GIS-based analysis of harp and hooded seal sighting locations on shore in the Southern Gulf of Maine

Ice seals (harp and hooded seals) were rarely seen in the Gulf of Maine before 1990 but have been sighted with increased frequency since. To explore these types of sightings, we developed an analysis technique for events that occur at the irregular border between two polygons. We used a geographic information system and non-parametric statistics to analyze 584 ice seal sightings in the southern Gulf of Maine. Compared to harp seals, hooded seals were sighted closer to deep water and were less healthy; sicker animals were more likely than healthy ones to be sighted near high-energy intertidal zones. Using Ordinal Logistic Regression, we also found that high seal sighting densities occurred more often near public land and in the southwest of the study region. Given the opportunistic nature of this data set, and its inherent reporting biases, these correlations should be interpreted carefully; however this technique may be useful to analyze other "border" events.