Table of Contents Abstract Introduction Methods and Data Results Discussion References Cited
Northeast Fisheries Science Center Reference Document 12-22
Update on Harbor Porpoise Take Reduction Plan Monitoring Initiatives: Compliance and Consequential Bycatch Rates from June 2009 through May 2010by Christopher D. Orphanides
National Oceanic Atmospheric Administration, National Marine Fisheries Service, Northeast Fisheries Science Center, 28 Tarzwell Dr., Narragansett RI 02882 USA
Web version posted October 10, 2012Citation: Orphanides CD. 2012. Update on harbor porpoise take reduction plan monitoring initiatives: compliance and consequential bycatch rates from June 2009 through May 2010. US Dept Commer, Northeast Fish Sci Cent Ref Doc. 12-22; 21 p. Available from: National Marine Fisheries Service, 166 Water Street, Woods Hole, MA 02543-1026, or online at http://www.nefsc.noaa.gov/nefsc/publications/
Information Quality Act Compliance: In accordance with section 515 of Public Law 106-554, the Northeast Fisheries Science Center completed both technical and policy reviews for this report. These predissemination reviews are on file at the NEFSC Editorial Office.
Harbor Porpoise Take Reduction Plan (HPTRP) compliance and bycatch rate analyses are updated for US Northwestern Atlantic gillnet fisheries using data from June 2009 through May 2010 (the 2009-2010 fishing season). The observed overall compliance rate with the HPTRP regulations was 46.3%. By region, the New England gillnet fishery had a compliance rate of 43.0%, while the Mid-Atlantic gillnet fishery had a compliance rate of 55.4%. Compliance with pinger regulations was determined solely by the number of pingers observed on a gillnet string; pinger functionality was not considered in the compliance rates because pinger functionality data for the 2009-2010 fishing season was limited to six trips. Bycatch rates from the 2009-2010 fishing season were compared to the regulations of the 1998 and 2010 HPTRP final rules, even though some of the 2010 HPTRP amendments were not implemented until March 22, 2010, and most were implemented after the completion of the 2009-2010 fishing season. All but two of the observed takes in the 2009-2010 fishing season occurred in times and areas that were either managed under the 1998 HPTRP regulations, or managed under the 2010 HPTRP amendments. Bycatch rates in the 2010 HPTRP areas associated with Consequence Closure Areas (CCAs) were well above the target rates that could trigger seasonal closures after the 2011-2012 fishing season. The bycatch rate in the 1998 and 2010 HPTRP Management Areas in nets that did not have the required number of pingers (0.058 harbor porpoise/mton landed) was higher than the bycatch rate from nets with the required number of pingers in the same times and areas (0.049 harbor porpoise/mton landed). However, the relative difference between these two rates has been greater in previous years. Pingers still appeared to reduce bycatch of harbor porpoises, although it was not possible to determine how many of the pingers deployed were actually functional and what the true bycatch rate was when a full set of working pingers was used.
Since the beginning of the Northeast Fisheries Observer Program (NEFOP) in 1989, harbor porpoise bycatch in gillnets has been the focus of much attention. Over the years, two Harbor Porpoise Take Reduction Plan (HPTRP) final rules have been put in place to reduce the serious injury and mortality of the Gulf of Maine/Bay of Fundy stock of harbor porpoises (Phocoena phocoena). The first HPTRP final rule was announced on Dec 2, 1998 (63 FR 66464) and implemented on January 1, 1999. From here on, these HPTRP regulations will be referred to as the 1998 HPTRP. Shortly after the 1998 HPTRP was implemented, a sharp decline in harbor porpoise bycatch occurred.
