 (Table
2a), were all spat less than 1 cm in length. The decapod crabs that
were eaten Atlantic rock crab (Cancer irroratus), blue crab (Callinectes
sapidus), lady crab (Ovalipes ocellatus), and Libinia sp.
were all juveniles. A diversity of tube-dwelling amphipods were also
eaten, especially Ampelisca abdita. Although several polychaete
species were identified as being eaten, only the tube-dwelling Asabellides
oculata and Sabellaria vulgaris, and the blood worm Glycera sp.,
were relatively common in the diet, i.e., occurring in the top
20 prey ranked by FO (Table 2a). The percentage
of empty stomachs that were found ranged from 2.9% in April 1997 to 42.2%
in January 1997; this variable generally ranged between 6.7 and 16.9%
for other sampling periods (Table 2a).
Unidentified organic matter (i.e., detritus) ranked as the most
frequently occurring diet item, followed by northern quahog siphons, Ampelisca
abdita, Atlantic surfclam siphons, and unidentified polychaetes or
their fragments (Table 2a). The TV of prey
or prey type for all samples was again dominated by unidentified organic
matter, Atlantic surfclam and northern quahog siphons,
the mysid Neomysis americanus (hereafter, "Neomysis"),
unidentified clam siphons, A. abdita, and unidentified polychaetes
(Table 2a). Other prey individually represented
a TV of less than 3%. As with FO, there was a high degree of intersample
variability (Table 2a).
For most prey, there were only small seasonal variations in the degree
of their use by winter flounder, but for some prey, there were obvious
differences. For example, there was minimal use of clam siphons during
January 1997 (Table 2a). At the same time,
there was increased use of Neomysis and nemerteans. Seasonal predation
peaks for other prey varied annually, i.e., there was relatively
high predation during one summer sampling, but not the other summer sampling,
covered in this survey (e.g., predation on juvenile Atlantic rock
crabs and Asabellides oculata; see Table
2a).
Other prey or items found in winter flounder stomachs in lesser quantities
were: green and red algae; anthozoans; nematodes; bryozoans; gastropods (juvenile Crepidula sp., Lacuna
vincta, Epitonium sp., Astyris lunata, and Nassarius
trivittatus); bivalve mollusks (Solemya velum, Nucula sp., Mulinia
lateralis, Tellina agilis, softshell (Mya arenaria)
siphons, and Lyonsia hyalina); polychaetes (Phyllodoce sp., Eteone sp.,
unidentified polynoids, Nephtys sp., Nereis succinea, N.
grayi, Nereis sp., unidentified capitellids, Asychis elongata, Clymenella
torquata, Spiochaetopterus oculatus, Sabellaria vulgaris, Diopatra
cuprea, Lumbrineris sp., Arabella iricolor, Pectinaria
gouldii, Melinna cristata, Nicolea venustula, and Pherusa
affinis); arachnids (juvenile Limulus polyphemus); copepods (unidentified
calanoids, harpacticoids, and cyclopoids, and the calanoid Pseudodiaptomus
coronatus); cumaceans (Diastylis sp.); tanaids (unidentified); isopods (Edotea
triloba and Cyathura sp.); amphipods (Lembos websteri, Ericthonius sp., Gammarus sp., Jassa
falcata, Hippomedon serratus, Orchomenella sp., Photis sp., Phoxocephalus
holbolli, Stenothoe sp., and Parametopella sp. (cypris?)); mysids (Heteromysis
formosa); decapod crustaceans (Pagurus sp., P. longicarpus,
xanthids (Dyspanopeus?), juvenile blue crabs, juvenile Libinia sp.,
and juvenile Ovalipes ocellatus); echinoderms (juvenile Echinarachnius
parma); tunicates (Molgula sp.); and sand, shell hash,
organic detritus, and manmade artifacts such as coal granules and synthetic
fibers.
Winter flounder diet changed with size/growth. This shift in use of
common prey was generally from small crustaceans (mysids and amphipods),
polychaetes, and detritus by smaller fish, to more bivalve mollusk siphons
by larger fish (Table 2b). Winter flounder
diet was examined for seasonal shifts in prey use as related to flounder
size and maturity. Because of small sample sizes for each of the four
size groups portrayed in Table 2b, the
samples were pooled into two groups: juvenile (less than 20 cm TL; Table
2c) and adult (greater than or equal to 20 cm TL; Table
2d). In the summer-fall, juvenile winter flounder focused their feeding
on northern quahog and Atlantic surfclam siphons, an amphipod (i.e., Ampelisca
abdita or A. vadorum), a tube-dwelling polychaete (Sabellaria
vulgaris), and detritus, although Neomysis became important
as prey in the winter (Table 2c). Other
prey were relatively evenly used during most seasons or showed no seasonal
pattern of use. For adults, the list of commonly eaten prey was condensed,
with only four distinct prey being notable, and seasonal sample sizes
were more irregular and often inadequate (Table
2d). Again, clam siphons were the dominant prey. The large bloodworm Glycera sp.
and juvenile Atlantic rock crabs were the only other prey with any seasonal
peaks.
Some studies of the winter flounder diet have shown that the diet closely
reflects environmental conditions and prey availability in the areas
in which the fish are collected (Frame 1974; MacPhee 1969). The winter
flounder diet in this study also showed differences in prey use that
varied among sampling strata, although sample sizes were small for some
strata, particularly for the channel habitats, Strata 7-9 (Table
2e, Table 2f). Some prey (e.g., Glycera sp.)
were eaten in similar proportion by juveniles and adults from the same
strata areas of the Estuary. Other prey (e.g., Neomysis, Crangon
septemspinosa (hereafter, "Crangon"), and Gammarus sp.)
were found in stomachs of juveniles or adults, but not both. The prey
of juvenile winter flounder among different strata suggest no habitat-related
patterns (Table 2e). There was no specific
association of prey with channels (Strata 7-9), nor with the western
or eastern areas, with the possible exception of the polychaetes Glycera sp.
and Sabellaria vulgaris and northern quahog siphons in the western
Strata 1-3, and Atlantic surfclam siphons in eastern Strata 4 and 6 (Table
2e). Predation by juveniles and adults on northern quahog siphons
appears restricted to less-saline, western Strata 1-3 and 6, and predation
on Atlantic surfclam siphons occurs in marine eastern Strata 4 and 5
and in channel Strata 7 and 8, as might be expected from the Atlantic
surfclam's salinity preferences.
Comparisons with Other Diet Studies
Other winter flounder dietary studies in and near the Estuary, or within
the coastal Middle Atlantic Bight, found a similar diet to that reported
here, i.e., opportunistic predation on benthic invertebrate macrofauna,
especially polychaetes and amphipods, and on zooplankton by the smallest
winter flounder sizes (Table 3). However,
there was an unusually high degree of molluscan siphon nipping in this
estuary compared to what has been reported elsewhere (Table 2 & Table 3; Lawler, Matusky & Skelly
Engineers 1980; Stehlik and Meise 2000). A lesser degree of molluscan
siphon nipping by winter flounder has been also reported in Canada (Medcoff
and McPhail 1952), Cape Cod Bay (Gilbert and Suchow 1977), Long Island
Sound (Carlson 1991), and near Woods Hole, Massachusetts (Frame 1974;
Lux et al.1996), and in a few other studies (Table
3), however. It has been assumed that this siphon nipping is nonlethal
to the mollusks, which can be fishery resources in their own right, and
that the siphons regenerate (Irlandi and Mehlich 1996).
Windowpane (Scophthalmus
aquosus)
Hudson-Raritan Estuary Results
Windowpane from YOY to adult (range of 2.5-35.0 cm TL, mean of 20.7
cm) are a year-round inhabitant of this estuary. Five hundred seventy
windowpane were examined from all areas, although slightly greater quantities
were available from the channels, especially in and near Raritan Channel,
Stratum 9 (Figure 3). At least 37 prey taxa
were identified in their diet. This prey spectrum included two mysid
species, three or more decapod crustacean species, seven amphipod species,
two or more copepod species, eight mollusk species, nine identifiable
species of larval or juvenile fish, and some miscellaneous, nonprey items
(green algae to coal fragments). This prey spectrum included a mix of
benthic, suprabenthic, and pelagic species.
Despite the overall diversity of prey consumed, windowpane have a relatively
focused diet. By FO for all samples, Neomysis was the dominant
prey at 65.9% (range of 33.7-93.3%). It was followed in importance by Crangon at
31.7% (range of 23.6-53.0%) and the suprabenthic amphipod Gammarus
lawrencianus at 9.5% (range of 0.8-39.0%). The other prey were eaten
at a low FO (i.e., less than 5%). The percentage of empty stomachs
ranged from 2.0% in July 1996 to 33.7% in January 1997, and was between
10 and 24% in other sampling periods (Table 4a).
