Population Estimates and Low DO Waters

Sampling Low Dissolved Oxygen Waters can Change Population Estimates

Ecofore researchers have been working with Lake Erie biologists from the Ohio Department of Natural Resources (ODNR) in Fairport, Ohio to better understand how hypoxia may influence ODNR’s annual fishery assessment surveys. Specifically, they are looking at how hypoxia may alter catchabilities of fish, and in turn, what impact this altered catchability (and altered spatial distribution of fish) may have on assessments of population size for economically important fisheries.Â

The researchers highlighted their preliminary findings in a presentation to the American Fisheries Society at their annual meeting in September 2010 in Pittsburgh, Pennsylvania. Here is the abstract from the presentation:

Lake stratification, occurring predominantly from July through September, often results in hypoxic conditions in the offshore waters (>15 m) of the central basin of Lake Erie. Below certain thresholds, fish exhibit avoidance behavior and may aggregate on the edges of the hypoxic zone. Monthly bottom trawl surveys are used to estimate yellow perch young-of-the-year and yearling indices. Sampling in the hypoxic zone with bottom trawls can result in atypically low catch rates. Adhering to sample design, where habitat becomes unsuitable, may invoke bias. Our first objective is to assess how hypoxic conditions affect the spatial distribution of yellow perch. We will determine the dissolved oxygen thresholds for yellow perch and if fish are aggregating at hypoxic edges. Secondly, we will assess how hypoxic conditions affect the yellow perch population estimates.  Some preliminary findings have shown that not sampling low dissolved oxygen areas could result in elevated estimates of indices and yellow perch populations.

Carey Knight, Ohio Department Natural Resources,
Ann Marie Gorman , Wildlife, Ohio Department Natural Resources
Troy Farmer, The Ohio State University
Stuart Ludsin, The Ohio State University
Kevin Pangle, The Ohio State University

(September 2010)