The relative importance of reproduction and survival for the conservation of two dolphin populations

Abstract

It has been proposed that in slow‐growing vertebrate populations survival generally has a greater influence on population growth than reproduction. Despite many studies cautioning against such generalizations for conservation, wildlife management for slow‐growing populations still often focuses on perturbing survival without careful evaluation as to whether those changes are likely or feasible. Here, we evaluate the relative importance of reproduction and survival for the conservation of two bottlenose dolphin (Tursiops cf aduncus) populations: a large, apparently stable population and a smaller one that is forecast to decline. We also assessed the feasibility and effectiveness of wildlife management objectives aimed at boosting either reproduction or survival. Consistent with other analytically based elasticity studies, survival had the greatest effect on population trajectories when altering vital rates by equal proportions. However, the findings of our alternative analytical approaches are in stark contrast to commonly used proportional sensitivity analyses and suggest that reproduction is considerably more important. We show that in the stable population reproductive output is higher, and adult survival is lower;the difference in viability between the two populations is due to the difference in reproduction;reproductive rates are variable, whereas survival rates are relatively constant over time;perturbations on the basis of observed, temporal variation indicate that population dynamics are much more influenced by reproduction than by adult survival;for the apparently declining population, raising reproductive rates would be an effective and feasible tool to reverse the forecast population decline; increasing survival would be ineffective. Our findings highlight the importance of reproduction – even in slow‐growing populations – and the need to assess the effect of natural variation in vital rates on population viability. We echo others in cautioning against generalizations based on life‐history traits and recommend that population modeling for conservation should also take into account the magnitude of vital rate changes that could be attained under alternative management scenarios.

Quantifying injury to common bottlenose dolphins from the Deepwater Horizon oil spill using an age-, sex- and class-structured population model

“…The 3.4% rate is also well above growth rates that have been observed or modeled for other Tursiops truncatus populations, i.e. 1.8 and 0.5% for Sarasota Bay, and Shark Bay, Australia, respectively (Manlik et al 2016, R. S. Wells unpubl. data), and well above the growth rates estimated from our Bayesian framework using age-at-death data for the 4 baseline BSE sites (range 1.1 to 2.8%).…”

“…increased reproduction or in creased survival), resulting in an accelerated growth rate that will then slow as the population increases. Elasticity analyses of matrix population models in odontocetes have suggested that non-calf survival could have the greatest influence on population growth (Brault & Caswell 1993), yet field studies have shown variability in reproductive rates over time and across stocks or pods, while non-calf survival rates remain relatively constant (Wells & Scott 1990, Brault & Caswell 1993, Manlik et al 2016. Other empirical data provide evidence for DD growth in at least 9 species of cetaceans: 8 of these showed evidence of DD birth rate, 5 showed evidence of DD age at first reproduction, and only 1 (Orcinus orca) showed evidence for DD juvenile or adult survival (Fowler 1984).…”

Looking for Evidence that Place of Residence Influenced Visitor Attitudes to Feeding Wild Dolphins?

“…The 116 completed questionnaires are analysed using 95% confidence intervals of proportions (reported as percentages) and Pearson' chi-square test for categorical data (Howell 2010) to investigate whether place of residence and/or DDC visitation influences visitor attitudes towards the feeding of wild dolphins and the tourism benefits of dolphin feeding. Numeric values appear as the Value ± 95% Confidence Interval, which is likely to contain the mean response of the broader visitor population.…”

“…The resident wild dolphin population of Koombana Bay is a major tourism drawcard for the regional city of Bunbury focused around the iconic Dolphin Discovery Centre tourist attraction (Bunbury Visitors Centre, 2016;Bunbury Geographe Tourist Strategy, 2015); Manlik et al, 2016 38′59.60″E), provides regulated beach based dolphin interactions; eco cruises; and dolphin swim tours, which all provide tourists with up-close dolphin encounters (DDC, 2015a). There is no feeding associated with the DDC eco cruises or the dolphin swim tours, but the DDC does provide minimalistic strictly controlled reward feeding as described above for the beach based dolphin interactions (DDC, 2015b).…”

Data from a survey to determine visitor attitudes and knowledge about the provisioning of wild dolphins at a marine tourism destination

“…The resident wild population of Indio-Pacific Bottlenose Dolphins ( Tursiops aduncus ) at Koombana Bay in the regional city of Bunbury, Western Australia and the local Dolphin Discovery Centre (DDC) are important drawcards for this marine tourism destination [2], [3], [4]. While visitors can experience the dolphins in regulated encounters coordinated by the DDC, anecdotal evidence suggests that people use private boats to seek out and interact with these wild dolphins on their own terms, which may have a negative impact on the resident dolphin population [1], [5].…”