Science Advisory Report 2019/047

Assessment of the Estuary and Northern Gulf of St. Lawrence (Areas 13 to 17, 12A, 12B, 12C and 16A) Snow Crab Stocks in 2018

Summary

• In 2018, all stocks in the northern Gulf of St. Lawrence (areas 13, 14, 15, 16, 17, 16A, and 12A, B, C) showed a decline in commercial biomass compared to 2017. Recruits (legal-size males that have moulted in the last one or two years) dominated the landings in areas 17, 16, 15 and 16A and showed a relative increase in the other areas in 2018 (except Area 12B). A decrease in the abundance of adolescents ≥ 78 mm suggests low recruitment to the fishery in 2019 in areas 12A, 13 (Quebec) and 14. Recruitment in areas 12A and 12B could depend on productivity in adjacent areas in the coming years. The absence of post-season trap surveys in Area 12B and specific conditions observed in Area 17 during this survey increase the uncertainty regarding the expected strength of recruitment in these areas.
• The purpose of conservation is to maintain an adequate male reproductive biomass in order to ensure the recovery or maintenance of the population in a given area. Recommendations assume that the natural mortality rate will be the same in 2019 as in previous years.
• The protocol for establishing the outlook for each area has been defined for this stock assessment and set out as a preamble to the summary for each area in the section below.

Outlook

• The outlook for each area includes three possible scenarios for establishing the 2019 TAC. These scenarios have been developed by taking into account an indicator combining the commercial catch per unit effort (CPUE) and the number per unit effort (NPUE) of commercial-size adult males from the post-season scientific survey, the uncertainty associated with this indicator, and related stock status indicators (crab carapace size and condition, expected recruitment), with the objective of ensuring sustainable resource management. The characteristics of each scenario are described below.

Higher scenario

• Greater likelihood of increased harvesting intensity for the upcoming season compared to the previous season;
• Harvest level that may result in fishing mortality exceeding the historical average;
• Harvesting pressure that may not be sustainable in the long term; and
• Likely decrease in abundance compared to the previous year if recruitment remains relatively stable or decreases.

Intermediate scenario

• Likelihood of moderate harvesting intensity for the upcoming season, similar to the previous season;
• Harvest level assumed to maintain fishing mortality close to the historical average; and
• Could maintain the stock at a level of abundance similar to the previous year.

Lower scenario

• Greater likelihood of lower harvesting intensity for the upcoming fishing season compared to the previous one;
• Cautious harvest level assumed to result in fishing mortality below the historical average; and
• Could lead to an increase in stock abundance compared to the previous year or maintain existing biomass over a longer period of time.

Ecosystem considerations

• Since 1990, the estimated area of favourable thermal habitat for snow crab (between -1°C and 3°C) was the lowest in 2015 for fishing areas 12A, 12C and 16A, and in 2016 for areas 12B, 16 and 17. In contrast, 2017 and 2018 showed near-average estimated areas of favourable thermal habitat in all fishing areas.

Area 17

• The TAC increased by 25% to 2,623 t from 2017 to 2018, and it was reached.
• The commercial CPUE decreased from 2017 to 2018 after three years of consecutive increases. It remains above the historical average of the time series.
• Landings were mostly made up of recruits, with the proportion of “intermediate-shell” crabs declining for a fourth consecutive year.
• The average size of crabs caught in the commercial fishery in 2017 and 2018 was similar and is just below the historical average.
• The commercial abundance index of the 2018 post-season survey was down sharply after four years of increases and below the average. The extent of the decline observed for the north shore was much more marked than for the south shore.
• The abundance of adolescents ≥ 78 mm in the post-season survey decreased between 2017 and 2018 and is below the average. However, trends differ between the two shores, with adolescents falling sharply in the survey on the north shore, with the 2018 value being the lowest observed to date, while they are up on the south shore compared with 2017, at a value just below the average.
• The last scientific trawl survey conducted in 2017 on the north and south shore predicted good recruitment until 2018, and then a subsequent decline in recruitment by 2020.
• The marked and unexpected decrease in the NPUE of all crab size categories in the post-season survey on the north shore, and only for this sub-area, is a significant source of uncertainty as to the reality of the decreases observed on the north shore in this survey between 2017 and 2018.
• The combined index (CI), derived from overall CPUE and NPUE in the fishing area, is down 25% from the 2017 value, which suggests that the biomass available to the fishery will be lower in 2019 than in 2018.

Outlook:

• The sharp decline in the combined index (CI) suggests that harvest should be reduced in 2019. However, given the uncertainty in the results of the post-season survey on the north shore and that stock status is likely to be better than the CI indicates, the decrease in the CI between 2017 and 2018 is used as a lower scenario.
  Higher scenario: A 5% decrease in the TAC compared with 2018.
  Intermediate scenario: A 15% decrease in the TAC compared with 2018.
  Lower scenario: A more than 25% decrease in the TAC compared with 2018.

