Developing a fishery independent estimate of biomass for snapper
SARDI Food Safety and Innovation
Mike A. Steer
Increased formalisation of harvest strategies for snapper across Australia’s four main jurisdictions (East Coast, Western Victoria, South Australia and Western Australia) was identified as a national priority (at the National Strategic Planning Workshop for Snapper Research – 1st March 2013). Two key processes were recognised as being fundamental to achieving this: 1. development of a snapper-specific integrated fishery model; and 2. integration of a fishery-independent estimate of abundance. Each jurisdiction is currently at a different level of advancement in their assessment and management capability, with WA leading the way. A snapper model is currently used to underpin the assessment of South Australia’s snapper resource, whereas Western Victoria is in the process of developing their own and the East Coast is yet to develop one. South Australia and Western Victoria are at a level where the development and integration of a DEPM, that would provide a fishery-independent estimate of biomass, would considerably enhance their respective stock assessment programs. The need for a DEPM is more urgent for South Australia, as recent structural changes in the snapper fishery have compromised the integrity of the time series of fishery-dependent statistics that have been relied on to assess the resource in the past. Fishery-independent estimates of snapper biomass are required to feed into the existing stock assessment model to ensure that future assessments and harvest strategies are developed from unbiased information. This research direction has been unanimously supported by the relevant stakeholders in South Australia’s Snapper Fishery. The Western Victorian fishery is likely to encounter similar issues to South Australia, particularly as their fishery is dominated by the recreational sector where the routine collection of catch and effort data to integrate into the assessment process is often challenging.
1. To develop a DEPM for snapper that provides the most accurate estimate of biomass and integrates with the on-going assessment and management of the resource.
This study was undertaken by the South Australia Research and Development Institute (SARDI). Through overcoming considerable technical challenges, this study was the first to successfully develop a relatively non-destructive molecular probe that can reliably identify Snapper (Chrysophrys auratus) eggs and larvae in mixed ichthyoplankton samples. This highly-specific molecular probe targets Snapper ribosomal (r)RNA and when conjugated with a reactive molecule produces a highly visible blue colour in positive reactions. Snapper eggs are subsequently easily detected using a standard stereo dissecting microscope. This novel use of an established molecular technique has re-invigorated the capability of using the daily egg production method (DEPM) to provide a fishery-independent estimate of spawning biomass for Snapper and has also increased its applicability to other species where egg identification has been problematic. This research has reduced the need to exclusively rely on fishery-dependent catch and effort data to assess Snapper fisheries and has demonstrated that the incorporation of the DEPM into South Australia’s existing assessment program is relatively cost-effective and likely to benefit the management and industry. Adding the DEPM will contribute an extra unbiased source of information that can be synthesised with existing fishery-dependent data streams that will lead to more confident assessments of the stock and ensure the long term sustainability of the State’s Snapper resource.Keywords: Snapper, Chrysophrys auratus, Spawning Biomass, Daily Egg Production Method, South Australia, In-situ Hybridisation, Egg Identification, Cost-Effective Application.