Summary of the Industry-DFO Collaborative Post-season Trap Surveys for Snow Crab in Div. 2J3KLOPs4R

Transcription

1 Wp: 2013/ Summary of the Industry-DFO Collaborative Post-season Trap Surveys for Snow Crab in Div. 2J3KLOPs4R by D.E. Stansbury, D. Fiander and D. Maddock Parsons

2 INTRODUCTION The industry-department of Fisheries and Oceans (DFO) collaborative post-season (CPS) trap surveys for snow crab started in 2003 in NAFO Div. 3KLPs4R. In 2005, 2007 and thereafter the survey has been conducted in NAFO Div. 2J. The Fisheries Science Collaborative Program (FSCP) which funds this survey has been developed by the DFO to bring together DFO scientists and Atlantic fishers to collaborate on fisheries science research. This document is meant to summarize the 9 years of surveys since 2004.The approach is to examine catch rate series based on mean number of male crab per trap over all the Newfoundland and Labrador region. Comparing NAFO divisions, the inshore and offshore components of each division where appropriate and finally down to the Crab Management Areas (CMA). We hope this document will be used as a catalogue of the survey series and a source of information for the fishing industry and science. METHODOLOGY The surveys, conducted by snow crab harvesters, focus on commercial fishing grounds within individual CMAs. Survey stations are fixed and generally follow a grid pattern, with maximum station spacing of 5 X 5 (Fig.1). At each station, 6 (inshore) or 10 (offshore) commercial (135 mm mesh) crab traps are set in each fleet. All crab caught are sexed and counted. Biological sampling of male crab is conducted at sea, by observers, from two traps at each station. Sampling includes determination of carapace width, shell condition, leg loss and presence of bitter crab disease (BCD). One small mesh trap is added at selected stations (Figs. 5-7) to collect information on pre-recruits and females. Incidents of BCD are also recorded. Male crab sampled from large mesh pots are classified based on size and shell condition for this analysis. Crab less than 95 mm are classified as sub-legal and those greater than or equal to 95 mm are classified as legal. For the catch rate analysis, two shell conditions (new, old) are used. For carapace width (CW) frequencies an additional category of soft shell is split from the new shell. Male crab sampled from small mesh pots are also classified on chelae height (CH). A model (Dawe et al. 1997) separates two clouds of chelae height on carapace width into adult ( large-clawed) and juvenile (small clawed). The model is defined as: CW =0.0806*CH Once a male develops a large claw it is terminally molted and will not continue to grow. This can happen at any size greater than 40 mm CW (Dawe et al. 2007). For spatial representation, stations have been grouped according to NAFO division, inshore and offshore component within the division and CMA within each shore component. Prior to 2010 only stations that were consistently sampled from 2004 to 2009 were used in this analysis. Since 2010, a set of CORE stations are now selected for inclusion in the analysis. The criteria for a CORE station follows loosely on the same criteria used for common stations that were used at the 2009 Regional Assessment Process (RAP). Thus, the stations occupied in 2009 and 2010 had no influence on whether a station was core or non-core. As done in previous years, 2003 was dropped from the criteria for core

