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Guttridge T.L.,University of Leeds | Guttridge T.L.,Macquarie University | van Dijk S.,University of Groningen | Stamhuis E.J.,University of Groningen | And 3 more authors.
Animal Cognition | Year: 2013

Social learning is taxonomically widespread and can provide distinct behavioural advantages, such as in finding food or avoiding predators more efficiently. Although extensively studied in bony fishes, no such empirical evidence exists for cartilaginous fishes. Our aim in this study was to experimentally investigate the social learning capabilities of juvenile lemon sharks, Negaprion brevirostris. We designed a novel food task, where sharks were required to enter a start zone and subsequently make physical contact with a target in order to receive a food reward. Naive sharks were then able to interact with and observe (a) pre-trained sharks, that is, 'demonstrators', or (b) sharks with no previous experience, that is, 'sham demonstrators'. On completion, observer sharks were then isolated and tested individually in a similar task. During the exposure phase observers paired with 'demonstrator' sharks performed a greater number of task-related behaviours and made significantly more transitions from the start zone to the target, than observers paired with 'sham demonstrators'. When tested in isolation, observers previously paired with 'demonstrator' sharks completed a greater number of trials and made contact with the target significantly more often than observers previously paired with 'sham demonstrators'. Such experience also tended to result in faster overall task performance. These results indicate that juvenile lemon sharks, like numerous other animals, are capable of using socially derived information to learn about novel features in their environment. The results likely have important implications for behavioural processes, ecotourism and fisheries. © 2012 Springer-Verlag.

White E.R.,University of California at Davis | Nagy J.D.,Arizona State University | Gruber S.H.,Bimini Biological Field Station
Biology Direct | Year: 2015

Background: Long-lived marine megavertebrates (e.g. sharks, turtles, mammals, and seabirds) are inherently vulnerable to anthropogenic mortality. Although some mathematical models have been applied successfully to manage these animals, more detailed treatments are often needed to assess potential drivers of population dynamics. In particular, factors such as age-structure, density-dependent feedbacks on reproduction, and demographic stochasticity are important for understanding population trends, but are often difficult to assess. Lemon sharks (Negaprion brevirostris) have a pelagic adult phase that makes them logistically difficult to study. However, juveniles use coastal nursery areas where their densities can be high. Results: We use a stage-structured, Markov-chain stochastic model to describe lemon shark population dynamics from a 17-year longitudinal dataset at a coastal nursery area at Bimini, Bahamas. We found that the interaction between delayed breeding, density-dependence, and demographic stochasticity accounts for 33 to 49% of the variance in population size. Conclusions: Demographic stochasticity contributed all random effects in this model, suggesting that the existence of unmodeled environmental factors may be driving the majority of interannual population fluctuations. In addition, we are able to use our model to estimate the natural mortality rate of older age classes of lemon sharks that are difficult to study. Further, we use our model to examine what effect the length of a time series plays on deciphering ecological patterns. We find that-even with a relatively long time series-our sampling still misses important rare events. Our approach can be used more broadly to infer population dynamics of other large vertebrates in which age structure and demographic stochasticity are important. Reviewers: This article was reviewed by Yang Kuang, Christine Jacob, and Ollivier Hyrien. © 2014 White et al.; licensee BioMed Central Ltd.

Guttridge T.L.,University of Leeds | Gruber S.H.,Bimini Biological Field Station | DiBattista J.D.,Hawaii Institute of Marine Biology | Feldheim K.A.,Pritzker Laboratory for Molecular Systematics and Evolution | And 3 more authors.
Marine Ecology Progress Series | Year: 2011

For marine predators there is a paucity of studies on social behaviour, and even fewer studies have quantified interactions between individuals. In the present study, we looked at the social structure and leadership of free-ranging juvenile lemon shark Negaprion brevirostris in a known aggregation site, Bimini, the Bahamas. Observations of these sharks were made from towers placed in a mangrove inlet, where clear, shallow, protected waters made it possible to record group compositions of externally colour-code tagged wild juvenile lemon sharks. Thirty-eight different individual sharks were observed to use the area over a 2 yr period. Results show repeated social interactions suggestive of active partner preference. In addition, we found that group structure was mostly explained by body length, and possibly by preference for relatives but not by sex. Finally, we observed that some sharks led more groups than others and that those lead individuals were usually larger than those following them. This study quantifies the social structure of a free-ranging shark population and provides novel insights into the social behaviour of juvenile sharks. © Inter-Research 2011.

Digirolamo A.L.,Florida Fish And Wildlife Conservation Commission | Gruber S.H.,Bimini Biological Field Station | Gruber S.H.,University of Miami | Pomory C.,University of West Florida | Bennett W.A.,University of West Florida
Journal of Fish Biology | Year: 2012

The relatively complex pattern of temperature selection exhibited by juvenile lemon sharks Negaprion brevirostris in the North Sound differed markedly from many previously described responses of fish preferenda. Thermal data demonstrated that juvenile N. brevirostris did not attempt to behaviourally maintain a constant eccritic temperature. Rather, juveniles selected progressively warmer temperatures throughout the day until reaching the highest temperatures available, and then moved to cooler temperatures during late evening and early morning hours. It is possible that by exploiting habitat thermal heterogeneity juvenile N. brevirostris prolong activities such as feeding or digestion well into the cooler parts of the evening. The complex pattern of temperature occupation by juvenile N. brevirostris within the thermally heterogeneous North Sound nursery is probably linked to key daily activities such as prey capture, predator avoidance and digestive efficiency. © 2012 The Authors. Journal of Fish Biology © 2012 The Fisheries Society of the British Isles.

Newman S.P.,University of Plymouth | Newman S.P.,Northumbria University | Handy R.D.,University of Plymouth | Gruber S.H.,Bimini Biological Field Station | Gruber S.H.,University of Miami
Environmental Biology of Fishes | Year: 2012

Ontogenetic variations in shark diet are often qualitatively inferred from dietary analysis and hindered by high levels of unidentified prey or small sample sizes. This study focused on nursery bound lemon sharks (Negaprion brevirostris, n = 396), enabling some control over the confounding variables of prey choice associated with ontogeny. Nursery bound lemon sharks exhibited weak ontogenetic variation in dietary composition with high levels of dietary overlap. Variation in prey preference of lemon sharks with ontogeny was complex, but revealed a continuous shift from predominantly opportunistic benthic foraging as neonates to more selective piscivory with increasing shark size while in the nursery. Lemon sharks demonstrated a discrete ontogenetic shift in the number of prey consumed and stomach content weight (Kruskal-Wallis tests p < 0.01), as well as prey size (ANOVA, p < 0. 001). All sizes of sharks exhibited positive size selection of prey (Mann-Whitney U tests, p < 0. 01). However, the lack of size preference by all but the largest lemon sharks for their major prey (yellowfin mojarra, Gerres cinereus), suggests neonate sharks, while capable of occasionally foraging on large prey, are relatively inept opportunistic foragers. This was evident in high diet breadth, low diversity of consumed prey and lower trophic level than larger sharks. This study represents the first quantitative analysis of ontogenetic variation in prey preference and size selection in sharks, indicating a flexible foraging tactic in lemon sharks and the importance of hunting ability and predator size in prey choice. © 2011 Springer Science+Business Media B.V.

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