oa Comparison of sex and size range of whale sharks and their sighting behaviour in relation to fishing lift nets in Borneo and Papua, Indonesia

Background The composition of sex and size of a population is important for management and conservation of marine organisms, including high mobility and global species such as the whale shark, Rhincodon typus. The presence of fish in lift nets in some Indonesian waters attracts feeding whale sharks. The objective of our study was to compare the sex, size and behaviour of whale sharks associated with lift nets in Cenderawasih Bay, Papua and Talisayan, East Kalimantan. Approach Data sampling was conducted for 52 days during April'June 2013 in Teluk Cenderawasih National Park, Papua and 60 days during August–October 2015 in Talisayan, East Kalimantan. Daily monitoring was carried out at lift nets located within the study area. Individual identification was conducted with photographic identification, sex determination was done through visual observation of the presence of reproductive organs, and size measurement was done by comparing the shark length with the observer–s height. Analysis of the fish catch was obtained by interviewing fishermen, and observation from the lift net was conducted to support the data. Results A total of 134 observations and 81 observations were recorded in Cenderawasih Bay (57 lift nets) and in Talisayan (43 lift nets), respectively. A total of 37 different whale shark individuals were identified in Cenderawasih Bay, and 30 different individuals were identified in Talisayan. More than 50% of the whale sharks in Cenderawasih Bay, and 80% in Talisayan, had scars on their bodies. In Cenderawasih Bay, scars were spread across the body: 20% of the scars were found on the fins, 20% on the main body including the gills, and 15.6% near the mouth area. In Talisayan, 70.6 % of the scars were found on the fins, 2.9% in the main body including the gills, and 17.6% near the mouth area. The scars result primarily from friction with fishing nets. The whale shark aggregations in Cenderawasih Bay and Talisayan were dominated by juvenile males. From a total of 37 individuals, only one female was found in Cenderawasih Bay, and from a total of 30 individuals, only two females were found in Talisayan. The dominant size of whale sharks in Cenderawasih Bay was in the range from 3–3.9 m total length, with the largest animals in the range of 6–6.9 m. In Talisayan, the dominant size range was 4–4.9 m total length, with the largest animals in the range of 6–6.9 m. The high abundance of smaller fishes that are caught in Cenderawasih Bay and Talisayan by lift nets could attract whale sharks to the area. The largest number of whale sharks seen in Cenderawasih Bay was 14 individuals on May 14th, 2013. The fishery catch in this area fluctuates, with the highest catch being 365 kg on May 9th, 2013. Whale shark activity in Talisayan was lower than Cenderawasih Bay, even with a greater lift net catch. The largest number of whale sharks seen in Talisayan was 8 individuals on August 25th, 2015. The lift net catch in this area also fluctuates, with the highest catch being 5,325 kg on August 25th, 2015. Conclusion The appearance and activity of whale sharks in Cenderawasih Bay and Talisayan have similar characteristics. These aggregations are dominated by males with a size range of 3–6 m, which are still categorized as juveniles. They were often present at the surface, performing feeding behaviours that correlate with lift net activity.