3 stations in all NAFO divisions. Therefore, core stations are stations that have been occupied consistently from 2004 to 2008 for NAFO divisions 3K, 3L and 3O. For NAFO division 2J and subdivision 3Ps the common stations sampled in 2007 and 2008 determined core stations. Stations sampled in 2007 for 4R offshore, determined the core stations, while inshore 4R are stations occupied consistently in 2004, 2006 and New for the 2012 survey, an additional 17 stations in 2J have been added to the core stations. Size frequencies plots are derived from core stations for both small and large mesh pots. Incidents of Bitter Crab Disease (BCD) are derived from new shelled crab from core stations for small mesh pots for both sexes in this analysis. There were 980 large pot core stations sampled in 2012, down from 1003 in 2011, but the same as in 2010 (Table 1). Using the criteria for CORE stations (see above), there is the potential of 1021 large mesh core stations in any given year. This occurred only in Every effort is been made to retain fishing core/common stations. Sampling of the small mesh pot stations has been consistent since 2009 at 152 stations. NAFO divisions 2J3KLOPs4R RESULTS The number of core stations occupied by year and NAFO division for large and small traps are given in Table 1. Total number of core stations fished in any one year varied from 798 to 1021 with most of the variability in NAFO sub-division 3Ps and division 4R. By using the core station criteria more stations are used in the analysis since 2010 than in previous years, when common stations were used. The number of stations sampled within each CMA is given in table 2. Even in Sub-division 3Ps and division 4R sampling within the CMA s have been consistent over the last 6 years One of the goals of the survey protocol is to start September 1 of each year. In most NAFO divisions, the start time is within 10 days of this, with the exception of 2J and 3O in the early years of the survey (Table 3). Prior to 2012, the within NAFO division duration of the survey has taken 46 days on average; maximum 87 days (3L 2009). However, in 2012, division 2J (80) and 4R (55) have taken the maximum number of days to complete, where as 3O (3) and 3Ps (18) has taken the fewest number of days.there has been considerable variation in the duration of the survey within and between divisions. NAFO divisions 3L and 3Ps averaged 59 and 53 days respectively to complete the survey whereas 2J and 4R were approximately 48 and 35 days respectively, while division 3K took 54. Average soak times have become less variable over the last 3 or 4 years of the survey within each CMA (Table 4). Given that the survey is a fixed station design, one would not expect a great deal of variation in depth fished within CMA (Table 5). A map of the CMA and the potential survey stations are presented in Figure 1. Geographical reference of the catch rate (mean number/tow) for large and small mesh traps are given in Figs

4 Divisional Overview Division 3K and 3L have similar catch rates in their inshore component for both new and old shell, legal size (=>95mm) crab until 2009, when there is a reduction in the 3K old shell component (Fig. 8.). For both divisions in the inshore the catch rate of old shelled crab is at a new high. NAFO subdivision 3Ps inshore is noticeably lower in the early years of the survey but has been increasing from 2004 to 2010 with some variability since. In the offshore, 3L is showing an increase in legal size crab whereas 3K and 3Ps are showing a decline There is also a decline in 2J since the start of the survey with perhaps a slight annual increase from 2009 through to Catch rates of sub-legal size in offshore 3L (Fig. 9) increased from 2006 to 2010 but have declined since. Subdivision 3Ps has also shown a decline since in 2010, while there is little change in the other divisions. NAFO division 2J NAFO Div. 2J has been surveyed for 6 consecutive years ( ) Catch-rate series for the various shell condition and size category are in Figures The legal size component of the sampled population is predominantly new shell crab in 2007 with a shift to older shelled animals in 2008 (Fig. 10). The old shell component is virtually non existent in 2009 but has returned to average levels in since. Annual size frequency shows no modal progression (Fig. 13). NAFO division 3K In NAFO Div. 3K (inshore and offshore) the catch rate series for sub-legal and legal size crab has fluctuated (Fig ). At the CMA level, 3KB has shown the highest catch rate among the CMA s and is also the most variable. Since 2007,both the sublegal and legal size catch varied together, suggesting possible year effects in the survey for CMA 3KB. In all the CMA s there is no evidence off a progression in catch rates as it relates to size. For example, knowing the change in catch rate of sub-legal crab does not give any predictive power with the change in catch rate for legal size crab (Fig 18). At the divisional scale the mode at 38 mm in the small mesh traps that was evident in 2007 (Fig 21) did not manifest itself with an increase in larger animals in subsequent years. Figures display the size frequency for inshore and off shore from large mesh trap. In the small mesh traps since 2006 (Fig ) there is a much higher proportion of terminally moulted sub-legal crab in the inshore than in the offshore. Annual size frequencies are shown in Figs from large mesh traps for individual CMA s. There are only 2 CMA (3KC, 3K4) using small mesh traps (Figs. 31 and 32) The increasing trend in percent occurrence of BCD in males in 3KC since 2004 ceased in 2008 and was at the lowest level in the time series in 2010 (Fig.33). Presently it is about 5% to 6 % in 2011 and Prevalence has never exceeded 10% for males 5

