ASFB Home > Potential Changes in Prey Population Structure Following Removal of Predators by Fishing

A Decade of Biotic Change in Tasmanian Marine Protected Areas

Neville Scott Barrett, Graham Edgar, Colin Buxton, Alastair Morton, Malcolm Haddon and Caleb Gardiner

Tasmanian Aquaculture and Fisheries Institute, HOBART, AUSTRALIA

Theme: TH4

Tasmania's first 'no-take' Marine Protected Areas (MPAs) were established a decade ago for conservation purposes. At this time a monitoring program was initiated to document changes occuring in the MPAs and to compare these with changes at external (fished) reference locations. By surveying reef fishes, invertebrates and plants, on an annual basis, a comprehensive database has been established. This allows some understanding of natural variability at this temporal scale and the extent that fishing, introduced species and range-extensions of habitat-modifying species, can influence this. Changes within the MPAs over this period indicate that fishing has had a substantial influence on the demographic structure of many species, particularly those targeted by fishers. Changes within the Maria Island MPA (the largest) relative to reference sites have included increases in fish species richness, the abundance of rock lobsters and large fish, and the mean size of fishes, rock lobsters and abalone. These increases may be related in turn to a 40% decline in the abundance of common sea urchins, and be evidence of cascading ecosystem effects related to protection from fishing. Several of the species increasing in abundance and/or size are known urchin predators (particularly rock lobsters). In time, the reduction in urchin numbers could lead to substantial ecosystem shifts as urchins are abundant in this region and known to be habitat-modifying species. These results show that MPAs at the Maria Island scale (7km) can be effective conservation reserves and invaluable reference areas for determining and managing the effects of fishing in the absence of historical baseline data.