The TV paralleled the FO. Neomysis made up 57.1% of the overall
diet by TV (range of 17.8-70.1%), with Crangon contributing 29%
(range of 21.3-47.7%). Most other prey individually represented less
than 0.1% of TV, although higher values occurred during some sampling
periods (Table 4a).
Other prey or items found in windowpane stomachs in lesser quantities
were: green algae; hydroids; nemerteans; gastropods (Lacuna
vincta, juvenile Crepidula sp., Nassarius trivittatus,
and Astyris lunata); bivalve mollusks (Mulinia lateralis, Nucula sp.,
unidentified, and blue mussel spat); cephalopods (unidentified
squid); polychaetes (unidentified); copepods (unidentified); cumaceans (unidentified); amphipods (Corophium sp., Jassa
falcata, Stenothoe sp., Hippomedon serratus, and Unciola sp.); mysids (Heteromysis
formosa); decapod crustaceans (Pagurus longicarpus, Palaemonetes
vulgaris, and unidentified zoea); fish (unidentified juvenile
flounder, unidentified juvenile fish, juvenile Atlantic menhaden (Brevoortia
tyrannus), juvenile herring (Alosa), juvenile red hake (Urophycis
chuss), juvenile cunner (Tautogolabrus adspersus), Menidia sp.,
juvenile Atlantic croaker (Micropogonias undulatus), and juvenile
sand lance (Ammodytes sp.)); and sand and coal pebbles.
There was seasonal variability in the consumption of some prey (e.g.,
the use of Neomysis peaked during the summer). The use of Crangon peaked
in the winter-spring, although it was a major prey in July 1996 samples
(Table 4a). G. lawrencianus was mostly
consumed in the fall, especially in 1996, as was the red copepod Pseudodiaptomus
coronatus.
There was a clear shift evident in prey use with windowpane growth
(e.g., from Neomysis as overwhelmingly dominant for windowpane
less than 20.0 cm TL, to Crangon for windowpane at larger sizes,
although Neomysis was dominant at all sizes (Table
4b). Small fish (e.g., Anchoa sp.) also become more
important for the larger-sized fish.
The results suggest some differences in prey use among strata and regions
(Table 4c). Neomysis seems to be
the basic prey in the Ambrose Channel to Verrazano Narrows area (Strata
6 and 7). Crangon, on the other hand, seems to be more often eaten
in the central-western areas of the Estuary (i.e., Strata 2, 3,
8, and 9). Other prey constituted an insignificant proportion (a TV of
less than 10%) of the diet in most areas, except in Strata 4 and 5 (the
marine shoals) where small or juvenile fish were eaten. Windowpane abundances
were highest in channels (Figure 3) where Neomysis might
be most abundant; see the "Forage Base" section for a discussion
of the habitat of Neomysis.
Comparisons with Other Diet Studies
No previous focused studies of the diet of this species are known for
this estuary, although Breder (1922b) commented that stomach contents
of a few specimens that he examined "consisted of crustacean remains,
probably schizopods [mysids]." In general, other studies of the
diet of this species in the Middle Atlantic Bight found mysids (especially Neomysis), Crangon,
and "nekton" (i.e., small fish and squid) to be primary
prey (Table 5), but smaller-sized windowpane
also ate copepods. For the continental shelf, Langton and Bowman (1981)
reported 40-60% of the windowpane that they had examined had empty stomachs,
but mysids and shrimp continued to dominate the diet offshore. The results
of the present study are consistent with those of other studies and with
Bigelow and Schroeder's (1953) general summary of the diet, except for
the relatively high use of G. lawrencianus as prey in the present
study.
Little
Skate (Raja erinacea)
Hudson-Raritan Estuary Results
Little skate (mostly adults) were commonly found throughout this estuary
during most seasons, except the summer (Figure
4; Wilk et al.1998). The stomachs of 332 little skate (range
of 33.0-49.0 cm TL, mean of 43.2 cm) were examined. Over 50 prey taxa
or items, which ranged from green algae to a variety of small fish, were
identified in the little skate diet. These prey taxa included 11 decapod
crustaceans, 6 amphipods, 5 polychaetes, 8 mollusks, 10 identifiable
fish, and miscellaneous prey or items (Table 6).
The most frequently found prey, overall, was Crangon at an FO
of 82.8% (range of 77.2-92.9%). This prey was followed by juvenile or
small Atlantic rock crabs at an FO of 49.5% (range of 7.1-75.3%), which
were often found in a soft-shell stage, then by Neomysis at an
FO of 16.3% (range of 6.1-28.5%) and Ovalipes ocellatus at an
FO of 10.9% (range of 1.2-36.4%). The remaining prey had overall FOs
of less than 10% (Table 6), with few empty
stomachs.
The TV parallels the FO, with Crangon having 29.6% (range of
20.3-90.1%) of the TV, Atlantic rock crabs having 18.6% (range of 4.7-38.1%),
and other prey having less than 10%, with the exception of the October
1996 sampling period when O. ocellatus had 15.6% (Table
6). A number of juvenile blue crabs were also eaten (Table
6).
Other prey or items found in little skate stomachs in lesser quantities
were: unidentified green algae; hydroids; nematodes; nemerteans; gastropods (Lacuna
vincta, Nassarius trivittatus, and Astyris lunata); bivalve
mollusks (blue mussels, Mulinia lateralis, northern quahog
siphons, and unidentified); polychaetes (Lumbrineris sp., Spiochaetopterus
oculatus, Arabella iricolor, Pherusa affinis, Diopatra
cuprea, and unidentified); copepods (Pseudodiaptomus coronatus); cumaceans (unidentified); isopods (Cirolana
concharum, and Cyathura sp.); amphipods (Leptocheirus
pinguis, Hippomedon serratus, Unciola sp., Ampelisca
abdita, and unidentified); decapod crustaceans (unidentified,
xanthids, Pagurus pollicaris, P. longicarpus, Palaemonetes
vulgaris, Dichelopandalus leptocerus, and Axius serratus); stomatopods (Squilla
empusa); fish (Raja sp. egg case fragments, juvenile
rock gunnel (Pholis gunnellus), juvenile windowpane, northern
searobin (Prionotus carolinus), unidentified searobins,
sand lance, smallmouth flounder (Etropus microstomus), goby (Gobiosoma sp.),
northern pipefish (Syngnathus fuscus), juvenile red hake, juvenile
winter flounder, and juvenile silver hake (Merluccius bilinearis));
and sand, wood fragments, and human artifacts such as coal granules,
iron rust flakes, and plastic particles.
Although little skate tended to be most common in this estuary in the
cooler months, and sample sizes are relatively small in the summer, there
appears to be a possible predation emphasis on Atlantic rock crabs and Neomysis during
the cooler months (Table 6).
Comparisons with Other Diet Studies
No previous studies of the diet of this species are known for this
estuary. However, the diet of this species has been studied elsewhere,
both on the Middle Atlantic Bight continental shelf, and within other
bays and estuaries (Table 7). These studies
also show that small crustaceans dominate the little skate diet; with
skate less than 20.0 cm TL eating small crustaceans (e.g., copepods,
mysids, and amphipods such as Unciola irrorata, Gammarus annulatus,
Leptocheirus pinguis, and Monoculodes edwardsi), and with
larger skate eating more decapod crustaceans, especially Crangon, Cancer sp., Dichelopandalus
leptocerus, and hermit crabs (Pagurus sp.). However, squid
and small fish (e.g., sand lance, butterfish (Peprilus triacanthus), "herring" (Alosa sp.?),
searobins, juvenile flounder, and red hake) were also eaten (Table
7). The diet of little skate from the Estuary (Table
6) is consistent with these other study results, and with the general
dietary summaries reported in Nichols and Breder (1927) and Bigelow and
Schroeder (1953).
Scup (Stenotomus chrysops)
Hudson-Raritan Estuary Results
Scup, mostly juveniles, were found from spring through fall in the
Estuary and were relatively widespread in distribution, although with
a tendency to be collected more often in the northern areas (Figure
5). The stomachs of 254 scup (range of 8.0-24.0 cm FL, mean of 12.9
cm) were examined. At least 39 items or prey taxa were identified in
their stomachs, including 8 polychaetes, 7 amphipods, 6 decapod crustaceans,
6 mollusks, 2 mysids, and other taxa (e.g., hydroids). The majority
of these prey were benthic, except for mysids and Gammarus lawrencianus (Table 8).
