Among-Population Variability of Fish Growth: III. Influence of Fish Community

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Abstract
We assessed the relationship between in situ fish growth and fish community descriptors in 12 yellow perch (Perca flavescens) populations that exhibited a 1.8 to 10-fold range in growth rates depending on age class. Data on the quantity and quality of food consumed were used to assess the mechanisms by which fish community composition influences in situ growth rates. Among-population variability in growth rates of the 12 perch populations was most strongly and consistently explained by the average density of the total fish community and/or the average density of cyprinids. A multivariate model involving fish average density and perch feeding levels explained 90% of the variance in perch growth. Perch growth rates decreased as fish average density increased (r2 = 0.60) and increased as feeding levels increased (r2 = 0.30). We found no significant relationship between the quantity of food consumed by perch and fish average density. The percent contribution of prey taxonomic groups to perch diet was not related to fish average density. We suggest that nonexploitative interactions (operating through increased activity costs) provides a more credible explanation for the negative relationship between perch growth and fish average density than does exploitative competition (decreased total quantities of food consumed or prey quality).