Projected Ocean Warming Poses a Challenge to Anadromous River Herring Populations

For anadromous species that utilize a range of habitats throughout their life cycle, the response to a changing global climate is inherently complex, and likely varies regionally.  Little work has examined the marine phase of the anadromous species complex, river herring, even though they occupy marine habitat for the majority of their lives.  We project potential effects of ocean warming along the U.S. Atlantic coast on river herring in two seasons (spring and fall), and two future time periods (2020 – 2060 and 2060 – 2100) by linking species distribution models to projected temperature changes from global climate models. Our analyses indicate that climate change will likely result in reductions in total suitable habitat across the study region, and poleward shifts in marine distributions of river herring. We also project that density will likely decrease for both species in fall, but may increase substantially for blueback herring in spring.  Finally, we demonstrate that current abundance may play an important role governing the relative impact of climate effects on future abundance; however, there is uncertainty surrounding current population size. Thus, establishing effective conservation efforts in the near term would likely improve population resiliency, and provide lasting benefits to river herring populations.