Since the implementation of the 1998 HPTRP, a meeting of the Harbor Porpoise Take Reduction Team (HPTRT) was convened in December 2007 in response to recent harbor porpoise bycatch estimates that were above the stock's Potential Biological Removal (PBR) level. The aim of this HPTRT meeting was to develop management actions that would reduce harbor porpoise bycatch in New England and Mid-Atlantic gillnet fisheries to levels below the stock's PBR and approaching the Zero Mortality Rate Goal (ZMRG), which is defined as 10% of PBR. To meet these goals, the meeting focused on addressing non-compliance with the HTPRP as well as harbor porpoise bycatch occurring outside of the 1998 HPTRP Management Areas (MAs).
In January 2008, the HPTRT discussions continued to address modifications to the 1998 HPTRP during a follow-up conference call. Based on the recommendations received from the HPTRT, NMFS published a proposed rule (74 FR 36058) on July 21, 2009 to amend the 1998 HPTRP. The modifications included an expansion of current HPTRP MAs, new management measures, implementation of a "consequence" closure area strategy in New England, and increased enforcement, monitoring, and outreach efforts.
On February 19, 2010 NMFS published a final rule (75 FR 7383) amending the 1998 HPTRP, which was virtually unchanged from the proposed rule. From here on, these HPTRP amendments will be referred to as the 2010 HPTRP. The 2010 HPTRP includes the same requirements and MAs as the 1998 HPTRP, with the following additions: 1) slight expansion in the size of the Massachusetts Bay MA as well as the pinger regulated season to include the month of November; 2) creation of the Stellwagen Bank MA (requiring pingers from November through May) and the Southern New England MA (requiring pingers from December through May); 3) implementation of the "consequence" closure area strategy; 4) creation of the Mudhole South MA in the Mid-Atlantic; 5) modification to the tie-down spacing requirement on large mesh gillnets in the Mid-Atlantic; and 6) slight modification to the northern boundary of the Waters off New Jersey.
On March 17, 2010 NMFS delayed the effective date for implementing new pinger requirements in the Stellwagen Bank and Southern New England MA from March 22, 2010 to September 15, 2010 (75 FR 12699). This was due to concerns expressed by members of the gillnet fishing industry regarding the lack of availability of pingers and the short time required to complete mandatory pinger authorization training. However, all other new 2010 HPTRP requirements became effective March 22, 2010.
One of the key new components of the 2010 HPTRP to address non-compliance is the Consequence Closure Area (CCA) strategy. Under this strategy, if the average bycatch rate from two consecutive management seasons in areas associated with a CCA exceeds a specified target bycatch rate, a seasonal closure of that CCA would be triggered. The CCA strategy involves three potential seasonal closure areas; these areas overlap with existing MAs. The Coastal Gulf of Maine CCA overlaps with the Mid-Coast, Stellwagen Bank, and Massachusetts Bay MAs. The
Eastern Cape Cod and Cape Cod South Expansion CCAs overlap with the Southern New England MA (Figure 1C). A plan to monitor the effectiveness of and compliance with the HPTRP was developed along with an improved enforcement strategy (NOAA Fisheries PRD 2010). Compliance with the HPTRP requirements is critical to maximizing the effectiveness of the HPTRP, and the development of the monitoring plan and enforcement strategy were intended to contribute significantly toward achieving the goals and objectives of the HPTRP. For more information on the 1998 and 2010 HPTRP regulations, view the NOAA Fisheries Service Northeast Regional Office's HPTRP website at: www.nero.noaa.gov/hptrp.
This paper reports the observed compliance rates with the 1998 and 2010 HPTRP requirements, and the observed bycatch rates for the HPTRP MAs using data collected during June 2009 through May 2010 (referred to as the 2009-2010 fishing season). However, it should be emphasized that the 2010-2011 fishing season was the first of two consecutive fishing seasons used to evaluate bycatch rates within potential CCAs. The fishing season evaluated in this paper (2009-2010) was not used to evaluate a potential CCA. It is assumed that the 2009-2010 fishing season bycatch rates may not be an accurate indication of bycatch rates after the full implementation of the 2010 HPTRP amendments.
