Development and evaluation of egg-based stock assessment methods for blue mackerel (Scomber australasicus) in southern Australia
SARDI Food Safety and Innovation
Timothy M. Ward
Stock assessment methods need to be developed for blue mackerel for a range of economic, ecological, social and legislative/administrative reasons. Perhaps most importantly, the large and valuable international markets for members of the genus Scomber, in conjunction with the apparently large stocks of blue mackerel off southern Australia, suggest that a commercial fishery for this species could generate significant export earnings. Furthermore, as the economic potential of this industry is well known, significant amounts of private and public funds have been invested trying to develop fisheries and processing facilities for this species. To date, the development of these industries has been impeded by the absence of the information required to establish appropriate TACs. In fact, trigger TACs in Commonwealth waters were halved recently as a precautionary response to scientific uncertainty regarding sustainable harvest levels. Blue mackerel is also prized as bait by recreational anglers and reliable estimates of the quantities taken by this sector is needed to determine the total impacts of fishing and to make informed decisions about resource sharing amongst stakeholders (see Attachments 1-5). The need for data from the recreational sector is most pressing off the NSW coast. There is also significant concern among recreational anglers that sustained commercial fishing for blue mackerel may affect the local abundance and availability of sportsfishes, such as tuna and billfishes. Australia’s recreational and charter fisheries for these sportfishes are economically important and provide a significant source of income for many regional communities (e.g. Port Stephens and southern NSW). If stocks of blue mackerels are not as large as commercial fishers claim, then the concerns of recreational fishers may be valid and further development of the commercial fisheries could potentially impact on the distribution, abundance and availability of sportfishes and the viability of the recreational and charter fisheries which they support. Similarly, the removal of large quantities of a key prey species could adversely affect populations of other marine predators, including marine mammals and seabirds. The species that prey on blue mackerel have considerable social and ecological significance. As a result, there is strong public pressure for Commonwealth and State governments to conduct research and develop management arrangements that will ensure that commercial harvesting of blue mackerel is ecologically sustainable. Commonwealth and state legislation, policies and strategies also require government agencies to ensure that the harvesting of fisheries resources not only provides maximum economic and social benefits to the Australian community, but also minimise impacts on other components of the ecosystem. In the cost recovery frameworks in which most fisheries management and research agencies currently operate, acquiring funds to conduct research in support of small and developing (albeit potentially valuable) fisheries is problematic. The augmentative funding requested in this proposal is needed to ensure that the harvest strategies that are developed for blue mackerel off southern Australia reflect the social significance of the species as well as the size and potential economic value of the resource, and take into account the potential ecological effects of the expansion of the commercial sector. The major impediment to the development of southern Australia’s commercial mackerel fisheries is the lack of quantitative information required to establish appropriate TACs. The most cost- and time-effective option for obtaining this information is to apply egg-based stock assessment methodologies, such as the Daily Egg Production Method (T.M. Ward et al. 1998, 2001; P. Ward et al. 2001). This project will (i) develop the methods for sampling adults and identifying and staging eggs that are required to apply egg-based stock assessment methods to blue mackerel and (ii) use the Daily Egg Production Method to calculate conservative estimates of minimum spawning biomass of blue mackerel off southeastern Australia.
1. To synthesise information available on the fisheries for blue mackerel in southern Australia. (Note that information on the biology of blue mackerel will be reviewed as part of the objectives that deal specifically with age and growth, reproductive biology, stock assessment, etc.).
2. To describe thestock structure of blue mackerel in south-eastern Australia.
3. To estimate the number, size, frequency and total weight of blue mackerel taken by recreational (charter, gamefish and trailer boat) fishers of the New South Wales coast.
4. To describe the spatial and temporal patterns of age and growth and compare the age structure of commercial catches and fishery independent samples of blue mackerel taken from throughout southern Australia.
5. To compare the spatial and temporal patterns of age commercial and recreational catches samples of blue mackerel taken from NSW.
6. To describe reproductive biology, especially spawning fractions and batch fecundity, of blue mackerel in South-eastern Australia.
7. To establish methods and criteria for identifying and staging the eggs and larvae of blue mackerel.
8. To estimate the distribution and abundance of eggs and larvae of small pelagic species in south eastern Australia (Scomber australasicus, Trachurus spp., Sardinops sagax, Engraulis australis, Etrumeus teres)
9. To develop and evaluate methods for estimating the spawning biomass of blue mackerel in southern Australia.
10. To evaluate potential harvest strategies for blue mackerel in southern Australia and provide preliminary estimates of the potential yields for each zone of the Commonwealth fishery
Principal Investigator: J.P. Keane, M. Lowry, L.J. McLeay, F.J. Neira, J.R. Ovenden, P.J. Rogers, R.J. Saunders, D. Schmarr, T.M. Ward, I.D. Whittington and D. Williams