Pacific Salmon Environmental and Life History Models: Advancing Science for Sustainable Salmon in the Future

<em>Abstract.—</em>Studies have documented reduced growth of salmon in response to competition with conspecific salmon and with other salmon species during early and late marine life stages. However, key questions remain as to whether density-dependent growth translates to reduced survival of salmon at sea and whether changes in ocean regimes, similar to that of 1976/1977, can alter this relationship. These questions are particularly important with respect to annual releases of numerous hatchery salmonids into the ocean. Few studies have tested these questions because the capacity of the ocean to support salmon is dynamic and reduced growth in Pacific salmon is often associated with great abundance of smaller fish which infers a higher overall survival rate, thereby confounding traditional statistical fisheries harvest modeling efforts. We review evidence from several recent studies suggesting that, when the density-dependent effect on growth at sea is large, salmon survival is lower with lower reproductive potential from survivors, and that the salmon carrying capacity of the ocean is influenced by climate change. We conclude that salmon growth and survival responses to oceanic changes can vary with season and life stage and that density-dependent growth at sea is an important, yet often elusive, mechanism affecting salmon survival. Pacific salmon life history models should account for these relationships.