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Growth of the native oyster Ostrea angasi using raft culture in Tasmania, Australia
Aquaculture, 19 (1980) 109-115 o Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
GROWTH OF THE NATIVE OYSTER OSTREA ANGASI CULTURE IN TASMANIA, AUSTRALIA
TREVOR
USING RAFT
G. DIX
Research and Resource Laboratory, Tasmanian Fisheries Development Taroona, Tasmania 7006 (Australia) (Accepted
109
Authority,
12 September 1979)
ABSTRACT Dix, T.G., 1980. Growth of the native oyster Ostrea angasi using raft culture in Tasmania, Australia. Aquacukure, 19: 109-115. Native oyster spat set on scallop shells in a hatchery showed seasonal growth and reached a mean shell length of 78.7 mm, 2 years after being suspended from a raft at North West Bay, Tasmania. Growth varied with suspension depth and to a lesser extent between ropes on the raft. Average dry weight condition index at harvest (115.6) indicated that the oysters were in very good condition although 42.7% died during the a-year trial.
INTRODUCTION
Tasmanian mariculture is currently limited to production of mussels and Pacific oysters, although the potential exists for a larger and more diverse industry (Dix, 1975). Recent industry interest in other potential mariculture species has included the native oyster, Ostrea angasi Sowerby, once farmed and dredged in quantity in Tasmania (Sumner, 1972). Basic biological information required to assess the present culture potential of 0. angusi is lacking and the present work sought to establish growth rates for the species using suspended culture techniques with spat raised in a laboratory hatchery at Taroona, Tasmania (Dix, 1976). MATERIALS
AND METHODS
Spat raised at the Fisheries Research Laboratory, Taroona and set on scallop shells (Dix, 1976) were transferred on 26 March 1975 to an experimental shellfish raft (Dix, 1975) at North West Bay (43” 2’34”S, 147” 16’22” E). Scallop shells with measured spat averaging 2.1 mm in length were inserted at 26cm intervals in the lay of nine ropes suspended from the raft. The top shell was about 30 cm below water level and 17 shells were housed on each rope.
110
Routine sampling was generally at monthly intervals and involved the following: reading and resetting a maximum-minimum thermometer suspended 1 m below water level; measuring to 1 mm with calipers the length of individual oysters on three shells at the surface, three at midwater and three at the bottom. Each shell was on a different rope and the number measured at a sampling ranged from 103 in March 1975 to 53 in December 1976. Two ropes were lost and never recovered after December 1976 and three other ropes detached from the raft in January 1977. These were recovered from the seabed and resuspended in February 1977. Surface salinities were not recorded at all samplings but readings in eight different months (August, October 1975; January-June 1976) fell within the range 31.5-35.1°/,,o. The main growth experiment was terminated on 23 March 1977. At this time one rope was left on the raft and all oysters from six ropes were returned to the laboratory and removed from their cultch shells. Size (mm, shell length, hinge to ventral margin) was recorded for the 2+-year-old oysters on each shell of the six ropes (357 measurements in all). Wet weight of individual oyster meats was recorded and individual condition indexes calculated for 51 oysters on one rope. Condition index, 1,000 X dry flesh weight (g)/shell volume (ml) was determined by the method of Westley (1961). The above observations provided growth and mortality data over the experimental period and, for the 2-year oysters mean flesh weight, mean condition index and lengths of oysters on different ropes at different depths. Trends in size with respect to growing depth were examined by an analysis of variance, fitting linear regression terms relating shell length to 15 of the depth levels (L)on five ropes (R). The full model had variation sources L, R and the interaction term L.R and successive reductions yielded sum of squares for L, R and L-R (e.g. sum of squares (R+L + L.R) - (L + L-R)= sum of squares for R adjusted for the other factors. The model’s GENSTAT programme accounted for missing values resulting from the loss of seven cultch shells from 15 levels on the ropes. The two lowest levels were excluded from analysis because of missing lower shells on most ropes and one of the six ropes removed in March 1977 was excluded because of excessive shell loss at other levels. RESULTS
Mortality and growth Of the 103 0. ter 3 months and 1976,34.0% had ther deaths were The oysters in
angasi measured on 26 March 1975,21(20.4%) had died afmortality after a year was 29.1%. After 15 months in July died and this increased to 42.7% after 18 months. No furrecorded. this sample grew to a mean length of 77.5 mm 2 years after
111
being placed in the sea. At this stage they had formed clusters growing out from the scallop shell cuftch (Fig. 1). Mean monthly growth increments ranged from 0 to 9.4 mm and showed a seasonal pattern with fastest growth occurring in the warmer months (Fig. 2). Analysis for oysters after 6 months showed a statistically significant correlation between monthly rate of growth and the mid point of the temperature range for that month (Corr. coeff. 0.57; 0.05 > P > 0.01).