The dominant items in the diet by FO were unidentified organic matter
at 35.8% (range of 21.3-46.1%), Neomysis at 32.3% (range of 17.3-50.0%),
bivalve mollusk remains at 14.3% (range of 1.3-26.7%), G. lawrencianus at
16.8% (range of 0.0-48.3%), Crangon at 15.2% (range of 3.9-30.7%),
unidentified polychaetes at 14.2% (range of 6.7-35.5%), and Ampelisca
abdita at 10.1% (range of 0.0-18.0%) (Table 8).
The contribution of prey to the overall TV parallels that to the overall
FO in the same order of contribution (Table 8).
There were few empty stomachs.
Other prey or items found in scup stomachs in lesser quantities were:
unidentified hydroids; unidentified nemerteans; gastropods (juvenile Crepidula sp.,
unidentified, and eggs); bivalve mollusks (Tellina agilis and Nucula sp.); polychaetes (Paranaites
speciosa, Asabellides oculata, Sabellaria vulgaris, Pectinaria
gouldii, Phyllodoce sp., Pherusa affinis, and Nereis sp.); copepods (Pseudodiaptomus
coronatus and unidentified calanoid); cirripeds (Balanus sp.); tanaids (unidentified); isopods (Cyathura sp.); amphipods (unidentified, Orchomenella sp., Photis sp.,
caprellids, Unciola sp., and Corophium sp.); mysids (Mysidopsis
bigelowi); decapod crustaceans (xanthid crabs, juvenile blue
crabs, and unidentified); and fish (silversides (Menidia sp.)
and unidentified).
There were few, notable, interannual or seasonal differences in the
diet of this basically warm-season species, with the possible exception
of predation on G. lawrencianus in 1996 that was not evident in
1997 (Table 8).
Comparisons with Other Diet Studies
Within this estuary, the only previous known data on the scup diet
is from the unpublished, preliminary 1976 results of the senior author,
who examined 13 juvenile fish from Strata 1, 3, and 4. He found that
the mostly frequently consumed prey were: the polychaete Asabellides
oculata and copepods in Sandy Hook Bay, polydorid polychaetes and
the dwarf surfclam Mulinia lateralis off Staten Island, and copepods
and blue mussel spat on Romer Shoal (Stratum 4).
Michelman (1988) found that the juvenile scup diet in Rhode Island
varied seasonally, but was still generally focused on benthic invertebrates,
such as polychaetes (e.g., maldanids, Nephtys sp., Nereis sp., and Pherusa
affinis), small decapod crustaceans (Pagurus sp. and other
crabs), Neomysis, amphipods (Leptocheirus pinguis and others),
as well as mollusks, a burrowing anemone (Ceriantheopsis americanus),
and fish eggs and larvae.
Most other studies found that scup less than 15 cm FL ate small invertebrates
such as copepods, polychaetes, amphipods, decapod crustaceans (especially
juvenile Atlantic rock crabs), and squid (Table
9); a number of qualitative or summary reports have found the same
(Baird 1873; Peck 1896; Nichols and Breder 1927; Hildebrand and Schroeder
1928; Bigelow and Schroeder 1953; Allen et al.1978). Linton (1901)
and Sedberry (1983) found that the diet of scup gradually shifted with
growth or size from small pelagic crustaceans to a variety of benthic
taxa. The results of the present study are basically consistent with
these other results, and show a strong reliance on benthic macrofauna
and detritus as prey.
Summer
Flounder (Paralichthys dentatus)
Hudson-Raritan Estuary Results
This species was most commonly collected during the summer and throughout
the Estuary, but especially along the New Jersey shore (Figure
6; Wilk et al.1998). The stomachs of 229 summer flounder (range
of 13.8-69.0 cm TL, mean of 36.0 cm) were examined. Over 35 prey species
or items were identified in their diet, including juvenile or small adults
of 12 species of fish, 5 species of decapod crustaceans, Neomysis,
and other taxa (Table 10). Crangon with
an FO of 49.5% (range of 34.4-78.0%) and Neomysis with an FO of
19.8% (range of 0.0-33.6%) were most frequently eaten. Unidentified fish
were next with an FO of 13.2% (range of 0.0-14.0%), and juvenile Ovalipes
ocellatus were prominent in the August 1997 stomach samples (Table
10).
The FO ranking was also followed by the TV ranking, with Crangon having
a TV of 29.4%, and Neomysis having a TV of 11.4% (Table
10). The percentage of empty stomachs ranged from 10 to 50%, with
the highest levels being found in the winter-spring period.
Other prey or items found in summer flounder stomachs in lesser quantities
were: unidentified algae; hydroids; bryozoans; gastropods (Crepidula
sp. and Nassarius trivittatus); bivalve mollusks (blue
mussel spat, Mulinia lateralis, Ensis directus, Nucula sp.,
and Tellina agilis); polychaetes (Sabellaria vulgaris and
unidentified); copepods (unidentified calanoid); isopods (Cyathura sp.); amphipods (caprellids, Gammarus
lawrencianus, and Ampelisca abdita); decapod crustaceans (juvenile
blue crabs, Pagurus longicarpus, and unidentified); and fish (juvenile
scup, cunner, rock gunnel, juvenile searobins, juvenile weakfish (Cynoscion
regalis), Menidia sp., juvenile striped searobin (Prionotus
evolans), juvenile black sea bass (Centropristis striata),
northern pipefish, juvenile Alosa herring, and juvenile grubby
(Myoxocephalus aenaeus)).
Summer flounder were mostly collected in the spring and summer (Table
10), so seasonal shift could not be examined. There were few notable
dietary differences between 1996 and 1997, although in 1997 summer
flounder made greater use of O. ocellatus and unidentifiable
juvenile flounder as prey. Most (85%) of the summer flounder examined
were 30 cm TL or more, and probably not YOY. Despite the small sample
size for YOY summer flounder, their diet differed little from that
of larger fish: Crangon and Neomysis dominated the diet,
with small Ovalipes and fish being of notable importance (Table
10).
With the number of samples being few (i.e., less than 30 samples
per stratum), and with the distribution of samples among strata being
small, the results of interstrata comparisons were inconclusive, although
there was a suggestion that Crangon were eaten commonly everywhere
except in the Romer Shoal and Ambrose Channel areas (Strata 4 and 7). Neomysis were
mostly found in stomachs examined from deeper channels (Strata 8 and
9) and near the Verrazano Narrows (Stratum 6), but also within Sandy
Hook Bay (Stratum 1). The latter observations perhaps reflected some
recent feeding in the unsampled Sandy Hook and Earl Naval Channels, located
between Strata 1, 2, and 4.
Comparisons with Other Diet Studies
No previous studies of the diet of this species are known for this
estuary.
In general, YOY summer flounder prey upon small fish (e.g., silversides,
mummichog (Fundulus heteroclitus), bay anchovy (Anchoa mitchilli),
and sticklebacks), and Palaemonetes, Crangon, and Neomysis shrimps
(Table 11). The species is highly opportunistic,
but its diet shifts ontogenetically, from small crustaceans at smaller
sizes, to fish prey at larger sizes. The diet of the predominantly YOY
and juvenile summer flounders examined in the Estuary, dominated by crustaceans
and small fish (Table 10), is consistent with
other studies (Table 11), and with the generalizations
of Hildebrand and Schroeder (1928), Ginsberg (1952), and Bigelow and
Schroeder (1953), which were often based on small or ambiguous sample
sizes.
Red Hake (Urophycis chuss)
Hudson-Raritan Estuary Results
Red hake were commonly collected in channels and the deep area below
the Verrazano Narrows (Gravesend Bay, Stratum 6; Figure
7) and during most seasons (Wilk et al.1998). The diet of
166 red hake (range of 4.3-39.0 cm TL, mean of 19.0 cm) was examined.
These fish were primarily juveniles and were most frequently collected
during cooler seasons. At least 33 prey species were identified in the
diet, including 7 decapod crustaceans, 9 amphipods, Neomysis,
7 juvenile fishes, and other taxa from algae to mollusks. Most prey were
benthic species.
Crangon with an FO of 77.6% (range of 56.3-100.0%), Neomysis with
an FO of 31.7% (range of 0.0-48.4%), Gammarus lawrencianus with
an FO of 20.9% (range of 0.0-100.0%), and unidentified organic detritus
with an FO of 10.6% (range of 0.0-20.6%) dominated the diet.
