A REGIONAL ANALYSIS OF LONG-TERM GRAY AND HARBOR SEAL STRANDING EVENTS
DOI Northeast Climate Adaptation Science Center Report.
Strong indicators of species' sensitivity, adaptive capacity, and overall vulnerability to climate change are provided by changes in phenology, the timing of recurring life events (Parmesan and Yohe, 2003). We possess poor information on climate induced shifts in phenology of marine organisms, especially top predators. The Gulf of Maine (GOM) Seasonal Migrants Project is an ongoing effort to determine the phenological changes occurring in the GOM across marine mammals, sea turtles, and other marine species of conservation concern. As part of that study, stranding data of injured or dead animals was explored for its utility to serve as supplemental data to amend more traditional survey data where observations are scarce. NOAA's Greater Atlantic Region Marine Mammal Stranding Network Database was examined for its utility as a potential long-term time series for the evaluation of phenological patterns and shifts. Although records from stranding events represent sick or injured animals, these data have been found to be reasonably comparable to survey data and provide useful information on species' distribution, abundance, and foraging ecology (Maldini et al., 2005; Staudinger et al., 2014; Johnston et al., 2012, 2015). In this study, we focused on stranding data of two marine mammal species, harbor seals (Phoca vitulina) and gray seals (Halichoerus grypus). It was anticipated these data would also be good indicators of the areas and habitats that seal populations use on a seasonal and annual basis in the region. Viable stranding data from Maine to North Carolina included 1,571 gray seals and 4,399 harbor seals from 2001 to 2015. This paper presents a summary of the spatial and temporal patterns of these data, and suggests their suitability as supplemental data to other GOM marine species phenological studies, such as the North Atlantic Right Whale Consortium database modeling efforts.