The differences in behavioral responses to a net obstacle between day and night in captive manatees; does entanglement happen at night?

• Published in: Fisheries science Vol. 77; no. 5; pp. 795 - 798
• Main Authors: Kikuchi, Mumi, Suzuki, Miwa, Ueda, Keiichi, Miyahara, Hirokazu, Uchida, Senzo
• Format: Journal Article
• Language: English
• Published: Japan Springer Japan 01-09-2011; Springer Nature B.V
• Subjects: Aquariums; Aquatic mammals; Behavior; Biomedical and Life Sciences; Endangered & extinct species; Experiments; Females; Fish & Wildlife Biology & Management; Fisheries; Fishery sciences; Fishing equipment; Fishing gear; Food Science; Freshwater & Marine Ecology; Life Sciences; Marine mammals; Original Article; Studies; Obstacle; Behavior
• ISSN: 0919-9268; 1444-2906
• DOI: 10.1007/s12562-011-0388-x

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.