Research Document - 2005/093

Scientific Advice for input to the Allowable Harm Assessment for Interior Fraser Coho Salmon

By Folkes, M., B. Ionson, J.R. Irvine

Abstract

In 2002, COSEWIC designated Interior Fraser River coho (IFC) as “endangered”. IFC could become legally listed in 2006 under the Species At Risk Act (SARA). This Working Paper was in response to a request to assess the potential for incidental harm permitting. Questions addressed in the Working Paper were: 1) What is the present/recent species trajectory? 2) What is the present/recent species status? 3) What is the expected order of magnitude/target for recovery? 4) What is the general time frame for recovery to the target? And 5) What is the maximum human-induced mortality which the species can sustain and not jeopardize survival or recovery of the species?

When IFC were assessed by COSEWIC, the rate of decline during the 3 most recent generations was ~60%, within IUCN’s endangered status criteria range. We now have 4 additional years of data during which escapements generally increased. The most recent 3 generations experienced increases ranging between 8% (North Thompson) and 132% (South Thompson). An immediate recovery goal for the Designated Unit (DU) was defined by the Interior Fraser Coho Recovery Team as exceeding a lower benchmark (three year geometric mean 20,000-25,000 wild spawners). Recent escapements for the DU exceed this benchmark, although escapements remain low relative to historical highs. Longer term (multi generation) escapement benchmarks range from 46,000 to 148,000 depending on the estimation model considered. Modelling results suggest that at current exploitations and marine survival there is less than 25% chance that spawner levels will reach one possible spawner objective of doubling by the end of three generations. It is assumed that longer recovery times will be necessary to assure higher chances of meeting target escapement levels. We cannot accurately forecast future marine survival. However, we can indicate the likely future status given differing levels of future survival. Simulation modelling suggests that, at the current exploitation rate and recent survival, the short term (2 year) probability of remaining above the survival benchmark is 90%, however the probability of remaining above that level in the longer term (3 generations) is ~50%. At the current exploitation rate and marine survival, the longer term probability of positive growth is <50%. Considering the uncertain nature of marine survival forecasting, it would be prudent to wait several more years before providing specific advice with regards to changing fisheries.

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