Crangon dominated the diet's TV at 39.0% (range of 23.3-50.0%),
followed again by Neomysis at 15.7% (range of 0.0-30.3%) (Table
12). The other prey were infrequently found in the stomachs, and
few stomachs were found empty. The inadequate samples in 1996 and during
warmer months (Table 12) prevent analysis
of seasonal or interannual variation in the diet of this species.
Other prey or items found in red hake stomachs in lesser quantities
were: green algae; hydroids; bivalve mollusks (Nucula sp., Tellina
agilis, blue mussel spat, and unidentified); polychaetes (unidentified
and Pherusa affinis); copepods (Pseudodiaptomus coronatus and
unidentified calanoid); isopods (Edotea triloba); amphipods (Phoxocephalus
holbolli, Unciola sp., Ampelisca abdita, Corophium sp., Jassa
falcata, Stenothoe sp., Hippomedon serratus, and unidentified); decapod
crustaceans (juvenile Libinia sp., Pagurus longicarpus,
juvenile Ovalipes ocellatus, Palaemonetes vulgaris, and
unidentified); fish (juvenile silver hake, juvenile red hake,
smallmouth flounder, juvenile searobin, juvenile weakfish, juvenile cunner,
unidentified juvenile flounder, and skate (Raja sp.) egg case
fragments); and wood fragments.
Comparisons with Other Diet Studies
The diet of red hake from the Estuary (Table
12) is consistent with other dietary studies for the species, with
crustaceans being primary prey. The only previous, quantitative study
of the diet of this species in Raritan Bay examined 45 subadults of
this species in spring 1976 within Sandy Hook Bay and off Staten Island
(Steimle, unpubl. data). That diet was dominated (i.e., a TV
of 92-100%) by Crangon. This result is consistent with Breder's
(1922b) earlier comment that the few red hake that he looked at in
Sandy Hook Bay in summer 1921 were "crammed full of large prawns";
these "prawns" were further defined as being Crangon in
Nichols and Breder (1927).
In the nearby New York Bight apex (outside the mouth of the Estuary),
over 1,000 red hake were examined and found to prey most commonly on Crangon,
various polychaetes (mostly Pherusa affinis and Nephtys incisa), Neomysis,
and benthic amphipods (Steimle 1985, 1994) (Table
13). Hildebrand and Schroeder (1928) observed that red hake that
were caught off Sandy Hook had gorged on sand lance. In general, the
summary of other studies (Table 13) and the
treatise by Bigelow and Schroeder (1953) show that juvenile red hake
eat a variety of small benthic and zooplanktonic invertebrates, but primarily
crustaceans. Steiner et al.(1982) reported that juvenile red hake
use shelter during the day (such as living sea scallops, Placopecten
magellanicus) and leave this shelter to feed at night. As red hake
grow, larger crustaceans such as decapods increase in importance in their
diet, and some fish are also eaten (Table 13).
Adult red hake were rarely collected within the Estuary (Wilk et al.1998).
Weakfish
(Cynoscion regalis)
Hudson-Raritan Estuary Results
Weakfish were another summer-fall inhabitant of the Estuary and were
collected mostly in or near channels, especially in Stratum 9, Raritan
Channel (Figure 8). The stomachs of 197 weakfish
(range of 7.5-54.0 cm TL, mean of 17.7 cm) were examined. Over 20 prey
species or items were identified in the diet, but they were dominated
by crustaceans and a few juvenile or small fish. Crangon and Neomysis were
the most frequently eaten prey, with only Gammarus lawrencianus and
digested fish (probably bay anchovy) being of any relative importance
(Table 14). There do not appear to be any
consistent interannual differences in the diet, although there were pulses
of the consumption of Neomysis, bay anchovy, and juvenile silver
hake in the diet during certain sampling periods (Table
14).
Other prey or items found in weakfish stomachs in lesser quantities
were: unidentified hydroids; gastropods (Nassarius trivittatus); polychaetes (unidentified); crustaceans (unidentified); copepods (Pseudodiaptomus coronatus); amphipods (Corophium
sp. and Unciola sp.); decapod crustaceans (Dichelopandalus leptocerus,
juvenile Ovalipes ocellatus, juvenile Atlantic rock crabs, and
juvenile blue crabs); fish (juvenile weakfish, juvenile Atlantic
menhaden, butterfish, juvenile unidentified flounder, and juvenile windowpane);
and human artifacts such as cellophane.
Comparisons with Other Diet Studies
The only previous information on the diet of this species known for
this estuary are comments by Breder (1922b) that, when he examined a
few adult weakfish from Sandy Hook Bay, he found that they had eaten
fish such as Atlantic menhaden [juveniles?] , silver perch (Bairdiella
chyrsoura), and anchovies, and squid and "prawns" [Crangon].
Another cursory diet examination by Lynch et al.(1977) of 25 juvenile
fish from the Raritan River (western boundary of the Estuary) also noted
that weakfish there also ate Crangon and fish. Within the upper
Hudson River Estuary (above Manhattan Island), Gladden et al.(1988)
reported that weakfish generally ate "fish and macroinvertebrates."
The summaries of the results of other weakfish studies (Table 15) and the generalized summary of Bigelow and Schroeder (1953)
show that the diet of this species can vary substantially among estuaries.
That is, it can be dominated by Crangon or small fish (especially
bay anchovy and juvenile weakfish) in some estuaries, but by mysids
(mostly Neomysis) or amphipods (e.g., Gammarus sp.)
in others. The earliest studies listed in Table 15 were less precise in defining prey, but the "shrimp," "prawns," or "mysids" that
they noted are almost certainly Crangon and Neomysis,
and suggest that there does not appear to be any substantial shift
in dominant prey over the decades, at least in the past century. Other
weakfish diet studies were not listed in Table
15 because of limitations or the general nature of their information, e.g.,
Eigenmann (1902), Linton (1901), Tracy (1910), Nichols and Breder (1927),
Hildebrand and Schroeder (1928), Lascara (1981), and Grecay (1990).
The pattern of weakfish predation within the Estuary seems to be typical
and focused on both Crangon and Neomysis, but small fish
(e.g., bay anchovy, butterfish, and weakfish) and Gammarus sp.
amphipods are also important (Table 14 and Table 15).
Spotted
Hake (Urophycis regia)
Hudson-Raritan Estuary Results
Spotted hake of all size and age classes were collected commonly during
the warmer months within the Estuary and mainly in channels, especially
Raritan Channel (Stratum 9, Figure 9). The
162 spotted hake (range of 6.5-33.0 cm TL, mean of 18.3 cm) which were
examined ate 30 prey taxa, ranging from hydroids to fish. The most frequently
eaten prey were crustaceans (i.e., Crangon, Neomysis,
and Gammarus lawrencianus) and small fish (Table
16). The copepod Pseudodiaptomus coronatus was frequently
eaten in half of the sampling periods. Few empty stomachs were found.
Crangon dominated the overall stomach volumes with a TV of 45.7%
(range of 31.3-60.9%) (Table 16).
Other prey or items found in spotted hake stomachs in lesser quantities
were: unidentified nematodes; bivalve mollusks (unidentified, Nucula sp.,
blue mussel spat, and juvenile Pitar morrhuanus); polychaetes (unidentified, Nereis sp.,
and Pherusa affinis); sipunculids (unidentified); crustaceans (unidentified); copepods (unidentified); amphipods (unidentified, Ampelisca
abdita, Jassa falcata, Hippomedon serratus, Unciola sp.,
and Ericthonius sp.); decapod crustaceans (juvenile Atlantic
rock crabs, Ovalipes oculata, Pagurus sp., Dichelopandalus
leptocerus, and Palaemonetes sp.); and fish (juvenile
silver hake, juvenile red hake, juvenile searobins, and smallmouth flounder).
Comparisons with Other Diet Studies
No previous studies of the diet of this species are known for this
estuary.
In general, other studies show that spotted hake usually eat larger
epibenthic crustaceans and small fish (Table 17).
Among the crustaceans eaten, Crangon, Neomysis, copepods,
other decapod shrimp, and crabs were prominent in the diet of this species.
The variety of fish identified in these other studies included bay anchovy
and sand lance among others. This diet spectrum is consistent with Bigelow
and Schroeder's (1953) review, the species' diet south of Cape Hatteras
(Burr and Schwartz 1986), and with the results of the present study (Table
16).
