Science Advisory Report 2018/038
Stock Assessment of Northern cod (NAFO Divisions 2J3KL) in 2018
Summary
- The stock is being assessed using an integrated catch-at-age model (NCAM), which allows quantification of uncertainty in estimated and projected stock status.
- Spawning Stock Biomass (SSB) remains in the critical zone in 2018, at 37% of the Limit Reference Point (LRP) (95% CI, 27-51%), down from 52% in 2017 and returning to the level of 2015. This represents an increase from the current estimate of the 2005 level of 3% of Blim.
- SSB was 423 Kt in 2017, and 315 Kt (95% CI, 224-445 Kt) in 2018. This decline results mainly from an increase in estimated natural mortality rate from 0.39 in 2016 to 0.74 (48% annual survival) in 2017 (averaged over ages 5-14).
- The estimated fishing mortality rate from all sources has increased from 0.014 in 2015 to 0.021 in 2016 and 0.025 in 2017 (averaged over ages 5-14).
- Recruitment (age 2) increased from lowest estimated levels of 36 million fish in 1995 to an average of 251 million in 2011-15. This recent average is 19% of the pre-collapse period of the 1980s.
- Ecosystem conditions are indicative of an overall low productivity state including low levels of key forage species such as capelin and shrimp. Capelin is anticipated to remain at low levels to at least 2019. This is expected to negatively impact cod productivity.
- In the 2016 assessment, a series of projections under various assumptions about fishery removals in 2016 and 2017 indicated median 2018 SSB would range from 0.6-0.66 (95% CI, 0.32-1.17) of the Blim level. In the current assessment, median 2018 SSB is estimated to be 0.37 (95% CI, 0.27-0.51) of Blim. This difference is driven by 2017 estimates of M that are 2 to 3 times higher than those assumed in the 2016 projections. This increase in M is consistent with ecosystem-wide information that is not directly used in the estimation.
- Natural mortality (M) plays an important role in projections for this stock. A key determinant of the projected 2019 SSB is natural mortality. If natural mortality rates in 2018 are appreciably different than those used, projected outcomes will differ from values reported above. Medium and long term projections were not carried out due to uncertainty about the level of future natural mortality.
- Projections carried out for one year indicated the probability of SSB in 2019 declining below current SSB (2018) with assumed catches of 80% to 120% of the estimated catch in 2017 (15, 054 t) ranged from 0.71 to 0.73. The probability of SSB reaching Blim by 2019 is very low (<0.01) for all the above catch levels. A projection with no fishing indicated a probability of 0.66 of SSB in 2019 declining below current levels, and a probability <0.01 of reaching Blimby 2019.
- 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.
This Science Advisory Report is from the March 19-22, 2018 Stock Assessment of Northern cod (Divs. 2J3KL). 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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