Reef manta ray life history and demography: is it really all about survival?
- Published
- Accepted
- Subject Areas
- Conservation Biology, Ecology, Marine Biology
- Keywords
- Conservation, Perturbation analysis, Life-history speed, Population projection model, Population dynamics, Marine protected areas, Wildlife trade
- Copyright
- © 2016 Smallegange et al.
- Licence
- This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ Preprints) and either DOI or URL of the article must be cited.
- Cite this article
- 2016. Reef manta ray life history and demography: is it really all about survival? PeerJ Preprints 4:e1886v1 https://doi.org/10.7287/peerj.preprints.1886v1
Abstract
Background. The trade in gill plates of devil and manta rays has increased greatly over the last two decades. The resulting increased mortality, in addition to mortality caused by by-catch, means that many ray populations are declining in size. The aim of this study was to ascertain the main demographic drivers of population change in reef manta rays (Manta alfredi) to increase our understanding of their demography and hence provide insight into potential conservation measures.
Methods. We developed a population projection model for reef manta rays and used published life history data to parameterise the model and also used these data as points of reference to compare our model output to. Because little is known about yearling and juvenile survival of reef manta rays, we conducted our analyses across a range of plausible survival rate values of yearlings, juveniles, and also adults.
Results. The model accurately captured observed patterns of variation in population growth rate, lifetime reproductive success and cohort generation time for different reef manta ray populations around the world. Varying the survival rates of the different life stages revealed that increasing adult annual survival rate always positively and additively affected population growth rate, lifetime reproductive success and cohort generation time. Variation in yearling and juvenile annual survival rate, however, had different and varying effects on the latter three population descriptors, highlighting the importance of obtaining accurate estimates of these survival rates from natural populations. Our elasticity analysis revealed that for both declining and stable populations, the population growth rate is most sensitive to changes in either juvenile or adult survival rate, depending on yearling and adult annual survival rate values.
Discussion. Many reef manta ray populations are declining, resulting in local extinction unless effective conservation measures are taken. Based on our detailed demographic analysis, we suggest that reef manta ray conservation would particularly benefit from focusing on increasing juvenile and adult survival.
Author Comment
This is a submission to PeerJ for review.