Striped Searobin (Prionotus evolans)
Hudson-Raritan Estuary Results
Adults and juveniles of this species were collected mostly during the
summer months, and in or near channels or within Sandy Hook Bay (Figure
10; Wilk et al.1998). The 153 samples of striped searobin
(range of 4.5-47.2 cm TL, mean of 21.4 cm) which were examined ate 34
identifiable prey taxa, but most frequently preyed upon Crangon, Neomysis,
and other crustaceans, and upon small or juvenile fish. Of interest was
the relatively frequent occurrence of small, approximately 1-3 mm, coal
granules or pebbles in their stomachs (Table 18).
The TV was dominated (45.8%, range of 37.4-71.4%) by Crangon (Table
18). The diet was similar for 1996 and 1997 (Table
18).
Other prey or items found in striped searobin stomachs in lesser quantities
were: unidentified hydroids; gastropods (unidentified, Nassarius
obsoletus, and N. trivittatus); bivalve mollusks (Nucula sp., Mulinia
lateralis, and Ensis directus); cephalopod (unidentified
squid); polychaetes (unidentified); crustaceans (unidentified); copepods (unidentified
and Pseudodiaptomus coronatus); isopods (Edotea triloba); amphipods (unidentified, Corophium sp.,
and Unciola sp.); mysids (Heteromysis formosa); decapod
crustaceans (xanthid crabs and unidentified crab fragments); fish (smallmouth
flounder, juvenile windowpane, juvenile anchovy, juvenile grubby, unidentified
juvenile flounder, juvenile searobin, juvenile black sea bass, and juvenile
stargazer (Astroscopus sp.)); and sand.
Comparisons with Other Diet Studies
There is only one other study of the diet of this species known for
this estuary. Manderson et al. (1999) examined 35 stomachs of
this species from shallow water in Sandy Hook Bay (near Stratum 1) and
its Navesink River tributary, at its southern border. They reported an
FO of 68% of YOY winter flounder in the searobin's diet, although Crangon and
other crustaceans were the primary prey.
A summary of most other quantitative studies of the diet of this species
from different areas shows that the diet was also based on crustaceans
(e.g., Crangon, Neomysis, copepods, amphipods, and
juvenile crabs) and small or juvenile fish (e.g., winter flounder,
striped and northern searobins, scup, windowpane, bay anchovy, Menidia,
northern pipefish, and probably others) as available (Table
19). Other, more generalized discussions of their diet, e.g.,
Bigelow and Schroeder (1953), also note a broad spectrum of prey in the
diet of this species, including crabs, amphipods, squid, bivalve mollusks,
polychaetes, small fish (herring and winter flounder), and algae. In
Richards et al.'s (1979) Long Island Sound study, they reported
that the prey of age 1+ searobin varied with habitat type (i.e.,
prey eaten on sandy bottoms were different from prey eaten on muddy bottoms).
For example, on sandy bottoms, the razor clam (Ensis directus)
was important. They also found that some predation showed no habitat-related
differences (e.g., on Neomysis, Crangon, and Ovalipes
ocellatus and other crabs), and concluded that the diet of the adult
striped searobin when at smaller sizes although having a great deal of
overlap with the sympatric but smaller northern searobin tended to reduce
competition for food by focusing on larger prey that were less specific
in their habitat preferences. The results of the present study are consistent
with the findings of other studies; although, again, one or more 2-5
mm diameter pebbles of coal or charcoal were observed in about 5% (range
of 3-17%) of the stomachs (Table 18).
Northern
Searobin (Prionotus carolinus)
Hudson-Raritan Estuary Results
This small species (range of 5.1-20.4 cm TL, mean of 15.1 cm) was collected
mostly during the summer, and mainly in the eastern areas of the Estuary, e.g.,
between Verrazano Narrows and Sandy Hook Bay (Figure
11; Wilk et al.1998). One hundred three northern searobin
stomachs were examined, and over 20 prey taxa were identified, which
were mostly crustaceans. The reoccurring prey group of Crangon, Neomysis, and Gammarus
lawrencianus were most frequently found in the stomachs. The contribution
of prey to TV parallels their contribution to FO, although juvenile Atlantic
rock crabs were of added importance to the diet of the large, August
1997 collection sample (Table 20). Coal pebbles
were also found in these stomachs, but only during one collection, and
then at an FO of 25% for the 87 fish examined (Table
20).
Other prey or items found in northern searobin stomachs in lesser quantities
were: hydroids (unidentified); nematodes (unidentified); bivalve
mollusks (blue mussel spat); polychaetes (unidentified); copepods (Pseudodiaptomus
coronatus); isopods (Edotea triloba); amphipods (Corophium sp., Ampelisca
abdita, and Leptocheirus pinguis); mysids (Heteromysis
formosa); decapod crustaceans (Pagurus longicarpus); fish (juvenile smallmouth flounder, juvenile striped searobin, and juvenile black sea
bass); and unidentified organic matter.
Comparisons with Other Diet Studies
No previous studies of the diet of this species are known for this
estuary.
Some results of other studies of the diet of this predator show that,
like its sibling species, the striped searobin, the northern searobin
also preys principally upon crustaceans, with Crangon, Neomysis,
amphipods, and copepods being prominent in the diet, but fish are eaten
to a lesser degree (Table 21). This dietary
pattern was also reported by Hildebrand and Schroeder (1928) and Bigelow
and Schroeder (1953). The smaller adult size of the northern searobin,
compared to the striped searobin, is a logical explanation for the difference
in the use of fish (although juvenile herring, winter flounder, weakfish,
bay anchovy, and others are reported as prey), and perhaps for the slightly
greater use of smaller macrofauna such as polychaetes and cumaceans.
In Long Island Sound, Richards et al. (1979) reported on the diet
of YOY and older northern searobins, and despite some ambiguity in their
results, the YOY of this species appeared to prey principally upon Neomysis and
copepods, based on numbers eaten. Larger fish were more focused on amphipods,
isopods, and small decapod crustaceans as prey. Mann (1974) found that
diet of this species varied with sediments and water depth. The summary
of results (Table 21) also shows that the
diet of northern searobin from this estuary (Table
20) is consistent with other studies (Table
21).
Striped Bass (Morone saxatilus)
Hudson-Raritan Estuary Results
Striped bass of small-to-medium size (range of 13.5-65.0 cm FL, mean
of 33.2 cm) were generally only collected by trawl within the Estuary
during the fall-winter, especially in western areas of the Estuary: Gravesend
Bay (Stratum 6) and channels (Figure 12; Wilk et
al.1998). The 81 striped bass which were examined ate a diversity
of prey, with greater than 20 identifiable species. The diet was dominated
by a variety of small or juvenile fish and crustaceans (Table
22). Many stomachs per collection (up to 100%) were empty. Crangon again
led in the diet with an FO of 62.3% (range of 54.5-75.9%) and TV of 50.3%
(range of 15.0-100.0%). All other prey occurred or contributed less than
5% to TV, except Neomysis (Table 22).
Other prey or items found in striped bass stomachs in lesser quantities
were: polychaetes (Nephtys sp.); isopods (Cirolana sp.); amphipods (unidentified
and Gammarus lawrencianus); mysids (Heteromysis formosa); decapod
crustaceans (Axius serratus); stomatopod (Squilla
empusa); fish (rock gunnel, juvenile searobin, juvenile unidentified
flounder, juvenile conger eel (Conger oceanicus), juvenile Urophycis sp.,
northern pipefish, bay anchovy, striped anchovy (Anchoa hepsetus),
juvenile winter flounder, and juvenile grubby).
Comparisons with Other Diet Studies
There are no data on the diet of striped bass from within this part
of the overall Hudson-Raritan Estuary. However, Lawler, Matusky & Skelly
Engineers (1980) and Gardinier and Hoff (1982) did report on the striped
bass diet in the Hudson River, 50 km north of the Verrazano Narrows.
There they found that juveniles, less than 20 cm FL, fed on a mix of
freshwater and marine organisms, including Gammarus and other
amphipods (e.g., Corophium, Leptocheirus, and Monoculodes),
insect larvae, copepods, isopods (e.g., Cyathura sp.),
polychaetes, small decapod crustaceans (Crangon and mud crabs),
and some small fish. While larger individuals were almost totally piscivorous,
preying on river herring, Atlantic tomcod (Microgadus tomcod),
bay anchovy, white perch (Morone americana), and killifish, they
occasionally ate small crustaceans. Gladden et al. (1988), possibly
summarizing the same data, also reported the species ate "fish and
macro invertebrates" in the same study area. Twenty-four, 7-39 cm
FL striped bass were also collected in the Raritan River during April
1976 - March 1977, but all of their stomachs were found empty (Lynch et
al. 1977).
