Science Advisory Report  2015/015

Assessment of Pacific Cod (Gadus Macrocephalus) for Hecate Strait (Area 5CD) in 2013

Summary

• Pacific Cod (Gadus Macrocephalus) is a commercially important species of cod that occurs along the entire coast of British Columbia. It is primarily caught by the groundfish trawl fishery and occasionally by the hook and line fishery. The majority of catches are taken in Hecate Strait (Area 5CD, ~700 t in 2013) and Queen Charlotte Sound (Area 5AB, ~180 t in 2013), although large catches were taken historically off the West Coast of Vancouver Island (Area 3CD).
• This advisory report refers only to the Hecate Strait stock, which was last assessed in 2004.
• Pacific Cod stocks in British Columbia are difficult to assess, primarily due to the relatively short time series of fishery-independent index of abundance data, changes in fishery selectivity over time, and historical changes in management and fishery operations. Historical changes include the transition to quotas (from the early 1990s to 1997), the introduction of 100% at-sea observer coverage (February 1996), and several voluntary and regulation mesh-size changes. There is very little reliable age composition data for this difficult-to-age species.
• The status of the Pacific Cod population in Hecate Strait was assessed using a Bayesian delay-difference model fit to fishery–independent survey data, commercial catch-per-unit-effort data, commercial catch data, and estimates of annual mean weights from the trawl fishery.
• Despite large uncertainty, biomass in Hecate Strait is estimated to have been gradually increasing since 2001.
• Recruitment is estimated to have been below the estimated long-term (56-year) average in most years for the past two decades.
• Estimates of fishery reference points based on maximum sustainable yield (MSY) were very sensitive to model assumptions, and differed substantially among model sensitivity cases. Unfished biomass (B₀) was also sensitive to model assumptions. The use of MSY-based and B₀-based reference points was consequently not supported for this stock.
• Alternative “historical” reference points are used based on those accepted for the previous assessment of this stock. They are:
1. an Upper Stock Reference point based on the estimated average biomass for the period 1956 to 2004;
2. a Limit Reference Point defined as the estimated minimum biomass from which the stock recovered to an above-average biomass level (namely the estimated biomass in 1971); and
3. a Limit Removal Rate calculated as the estimated average fishing mortality for the period 1956-2004.
• Advice to managers is provided in a decision table that summarizes the probability of breaching reference points at a range of fixed catches for a one-year projection. Due to model sensitivity to a number of model assumptions, the table uses a model-averaging approach intended to integrate results from the use of alternative model assumptions.
• Under a 2014 catch similar to the 2013 catch (approximately 700 t), the projected biomass at the start of 2015 is estimated to have a 0.56 probability of being below the historical Upper Stock Reference point and a 0.17 probability of being below the historical Limit Reference Point. The probability that the fishing mortality rate in 2014 will be above the Limit Removal Rate is estimated to be zero.

This Science Advisory Report is from the January 9-10, 2014 Assessment of British Columbia Pacific Cod for Hecate Strait (Area 5CD) and Queen Charlotte Sound (Area 5AB) in 2013. 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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