Evidence for morphometric differentiation of wild and captively reared adult coho salmon: a geometric analysis

As part of a comprehensive genetic evaluation of reproduction in naturally spawning coho salmon, Oncorhynchus kisutch, we examined morphometric variat ion in captively reared and wild adults from Hood Canal, Washington (U.S.A. ) for evidence of differentiation between these groups. We collected captiv ely reared fish as parr from two stocks and reared to adulthood at a freshw ater hatchery, maturing in 1995 and 1996; we sampled closely size-matched w ild fish as they returned to a neighboring stream in both years. Multivaria te analysis of shape variation by Procrustes coordinates, visualized by thi n-plate splines, indicated that the captively reared adults were differenti ated from the wild fish by sharply reduced sexual dimorphism as well as sma ller heads and less hooked snouts, increased trunk depth, larger caudal ped uncles, shorter dorsal fins, larger hindbodies and a reduction in body stre amlining. The differences between the captively reared and wild fish were s imilar to but more pronounced than some differences previously reported bet ween hatchery and wild coho salmon. The magnitude and pattern of difference s suggested that at least some of them were environmentally induced. Shape variation showed an allometric relationship with variation in body (measure d as centroid) size. Morphometric variation was a poor correlate of most sp awning behaviors. Nevertheless, our results suggest that the morphometric c onsequences of captive rearing for mate selection and reproductive activity of spawning fish may limit its effectiveness as a restorative tool.