A common argument from the fishing industry is that we do not need marine parks because South Australian fisheries are already managed sustainably. This argument is invalid for one simple reason: Sustainable fishery management is about ensuring fishery productivity. This does not mean that the fishing practices don’t cause environmental harm or that the fishing practice is sustainable for other species in the ecosystem.
The simplest definition of a sustainably managed fishery is one that maintains fish stocks. In other words, a fishery in which the recruitment of new fish balances the removal of fish through catching or natural mortality. So, while fishery stocks may be managed so that we can maintain, or even enhance, the fishable biomass of the target species, this does not mean that other species in the ecosystem are similarly sustained or protected.
Many fisheries have significant detrimental impacts, including habitat destruction and / or the by-catch of non-target species.
Two examples that illustrate the potential for so called “sustainable” fisheries to have a significant impact are:
- the destruction of benthic habitats, e.g. associated with bottom trawl fisheries such as prawn fishing
- impacts on endangered species (including deaths of endangered Australian sea lions) from activities such as gillnet fishing.
Studies on Australian prawn fisheries have shown that by-catch can be as high as 10 tonnes of by-catch per tonne of prawns caught. In many cases this by-catch comprises rare, threatened or endangered species. In South Australia these include pipe fish and sea horses, sea squirts, sponges, giant cuttlefish and a number of commercially important species including under-size whiting and berried blue crabs.
Similarly gill-net fishing in South Australia has been identified as a key threat to the survival of Australian sea lions, listed as vulnerable under the EPBC Act. More than 80% of Australian sea lions – Australia’s only endemic seal - live in South Australian waters. Recent work by SARDI Aquatic Sciences has demonstrated that by-catch of Australian sea lions in the shark gillnet fishery represents a key threat to their survival.
In summary – the term "sustainable fishing" in South Australia only means that the productivity of fish stocks are managed. IT DOES NOT MEAN that fishing is free of impacts on the environment or that ecosystem integrity is maintained. In fact, fishing remains one of the most significant threats to marine biodiversity and the survival of many key species that contribute to the richness and diversity of coastal waters.
This is why we need sanctuary zones – to ensure that there are some "no-take" areas that remain free of the destructive impacts of fishing.