Fig. 1. Cluster of Osfrea angasi attached to a scallop shell and cleaned of fouling. Scale line 5 cm.
Size and condition at harvest Overall mean length for the 357 harvested oysters was 78.7 mm (SD. 10.60). The mean length of oysters at different depths (ropes combined} ranged from 83.4 to 68.3 mm and showed a tendency to decrease with increasing water depth (Fig. 3). The analysis of variance (Table I) indicated that this trend has statistical significance. Oyster size varied to a lesser extent between ropes (mean sizes on each rope 75.3,76.4,76.4,78.4,80.9 mm) and a rope/level interaction is apparent. Average live weight for a subsample of 51 was 48.2 g (SD. 19.12) and wet flesh weight 7.28 g (SD. 2.79). Condition index for these oysters averaged 115.6 (S.D. 18.0).
Month
1976 and Year
Fig. 2. Growth curve (shell length, umboventral margin, mm) of Ostreo angasi and maximum-minimum temperature recordings at North West Bay, March 1975-March 1977.
TABLE I Analysis of variance of shell length (mm) of Ostrea ongasi at 15 depth levels (L) on 5 ropes (R) Variation source R L L-R Residual
d.f.
4 14
49 289
Adjusted s. sq.
Mean Sq.
F
989 3299 8409 27273
247.25 235.64 171.61 94.36
2.62* 2.50*” 1.82*
*5% level and ** 1% level of significance.
113
Depth
interval
Fig. 3. Average shell length (mm) of Ostrea angasi grown at 15 different 30 cm below water surface and remaining oysters at 26-cm intervals.
depths.
Depth
1,
DISCUSSION
Despite the early significance of Ostrea angasi as a dredged and farmed oyster in Tasmania, basic growth data for comparison with present findings are lacking. Limited information is available for the species collected as spat and grown on terra cotta tiles suspended from a jetty in South Australia (Hodson, 1963). Average length increments for groups measured up to 8 months from May 1963 and up to 6 months from July 1963 were about 5 mm per month, although 41% of the 29 monitored died within 10 months of settlement. Despite data limitations it appears that 0. angasi grew faster in South Australia where recorded temperatures (11.8-25.2%) were higher than at North West Bay, Tasmania. Stead (1971) presents growth data for the closely related 0. lutaria, measured in the south of New Zealand. Bot~m-mown and caged oysters there took from 21 to 36 months to reach market size of 70 mm length and 40 g five weight depending on the growing area. Ostrea angasi reached this size af, ter less than 24 months at North West Bay. The European flat oyster, 0. edulis is grown in Great Britain, France, Spain, The Netherlands, Japan and the United States of America. The time taken to grow to market size (considered 75 mm length, 65 g live weight by
114
Bardach et al., 1972) varies widely in different areas and may be up to 4.5 years (Walne, 1958,197O; Dahlstrom, 1965; Sheldon, 1968; Askew, 1972; Bardach et al., 1972; Sunderlin and Tobias, 1976). Significant factors affecting growth rates include temperature and culture method. Seasonal growth which was related to temperature in 0. angasi is apparent in data from most of the cited 0. edulis publications. Oysters generally grow faster under suspended culture than when bottom grown. Growing depth can be of significance also, as indicated for 0. angusi. Condition as well as shell size is significant in judging oyster marketability. Korringa (1956, cited