PARENT SESSION
Contributed Oral Session 62: Fish Predation and Morphology
Tuesday, August 9, 1:30 PM - 5:00 PM, Meeting Room 518 C, Level 5, Palais des congrès de Montréal

Linking macroinvertebrate dynamics to individual stream fish growth in a long-term study site.

Ojala, Jeffrey^*,1, Nislow, Keith^{1, 2}, Letcher, Benjamin^{1, 3}, ¹ University of Massachusetts, Amherst, MA, USA² USDA - Forest Service, Amherst, MA, USA³ USGS - Biological Resources Division, Turners Falls, MA, USA

ABSTRACT- Variation in the availability of macroinvertebrate prey may be an important determinant of growth variation in stream salmonids. However, few studies possess the requisite detailed information (multiple recaptures of marked individual fish, frequent samples of invertebrate prey availability and use) to make these links explicitly. We tested the relationship between macroinvertebrate availability and use and seasonal variation in the growth rates of three sympatric species of stream salmonids (Atlantic salmon, brook trout, and brown trout) in a long-term study site. Our goal was to determine 1) the factors which influenced prey selectivity within and among the three co-occurring species 2) the concordance between seasonal patterns of prey availability and individual fish growth 3) the interaction between physical factors, prey availability and fish growth. Our preliminary results indicate that all three fish species exhibit a pronounced, concordant peak in growth (> 80% of total annual growth over < 14% of the total year) that appears to be associated with a combination of physical factors (high drift flux rates, high availability of large invertebrate prey). These results indicate that seasonal dynamics in physical conditions (flow, temperature) and invertebrate phenology may combine to produce a critical period for individual growth in stream salmonids.

Key words: salmonid growth, prey selection, seasonal variation