Seafood CRC: bioeconomic evaluation of commercial scale stock enhancement in abalone
Department of Primary Industries and Regional Development (DPIRD) WA
Seeding of hatchery-produced marine animals into productivefisheries, known as stock enhancement, is becoming a sought-after fisheriesmanagement strategy around the world. Stock enhancement is based on theprinciple that fish stocks are generally recruitment limited and that thecarrying capacity of the ecosystem is rarely reached. This indicates that thesystem can accommodate a greater number of fish compared to what is naturallyproduced (recruited) from the breeding stock. Therefore, hatchery-producedanimals can be released into wild populations to “fill the space” between thenatural recruitment and the carrying capacity of the system, thereby increasingthe overall biomass and subsequently the catch and profitability of fisheries.
However, stock enhancement programs worldwide have hadlimited success, which has led to a cautious approach and the scientificallyrigorous protocol called the “Responsible Approach” to stock enhancement. Thisapproach details fundamental principles of stock enhancement, including naturalecological processes, economic performance and development of governance, as inthe past a lack of understanding of these principles has hindered the practiceof stock enhancement.
Abalone enhancement programs are no exception to this, withmany studies around the world struggling to have commercial success. Givenabalone fisheries are high value, low volume and in Australia have beensustainably managed over a long period of time, Australian abalone fisheriesare well placed to incorporate stock enhancement as a fisheries managementstrategy. Therefore, the focus of this project was to evaluate the potential ofcommercial-scale stock enhancement of Greenlip Abalone (Haliotis laevigata) inWestern Australia. In doing this, the project aimed to address some of thecurrent knowledge gaps in abalone stock enhancement within Australia byconducting a series of large-scale juvenile Greenlip Abalone releases intonatural habitats within a commercial fishery.
These stock enhancement experiments allowed investigationinto biological data such as long-term growth and survival estimates, whichindicated that released juvenile abalone (Age 1.5 and ~ 30 mm) reach legalminimum length (140 mm) at approximately 5 years of age and there is clearevidence of these abalone being commercially fished. Release mortality isconsidered critical as initial (6 month) survival differs significantly amongsites but not beyond this time period. Given the effect of habitat variation onabalone survival, the development of a population survey technique thatmeasured density, as a function of available habitat was important to assesspopulation and ecological responses of enhancement.
In examining the carrying capacity of the ecosystem,releases of juvenile abalone were able to initially increase densitiessignificantly (up to 800%), however after 2.5 years they stabilised at 8 perm2, which was still an increase of 400% above baseline densities. This was thepredicted carrying capacity with the enhanced abalone cohort represented 50% ofthe population and demonstrates that the system is recruitment limited and canaccommodate greater abalone biomass. Given no environmental effects fromenhancement were detected other than the increase in abalone density, itsuggests that as long as release densities are controlled within naturallimits, successful stock enhancement can be attained for this species withminimal ecological impacts.
This greater understanding of natural population processesand new quantitative approaches to determining viable habitat and associatedrelease densities, allowed a bioeconomic evaluation of commercial-scale stockenhancement to be conducted. This bioeconomic analysis also took into accountcurrent fishery assessment information and economic data collected from thecommercial industry. The analysis was initially conducted on a WesternAustralian fishery with enhancement targets defined as a function of naturalrecruitment and compared to current harvest strategies. It was then applied tothe Australian Greenlip Abalone fishery as a whole and revealed significanteconomic potential for stock enhancement programs. To achieve this potential anintegration of enhancement inputs and harvest strategy outputs is essential,where they are considered part of the same fisheries management system.
Given the bioeconomic evaluation indicated that abalonestock enhancement within Australia is potentially viable; a methodology for thecommercial enhancement of juvenile Greenlip Abalone into the areas of theWestern Australian abalone fishery was investigated. This methodologystandardised the logistics, schedule and techniques of enhancement into amanual for the training and education of organisations and personnel throughoutAustralia, that plan on utilising stock enhancement as an abalone fisherymanagement strategy.
New diagnostic genomic tools were developed to study naturalpopulation genetic structure and monitor the success of stock enhancement in acommercial Greenlip abalone fishery within Western Australia. Samples from 372Greenlip abalone collected from 13 locations from across the WA fishery wereanalysed using the new tools, and produced 69,720 high quality genomic markersin the form of SNP’s (single nucleotide polymorphisms). The screening ofgenome-wide variation in samples collected from the wild shows that ‘neutral’SNPs (i.e. DNA markers that are not under the influence of natural selection)support the existence of one single abalone population with high connectivityacross the geographic range sampled. However, when the SNP markers undernatural selection were examined, five genetically distinct groups ofpopulations for Greenlip abalone were identified. Significant associationsbetween the distribution of these adaptive groups and the spatial variation ofkey environmental parameters, including differences in temperature andoceanographic variables were found. This finding will help managers selectwhich abalone populations are likely to perform best in specific environments(i.e. likely fitness), consequently improving the chances of successful stockenhancement programs.
Overall these results suggest that if the general principlesof abalone stock enhancement, including ecological processes and the carryingcapacity of the system, genetic, economic parameters, governance (policy) andbio-security are understood and brought together, then commercial-scaleenhancement of Greenlip Abalone is feasible in Australian abalone fisheries.
1. To estimate long-term growth and survival of enhanced greenlip abalone
2. Undertake a bioeconomic analysis of large scale stock enhancement in greenlip abalone
3. To evaluate appropriate wild-stock management protocols that facilitate stock enhancement
4. Develop biosecurity protocols for stock enhancement