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Spatial and temporal variation in growth and age composition of the temperate wrasse Notolabrus fucicola in Tasmanian waters


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Ewing, GP 2004 , 'Spatial and temporal variation in growth and age composition of the temperate wrasse Notolabrus fucicola in Tasmanian waters', Research Master thesis, University of Tasmania.

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The mechanisms that determine the age and size structure of a population are not well
understood for temperate reef species and are functionally divided into pre-settlement
and post-settlement processes. Their relative importance in structuring populations
can be inferred from spatial comparisons of adult age composition and growth rates,
provided factors that obscure or bias the ability to detect signals from early life history
are considered. These factors include migration, fishing mortality and methodological
issues such as ageing errors and size-selectivity of sampling gears.
The biological features that promote Notolabrus fucicola as a suitable species for
demographic research and the highly variable hydrology of the east and southeast
coasts of Tasmania, provide an opportunity for examination of the relative roles of
pre-and post-recruitment processes in structuring temperate reef populations. In
addition, N. fucicola is the primary target of a commercial live wrasse fishery that has
developed over the last decade in Tasmania, necessitating an understanding of its
population dynamics for effective management.
Notolabrus fucicola were collected using baited traps from six locations around the
east and southeast coasts of Tasmania. A methodology for age estimation was
developed using thinly sliced transverse sagittal otolith sections and the periodicity
and timing of increment formation, location of the first annual increment and
precision of age estimations were validated.
A size-selectivity function for the traps was calculated directly from sampling an
isolated population of N. fucicola of known size structure, generated from a simulated
fish-down using tags. The selectivity function was used to reconstruct the raw size
and age structures from which fishing mortality was estimated. Fishing mortality
varied spatially, with strong mortality prior to the minimum legal size limit implied at
some sites.
Spatial comparisons of growth were not biased by fishing mortality and indicated that
growth rates followed the sea surface temperature gradient, but did not follow trends
in fishing mortality, diet or reef structure. Given that growth is sensitive to resource limitation,
the spatial trend in growth rates suggested that populations of N. fucicola
were not structured by post-settlement density-dependent mortality.
Spatial and temporal comparisons of selectivity-corrected age compositions, whilst
primarily detecting differences in the level of fishing mortality between sites,
indicated low variation in relative year class strength. This result is consistent with
recent findings suggesting that N. fucicola are well adapted to maximize larval
survival despite the highly variable coastal hydrography. Thus, it is likely that
populations of the temperate wrasse N. fucicola are primarily structured by larval

Item Type: Thesis - Research Master
Authors/Creators:Ewing, GP
Keywords: Wrasses
Copyright Holders: The Author
Copyright Information:

Copyright 2004 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 ( MAppSc. )--University of Tasmania, 2004. Includes bibliographical references

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