Conditional success

Posted on September 26, 2009


One way of studying the responses of predators to changes in the abundance of their prey is to monitor the status of both predator and prey populations over time, which is usually a costly and time-consuming operation.  A simpler, albeit indirect, alternative is to assume that a predator’s body condition (its weight for a given length) reflects its growth rate, feeding success and, and therefore the availability of prey.  This assumption has been supported in studies of walleye (Sander vitreus, a perch-like fish) inOneida Lake,New York.  Analysis of data collected over 23 years revealed that the body condition of walleye was directly related to their growth rate (as deduced from scale rings) and prey fish abundance (based on trawl catches and mark-recapture experiments).  However, in some other studies of fish body condition, such correlations were weak or non-existent.  Therefore, before using predator condition as an indicator of prey fish abundance, preliminary work should be done to confirm that predator and prey populations in the target water body are closely coupled. 

Reference: Vandervalk, A.J., Forney, J.L. & Jackson, J.R.  2008.  Relationships between relative weight, prey availability, and growth of walleyes in Oneida Lake, New York.   North American Journal of Fisheries Management 28,1868–1875.

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Posted in: fish, predation