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Executive Summary EXECUTIVE SUMMARY The New Zealand aquaculture industry is presently dominated by the production of Greenshell™ mussels in terms of total yield, water-space utilisation and total revenue. However, there has been recent emphasis by a number of mussel farmers in the Marlborough Sounds to amend permits and consents so that other bivalve species can be farmed. In response to this, the Ministry of Fisheries commissioned the Cawthron Institute to use available information to perform a desktop investigation into the marginal differences between the environmental interactions of a range of bivalve species to underpin stocking density guidelines. A hazard assessment was used to identify the major environmental interactions between bivalves and the surrounding marine environment and this highlighted several major risk pathways, several of which were through the feeding and excretory behaviour of the bivalve crop. Marginal differences between the transfer of material by the different species were therefore investigated using a range of feeding models and environmental data from the Marlborough Sounds and Glenhaven Aquaculture Centre. The key result from analysis of the marginal differences between a range of bivalve species was that mussels generally appear to exhibit the highest clearance and excretion rates of the bivalves considered. Similarly, biodeposition intensity greater than 400 g/day/1000ind occurred most frequently in mussels (40%) followed by, scallops (33%), cupped oysters (29%), flat oysters (11%), and finally clams/cockles (6%). Overall, it appears that based on the model utilised here, the substitution of mussels, specifically Perna canaliculus, with any of the other alternate species/groups proposed would not be likely to increase either the clearance of the surrounding water, the biodeposition of suspended matter or the amount of dissolved ammonia through excretion. In fact, on an equivalent numbers basis substitution with any of the alternate groups may reduce these interactions, especially where either flat oysters or clams/cockles are considered. This is a key result of this study and suggests that there is no strong evidence in terms of material processed by the different bivalves considered here to restrict the stocking density of non-mussel bivalves to substantially lower densities by comparison to the stocking densities used for mussels. The hazard assessment also identified that farming structures can potentially lead to changes in the surrounding environment through the alteration of water flows. Scaling analyses were performed that highlight the relative differences in cross-sectional areas posed by different farming methods. The results from this analysis indicate that the present mussel farming practices occupy a greater cross- sectional area by comparison with the other methods that are presently used. Hence there is little evidence to suggest that the stocking densities of other species using different growing techniques, as described here, should be more overly restricted by comparison with present marine farming practices. Cawthron Report No. 1192 iii October 2006 TABLE OF CONTENTS EXECUTIVE SUMMARY.........................................................................................................III 1. INTRODUCTION..............................................................................................................1 1.1. Scope and objective.................................................................................................................................. 1 2. BACKGROUND INFORMATION......................................................................................1 2.1. Potential species and culture methods...................................................................................................... 1 2.2. Diseases ................................................................................................................................................... 4 3. HAZARD ASSESSMENT .................................................................................................6 4. METHODOLOGY .............................................................................................................9 4.1. Material fluxes ........................................................................................................................................... 9 4.1.1. Literature search ..................................................................................................................................... 10 4.1.2. Environmental datasets........................................................................................................................... 11 4.1.3. Shellfish size ........................................................................................................................................... 11 4.1.4. Comparative histograms ......................................................................................................................... 12 4.2. Attenuation of water flows ....................................................................................................................... 12 5. RESULTS.......................................................................................................................13 5.1. Differences in the material fluxes using Beatrix Bay data........................................................................ 13 5.1.1. Environmental data in Beatrix Bay .......................................................................................................... 13 5.1.2. Clearance Rate histograms for Beatrix Bay ............................................................................................ 14 5.1.3. Ammonia nitrogen excretion rate histograms for Beatrix Bay.................................................................. 17 5.2. Differences in material fluxes using Glenhaven Aquaculture Centre pond data...................................... 18 5.2.1. Environmental data for Glenhaven.......................................................................................................... 18 5.2.2. Clearance rate histograms for Glenhaven............................................................................................... 21 5.2.3. Total rejection rate histograms for Glenhaven......................................................................................... 24 5.3. Attenuation of current flows..................................................................................................................... 26 6. SUMMARY AND RECOMMENDATIONS ......................................................................28 7. REFERENCES...............................................................................................................31 8. APPENDICES ................................................................................................................33 LIST OF FIGURES Figure 1. Example of an ‘ear’ hung scallop......................................................................................... 2 Figure 2. Examples of culture systems used for oysters. L-R: baskets, trays, Rotoshells. ............... 3 Figure 3. Influence diagram detailing the likely hazards (in a risk assessment sense) associated with the establishment of a suspended bivalve farm. .......................................................... 6 Figure 4. Beatrix Bay temperature data recorded between 1994 and 2006..................................... 13 Figure 5. Chla data recorded for Beatrix Bay between 1994 and 2006............................................ 14 Figure 6. Comparative histograms showing the range and relative frequency of predicted clearance rates by bivalve group for Beatrix Bay. .............................................................................. 15 Figure 7. Comparative histograms showing the range and relative frequency of predicted ammonia nitrogen excretion rates by bivalve group for Beatrix Bay. ................................................ 18 Figure 8. Daily temperature data recorded for seawater ponds at the Glenhaven Aquaculture Centre between May and October 2006........................................................................................ 19 Cawthron Report No. 1192 v October 2006 Figure 9. Daily chlorophyll a data recorded for seawater ponds at the Glenhaven Aquaculture Centre between May and October 2006............................................................................ 20 Figure 10. Daily total particulate matter data recorded for seawater ponds at the Glenhaven Aquaculture Centre between May and October 2006. ...................................................... 21 Figure 11. Comparative histograms showing the range and relative frequency of predicted clearance rates by bivalve group for the Glenhaven Aquaculture Centre ponds............................... 22 Figure 12. Comparative clearance rate histograms for P. canaliculus and P. novaezelandiae models from similar NZ studies by Teaioro (1999) and Keeley (2001) applied to the Glenhaven Aquaculture Centre pond data........................................................................................... 23 Figure 13. Comparative histograms of C. gigas CRs by population and individual assessment methods adapted from Barille et al.(1997) and applied to the Glenhaven Aquaculture Centre pond data. .............................................................................................................. 24 Figure 14. Comparative histograms showing
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