In general, most dietary studies of this species found seasonal and
regional variability in prey (Table 23) that
often reflected differences in local environmental conditions (e.g.,
salinity), in the size of the fish examined, and/or in the time of year
(e.g., Bigelow and Schroeder 1953). There is a clear and well
documented ontological shift in predation focus from small crustaceans
(e.g., copepods, amphipods, and mysids) and small or juvenile
fish for the youngest and smallest striped bass, to larger fish and crustaceans
(e.g., crabs and shrimp) for the older and larger striped bass.
The smaller-sized striped bass examined in the present survey ate a mix
of small crustaceans and fish (Table 22).
Clearnose
Skate (Raja eglanteria)
Hudson-Raritan Estuary Results
Clearnose skate were collected in the sandier, eastern polyhaline areas
within the Estuary, such as Lower Bay, Gravesend Bay, East Bank, Romer
Shoal, Sandy Hook Bay, and Raritan Channel (Strata 1, 3-6, 9; Figure
13), and during the summer (Wilk et al.1998). The diet of
the 71 clearnose skate which were examined (range of 49.0-86.0 cm TL,
mean of 63.3 cm) included a diversity of crustaceans, fish, and other
prey (Table 24). Crangon, juvenile
or small Atlantic rock crabs and Ovalipes ocellatus, and fish
were most frequently found in the stomachs and contributed most to overall
stomach volumes (Table 24). No empty stomachs
were found.
Other prey or items found in clearnose skate stomachs in lesser quantities
were: unidentified algae; mollusks (unidentified); amphipods (unidentified); mysids (Neomysis americana); decapod
crustaceans (Pagurus longicarpus and juvenile Libinia sp.);
and fish (unidentified juvenile hake, juvenile striped searobin,
juvenile black sea bass, rock gunnel, juvenile searobins, and gobies).
Comparisons with Other Diet Studies
No previous studies of the diet of this species are known for this
estuary. In fact, information on the diet of this species in general
is very weak, and only available from a few studies (Table
25). In Delaware Bay, Fitz and Daiber (1963) examined the diet of
this species and found that it also most commonly ate Crangon (i.e.,
an FO of 60%), Ensis directus (i.e., an FO of 36%), mud
crabs (i.e., an FO of 20+%), and to a lesser degree, a variety
of other small crustaceans, bivalve mollusks, and small fish such as
weakfish and windowpane. Prey volume or weight contributions were not
noted, but numerically, Crangon was still the dominant prey, and Neomysis was
second in importance. Fritz and Daiber (1963) also noted that in the
fall the skate ate more Neomysis, decapod crustaceans, and fish,
but in the spring they focused more on Crangon and Ensis.
Kimmel (1973) examined a small collection of juveniles (less than 44
cm TL) of this species at the mouth of Chesapeake Bay and found that Crangon, Ensis,
and the mud shrimp Upogebia affinis volumetrically dominated stomach
contents, but that a variety of epifaunal invertebrates (especially crustaceans)
and small fish (searobins and hake) were also eaten. The diet described
by the 1973 Kimmel paper is consistent with the prey that Hildebrand
and Schroeder (1928) noted in the few clearnose skate that they examined
from inside Chesapeake Bay. In the present study, the only prey that
was found that have not been previously reported to be important in the
diet were Atlantic rock crabs and O. ocellatus (Table 24 and Table 25).
Bluefish
(Pomatomus saltatrix)
Hudson-Raritan Estuary Results
Juvenile, YOY (range of 7.0-13.5 cm FL, mean of 8.9 cm) bluefish were
collected in the summer-fall in the Estuary, and mostly in or near channels
(Figure 14; Wilk et al.1998). The stomachs
of 63 bluefish were examined; 62 of these were from one collection August
1997. Fish, Crangon, and Neomysis dominated their diet
(Table 26). The identifiable fish prey included
mostly midwater forms: butterfish, silversides, anchovies, but also juvenile
black sea bass.
The only other prey or items found in bluefish stomachs were unidentified
algae and the polychaete Nereis succinea.
Comparisons with Other Diet Studies
Since only juvenile bluefish were collected and examined in this study,
the following summary keeps that focus. Friedland et al.(1988)
examined the diet of YOY bluefish in this estuary and reported that fish
dominated the diet (by FO and TW) in Sandy Hook Bay (Stratum 1), especially
bay anchovy, silversides, and killifish; however, Crangon were
almost equally important, along with Neomysis. Breder (1922b)
also notes that a small bluefish, also caught in Sandy Hook Bay, had
a sand lance in its stomach. A limited study of the diet of bluefish
in the Raritan River and adjacent western Raritan Bay found that
juveniles (3-22.5 cm TL) collected by seine had eaten mummichog, bay
anchovy, silversides, Crangon, Palaemonetes sp., and
unidentified fish, while larger bluefish (greater than 37 cm FL) collected
by gill net had eaten Atlantic menhaden, spot (Leiostomus xanthurus),
bay anchovy, and Crangon (Lynch et al.1977).
In the adjacent brackish Hudson River, YOY bluefish consumed a variety
of fish during their summer residency, including juvenile striped bass,
white perch, American shad (Alosa sapidissima), blueback herring
(A. aestivalis), Atlantic tomcod, silversides, bay anchovy, and
occasionally other species, as well as blue crabs (Juanes et al.1993;
Buckel et al.1999) (Table 27).
In nearby southern Long Island, New York, and elsewhere in the coastal
Middle Atlantic Bight, juvenile bluefish were reported to commonly eat
small schooling fish such as silversides, bay anchovy, butterfish, killifishes,
juvenile Atlantic menhaden, herring, and weakfish, as well as benthic
fish such as winter flounder, spot, and Atlantic tomcod (Table
27; Greenley 1939; Tatham et al.1984). Small crustaceans,
such as Palaemonetes sp., Crangon, and Neomysis also
dominated the YOY or juvenile bluefish diet (Table
27). The diet of the relatively small sampling of juvenile bluefish
examined in the present study (Table 26) show
that Friedland et al.'s (1988) findings are probably representative
of the species' diet within the Estuary, are typical for this life stage
of the species (Table 27), and are consistent
with previous dietary summaries (Baird 1873; Nichols and Breder 1927;
Hildebrand and Schroeder 1928; Bigelow and Schroeder 1953; Richards 1976).
Winter
Skate (Raja ocellata)
Hudson-Raritan Estuary Results
Adult winter skate were collected from all areas of the Estuary during
the cooler seasons, but they were especially abundant in or near channels
(Figure 15; Wilk et al.1998). The 57
winter skate (range of 36.0-77.0 cm TL, mean of 55.8 cm) which were examined
ate a diverse diet of benthic invertebrates and fish. Crangon was
also a major item in the diet, both in terms of FO and TV. Other crustaceans
and a variety of small or juvenile fish (e.g., Atlantic herring
(Clupea harengus), sculpin, sand lance, and winter flounder) were
also commonly consumed (Table 28).
Other prey or items found in winter skate stomachs in lesser quantities
were: hydroids; nematodes (probably parasitic); gastropods (Nassarius
trivittatus), bivalve mollusks (unidentified, Mulinia lateralis,
and Ensis directus); polychaetes (unidentified); mysids (Neomysis); decapod
crustaceans (unidentified crab fragments, Pagurus longicarpus, Dichelopandalus
leptocerus, and juvenile blue crab); stomatopods (Squilla
empusa); and fish (juvenile Atlantic herring, juvenile red
hake, goby, unidentified juvenile sculpin, and smallmouth flounder).
Comparisons with Other Diet Studies
No previous studies of the diet of this species are known for this
estuary.
Nichols and Breder (1927) and Bigelow and Schroeder (1953) noted the
importance of Atlantic rock crabs and squid in the diet of this species
in New England waters, and that this species also ate a variety of other
benthic invertebrates (e.g., polychaetes, amphipods, shrimp, and
razor clams) and small fish, such as juvenile skates, eels, herrings,
smelt, sand lance, mackerel, butterfish, cunner, sculpins, and silver
and Urophycis hake. The few available quantitative studies, including
the present study, are consistent with this overview (Table
29), except that the present study shows a higher use of flounder
as prey (Table 28).
Black
Sea Bass (Centropristis striata)
Hudson-Raritan Estuary Results
There was a significant recruitment of juvenile black sea bass into
the Estuary in the summer-fall of 1997. (Juveniles were rarely collected
in other survey years, and adults were seldom found within the Estuary.)