This paper can be considered an update to the series of papers that reviewed bycatch rates and HPTRP compliance for the past two fishing seasons (2007-2008 and 2008-2009, Orphanides et al. 2009 and Orphanides 2010, respectively). The Orphanides et al. (2009) paper also discussed pinger tester development, while the present paper will update this and report on the deployment of pinger testers during the 2009-2010 season.
Bycatch and Compliance
The NEFOP data were used to calculate bycatch and compliance rates. Bycatch rates were calculated as the number of observed harbor porpoise takes per observed metric tons (mtons) of live fish landed. Recorded dressed landed weights were converted to live weights using established conversion factors (Warden and Orphanides 2008). Metric tons of fish landed were used to calculate bycatch rates to be consistent with how annual harbor porpoise bycatch estimates are calculated (e.g., Orphanides 2010), and because 2010 HPTRP CCAs are tied to bycatch rates using this unit of effort. Landings are used to calculate annual harbor porpoise bycatch estimates because landings are the only unit of effort that are both statistically appropriate and available in the databases used to estimate the bycatch for the total fishery (Orphanides and Palka 2007).
Rare missing values in the NEFOP database were imputed using medians from representative strata using methods described in Warden and Orphanides (2008). After imputing missing values from representative strata, 3.5% (125 out of 3525) of the observed hauls still had missing values in the variables used in the bycatch and compliance analysis. Two hauls with incidental harbor porpoise takes were missing twine size information. One haul was in the Waters off New Jersey where twine size is regulated, though the other haul was in the Gulf of Maine where twine size is not regulated under the HPTRP. Mesh size was recorded on all observed hauls. For 99.2% (3496 out of 3525) of the hauls, mesh size was recorded as a single value, for 0.8% of the hauls (28 of 3525), it was recorded as minimum and maximum values, and one value was imputed from other mesh sizes on the trip. When a minimum and maximum range was recorded, a simple average of these two mesh sizes was used in this analysis. Twine size was imputed on 5.8% of the observed hauls (203 out of 3525), which accounted for most of the imputed values used in this analysis. Out of 707 hauls observed using tie-downs, ten hauls (1.4% of those using tie-downs) were observed as having used tie-downs without recording the length of the tie-downs, and one of these hauls had an incidental take of harbor porpoise. However, none of these occurred within HPTRP MAs and so do not impact compliance calculations. Latitude and longitude was imputed for 17 (0.5%) out of 3525 hauls, and was missing for 36 (1.0%) hauls. These missing locations were left unknown and therefore were not included when compliance and bycatch information was summarized by area. The number of pingers on a haul was not recorded for 1.0% of hauls with known pinger use (6 out of 588). For these hauls, the number of pingers also could not be determined from examination of the NEFOP gear logs and observer comments. However, none of these six hauls had observed harbor porpoise bycatch.
Recorded gear configurations were used to check for HPTRP compliance. The gear requirements that were checked within the time/areas defined within the HPTRP included: pinger use, net length, twine size, number of nets per string, tie-down length, and tie-down use. Additionally, compliance with seasonal HPTRP closures to gillnet fishing was examined. In the Mid-Atlantic for large mesh and small mesh gillnets, the regulations for the tie-down spacing and number of nets per vessel were not investigated because this information was not recorded on observer logs.
Pinger functionality was assessed for the six trips where pinger testers were employed. For these six trips, the total percentage of functional pingers was quantified, as was the true compliance (where pingers were both functional and present in the proper number). However, since limited pinger functionality data was available for this time period, pinger functionality data were not included in the compliance calculations.
In the New England gillnet fisheries during times and areas where pingers are required, a typical gillnet string with 10 300-ft long nets is required to have 11 working pingers on the string (one pinger on each end of the string, and one in between each net). The presence of the proper number of pingers was assessed. In addition, pinger use in less than the required numbers was also assessed to examine attempted compliance and to provide a complete investigation of pinger use in the fishery. However, it is thought that only the use of the proper number of functional pingers will achieve bycatch reduction goals (Palka et al. 2008). It is also important to note that the pinger compliance for this analysis did not assess whether pingers were functioning properly, but simply whether the required number of pingers was present on nets.
