Research Document 2018/002

Information on the Potential for Recovery of Cusk (Brosme brosme) in Canadian Waters

By L.E. Harris, M. Greenlaw, Q. McCurdy, and D. MacDonald

Abstract

Cusk (Brosme brosme) was reassessed as Endangered by the Committee on the Status of Endangered Wildlife in Canada (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) of Cusk was observed, has fluctuated without trend since 1999. This suggests that the population abundance has stabilized.  The 3-year geometric mean (2011-2013) of the Cusk CPUE in the Halibut Industry Survey is 17.9kg/1000 hooks, which suggests that the stock is in the cautious zone when utilizing the DFO Precautionary Framework. The Limit Reference Point is 13.3kg/1000 hooks in the Halibut Industry.  The Upper Stock Reference Point of 26.6kg Cusk/1000 hooks in the Halibut Industry Survey is the proposed population recovery target.

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 Cusk reported landings for the 2012 fishing year in Maritimes Region were 462.2mt. The 2012 Cusk landings for the Gulf Region and Newfoundland and Labrador Region were 0.043mt and 1.88mt, respectively. The Cusk bycatch for 2012 in Lobster Fishing Area (LFA) 41 was estimated at 8.6mt. The 2006/2007 estimate of bycatch in LFA 34 was 344mt. Cusk catches in other LFAs have not been estimated.  Cusk CPUE in the Halibut Industry Survey has fluctuated without trend for the past 14 years suggesting that the population can sustain recent levels of fishing mortality without jeopardizing survival of the species. A reduction in fishing mortality may be required for the species to achieve the proposed recovery target for abundance.

There is no evidence of a reduction in the range of Cusk. 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. The proposed distribution target for recovery is to maintain current distribution. Preliminary analyses suggest the six most influential environmental variables on Cusk habitat suitability, ranked using the Random Forest Model, 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.

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