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2012 review of the OstreaAngasi fishery
1.Summary of OstreaAngasi fishery since the introduction of the management plan
Native oysters (Angasi)are managed under the minor shellfish fishery which was introduced in April 2007. There are only two licences to allow commercial harvest of wild grown Angasi and harvest is limited to Georges Bay.
As part of the minor shellfish fishery, stocks of the Angasi in Georges Bay are assessed every two to three years by means of field surveys overseen by the Institute of Marine and Antarctic Studies (IMAS). An estimate of the biomass can then be determinedand10% of that biomass is allocated as the TAC for the commercial fishery. IMAS identified 10% as being an internationally accepted, highly precautionary figure which provides a significant safety buffer for the fishery. This is particularly the case as the population is assessed so regularly, providing the opportunity for timely adjustment of the TAC if required. This process was described in detail in the minor shellfish policy paper which was accepted by SEWPaC prior to the management plan being introduced in 2007.
In line with the policy, surveys of the stock wereconducted in 2008 and 2010. Copies of the resulting reports are attached. Although the surveys clearly indicate that stocks remain consistently strong in the bay, the number harvested has been well below the allocated TAC with fishers only taking around three to four percent of the allocated stock. This is due purely to marketing issues and as can be seen by the survey results, is not a reflection of the stock.
The beach price for Angasi has remained stable at around $6.50 per dozen since the inception of the management plan.
Angasi Fishery
Licensing Year / Stock(no. oysters based on closest survey) / TAC
(dozens) / Dozens harvested / Value ($6.50/Doz)
2008/2009 / 4.96 million / 41,000 / 1,395 / $ 9,067
2009/2010 / 4.96 million / 41,000 / 1,677 / $10,900
2010/2011 / 4.68 million / 39,000 / 1,507 / $ 9,795
Progress towards recommendations made in the assessment of the Tasmanian Angasifishery.
Recommendation 1:DPIW to advise the Department of the Environment and Water Resources (DEW) of any material change to the TAS ShellFish Fishery management arrangements that could affect the criteria on which Environment Protection and Biodiversity Conservation Act 1999decisions are based, within three months of that change being made.
Response: There has been no significant change to the management arrangements.
Recommendation 2: Reports to be produced andpresented to DEW annually, and to include:
i. Information sufficient to allow assessment ofthe progress of DPIW in implementing therecommendations made in the Assessment ofthe Harvest of Native Oysters from theTasmanian Shellfish Fishery 2007; and
ii. A description of the fishery, managementarrangements in place, recent catch data forthe native oyster section of the fishery, statusof target stock, interactions with protectedspecies, impacts of the fishery on theecosystem in which it operates and researchand monitoring outcomes.
Information should only be provided on those aspectswhich are relevant to the fishery and that articulate‘changes’ since the last annual report.
Response: A review of our records has shown that there has been an oversight in the reporting on this industry. The annual reports were overlooked due to confusion arising from correspondence from your Department to DPIPWE which listed all Tasmanian Fisheries requiring assessmentbut did not include any mention of native oysters. This in conjunction with the fact that there was minimal activity in native oyster fishery and a lack of familiarity with the process resulted in the oversight. It is now understood that assessments and annual reports are distinct requirements so the error has been noted and will be rectified for future years.
Recommendation 3: DPIW to monitor the status of native oysters in relation to reference points. Within 3 months of becoming aware of a reference point being triggered, DPIW to develop a clear timetable for the implementation of appropriate management responses.
Response:With an annual harvest only reaching about 3% of the available TAC, no trigger points have been approached. It should be noted that in this fishery, the regular surveys and the precautionary setting of 10% of stocks as the TAC precludes any trigger points being reached as adjustments are made in advance based on stocks available.
Recommendation 4: By December 2011, DPIW toconduct a survey on the stock structure and density ofnative oysters on the Main Bed, Eastern Bed and theAkaroa Bed to inform management arrangements,particularly with regards to setting the annual total allowable catch.
Response: The survey was conducted in 2010 (report attached) which showed that stocks remain healthy.
Recommendation 5: DPIW to develop a researchstrategy for native oysters and implement onceresources allow. Research should focus on growth andrecruitment of native oysters.
Response: There are only eight licences in total contributing to the minor shellfish trust fund and only two of these are for native oysters. Money available for research into the industry is therefore not readily available. The available funds were recently allocated to a project on investigating Katelysia in Ansons Bay and similar studies are still required for Venerupis and Angasi in Georges Bay when the funds are available.
