Research Document 2018/018

Assessment of the Northern Cod (Gadus morhua) stock in NAFO Divisions 2J3KL in 2016

By Brattey, J., Cadigan, N., Dwyer, K. S., Healey, B. P.,Ings, D. W., Lee, E. M., Maddock Parsons, D., Morgan, M. J., Regular, P., Rideout, R. M

Abstract

The Northern cod (Gadus morhua) stock that inhabits waters off southern Labrador and eastern Newfoundland eastward to the edge of the continental shelf in the Northwest Atlantic Fisheries Organization (NAFO) Divisions (Divs.) 2J3KL was assessed through a Regional Peer Review Process (RPR) conducted during March 21-24 and March 30-31, 2016 in St. John’s, Newfoundland and Labrador (NL). This stock is currently under a three-year management cycle, and the current assessment provided catch advice for 2016-18. The assessment also identified an indicator (based on 3 year projections of DFO research vessel (RV) total [2+] biomass) that could be used to determine whether a full assessment is warranted during interim years. The current assessment was based mainly on a new state-space population dynamics model (Northern Cod Assessment Model, NCAM) that integrates much of the existing information about the productivity of the stock. Key features of the new model are that it provides annual estimates of natural mortality (M) and fishing mortality (F) rates along with measures of uncertainty; the model also estimates catch and requires an interval identifying a likely range of catch (upper and lower bounds).The model integrates information from DFO RV autumn trawl surveys (1983-2015), Sentinel fishery surveys (1995-2014), inshore acoustic surveys (1995-2009) fishery catch age compositions, and partial fishery landings (1983-2015), and tagging (1983-2015). The latest assessment indicated that stock abundance (ages 2+) has increased from 194 million cod in 2005 to 894 million in 2015. Total biomass (ages 2+) has increased from 78 Kt in 2005 to 539 Kt in 2015. Spawning stock biomass (SSB) has increased from 25 Kt in 2005 to 300 Kt in 2015. Recruitment (age 2) improved slightly in the last decade and the average number of age 2s from the 2011-13 year classes corresponds to about 25% of the numbers of age 2s observed in year classes of the 1980s. Stock status is improving, increasing from 3% of B_lim in 2005 to 34% of B_lim in 2015, but SSB has been well into the critical zone since the stock collapse. Three year projections (to 2018) were also undertaken to investigate the potential impact of a range of catch options from zero catch (no fishing) to a 5-fold increase in catch, based on model estimates of total catch for 2015 (6,900 t). The results indicated a high probability of achieving a 3-year 28% SSB interim growth milestone over the full range of catch options. Projections also indicate a low risk (<4%) that SSB will decline by 2018 to below the 2015 value, but also a low probability (5-8%) that the stock will grow out of the critical zone and exceed B_lim in 2018. The stock is projected to grow but still be much less than B_lim (60-66%) and remain in the critical zone in 2018 over the full range of catch options considered, including no fishing. Consistency with the DFO decision-making framework incorporating the precautionary approach requires that removals from all sources must be kept at the lowest possible level until the stock clears the critical zone.

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