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An ecological study of Tasmanian flounder

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Crawford, CM (1984) An ecological study of Tasmanian flounder. PhD thesis, University of Tasmania.

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Abstract

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.

Item Type: Thesis (PhD)
Keywords: Pleuronectidae, Flatfishes
Copyright Holders: The Author
Copyright Information:

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).

Additional Information:

Thesis (Ph.D) - University of Tasmania, 1984. Bibliography: leaves 155-167

Date Deposited: 09 Dec 2014 00:16
Last Modified: 10 May 2016 00:56
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