Area 16

• The 2018 TAC was similar to the 2017 TAC of 3,648 t and it was reached.
• The commercial CPUE has been declining since a high CPUE period was observed in 2013–2015 and it was below the historical average in 2018.
• Landings consisted mostly of recruits. The proportion of recruits increased for the third consecutive year, while that of intermediate-shell crabs decreased.
• The average size of landed crabs in the commercial fishery decreased between 2017 and 2018 and is just above the average.
• With the exception of 2015, the commercial abundance index of the post-season survey has been declining since 2013, when the highest value in the series was observed. The 2018 value was the lowest since 2002.
• The abundance of adolescents ≥ 78 mm in the post-season survey has increased slightly since 2017 and is at the average level, which does not suggest a significant increase in recruitment for 2019.
• The CI decreased by 13% compared with 2017, which suggests that less biomass will be available to the fishery in 2019 than in 2018.
• Monitoring of the snow crab population in Sainte-Marguerite Bay suggests that recruitment, in terms of legal crab numbers associated with the 2007 recruitment wave, will decrease from 2018 for about three years, before the positive effect of the 2015–2016 wave is felt. Good recruitment of legal males is anticipated from 2022–2023.

Outlook:

• The 13% decrease in the CI, in a context where fishing recruitment is expected to decline until 2021, suggests that the TAC should be reduced in 2019.
  Higher scenario: A 10% decrease in the TAC compared with 2018.
  Intermediate scenario: A 20% decrease in the TAC compared with 2018.
  Lower scenario: A more than 20% decrease in the TAC compared with 2018.

Area 15

• The TAC remained the same in 2018 at 631.7 t, and was reached.
• The commercial fishery CPUE declined for a third consecutive year and is now below the historical series average. Landings mainly consisted of recruits, whose proportion increased for a second consecutive year, while that of intermediate-shell crabs decreased.
• The average size of crabs caught in the commercial fishery increased slightly between 2017 and 2018. These at-sea measurement values have been fairly stable for the past 10 years and are among the highest in history.
• The commercial abundance index of the post-season survey has decreased over the past three years, with a marked decrease between 2017 and 2018.
• The abundance of adolescents ≥ 78 mm has been relatively stable in the post-season survey over the past five years.
• The CI is down 29% from the 2017 value. This was the third consecutive decline. This decline in the index suggests that there will be less biomass available to the fishery in 2019 than in 2018.

Outlook:

• A third decline in the CI in a context where recruitment to the fishery is expected to remain low in the short term suggests that the TAC should be reduced in 2019.
  Higher scenario: A 25% decrease in the TAC compared with 2018.
  Intermediate scenario: A 30% decrease in the TAC compared with 2018.
  Lower scenario: A more than 30% decrease in the TAC compared with 2018.

Area 14

• The TAC decreased by 10% in 2018 to 617.3 t. It was almost reached.
• The commercial fishery CPUE declined sharply for the second consecutive year and is below the historical average in 2018. Landings consisted primarily of intermediate-shell crab in 2018.
• The average size of crabs caught in the commercial fishery shows a strong upward trend between 2012 and 2018, with the last year being among the highest values.
• The commercial abundance index of the post-season survey has declined significantly over the past four years, to below the historical average in 2018.
• The abundance of adolescents ≥ 78 mm has remained low and fairly stable in the post-season survey over the past four years, which suggests that recruitment to the fishery will not increase in 2019.
• The CI decreased by 38% from 2017 to 2018. This is the fourth consecutive decline, which suggests that the biomass available for fishing in 2019 will be lower than in 2018.

Outlook:

• A significant decrease (38%) in the CI with no indication of improved recruitment suggests that the TAC should be reduced in 2019.
  Higher scenario: A 25% decrease in the TAC compared with 2018.
  Intermediate scenario: A 35% decrease in the TAC compared with 2018.
  Lower scenario: A more than 35% decrease in the TAC compared with 2018.

Area 13

• The TAC remained unchanged at 406 t, and was not reached (landings of 328.8 t).
• After several years of relatively high values, the commercial fishery CPUE declined sharply from 2017 to 2018, and is below the historical average in 2018. Landings consisted primarily of intermediate-shell crab in 2018.
• Average size of crabs caught in the commercial fishery decreased over the past two years to below the historical average in 2018. It should be noted that the decrease in the average size of crabs caught in the commercial fishery could be associated with the lack of at-sea sampling on the south side, and a northward shift in fishing effort covered by the At-Sea Observer Program.
• The commercial abundance index of the post-season survey on the north side of the area declined sharply for a second consecutive year and is at the level of the historical average in 2018. The 2018 value for the south side of the area is up from the previous year, but remains below the historical average, and is among the lowest values in the historical series.
• The abundance of adolescents ≥ 78 mm remained low and stable in the post-season survey, which does not suggest a significant increase in the recruitment to the fishery in 2019.
• The CI decreased by 42% from 2017 to 2018. The biomass available to the fishery in 2019 could be lower than in 2018.

Outlook:

• The significant decrease (42%) in the CI, while recruitment is expected to remain low, suggests decreasing the TAC in 2019. In the presence of a stock harvested at a lower intensity than neighbouring fishing areas since its reopening, the area’s CI value was used as a reference for the lower scenario, which reflects this specific aspect.
  Higher scenario: A 25% decrease in the TAC compared with 2018.
  Intermediate scenario: A 35% decrease in the TAC compared with 2018.
  Lower scenario: A more than 45% decrease in the TAC compared with 2018.

