Preliminary ecological results
Using the SealNet facial recognition software package and a small, initial dataset sampled across two years (2019 and 2020) in Casco Bay, we identified four individuals in the datasets from both years, indicating a small degree of local site fidelity across years during the months of June and July. All four seals were found on the haul-out site, Brandt Ledges, in 2019. In 2020, the four seals were photographed again within 1-3 nautical miles of Brandt Ledges: one was photographed on Branning Ledges, two were photographed at the Mitchell Field site, and one was photographed on the Whaleboat Island site. This result supports previous results suggesting site fidelity among harbor seals off the coast of NE Scotland . It is also interesting to note that two of the individuals found in the dataset from both years, Clove and Petal, were found together initially on Brandt Ledges on one day in 2019, and then found together again in 2020 at the Mitchell Field site. These results suggest that SealNet software may be useful in future long-term studies of social relationships in harbor seals. Previous studies have examined competitive relationships among harbor seals , however further research is needed to examine other questions related to social behavior, including social fidelity, persistence of family groups, and other social dynamics.
Our preliminary ecological results suggest some site-fidelity of harbor seals in Middle Bay as well as site-fidelity to neighboring haul-out sites within the bay. A more extensive ecological study is underway to determine the degree of site fidelity and spatial connectivity of haul-out sites in this region. In addition, our results provide an estimated population size of approximately four thousand seals utilizing Middle Bay, although more extensive photographic data will help refine this population estimate. Current estimates of harbor seal abundance are outdated, suggesting a population of 38,014 individuals in the whole of Maine in 2001 ( followed by an aerial survey done in 2012 determining a population of 75,834 individuals (). Accurate local and regional population estimates are imperative to understanding dynamics of seal abundance in relationship to anthropomorphic and climate changes to coastal marine environments as well as the impact of an increasing great white shark population.
The use of facial recognition software to identify individuals in wild populations is a relatively new area of research being primarily utilized in studies of land mammals such as lemurs and brown bears (Crouse et al., 2017). Our research extends the use of such methods to marine mammal species. Facial biometrics are not the only measure that can be used for automated identification of seals. For example, a recent, groundbreaking study utilized pelage markings found on the seals coat to identify grey seal individuals near Wales (Langley et al., 2020). Given that coat patterns may change across seasons during molting or over time in harbor seals, facial biometrics may offer and additional and/or more reliable method of identification. Thus, developing facial recognition techniques for harbor seals allows for a rapid, non-invasive means for detailed study of an economically and ecologically important species. Importantly, researchers can customize the software and the GUI to suit their own needs at each step of data collection—training the face detector for additional species, modifying the alignment procedure, or preprocessing images for face recognition.