5 in either CMA. The incidents of BCD in females in 3K4 have increased since 2005 to 15 % in 2010 and have since declined to about 6% in NAFO division 3L In 3L inshore, the catch rate series had varied little for legal size crab (Fig. 34) while the offshore series has increased from 2007 to 2012 (Fig. 35). Immediate recruits, as indicated by new shell crab (Fig 34 Lower panel), catch rate has changed little over the time series along with the catch rate for old shell animals. The sub legal size crab catch rates has declined in 2012 in all inshore CMAs with the exception of 6B-Conception Bay (Fig 36). In 3L offshore, Immediate recruits catch rate has steady increased from 2007 to the highest observed level in 2012 (Fig. 35 lower panel). Old shell crab has all showed an increase from 2008 to 2011 but declined in Sub-legal catch rates peaked in 2009 or 2010 in all offshore CMAs and showed significant declines since, except in CMA 8B (Fig. 37). The average size of old shell crab sampled from large mesh traps (at the divisional scale) declined from 101 mm (CW) in 2004 to 95 mm in (Fig 40). The average size for new shell animals has increased from 95 mm in 2009 to 101 mm in The mean size of small clawed crab increased from 65 to 85 mm (CW) from 2006 to 2012 (Fig. 41). Figures display the size frequency for inshore and offshore from large and small mesh trap. There is evidence of modal progression displayed in 3L offshore from the small mesh pots (Fig. 45). This modal progression has been driven by the samples taken from MSEX (Fig. 63). A similar, but not as clear progression from 2006 to 2009 is also shown in CMA 9A, but here we miss the modes in 2007 and 2008 (Fig. 61). This continued growth is evident in 2010 with a mode at 97 mm for new shell crab sampled from the large mesh plots (Fig. 51). Annual size frequencies are shown in Figures from large mesh traps for individual CMA s. Size frequencies from small mesh traps are displayed in Figs Trinity and Conception bays have both exhibited outbreaks of BCD over the years (Fig. 64). Trinity Bay (6A) had percent occurrence of BCD over 40% in females while most other CMA s were less than 15%. Conception Bay (6B) has alternated between 20 and 5% since 2003 to 2006, with little in the 2007 sampling. For 2008, all CMAs had less than 5% infection with the exception of Conception Bay which was slightly above 10%. In 2009, 2010 and 2011, there was little to no BCD observed in any of the 3L CMA s. However, Conception Bay (6B) had percent infection near 10% in 2012 (Fig. 64). NAFO division 3O In CMA 8B the only CMA in NAFO division 3O, the catch rate series has varied without trend for legal size crab (Fig. 65). Size frequency plots from large mesh pots showed no modal progression (Fig. 68). There was no small mesh pots used in NAFO division 3O in 2011 however, modal progression is quite evident from 2005 to 2010, with another new pulse of possible recruitment at 35 mm size in 2012 (Fig. 70). There has never been BCD observed in division 3O in this survey (Fig. 71). 6

6 NAFO subdivision 3Ps The catch rate series in 3Ps inshore had over doubled for sub-legal (12-28 crab/trap) from 2006 to 2007(Fig. 72). This increase has culminated in a greater than 70% increase of legal size crab in However, this coherence did not continue into 2009 and In 2010 the catch rate for legal size crab was the highest in the time series and the majority of these crabs were new shelled immediate recruits. For 2011, there is a marginal increase in both legal and sub-legal size crab in In the offshore, the sub-legal and legal catch rates have declined since 2009 or 2010 (Fig. 73). Where once there was a large residual old shell component present in 2010 and 2011, this is now reduced along with the immediate recruits since At the CMA level, 10BCD has shown the highest catch rate among CMA s for both sublegal and legal size crab (Fig. 74) with a substantial increase in legal size in 2009 that may be an anomaly given the 2010 value. The exception we seen in 2011 in 11S legal size crab catch rate appears anomalously high given perhaps very low values for The increases in sub-legal size catch rates are evident in the size frequencies for inshore and offshore from large and small mesh trap (Figs ). Annual size frequencies are shown in Figs from large mesh traps for individual CMA s. Size frequencies from small mesh traps are displayed in Figs BCD has not been detected in Levels of BCD have never been observed above 10% in the survey in 3Ps (Fig 90). NAFO division 4R The catch rate series in 4R inshore has been low relative to all other NAFO divisions in the NL region. Catch rates for sub-legal size crab has doubled from 2008 to 2009 (Fig. 91). This increase has led to a doubling in legal size crab catch rate in However, this relationship does not continue as there was a steady decrease in sublegal crab from 2010 to 2012 with legal size crab at its highest values in 2011 and These high catch rates are predominantly new shelled legal size crab in all inshore CMAs with little residual old shell crab (Fig. 94). The offshore has been sampled in 2003 and and the catch rates have been relatively low (Fig. 92). There was no indication of immediate recruits in the survey for the entire time series. Annual size frequencies for the division are shown in Figures from large and small mesh traps. Modal progression is evident from 2009 to 2012 in large mesh traps at the divisional level (Fig 95) lead by the progression in the inshore (Fig 97) predominantly in Bay St. George (12C) and Bonne Bay (12G) figures 100 & 103. This recruitment pulse 7