by Walne, 1970) considered 0. edulis with a condition index of 100 as “good quality” and at 110 “very good”. Under these criteria 0. angasi harvested at North West Bay were in very good condition. Although Ostrea angusi grew more slowly than Crussostrea gigas grown by similar methods in Tasmania (C.E. Sumner, in preparation) growth rates indicate that the native oyster has some culture potential. Mortality recorded during the growth experiment is, however, considered excessive. Although spat were settled on scallop shells in a hatchery, this source would not be advocated for pilot commercial trials. Observations at North West Bay and elsewhere in Tasmania during the course of scallop field culture experiments (T.G. Dix, unpublished) suggest that 0. angusi spat could be collected during summer in commercial quantities. Mortality of such wild oysters might be lower and if collected during early summer (December), initial growth increments would be greater than those for the experimental oysters which were not placed in the sea until early autumn. ACKNOWLEDGEMENTS
Technical assistance, particularly from Richard Prebble and Carol Ferguson is appreciated. Terry Koen assisted with biometrical advice and Colin Sumner reviewed the manuscript. The work was part of a programme supported by a grant from the Fishing Industry Research Trust Account, Canberra.
REFERENCES Askew, C.G., 1972. The growth of oysters Ostrea edulis and Crassostrea gigas in Emsworth Harbour. Aquaculture, 1: 237-259. Bardach, J.E., Ryther, J.H. and McLarney, W.O., 1972. Aquaculture: The Farming and Husbandry of Freshwater and Marine Organisms. Wiley, Interscience, New York, N.Y., 868 pp. Dahlstrom, W.A., 1965. Survival and growth of the European flat oyster in California. Proc. Ntl Shellfish Assoc., 55: 9-17. Dix, T.G., 1975. Farming the sea. In: M.R. Banks and T.G. Dix (Editors), Resources of the Sea. Symposium of Royal Society of Tasmania, November 1974, pp. 93-100. Dix, T.G., 1976. Laboratory rearing of larval Ostrea angasi in Tasmania, Australia. J. Malac. Sot. Aust., 3 (3-4): 209-214.
115 Hodson, A.C., 1963. A Preliminary Investigation of some Aspects of the Biology of the Port Lincoln Oyster (Ostreo angasi) at Stansbury, South Australia. B.Sc. (Hons) thesis, University of Adelaide. Sheldon, R.W., 1968. The effect of high population density on the growth and mortality of oysters (Ostrea edulis). J. Cons. Perm. Int. Explor. Mer, 31: 352-363. Stead, D.H., 1971. Observations on the biology and Ecology of the Foveaux Strait Dredge Oyster (Ostrea Jutaria Hutton). N.Z. Mar. Dep. Fish. Tech. Rep., 68: 49 pp. Sumner, C.E., 1972. Oysters and Tasmania, Part 1. Tas. Fish. Res., 6(2): l-15. Sunderlin, J.B. and Tobias, W.J., 1976. Growth of the European oyster, Ostrea edulis Linne, in the St. Croix artificial upwelling mariculture system and in natural waters. Proc. Ntl Shellfish. Assoc., 65: 43-48. Walne, P.R., 1958. Growth of oysters (Ostrea edulk L.). J. Mar. Biol. Assoc. U.K., 37: 591-602. Walne, P.R., 1970. The Seasonal Variation of Meat and Glycogen Content of Seven Populations of Oysters Ostrea edulis L. and a review of the Literature. Fish. Invest. Lond. Ser. 2, 26(3): 35 pp. Westley, R.E., 1961. Selection and evaluation of a method for quantitative measurement of oyster condition. Proc. Ntl Shellfish. Assoc., 50: 145-149.
