What questions are we asking, and why?

By the mid- 2000s, a growing body of evidence had identified dams and low marine survival among the most impactful stressors contributing to the decline of Atlantic Salmon in Maine. Less than 1% of salmon migrating to the ocean for the first time survive to return to their natal streams. Researchers referred to this period in the salmon life history as a “black box” to highlight data gaps that needed to be addressed to fully understand where and why so many salmon were dying during their migration.   

What questions are we asking about marine survival?

From 2008 to 2010, researchers from multiple disciplines convened for a series of workshops to share perspectives, review research to-date, and identify research priorities, focusing on those that could impact local and regional management. Together, they developed six testable hypotheses addressing the low survival rate of Gulf of Maine Salmon:

6 hypotheses to address low survival rates of Gulf of Maine Atlantic Salmon

  1. Climate change and variability have altered oceanic salmon habitat, affecting marine survival of Gulf of Maine Atlantic salmon;
  2. Altered oceanographic conditions have led to changes in migration routes/behavior, resulting in reduced marine survival of Gulf of Maine Atlantic salmon;
  3. Changes in Northeast Shelf marine communities have altered Atlantic salmon food webs, resulting in reduced marine survival of Gulf of Maine Atlantic salmon;
  4. Populations of other diadromous species in the Gulf of Maine have declined, resulting in reduced marine survival of Gulf of Maine Atlantic salmon;
  5. Climate change has disrupted the correspondence between freshwater and saltwater conditions, leading to greater mortality rates of smolts and affecting marine survival of Gulf of Maine Atlantic salmon; and
  6. A loss of genetic diversity has reduced life history diversity, including adult run timing and variability in marine migration routes, affecting marine survival of Gulf of Maine Atlantic salmon.

Since the workshop, NOAA, along with other partners, has been working to address and gather data on all six hypotheses. The Penobscot River Estuary Research Project evolved in response to the fourth hypothesis.