Science Advisory Report 2018/024

Assessment of Newfoundland and Labrador Snow Crab.

Summary

Divisions 2HJ3KLNOP4R

• Landings most recently peaked at 53,500 t in 2009 and have since gradually declined to 34,000 t in 2017, their lowest level in two decades. Overall effort has remained at four to five million trap hauls in each of the past six years.
• Overall catch per unit of effort (CPUE) was at a two-decade low in 2017 with most divisions at or near historical lows.
• Despite a modest increase in 2017, the trawl survey exploitable biomass index has remained at its lowest observed level for the past three years. Meanwhile, the trap survey index has been at its lowest observed level in the past two years.
• Overall recruitment into the exploitable biomass has been very low in recent years and survey data suggest recruitment available to the 2018 fishery will remain low in most divisions. However, survey and environmental data suggest modest increases in recruitment could occur in some divisions over the next two to four years.
• Total mortality in exploitable crab has increased to be at or near time-series highs in recent years in all divisions.
• Status quo removals would maintain two-year average exploitation rate indices near or above long-term median levels in all divisions. New time-series highs would occur in Divisions 3L Inshore, 3LNO Offshore, and 4R3Pn.
• The relatively low level of residual biomass (old-shelled adult crab) at all sizes in all divisions in recent years is concerning given it is generally associated with low CPUE and high levels of discards in the fishery. Increasing recruitment potential in some divisions, coupled with a low residual biomass suggests that wastage of soft-shelled pre-recruits could become more problematic in the fishery in the next few years.

Divisions 2HJ

• Landings have remained at 1,700 t for the past four years while effort has remained at its lowest level in two decades.
• CPUE has remained near the decadal average in recent years, reflecting trends throughout the division.
• The exploitable biomass index has changed little during the past decade with the exception of a 2014 spike.
• Recruitment into the exploitable biomass has changed little during the past decade with the exception of a 2014 spike. The 2017 trawl and trap surveys suggest recruitment will remain unchanged in 2018.
• The exploitable biomass has consisted largely of incoming recruits for the past six years (75%), with few old-shelled crab. This suggests high mortality of large adult male crab.
• Total mortality in exploitable crab has been at or near its highest level in recent years. The exploitation rate index has been above the long-term average for the past two years. Status quo removals in 2018 would maintain the two-year average exploitation rate index at a relatively high level.

Division 3K

• Landings declined by 66% since 2009 to a time-series low of 5,450 t in 2017. Effort has been maintained near a two-decade low for the past five years.
• CPUE has been low for the past seven years reflecting trends in most management areas.
• The post-season trawl survey exploitable biomass index increased in 2017 from a historic low in 2015‑16. Although the post-season trap survey(s) index has remained near a historical low for the past three years slight improvements were seen in some nearshore management areas in 2017.
• Recruitment increased from time-series lows in both the post-season trawl and trap survey(s) from 2016 to 2017. The 2017 trawl and trap surveys suggest recruitment should increase in 2018.
• The exploitable biomass has consisted largely of incoming recruits throughout the time-series (50-75%), with few old-shelled crab. This suggests high mortality of large adult male crab.
• Total mortality in exploitable crab has been at or near its highest level in recent years. The exploitation rate index has been at a decadal high during the past two years. Status quo removals in 2018 would decrease the exploitation rate, with the two year average index being below the time-series median level.

Divisions 3LNO Offshore

• Landings declined by 26% from 2016 to 18,050 t in 2017, the lowest level in two decades. Effort expanded rapidly from 1992 to the mid-2000s and has oscillated at a similar level since.
• Overall CPUE most recently peaked near a time-series high in 2013 and has since declined by 41% to its lowest level since 1992. Substantial declines have occurred in all management areas in recent years, although catch rates remain relatively high in the central portions of the division.
• The exploitable biomass index remains at or near time-series lows in both the trawl and trap surveys.
• Overall recruitment into the exploitable biomass has been at or near time-series lows in both the trawl and trap surveys in the past two years. This reflects low levels throughout all management areas. No major increases in the exploitable biomass are expected in 2018.
• Total mortality in exploitable crab has been steadily increasing since 2009 to be at or near its highest level in most recent years. The exploitation rate index increased by a factor of five from 2014 to 2017. Status quo removals in 2018 would maintain the two year average exploitation rate index at a historic high.

