Science Advisory Report  2013/070

Recovery Potential Assessment for the Anticosti Island Atlantic Salmon Metapopulation

Summary

• Atlantic salmon inhabit 25 rivers in the Anticosti Island Designatable Unit (DU 9). Over half (53%) the Anticosti Island Atlantic salmon population is concentrated in the Jupiter (28%), De la Chaloupe (13%) and Aux Saumons (12%) rivers.
• A stochastic state model was used to study the renewal dynamics of the Anticosti Island metapopulation. The study of the Anticosti Island metapopulation’s trajectory from 1993 to 2007 confirmed the decrease in the number of adults indicated by COSEWIC, with an average overall decrease of 43% in that time period. However, the study of the trajectory over the last three generations (1997 to 2011) appeared to indicate the trend was reversing. Abundance estimates for recent years showed an increase in numbers since 2006, although the abundance of adults returning to Anticosti rivers decreased in 2011 and 2012. Overall, the metapopulation remained fairly constant at about 3 500 adults between 2006 and 2012.
• A Ricker model stock-recruitment relationship, based on specific metapopulation data was used to estimate a reference point (S_MSY) equivalent to the level of stock that will achieve maximum sustainable yield (MSY). A recovery target equivalent to the 95th percentile of the S_MSY was established. The target is a population of 2 100 spawners and should allow both the survival of the metapopulation and maximum sustainable yield for sport fishing.
• Based on current parameters of the metapopulation’s renewal dynamics, the probability that broodstock producing adult returns from 1990 to 2017 was greater than or equal to the recovery target (2 100 individuals) is between 0.55 and 1. With respect to spawners producing returns from 2018 to 2032, uncertainty regarding abundance increases with time and this probability therefore decreases. The probability remains above 0.50 regardless of the assumption on the metapopulation’s productivity and the recreational fishery’s exploitation pattern. Based on current metapopulation parameters and in the worst case scenario (management measures in force before 2000), the probability that the stock will drop below the recovery target within the next 15 years is about 0.30.
• The connectivity of the various types of habitats used by salmon throughout their life cycle is essential. In freshwater, the whole river appears crucial. The Anticosti Island productive freshwater habitat is assessed at 4 463 368 Production Units (PU). The Anticosti rivers are rarely disturbed by human activities. However, strong natural variations in the water level and the particular geological structure of this area could be limiting factors for the metapopulation.
• A lower survival rate during the maritime phase may be one of the main causes of decline. Widespread changes throughout the North Atlantic ecosystem, which are still not fully understood, remain a major concern. Similar patterns in large groups of stock or throughout the North Atlantic Ocean bring to mind global factors affecting all stocks during their time at sea.

This Science Advisory Report is from the December 4 and 5, 2012 meeting on the recovery potential assessment of Anticosti Island Atlantic salmon. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada Science Advisory Schedule as they become available.

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