Development of a lake-wide multi-species fishery-independent survey for Great Slave Lake

Abstract

A lake-wide depth-stratified summer fish survey using multi-mesh experimental gillnets was developed as a fishery independent sampling program for Great Slave Lake. To support assessments of stock productivity, a suite of biological data (e.g., fish length, weight, sex, condition, health attributes) and samples (e.g., ageing structures, stomachs, genetic samples) will be collected for individual fishes. Otoliths, pectoral fin rays, and scales will be collected for fish ageing. Otoliths are the preferred ageing structure, and it is unclear whether fin rays or scales are the preferred alternate; additional research on ageing accuracy and consistency with fish fin rays and scales in Great Slave Lake is needed. In addition to fish sampling, zooplankton nets and benthic grabs will be used at each site to provide data on lower trophic levels to support ecosystem assessments. Environmental data (e.g., depth profiles for dissolved oxygen, chlorophyll a, pH, water temperature and turbidity, weather and wave conditions) will be recorded at each site. This survey is Fisheries and Oceans Canada’s first ecosystem-level survey program for Great Slave Lake and was developed without previous estimates of variability or species distributions; therefore, the sampling program will need to undergo a preliminary review after three years and a full review after five years. To establish empirical relationships between additional environmental variables and stock production: Water samples should be collected for nutrient analyses so that probe-derived chlorophyll a data can be related to phytoplankton composition. Secchi disc and water colour measurements should be taken at all stations to allow comparison with historical data. Data could be obtained from existing weather buoys and temperature loggers could be deployed on fishing nets.