Abstract
Population assessments of fish species often rely on data from surveys with different objectives, such as measuring biodiversity or community dynamics. These surveys often contain spatial–temporal dependencies that can greatly influence conclusions drawn from analyses. Pygmy whitefish (PWF, Prosopium coulterii) populations in Lake Superior were recently assessed as Threatened by the Committee on the Status of Endangered Species in Canada, which motivated a thorough analysis of available data to improve our understanding of its population status. The US Geological Survey conducts annual bottom trawl surveys in Lake Superior that commonly capture PWF. We used these data (1989–2018) to model temporal trends in PWF biomass density and make lake-wide population projections. We used a Bayesian approach, integrated nested Laplace approximation (INLA), and compared the impact of including different random structures on model fit. Inclusion of spatial structure improved model fit and conclusions differed from models omitting random effects. PWF populations have experienced periodic fluctuations in biomass density since 1989, though 2018 may represent the lowest density in the 30-year time series. Lake-wide biomass was estimated to be 71.5 t.
Highlights
Fish population assessments, whether for the purposes of conservation or fisheries management, must often rely on data from monitoring surveys designed to meet other objectives
Monitoring surveys may be designed with a focus on biodiversity or community dynamics, but are out of necessity, used to assess single-species population trends and stock assessments
The long-term trend analysis found no evidence of a significant trend in PWF catch probability through time regardless of model fit (Figure 2) and the standard deviation associated with the year effect was low (
Summary
Whether for the purposes of conservation or fisheries management, must often rely on data from monitoring surveys designed to meet other objectives. The U.S Geological Survey (USGS) conducts an annual bottom trawl survey in Lake Superior to assess the status and trends of the prey fish community (Vinson et al 2018). Nearshore trawls in United States waters of the lake have been conducted since the early 1960s. While designed as a prey fish community survey, prior analyses have shown that it does provide reliable species level population metrics for some commercially important species, such as lake whitefish (Coregonus clupeaformis; Curtis et al 1993) and cisco (Coregonus artedi; Yule et al 2006). Potential improvements to the survey have been identified (Yule et al 2008), but not implemented
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