GROWTH OF THE NATIVE OYSTER OSTREA ANGASI CULTURE IN TASMANIA, AUSTRALIA
TREVOR
USING RAFT
G. DIX
Research and Resource Laboratory, Tasmanian Fisheries Development Taroona, Tasmania 7006 (Australia) (Accepted
109
Authority,
12 September 1979)
ABSTRACT Dix, T.G., 1980. Growth of the native oyster Ostrea angasi using raft culture in Tasmania, Australia. Aquacukure, 19: 109-115. Native oyster spat set on scallop shells in a hatchery showed seasonal growth and reached a mean shell length of 78.7 mm, 2 years after being suspended from a raft at North West Bay, Tasmania. Growth varied with suspension depth and to a lesser extent between ropes on the raft. Average dry weight condition index at harvest (115.6) indicated that the oysters were in very good condition although 42.7% died during the a-year trial.
INTRODUCTION
Tasmanian mariculture is currently limited to production of mussels and Pacific oysters, although the potential exists for a larger and more diverse industry (Dix, 1975). Recent industry interest in other potential mariculture species has included the native oyster, Ostrea angasi Sowerby, once farmed and dredged in quantity in Tasmania (Sumner, 1972). Basic biological information required to assess the present culture potential of 0. angusi is lacking and the present work sought to establish growth rates for the species using suspended culture techniques with spat raised in a laboratory hatchery at Taroona, Tasmania (Dix, 1976). MATERIALS
AND METHODS
Spat raised at the Fisheries Research Laboratory, Taroona and set on scallop shells (Dix, 1976) were transferred on 26 March 1975 to an experimental shellfish raft (Dix, 1975) at North West Bay (43” 2’34”S, 147” 16’22” E). Scallop shells with measured spat averaging 2.1 mm in length were inserted at 26cm intervals in the lay of nine ropes suspended from the raft. The top shell was about 30 cm below water level and 17 shells were housed on each rope.
110
Routine sampling was generally at monthly intervals and involved the following: reading and resetting a maximum-minimum thermometer suspended 1 m below water level; measuring to 1 mm with calipers the length of individual oysters on three shells at the surface, three at midwater and three at the bottom. Each shell was on a different rope and the number measured at a sampling ranged from 103 in March 1975 to 53 in December 1976. Two ropes were lost and never recovered after December 1976 and three other ropes detached from the raft in January 1977. These were recovered from the seabed and resuspended in February 1977. Surface salinities were not recorded at all samplings but readings in eight different months (August, October 1975; January-June 1976) fell within the range 31.5-35.1°/,,o. The main growth experiment was terminated on 23 March 1977. At this time one rope was left on the raft and all oysters from six ropes were returned to the laboratory and removed from their cultch shells. Size (mm, shell length, hinge to ventral margin) was recorded for the 2+-year-old oysters on each shell of the six ropes (357 measurements in all). Wet weight of individual oyster meats was recorded and individual condition indexes calculated for 51 oysters on one rope. Condition index, 1,000 X dry flesh weight (g)/shell volume (ml) was determined by the method of Westley (1961). The above observations provided growth and mortality data over the experimental period and, for the 2-year oysters mean flesh weight, mean condition index and lengths of oysters on different ropes at different depths. Trends in size with respect to growing depth were examined by an analysis of variance, fitting linear regression terms relating shell length to 15 of the depth levels (L)on five ropes (R). The full model had variation sources L, R and the interaction term L.R and successive reductions yielded sum of squares for L, R and L-R (e.g. sum of squares (R+L + L.R) - (L + L-R)= sum of squares for R adjusted for the other factors. The model’s GENSTAT programme accounted for missing values resulting from the loss of seven cultch shells from 15 levels on the ropes. The two lowest levels were excluded from analysis because of missing lower shells on most ropes and one of the six ropes removed in March 1977 was excluded because of excessive shell loss at other levels. RESULTS
Mortality and growth Of the 103 0. ter 3 months and 1976,34.0% had ther deaths were The oysters in
angasi measured on 26 March 1975,21(20.4%) had died afmortality after a year was 29.1%. After 15 months in July died and this increased to 42.7% after 18 months. No furrecorded. this sample grew to a mean length of 77.5 mm 2 years after
111
being placed in the sea. At this stage they had formed clusters growing out from the scallop shell cuftch (Fig. 1). Mean monthly growth increments ranged from 0 to 9.4 mm and showed a seasonal pattern with fastest growth occurring in the warmer months (Fig. 2). Analysis for oysters after 6 months showed a statistically significant correlation between monthly rate of growth and the mid point of the temperature range for that month (Corr. coeff. 0.57; 0.05 > P > 0.01).
