A variety of methods for limiting effort or catch (known as input and output controls respectively) are already in place for different fisheries within Australia. Input controls limit effort and include restrictions on the number of licences, type of gear, or times when harvesting may take place (e.g., seasonal closures). Output controls limit the quantity or characteristics of the stock that may be collected and may include individual bag limits, size limits, and /or a Total Allowable Catch (TAC) or Individual Transferable Quota. While these options are fairly well developed, they have had limited success in many instances due to problems with enforcement and dealing with single species management.


Since the fecundity of many marine invertebrates increases with age and size, the choice of legal size limits is critical. While minimum legal sizes are widespread, and aim to preserve individuals until they have at least obtained reproductive age, it can also be important to restrict collection of very large individuals, as their removal can have a disproportionate effect on the reproductive output of the population. For example, overfishing of scallops in Queensland might be addressed by selective protection of brood stock as an alternative to restricting effort or actively enhancing the stock (Dredge 1988). Consequently, some management plans have introduced maximum as well as minimum size limits (e.g., Western Rock Lobster fishery in WA). Such maximum size limits may be increasingly necessary as improvements in technology (and economic imperatives) enable (or force) fishers to exploit populations in increasingly distant and difficult areas, which might formerly have served as refuges for some large individuals. For instance, the imposition of a maximum size limit in the WA rock lobster fishery was in response to the advent of GPS, which enabled fishers to accurately locate deep offshore reefs.


In NSW, commercial fishing for the blacklip abalone, Haliotis rubra is regulated by a variety of controls such as minimum size limits and a Total Allowable Commercial Catch (TACC). While the catch has remained stable for about the last five years (as a result of the TACC being fixed at 333 tonnes), the size-structure and growth of individuals are suggestive of high exploitation rates (Andrew et al. 1997). The fishery is dominated by individuals that have recently recruited to the fishery (i.e. reached the minimum legal size of 115 mm). These recent recruits make up a large proportion (50-95%) of the commercial catch in all zones (Andrew et al. 1997), the accumulated stock of old, large abalone apparently having been seriously depleted over the life of the fishery. Catch rates in NSW (about 20 kg hr-1) are also much lower than in Tasmania and Victoria (above 50 kg hr-1), due mainly to the additional time required finding abalone above the length limit (Andrew et al. 1997). The NSW abalone fishery appears to be very different to those of Victoria and Tasmania, which have annual catches of over 1500 tonnes and over 3000 tonnes (respectively). This probably results from a combination of biological, ecological and other factors, as well as patterns of management. However, it is interesting to note that the legal minimum sizes in both Victoria and Tasmania are considerably higher (120 mm and 132 mm respectively) than in NSW, resulting in the presence of greater numbers of larger (more fecund) individuals in the population (Andrew et al. 1997).


In cases where stocks appear to be over exploited, one management option is to reduce fishing levels, for instance through a reduction in the number of licenses. This has occurred in several fisheries, including the NSW abalone fishery. A reduction in fishing levels is currently being pursued on the Great Barrier Reef, with a planned gradual reduction through buy-back of some licenses, restriction in the area available for trawling, and limitation on the number of days of trawling. While current levels of exploitation may be sustainable, any new incentive for new or latent license-holders to enter the fishery (e.g., increases in price, depletion of alternative species) could result in significant depletion beyond the immediate control of managers. In Queensland, for instance, it is well known that there are a number of latent (“sleeping”) licenses to operate on the GBR, a fact which has had to be taken into account in discussions and negotiations about the reduction of fishing pressures on the Reef, and calculations of the effect of proposed buy-backs etc. In the future, perhaps, fishers may need to use their licenses to at least a minimal level each year in order to be keep them (see above).

Copyright © Environment Australia, 2002
Department of Environment and Heritage