Scallops (Pectinidae) are characterised by fluctuating recruitment and wide and patchy distribution, making it notoriously difficult to manage these fisheries. A few species of scallops are fished commercially in Australian waters but the example below relates to the fishery based on Pecten fumatus in the Bass Strait area.

 

In Bass Strait, the status of scallop stocks is still classed as “uncertain” following a long history of over-harvesting and stock depletion (Caton et al. 1998). During the 1970s, the discovery of new beds in the central Bass Strait area led to the rapid expansion of the scallop industry. The total catch peaked in 1982-83 at close to 12,000 tonnes, with the number of participating vessels tripling in two years to 231 (Young and Martin 1989; Zacharin 1990). However, the catching capacity of the scallop fleets had developed to the point where once a bed was located, fishing effectively removed it (Caton et al. 1998), making the industry unsustainable. The main beds were depleted by 1985, the last major bed – Banks Strait – was fished out during 1986, and the fishery had effectively collapsed by 1987, when Tasmanian vessels landed less than 500 tonnes (a drop of 95% in 6 years) and Victorian vessels landed 220 tonnes (a drop of 90% over the same period) (McLoughlin 1994). Closures were introduced, as surveys found severe stock depletion and a lack of recruitment, with little sign of scallop beds in some areas (McLoughlin 1994), and the fishery was divided into three management zones, a Tasmanian and Victorian zone (extending 20 nautical miles off each State’s coast), and a Commonwealth-managed Central Zone. There appeared to be some improvement in 1993-94, but this may have been largely due to an extraordinary settlement event (Zacharin 1994), and there is uncertainty as to the true extent of recovery (Caton et al. 1998). For instance, in the Central Zone (Commonwealth) fishery, the catch rate increased from about 3 bags per hour dredging in 1994-95 to about 5 bags per hour in 1997, but meat yields decreased from 1047 tonnes in 1994 to 690 tonnes in 1997. Total wholesale value of the 1997 catch was A$10 million, compared with A$20 million in 1995 and 1994.

 

During the 20 year history of the Bass Strait fishery few, if any, commercially fished beds have supported exploitation for more than two consecutive seasons. Single recruitment events result in discrete scallop beds of single year classes quickly fished out before they attained full spawning potential (McLoughlin 1994; Caton et al. 1998). Exploited beds do not, in general, appear to regenerate or provide additional year classes of scallops in the time frame of the current fishery (McLoughlin 1994). The over-harvesting of stocks is compounded by the damage caused by the scallop dredges, with evidence from dredge trials showing that up to 50% of scallops in the dredge’s path may be damaged (Zacharin 1994). Damaged scallop beds attract starfish predators and Vibrio infection and tend to die out if not harvested (Zacharin 1994). Damage to the substrate and benthic communities by the dredges is considerable (e.g., Harris and Ward 1999) with a study in the UK showing that the majority of the damage to the larger invertebrates is during the dredging operation itself and remains unobserved on the seabed rather than in the bycatch (Jenkins et al. 2001).

 

The Bass Strait Scallop Consultative Committee, designed to coordinate management approaches among the three jurisdictions, developed a five-year strategic research plan in 1998 that identified the development of an “environmentally friendly” scallop dredge as being one of the priority research areas. A new five year strategic research plan was developed this year (2002).

 

In NSW, commercial harvesting of Pecten fumatus peaked in 1970/71 but Gorman and Johnson (1972) concluded that a single recruitment event was responsible for the fishery and without further recruitment the commercial prospects were not good. Their study led to the perception of the “boom and bust” nature of the scallop fishery in NSW (Williams et al. 1993). Scallop fisheries elsewhere in Australia and the world also follow this pattern (Fuentes et al. 1992). The scallop fishing industry in Jervis Bay has been closed down since late 1991 after over-harvesting reduced stock levels to the point where fishing became uneconomic (Fuentes 1994).

 

In Queensland, Dredge (1988) suggested that scallops (Amusium balloti) have been subject to recruitment overfishing, the effective effort directed at the scallop stock having increased by a factor of 14 between 1977 and 1987, while the annual catch fell from a peak of 1220 tonnes in 1982 to 450 tonnes in 1987. Amusium is also fished in Western Australia (Harris et al. 1999) and work has been carried out on its aquaculture potential (Cropp 1993).

 

The aquaculture of Pecten theoretically has the potential to alleviate some of the pressure on wild populations, although it does not address the problem of the large investments already made in the commercial wild scallop fisheries sector. Currently the culture of scallops is not as well developed as that for mussels or oysters. In Tasmania, for example, it has been conducted on parts of the east coast for about ten years, but there are only two enterprises growing significant quantities of scallops, and they rely largely on collection of spat from the wild (DPIWE 1999).



Copyright © Environment Australia, 2002
Department of Environment and Heritage