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Abstracts of Conference Presentations

 

Overview of White Shark (Carcharodon carcharias) Research at Seal Island, South Africa. 

Presented at VII European Elasmobranch Association Meetings, London, England, October 2004

R. Aidan Martin, N. Hammerschlag, and C. Fallows

Predatory behaviour, residency patterns, and social organisation of White Sharks were studied at Seal Island in False Bay, South Africa, from 1997-2003. Of 2088 predatory attacks on CapeFur Seals (Arctocephalus pusillus pusillus) recorded during the study period, frequency and success rate were analysed according to 12 biotic and abiotic factors. Attacks were primarily on lone in-coming YOY seals, were spatiotemporally clustered at the primary pinniped entry/exit point at the south terminus of the Island, and occurred almost exclusively during winter (May-September), mostly within two hours of sunrise. Predatory success rate averaged 47%, but increased to 55% under scotopic conditions and decreased to 40% under photopic conditions. Certain individual White Sharks exhibit idiosyncratic predatory behaviour resulting in success rates up to 80%, suggesting some degree of trial-and-error learning. Using total pigmentation pattern, analysed according to 68 discrete topographic regions, 262 individual White Sharks were catalogued and their residency patterns and intraspecific associations discerned from re-sightings data. Individuals were re-sighted as often as 28 times over the study period, suggesting a high degree of philopatry. Residence times for individuals ranged from 1-18 days, averaging 2-3 days. Known individuals appear to travel in loose groups of 2-6. Sixteen categories of overt agonistic behaviour have been defined and documented, appearing to occur only between individuals of separate groups. Social hierarchy under baited contexts appears to be largely size-dependent, with individuals as little as 5% longer dominant over smaller conspecifics, but sex and degree of melanism may also be factors.

Key words: predatory behaviour, residency pattern, philopatry, social organisation, dominance hierarchy, agonistic display

 

Behavioural Ecology of Whale Sharks (Rhincodon typus): Research Opportunities and Implications for Ecotourism Management

Presented at the International Whale Shark Conference, Perth, Australia, May 2005

R. Aidan Martin, Fish Museum, Zoology Department, University of British Columbia, Vancouver, Canada

Behavioural ecology of whale sharks is very incompletely known. Recent rapid development of whale shark-based ecotourism at several widespread localities risks deleterious impacts on the behaviour, habitat, and ecology of the target species. Available information on behavioural ecology of whale sharks is synthesised from the published literature, anecdotes from reliable observers, and personal observations, and reviewed within the framework of theoretical behavioural ecology. This review reveals opportunities to fill in critical knowledge gaps and minimise negative ecotourism impacts. Topics covered include: distribution, habitat, swimming, migration, sensory biology, predators, diet and foraging, social behaviour, reproductive biology, life history, faunal associations, interactions with humans, and ecotourism threats. If carefully managed, whale shark ecotourism is probably sustainable, fostering continued research on and protection of the species as well as conservation of the local habitats where it aggregates predictably.

 

Phylogeny of Extant Elasmobranchs: Conflicting Methodologies and Interpretations.

Presented at VII Indo-Pacific Fish Conference, Taipei, Taiwan, May 2005

R. Aidan Martin, Fish Museum, Zoology Department University of British Columbia, Vancouver, Canada

Extant elasmobranchs feature conservative morphology, low genetic diversity, low rate of genetic change, and a long but vexingly incomplete fossil record. Cladistic, phenetic, and evolutionary systematic interpretations of elasmobranch morphology have spawned numerous conflicting phylogenetic hypotheses. Molecular genetic approaches have provided novel insights into elasmobranch systematics and are very much in vogue, but are frustrated by homoplasies and difficulties in resolving clades featuring short internodes and long terminal branch lengths. Palaeontological approaches to elasmobranch phylogeny are based largely on the morphology of isolated fossilized teeth, the limitations of which further complicate reconstructing their evolutionary history. Scientific biases, including phyletic gradualism, dichotomy seeking, and the principle of parsimony, introduce further problems. Recently, the widely used elasmobranch phylogenetic scheme proposed by Compagno has come under revision by new approaches and interpretations. The following examples will be discussed: 1) recent removal of batoids as derived squalomorph sharks, based on strong molecular evidence, has resulted in a fragile cladistic topology; 2) recent mtDNA revision of Lamniformes placed Carcharias in a separate family from Odontaspis but failed to support a monophyletic Alopiidae; and 3) within the family Carcharhinidae, recent molecular evidence generates hundreds of equally parsimonious trees and suggests that the family is paraphyletic unless Sphyrnidae is included. Strengths and weaknesses of these differing phylogenetic approaches to reconstructing phylogeny of extant elasmobranchs are reviewed and their implications for further work are reviewed.

Session: Taxonomy, Phylogeny, and Biogeography of Indo-Pacific Chondrichthyans (Peter Last, organiser)

 
 

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Text and illustrations R. Aidan Martin
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