Occurrence Patterns and Social Behaviors of Humpback Whales (Megaptera novaeangliae) Wintering off Puerto Rico, USA

Abstract

Occurrence patterns and social behaviors of North Atlantic humpback whales (Megaptera novaeangliae) (NAHW) wintering off Puerto Rico were investigated to examine the relationship of this area to the aggregation wintering off the Dominican Republic. I described winter occurrence, movement and association patterns, and the relationship of group associations with bathymetric features in Mona Passage, immediately west of Puerto Rico. Data were collected from boat, land, and aerial surveys from 2011 to 2014. Acoustic data were collected with hydrophones deployed from a small vessel and units mounted to the sea floor, to determine the presence of singers (males). Photo-identification of individuals was used to describe intermixing of whales between higher latitudes and the study area. Social behaviors were described between intra- and inter-specific associations.

A pilot study was conducted January-March 2011 from land platforms using scan sampling. In 2012, boat-based data collection and aerial reconnaissance were added. A total of 240.9 hours vessel, 13.0 hours aerial, and 303.6 hours land observations were conducted over 165 days. One hundred ninety-seven groups of humpback whales were observed with N = 331 individuals: 91 (46.2%) singletons, 67 (34%) dyads, 17 (8.6%) mother-calf pairs, 8 (4.1%) in competitive breeding groups, 8 (4.1%) mother-calf-escort groups, and 6 (3.1%) mixed-species associations. Group associations were not random. A multinomial linear regression model supported group composition and behaviors were correlated with “hotspots” associated with four bathymetric features. Dyads and surface active groups were dispersed among features in deeper water. Singletons were observed further from a shelf edge, while singing males were closely associated with a shelf edge. Mother-calf pairs occurred nearshore in shallow water moving offshore when accompanied by an escort. Identification photos matched against the NAHW catalog indicated movement between most feeding grounds and throughout the West Indies. It is important to continue and expand this study in Puerto Rico to monitor long-term population changes, and as a means of predicting where human activity overlaps with NAHW occurrence, especially due to possible U.S. delisting of NAHW as endangered.