1998 HPTRP Compliance
The overall observed compliance rate to the HPTRP for the period June 2009 - May 2010 was 46.3% (Table 1). The total observed compliance rate for New England was 43.0%, with the highest New England compliance rate within the Cape Cod South MA (85.2%), and lowest rate within the Offshore MA (21.3%). No hauls were observed in the Northeast Closure Area or in the Cashes Ledge Closure Area when they were closed to gillnets. The Mid-Atlantic had similarly poor compliance rates, with an overall rate of 55.4%. The highest Mid-Atlantic compliance rate was within the small mesh hauls in the Waters off New Jersey MA (87.5%), and the lowest rate among areas with more than one haul observed was within the large mesh hauls in the Southern Mid-Atlantic MA (29.0%). For a description of the 1998 HPTRP regulations see Table 2 and Figures 1A and 1B.
In the New England sink gillnet fishery, all non-compliant hauls were out of compliance because they did not have the required number of pingers. No fishing was observed in areas closed to all gillnet fishing (Table 3). Among the pingered hauls in the 1998 HPTRP New England MAs, 21.5% (98 out of 455) contained greater than or equal to 90%, but less than 100% of the required number of pingers (Table 4). It is important to note that the pinger compliance for this analysis did not assess whether pingers were functioning properly, but simply whether the required number of pingers was present on the nets.
Outside of the 1998 HPTRP New England MAs that required pingers, 7.6% (84 out of 1099) of the observed New England hauls used pingers in a fashion that would be compliant, if they were within a MA requiring pingers (Table 4). Roughly two thirds of these New England pingered hauls outside of 1998 HPTRP MAs occurred within the 2010 HPTRP Stellwagen Bank and Southern New England MAs (35.7%, 30 out of 84, and 33.3%, 28 out of 84, respectively).
Pinger testers were present on 7 trips during the study period, 4 in December 2009, 2 in January 2010 (Table 5), and 1 in March 2010. These trips comprised 22 hauls, though 7 hauls had no pingers on the nets and were not included in this summary, including all 4 hauls on the March 2010 trip. Of the observed pinger tester hauls with pingers on the nets, 9 were in the Mid-Coast MA, 3 in the Massachusetts Bay MA, and 3 in the 2010 Stellwagen Bank MA. No harbor porpoise were incidentally caught on any of the trips where pinger testers were present. Seventy-nine percent of pingers tested were working. On roughly half of the tested hauls (8 of 15), all pingers that were present were working, though they may not have had the proper number of pingers. Among the tested hauls, 6 had the proper number of pingers present, but only 1 of these had all pingers working. A third of these (2 of 6) were in the 2010 Stellwagen Bank MA, where pingers were not yet required. On a third of the tested hauls (5 of 15) it was reported that at least one pinger was lost. This loss rate is much higher than that reported on observed hauls with pingers that did not have the pinger testers. Only 6 of 573 (1.0%) New England hauls deployed with pingers, but without pinger testers, reported a pinger lost.
Only half of the observed hauls (6/12) with incidental harbor porpoise takes within 1998 HPTRP MAs were compliant with the 1998 HPTRP regulations (Table 6). Among the 6 non-compliant hauls in the New England 1998 HPTRP MAs, 5 Mid-Coast MA hauls used pingers, but not enough to be compliant. In addition, 10 hauls with a total of 11 takes occurred in the area that would become the Southern New England 2010 HPTRP MA, which was not in place at the time of the takes. These incidental takes occurred in two primary areas; 6 occurred in the southern portion of the area that would become the Southern New England MA, and 5 occurred on 4 hauls east of Cape Cod (Figure 2).
