Fishy forensics tap food webs of the sea

21/01/04: With the help of recreational fishers, CSIRO's research will provide important information on the feeding and biology of some prized sportfish species in northern Australia, such as longtail tuna.

Scientists at CSIRO are delving deep into the stomachs of predatory fishes to discover ‘who eats who’ in the Gulf of Carpentaria.

They are collecting fish of all ages and sizes, from the Gulf to south-eastern Queensland, as part of a 12-month study to understand how the fish feed, age and breed.

A better understanding of marine food webs in the region will support ecosystem-based management of northern fisheries, such as the $140 million Northern Prawn Fishery.

The main focus species are longtail tuna, mackerel tuna, frigate mackerel, leaping bonito, cobia and golden trevally.

‘Very little is known about these species, despite their importance to commercial fisheries in some parts of the world, and to recreational fishers in Australia,’ CSIRO fish biologist Dr Shane Griffiths says.

The fish are being collected with the cooperation of fishers, and sent to the CSIRO Marine Laboratories at Brisbane where their stomach contents, otoliths (earbones) and gonads are analysed.

‘We plan to have collected and analysed about 100 fish from each species by the end of this pilot project,’ Griffiths says.

‘We hope to determine what they eat from the stomach contents, and their spawning times, stage of maturity, and egg or sperm production from the gonads.

‘The number of annual growth bands in their tiny otoliths will give us clues to their ages and growth rates.’

Griffiths says specimens are also being collected from south-eastern Queensland to cover the whole size range of each species, many of which are thought to spawn in northern waters and move further south as they grow.

He says the study will yield a basic understanding of the feeding relationships between pelagic fishes and other components of the ecosystem, such as fish and invertebrate species that live on or near the seabed.

It will also help identify future research needs, so that scientists can address questions such as whether pelagic fishes are major predators of economically significant prawns and squid in the valuable Northern Prawn Fishery.

The information will also feed into a northern Australian ecosystem model being developed by Griffiths’ colleagues.

CSIRO scientists would appreciate the donation of any unwanted fish of the species of interest to this research from fishers in the Brisbane area.

Source: http://www.marine.csiro.au