Browsing by Author "Fulford, Richard Stewart"

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    Food Web Interactions of Larval Yellow Perch, Perca flavescens, in Lake Michigan: Implications for Recruitment
    (2005-01-16) Fulford, Richard Stewart; James Rice, Committee Chair; Kenneth Pollock, Committee Member; Peter Rand, Committee Member; James Gilliam, Committee Member
    Variability in annual recruitment for many fishes is correlated with survival during the larval phase. Yellow perch in Lake Michigan have experienced sustained recruitment failure since 1990 and this has been blamed on low larval survival. Direct examination of factors important to larval yellow perch survival in Lake Michigan is complicated by the large size of the lake (52,000 km2) and the short length of the pelagic larval period (30-40 days). Individual-based modeling is a valuable indirect method for assessing the importance of multiple factors to larval survival. I used an individual-based modeling approach combined with field data collection to test four hypotheses regarding factors limiting survival of larval yellow perch in Lake Michigan. I tested whether larval survival is limited by prey community composition, size-selective predation, advection of larvae into offshore habitat or an interaction of these factors. I sampled larval and zooplankton abundance in Lake Michigan along a transect from 1 – 32 km from shore in 2000 and 2001. I conducted laboratory experiments to quantify larval vulnerability to predation by three typical predators as a function of both predator and prey size. I also conducted laboratory experiments to quantify larval selectivity for different zooplankton prey as a function of larval size and prey community composition. I used the results of these experiments to develop an individual-based model specifically to describe growth and survival of larval yellow perch. Field data suggest that larval yellow perch are being transported from the nearshore to the offshore zone of Lake Michigan, but the timing of this transport varies between years. Model simulations in which the offshore prey community and the timing of larval advection were both varied suggested that larval survival will be highest in years when advection occurs within two weeks of peak hatch, allowing larvae to exploit offshore prey resources early during ontogeny. The model predicts that larvae will make foraging decisions based on prey availability as well as innate preference and they will change their diet if they are exposed to different prey communities. Model simulations also demonstrated that predation currently may not be an important factor for survival of larval yellow perch in Lake Michigan. This result is because alewife is the only fish abundant in Lake Michigan known to eat larval yellow perch. Experimental results suggest that alewife feeding rate on larval yellow perch is a positive function of larval density; yellow perch densities are currently too low to induce significant predation by alewife. Predation appears to be more important in smaller systems where larval densities are higher and larvae are exposed to other predator species. Larval survival in Lake Michigan appears to be primarily limited by an interaction of prey community composition and the timing during the larval period of offshore advection. Both factors vary between years and a good year-class is predicted when the offshore prey community is rich in cyclopoid copepods and larvae are advected offshore early. Early access to cyclopoid copepods results in an earlier transition from feeding on rotifers to feeding on copepods, which is predicted to increase larval growth and decrease mortality. These results suggest that survival of larval yellow perch in Lake Michigan is affected more by density-independent factors such as physical transport and prey community composition; Lake Michigan more closely resembles a marine environment than a typical lake with respect to larval recruitment processes. The unique aspects of larval yellow perch dynamics in Lake Michigan must be considered when applying lessons learned from analysis of larval yellow perch in other lakes to understanding survival of larval yellow perch in a large meso-oceanic system like Lake Michigan.