Search

Humpback whales wintering in the northern Philippines and Okinawa, Japan, belong to the western North Pacific subpopulation, now recognised as a distinct population segment. The numbers for this subpopulation are low hence it is being proposed to be listed as endangered. Although previous research revealed movements between breeding grounds, the relationship between these areas remain little understood. Recent survey efforts in the Philippines resulted in a total of 234 photo-identified individuals from 1999-2016 while Okinawa had 1,445 from 1991-2014. Within the seasons a total of 100 matches were found between the two breeding grounds including 38 males and 24 females while the rest were unknown. Within these matches, eight individuals were recorded moving within seasons, including two individuals moving across seasons multiple times. The two whales were both males, where one was recorded in both breeding grounds in three different seasons (2005, 2008 and 2012). The shortest duration of recorded sightings between grounds was one whale seen in the Philippines in late March 2012 and in Okinawa 13 days later. More females with calves were sighted in the Philippines than in Okinawa and this may indicate the Philippines as a preferred nursing ground.

The species-specific host-recognition system of anemonefish was examined experimentally, with a particular focus on the function of imprinting using naive Amphiprion ocellaris juveniles. Anemonefish parents lay their eggs very close to their host anemone so the eggs are almost always touched by the host's body or tentacles. Here, we demonstrate the embryonic and immediate post-hatching learning of chemical cues via the parents' host in A. ocellaris through a host-exchange experiment with egg batches during hatching. The memory obtained from such imprinting operates at the time when juveniles first search for their hosts. Unexpectedly, innate recognition was found to exist not only in the symbiotic host species but also weakly in two non-partner species. Innate recognition alone is not sufficient. Imprinting via the parents' host complements innate recognition, leading to rigid species-specific host recognition. Imprinting by the parents' single host provides a sufficient cue for reaching the two host species. Furthermore, when combined with imprinting, innate recognition of non-partners serves to supplement the recognition of those species, leading to substitute partnerships that are only observed in some localities. Potential functions of imprinting in the host-recognition system are discussed. The “spare recognition hypothesis” and the necessity of clear distinctions between symbiotic and substitute species are also proposed here.

Entanglement in fishing gear occurs in endangered manatees and may result in serious injury or death. Such incidents may happen more frequently at night when the animal’s visual sense is limited. In this study, we examined the differences in behavioral response of captive manatees to a net obstacle during light (day) and dark (night) periods. We used a plastic net as the obstacle, and video-recorded the manatees’ behavior. The experiments showed that captive manatees avoided the obstacle during the day more frequently than at night, which suggests that the manatees can perceive the obstacle more readily during light periods. However, there was no difference in the frequency of bumping or actively touching the obstacle between light and dark periods. The results suggest that the manatees can recognize the net obstacle even at night by purposely touching it, but they avoid it less frequently, and that entanglement during light periods may occur during accidental bumping, rather than from a failure to recognize it altogether.

MIWA SUZUKI1, TERUO TOBAYAMA2, ETSUKO KATSUMATA2, SENZO UCHIDA3, KEIICHI UEDA3, MOTOI YOSHIOKA4, AND KATSUMI AIDA1. 1 Graduated School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo, Tokyo, 113-8657, Japan (miwa@marine.fs.a.u-tokyo.ac.jp), 2 International Marine Biological Research Institute (Kamogawa Sea World), Higashi-cho, Kamogawa, Chiba, 269-0041, Japan, Okinawa Expo Aquarium, Motobu-cho, Okinawa, 905-0206, Japan, a Faculty of Biosources, Mie University, Kamihama-cho, Tsu, Mie, 514-8507, Japan.

Des observations de requins captifs ont permis d'apporter de nouveaux elements dans l'etude du processus de retournement de l'intestin valvulaire. Comparaison anatomique de la position de l'estomacopylorique, la longueur et le type de valve intestinale dans differentes especes d'elasmobranches afin de donner des bases morphologiques aux mecanismes d'eversion gastrique