Division 3L Inshore

• Landings declined by 29% from a historical high in 2015 to 6,000 t in 2017. Effort has nearly doubled since 2013 to a historical high in 2017.
• Overall CPUE has declined by 56% since 2013 to its lowest level in 28 years. There have been strong declines throughout the division in recent years.
• The post season trap survey exploitable biomass index has declined by 73% since 2012, reaching a time-series low in 2017. The 40% overall change from 2016 to 2017 reflects declines to time-series lows in all management areas.
• Overall recruitment has steadily declined for the past three years to a time-series low in 2017. Recruitment indices from Fisheries and Oceans Canada (DFO) and collaborative post-season (CPS) trap surveys in all management areas were at or near their lowest levels in 2017. No major improvements in biomass available to the fishery are expected in the short-term.
• The overall trap survey-based exploitation rate index has increased from 2013 to a time‑series high in 2017. Maintaining status quo removals would increase the two-year average exploitation rate index to an exceptionally high level in 2018, with all management areas reaching or remaining near time-series highs.
• The scenario of a depleted exploitable biomass coupled with low recruitment prospects and high exploitation rate indices suggests minimal potential for improvements in the short term.

Subdivision 3Ps

• Landings declined from a recent peak of 6,700 t in 2011 to a time-series low of 1,200 t during the past two years. Effort has declined by 44% since 2014 to be near its lowest level in two decades. The TAC has not been taken in eight years.
• CPUE has steadily declined since 2009 to a record low in the past two years, reflecting precipitous declines throughout the major fishing areas of the Subdivision in recent years.
• The in-season trawl survey exploitable biomass index was at a time-series low in 2016 but improved slightly in 2017. However, the post-season trap survey index suggests considerable improvements in the exploitable biomass throughout the major fishing grounds.
• Overall recruitment into the exploitable biomass has been at its lowest observed level in recent years but increased slightly in 2017.
• Prospects for recruitment into the exploitable biomass in 2018 have improved from the lowest levels experienced in recent years. Survey data of pre-recruit abundance suggest improving prospects for the next few years.
• In 2017, total mortality in exploitable crab was high but the exploitation rate index declined sharply to a relatively low level. Assuming the exploitable biomass remains at the current level, status quo removals would result in an exploitation rate index near the long-term median in 2018.
• Discards comprised half the catch in the past two years. This is concerning as fishing under elevated mortality levels on small and pre-recruit crab could impair reproductive capacity or yield from forthcoming recruitment.

Divisions 4R3Pn

• Landings have steadily declined since a recent peak in 2013. Meanwhile, effort has remained at a low level.
• CPUE has declined since 2013 to below the long-term median, reflecting trends throughout all major fishing areas.
• The trap survey exploitable biomass index most recently peaked in 2012 and has since declined to a time-series low in 2017, reflecting trends in all surveyed areas.
• Recruitment into the exploitable biomass has been very low for the past four years. Survey data from 2017 suggest no improvements are expected in 2018.
• The overall exploitation rate index has increased since 2013, reflecting trends in all surveyed areas.  Status quo removals would elevate the two-year average exploitation rate index to an exceptionally high level in 2018, with all surveyed management areas reaching new time-series highs.
• The scenario of a low exploitable biomass and CPUE, coupled with an approaching pulse of pre-recruit crab in crab management area (CMA) 12EF suggests that excessive fishing in 2018 could be detrimental to yield in subsequent years due to associated high soft-shell mortality.

Ecosystem Perspective

• The snow crab thermal habitat index (defined as the areal extent of <2°C bottom water) has returned to near-average conditions in all divisions in recent years.
• Ecosystem conditions in the Newfoundland and Labrador (NL) Bioregion are indicative of an overall low productivity state. Current total shellfish and finfish biomass is at a level similar to that observed in the mid-1990s. However, shellfish make up a much lower proportion of that biomass.
• Predation on snow crab has been high in recent years, associated with low availability of core forage species like capelin and shrimp. However, there was a sharp decline in predation on snow crab in 2017.

This Science Advisory Report is from the February 20-21, 2018 Newfoundland and Labrador Snow Crab Assessment. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

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