Effects of long-term changes in the benthic community on yellow perch in Saginaw Bay, Lake Huron

Abundance, mortality, age and growth, food habits, and energetics of a yell ow perch Perca flavescens population were investigated in eutrophic Saginaw Bay, Lake Huron during May to October, 1986 to 1988, and compared populati on characteristics with historical data from rimes when eutrophic condition s were less severe. During 1986 to 1988, yellow perch were abundant, but gr ew slowly and experienced high natural mortality. A size threshold was pres ent at 150 to 180 mm beyond which few individuals survived, and sex ratios became biased toward males. An energetic model suggested that yellow perch were food limited; as they increased in size they spent a greater proportio n of the growing season near maintenance ration. Low feeding rates were a c onsequence of subsistence on small chironomid larvae. Piscivory provided li ttle energetic relief: Historical data suggested that availability of large benthic prey such as nymphs of the burrowing mayfly Hexagenia was importan t to yellow perch. Yellow perch formerly consumed Hexagenia, but mayflies w ere extirpated from Saginaw Bay during 1953 to 1965, and never recovered. W hen Hexagenia was present, yellow perch growth was moderate to fast dependi ng on population size, size thresholds were not present, and yellow perch r eached large size and older age despite moderate to high fishing mortality. Decreases in yellow perch growth rates during 1952 to 1955 coincided with extirpation of Hexagenia. Fast growth of yellow perch did occur after Hexag enia became extirpated but only when fishing mortality was high, population size was small, and some large benthic invertebrates remained. Eutrophicat ion of Saginaw Bay appeared to affect yellow perch by changing species comp osition and reducing size structure of the benthic community.