Abstract
Many large marine species are vulnerable to anthropogenic pressures, and substantial declines have been documented across a range of taxa. Many of these species are also longlived, have low individual resighting rates and high levels of individual heterogeneity in capture probability, which complicates assessments of their conservation status with capture−mark− recapture (CMR) models. Few studies have been able to apply CMR models to whale sharks Rhincodon typus, the world’s largest fish. One of their aggregation sites off Mafia Island in Tanzania is characterised by unusually high residency of this Endangered species, making it an ideal target for CMR methods. Three different CMR models were fitted to an 8 yr photo-identification data set to estimate abundance, population trend and demographic parameters. As anticipated, resighting rates were unusually high compared to other aggregations. Different CMR models produced broadly similar parameter estimates, showing a stable population trend with high survivorship and limited recruitment. Tagging and biopsy sampling for concurrent research did not negatively affect those sharks’ apparent survival or capture probabilities. Scenario-based power analyses showed that only pronounced abundance trends (±30%) would be detectable over our study period, at a 90% level of probability, even with the relatively high precision in yearly abundance estimates achieved here. Other, more transient whale shark aggregations, with reduced precision in abundance estimates, may only be able to confidently detect a similar trend with CMR models after 15−20 yr of observations.
Original language | English (US) |
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Pages (from-to) | 231-248 |
Number of pages | 18 |
Journal | Endangered Species Research |
Volume | 47 |
DOIs | |
State | Published - 2022 |
Bibliographical note
Funding Information:This project was funded by Aqua-Firma, the Shark Foundation, WWF Tanzania, WWF Sweden/ SIDA, Waterlust, 2 private trusts, and Patreon supporters. We thank Liberatus Mokoki and his team for their assistance in the field, and Jason Rubens, Mathias Igulu, Haji Machano, Paul Kugopya, Sware Semesi, the WWF Tanzania team as well as Amin Abdallah from the Mafia Island Marine Park for facilitating the project. Thanks to Carlos Omari and the team at Whale Shark Lodge and to Jean and Anne de Villiers for hosting us. Thanks to Fernando Cagua for his help in the field and his feedback on the manuscript. We thank Kenny Wolfe, Jens Paulsen, Rilke Ballero, Alexandra Watts, Stella Diamant, Sophia Lind, Lydie Couturier and David Robinson for their help in the field and Alina Riensema and Michael Pfundt for help with photo-ID processing. We thank all citizen scientists who contributed photo-ID data, particularly the team from Kitu Kiblu. Thanks also to the MMF team and board for administrative support
Funding Information:
Acknowledgements. This project was funded by Aqua-Firma, the Shark Foundation, WWF Tanzania, WWF Sweden/SIDA, Waterlust, 2 private trusts, and Patreon supporters. We thank Liberatus Mokoki and his team for their assistance in the field, and Jason Rubens, Mathias Igulu, Haji Machano, Paul Kugopya, Sware Semesi, the WWF Tanzania team as well as Amin Abdallah from the Mafia Island Marine Park for facilitating the project. Thanks to Carlos Omari and the team at Whale Shark Lodge and to Jean and Anne de Villiers for hosting us. Thanks to Fernando Cagua for his help in the field and his feedback on the manuscript. We thank Kenny Wolfe, Jens Paulsen, Rilke Ballero, Alexan-dra Watts, Stella Diamant, Sophia Lind, Lydie Couturier and David Robinson for their help in the field and Alina Riensema and Michael Pfundt for help with photo-ID processing. We thank all citizen scientists who contributed photo-ID data, particularly the team from Kitu Kiblu. Thanks also to the MMF team and board for administrative support.
Publisher Copyright:
© The authors 2022. Open Access under Creative Commons by Attribution Licence. Use, distribution and reproduction are un - restricted. Authors and original publication must be credited
Keywords
- Conservation
- Elasmobranch
- Lambda
- Megafauna
- Population monitoring
- Power analysis
ASJC Scopus subject areas
- Ecology
- Nature and Landscape Conservation