Area 16A

• The TAC decreased by 10% to 412.9 t in 2018, and it was not reached (landings of 369 t). The fishery was closed as of July 14, 2018, due to an increase in the proportion of white crab in catches.
• The commercial fishery CPUE decreased for a fourth year. The 2018 CPUE is the lowest since the series began in 2004. Landings consisted of a large majority of recruits in 2018.
• The average size of crabs caught in the commercial fishery remained stable between 2017 and 2018, and is at the historical average.
• The commercial abundance index of the post-season survey has declined significantly over the past four years.
• The abundance of adolescents ≥ 78 mm remained low and relatively stable in the post-season survey between 2017 and 2018, which does not suggest an increase in recruitment to the fishery in 2019.
• The CI was down for the fourth consecutive year (24% decrease from 2017 to 2018). This decline in the index suggests that there will be less biomass available to the fishery in 2019 than in 2018.

Outlook:

• The 24% decrease in the CI, which was the fourth consecutive one, suggests that the TAC should be reduced in 2019, in a context where recruitment is expected to remain stable and/or low.
  Higher scenario: A 25% decrease in the TAC compared with the 2018.
  Intermediate scenario: A 30% decrease in the TAC compared with the 2018.
  Lower scenario: A more than 30% decrease in the TAC compared with the 2018.

Area 12C

• The TAC decreased by 10% to 256.4 t, and was not reached (landings of 235 t).
• The commercial fishery CPUE is down for the second consecutive year. The CPUE in 2018 is among the lowest values observed in 25 years. Landings consisted primarily of intermediate-shell crab, and they declined between 2016 and 2018.
• The average size of crabs caught in the commercial fishery remained close to the historical averages at sea and dockside in 2018.
• The commercial abundance index of the post-season survey decreased significantly over the past four years.
• The abundance of adolescents ≥ 78 mm remained low and fairly stable in the post-season survey between 2014 and 2018, which does not suggest an increase in recruitment to the fishery in 2019.
• The CI decreased for a fourth consecutive year, with a 26% decrease from 2017 to 2018. This decline in the index suggests that there will be less biomass available to the fishery in 2019 than in 2018.

Outlook:

• The 26% drop in the CI, during a period of stable and low recruitment, suggests that the TAC should be reduced in 2019.
  Higher scenario: A 25% decrease in the TAC compared with the 2018.
  Intermediate scenario: A 30% decrease in the TAC compared with the 2018.
  Lower scenario: A more than 30% decrease compared with the 2018.

Area 12B

• The 2018 TAC was intended to enable monitoring of snow crab yields for this stock, which is considered to be in poor condition, but whose exact status is uncertain due to the absence of post-season surveys in 2017 and 2018.
• The TAC decreased by 28.6% between 2017 and 2018 to 125 t. The TAC was not reached, with landings of only 40 t. The area has been neglected by some fishers for various reasons and fishing effort has not been high, which may partly explain why the TAC has not been met.
• The CPUE increased slightly, but is the second-lowest value in the historical series.
• Landings consisted primarily of intermediate-shell crabs.
• The average size of crabs caught in the commercial fishery remained similar to that of 2017 and is among the lowest values observed since the beginning of the historical series.
• A significant increase in the favourable thermal habitat available in the area was observed between 2016 and 2018.

Outlook:

• The non-attainment of the TAC, low catch rates, small size and low recruitment of snow crab suggest that stock status did not improve in 2018. Given the uncertainty about the exact status of the biomass in this area, it is impossible to make specific recommendations.
• It is recommended that harvest be set at the lowest level possible for monitoring of the area, further to a consultation between the fishing industry and Fisheries and Oceans Canada (Ecosystem and Fisheries Management sector).

Area 12A

• The TAC was increased by 7% to 105.5 t from 2017 to 2018, and it was reached.
• The commercial fishery CPUE remained similar in 2018 to that of 2017 and is among the lowest values observed.
• Landings consisted primarily of intermediate-shell crab.
• The average size of crabs caught in the commercial fishery increased between 2017 and 2018, and is above the average.
• All abundance indices from the 2018 post-season survey are declining or fairly stable and are among the lowest values observed in the historical series. In particular, the abundance of adolescents ≥ 78 mm declined between 2017 and 2018, suggesting a decline in recruitment in 2019.
• The CI decreased by 7% compared with the 2017 value. The biomass available to the fishery in 2019 could be lower than in 2018.

Outlook:

• The slight decline in the CI suggests that the TAC should be reduced in 2019 compared with 2018:
  Higher scenario: Status quo of the TAC compared with 2018.
  Intermediate scenario: A 7% decrease in the TAC compared with 2018.
  Lower scenario: A more than 10% decrease in the TAC compared with 2018.

This Science Advisory Report is from the February 12 and 14, 2019, meeting on the Assessment of the Estuary and northern Gulf of St. Lawrence Snow Crab stocks. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

Science Advisory Report 2019/047 (PDF, 3,094 KB)