These juveniles were widespread in occurrence with a slight tendency
to be found in or near channels (Figure 16;
Wilk et al.1998). The August 1997 survey collected 46 juveniles
41 with nonempty stomachs (range of 2.9-29.0 cm TL, mean of 10.8 cm,),
mostly at sites where colonies of redbeard sponge (Microciona prolifera)
were collected. Various crustaceans dominated the diet, especially Crangon, Neomysis, and
juvenile Atlantic rock crabs. The crustacean prey also included copepods,
amphipods, isopods, and other small or juvenile decapods (Table
30). Several species of small or juvenile fish (e.g., cunner,
goby, Atlantic menhaden, and possibly anchovy) were also eaten, as were
some other benthic invertebrate taxa.
Other prey or items found in their stomachs in lesser quantities were: poriferans (unidentified); anthozoans (unidentified); nematodes (unidentified); gastropods (juvenile Crepidula sp.); bivalve
mollusks (Ensis directus); polychaetes (unidentified
and Asabellides oculata); copepods (unidentified and Pseudodiaptomus coronatus); isopods (Edotea
triloba and Cirolana concharum); amphipods (Ericthonius sp., Stenothoe sp.,
and caprellids); decapod crustaceans (juvenile Ovalipes ocellatus and Pagurus sp.);
and fish (goby, juvenile cunner, and unidentified).
Comparisons with Other Diet Studies
No previous studies of the diet of this species are known for this
estuary.
In other Middle Atlantic Bight estuaries, juvenile black sea bass prey
principally upon small benthic crustaceans such as isopods, amphipods,
small mud crabs, Crangon, mysids, and copepods, and upon small
fish such as northern pipefish, anchovies, and silversides (Hildebrand
and Schroeder 1928; Bigelow and Schroeder 1953; Richards 1963; Kimmel
1973; Allen et al.1978; Festa 1979; Orth and Heck 1980; Werme
1981). Kimmel (1973) noted that polychaetes (e.g., Nereis sp.
and Glycera sp.) can be important, too, and that the dominant
prey shifted with fish growth (i.e., from small crustaceans such
as Neomysis and various amphipods, to decapod crabs and polychaetes).
Most of the black sea bass collected in the Estuary were YOY and older
juveniles (Wilk et al.1998), but adults in other coastal areas
have been reported to feed upon a variety of epifaunal and infaunal invertebrates,
especially crustaceans, squid, and small fish (Bigelow and Schroeder
1953; Richards 1963; Mack and Bowman 1983; Steimle and Figley 1996).
The diet of the juvenile black sea bass examined in the Estuary was dominated
by small crustaceans (Table 30) and was similar
to the diet of the species reported in other studies (Table
31).
Spot (Leiostomus
xanthurus)
Hudson-Raritan Estuary Results
Spot are generally found in the Estuary in the summer-fall, and were
especially common in or near the Raritan Channel (Stratum 9) and Sandy
Hook Bay (Stratum 1, Figure 17) (Wilk et
al.1998). Forty-seven spot (range of 12.8-18.5 cm FL, mean of 15.4
cm) were collected in fall-winter 1996. The tube-dwelling amphipod Ampelisca
abdita dominated the identifiable prey, but Crangon and Neomysis were
also prominent. Other benthic invertebrates, including the copepod Pseudodiaptomus
coronatus, constituted the rest of the stomach contents, which also
contained a notable amount of unidentifiable organic matter or detritus
(Table 32).
Other prey or items found in spot stomachs in lesser quantities were:
green algae; bivalve mollusks (unidentified spat); polychaetes (unidentified);
and amphipods (Corophium sp., Gammarus lawrencianus,
and unidentified).
Comparisons with Other Diet Studies
No previous studies of the diet of this species are known for this
estuary.
In southern New Jersey, Festa (1979) found that YOY spot ate copepods
and amphipods (e.g., Ampelisca sp.), while larger juveniles
also included a variety of polychaetes in the diet. Elsewhere, various
studies show that YOY spot ate calanoid and harpacticoid copepods, a
variety of other small crustaceans including larvae, and detritus; while
larger juveniles (11-16 cm FL) ate more amphipods such as Ampelisca
macrocephala (Table 33). Within Chesapeake
Bay, Hildebrand and Schroeder (1928) reported that the species ate "small
and minute crustaceans and annelids, together with smaller amounts of
small mollusks, fish and vegetable debris". Smith et al.(1984)
added that a wide diversity of plant material and benthic macrofauna
was eaten. The diet of the spot examined from this estuary focused on
small benthic organisms and detritus (Table 32),
and is consistent with other dietary studies for the species (Table
33).
American
Lobster (Homarus americanus)
Hudson-Raritan Estuary Results
A total of 47 American lobsters were collected during five seasons,
mainly from Romer Shoal, Gravesend Bay, Chapel Hill, and Raritan Channel
(Figure 18). The collections were a mix of
juveniles and small adults (range of 2.8-9.9 cm carapace length, mean
of 5.8 cm). The highly macerated state of the stomach contents, and the
American lobster's known tendency to eat calcareous shell fragments,
make identification of all true prey tentative. Species or items that
could be identified from the diverse, particulate material in the stomach
were included in this analysis, however. The dominant items evident in
the stomachs were fragments of decapod crustaceans, especially Atlantic
rock crabs, Pagurus sp., and Ovalipes ocellatus. Other
items that were found suggest a range of taxa being eaten (i.e.,
hydroids to skate egg cases), as well as human artifacts such as coal
pebbles, fragments of plastic and rubber, and synthetic fibers (Table
34).
Other prey or items found in American lobster stomachs in lesser quantities
were: gastropods (Crepidula fornicata, Nassarius
trivittatus, Lacuna vincta, Turbonilla sp., and Euspira operculums); bivalve
mollusks (Mulinia lateralis); polychaetes (unidentified, Nereis succinea,
and Spiochaetopterus oculatus); arachnids (juvenile Limulus
polyphemus); cirripeds (Balanus sp.); decapod crustaceans (P.
longicarpus, O. ocellatus, and juvenile Callinectes sp.);
and echinoderms (Arbacia punctulata).
Comparisons with Other Diet Studies
No previous studies of the diet of this species are known for this
estuary.
Steimle (1994) examined the diet of American lobster collected outside
the mouth of this estuary. He reported that the diet varied among three
collection sites that were variably influenced by sewage sludge disposal,
and among bimonthly collections, although few American lobster were collected
during winter. At the least-sludge-affected sites (probably being most
appropriate for comparison with this estuary), the American lobsters
were primarily eating Atlantic rock crabs, unidentified fish, the polychaete Pherusa
affinis, and algae (Table 35). He also
noted obvious human artifacts in the stomachs, especially animal hair
and synthetic fibers.
In Long Island Sound, Weiss (1970) reported American lobsters also
ate crustaceans, especially Atlantic rock crabs, mollusks such as Lacuna
vincta and the blue mussel, and the polychaete Nereis virens.
Other American lobster diet studies have been conducted outside the Middle
Atlantic Bight area (e.g., in the sub-boreal Gulf of Maine and
for Canadian populations). The diet of small American lobsters collected
in the Estuary in the present study (Table 34)
is consistent with the few available studies summarized in Table
35, and with the more general comments of Herrick (1911).
Tautog
(Tautoga onitis)
Hudson-Raritan Estuary Results
Fifty-one tautog (range of 8.4-58.0 cm TL, mean of 37.5 cm) were collected
and examined, primarily during the warmer seasons and from Romer Shoal,
East Bank, Gravesend Bay, and, to a lesser degree, nearby areas (Figure 19). A variety of decapod crustaceans and mollusks were the most
frequently eaten prey, with Atlantic rock crabs, xanthid crabs (including Dyspanopeus
sayi), and blue mussels being prominent in the diet (Table
36).
Other prey or items found in tautog stomachs in lesser quantities were:
hydroids; gastropods (unidentified, Crepidula sp., and
unidentified eggs); bivalve mollusks (Anadara ovalis and
juvenile northern quahogs); cirripeds (Balanus sp.); amphipods (Gammarus sp.
and Ericthonius sp.); decapod crustaceans (unidentified
and juvenile Libinia sp.); and shell hash.
Comparisons with Other Diet Studies
No previous studies of the diet of this species are known for this
estuary, although Duffy-Anderson and Able (1999) mention that the diet
of juvenile tautog held in cages in New York harbor appears to be "harpacticoid
copepods, mysids, and amphipods."
Steimle and Shaheen (1999) summarized the diet of tautog, which has
been resummarized in this report as Table 37.
