University of Tasmania
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An ecological study of Tasmanian flounder

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posted on 2023-05-26, 21:53 authored by Christine CrawfordChristine Crawford
The ecology of the juveniles of two species of Tasmanian flounder, Rhombosolea tapirina and Ammotretis rostratus, which occur sympatrically on nursery grounds was investigated in order to determine which environmental parameters are important in habitat selection and resource partitioning. The reproductive strategies of adults also were examined and methods were developed for the cultivation of flounder. A third species, Ammotretis lituratus, was caught in low numbers and some aspects of the ecology of this species are also discussed. Field studies showed that both R. tapirina and A. rostratus juveniles were abundant on estuarine sandflats and were concentrated mostly in shallow water (0-1 m depth). They apparently partially partitioned the spatial and trophic resources of the habitat but were not segregated temporally. Newly-metamorphosed juveniles of both species occurred in the highest densities from late winter to early summer. Although they were widely distributed within the estuary, A. rostratus was most abundant at the mouth and R. tapirina on the extensive shallow sandflats. A. rostratus juveniles also were caught more frequently in deeper water (1 m) than in the shallows whilst R. tapirina did not show a clear pattern of depth distribution over 0-1 m depth. Newly-metamorphosed juveniles of both species were daytime feeders and consumed the same food organisms - predominantly amphipods, harpacticoids and polychaetes. However, the relative proportions of each food type eaten differed between the species. A. lituratus juveniles were caught only on semi-exposed beaches. They, therefore, were segregated spatially from the major populations of the other two flounder species. Experimental studies indicated that the field distributions of R. tapirina and A. rostratus juveniles were related to their differing swimming abilities, preferred substrate types and possibly levels of turbulence. Temperature and salinity preferences were not considered to be as important. The results also suggested that the larvae of R. tapirina and A. rostratus are dependent on water movements to transport them towards nursery grounds. An ontogenetic change in preferred salinity was observed in both species, and position in the water column in R. tapirina, at metamorphosis. These factors, in association with a preference for fine sand and probably shallow water, would play a role in guiding larvae towards settling on estuarine sandflats. R. tapirina and A. rostratus adults appeared to have a similar reproductive strategy of a prolonged spawning season, serial spawning, relatively high fecundity and both species were mature for the first time at approximately the same length. These two species were cultivated in the laboratory to the post-metamorphosis stage. The high survival rates obtained indicate that both species could be readily cultured using the techniques developed. Developmental stages of eggs and larvae were described and were used to identify planktonic stages.


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Copyright 1984 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s). Thesis (Ph.D) - University of Tasmania, 1984. Bibliography: leaves 155-167

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