Fig. 1. Cluster of Osfrea angasi attached to a scallop shell and cleaned of fouling. Scale line 5 cm.
Size and condition at harvest Overall mean length for the 357 harvested oysters was 78.7 mm (SD. 10.60). The mean length of oysters at different depths (ropes combined} ranged from 83.4 to 68.3 mm and showed a tendency to decrease with increasing water depth (Fig. 3). The analysis of variance (Table I) indicated that this trend has statistical significance. Oyster size varied to a lesser extent between ropes (mean sizes on each rope 75.3,76.4,76.4,78.4,80.9 mm) and a rope/level interaction is apparent. Average live weight for a subsample of 51 was 48.2 g (SD. 19.12) and wet flesh weight 7.28 g (SD. 2.79). Condition index for these oysters averaged 115.6 (S.D. 18.0).
Month
1976 and Year
Fig. 2. Growth curve (shell length, umboventral margin, mm) of Ostreo angasi and maximum-minimum temperature recordings at North West Bay, March 1975-March 1977.
TABLE I Analysis of variance of shell length (mm) of Ostrea ongasi at 15 depth levels (L) on 5 ropes (R) Variation source R L L-R Residual
d.f.
4 14
49 289
Adjusted s. sq.
Mean Sq.
F
989 3299 8409 27273
247.25 235.64 171.61 94.36
2.62* 2.50*” 1.82*
*5% level and ** 1% level of significance.
113
Depth
interval
Fig. 3. Average shell length (mm) of Ostrea angasi grown at 15 different 30 cm below water surface and remaining oysters at 26-cm intervals.
depths.
Depth
1,
DISCUSSION
Despite the early significance of Ostrea angasi as a dredged and farmed oyster in Tasmania, basic growth data for comparison with present findings are lacking. Limited information is available for the species collected as spat and grown on terra cotta tiles suspended from a jetty in South Australia (Hodson, 1963). Average length increments for groups measured up to 8 months from May 1963 and up to 6 months from July 1963 were about 5 mm per month, although 41% of the 29 monitored died within 10 months of settlement. Despite data limitations it appears that 0. angasi grew faster in South Australia where recorded temperatures (11.8-25.2%) were higher than at North West Bay, Tasmania. Stead (1971) presents growth data for the closely related 0. lutaria, measured in the south of New Zealand. Bot~m-mown and caged oysters there took from 21 to 36 months to reach market size of 70 mm length and 40 g five weight depending on the growing area. Ostrea angasi reached this size af, ter less than 24 months at North West Bay. The European flat oyster, 0. edulis is grown in Great Britain, France, Spain, The Netherlands, Japan and the United States of America. The time taken to grow to market size (considered 75 mm length, 65 g live weight by
114
Bardach et al., 1972) varies widely in different areas and may be up to 4.5 years (Walne, 1958,197O; Dahlstrom, 1965; Sheldon, 1968; Askew, 1972; Bardach et al., 1972; Sunderlin and Tobias, 1976). Significant factors affecting growth rates include temperature and culture method. Seasonal growth which was related to temperature in 0. angasi is apparent in data from most of the cited 0. edulis publications. Oysters generally grow faster under suspended culture than when bottom grown. Growing depth can be of significance also, as indicated for 0. angusi. Condition as well as shell size is significant in judging oyster marketability. Korringa (1956, cited