7 in CMA 12C is detected one year earlier in 2008 using the small mesh traps (Fig 105). Unfortunately there have been no other significant signs of recruitment since. No significant level of BCD has been recorded in 4R during this survey (Fig. 109). DISCUSSION The 109 figures in this catalogue are meant to be informative to both scientists and crab harvesters. Each reader we hope will find the summaries suitable to their level of interest, whether it is at the regional, divisional, inshore vs. offshore or to their own CMA. This survey was first used in the Regional Assessment Process (RAP) in 2006 and should continue into the further to give a post-season index of crab abundance at the appropriate spatial level required. This survey is the only source of fishery independent data for most of the 30 CMAs in the Newfoundland and Labrador region. ACKNOWLEDGMENTS We would like to thank all harvesters that have taken part in the survey over the seven years. Without a co-operative working arrangement this work would not be possible. I would also like to thank the staff of the FSCP section at DFO NL region for providing data and given clarification on issues. REFERENCE Dawe, E., D. Mullowney, D. Stansbury, D. Taylor, E. Hynick, P. Veitch, J. Drew, G. Evans, E. Colbourne, P. O Keefe, K. Skanes, D. Fiander, R. Stead, D. Maddock Parsons, P. Higdon, T. Paddle, B. Noseworthy, and S. Kelland An Assessment of Newfoundland and Labrador Snow Crab in CSAS Res. Doc. 2009/057, 160 p. 8

8 Table 1. Number of core stations sampled using large and small mesh traps by NAFO Divs. And Year. Large Mesh NAFO TOTAL 2J K L O PS R TOTAL Small Mesh NAFO TOTAL 2J K L O PS R TOTAL

9 Table 2. Number of Core Stations for ALL Years by CMA. Large mesh. Large mesh NAFO manare a J 2J K 3k KB KBC KC KD L> LEX A A B C A B A MS MSEX NS O 3O PS 10A BC D E S SX C E F G OFF

10 Table 3. Number of Core Stations for ALL Years by CMA. Small mesh. Small Mesh NAFO manar ea K 3K KBC 4 3KC LEX 2 3L 6A B C B 5 9A MSEX NS O 3O PS 10A E S R 12C E 1 12F G OFF

