Phenological Variation in Spring Migration of Adult River Herring in Coastal Massachusetts.

Sheppard, John¹, Rebecca Dalton², Henry Legett³, Adrian Jordaan⁴, Michelle Staudinger⁵, ¹Massachusetts Division of Marine Fisheries, New Bedford, MA, ²United States Environmental Protection Agency, Research Triangle Park, Durham, NC, ³Smithsonian Environmental Research Center, Edgewater, MD, ⁴University of Massachusetts, Amherst, MA, ⁵Northeast Climate Action Science Center, Amherst, MA

We determined the extent of phenological shifts in adult river herring as they migrated from ocean to freshwater environments during spring to spawn at 12 Massachusetts streams. We evaluated broadscale oceanic and atmospheric drivers that trigger their movements, including sea surface temperature, North Atlantic Oscillation index, and Gulf Stream index. Run timing metrics of initiation, peak run timing, end, and duration were found to vary among sites. Overall, winter sea surface temperature, spring and fall transition dates, and annual run size were the strongest predictors of run initiation and median dates, while a combination of within-season and seasonal-lag effects influenced run end and duration timing. Disparate results observed across the 12 spawning runs suggest that regional environmental processes were not consistent drivers of phenology and local environmental and ecological conditions may be more important. We examined the local influence of environmental factors on daily migration patterns and compared seasonal run dynamics and environmental regimes among streams. Our results suggest that water temperature was the most consistent variable influencing migration, whereas the effects of streamflow and lunar phase were inconsistent, likely due to anthropogenic manipulations and stream connectivity. Geographic patterns in run dynamics and thermal regimes suggest that the more northerly runs in this region are relatively vulnerable to climate change due to migration occurring later in the spring season, at warmer water temperatures, and during a narrower temporal window compared to southern runs. Results from these studies may have several management implications which are discussed.