ASFB Home > The effects of spatial and temporal factors on the abundance of seven key finfish species along south-western Australia.

Cestodes in Sharks and their Use as Biological Tags

Janette Psaroudis

University Of Melbourne, RESERVOIR, AUSTRALIA

THEME: ASFB

Sharks are highly vulnerable to overfishing due to slow growth rates and low fecundity. Insufficient information about mixing rates between regions contributes to uncertainties in stock assessments, hindering management efforts. Since the 1930s, parasites have provided invaluable information about the stock structure, migration and philopatry of teleost fish species, but parasites have never been used to provide information about chondrichthyans and the current taxonomic literature for chondricthyan parasites is very limited. This study assessed the value of cestode parasites as biological tags for sharks, using the gymmy shark, Mustelus antarcticus as an example. Stock structure was investigated by analysing the abundances of several cestode species from the spiral valve (lower intestine) of sharks, from five regions throughout southern Australia. Regions were sampled during different years and seasons, but as most cestodes have complex lifecycles, it is unlikely that these effects were signigicant. Assuming no time effects, four separate sub-stocks were apparent and hypotheses to explain the geographic variation of these parasites involved aspects of prey distribution, water temperature and depth. A study of captive gymmy sharks suggested that the cestodes of these sharks are 'long-lived' within the host. Parasite abundance was also found to increase with shark length, which provided further evidence for longevity. This study demonstrates the potential for parasites to provide valuable information about shark stocks and the application of this technique to other Chondrichthyan species should be fully explored.