Native Oyster Survey 2008
2.GeorgesBay Native Oysters (Ostrea angasi).
A small native oyster fishery operates in GeorgesBay with a number of separate beds being available for harvesting (Fig.1).
Figure 1. A habitat map of part of GeorgesBay with eight separate native oyster beds delineated.
The separate beds were delineated using a GPS unit to record the separate bed boundaries. This provided estimates of the area of each bed and its location (Fig. 1).
Six of the beds were sampled using a quarter square metre quadrat. This was treated as a stratified random survey for analytical purposes. It was calculated as numberso foysters as well as biomass of oysters.
A total area of oyster bed of 55,056 m2 made up the six beds surveys (beds 1,2,4,5,6 and 7). A mean density of oysters per m2 = 90.2 with a mean weight per m2 of 3.046 kg.
This implied a biomass of 670.5 t ± 102.1 t or a total population of 4.96 million oysters.
At 16 % of available biomass this equates to 107 t or 66,000 dozen (which are approximately equivalent.
A length to Weight relationship was developed which was used to calibrate the biomass estimates by converting lengths to weight (Fig. 2).
Figure 2. Length to weight relationship for GeorgesBay native oysters.
Native Oyster Survey 2010
3.Georges Bay Native Oysters (Ostrea angasi).
A small native oyster fishery operates in Georges Bay with a number of separate beds being available for harvesting (Fig.1).
Figure 1. A habitat map of part of Georges Bay with eight separate native oyster beds delineated.
The separate beds were delineated many years ago using a GPS receiver to record the separate bed boundaries. This provided estimates of the area of each bed and its location (Fig. 1).
Seven of the beds were sampled using a quarter square-metre quadrat. 1935 oysters were collected and measured from 100 quadrats. This assessment used a stratified random design for analytical purposes, and calculated numbers of oysters as well as biomass of oysters.
A length to weight relationship was developed which was used to calibrate the biomass estimates by converting lengths to weight (Fig. 2). Length-weight relationships were established following each of the previous surveys and these could have been used for this assessment; however, there was uncertainty about the effects that any seasonal variation in weight may have had on the length-weight relationship (this survey was done in May, the others at different times of the year), and consequently the process was repeated for this survey.
The total area of oyster bed was 69,895 m2 made up of the seven beds surveyed (beds 1,2,4,5,6,7 and 8). Bed 3 was excluded from the previous survey because it was not fished, so it was also excluded from this survey. The mean density across all seven surveyed beds was 67 oysters per m2, with a mean weight per m2 of 8.15 kg.
This implied a biomass of 569.52 t ± 78.87 t or a total population of 4.68 million oysters.
At 10 % of available biomass, the fishery TAC equates to 56.59 t or 39,025 dozen oysters, which are approximately equal.
The total number of oysters in the fishery has changed little since 2008 (Table 1). This is due to a decline in density which was offset by an increase in area of the 2010 fishery, compared with 2008. In 2010, bed 8 was surveyed, but not bed 3. The total area of the surveyed beds in 2010 (69,895 m2) was consequently greater than in 2008 (55,036 m2).
In 2010, the mean density was 67 oysters per m2 or 8.15 kg/m2, compared with 90 oysters per m2 or 12.12 kg/m2 in 2008. The inclusion of the low-density bed 8 in the 2010 survey contributed to much of the reduction in mean density across all surveyed areas compared with the 2008 fishery.
The distribution of oysters on the seabed has changed over the years, and contributes to uncertainty in the biomass estimate. Beds 1, 2, 3 and 8 all have comparatively low density, to the extent that beds 2 and 3 would probably be no longer regularly fished. Bed 8 is large (21% of the mapped area), with variable density within the patch.
In contrast, the habitat containing oysters extends beyond the perimeters of beds 4, 5, 6 and 7 (i.e. outside the mapped areas), and density appears to have increased here so that this extended area is now fishable. Estimates of stock size are influenced by the boundaries selected for sites. One option for future surveys is re-mapping and exclusion of the non-productive beds although this would not be a trivial task. The fishery has been so lightly exploited during the past 10 years that the industry participants are not sufficiently familiar with the bottom to be able to delineate the productive areas with the required accuracy. If there is an upturn in market demand then fishing would presumably become more intense and divers will gain a better appreciation of productive bottom. This would increase their ability to create more accurate maps.
Table 1. Comparison between weights and numbers from 2008 and 2010 surveys:
Figure 2. Length to weight relationship for Georges Bay native oysters, May 2010.
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