Life History
Synopses for Selected Fish Species Inhabiting the Hudson River
Estuary
Understanding habitat requirements of the selected
fish species in the Hudson River estuary requires an understanding
of the distribution and environmental limitations for each life stage
found in the estuary. A synopsis of the life history of each selected
species reveals that a variety of habitats and regions of the Hudson
River estuary are utilized; it also reveals some disagreement in the
literature, as well as a general lack of information on specific habitat
requirements for all life stages. Included in this appendix are 11
complementary figures (Figures A1-A11) for the 11 selected species
which schematically present spatial distribution by life stage. References
cited in this appendix are listed in the "References Cited" section
of this document.
The Atlantic sturgeon, Acipenser oxyrhynchus,
is an anadromous species of the Hudson River. The following account
of life history is summarized from Bain et al. (1995). Adult
Atlantic sturgeon live along the Atlantic coastline for approximately
10 yr before migrating into coastal rivers. Males enter the Hudson
River in early April, before the females. Atlantic sturgeon do not
spawn annually, with 2-5 yr between spawning events. Spawning occurs
well upstream from the salt front; larvae are known to be intolerant
of euryhaline environments.
Eggs are demersal and adhesive. The larvae remain
close to the river bottom for some time. Juveniles are fairly evenly
distributed in the Hudson River during summer, with their highest concentration
between Kingston and Haverstraw Bay (Rkm 140 and 63, respectively).
After summer, when water temperatures fall below 20°C, juveniles
are found in high numbers between the Bear Mountain Bridge and the
George Washington Bridge (Rkm 74 and 19, respectively). This tighter
distribution is thought to represent an overwintering area for juvenile
Atlantic sturgeon. Juveniles move back upstream in early spring, and
do not migrate out of the Hudson River until 2-6 yr of age. Adults
spend approximately 10 yr at sea before maturation and subsequent inland
migration. Males and females mature at different ages, approximately
12 and 15 yr of age, respectively.
The shortnose sturgeon, A. brevirostrum, is
considered to be a nonmigratory, euryhaline fish. In the Hudson and
other large rivers, adult shortnose sturgeon overwinter in deep polyhaline
water downstream from the spawning grounds to which they will travel
in the following spring when water temperatures reach 8-9°C (Dadswell et
al. 1984). In the Hudson River, spawning occurs in April and May
between Coxsackie and Troy (Dadswell et al. 1984; Hoff et
al. 1988). Detailed information on spawning habitat is available
for shortnose sturgeon of the Savannah River, South Carolina (Smith et
al. 1993), which may or may not apply to those of the Hudson River.
Adults are thought to move downstream in May and June, after spawning
(Hoff et al. 1988).
Eggs of the shortnose sturgeon are demersal and adhesive
(Dadswell et al. 1984). Larvae and juveniles are probably benthic,
remaining in deep water where currents are strong (Dadswell et al. 1984;
Hoff et al. 1988). As a result, little is known about the early
life stages. In addition, identification of young specimens (eggs,
larvae, and juveniles) is extremely difficult because of overall similarity
to young Atlantic sturgeon (Hoff et al. 1988). Some workers
(i.e., Hoff et al. 1988) believe that the larvae disperse
downstream during summer, whereas others (i.e., Dadswell et
al. 1984) believe that young shortnose sturgeon remain above the
salt front until they reach 45 cm total length (TL). Upon attaining
adult size (45-50 cm TL), shortnose sturgeon move downriver in fall,
and back upriver in spring (Dadswell et al. 1984).
Sexual maturation is thought to be at 3-4 yr of age
for males, and probably 6-8 yr of age for females, in the Hudson River
(Dadswell et al. 1984). The age of maturation for females is
based on age at first spawning. It is unknown how frequently shortnose
sturgeon in the Hudson River spawn; in Canada, females spawn every
3 yr, and males every other year (Dadswell et al. 1984).
The alewife, Alosa pseudoharengus, is an anadromous
species of the Hudson River (Schmidt and Stillman 1994). Adult alewife
spend most of the year in coastal Atlantic waters, migrating into the
Hudson River (and other estuaries) to spawn. Alewife probably return
to their natal river to spawn (Klauda et al. 1991). Alewife
usually enter the Hudson River in early spring, prior to mid-May (Schmidt et
al. 1988).