Dorf (1994) found that juveniles in Narragansett Bay, Rhode Island, ate
various amphipods and copepods (mostly harpacticoids). Grover (1982)
found a similar juvenile diet on the ocean side of Long Island, New York,
as did Sogard (1992) in a southern New Jersey estuary. Nichols and Breder
(1927) also noted seaweed in the diet of young tautog. The diet of older,
2-3 yr old juveniles was generally found to shift to mollusks, primarily
blue mussels (Dorf 1994; Lankford et al.1995), but Festa (1979)
reported mud crabs to be a primary item in the diet of larger juveniles
in southern New Jersey.
Adult tautog are generally reported to prey primarily upon blue mussels,
but also upon barnacles, crabs (Pagurus sp., Atlantic rock, and
others), sand dollars (Echinarachnius parma), various amphipods, Crangon and
other shrimp, American lobsters, scallops and other mollusks, and polychaetes
(Hildebrand and Schroeder 1928; Bigelow and Schroeder 1953; Festa 1979;
Steimle and Ogren 1982). Steimle (in review) found that besides blue
mussels, the large anemone Metridium senile and razor clams (Ensis
directus) can be important prey in Delaware Bay. The results of the
present study (Table 36) reaffirm the importance
of "shellfish," crustaceans, and mollusks, in the tautog diet.
Smooth
Dogfish (Mustelis canis)
Hudson-Raritan Estuary Results
This relatively large (range of 55.0-111.0 cm TL, mean of 74.6 cm)
visitor to the Estuary was collected in modest numbers (i.e.,
42 specimens) during the warm seasons of both survey years, and mostly
from Romer Shoal, East Bank, Gravesend Bay, nearby eastern Lower Bay
areas, and near the Raritan Channel (Figure 20).
It primarily ate a variety of decapod crustaceans and mollusks, and an
occasional fish. Among the decapod prey, Crangon, Atlantic rock
crabs, and Ovalipes ocellatus were commonly eaten, and the most
notable molluscan prey was the razor clam Ensis directus (Table
38).
Other prey or items found in smooth dogfish stomachs in lesser quantities
were: bivalve mollusks (Atlantic surfclam); cephalopods (unidentified
squid); polychaetes (unidentified and Glycera sp.); decapod
crustaceans (Pagurus pollicaris, Pagurus sp., and Libinia sp.); stomatopods (Squilla
empusa); and fish (juvenile Atlantic menhaden, northern pipefish,
and lined seahorse (Hippocampus erectus)).
Comparisons with Other Diet Studies
No previous studies of the diet of this species are known for this
estuary.
Rountree and Able (1996) examined the diet of YOY of this species in
a southern New Jersey estuary and found small Palaemonetes sp.
and Crangon shrimp as the dominant prey, followed by unidentified
polychaetes and crabs, blue crabs, and a variety of other benthic invertebrates
(especially crustaceans); very few fish were eaten (Table
39). These results were similar to an early study, near Atlantic
City, New Jersey, by Breder (1921) who reported that various crabs, eel
grass, detritus, and fish were the most common items in the stomachs
of smooth dogfish less than 64 cm TL. Nichols and Breder (1927) noted
a preference for eating young American lobster and blue crabs, as well
as other crustaceans, fish, and a variety of benthic macrofauna. Bigelow
and Schroeder (1953) also commented on the potential heavy predation
of smooth dogfish on American lobsters in Buzzards Bay, Massachusetts,
as well as predation on Atlantic menhaden and tautog. Festa (1979) examined
12 juvenile smooth dogfish from southern New Jersey and found that blue
crabs dominated (i.e., a TV of 91%) the diet, followed by "bay" [Crangon?]
and Palaemonetes shrimp and juvenile weakfish. The present examination
of the smooth dogfish diet in the Estuary (Table
38) shows that the species basically eats larger crustaceans and
fish, which is consistent with the results of most other studies (Table
39).
Silver
Hake (Merluccius bilinearis)
Hudson-Raritan Estuary Results
In general, silver hake were only collected as juveniles (range of
6.5-15.0 cm TL, mean of 10.1 cm) in the Estuary, and then primarily during
the fall and in or near channels (Figure 21;
Wilk et al.1998). Juvenile silver hake were not commonly available
for examination except in November 1997 when 29 were collected. Crustaceans
were the most common and important taxa in the diet, especially Crangon, Neomysis, Gammarus
lawrencianus, and Ampelisca abdita, but small or juvenile
fish were also eaten (e.g., silver hake, Atlantic menhaden, and
probably anchovies). Both benthic and midwater fauna were eaten (Table
40).
Other prey or items found in silver hake stomachs in lesser quantities
were: crustaceans (unidentified); cumaceans (unidentified); isopods (Edotea
triloba); amphipods (unidentified, Jassa falcata, Hippomedon
serratus, and Unciola sp.); decapod crustaceans (Palaemonetes sp.);
and fish (juvenile Atlantic menhaden).
Comparisons with Other Diet Studies
No previous studies of the diet of this species are known for this
estuary.
Table 41 summarizes dietary studies for
juvenile and older silver hake that could be relevant to the present
study. Schaefer (1960) and Steimle (1985) examined stomachs of this species
collected just outside this estuary, and found that mysids (mostly Neomysis), Crangon,
small unidentifiable fish, and YOY silver hake were the most important
prey for near adult and adult fish. Schaefer (1960) also examined adults
caught by hook-and-line on a surf-zone fishing pier in Long Branch, New
Jersey (20 km south of the mouth of the Estuary), and found a slightly
different diet from that found offshore. Inshore, he found that silver
hake ate amphipods, Crangon, YOY silver hake, and mysids, in that
order of relative importance. Richards (1963) reported a similar diet
in Long Island Sound. On the continental shelf, Sedberry (1983) and Bowman et
al.(1987) found that juvenile (i.e., less than or equal to
20 cm TL) silver hake ate various crustaceans, including euphausids and
the hyperid amphipod Parathemisto gaudichaudi. Smaller, YOY silver
hake (i.e., less than 5 cm TL) ate benthic and pelagic amphipods;
larger YOY (i.e., between 5 and 10 cm TL) ate Crangon and Dichelopandalus
pinguis [leptocerus?] shrimp, amphipods, small fish (sand
lance and smaller silver hake), and squid. The juveniles collected in
the Estuary during the present study ate a diet consistent with those
studies noted in Table 41, with such studies
as Jensen and Fritz (1960) and Vinogradov (1984), and with the generalizations
of Bigelow and Schroeder (1953). Bowman et al. (1987) report that
silver hake are mostly nocturnal feeders, and if so, mid-day collections
might involve some loss of information by the digestion of softer prey.
Few adult silver hake are collected in the Estuary (Wilk et al.1998).
Less
Abundant Predators
The following predators were collected in lesser quantities and in
more limited areas. Their diets are only briefly documented here, with
identifiable prey being listed in order of their relative importance
to overall stomach content volumes.
Fourspot Flounder (Paralichthys oblongus)
Forty-one examples of this predator were collected from several strata,
and ranged between 6.7 and 33.0 cm TL (mean of 15.1 cm). Crangon,
unidentified fish, Neomysis, and unidentified decapod crustacean
zoeae were prominent in the diet.
Grubby (Myoxocephalus aenaeus)
Twenty-six specimens, ranging between 3.8 and 13.0 cm TL (mean of 7.9
cm), were collected mostly in the Lower Bay to East Bank area (Strata
3 and 5). They ate Crangon, Neomysis, juvenile Atlantic
rock crabs, juvenile black sea bass, the tubiculous amphipod Corophium sp.,
the isopod Cyathura sp., caprellid amphipods, and the sand-tube
worm Sabellaria vulgaris.
White Perch (Morone americana)
Twenty-one white perch were collected, mostly in western Raritan Channel
(Stratum 9), and ranged between 16.0 and 27.7 cm TL (mean of 21.0 cm).
These fish ate Crangon, unidentified small or juvenile fish, unidentified
crustaceans, gobies (Gobisoma sp.), Neomysis, Palaemonetes sp.,
and Gammarus sp.
Northern Kingfish (Menticirrhus saxatilis)
Sixteen kingfish were collected, mostly in the Lower Bay to East Bank
area (Strata 3 and 5), and ranged between 7.5 and 16.5 cm TL (mean of
10.9 cm). They ate Crangon, Gammarus lawrencianus, anchovies,
unidentified polychaetes, unidentified crab, Neomysis, and Pagurus sp.
Smallmouth Flounder (Etropus microstomus)
Twelve specimens of this flounder were collected, mostly in the Lower
Bay to East Bank area (Strata 3 and 5), and ranged between 11.3 and 15.0
cm TL (mean of 12.7 cm). These fish ate Crangon, Pagurus longicarpus, Neomysis, Pagurus sp.,
and Gammarus lawrencianus.
Spi
