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Influence of environmental factors on population structure of Arrow Squid Nototodarus gouldi: Implications for stock assessment

Green, CP 2011 , 'Influence of environmental factors on population structure of Arrow Squid Nototodarus gouldi: Implications for stock assessment ', PhD thesis, University of Tasmania.

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As separate stocks within a fishery can function differently, ensuring
sustainability of each is fundamental when establish or refining management
regulations and relies on a firm comprehension of the biological, recruitment,
growth, predator-prey, and mortality characteristics in response to environmental
factors and fishing pressure. The aim of this study was to analyse the population
structure, recruitment variability, migratory characteristics, and catch composition of
the arrow squid Nototodarus gouldi collected in the Great Australian Bight (GAB)
and Victoria from 2007 – 2009. Nototodarus gouldi is a common oceanic
ommastrephid found in waters of southern Australia and are considered
commercially and ecologically important. Although research on N. gouldi has
already provided biological and population characteristics for fisheries assessments,
better estimates of temporal and spatial variability of population structure and the
processes responsible are required. Completing their lifecycle in less than one year,
N. gouldi exhibited substantial variability in growth, spatial distribution, and
recruitment; processes considered to be highly influenced by environment and
oceanic factors such as water temperature and productivity. Comparing statolith
shape and biological characteristics from squid collected in Victoria to squid
collected in the GAB suggested significant phenotypic heterogeneity in stocks;
whereas statolith elemental composition analysis indicated that N. gouldi caught at
either location hatch throughout their distribution. Both male and female N. gouldi
grew faster and were larger in cooler waters off Victoria compared with warmer
waters of the GAB. The correlation of sea surface temperature (SST) with growth
showed that juveniles experiencing greater SST resulted in slower growth in the
GAB; however, juveniles experiencing greater SST had faster growth in Victoria.
Distribution of hatch dates calculated from statolith age estimates suggested that N.
gouldi collected in Victoria and the GAB during 2007 – 2009 hatch year round with
peaks of greater recruitment. Comparing the catch composition of N. gouldi caught
inshore from the jig fishery to squid caught offshore from the trawl fishery using
measures of size and growth suggested that squid caught inshore by jiggers were
larger, consisted of more males than females, and had a greater percentage of mature
females. However, statolith elemental composition from N. gouldi collected at inshore and offshore locations was likely to be driven by uniform ocean water
chemistry and squid physiological processes. Based on biology, reproductive,
recruitment, and growth characteristics of N. gouldi found in southern Australia,
current fishing effort is unlikely to jeopardize the sustainability of the resource.

Item Type: Thesis - PhD
Authors/Creators:Green, CP
Keywords: arrow squid, population, stock, environment growth, sustainability, assessment
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