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UBC Theses and Dissertations

Evidence for adaptive relationships between body morphology, body size and swimming performance in British Columbia populations of juvenile coho salmon, Oncorhynchus kisutch Taylor, Eric Burke


Morphological comparison of ten populations of juvenile coho salmon, Oncorhynchus kisutch, from streams tributary to the Fraser River upstream of Hell's Gate and streams in the lower Fraser Valley and Strait of Georgia region suggested that coastal juveniles were more robust (deeper bodies and caudal peduncles, shorter heads and larger median fins) than interior juveniles. Discriminant function analysis indicated that juvenile coho could be identified as to river of origin with 71 percent accuracy; juveniles from coastal streams were less successfully classified as to stream of origin (48-64 percent) than juveniles from interior streams (83-93 percent); however, juveniles could be successfully identified as of either coastal or interior in origin with 93 percent accuracy. Features of body robustness were important in discriminating between coastal and interior individuals. Three populations were studied in detail: Coldwater River (interior), Wade Creek (lower Fraser River Valley) and Morrison Creek (east coast of Vancouver Island). In these populations the coastal-interior morphological differences were consistent over successive years, and in laboratory reared individuals. These experiments suggest that the morphological differences between coastal and interior fish are, at least, in part inherited. In addition, adult coho from the Coldwater River and Morrison Creek, exhibited morphological differences similar to the juveniles. Burst swimming tests, using both wild and laboratory reared individuals from the three study streams, indicated that in the first few hundredths of a second of a "fast-start" the robust-bodied coastal juveniles attain greater burst velocities than similar sized interior juveniles. In addition, newly emerged fry from Morrison Creek attained greater burst velocities, and had greater survival from predation, than Wade Creek fry. Both Wade Creek and Morrison Creek are coastal populations but Morrison Creek fry are larger at emergence than Wade Creek fry. In frictional drag determinations and stamina swimming experiments, the fusiform interior (Coldwater River) juveniles had both lower drag coefficients and greater stamina than the robust-bodied individuals from Wade and Morrison creeks. These observations suggest that body form in juvenile coho salmon is adaptive. The fusiform body shape of interior coho may be the result of selection for increased sustained swimming performance due to the long and difficult freshwater migrations these stocks must perform. In contrast, since coastal populations make relatively short freshwater migrations, body form may be subject to less intense selection. Body form in coastal coho, however, may be subject to selection for features that reduce susceptibility to predation, i.e. deep, robust bodies and large fry at emergence.

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