Fisheries management is complex, involving a range of socio-political issues as well as biological concerns. Amongst the biological issues are problems with over-harvesting, harmful methods of harvesting and the continual degradation of important fish habitats.

Researchers at the Australian Institute of Marine Science have been monitoring reef and coastal fish stocks within the Great Barrier Reef Marine Park for more than 15 years, helping to answer some of the questions vital to the effective management of tropical fisheries. Initially the project focused on mapping habitats and biodiversity. Today the project has evolved into studying key processes - for example, the response of fish populations to over-fishing and the natural replenishment of populations.

The goal of the project is to provide a strong scientific base of information to support natural resource managers to make policy decisions. When AIMS researchers first began monitoring selected sites on the Great Barrier Reef (GBR) in 1981, there was little knowledge about the dynamics of fish populations on coral reefs anywhere. The last 15 years of research has enabled AIMS scientists to challenge earlier notions about coral reefs. Whereas the scientific community in the past had focused on the ‘balance of nature’ and tried to measure their carrying capacities, the long-term nature of AIMS research has shown that reefs are dynamic ecosystems, changing in response to currents, weather, influx of nutrients and numerous other variables. Scientists are now focusing on understanding what determines the number of fish larvae which replenish populations: is it the amount of available food? the number of predators? or the currents which bring larvae into an area? What determines if fish spawning will produce many juveniles in one year and few in another? What kinds of effects do human-induced changes have on fish populations versus natural disturbances brought on by cyclones or crown-of-thorns starfish outbreaks? Scientists must understand the dynamics of the many processes occurring in the marine environment in order to answer such questions.

On the Great Barrier Reef (GBR), numerous patches of reef habitats support populations of fish that are only connected by the exchange of drifting spawn. Researchers do not know the extent and consistency of these connections, but studying them is crucial to understanding the productivity and sustainability of the fish stocks on coral reefs. During the last 5 years, AIMS researchers have sampled the Great Barrier Reef Marine Park extensively in order to locate the preferred nurseries of selected larval fishes and to determine how they travel between spawning ‘sources’ and recruitment ‘sinks’. This has revealed new information about their abundance, ecology and behaviour, which scientists are currently assimilating into water circulation models. Researchers are using these computer simulations to help predict the connections among coral reefs.

AIMS researchers are also taking their knowledge of Australia’s east coast to the west, starting comparative studies on the reef systems of northwestern Australia. During the next few years, scientists from several projects will combine their different skills to understand how food chains work in the sea. Researchers will be using new instruments to help them with their investigations. For example, reflections from the tiny marine plants in the plankton will be monitored by a satellite with special sensors sent into space by NASA. The Institute’s researchers will be among the first users of this information to determine how primary production in the open ocean may affect future coral reef fish stocks.

Researchers at AIMS are also looking at secondary production in the open ocean, which is provided by the tiny zooplankton herbivores which graze on marine plants and which in turn are eaten by larger larval fishes. Vertical plankton hauls at night will estimate the total zooplankton biomass. By capturing larval fish in the late afternoon and then by examining their stomach contents, scientists can gain an idea of the sorts of food that larval fish prefer and the amounts eaten by fish during one day.

In addition to their work on both coasts of Australia, researchers within the project are actively involved in collaborative international research aimed at improving fisheries management throughout the world. Among these projects are studies of larval supply to the Eastern Pacific and Atlantic coral reef communities sponsored by the National Geographic Society and the Smithsonian Institute, a cooperative study with France investigating the sustainability of wild fry harvests in French Polynesia, and a study of spawning cycles of fish in Australia’s northern neighbours, Indonesia and Papua New Guinea.

The future of the world’s fish stocks relies on research organisations such as the Australian Institute of Marine Science investigating the myriad of variables involved in fish population dynamics and coming up with innovative solutions to assist with their sustainable exploitation and long-term conservation.