Habitat-Based Abundance Benchmarks for Lake Sockeye CU’s in the Skeena Watershed

This report describes the results of a habitat-based assessment of the Skeena lake sockeye CUs to evaluate stock status and develop benchmarks for Skeena sockeye.

Introduction

Although stock-recruit analysis has been the main method for establishing benchmarks for lake sockeye Conservation Units (CU’s) in the Skeena watershed to date (Korman and Cox-Rogers 2012), habitat-based abundance benchmarks may have application as well. For example, the lake rearing capacity estimates (Rmax juveniles and Smax spawners) from the photosynthetic rate (PR) model of Shortreed et al (2000) and Cox-Rogers et al (2010) can be used to independently assess status and develop benchmarks. Holt et al (2009) endorse using carrying capacity to develop salmon CU benchmarks, especially in cases where estimates of Smsy are not available because recruitment and/or productivity data are missing or uncertain. Where stock-recruit data are available, independent Smax priors from habitat studies can help establish better estimates of intrinsic productivity in stock-recruit analyses (Walters et al 2008) as applied by Grant et al (2011) and Korman and Cox-Rogers (2012). Finally, where data on spawner abundance are not available or are of poor quality (e.g. the majority of BC sockeye CU’s) juvenile abundance may provide a rough indication of spawning status (Holt et al 2009).

For Skeena sockeye lakes, data on juvenile abundance has been collected from rotational acoustic surveys since the mid-1990’s (Cox-Rogers et al 2010) and is routinely compared against juvenile rearing capacity estimates (Rmax) for general status assessment. Escapement survey data (where available) can also be compared against Smax spawners for assessing general status. In this paper, provisional upper and lower benchmarks from PR-based Rmax and Smax for Skeena sockeye lakes are suggested, and recent status relative to these benchmarks is compared.