Corey_Green_Thesis_28_October_2011_single_sided_signed.pdf (3.46 MB)
Influence of environmental factors on population structure of Arrow Squid Nototodarus gouldi: Implications for stock assessment
thesisposted on 2023-05-26, 07:10 authored by Green, CP
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 ‚Äö- 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 ‚Äö- 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.
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