Blue whales (Balenoptera musculus) in the Canal Moraleda and Golfo Corcovado, Chile

摘要

Blue whales are known principally by two contrasting accolades, firstly, as being the largest animal to have ever lived on Earth, and secondly, as having been hunted to near extinction during twentieth century whaling. During the whaling era over four thousand animals were caught in Chilean waters alone. The species has been slow to recover from almost total decimation and hence a valuable discovery was made in 1993, when a small blue whale population of approximately 230 individuals was found in the Gulf of Corcovado in the Chiloense Ecoregion of Southern Chile. Genetic, acoustic and morphometric studies indicate that these blue whales are part of a wider Southeast Pacific population that is distinct from both the Antarctic (B. musculus intermedia) and “pygmy” (B. musculus brevicauda) blue whale subspecies. Further investigations are required to establish the degree of isolation of the population and the health and viability of the individuals within it; this was the goal of the work described here, which was a joint effort between WHOI and the Melimoyu Ecosystem Research Institute (MERI). A thirteen day cruise (15–27 March 2014), departing the port of Dalcahue on Chiloé Island, Chile, resulted in the deployment on blue whales of 5 digital acoustic tags (DTAGs), which are miniature sound and orientation recording tags that are attached via suction cups. A total of 21 hr 11 min of blue whale DTAG data were collected, consisting of five tag deployments on four individual blue whales. One simultaneous deployment was achieved, of a presumed mother and juvenile pair. The mean deployment duration was 4.5 hr (S.D. 4.3), with the longest at 10 hr 08 min. Tag data revealed dives to be generally shallow, predominantly between 10 and 50 meters in depth, with a maximum depth of 139 m. Sloughed skin was found on the suction cups of all recovered tags, and fecal samples were collected on three occasions; these samples were preserved and will be u- ed for genetic (e.g. sexing, relatedness and population studies), dietary and pollutant analyses. Acoustic data on the tags revealed numerous faint (non-focal) blue whale calls, characteristic of those described previously in this area by other researchers. In addition, in the one simultaneous tag deployment of a presumed mother (bm082a) and juvenile (bm082b), an apparent call exchange was observed between the juvenile whale and a more distant animal. Photo-identification images (12,605) were collected of seven marine mammal species during 30 encounters. Ten blue whale groups and 10 humpback whale groups were photo documented, and a total of five and 11 different individuals were photo-identified respectively. Acoustic recordings were made opportunistically when other marine mammal species were encountered. These included Peale's dolphins (Lagenorhynchus australis), Chilean dolphins (Cephalorhynchus eutropia), and bottlenose dolphins (Tursiops truncatus), for a total of 3.2 hours of recordings. All recordings contained sounds produced by the species of interest. Overall, this newly established relationship between MERI and WHOI has the potential to greatly increase knowledge of the biology, ecology and behavior of blue whales, as well as of several other marine mammal species, in the Canal Moraleda and Gulf of Corcovado. This work will also yield insights into how blue whales utilize the study area, and will provide information for policy makers regarding how best to protect the unique habitats that exist within the Canal Moraleda and Gulf of Corcovado.