Humpback whale (Megaptera novaeangliae) is îne of the larger baleen whales, adults range in length 12–16 metres. Humpbacks has a distinctive body shape, with unusually long pectoral fins and a knobbly head. It is an acrobatic animal, often breaching and slapping the water with its tail flukes and pectoral fins.
Humpbacks feed only in summer in subpolar and temperate waters, including waters of the Russian Far East. Their diet consists mostly of krill and small fish. In Karaginsky Island area we observed humpbacks feeding on Pacific sand lance (Ammodytes hexapterus). In Commander Islands they most likely feed on Calanus sp. and krill. In winter humpbacks migrate to tropical or sub-tropical waters to breed and give birth. Males at the breeding grounds produce a complex whale song, which lasts for 10 to 20 minutes and is repeated for hours at a time. The purpose of the song is not yet clear, although it appears to have a role in mating. During the winter, humpbacks fast and live off their fat reserves.
We compared 1929 individual photographs of humpback whales identified in the waters of the Russian Far East in 2005-2017 with the catalogs from the breeding grounds: Asia (Ogasawara, Okinawa and the Filippines), Hawaii and Mexico. Among the whales found in the catalogs from breeding grounds, the whales from the Okinawa-Philippine breeding ground prevailed at the majority of explored sites, except the Eastern Chukotka and the Gulf of Anadyr. The overall match rate was higher in the mainland Kamchatkan sites (Karaginsky Gulf, Eastern Kamchatka and Koryak coast) and consisted mostly of whales from the Asian breeding ground. In the Commander Islands, the amount of overall matches was lower; about 60% of matched whales came to the Commander Islands from Asia, about 30% from Hawaii and about 10% from Mexico. In Senyavin Strait (Eastern Chukotka) and in the Gulf of Anadyr there were more whales breeding in Hawaii. In the Gulf of Anadyr and off the Commander Islands we found the whales from all breeding regions of the North Pacific, except Central America. The percentage of whales that matched between different regions within the Russian Far East averaged only 4.5%, with a maximum of 13.8% for eastern Kamchatka and 12.6% for Karaginsky Gulf. The highest number of matches was found between adjacent feeding grounds: the Commander Islands and mainland Kamchatka sites.
Genetic analysis of biopsy samples taken from humpback whales showed that three feeding grounds where enough samples have been collected – Commander Islands, Karaginsky Gulf and Eastern Chukotka – differed significantly by the frequency of mtDNA haplotypes. In contrast, nuclear DNA polymorphisms, determined at eight microsatellite loci, did not reveal any differentiation. Comparing our mtDNA results to those from a previous ocean-basin study reinforced the differences between the feeding sites. Humpback whales from the Commanders and Eastern Chukotka appeared most similar to those of the western Gulf of Alaska and the Aleutian feeding grounds, while Karaginsky differed from all other North Pacific feeding grounds (including the Commanders and Eastern Chukotka). Comparison to breeding grounds suggests mixed origins for the three feeding sites; there are likely connections between Karaginsky and the Philippines and to a lesser extent to Okinawa, Japan; the Commanders are linked to the Mexican breeding grounds; Eastern Chukotka was similar to Ogasawara and Mexican breeding grounds.
Entanglement in fishing gear is the largest anthropogenic threat for most humpback whale populations. We found that about 40% of humpback whales from the Commander Islands, 52% from Karaginsky Gulf and 46% from Chukotka had scars from entanglement.
In sum, both genetic and photoidentification results suggest that the feeding aggregation in Karaginsky Gulf is the most distinct and consists mainly from the whales breeding in Asia (Okinawa and the Philippines), while aggregations in the Commander Islands and Chukotka have mixed origins, with whales migrating from Asia, Hawaii and Mexico. These results are especially important because of the recent changes in humpback whale status both in the US and in Russia. In the US, the Asian population of humpback whales has been recently listed as Threatened. In Russia, humpback whale is planned to be excluded from the Russian Red Book as a recovered species that is no more threatened. Our results demonsrate the need for conservation of Karaginsky Gulf as an important feeding ground for the threatened Asian population and highlight the demand for the new conservational strategies for migratory cetacean species.