SASAP: Consistency, causes, and consequences of declining size and age of Alaskan salmon

Decreases in the body size and age of returning adult salmon have been noted for several Alaskan salmon species. Size and age declines have the potential to impact the biomass and stability of salmon populations. Despite evidence for decreased size and age of spawning adult salmon for some species and rivers, a comprehensive synthesis of size and age trends across species and populations is currently lacking. Several potential drivers of size and age shifts have been proposed, including fisheries, climate change, and density dependence at sea. However, the consistency of trait changes across populations and the contributions of the various potential drivers are unknown. Understanding the consistency and causes of age and size changes is important because these traits underlie many important aspects of ecological function and the value of salmon for human use. The aims of this working group are to examine the consistency, causes, and consequences of declining size and age in five species of Pacific salmon in Alaska. Specifically, we will ask: 1. Consistency: How consistent are changes in size and age across species, regions, and populations? 2. Causes: How are changes in size and age related to variation in potential drivers, including fisheries, climate change, and density dependence at sea? 3. Consequences: What are the consequences of age and size changes for the ecological, economic, and cultural value of salmon? We will synthesize existing data on Alaskan salmon size and age trends across species, regions, and populations to assess whether declines in size and age noted for some populations are widespread. We will examine the relationships between size and age changes and potential drivers, including fishing mortality, climate change, and density dependence. Finally, we will examine the consequences of size changes for ecosystems and human uses, including ecological implications for coastal, riverine, and interior ecosystems and the economic and cultural value of salmon for the people of Alaska. Our data synthesis will contribute basic insights into the causes and consequences of contemporary trait changes in wild populations and applied insights into how to successfully manage economically and culturally important biological resources in an era of rapid environmental change.