The loss and compromise of habitat is a problem that affects all Australian commercial and recreational fisheries (Zann et al. 1996). A recent review (funded by FRDC) of fisheries habitat research in Australia (Cappo et al. 1998) found that more action is needed to rehabilitate degraded habitats, of which coastal wetlands are particularly important. Cappo et al. 1998 also found that understanding of impacts on fish stocks was hampered by lack of knowledge regarding natural variation in populations and habitats.
Priorities for further habitat research have been emphasised by Cappo et al. (1998) and are reflected in FRDC’s Ecosystems Protection Program. This project has particular implications for protecting and enhancing fisheries habitats in the following specific areas:
1. Defining and monitoring the utilisation of a major habitat type in the coastal zone and assessing the role of that habitat in fisheries production;
2. As a trial for a self-sustaining management strategy that will actively encourage fisheries habitat rehabilitation, regardless of the site/fishery involved; and
3. By providing a direct benefit to fisheries habitats and therefore the associated fish stocks in the local region.
There is currently specific concern in the Southern Shark Fishery regarding the status of school shark stocks, with catches falling steadily from 2026 tonnes in 1986 to 749 tonnes in 1997 (Walker 1998, Punt and Walker 1998). However, there is a differential between the status of school shark stocks and those of gummy shark, which are considered to be sound. Thus there is a clear need to introduce measures which assist in rebuilding school shark stocks without adversely affecting sustainable catches of gummy sharks. There is also an identified need to protect school shark pre-recruits, which appear to be increasingly hard to find.
School sharks give birth during November and December in protected bays and channels on low-energy coastlines in Victoria and Tasmania (Olsen 1954; Stevens and West 1997). Although newborn sharks are found outside these areas, school shark nursery areas are regarded as 'critical habitat' for this species. This nursery habitat type has suffered significant loss throughout southern Australia, initially as a result of farming practices and subsequently from coastal development. Hence, in addition to concerns about the effects of fishing on the breeding stock, there is concern that loss of school shark nursery habitat may be causing further stock reduction or inhibiting management attempts at rebuilding the stock. Thus, there is a critical need to protect, restore and/or enhance nursery habitats for juvenile school shark as part of a strategy to improve recruitment to the fishery and contribute to restoring stocks.
Many of the important nursery areas for school shark (and other fish species) have been altered through human activities. For example, the 'State of the Marine Environment Report for Australia' indicates that several of the most important school shark nursery areas have lost large areas of seagrass. In Victoria, Western Port Bay has lost 17,800 hectares (and 85% of the seagrass biomass) and, in Tasmania, the Pittwater Estuary has lost 1201 hectares and Norfolk Bay has lost 2148 hectares.
Action to arrest the trend in degradation of school shark 'critical habitat' and to rehabilitate lost habitat is essential if school shark is to be a resource that can be used sustainably. The shark fishing industry initiative to inundate Black Swamp with seawater is the first attempt at rehabilitation of a school shark nursery area. This initiative will also provide additional habitat and potential nursery area for other commercial (MacDonald 1997) and recreational (Hall and MacDonald 1986) species abundant in Corner Inlet (Gunthorpe, in prep). Some of these other species which have high commercial value or are sought after by recreational fishers include snapper, gummy shark, southern garfish, greenback flounder, flathead and King George whiting.
Corner Inlet is an excellent location for trialling restoration of coastal wetlands and estuarine fish habitats, given:
- it was formerly acknowledged as an important juvenile school shark nursery habitat;
- the drained coastal wetlands of Corner Inlet formerly provided nursery areas and adult habitat for many other fish species utilised by commercial and recreational fishers;
- extensive areas of such habitat have been lost in the inlet through the construction of sea walls, resulting in mangrove, seagrass and saltmarsh communities being converted to pasture;
- there is significant potential for restoration of additional areas of the inlet outside the specific area involved in the trial;
- the project has generated widespread local support and enthusiasm from a variety of stakeholders, including offshore and inshore fishermen, landholders, local council and the community; and,
- nationally there may be hundreds of drained coastal wetlands that could be restored and managed through a similar approach should the trial prove successful. This wider potential application is demonstrated by the breadth of support for this project from fisheries managers in other states.
Gunthorpe, L. (in prep). Corner Inlet fish habitats – 1998 (Compiled by Fish Habitat Assessment Group) (Fisheries Victoria: Melbourne).
Hall, D. N., and MacDonald, C. M. (1986). A survey of recreational fishing in Corner Inlet and Nooramunga, South Gippsland. Marine Fisheries Report No. 8. (Fisheries and Wildlife Service: Melbourne).
Olsen, A. M. (1954). The biology, migration, and growth rate of the school shark, Galeorhinus australis (Macleay) (Carcharhinidae) in south-eastern Australian waters. Australian Journal of Marine and Freshwater Research 5, 353-410.
MacDonald, C. M. (1997). Corner Inlet - Nooramunga fin fisheries 1994. Fisheries Assessment Report Series . Report No. 3. 50 pp. (Department of Natural Resources and Environment: Melbourne).
Punt, A. E., and Walker, T. I. (1998). Stock assessment and risk analysis for the school shark Galeorhinus galeus (Linnaeus) off southern Australia. Marine and Freshwater Research 49 (in press).
Stevens, J. D., and West, G. J. (1997). 'Investigation of school and gummy shark nursery areas in south eastern Australia.' 77 pp. (CSIRO Marine Research: Hobart.)
Walker, T. I. (1998). Can shark resources be harvested sustainably? A question revisited with a review of shark fisheries. Marine and Freshwater Research 49 (7).
Zann et al. (1996). The State of The Marine Environment, Report for Australia, GBRMPA.