The study by Timothy Cline, Jan Ohlberger and Daniel Schindler of UW’s School of Aquatic and Fishery Sciences found that species with complex life cycles, including those migrating between different habitats to complete their life cycles, may be particularly sensitive to global change. This is because each life cycle stage is influenced by a unique set of natural and anthropogenic stressors, the report said.
The research involved using of multivariate time-series models to quantify changes in the prevalence of different life-history strategies of sockeye salmon from Bristol Bay, Alaska, over the past half century looking specifically at how they partition their lives between freshwater habitats and the ocean. During their life cycle, distinct life stages differ in their sensitivity to individual stressors, particularly temperature, the report noted. And effects of environmental change experienced by a population in one habitat affect their ecology in other life stages through developmental links in the process of completing their life cycle.
Researchers contend that climate warming has decreased the time spent by salmon in their natal freshwater habitat, as climate-enhanced growth opportunities have enabled earlier migration to the ocean. They also concluded that migration from freshwater at a younger age and increasing competition from wild and hatchery-released salmon, have tended to delay maturation toward spending an additional year feeding in the ocean.
According to the report, these stressors combine to reduce the size-at-age of fish vulnerable to commercial fisheries and have increasingly favored a single-age class, potentially affecting the age class complexity that stabilizes this resource.