Science Advisory Report  2014/034

Assessment of Lobster (Homarus americanus) in Lobster Fishing Area 41 (4X + 5Zc)

Summary

Fishery

• The Total Allowable Catch (TAC) for Lobster Fishing Area (LFA) 41 was established at 720 t in 1985 based on landings history and has remained unchanged.
• Fishing effort has been declining due to increased catch per unit effort (CPUE) and changes to fishing strategy.
• The size structure has remained relatively stable and dominated by mature sizes indicating a low exploitation level. Relative F (fishing mortality) calculated from landings and biomass estimates from the summer survey is low and declining in recent years.

Framework and Assessment

• A Precautionary Approach proposed for lobster in LFA 41 uses multiple primary indicators with boundaries to guide in setting harvest control rules and secondary indicators to aid in interpreting changes in the primary indicators. There is no single reference point for this fishery.
• When interpreting the primary indicators, if all indicators remain above the upper boundary, the population is considered to be in the healthy zone. The stock would enter the cautious zone only if the abundance declined below the boundary and the size indicators also declined to below the boundary. When upper boundaries have been crossed for the primary indicators, the secondary indicators should be reviewed for further context on what is happening in the stock.
• All indicators are above the upper boundaries and LFA 41 is considered to be in the healthy zone.
• Primary indicators include mean number per tow from the Maritimes Region research vessel (RV) trawl survey (summer 4X, winter 5Z), number per tow of large female lobsters (>140 mm CL) (Summer RV survey 4X; USA NMFS Fall RV Survey 5Z), and median size from trawl surveys and at-sea samples of the commercial catch.
• The large size indicator is a proxy for exploitation rate and changes in reproductive potential. It is based on the mean number per tow of females > 140 mm CL in the Maritimes Region RV summer trawl survey (4X 1999-2013) and the USA NMFS trawl surveys for 5Z (1983-2012).
• Median female size indicators based on trawl surveys and at-sea samples are proxies for exploitation rate and changes in reproductive potential.
• Secondary indicators on proportion of survey sets with lobsters, sex ratio, number per tow of recruit sizes, and trends in adjacent fisheries aid in interpreting changes in the stock. They provide important information about the ecosystem and the fishery, and aid in determining the type of response if the stock entered the cautious zone.

Ecosystem Considerations

• Given the current low biomass levels of some potential lobster predators, there is no expectation of a near-term increase in the natural mortality of lobsters.
• The percentage of the area of LFA 41 contacted by lobster traps was estimated from the effort data. The estimates indicate that a very low and decreasing percentage of the bottom is contacted by traps, with an overall estimate for LFA 41 in 2012 of 0.0005%.
• In 2012, sea surface temperature was above the 1981-2010 average temperature and July bottom temperatures were also well above the 1981-2010 average. For 2013, sea surface temperatures (up to November) and July bottom temperatures were above the 1981-2010 average temperature, but by a lesser extent than 2012.
• LFA 41 at-sea samples record the levels of incidental catch. Estimates of 2012 incidental catch, including discarded and retained catch was 46 t. The overall incidental catch has declined since 2006 (164 t). The end of the directed Jonah Crab fishery (2008) and concentration on areas of highest lobster CPUE are believed to have contributed to the reduced incidental catch. High survival is expected for invertebrates, but survival is lower for some fish species.

This Science Advisory Report is from the December 3-4, 2013 and January 9, 2014 Review of the Framework and Assessment of LFA 41 (4X + 5Zc) Lobster. 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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