Author (Your Name)

Charles K. CobbFollow

Date of Award


Document Type

Honors Thesis (Open Access)


Colby College. Environmental Studies Program


Loren McClenachan

Second Advisor

Nicholas Record

Third Advisor

Denise Bruesewitz


Anadromous fish play important roles in food webs and nutrient cycling in both aquatic and marine ecosystems. As a result of climate change however, anadromous fish’s migration timing has begun to change, with potentially deleterious consequences to both anadromous fish, and the species that depend on them. Western coastal US studies have linked earlier anadromous fish returns to warming marine temperatures and changes in river flow regimes, but the exact temperatures thresholds that anadromous fish respond to, and the relative importance of temperatures and river flows, remain somewhat unknown. Additionally, there has been relatively little research on anadromous fish phenology on the east coast, especially in the Gulf of Maine, which is warming faster than 99% of the world’s oceans. This research addresses this gap by using time series datasets to determine how river discharge and marine sea-surface temperatures have altered migration timing of river herring and American shad in New England. River herring and American shad return times got significantly earlier over the 30-year study period, a trend driven mainly by the earlier onset of warming in the fish’s marine habitat. River discharge was not as strongly related to migratory timing as marine temperature phenological indices, but played an important secondary role, especially in years with spring high flows. Overall, this research shows that climate change is having significant impacts on anadromous fish in New England, and highlights the need to account for climate impacts in fisheries management.


Phenology, river herring, American Shad, Gulf of Maine, climate change, migration timing