Bryde's whale (Balaenoptera brydei) stable associations and dive profiles: New insights into foraging behavior

Abstract

Bryde’s whales (Balaenoptera brydei) are the least known of the large baleen whales and there are still some questions about their taxonomy and the number of species (Kato 2002). Indeed, previous studies of Bryde’s whale feeding ecology were based only on observational events (e.g., Siciliano et al. 2004) and on stomach contents (e.g., Kawamura 1980, Murase et al. 2007). Rorqual whales are known to display lunge feeding behavior (Werth 2000); however, there has been no evidence of Bryde’s whales lunge feeding at depth. Apart from a few studies that have used time depth recorders (TDRs) to analyze the dive profiles and feeding behaviors of fin whales in the Mediterranean Sea (Panigada et al. 1999) and of fin and blue whales in the Gulf of California (Croll et al. 2001), knowledge of the dive profiles of other Balaenoptera species is unknown. Watkins et al. (1979) successfully tracked separately two adult Bryde’s whales with radio tags, providing some surfacing data; however, no dive data were obtained. This study is the first to analyze dive data from TDRs attached to Bryde’s whales to examine foraging behavior from dive profiles. Data on individual associations over consecutive years, which is scarce for any baleen whale species, are presented and new insights into foraging behavior given. In the waters around Madeira Island (southeast North Atlantic, 32◦N, 17◦W) Bryde’s whales can frequently be found alone or in groups of two to five individuals between the months of June and November. During tagging surveys, carried out using the Madeira Whale Museum’s (MWM) 6.5 m inflatable boat Roaz in 2006, two individual adult Bryde’s whales were tagged on 27 June at 6 km off the southeast coast of the island. The tags used were Mk9 mold 161 (up to 1,000 m) TDR (Wildlife Computers, Redmond, WA) set to sample once per second and very high-frequency (VHF) radio transmitters with a 34 cm semirigid wire antenna (Telonics, Mesa, AZ)