Science Advisory Report  2014/048

Update to the Recovery Potential for Cusk in Canadian Waters

Summary

• Cusk (Brosme brosme) was assessed as Threatened by Committee on the Status of Endangered Wildlife in Canada (COSEWIC) in 2003. In 2013, the Governor in Council decided not to add Cusk to the List of Wildlife Species at Risk set out in Schedule 1 Species at Risk Act (SARA). Cusk was reassessed as Endangered by COSEWIC in November 2012 for reasons that include long-term declines beginning in the 1970s.
• Commercial catch rates for Cusk have declined since the 1980s. The extent of the decline in abundance cannot be reliably estimated. The Halibut Industry Survey, which began after the decline in commercial catch per unit effort (CPUE) was observed, has fluctuated without trend since 1999. This suggests that the population abundance has stabilized.
• The reference points for Cusk under the DFO Precautionary Framework were set at an Upper Stock Reference (USR) of 26.6 kg/1000 hooks and a Limit Reference Point (LRP) of 13.3 kg/1000 hooks in the Halibut Industry Survey. The 3-year geometric mean (2011-2013) of the Cusk CPUE is 17.9 kg/1000 hooks, which suggests that the stock is in the cautious zone. The Upper Stock Reference Point of 26.6 kg/1000 hooks in the Halibut Industry Survey is the proposed population recovery target.
• There is no evidence of a reduction in the range of Cusk. The proposed distribution target for recovery is to maintain current distribution.
• Fishing is the only known major source of human-induced mortality of Cusk in Atlantic Canada. Groundfish longline and lobster pots are considered the greatest threats based on landings records and discard estimates, respectively.
• The most recent landings estimates for a full fishing year are from 2012. The Cusk reported landings for the 2012 fishing year in Maritimes Region were 462.2 mt (Table 1). The 2012 Cusk landings for the Gulf Region and Newfoundland and Labrador Region were 0.043 mt and 1.88 mt, respectively.
• The Cusk bycatch for 2012 in Lobster Fishing Area (LFA) 41 was estimated at 8.6 mt. The 2006/2007 estimate of bycatch in LFA 34 was 344 mt. Cusk catches in other LFAs have not been evaluated.
• It appears that the population can sustain recent levels of fishing mortality without jeopardizing survival of the species considering Cusk CPUE in the Halibut Industry Survey has fluctuated without trend for the past 14 years. A further reduction in fishing mortality may be required for the species to achieve the proposed recovery target for abundance. It is not known if there are limiting factors (e.g. high natural mortality) that will prevent Cusk from recovering. Habitat does not appear to be, nor is likely to become, a limiting factor to Cusk survival and recovery. There are no known anthropogenic threats that have reduced Cusk habitat quantity or quality.
• Cusk have a fairly generalized diet. DFO data from Canadian waters indicate that crustaceans, primarily decapods comprised of various crab species and krill species; various fish species, including Silver Hake, Atlantic Herring, American Plaice and Atlantic Argentine; and molluscs, primarily Short-Fin Squid, are the main components of Cusk diet.
• Preliminary analyses suggest the six most influential environmental variables on Cusk habitat suitability, ranked using the Random Forest Model (Figure 6), were salinity variability, winter total suspended matter 2006-2010, fall benthic temperature, depth, root mean square (RMS) current stress, and winter benthic temperature. These variables are expected to have both indirect and direct relationships on Cusk distribution patterns.
• Cusk are most common on hard, rocky bottom or gravel and have been observed hiding in crevices. The benthic complexity index was not in the top ten predictors in the model, perhaps reflecting insufficient data on benthic complexity.
• Possible mitigation measures to decrease fishing mortality include: mandatory release; area closures for the groundfish longline and lobster fisheries; implementation of an avoidance protocol; and identification and implementation of best-handling practices to maximize post-release survival.

This Science Advisory Report is from the February 12-13, 2014, Update on Recovery Potential for Cusk (Brosme brosme). 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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