North Atlantic humpback whale (Megaptera novaeangliae) hotspots defined by bathymetric features off western Puerto Rico

Abstract

North Atlantic humpback whales (Megaptera novaeangliae (Borowski, 1781)) are increasing in number, necessitating current data from winter areas for assessing potential interactions with humans. Occurrence patterns of humpback whales wintering off Puerto Rico were investigated to predict where whales aggregate in nearshore areas. Here we describe the relationship between group associations of humpback whales and bathymetric features off western Puerto Rico. Data were collected from 2011 to 2014. Effort consisted of 240.9 vessel h, 13.0 aerial h, and 303.6 h of land observations conducted over 165 days. A total of 197 humpback whale groups were observed with n = 331 individuals: 91 (46.2%) singletons, 67 (34%) dyads, 17 (8.6%) mother–calf pairs, 8 (4.1%) competitive groups, 8 (4.1%) mother–calf–escort groups, and 6 (3.1%) mixed-species associations. A linear regression model supported that group composition correlated with hotspots associated with four bathymetric features. Dyads and competitive groups were dispersed among features in deeper water. Singletons were observed farther from a shelf edge, whereas singing males were closely associated with a shelf edge. Mother–calf pairs occurred nearshore in shallow water; however, when mother–calf pairs were sighted with an escort, they were offshore. This study is especially important ahead of possible removal from the Endangered Species list.

Acoustic Signaling by Singing Humpback Whales (Megaptera novaeangliae): What Role Does Reverberation Play?

“…Explosions produced in coastal environments can generate reverberation lasting 30 s or more, mainly because of scattering of incident sound by bottom irregularities [55]. Little is known about how singers decide when and where to sing, but recent research suggests that bathymetric features are predictive of where singers are likely to be found [49]. In particular, singers are consistently found in shallow waters (< 200 m deep), over harder bottoms that are relatively flat [3, 59].…”

“…In particular, singers are consistently found in shallow waters (< 200 m deep), over harder bottoms that are relatively flat [3, 59]. In Puerto Rico, singers tend to congregate near the edges of shelves [49]. Although both types of environments tend to be highly reverberant [30, 57], the extent to which songs generate sustained reverberant bands is likely to vary considerably as a function of a singer’s position as well as the acoustic features of constituent units within a song [3, 48].…”

“…The hydrophone was connected to a pre-amplifier (Cetacean Research Model SS03), which fed into a digital recorder (Sony MD Walkman Mz-NH900, recording in.wav format), sampling at a rate of 44.1 kHz. Bathymetry in the area where the recording was made involves a shallow-water shelf (< 100 m deep), just off the coast, that borders a rapid drop off to more than 600 m deep [48, 49]. …”

From Whaling to Tagging: The Evolution of North Atlantic Humpback Whale Research in the West Indies

“…Mignucci-Giannoni (1998) compared humpback sightings (published and unpublished, up to 1985) off Puerto Rico and the Virgin Islands and found that those whales also prefer shallow, nearshore waters with little slope. A recent study off the western coast of Puerto Rico found that mother-calf pairs were most often found nearshore in shallow water, while singers were found more frequently along the shelf edge than other areas in Mona Passage (MacKay et al, 2016). Depth did not appear to be a factor for the presence of single nonsinging whales (MacKay et al, 2016).…”

“…A recent study off the western coast of Puerto Rico found that mother-calf pairs were most often found nearshore in shallow water, while singers were found more frequently along the shelf edge than other areas in Mona Passage (MacKay et al, 2016). Depth did not appear to be a factor for the presence of single nonsinging whales (MacKay et al, 2016).…”