In the Mid-Atlantic 1998 HPTRP MAs, 8 harbor porpoises were taken on 4 hauls, three of which were compliant with closed area and gear modification requirements (no pingers are required in the Mid-Atlantic) (Table 6). The non-compliant haul was non-compliant due to exceeding the maximum required tie down length. This haul also took place in a time and area that would be closed under the 2010 HPTRP (Mudhole South MA); however, the final rule amending the HPTRP became effective on March 22, 2010, which was after the seasonal closure of this area would have taken place (February 1 through March 15). Therefore, the area was not closed at the time the take occurred. All Mid-Atlantic hauls with takes occurred in the Waters off New Jersey MA in hauls with large mesh.
In the Mid-Atlantic, 19.7% (17 out of 86) of all non-compliant hauls occurred in a closed area (Table 1 and Table 3). The majority of non-compliant hauls (89.5%, 77 out of 86) occurred on large mesh strings. More than a third (37.2%, or 32 out of 86) of non-compliant Mid-Atlantic hauls exceeded the limit on the number of nets per haul. Among non-compliant hauls, only a handful (3.5%, 3 out of 86) had multiple violations, such as having too many nets on a string and not fishing with tie-downs on the same string (Table 2).
The observed harbor porpoise bycatch rate in the Mid-Coast MA (0.091 harbor porpoise/mton landed) was the highest of any MA in New England (Table 7). The bycatch rate in the neighboring 1998 HPTRP version of the Massachusetts Bay MA (prior to its slight expansion in the 2010 HPTRP) (0.088 harbor porpoise/mton landed) was just slightly lower than in the Mid-Coast. The bycatch rate within the Cape Cod South MA was 0.032 harbor porpoise/mton landed. The 2010 HPTRP expanded that area to the Southern New England MA (see Figure 1), and the bycatch rate within that larger area was higher at 0.075 harbor porpoise/mton landed because the bycatch rate within the additional area was high (0.085 harbor porpoise/mton landed). The difference between these two regions is likely real, but could be due in part to a more than three times larger sample size in the Southern New England area outside of the Cape Cod South MA. On the opposite end of the spectrum, the Offshore MA and the 2010 HPTRP Stellwagen Bank MA both had more than 160 hauls observed and each had an observed bycatch rate of zero. Also non-HPTRP areas had a low bycatch rate of 0.007 harbor porpoise/mton landed.
Bycatch rates in the Mid-Atlantic varied considerably by area. An extremely high bycatch rate of 0.500 harbor porpoise/mton landed was observed in the Waters off New Jersey MA (Table 7). This excludes the Mudhole North MA, but includes the area of the Mudhole South MA. The Mudhole South MA was part of the Waters off New Jersey MA during this time, prior to the creation of the Mudhole South MA as a separate area with more stringent requirements. But, no matter how the area is divided up, the end result is a very high bycatch rate in the region off New Jersey (0.418 harbor porpoise/mton landed in Waters off New Jersey, Mudhole South, and Mudhole North MAs combined). No takes were observed in the Southern Mid-Atlantic.
Bycatch rates in areas associated with 2010 HPTRP CCAs were well above the 2010 HPTRP target bycatch rates. The combined bycatch rate for the areas associated with the Coastal Gulf of Maine CCA was 0.060 harbor porpoise/mton landed, or nearly twice the HPTRP 2010 target rate for that area (0.031 harbor porpoise/mton landed) (Table 7). The bycatch rate for the area associated with the Eastern Cape Cod and Cape Cod South Expansion CCAs was 0.075 harbor porpoise/mton landed, or more than three times the 2010 HPTRP target bycatch rate for that area (0.023 harbor porpoise/mton landed). However, it should be emphasized that the 2010 HPTRP CCA management measures were not in place during the fishing season evaluated in this paper, June 2009 - May 2010. Monitoring of the areas associated with the Consequence Closure Areas began on September 15, 2010.
