MSI: Diet by Stomach Content Analysis
Fish diet studies require detailed examination of stomach contents, a particular area of expertise of the FEDZ lab. Stomachs are excised and weighed, and the food bolus is teased apart under the microscope to count and identify a wide range of prey using taxonomic keys and qualitative indices. The digested prey are often only 1-2 mm in size and in pieces, making them more difficult to identify than fresh zooplankton.
The figure at left shows hatchery and wild juvenile chum salmon use of prey communities from May-July in 2004. Wild chum tend to eat more energy-rich drift insects in spring nearshore habitats of the inner and middle Taku River Estuary, while hatchery chum consume more pelagic zooplankton prey. Diets are less partitioned by these fish stocks in outer Taku Inlet and later converge completely in the epipelagic habitat of Icy Strait. Unless a negative effect such as poorer condition or lower feeding success is identified, competition is not necessarily indicated by these early differences in prey composition.
Diet studies are also critical in determining the consumption of zooplankton stocks by juvenile salmon. The Figure below depicts use of pelagic zooplankton prey biomass by 3 species of juvenile salmon in 2001. Diets of these species overlap to some extent, but abundant food resources allow highly successful feeding during the June period of peak salmon abundance in Icy Strait. Such FEDZ-lab data are used in bioenergetic models to address broad questions about the relative carrying capacity of different regions of Southeast Alaska.
Contact:
Molly Sturdevant or Emily Fergusson
Auke Bay Laboratories
Alaska Fisheries Science Center, NOAA Fisheries
Ted Stevens Marine Research Institute
17109 Pt Lena Loop Rd
Juneau, AK 99801
Molly.Sturdevant@noaa.gov
Emily.Fergusson@noaa.gov
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