Spawning usually occurs in freshwater tributaries,
in relatively shallow water with a slow current (Schmidt et al. 1988);
in fact, the alewife is the only anadromous fish species commonly found
in freshwater tributaries of the Hudson River (Schmidt and Stillman
1994). Eggs and larvae are not morphologically distinguishable from
those of blueback herring (A. aestivalis), and for this reason,
the two species are typically referred to as "river herring" (Dovel
1981; Schmidt et al. 1994). The role of blueback herring in
tributaries is still unclear; however, because adult alewife are frequently
sampled from freshwater tributaries during the spawning season, it
has been assumed that most, if not all, of the eggs and larvae found
in the freshwater tributaries are alewife (Schmidt et al. 1994).
This contradicts earlier findings in which alewife eggs and larvae
were presumed to be present in the main river channel (Boreman 1981).
In addition to the differences in spawning location, larvae and eggs
can also be distinguished by their temporal distribution, because alewife
spawn about a month earlier than blueback herring (Hildebrand and Schroeder
1928; Schmidt et al. 1988).
Eggs are essentially pelagic, somewhat adhesive,
and demersal in still water (Hildebrand 1963; Norden 1967; Lippson
and Moran 1974; Klauda et al. 1991). In the Chesapeake Bay area,
alewife larvae and juveniles may move further upstream to avoid intrusion
of saltwater (Klauda et al. 1991). Larvae and juveniles remain
in the freshwater tributaries of the Hudson River until June. At this
time, juvenile alewife move out of the nursery areas of the tributaries
and make their way downstream to the lower Hudson River and into the
Atlantic Ocean (Schmidt et al. 1988), although capture of yearlings
suggests some may overwinter in the estuary during the first year of
life.
Alewife feed primarily on amphipods, mysids, copepods,
small fish, and fish eggs (Leim and Scott 1966).
The blueback herring, A. aestivalis, is an
anadromous fish of the Hudson River (Klauda et al. 1991). Adults
remain in coastal waters of the Atlantic Ocean and migrate upriver
to spawn, as do alewife. Blueback herring usually spawn later in the
spring than alewife, and in different habitat (Schmidt et al. 1988).
Blueback herring prefer to spawn in relatively deep freshwater with
swift currents on hard substrates of either gravel or sand (Schmidt et
al. 1988; Klauda et al. 1991). It has been noted that this
habitat preference is mainly seen in northern populations where blueback
herring are sympatric with alewife, and, conversely, southeastern blueback
herring spawn in lentic as well as lotic water (Klauda et al. 1991).
It has been observed that blueback herring do not move as far upstream
in tributaries as alewife (Loesch 1968, 1969), and recent studies in
the Hudson River suggest that blueback herring spawn mainly in the
main channel of the estuary, whereas alewife spawn more in tributaries
(Schmidt et al. 1994). The single peak, seen in late May, in
the temporal distribution of "river herring" eggs in the
main channel (Boreman 1981) may therefore represent eggs of blueback
herring.
Eggs of the blueback herring are pelagic, somewhat
adhesive, and demersal in still water (Hildebrand 1963; Norden 1967;
Lippson and Moran 1974; Klauda et al. 1991).
"River herring" larvae found in the main channel of
the Hudson River estuary are thought to be blueback herring; larvae
probably remain in nearshore habitat (Schmidt et al. 1994).
Juveniles move downriver in July, later than alewife (Boreman 1981;
Schmidt et al. 1988).
Food of blueback herring consists mainly of plankton,
copepods, pelagic shrimp, and early life stages of small fishes (Scott
and Crossman 1973).
The American shad, A. sapidissima, is a highly
migratory species of the Hudson River, and is often cited as a classic
example of an anadromous fish. Adults move into the Hudson River from
Atlantic waters in early spring, usually beginning in March or April
(Boreman 1981), depending on the water temperature of the river, which
must be 12°C or above before the shad begin their run (Bigelow
and Schroeder 1953). Adult American shad do not eat when running or
spawning, and will not do so until they begin the postspawning downriver
migration to the Atlantic, eating along the way (Bigelow and Schroeder
1953). Spawning occurs mainly at night (Bigelow and Schroeder 1953;
Ross et al. 1993), in shallow freshwater of moderate current
(Schmidt et al. 1988), and on various substrates (Bigelow and
Schroeder 1953).
