Science Advisory Report  2014/032

Assessment of the interior Fraser River Coho Salmon Management Unit

Summary

• Coho Salmon in southern British Columbia, including those destined to the interior Fraser River watershed, experienced severe abundance declines in the 1990’s. DFO responded by introducing management measures to significantly reduce fishery exploitations. In 2006, DFO published a conservation strategy outlining recovery objectives for interior Fraser River Coho Salmon.
• Interior Fraser Coho Salmon were designated as endangered by COSEWIC in 2002. The Interior Fraser Coho Recovery Team (IFCRT) was established and in 2006 the Conservation Strategy for Coho salmon (Oncorhynchus kisutch), Interior Fraser River Populations was published (IFCRT, 2006).
• Recent improvements in Coho Salmon escapements, and the potential opportunity for increased salmon harvest of more abundant stocks and species, currently constrained by measures in place to protect Coho Salmon, led to a request for science advice to determine the impact of increased harvest on Coho Salmon originating from the Interior Fraser River management unit.
• The Interior Fraser Management Unit is comprised of five Wild Salmon Policy Conservation Units, each of which is made up of 1-3 subpopulations.
• For the most recent generation (2010-2012), aggregate wild Coho Salmon escapement to the Interior Fraser River watershed averaged 36,000 spawners, well above the short term conservation strategy recovery objective of 20,000 spawners, but below the longer term objective of 40,000 spawners.
• Two distinct periods of productivity were evident in the observed data: a higher productivity period during 1978-1993 and a lower productivity period during 1994-2012. During the current low productivity period, there have been eight years when productivity was less than one recruit/spawner; meaning that Interior Fraser Coho Salmon were unable to replace themselves, the most recent being 2010.
• Several stock-recruit models were evaluated and the Ricker model was determined to be the best model for the current period of low productivity. Using the Ricker model, closed-loop simulations were used to project the probabilities of achieving the recovery objectives set out in the Conservation Strategy (IFCRT, 2006) at various potential exploitation rates; the results formed the basis of advice to management in a decision table.
• In the current low productivity period, at existing exploitation rates of approximately 13%, the probability of achieving the short term recovery objective within 1, 2 or 3 generations is 0.65, 0.71 and 0.73, respectively. If exploitation is raised to 30%, those probabilities decrease to 0.51, 0.52 and 0.50. The probability of meeting the longer term objective is low regardless of exploitation.
• Managers should be aware that there are potentially significant sources of uncertainty with respect to estimates of fishery exploitation, escapement, stock recruitment parameters and, hence, probabilities of achieving recovery objectives. Since implementation error (variability in the ability to implement a change in exploitation), which is not captured in the models, probability estimates are likely optimistic.

This Science Advisory Report is from peer review meeting on the Interior Fraser River Coho Salmon Interim Assessment held on 23-24 January 2014. 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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