A new book about Samaná humpback whales

A COLLABORATION BETWEEN
PROGRAMA ECOMAR
AND CEBSE

Book title: Humpback whale (Megaptera novaeangliae) data
from Samana Bay, Dominican Republic (in Spanish)

Liliana Betancourt-Fernández and Alejandro Herrera-Moreno

Bathymetric modelling of the whale watching area of Samaná Bay (Dominican Republic) is presented as a descriptive base of the submarine topography, highlighting topographic features relevant to the distribution of whales, such as the Whale's Hole and Canadaiqua Bank. An oceanographic characterization is also offered with basic information about the horizontal and vertical distribution of several oceanographic variables, obtained in collaboration with the Sailboat School Corwith Cramer, wind system, and wave patterns during the months of the whale season. Data on distribution, habitat use, social groups, relative abundance and photoidentification of humpback whales were obtained from commercial whale-watching vessels during January to March in the years 2004 to 2006, in Samaná Bay.

During the three years of study there were 1,333 sightings totalling 3,044 whales sighted, during 667 trips. The data reveal distinct variation patterns in the bi-weekly spatial distribution during the three months of season. At the end of January and during March the sightings are dispersed and are located toward the mouth of the bay and the oceanic region, while in February they are con-centrated more inside the bay, with many sightings beyond Cayo Levantado. Nevertheless, the 80% of all sightings are over Canadaiqua Bank, on and South of the Whale's Hole, and to the East of Cayo Levantado. The comparison of almost two decades of data (1988 to present), shows that humpback whales have continued visiting the Samaná Bay year after year. The areas and timing of aggregation have also remained the same. This highlights the bay's importance as a reproductive area in the Caribbean and Atlantic region.

The dominant social groups were couples, mothers with calves, solitary whales, and competitive groups. The dominant groups observed reflect the pattern of whale watching, with proportions biased by selectivity, rather than the natural composition. The distribution of social groups reveals that those with calves present have a greater number of sightings inside the bay than in the oceanic region. For mothers with calves, sightings were most frequently observed at inner and shallower positions, while other humpback whale groups were distributed throughout all depth ranges.

Relative abundance estimates, standardizing the biweekly data by trip, shows that 2004 was a year of higher abundance than 2005. Estimates in 2004 were 1.88 to 4.15 sightings/trip and 4.42 to 8.81 whales/trip, with a distinct peak during the first two-week period of February. Estimates in 2005 were 1.17 to 2.58 sightings/trip and 2.44 y 6.00 whales/trip, with a peak in the second two-week period of February. The relative abundance estimates considering only the daily data of the Ship Victoria II, standardized by hour, show a statistical significance between the years 2004 and 2005. In the 2004 the number of sightings/hour averaged 0.85, with maximum and minimum, of 1.70 and 0.20, respectively. In 2005, the average was 0.66, the maximum of 1.45 and the minimum 0.19. As a trend relative abundance has a parabolic relation with the time of season.

The data presented herein extends the sightings interval to the end of the reproductive season and the spatial range of sightings to new areas not previously reported. Our preliminary results of photoidentification and resighting shows values of occurrence from two to three days and from one to thirty days of occupation. These results demonstrate the importance of the opportunistic whale watching commercial platforms to obtain valuable permanent, descriptive and predictive information about the spatial-temporal distribution of humpback whales.