Eggs are demersal and nonadhesive (Bigelow and Schroeder
1953), and hatch after 2-17 days, depending on water temperature (Boreman
1981). Bigelow and Schroeder (1953) report that eggs raised in water
at 12°C hatch between 12 and 15 days. Eggs are found in the spawning
areas (Boreman 1981), and are not associated with any particular habitat
type (Ross et al. 1993). In a 1974 study, egg abundance peaked
in May (Boreman 1981); yolksac larval abundance has also been reported
to peak in May (Schmidt et al. 1988). Yolksac larvae absorb
their yolk in 4-5 days in water at 17°C (Boreman 1981). Larvae
are reported to frequent riffle pools where water is of moderate depth
and variable velocity and direction (Ross et al. 1993). Both
feeding and yolksac larvae are planktonic; dispersal therefore occurs
by passive transport (Boreman 1981; Schmidt et al. 1988). Juveniles
are found downriver from the spawning grounds (Boreman 1981) beginning
in June, with peak abundance in July (Schmidt et al. 1988).
Juvenile habitat preference in the Hudson River seems to be positively
correlated with depth, turbidity, and current velocity, possibly as
an effect of food distribution (Ross et al. 1993). Most juveniles
complete their migration from freshwater into the Atlantic by late
fall or early winter (Bigelow and Schroeder 1953; Boreman 1981; Schmidt et
al. 1988).
Adult American shad overwinter in the deep water
of the Atlantic and Gulf of Maine (Boreman 1981). They move closer
to their natal river in the spring, due to their strong homing ability
(Boreman 1981). Adult American shad are euryhaline, but only enter
freshwater to spawn (Bigelow and Schroeder 1953).
The Atlantic tomcod, Microgadus tomcod, is
a euryhaline fish of the Hudson River estuary. It is not considered
to be migratory per se, but does show significant, seasonal,
upriver/downriver movement within the estuary. Spawning of Atlantic
tomcod takes place under ice, mainly from December to January (Bigelow
and Schroeder 1953; Boreman 1981; Klauda, Moos, and Schmidt 1988; McLaren et
al. 1988; Dew and Hecht 1994). The winter spawning occurs upriver
mainly in fresh and possibly in brackish water (Boreman 1981; Klauda,
Moos, and Schmidt 1988; Dew and Hecht 1994).
Eggs are demersal (Bigelow and Schroeder 1953; Boreman
1981; Klauda, Moos, and Schmidt 1988). The state of adhesion or nonadhesion
of eggs is unknown, due to the difficulty of winter collection; conflicting
opinions range from nonadhesive (Boreman 1981), to probably adhesive
(Klauda, Moos, and Schmidt 1988), to adhesive (Bigelow and Schroeder
1953). Hatching occurs in freshwater (Dew and Hecht 1994) after 24-60
days in February and March (Klauda, Moos, and Schmidt 1988; Dew and
Hecht 1994). Yolksac larvae reach peak abundance in mid-March, and
post-yolksac larvae reach peak abundance in mid-April (Klauda, Moos,
and Schmidt 1988). The yolksac larval period is approximately 4 wk,
and the feeding larval period is approximately 6 wk (Boreman 1981).
Larvae disperse downriver to Rkm 19-53 by mid-May (Klauda, Moos, and
Schmidt 1988). The lower Hudson River is considered to be a nursery
area for young Atlantic tomcod (McLaren et al. 1988). Juveniles
are thought to peak in mid-May, mainly in the Tappan Zee and Yonkers
regions (Klauda, Moos, and Schmidt 1988), although earlier reports
show that juveniles did not appear until early August (Boreman 1981).
They move upriver in mid-spring (Dew 1995), possibly to remain in brackish
water as the salt front moves upriver (Klauda, Moos, and Schmidt 1988).
