Estimates of abundance and migratory destination for North Pacific humpback whales in both summer feeding areas and winter mating and calving areas
Paul R. Wade
The first comprehensive photo-identification study of humpback whales throughout the North Pacific occurred in 2004-2006 during the SPLASH project(Structure of Populations, Levels of Abundance and Status of Humpbacks).Photo-identification data were collected for three years (2004-06) in winterareas and for two years (2005-06) in summerareas. Total abundance for the entire North Pacific was estimated by Barlow et al. (2011) to be 21,808 (CV=0.04). Here we estimate abundance within all sampled winterand summerareas in the North Pacific, as well as estimate migration rates between these areas. Based on genetic analyses (Baker et al. 2013) and an examination of migratory destinations, winterareas were defined to be (1) Asia (including Ogasawara, Okinawa, and the Philippines), (2) Hawai’i, (3) Mexico, and (4) Central America. Based primarily on interchange (or lack thereof) between adjacent areas, and an examination of migratory destinations,summerareas were defined to be (1) Russia, (2) the Aleutian Islands and Bering Sea, (3) the Gulf of Alaska, (4) SoutheastAlaskaand northern British Columbia, (5) southern British Columbia and Washington, and (6) California and Oregon. A multi-statemark recapture model was fit to the photo-identification data using a six-month time-step, with the four winterareas and the six summerareas defined to be the sample strata. Results show thereis a strongmigratory connection between the Russiafeeding area (N=1,340, CV=0.30) and the Asia winterarea(N=1,084, CV=0.09). The feeding areas in Alaska, as well as northern British Columbia, support the majority of the North Pacific population, including the Aleutian Islands and Bering Sea (N=7,758, CV=0.20), the Gulf ofAlaska (2,129, CV=0.08), and SoutheastAlaskaand northern British Columbia (N=5,890, CV=0.08). Those feeding areas all have a strong migratory link to Hawaii(N=11,540, CV=0.04), with the link between SoutheastAlaska/northern British Columbia and Hawaii (0.98) particularly high. In return, nearly all Hawaiian whales migrate to Alaska and northern British Columbia. The migratory destination of whales that winter in Mexico (N=2,913, CV=0.07) is the most diverse, with whales going to all feeding areas. Nearly all Central American whales (N=755, CV=0.24) migrate to California and Oregonto feed (0.97), but the California/Oregonfeeding area (N=1,477, CV=0.13) represents a mix of whales fromMexicoandCentral America.