title: Laser photogrammetry improves size and demographic estimates for whale sharks.
abstract: Whale sharks Rhincodon typus are globally threatened, but a lack of biological and demographic information hampers an accurate assessment of their vulnerability to further decline or capacity to recover. We used laser photogrammetry at two aggregation sites to obtain more accurate size estimates of free-swimming whale sharks compared to visual estimates, allowing improved estimates of biological parameters. Individual whale sharks ranged from 432-917 cm total length (TL) (mean ± SD = 673 ± 118.8 cm, N = 122) in southern Mozambique and from 420-990 cm TL (mean ± SD = 641 ± 133 cm, N = 46) in Tanzania. By combining measurements of stranded individuals with photogrammetry measurements of free-swimming sharks, we calculated length at 50% maturity for males in Mozambique at 916 cm TL. Repeat measurements of individual whale sharks measured over periods from 347-1,068 days yielded implausible growth rates, suggesting that the growth increment over this period was not large enough to be detected using laser photogrammetry, and that the method is best applied to estimating growth rates over longer (decadal) time periods. The sex ratio of both populations was biased towards males (74% in Mozambique, 89% in Tanzania), the majority of which were immature (98% in Mozambique, 94% in Tanzania). The population structure for these two aggregations was similar to most other documented whale shark aggregations around the world. Information on small (<400 cm) whale sharks, mature individuals, and females in this region is lacking, but necessary to inform conservation initiatives for this globally threatened species.
authors: Marine Megafauna Foundation , Praia do Tofo Inhambane , Mozambique ; CSIRO Oceans and Atmosphere Flagship , Brisbane Queensland , Australia.
authors: Christoph A
authors: CA
authors: Rohner
authors: CSIRO Oceans and Atmosphere Flagship , Brisbane Queensland , Australia ; Centre for Applications in Natural Resource Mathematics (CARM), School of Mathematics and Physics, The University of Queensland , St Lucia Queensland , Australia.
authors: Anthony J
authors: AJ
authors: Richardson
authors: Marine Megafauna Foundation , Praia do Tofo Inhambane , Mozambique.
authors: Clare E M
authors: CE
authors: Prebble
authors: Marine Megafauna Foundation , Praia do Tofo Inhambane , Mozambique ; Wild Me , Praia do Tofo Inhambane , Mozambique.
authors: Andrea D
authors: AD
authors: Marshall
authors: School of Biomedical Sciences, The University of Queensland , St Lucia Queensland , Australia.
authors: Michael B
authors: MB
authors: Bennett
authors: Biophysical Oceanography Group, School of Geography, Planning and Environmental Management, The University of Queensland , St Lucia Queensland , Australia.
authors: Scarla J
authors: SJ
authors: Weeks
authors: KwaZulu-Natal Sharks Board , Umhlanga , South Africa ; Biomedical Resource Unit, University of KwaZulu-Natal , Durban , South Africa.
authors: Geremy
authors: G
authors: Cliff
authors: KwaZulu-Natal Sharks Board , Umhlanga , South Africa ; Biomedical Resource Unit, University of KwaZulu-Natal , Durban , South Africa.
authors: Sabine P
authors: SP
authors: Wintner
authors: Marine Megafauna Foundation , Praia do Tofo Inhambane , Mozambique ; Wild Me , Praia do Tofo Inhambane , Mozambique.
authors: Simon J
authors: SJ
authors: Pierce
keywords: Africa; Age & growth; Conservation biology; Elasmobranch