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Title: Functional ecology of the southern stingray, Dasyatis americana
Author: Tilley, Alexander
ISNI:       0000 0004 2717 5417
Awarding Body: Prifysgol Bangor University
Current Institution: Bangor University
Date of Award: 2011
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The global decline of large sharks has fuelled a rapidly expanding field of research into their ecological role within coastal and pelagic systems, yet the ecological importance of smaller mesopredatory elasmobranchs is largely unknown. The goal of this study was to evaluate the functional ecology of the southern stingray in a system of known predator abundance using wildlife surveys, acoustic tracking and stable isotope analysis. Elasmobranch community composition (number of species) and population size were estimated at Glovers Reef Atoll, Belize, and distribution was quantified according to habitat type and prey density. Dasyatis americana was the most abundant elasmobranch in lagoon and shallow forereef habitats with an overall atoll population of 5500 individuals; the lagoon population was dominated by female rays (3: 1), and stingray habitat use was influenced by individual size and diel stage. Benthic prey availability correlated with depth and habitat complexity in lagoon margins, yet large female and juvenile rays were abundant in the depauperate shallow sand flat areas during daylight, suggesting the use of this habitat for thermal and safety advantages respectively. Active tracking of rays illustrated heightened crepuscular activity by rays in all life stages, with intermittent activity through day and night. Activity space was larger during daylight and increased with ontogeny, with large (>70 cm) individuals remaining active at night suggesting use of a size refuge. Analysis of movement path structure showed stingray response to two distinct spatial scales, corresponding to topographical features of their landscape. Rays orientate and utilise foraging patches up to a scale of >- 100 m, but move randomly at greater spatial scales >3 km, suggesting rays may use the distribution of patch reefs as a network of refuges, connected by pathways of potential foraging areas as seen in some terrestrial animals. Stable isotope analysis revealed stingrays are reliant upon a diverse prey base and forage opportunistically on a number of prey groups, causing little overlap in isotopic niche space with sympatric shark species. Mixing models showed bivalves and invertebrate worms proportionately more important in diet compared to crustaceans and teleost fish. The combined findings of this study indicate that predation risk has a strong influence on stingray behaviour, causing a trade-off of energy for safety in juveniles in terms of movement periodicity and habitat preference. The dietary breadth of stingrays implies their key importance in stabilising benthic communities to trophic perturbations, however population and habitat use changes resulting from a release of predation pressure may significantly impact benthic community structure. This study represents an important step towards a greater understanding of the basic ecology of these organisms, which is crucial to making informed management decisions for species and ecosystem conservation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available