Dolphin population specialized in foraging with artisanal fishers requires zero-bycatch management to persist
Abstract
1. The small population paradigm assumes that populations with low numbers of individuals intrinsically have a high probability of extinction. The small population of Lahille's bottlenose dolphins Tursiops truncatus gephyreus that specializes in foraging with artisanal fishers in Laguna, southern Brazil, faces human pressures including bycatch in fishing gear. The viability of this population was modelled over 30 and 100 years under different levels of bycatch, including the current scenario of two bycatches every year, two scenarios with higher incidence of bycatches and three management scenarios. The sensitivity of predicted growth rates to fixed-proportion and observed-variation changes in life history parameters was explored. 2. The current scenario predicted a declining population (r = -0.014; λ = 0.986) with a high probability of extinction in the long term (PE = 0.71). A small increase in bycatches would result in a marked increase in the probability of extinction. Management scenarios seem promising, but only the zero-bycatch management scenario would make the difference between a declining and an increasing population. 3. As expected for slow-growing species, population growth rate was most sensitive to proportional changes in adult female and juvenile survival. However, considering observed variation in vital rates, population dynamics were most influenced by variation in reproductive rates. 4. To determine the highest priority for management action, another simulation was made of how additional threat scenarios of recognized human activities (i.e. bycatch influencing adult survival and increased underwater noise or pollution influencing calf survival) would affect population dynamics. Population growth rate was very sensitive to changes in adult bycatch (especially females), as expected, and only subtly sensitive to a reduction in calf survival. 5. The current level of bycatch is unsustainable. Bycatch needs to be eliminated to maximize the probability of long-term persistence of this dolphin population. However, this population's persistence could be threatened by natural variation in reproductive rates.
Citation
Bezamat , C , Hammond , P S , Castilho , P V , Simões-Lopes , P C & Daura-Jorge , F G 2021 , ' Dolphin population specialized in foraging with artisanal fishers requires zero-bycatch management to persist ' , Aquatic Conservation: Marine and Freshwater Ecosystems , vol. 31 , no. 11 , pp. 3133-3145 . https://doi.org/10.1002/aqc.3694
Publication
Aquatic Conservation: Marine and Freshwater Ecosystems
Status
Peer reviewed
DOI
10.1002/aqc.3694ISSN
1052-7613Type
Journal article
Description
This study was conducted as part of a PhD thesis in the Graduate Programme in Ecology at the Federal University of Santa Catarina, with funding provided by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq – 407190/2012-0) and Fundação de Amparo à Pesquisa e Inovação do Estado de Santa Catarina (FAPESC – TR2012000295). This study is also part of the SELA Long-Term Ecological Research Programme (PELD CNPq – 445301/2020-1). C.B. received a doctoral scholarship from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); P.C.S.L. received a research grant from CNPq (305573/2013-6); F.G.D.J. received a research grant from CNPq (308867/2019-0).Collections
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