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Recreational fishing is high on the list of the most popular leisure activities enjoyed by Australians.
 And, it stands to reason, with the steady growth of the nation's population, that there is an accompanying increase in the pressure on the country's existing fish stocks.
Other pressures, like the detrimental effects of algal blooms, have further added to this pressure.
The successful management of the nation's fish resources relies to a large extent on the availability of accurate information about the biology and behaviour of the most sought-after species.
Researchers from the School of Biological and Environmental Sciences at Murdoch University have been pioneer providers of much of the required information, particularly for those commercial and recreational species which spend a significant part of their lifetime in our estuaries and coastal marine waters.
For more than two decades, researchers from the University, led by Professor Ian Potter, have spent thousands of hours engaged in researching and producing a prolific number of papers in international journals pertaining to many of the 51 estuaries located along the 2400 kilometres of coastline in Australia's South-West corner.
These studies have produced invaluable data on the distribution, growth, age composition and breeding cycles of many of the more abundant species that spend all or part of their lives in the estuaries of Australia's temperate regions.
"There are more and more people recreationally fishing and therefore fish stocks are coming under ever-increasing pressure," he said. "So what fisheries managers need is good, solid, relevant biological data on which they can base their management policies," said Professor Potter.
"It is of particular importance to make sure that the fish are not being fished until they have had a chance to breed for the first time, and that their habitats are being adequately protected.
"Data on the age and growth of the fish, and their length and age at maturity, are thus the sort of parameters that are required by fisheries managers to develop management policies to help protect the fish stocks in marine waters and estuaries.
"The Fisheries Department then uses commercial and recreational catch statistics to produce models to see what is happening to the stock, to see whether the numbers of these species are declining, remaining stable or increasing."
It is no accident that one of the biggest supporters of Professor Potter's work is the Western Australian Fisheries Department. It also comes as no surprise that a number of the postgraduate researchers who have worked with Professor Potter, including Dr Rod Lenanton, Dr Chris Chubb and Dr Dan Gaughan, are research scientists at the Department.
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Professor Potter said the research projects have benefited greatly from considerable support over the years from the Fisheries Research Development Corporation (FRDC), as well as the WA Fisheries Department. In addition many people involved in commercial and recreational fishing have been of enormous benefit to the research, supplying a large quantity of fish carcasses for analysis.
Murdoch researchers have gathered data on a variety of important species including King George whiting, black bream, dhufish, flathead, cobbler, sea mullet and Australian herring. Most of the data have been gathered from field studies in seven representative estuaries  all popular recreational fishing spots: the Swan/Canning Estuary, Moore River Estuary, Leschenault Inlet, Blackwood River Estuary, Peel-Harvey Estuary, Wilson Inlet, and the Nornalup-Walpole Estuary. Although most of these estuaries are open to the sea all year round, some are intermittently or seasonally closed.
Professor Potter emphasised the crucial role that has been played by numerous and enthusiastic honours and PhD students in facilitating these studies.
Estuaries are considered to be of great importance to fish because they are not only the home for a variety of species, but also provide the nursery areas for some of our most popular marine species.
Many of our most sought-after commercial fish species spend the juvenile stage of their lives in estuaries. Some of the species also use nearby protected, nearshore marine waters as nursery areas.
It is believed the high productivity of estuaries enables juvenile fish to grow rapidly and thereby become less susceptible to predation. As these fish increase in size, they move offshore into deeper waters where some attain lengths of more than 500mm.
It has also revealed additional data about the estuarine environments favoured by the fish including information on salinity, vegetation, food-chains and the estuarine subregions of most significance at different times during the species' life cycles.
"Knowledge about such matters as when the marine species are inhabiting the estuaries, where they spawn and the duration of their life cycles is all of prime importance to successful management," said Professor Potter.
The significance of this information was reflected in a recent review of fish in South-Western Australian estuaries by Professor Potter and Post-Doctoral Research Fellow Glenn Hyndes in which they reported that in one particular estuary: "analysis of commercial catch statistics, allied with field sampling, indicates that the abundance of species has been influenced by fishing pressure in some estuaries and can be enhanced or deleteriously affected by eutrophication, depending on the type of algae that is produced as a result of nutrient enrichment."
Current work is exploring the extent to which the changes in salinity and reduction in blue-green algal blooms that have occurred in the Harvey Estuary have influenced the abundance of crabs, prawns and fish in that ecosystem.
It is this sort of information that, through resulting fisheries management, will ensure the hundreds of thousands of people who cast a fishing line into the nation's waters each year will be able to continue to do so in the years ahead.
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