Among the 29 harbor porpoises observed incidentally taken during the 2009-2010 management seasons, only 2 (6.9%) were taken outside of the 1998 or 2010 HPTRP management times and areas. More than a third of the observed incidental takes (11 out of 29 harbor porpoises) were observed in areas that were not historically regulated under the 1998 HPTRP, but would be included in the 2010 HPTRP amendments. The remainder (16 harbor porpoises, 62.1%) occurred within the 1998 HPTRP MAs (Figure 2, Table 6, and Table 7). One of these 16 animals was observed in waters that would be closed under the 2010 HPTRP as part of the Mudhole South MA, but was open at the time as a part of the Waters off New Jersey MA. Among observed hauls in New England, the additional 2010 HPTRP MAs had a higher bycatch rate (0.065 harbor porpoise/mton landed) than the 1998 HPTRP MAs (0.047 harbor porpoises/mton landed) and non-HPTRP times and areas (0.007 harbor porpoises/mton landed) (Table 7).
Bycatch rates with compliant pinger use varied by MA, where compliance is defined solely in terms of using the correct number of pingers because the functionality of the pingers is unknown (Table 8). Overall, the bycatch rate in the 1998 or 2010 HPTRP MAs was only about 16% less on compliant pingered hauls (0.049 harbor porpoise/mton landed) than on non-compliant hauls (0.058 harbor porpoises/mton landed) that had less than the required number of pingers for the same times and areas. It should also be noted that the more than two-thirds of observed hauls had fewer than the required number of pingers. The bycatch rate for compliant Mid-Coast MA hauls was far less than for non-compliant Mid-Coast MA hauls. However, the bycatch rates were higher in the Cape Cod South and Massachusetts Bay MAs in non-compliant hauls as compared to compliant hauls, though in each case only one take was observed in the compliant MA hauls (Table 8).
Compliance levels for the 2009-2010 fishing season were similar to those of the previous fishing season (2008-2009) in the Mid-Atlantic, and worse in New England. In the Mid-Atlantic, this season's compliance (55.4%) was about the same as in the previous management season (56.3%), though it was still poor. Compliance in New England this season (43.0%) was quite a bit lower than during the 2008-2009 fishing season (51.9%) (Orphanides 2010b). This fishing season's compliance in large mesh in the Southern Mid-Atlantic and Offshore MAs was particularly low (29.0% and 21.3%, respectively) (Table 1), though no harbor porpoise incidental takes were observed in either MA. In contrast, the small mesh Southern Mid-Atlantic MA and the Cape Cod South MA both had compliance rates over 80% (Table 1). These compliance levels were associated with no observed bycatch in the Southern Mid-Atlantic MA, and one bycatch event in the Cape Cod South MA. As in past years, no hauls were observed in New England closed areas, while several were observed in Mid-Atlantic closed areas (Table 3) (Orphanides et al. 2009, Orphanides 2010b).
New England pinger compliance rates presented in this paper are likely to be an over-estimate of the actual compliance rates if the limited sample of pinger tester data is representative of the fishery. For the vast majority of observed hauls, it was not known whether the pingers present were functional. However, of the 15 hauls for which pingers were tested, only one haul (6.7%) had the proper number of pingers on the nets and all of the pingers working. Looking more broadly, just over half, or 8 of 15, of the hauls tested had all present pingers on each string functioning, however, 7 of 8 did not have the proper number of pingers on their nets. Admittedly, this is a small sample of tested hauls, but if the results are representative of actual pinger functionality, then the actual compliance rate estimate would be half or less than the estimates presented here in Table 1, and thus would be at or below the 20 percent range.
