Demographics and feeding ecology of whale sharks at Mafia Island, Tanzania

Handle URI:
http://hdl.handle.net/10754/550818
Title:
Demographics and feeding ecology of whale sharks at Mafia Island, Tanzania
Authors:
Cagua, Edgar F. ( 0000-0001-5867-3687 ) ; Cochran, Jesse ( 0000-0002-6027-5052 ) ; Rohner, Chris; Igulu, Mathias M; Rubens, Jason; Pierce, Simon J; Berumen, Michael L. ( 0000-0003-2463-2742 )
Abstract:
Background. The Western Indian Ocean is a globally important region for the whale shark Rhincodon typus, with well-studied coastal aggregation sites in southern Mozambique, Seychelles and Djibouti. Here we present an overview of a new study at Mafia Island, Tanzania. Methods. We monitored whale shark abundances on 103 boat trips from October 2012–March 2013. We also used passive acoustic telemetry (VEMCO® V16 tags) and photographic identification to monitor the residency times and local movements of 29 tagged individuals. Shark sizes were estimated using laser photogrammetry. Results. In total we observed 87 individual sharks with a mean of 5.1 ± 5.2 (± SD) per trip and a peak in December of 8.2 ± 6.3. Total length ranged from 4.1 to 9.7 m and almost all sharks were immature. After boat-based visual observations dropped to zero in March 2013 (with the same ongoing sampling effort), the acoustic array still detected 75% of tagged sharks. Tagged individuals were detected by the acoustic array for 73 ± 40 days on average. They showed a strong site fidelity to a 15 km2 area in the inner part of the bay and then progressively moved offshore at the end of the season, matching a decrease in plankton abundance. Sharks were mostly observed feeding on dense patches of the pelagic shrimp Lucifer hanseni, often in association with planktivorous fishes. Photo IDs from 2007-09 and 2012-13 indicate that a large proportion of the juvenile individuals return to Mafia Island each spring-summer. Conclusion. The size range and gender distribution of whale sharks at Mafia Island is similar to other coastal aggregations in the Indian Ocean, but the relatively high site fidelity and residency time stands in contrast.
KAUST Department:
Red Sea Research Center (RSRC)
Citation:
Cagua EF, Cochran J, Rohner C, Igulu MM, Rubens J, Pierce SJ, Berumen ML. (2013) Demographics and feeding ecology of whale sharks at Mafia Island, Tanzania. PeerJ PrePrints 1:e81v2 https://dx.doi.org/10.7287/peerj.preprints.81v2
Publisher:
PeerJ
Journal:
PeerJ The Third International Whale Shark Conference
Issue Date:
17-Oct-2013
DOI:
10.7287/peerj.preprints.81v2
Type:
Article
Additional Links:
https://dx.doi.org/10.7287/peerj.preprints.81v2
Appears in Collections:
Articles; Red Sea Research Center (RSRC)

Full metadata record

DC FieldValue Language
dc.contributor.authorCagua, Edgar F.en
dc.contributor.authorCochran, Jesseen
dc.contributor.authorRohner, Chrisen
dc.contributor.authorIgulu, Mathias Men
dc.contributor.authorRubens, Jasonen
dc.contributor.authorPierce, Simon Jen
dc.contributor.authorBerumen, Michael L.en
dc.date.accessioned2015-04-28T12:04:53Zen
dc.date.available2015-04-28T12:04:53Zen
dc.date.issued2013-10-17en
dc.identifier.citationCagua EF, Cochran J, Rohner C, Igulu MM, Rubens J, Pierce SJ, Berumen ML. (2013) Demographics and feeding ecology of whale sharks at Mafia Island, Tanzania. PeerJ PrePrints 1:e81v2 https://dx.doi.org/10.7287/peerj.preprints.81v2en
dc.identifier.doi10.7287/peerj.preprints.81v2en
dc.identifier.urihttp://hdl.handle.net/10754/550818en
dc.description.abstractBackground. The Western Indian Ocean is a globally important region for the whale shark Rhincodon typus, with well-studied coastal aggregation sites in southern Mozambique, Seychelles and Djibouti. Here we present an overview of a new study at Mafia Island, Tanzania. Methods. We monitored whale shark abundances on 103 boat trips from October 2012–March 2013. We also used passive acoustic telemetry (VEMCO® V16 tags) and photographic identification to monitor the residency times and local movements of 29 tagged individuals. Shark sizes were estimated using laser photogrammetry. Results. In total we observed 87 individual sharks with a mean of 5.1 ± 5.2 (± SD) per trip and a peak in December of 8.2 ± 6.3. Total length ranged from 4.1 to 9.7 m and almost all sharks were immature. After boat-based visual observations dropped to zero in March 2013 (with the same ongoing sampling effort), the acoustic array still detected 75% of tagged sharks. Tagged individuals were detected by the acoustic array for 73 ± 40 days on average. They showed a strong site fidelity to a 15 km2 area in the inner part of the bay and then progressively moved offshore at the end of the season, matching a decrease in plankton abundance. Sharks were mostly observed feeding on dense patches of the pelagic shrimp Lucifer hanseni, often in association with planktivorous fishes. Photo IDs from 2007-09 and 2012-13 indicate that a large proportion of the juvenile individuals return to Mafia Island each spring-summer. Conclusion. The size range and gender distribution of whale sharks at Mafia Island is similar to other coastal aggregations in the Indian Ocean, but the relatively high site fidelity and residency time stands in contrast.en
dc.publisherPeerJen
dc.relation.urlhttps://dx.doi.org/10.7287/peerj.preprints.81v2en
dc.rightsThis is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.en
dc.subjectpassive acoustic telemetryen
dc.subjectwhale shark aggregationen
dc.subjectLucifer hansonien
dc.subjectsite fidelityen
dc.subjectplanktivoryen
dc.titleDemographics and feeding ecology of whale sharks at Mafia Island, Tanzaniaen
dc.typeArticleen
dc.contributor.departmentRed Sea Research Center (RSRC)en
dc.identifier.journalPeerJ The Third International Whale Shark Conferenceen
dc.eprint.versionPre-printen
dc.contributor.institutionManta Ray and Whale Shark Research Centre, Marine Megafauna Foundation, Inhambane, Mozambiqueen
dc.contributor.institutionMarine Fisheries Research, Tanzanian Fisheries Research Institute, Dar es Salaam, Tanzaniaen
dc.contributor.institutionWorld Wide Fund for Nature, Dar es Salaam, Tanzaniaen
dc.contributor.institutionWild Me, Inhambane, Mozambiqueen
dc.contributor.institutionBiology Department, Woods Hole Oceanographic Institution, Woods Hole, United Statesen
kaust.authorCagua, Edgar F.en
kaust.authorCochran, Jesseen
kaust.authorBerumen, Michael L.en
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