Humpback whales are a species of large whale that reach 13 meters in length. During summer, they feed in cold high latitude waters such as those off of Russia and Alaska, then in winter migrate to lower latitudes including the waters off of Okinawa or Hawaii to breed and raise their young. Every year, humpback whales migrate to Okinawa during winter season and there are instances where dead humpback whales are found stranded on a beach, or they are accidently caught (bycatch) in one of the fixed nets near the coast of Okinawa.
Based on previous surveys, Okinawa Churashima Foundation has conducted a study that searched for further details of strandings and bycatches of humpback whales. As a result, there were a total of 7 strandings and 5 cases of bycatch were confirmed in past 22 years. In recent years, the numbers of strandings and bycatches have increased. This is thought to be due to increasing numbers of humpback whales around the world. All the stranded humpback whales were between 3.6 meters and 10.3 meters in length, under 6 years old, and therefore sexually immature. No sexually mature individual was found. This result indicate that sexually immature humpback whales being more commonly stranded compared with the mature individuals. Regarding humpback whale bycatch, all 5 individuals were able to free themselves from the fixed net, and 3 of these individuals were also identified the following year when they migrated back to Okinawan waters. Individual identification was possible by studying the unique ventral fluke patterns of the humpback whales.
There are still many unknowns regarding humpback whale ecology, however through the continuation of this survey as well as collecting basic data, we hope it will aid in the conservation of this species and also support the whale watching industry in Okinawa.

Authors

Haruna Okabe, Nozomi Kobayashi, Naoto Higashi, Kouji Tokutake, Hirokazu Miyahara, Senzo Uchida (Bold letters: Staff members of Okinawa Churashima Foundation)

Title of Paper

Strandings and bycatches of humpback whales (Megaptera novaeangliae) between 1996 and 2018 around Okinawa Island, Japan

Title of Journal

Fauna Ryukyuana

Article link

http://w3.u-ryukyu.ac.jp/naruse/lab/Contents_J_files/49-2_Okabe_etal.pdf