11 Table 4. Start and End Dates of the Survey in each NAFO Div. and Year. Timing of surveys for Core Stations. NAFO YEAR StartDate EndDate # Days NAFO YEAR StartDate EndDate # Days 2J Oct 02-Oct 1 3PS Oct 14-Nov Aug 27-Oct Sep 25-Nov Sep 27-Oct Aug 06-Oct Sep 20-Oct Sep 06-Nov Sep 29-Oct Aug 31-Oct Sep 21-Oct Sep 06-Nov Aug 17-Nov Sep 14-Nov Sep 20-Oct Aug 05-Nov 67 3K Oct 17-Nov Aug 24-Sep Sep 09-Oct Sep 20-Sep Aug 20-Oct Sep 21-Sep Sep 17-Oct 41 4R Sep 22-Sep Aug 25-Oct Sep 04-Oct Aug 25-Oct Sep 25-Oct Sep 21-Oct Sep 19-Oct Sep 21-Oct Aug 03-Oct Aug 09-Nov Sep 13-Oct Sep 22-Oct Sep 01-Oct Sep 23-Oct Aug 26-Oct 57 3L Oct 19-Nov Aug 14-Oct Sep 23-Nov Sep 28-Oct Aug 01-Nov Sep 14-Oct Sep 07-Nov Aug 26-Sep Sep 27-Oct Sep 27-Nov Aug 09-Nov Aug 04-Nov Sep 30-Oct Sep 25-Sep 21 3O Sep 12-Nov Aug 21-Sep Sep 09-Oct Sep 21-Sep Sep 21-Oct Sep 23-Sep Aug 29-Sep Aug 23-Sep Sep 16-Sep Sep 08-Sep 3 4

12 Table 5. Average soak times for Core Stations by NAFO Div., Year and Crab Management Area. (CMA). (Large Mesh) Large Mesh NAFO CMA J 2J K 3K L 3KB KBC KC KD L> LEX A A B C A B A MS MSEX NS O 3O PS 10A BC D E S SX R 12C E F G OFF

13 Table 6. Average soak times for Core Stations by NAFO Div., Year and Crab Management Area. (CMA). (Small Mesh) Small Mesh 3K 3K KBC 45 3KC L 3LEX 8 6A B C A 14 9A MSEX NS O 3O PS 10A E S R 12C E 16 12F G OFF

14 Table 7. Minimum and Maximum depths by CMA for Core Stations. (Large Mesh) Large Mesh NAFO manare a min max min max min max min max min max min max min max min max min max min max 2J 2J K 3K KB KBC KC KD L 3L> LEX A A B C A B A MS MSEX NS O 3O PS 10A BC D E S SX C E F G R OFF

15 Table 8. Minimum and Maximum depths by CMA for Core Stations. (Small Mesh) Small Mesh NAFO manar ea min max min max min max min max min max min max min max min max min max min max 3K 3K KBC KC LEX A B C B A MSEX NS O 3O PS 10A E S R 12C E F G OFF

16 ALL STATIONS Crab Management Areas. Survey Stations Core Stations Figure 1. Map of Crab Management Area (CMA-top), Potential survey stations- (bottom left) and core stations (bottom right). (The years in red are the years used to define core stations in each area ) 9

17 Figure 2. Catch distribution (mean numbers/trap) for for large mesh traps. 10

18 Figure 3. Catch distribution (mean numbers/trap) for for large mesh traps 11

19 Figure 4. Catch distribution (mean numbers/trap) for for large mesh traps. 12

20 Figure 5. Catch distribution (mean numbers/trap) for for small mesh traps. 13

21 Figure 6. Catch distribution (mean numbers/trap) for for small mesh traps. 14

22 Figure 7. Catch distribution (mean numbers/trap) for for small mesh traps. 15

23 Figure 8. Distribution of small mesh trap locations in 2012 (top left) and 2013 (top right). Bottom panels show changes made in 2013 for station locations added (bottom left) and removed (bottom right) from the survey. 16

24 Figure 9. Annual CPUE (mean #/tow) for new and old shell crab 95mm in the inshore and offshore by NAFO Div. Data summarized for core stations by year. 17

25 Figure 10. Annual CPUE (mean #/tow) for sub legal (<95mm cw) and legal ( 95mm cw) size crab in the inshore and offshore of each NAFO Div. Data summarized for core stations. Both shell types combined. 18

26 Figure 73. Annual CPUE (mean #/tow) from core stations in the Inshore for sub legal (<95mm) and legal ( 95mm) size crab (top panel). Annual CPUE (mean #/tow) for legal size crab only by shell type (new and old) (lower panel). 81

27 Figure 74. Annual CPUE (mean #/tow) from core stations in the Offshore for sub legal (<95mm) and legal ( 95mm) size crab (top panel). Annual CPUE (mean #/tow) for legal size crab only by shell type (new and old) (lower panel). 82

28 Figure 75. Mean #/tow for sub legal (<95mm cw top panel) and legal ( 95mm bottom panel) size crab by Crab Management Area. 83

