Movements and population structure of humpback whales in the North Pacific

Despite the extensive use of photographic identification methods to investi gate humpback whales in the North Pacific, few quantitative analyses have b een conducted. We report on a comprehensive analysis of interchange in the North Pacific among three wintering regions (Mexico, Hawaii, and Japan) dea ch with two to three subareas, and feeding areas that extended from souther n California to the Aleutian Islands, Of the 6,413 identification photograp hs of humpback whales obtained by 16 independent research groups between 19 90 and 1993 and examined for this study, 3,650 photographs were determined to be of suitable quality, A total of 1,241 matches was found by two indepe ndent matching teams, identifying 2,712 unique whales in the sample (seen o ne to five times). Site fidelity was greatest at feeding areas where there was a high rate of resightings in the same area in different years and a lo w rate of interchange among different areas. Migrations between winter regi ons and feeding areas did not follow a simple pattern, although highest mat ch rates were found for whales that moved between Hawaii and southeastern A laska, and between mainland and Baja Mexico and California. Interchange amo ng subareas of the three primary wintering regions was extensive for Hawaii , variable (depending on subareas) for Mexico, and low for Japan and reflec ted the relative distances among subareas. Interchange among these primary wintering regions was rare. This study provides the first quantitative asse ssment of the migratory structure of humpback whales in the entire North Pa cific basin.