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Research Document 2020/025

Interior Fraser Coho Salmon Recovery Potential Assessment

By Arbeider, M., Ritchie, L., Braun, D., Jenewein, B., Rickards, K., Dionne, K., Holt, C., Labelle, M., Nicklin, P., Mozin, P., Grant, P., Parken, C., and Bailey, R

Abstract

The Interior Fraser Coho Salmon (IFC) (Oncorhynchus kisutch) Designatable Unit (DU) was assessed as Threatened by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) in 2016, and is currently under consideration for addition to Schedule 1 of the Species at Risk Act. This Recovery Potential Assessment (RPA) provides descriptions and status of populations, habitat, threats and limiting factors, possible recovery targets and population projections, as well as recommendations regarding mitigation and allowable harm. The initial decline in IFC is attributed to decreased smolt-to-adult survival and lagged fisheries management response; however, subsequent management has halted further decline. The population trajectory since 2005 appears flat, with uncertainty. Quantification of suitable freshwater habitat represents a knowledge gap for IFC. Threats with the highest ranked risk (modifications to catchment surfaces, linear development, and agricultural and forestry effluent) were associated with landscape-level modifications affecting whole watersheds. As well, threats from both anthropogenic and natural factors will be exacerbated by climate change and cumulative impacts. General types of mitigation measures were recommended because a landscape-level approach that may benefit multiple COSEWIC-assessed salmonids and freshwater species is likely the most effective approach, and would require a collaborative effort among multiple government, First Nations, and non-government agencies that is beyond this RPA. The suggested DU-level natural-origin spawner abundance target of a 3-year geometric mean of 36,935 is based on observed abundances that met a distribution goal of 1000 spawners per subpopulation. Projections of growth to the recovery target under different fishing mortality and smolt-to-adult survival regimes was based on a stock-recruit analysis from brood years 1998-2013, but contains several caveats and conditions. Three models, based on different hypothesized population dynamics, were updated from a previous CSAS assessment and their forward projection results were given equal weight and model-averaged. Results indicate that positive population growth and reaching the recovery target under current conditions (average exploitation rate of 12.5% and smolt-to-adult survival of 1.0%) is 41% or "about as likely as it is not likely". If smolt-to-adult survival continues like current conditions and no impacts to freshwater habitat and egg-to-smolt survival occur, IFC are likely (≥ 66% chance) to have positive population growth at a fishing mortality of 6%; however, the risks imposed by climate change and continued anthropogenic development add notable uncertainty. Therefore, it is recommended that only activities in support of the survival and recovery of the species, which may result in possible mortalities (e.g. stock assessment, research, or mitigation activities), be permitted to ensure positive population growth.

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