In the financial year 1997/98 all Tasmanian fin fish farms experienced increased levels of seal interaction resulting in tangible losses of around $1.5 million. 164 seals were trapped and relocated in 1996/97 compared with 37 the year before and 10 when this form of management was first introduced. In response to the increase in interactions, the industry spent an estimated $ 1 million on upgrading predator nets over the last financial year. Licensed shooting, trapping and relocation of seals have been used by the industry, in conjunction with the Department of Environment and Land Management, in previous years, but these methods are not considered to be either acceptable (because of risk of spreading disease, animal ethics concerns and fishery management issues), or cost effective.
The Tasmanian Atlantic Salmon industry is set to expand substantially in the short to medium term, with production projected to double within 5 years. With this expansion, new areas, both near shore and off shore will be developed for marine farming. Seal predation will be at least, if not more significant in these areas. The development of some aquaculture projects in other states, notably Western Australia, has been postponed due to perceived potential problems with seals, and the inadequacies in current stock protection systems.
The Southern Bluefin Tuna farming industry in South Australia, while relatively new already suffers large losses due to predation by sharks and seals. Losses due to predation by sharks and seals have a substantial impact on the industry, with annual direct losses estimated at $1.2 million and growing rapidly. Existing predator deterrent methods have not proven to be effective for the farming or towing conditions experienced by the industry. This project will contribute directly to the tuna industry by providing reviews of predator systems and designs of new nets to restrict predators affects on farms.
This Project was funded by the Fisheries Research & Development Corporation(FRDC) for the “Development of a Stock Protection System for Flexible Oceanic Pens Containing Finfish“. The Project has been developed in conjunction with the Tasmanian Salmonid Growers Association(TSGA) & the Tuna Boat Owners Association(TBOA).
Both salmon and tuna farmers have a particular problem with seal predation. Seal predation leads to loss of valuable stock and possibly expensive repairs. In the past, before net strength was increased, seal damage to salmon nets had resulted in larger numbers of farmed salmon escaping. Anecdotal evidence suggests seals indirectly cause a decrease in the growth rate through a reduction in feeding, although it must be pointed out that fish do habituate to the presence of divers in the pens and thus possibly seals outside. Similarly, the farmed fish appear untroubled by the presence of seals hunting wild fish in the area (3 observations to date within this project term). Seals are one of the chief problems facing salmon growers in Tasmania., along with jellyfish, diseases(such as gill amoeba), fouling of lease sites, and high water temperatures. The latter are a problem in summer and seals mainly in winter.
According to reference, D Pemberton and P.D. Shaughnessy, Interaction between seals and Marine Fish-Farms in Tasmania, both the Australian Fur Seal and the Leopard Seal are found in the waters of the Tasmanian salmon industry, though the New Zealand Fur Seal is known to be migrating to Tasmanian waters. The Southern Elephant Seal is also present in Tasmanian waters. In the waters of the tuna industry of Port Lincoln, the predominant seals are the Australian Sealion and the New Zealand Fur Seal.
Shark interaction with salmon farmers has occurred when pens have been towed across Storm Bay and when the pens have been moored on site by typically Blue Whaler and “doggie” sharks respectively. The incidences of shark interaction when towing is typically a summer occurrence where Blue Whaler sharks are attracted to the morts in the pen. The Huon River is a known “doggie” shark nursery and doggie shark interaction can be substantial in some seasons, though it is always dependent upon the number of morts left in the pens. This is a typical issue which can be rectified by efficient management practises. The above is taken from interviews with salmon farmers. The interaction between sharks & tuna farmers has been documented in the Marine Animal Interaction Working Group Workshop, 25-26 May 1998, Primary Industry & Resources SA, Fisheries and Aquaculture. This reference states that the nature and extent of shark interactions is detailed insufficiently.
In addition to predation from the water, fish farmers also face predation from birds. The cormorant is known to predate on commercially raised salmon, attempting to reach the salmon by aerial attacks, and many(up to 600 in 1999), are shot as a result. Silver Gulls also pose a problem for “smaller” salmon. Predation of tuna by birds is a non issue as the tuna are a much “larger” fish; the concern is more that the birds are accessing the feed stock prior to the tuna feeding. The vast numbers of gulls which feed both at tip sites and on farms pose a risk of disease transmission for both industries Management practises to reduce gull interactions are widely used and can be very effective
Flexible Oceanic Pens are the foundation of fish farm cage systems in Australia due to their robustness in inshore waters, their relative inexpensive capital cost, and their ability to be easily transported whilst stocked. This project was initiated due to the ever increasing predation problem on farmed salmon and tuna in Australia on Flexible Oceanic Pens.
The project concluded that there is no simplistic solution to the predation problem; rather a concerted multi-faceted effort should be undertaken across both the salmon and tuna industries.
Keywords: Aquaculture, Anti-predation, Predation, Seals, Birds.