In the Hudson River, males and females both sexually
mature between 11 and 12 mo, during their first fall (Boreman 1981;
Klauda, Moos, and Schmidt 1988; McLaren et al. 1988). Adult
Atlantic tomcod therefore spawn in their first year. Atlantic tomcod
are not thought to move out of the Hudson River estuary during their
life span, although they are found frequently in mouths of estuaries
when not spawning (Bigelow and Schroeder 1953).
The bay anchovy, Anchoa mitchilli, is a coastal
species which enters the lower Hudson River in April as adults (Woodhead et
al. 1992). Adults are present in the lower estuary in high numbers
in the summer, and are absent from the estuary in the winter (Woodhead et
al. 1992). Egg collections suggest spawning occurs in the lowest
regions of the Hudson River and probably out into coastal waters (Boreman
1981). Spawning is typically in water less than 20 m deep (Richards
1959); spawning activity in the lower Hudson River occurs from early
June to mid-August and perhaps beyond, as suggested by a study of anchovy
spawning in nearby Long Island Sound (Richards 1959). Since the minimum
age at maturity is 2.5 mo at a size between 30 and 40 mm (Stevenson
1958), it is likely that bay anchovies spawn in their first year of
life.
Eggs are pelagic (Klauda et al. 1991) and
hatch in about 24 hr; yolksacs are absorbed in another 24 hr (Boreman
1981). Anchovy eggs have been collected in the Hudson River estuary
up to Rkm 88 (Boreman 1981). The distribution of young anchovy shifts
upriver as development progresses through summer. Post-yolksac larvae
metamorphose in August and September (Woodhead et al. 1992).
Juveniles in Chesapeake Bay prefer freshwater habitats (Klauda et
al. 1991); this may also be the case for juveniles in the Hudson
River as suggested by the upriver shift in distribution mentioned earlier.
In the Hudson River, juvenile anchovy emigrate to sea in the fall;
few remain in the estuary after November (Woodhead 1991).
Although no tagging studies have been conducted on
Hudson River bay anchovy, studies elsewhere suggest that oceanic movements
are limited to inshore-offshore migrations (Hildebrand 1963). Bay anchovy
feed on detrital material and small planktonic animals in the Hudson
River estuary (Boyce Thompson Institute for Plant Research 1977).
Bluefish (Pomatomus saltatrix) are ocean spawners;
larval and early juvenile development also occurs offshore. Bluefish
first appear in estuaries as juveniles and, in the Northeast, usually
arrive in the lower Hudson in late summer and fall (Boyle 1968). The
distribution of larvae offshore is fairly well studied (Kendall and
Walford 1979), but that of early juveniles is less known. Very little
information is available on habitat requirements, food habits, or multispecies
interactions in the oceanic phase. Juvenile bluefish generally appear
in nearshore coastal waters in two waves, one in spring and another
in summer, suggesting two spawning periods or a protracted spawning
season offshore (Sargent and Boreman 1984).
In estuaries, juvenile bluefish are piscivorous,
feeding on a wide variety of prey items (Marks and Conover 1993). Juvenile
bluefish in the Hudson River feed on bay anchovy, white perch, American
shad, river herring, and striped bass (Texas Instruments 1976b; Juanes et
al. 1993).
The largemouth bass, Micropterus salmoides,
is a freshwater-oligohaline, nonmigratory species inhabiting the Hudson
River. When preparing to spawn, adult largemouth bass select appropriate
sites in which to construct nests and to fertilize and deposit eggs.
In the Hudson River, spawning and nesting habitat typically consists
of protected coves and bays, and almost never exposed shoreline (Nack et
al. 1993). Miller and Kramer (1971) found high mortality rates
for eggs and larvae due to exposure to wind-induced waves, which explains
why largemouth bass seem to prefer lentic habitat. Also, while specific
effects of tidal action on developing eggs are unknown, stable water
levels are associated with high recruitment (Von Geldern 1971). Nesting
in coves and bays may slightly mitigate effects of tidal action. Temperature
may be an important environmental cue for the timing of spawning because
the early season nests seem to be in areas of warmer water (Nack et
al. 1993).