29 Figure 76. Annual CPUE (mean #/tow) from core stations for legal ( 95mm) size crab by shell type (new and old) by Crab Management Area. 84

30 Figure 77. Annual size frequencies of crab by shell condition (soft, new, and old) sampled from core stations using large mesh pots from the NAFO Div. Sample size indicated by N=. Mean carapace width (mm) by shell condition given in the legend. Black bar indicates legal size. 85

31 Figure 78. Annual size frequencies of crab by claw type (unknown, small and large) sampled from core stations using small mesh pots from the NAFO Div. Sample size indicated by N=. Mean carapace width (mm) by shell condition given in the legend. Black bar indicates legal size. 86

32 Figure 79. Annual size frequencies of crab by shell condition (soft, new and old) sampled from core stations using large mesh pots from the inshore of each NAFO Div. Sample size indicated by N=. Mean carapace width (mm) by shell condition given in the legend. Black bar indicates legal size. 87

33 Figure 80. Annual size frequencies of crab by shell condition (soft, new and old) sampled from core stations using large mesh pots from the offshore of each NAFO Div. Sample size indicated by N=. Mean carapace width (mm) by shell condition given in the legend. Black bar indicates legal size. 88

34 Figure 81. Annual size frequencies of crab by claw type (unknown, small and large) sampled from core stations using small mesh pots from the inshore of each NAFO Div. Sample size indicated by N=. Mean carapace width (mm) by shell condition given in the legend. Black bar indicates legal size. 89

35 Figure 82. Annual size frequencies of crab by claw type (unknown, small and large) sampled from core stations using small mesh pots from the offshore of each NAFO Div. Sample size indicated by N=. Mean carapace width (mm) by shell condition given in the legend. Black bar indicates legal size. 90

36 Figure 83. Annual size frequencies of crab by shell condition (soft, new and old) sampled from core stations using large mesh pots from each Crab Management Area. Sample size indicated by N=. Mean carapace width (mm) by shell condition given in the legend. Black bar indicates legal size. 91

37 Figure 84. Annual size frequencies of crab by shell condition (soft, new and old) sampled from core stations using large mesh pots from each Crab Management Area. Sample size indicated by N=. Mean carapace width (mm) by shell condition given in the legend. Black bar indicates legal size. 92

38 Figure 85. Annual size frequencies of crab by shell condition (soft, new and old) sampled from core stations using large mesh pots from each Crab Management Area. Sample size indicated by N=. Mean carapace width (mm) by shell condition given in the legend. Black bar indicates legal size. 93

39 Figure 86. Annual size frequencies of crab by shell condition (soft, new and old) sampled from core stations using large mesh pots from each Crab Management Area. Sample size indicated by N=. Mean carapace width (mm) by shell condition given in the legend. Black bar indicates legal size. 94

40 Figure 87. Annual size frequencies of crab by shell condition (soft, new and old) sampled from core stations using large mesh pots from each Crab Management Area. Sample size indicated by N=. Mean carapace width (mm) by shell condition given in the legend. Black bar indicates legal size. 95

41 Figure 88. Annual size frequencies of crab by claw type (unknown, small and large) sampled from core stations using small mesh pots from each Crab Management Area. Sample size indicated by N=. Mean carapace width (mm) by shell condition given in the legend. Black bar indicates legal size. 96

42 Figure 89. Annual size frequencies of crab by claw type (unknown, small and large) sampled from core stations using small mesh pots from each Crab Management Area. Sample size indicated by N=. Mean carapace width (mm) by shell condition given in the legend. Black bar indicates legal size. 97

43 Figure 90. Annual size frequencies of crab by claw type (unknown, small and large) sampled from core stations using small mesh pots from each Crab Management Area. Sample size indicated by N=. Mean carapace width (mm) by shell condition given in the legend. Black bar indicates legal size. 98

44 Figure 91. Annual percent occurrence of Bitter Crab Disease (BCD) estimated from samples taken from small mesh pots from core stations for males and females new shell crab by Crab Management Area (CMA). Sample size indicated above each bar. 99