Very high bycatch rates (0.500 harbor porpoise/mton) and limited compliance (59.7%) in the Waters off New Jersey continue to be a problem, though observed effort during the MA time period is limited (Table 7). A high bycatch rate in the 2010 HPTRP Southern New England MA shows the importance of this MA in limiting future bycatch. The bycatch rate in Southern New England (not including Cape Cod South MA) during the 2009-2010 season (0.085 harbor porpoise/mton) was less than during the 2008-2009 season (0.117 harbor porpoise/mton), though it was still among the highest rates observed in New England. In contrast, no incidental takes were observed in the 2010 HPTRP Stellwagen Bank MA in the 2009-2010 season, whereas bycatch rates in this area had very high bycatch rates in the previous two management seasons (0.320 harbor porpoise/mton in 2008-2009 and 0.302 harbor porpoise/mton in 2007-2008) (Orphanides et. al. 2009, Orphanides 2010). On the other hand, the Massachusetts Bay MA, right next to Stellwagen Bank MA, had one of the highest MA bycatch rates in New England for the 2009-2010 season.
Despite the lack of observed bycatch in the Stellwagen Bank MA, bycatch patterns for the 2009-2010 fishing season looked fairly similar to those from the previous fishing seasons (Orphanides et al. 2009, Orphanides 2010b). As in the past, the majority of the bycatch occurred in either 1998 or 2010 HPTRP MAs, with very little bycatch occurring outside of 1998 and 2010 MAs. Clusters of bycatch occurred in the Hudson Canyon region (in the general area of the Mudhole North, Mudhole South, and Waters off New Jersey MAs), south of the Cape Cod South MA but within the 2010 HPTRP Southern New England MA, and in the Gulf of Maine in the region of Massachusetts Bay, and southern Mid-Coast MA (Figure 2). Another similarity to previous management seasons was that the bycatch rates in the CCA-associated areas were over twice the target rate needed to avoid closures in the future. However, it should be noted that the 2010 HPTRP management measures, including some new pinger requirements, were not yet in place for the 2009-2010 season.
A change from previous management seasons was the contrast between bycatch rates on hauls with the full complement of pingers versus those with fewer than the required number of pingers. In the previous two seasons, the bycatch rates on hauls with the proper number of pingers were on average roughly 50-70% less than those on hauls without the required number of pingers (Orphanides et al. 2009, Orphanides 2010b). This corresponds with the differences in bycatch rates Palka et al. (2008) found in earlier years between hauls with the required number of pingers and non-pingered hauls. During the 2009-2010 fishing season, the bycatch rate on hauls with a full complement of pingers was still lower than non-pinger compliant hauls, though the difference was not as great (0.049 versus 0.058 harbor porpoise/mton landed). As with all bycatch rates, annual variability is expected. So, this outcome could simply reflect that variability.
Pinger functionality, or lack thereof, could be playing a role in these bycatch rates. For most hauls, it was not known whether pingers present were functional. Using data collected in previous years, it appears that bycatch rates increase on nets with some pingers, but not the proper number (Palka et al. 2008). So, the relatively high bycatch rates on hauls with a full complement of pingers could be explained if a high enough portion of these nets contained pingers that were not working. Alternatively, the difference in compliant and non-compliant bycatch rates could be influenced by unequal sample sizes of hauls with and without pingers in many MAs. Overall, the number of hauls with a full complement of pingers was less than half the number of hauls without a full complement of pingers. However, in the Mid-Coast MA the sample size was relatively large, and the number of hauls with a full complement of pingers was fairly similar to the number of hauls without the required number of pingers. In this region with similar sample sizes, the bycatch rate was far lower on pinger-compliant hauls as compared to that on pinger non-compliant hauls (0.033 versus 0.142 harbor porpoise/mton landed).
Reducing bycatch in the US Northwest Atlantic gillnet fisheries is largely dependent on compliance with HPTRP regulations. Pingers need to be both present in the proper numbers, and functioning properly to be an effective deterrent to harbor porpoise bycatch (Palka et al. 2008). Pinger functionality is beginning to be assessed by NEFOP, but the sample size for the 2009-2010 fishing season was not large enough to get an accurate picture of how many pingers are functioning and to what extent present but non-functioning pingers are affecting the bycatch rates of strings with a full complement of pingers.
