Juvenile salmon mortality

My doctoral work and related studies generally fall into three areas: single-stock case studies of juvenile salmon mortality; multi-stock synthesis analyses to draw inferences about migration and mortality patterns across several species and watersheds; and development of mark-recapture and biotelemetry methodology.

Single-stock case studies

Several case studies with juvenile salmon in southern British Columbia were conducted in collaboration with others using the Pacific Ocean Shelf Tracking Project (POST) biotelemetry array. Examples include:

  • We compared wild and hatchery-reared steelhead trout from the Cheakamus River and found that the marine survival advantage of wild fish was established very early during the migration, even before ocean entry. The 2-fold survival difference was maintained throughout ocean life until adults returned to spawn.  see abstract
  • We experimentally evaluated the potential effect of solar ultraviolet-B radiation on coho and sockeye salmon to test the hypothesis from hell, that UV-B exposure during freshwater rearing kills juvenile salmon after ocean entry. We found no effect on survival during the smolt migration despite reduced growth rates from UV-B exposure, suggesting that other causes of depressed marine survival are more likely.  see abstract or get pdf
  • We quantified movement and mortality patterns of coho salmon and steelhead in Howe Sound using mobile tracking methods, and found no evidence of spatial bias in mortality locations after ocean entry, suggesting that mortality was not highly concentrated right at the river mouth as previously hypothesized.  see paper
  • We described movements and estimated survival of Cultus Lake sockeye salmon during the downstream and early ocean migration through the Strait of Georgia.  see abstract or get pdf
  • We found very high mortality of endangered Thompson River coho salmon during the seaward migration in the Thompson and Fraser Rivers.  see abstract or get pdf
  • We described movements and mortality patterns of Cheakamus River steelhead trout during the downstream and early ocean migration.  see paper

Multi-stock analyses

In other analyses, we combined multiple salmon populations into the same analysis to increase power to evaluate various factors affecting survival or migration patterns. We found:

  • There was tremendous variation among species, watersheds, and rearing histories in mortality of juvenile salmon during the downstream and early ocean migration. We showed that for some populations, greater mortality occurs later in ocean life than originally expected.  see abstract or get pdf
  • Downstream survival of steelhead and Chinook salmon in the Columbia River, which has an extensive system of dams, was similar to that of steelhead and Chinook salmon in the Fraser River, which has no dams.  see abstract or get pdf
  • Steelhead, especially fish reared in hatcheries, had slower downstream migration rates than coho, sockeye, or Chinook salmon, possibly related to freshwater residualization. Coho salmon, on the other hand, were slower than other species after ocean entry, likely related to temporary residency in inshore waters. Surprisingly, after controlling for other factors, body length had no effect on travel speed after ocean entry.  see abstract or get pdf 
  • Among populations, size-related survival differences occurred during the downstream migration; within populations, selection against smaller individuals occurred during the early ocean migration.  see my thesis
  • Some mortality components during the downstream and inshore migration were independent of travel distance, suggesting high mortality periods soon after release in freshwater and soon after ocean entry.  see my thesis

  • Seasonal and diurnal migration timing strategies affect juvenile salmon survival differently in large and small rivers, likely attributable to differential visual predation risk.  in review

 

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