Abstract Title

Session S-02D: Pelagic Ecology in the Salish Sea II

Keywords

Species and Food Webs

Start Date

30-4-2014 1:30 PM

End Date

30-4-2014 3:00 PM

Description

Our knowledge of historical baselines for many marine fisheries is scant, making it difficult to determine the extent of change in commercial and non-commercial stocks alike. Providing a unique glimpse at entire communities and relatively easy to sample, ichthyoplankton surveys are a valuable tool for assessing change in populations. Our study evaluates the degree of spatial and temporal variation in larval fish assemblages across the sub-basins of Puget Sound by comparing historical and current surveys. Historical data for comparison was drawn from a study in 1967 conducted throughout the sub-basins (Waldron 1972). Larval fish were also collected in April of 2011, using a combination of horizontal and vertical tows, at 77 sample sites across a similar spatial extent. Although densities were fairly constant in both studies, we found a region-wide decrease in the density of previously dominant families, most notably in Merluccidae (hake) and Gadidae (cod) which experienced a 98% and 85% decrease, respectively, as well as the total disappearance of smaller, poorly understood families like Cyclopteridae (lumpsuckers). Within sub-basins, a substantial change at a compositional level was observed, shifting away from few, dominant families to more diverse assemblages. These findings reflect significant temporal and spatial changes in ichthyoplankton assemblages over the past 44 years that parallel changes in commercial harvest practices. When examined alongside coastal larval data over the same time frame, we found coastal stocks do not follow trends observed in Puget Sound in terms of changes in species composition or disappearances. In demonstrating the value of larval studies as a tool to assess long-term composition and density changes, we call for additional efforts to describe and monitor larval fish densities in Puget Sound to better our understanding of adult population dynamics.

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Apr 30th, 1:30 PM Apr 30th, 3:00 PM

Temporal and spatial variation in springtime ichthyoplankton assemblages in Puget Sound: the search for an ecological baseline

Room 611-612

Our knowledge of historical baselines for many marine fisheries is scant, making it difficult to determine the extent of change in commercial and non-commercial stocks alike. Providing a unique glimpse at entire communities and relatively easy to sample, ichthyoplankton surveys are a valuable tool for assessing change in populations. Our study evaluates the degree of spatial and temporal variation in larval fish assemblages across the sub-basins of Puget Sound by comparing historical and current surveys. Historical data for comparison was drawn from a study in 1967 conducted throughout the sub-basins (Waldron 1972). Larval fish were also collected in April of 2011, using a combination of horizontal and vertical tows, at 77 sample sites across a similar spatial extent. Although densities were fairly constant in both studies, we found a region-wide decrease in the density of previously dominant families, most notably in Merluccidae (hake) and Gadidae (cod) which experienced a 98% and 85% decrease, respectively, as well as the total disappearance of smaller, poorly understood families like Cyclopteridae (lumpsuckers). Within sub-basins, a substantial change at a compositional level was observed, shifting away from few, dominant families to more diverse assemblages. These findings reflect significant temporal and spatial changes in ichthyoplankton assemblages over the past 44 years that parallel changes in commercial harvest practices. When examined alongside coastal larval data over the same time frame, we found coastal stocks do not follow trends observed in Puget Sound in terms of changes in species composition or disappearances. In demonstrating the value of larval studies as a tool to assess long-term composition and density changes, we call for additional efforts to describe and monitor larval fish densities in Puget Sound to better our understanding of adult population dynamics.