NOAA Fisheries, Protected Species Division (PRD). 2010. Harbor Porpoise Take Reduction Plan Monitoring Strategy: Monitoring the Effectiveness and Regulatory Compliance of the Harbor Porpoise Take Reduction Plan (HPTRP). p18. Available from: http://www.nero.noaa.gov/prot_res/porptrp/doc/HPTRP%20Monitoring%20Summary%204-2-2010.pdf
Orphanides CD, Palka DL. MS 2007. Landings: the Unit of Effort for Bycatch Rates in Gillnet Fishing Gear. Harbor Porpoise Take Reduction Team (HPTRP) Meeting Materials. Binder Document 3d. Available from National Marine Fisheries Service, Northeast Regional Office, 55 Great Republic Drive, Gloucester, Massachusetts, 01930-2298.
Orphanides CD. 2010. Estimates of Cetacean and Pinniped Bycatch in the 2007 and 2008 Northeast Sink Gillnet and Mid-Atlantic Gillnet Fisheries. US Dept Commer, Northeast Fish Sci Cent Ref Doc. 10-10; 45 p. Available from: National Marine Fisheries Service, 166 Water Street, Woods Hole, MA 02543-1026 or http://www.nefsc.noaa.gov/publications/crd/
Orphanides CD. 2010b. Update on Harbor Porpoise Take Reduction Plan Monitoring Initiatives: Compliance and Consequential Bycatch Rates from June 2008 through May 2009. US Dept Commer, Northeast Fish Sci Cent Ref Doc. 10-22; 23 p.Available from: National Marine Fisheries Service, 166 Water Street, Woods Hole, MA 02543-1026, or online at http://www.nefsc.noaa.gov/publications/crd/
Orphanides CD, Wetmore S, Johnson A. 2009. Update on Harbor Porpoise Take Reduction Plan Monitoring Initiatives: Compliance and Consequential Bycatch Rates from June 2007 through May 2008, Pinger Tester Development and Enforcement from January 2008 through July of 2009. US Dept Commer, Northeast Fish Sci Cent Ref Doc. 09-14; 16 p. Available from: National Marine Fisheries Service, 166 Water Street, Woods Hole, MA 02543-1026 or http://www.nefsc.noaa.gov/publications/crd/
Palka DL, Rossman, MC, VanAtten, AS, and CD Orphanides. 2008. Effect of pingers on harbour porpoise bycatch in the US northeast gillnet fishery. J. Cetacean Res. Manage. 10(3):217-226.
Warden ML, Orphanides CD. 2008. Preparation of the Northeast Fisheries Observer Program gillnet data for use in bycatch analyses of protected species. US Dept Commer, Northeast Fish Sci Cent Ref Doc. 08-17; 44 p. Available from: National Marine Fisheries Service, 166 Water Street, Woods Hole, MA 02543-1026 or http://www.nefsc.noaa.gov/publications/crd/
Waring GT, Josephson E, Maze-Foley K, Rosel, PE, editors. 2011. U.S. Atlantic and Gulf of Mexico Marine Mammal Stock Assessments -- 2010. NOAA Tech Memo NMFS NE 219; 598 p. Available from: National Marine Fisheries Service, 166 Water Street, Woods Hole, MA 02543-1026, or online at http://www.nefsc.noaa.gov/publications/tm/
 PBR is defined as the maximum number of animals that may be removed from a marine mammal stock while allowing that stock to reach or maintain its optimum sustainable population. For the specifics on the harbor porpoise PBR, see the harbor porpoise stock assessment chapter in the most recent report on the US Atlantic and Gulf of Mexico Marine Mammal Stock Assessments (Waring et al. 2011) (http://www.nefsc.noaa.gov/publications/tm/tm219/)