Eggs are adhesive, sticking to one another in a mass
and to the substrate upon which they are laid, such as gravel or roots
(Breder and Rosen 1966). Male largemouth bass guard the nests, even
after the eggs have hatched (Breder and Rosen 1966). Larvae and juveniles
use the area around nesting sites as nursery habitat (Green et al. 1988;
Green et al. 1989; Nack et al. 1993). Presumably, these
preadult life stages remain in the tributaries where they would be
protected from waves, unstable water levels, as well as some predators.
Adult largemouth bass also prefer lentic water in
protected areas, especially in winter (Carlson 1992). Largemouth bass
are believed to seek shelter from tide-affected areas in winter when
their metabolic rates are low (Carlson 1992). Largemouth bass tend
to leave overwintering sites when water temperature rises to 10°C
(Nack et al. 1993).
Striped bass (Morone saxatilis) spawn in the
fresh-brackish reach of the Hudson River, concentrating between Rkm
54 and 88, from early May through June (Boreman 1981). Striped bass
eggs are semibuoyant (Hardy 1978). The yolksac larval stage runs 3-6
days, and the feeding (post-yolksac) larval stage may last 4 wk (Boreman
and Fletcher 1993). The distribution of the early life stages in the
river has been well documented (e.g., see Boreman and Klauda
1988), showing that the fish distribute both upriver and downriver
as they develop. Timing of movement of juveniles out of estuarine nursery
areas varies among stocks; in the Hudson River, age 0 fish move out
of the river to estuaries in Long Island Sound and New Jersey. By age
1, these fish are participating in coastal migrations. Temperature
is usually implicated in triggering migrations, but further studies
relating movement and environmental conditions or prey availability
seem warranted. Coastal movement of striped bass tagged in the Hudson
River is extensive, but concentrated between Cape May and Cape Cod
(McLaren et al. 1981).
Food habits studies conducted in the estuary (Texas
Instruments, Inc. 1976a) suggest that age-0 striped bass feed primarily
on harpacticoid, calanoid, and cyclopoid copepods, Gammarus spp.,
and chironomid larvae, progressing to fish as they age. Striped bass
greater than 75 mm feed on bay anchovies, and striped bass greater
than 116 mm feed on clupeids, Atlantic tomcod, mummichogs, Morone spp.,
and banded killifish. White perch, bluefish, Atlantic tomcod, largemouth
bass, and smallmouth bass have been reported as potential predators
on striped bass larvae (McFadden et al. 1978).
In the Hudson River, the white perch, M. americana,
is a nonmigratory euryhaline species which is widely distributed throughout
the river. Spawning occurs from April to June (Bigelow and Schroeder
1953; Klauda, McLaren, et al. 1988) or July (Boreman 1981),
with peak egg deposition in mid-May to early June in the upper Hudson
(Klauda, McLaren, et al. 1988). Spawning takes place mainly
in freshwater (Englert and Sugarman 1988; Klauda, McLaren, et al. 1988)
in a variety of protected habitats, such as shallow flats, embayments,
and tidal creeks (Klauda, McLaren, et al. 1988).
Eggs are demersal and adhesive (Bigelow and Schroeder
1953), and hatch after only 1.5-2 days (Boreman 1981). Yolksac larvae
are found in the same areas as the eggs, probably as a result of the
short duration of the larval stages (3-5 days) (Klauda, McLaren, et
al. 1988). Feeding larvae are more widely distributed due to their
higher mobility, and disperse downriver in July (Klauda, McLaren, et
al. 1988). This finding on post-yolksac larval distribution conflicts
with earlier sampling data from the 1970s which indicated that both
egg and larval stages are widely distributed in the Hudson, with larval
stages found between Rkm 39 and 201 (Boreman 1981). Juveniles first
appear in June, dispersing downriver and into the shorezone during
the end of summer; juveniles were mainly found close to shore in October,
but then moved into deeper water by December (Klauda, McLaren, et
al. 1988).
Adult white perch sexually mature at age 4 in males,
and age 5 in females (Klauda, McLaren, et al. 1988). There is
no known habitat preference for adults; they are widely distributed
in the Hudson River in both brackish and freshwater habitats (Klauda,
McLaren, et al. 1988), but remain in the river for their entire
life span (Boreman 1981).