by Walne, 1970) considered 0. edulis with a condition index of 100 as “good quality” and at 110 “very good”. Under these criteria 0. angasi harvested at North West Bay were in very good condition. Although Ostrea angusi grew more slowly than Crussostrea gigas grown by similar methods in Tasmania (C.E. Sumner, in preparation) growth rates indicate that the native oyster has some culture potential. Mortality recorded during the growth experiment is, however, considered excessive. Although spat were settled on scallop shells in a hatchery, this source would not be advocated for pilot commercial trials. Observations at North West Bay and elsewhere in Tasmania during the course of scallop field culture experiments (T.G. Dix, unpublished) suggest that 0. angusi spat could be collected during summer in commercial quantities. Mortality of such wild oysters might be lower and if collected during early summer (December), initial growth increments would be greater than those for the experimental oysters which were not placed in the sea until early autumn. ACKNOWLEDGEMENTS
Technical assistance, particularly from Richard Prebble and Carol Ferguson is appreciated. Terry Koen assisted with biometrical advice and Colin Sumner reviewed the manuscript. The work was part of a programme supported by a grant from the Fishing Industry Research Trust Account, Canberra.
REFERENCES Askew, C.G., 1972. The growth of oysters Ostrea edulis and Crassostrea gigas in Emsworth Harbour. Aquaculture, 1: 237-259. Bardach, J.E., Ryther, J.H. and McLarney, W.O., 1972. Aquaculture: The Farming and Husbandry of Freshwater and Marine Organisms. Wiley, Interscience, New York, N.Y., 868 pp. Dahlstrom, W.A., 1965. Survival and growth of the European flat oyster in California. Proc. Ntl Shellfish Assoc., 55: 9-17. Dix, T.G., 1975. Farming the sea. In: M.R. Banks and T.G. Dix (Editors), Resources of the Sea. Symposium of Royal Society of Tasmania, November 1974, pp. 93-100. Dix, T.G., 1976. Laboratory rearing of larval Ostrea angasi in Tasmania, Australia. J. Malac. Sot. Aust., 3 (3-4): 209-214.
115 Hodson, A.C., 1963. A Preliminary Investigation of some Aspects of the Biology of the Port Lincoln Oyster (Ostreo angasi) at Stansbury, South Australia. B.Sc. (Hons) thesis, University of Adelaide. Sheldon, R.W., 1968. The effect of high population density on the growth and mortality of oysters (Ostrea edulis). J. Cons. Perm. Int. Explor. Mer, 31: 352-363. Stead, D.H., 1971. Observations on the biology and Ecology of the Foveaux Strait Dredge Oyster (Ostrea Jutaria Hutton). N.Z. Mar. Dep. Fish. Tech. Rep., 68: 49 pp. Sumner, C.E., 1972. Oysters and Tasmania, Part 1. Tas. Fish. Res., 6(2): l-15. Sunderlin, J.B. and Tobias, W.J., 1976. Growth of the European oyster, Ostrea edulis Linne, in the St. Croix artificial upwelling mariculture system and in natural waters. Proc. Ntl Shellfish. Assoc., 65: 43-48. Walne, P.R., 1958. Growth of oysters (Ostrea edulk L.). J. Mar. Biol. Assoc. U.K., 37: 591-602. Walne, P.R., 1970. The Seasonal Variation of Meat and Glycogen Content of Seven Populations of Oysters Ostrea edulis L. and a review of the Literature. Fish. Invest. Lond. Ser. 2, 26(3): 35 pp. Westley, R.E., 1961. Selection and evaluation of a method for quantitative measurement of oyster condition. Proc. Ntl Shellfish. Assoc., 50: 145-149.