Community structure and biology of the elasmobranchs of Hervey Bay, southeast Queensland, Australia

Adrian Gutteridge (2011). Community structure and biology of the elasmobranchs of Hervey Bay, southeast Queensland, Australia PhD Thesis, School of Biological Sciences, The University of Queensland.

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Author Adrian Gutteridge
Thesis Title Community structure and biology of the elasmobranchs of Hervey Bay, southeast Queensland, Australia
School, Centre or Institute School of Biological Sciences
Institution The University of Queensland
Publication date 2011-09
Thesis type PhD Thesis
Total pages 189
Total colour pages 23
Total black and white pages 166
Language eng
Subjects 060308 Life Histories
070403 Fisheries Management
060205 Marine and Estuarine Ecology (incl. Marine Ichthyology)
Abstract/Summary The implementation of fisheries-dependent and fisheries-independent sampling was used to assess the community structure of elasmobranchs within Hervey Bay, Queensland, Australia. Hervey Bay is the largest embayment on Australia’s east coast and the elasmobranch community within the bay was previously unstudied. Fisheries-dependant sampling focused on the Hervey Bay component of the East Coast Inshore Fin Fish Fishery (ECIFFF) by investigating the composition of sharks within the fishery and providing a preliminary population assessment on two commonly captured species. Fisheries-independent sampling investigated the population structure and habitat partitioning of elasmobranchs within Hervey Bay, by intensively sampling three sites over a two year-period. Lastly, the biology and ecology of the most commonly encountered shark during fisheries-independent sampling, the slit-eye shark Loxodon macrorhinus, was investigated to provide detailed life history information for this understudied species. Thirteen species of shark were recorded from market surveys and observer trips conducted within the ECIFFF of Hervey Bay. Carcharhiniform sharks, particularly fam. Carcharhinidae, dominated the catch with the spinner shark Carcharhinus brevipinna, the milk shark Rhizoprionodon acutus and the blacktip whaler complex of C. tilstoni and C. limbatus the most abundant species. Preliminary stock assessments were carried out for C. brevipinna and C. tilstoni/limbatus, indicating that C. brevipinna was overfished and C. tilstoni/limbatus was fished at moderate to high levels. However, as the catch of both species was predominantly age-0 animals, demographic analysis is required to determine how the current fishing pressures are affecting the overall populations. A two-year fisheries-independent survey within Hervey Bay sampled elasmobranchs from three c. 10 km equidistant sites, Moon Point, Point Vernon and German Creek. The sampled elasmobranch fauna was abundant and highly diverse, with 30 species identified. Although neonates were seldom caught, the high proportion of species with juveniles as the most common age-class suggest that Hervey Bay acts as an important area for the early life-stages of many elasmobranchs. Spatial habitat partitioning was detected by elasmobranchs among the three sampled sites, with the most abundant shark during fisheries-independent sampling, L. macrorhinus, being caught exclusively at Moon Point. Temporal partitioning was also evident, with summer months having the highest catch rates and diversity of any season. The diet of L. macrorhinus was dominated by teleosts, with prawns and cephalopods forming the second and third most important prey groups, respectively. Although it was hypothesised that the high abundance of L. macrorhinus at Moon Point was driven by prey availability, there was no overlap between the diet and the distribution of surrounding prey communities sampled using baited remote underwater video (BRUV). Rather, the species demonstrated a high affinity toward the clear water present at Moon Point, opposing three other commonly encountered shark species that appeared to favour turbid water. Combined, these results suggested that the distribution of L. macrorhinus was not driven by prey availability, but other factors, such as predator avoidance or a reduction in inter-specific competition. The life-history of L. macrorhinus was investigated within Hervey Bay. Total length at (LT) 50 % maturity (L50) for females and males, was 665 mm and 717 mm, respectively. Females produced annual litters of between 1 - 2 pups (mean 1.9 ± 0.3 S.D.) with mating occurring from December–February. Ovulation occurred from December–March, with parturition the following December and January after a gestation of 9–12 months. Three growth models were used to examine length-age relationships, with the 3-parameter von Bertalanffy providing the best fit for females and males. For females, L∞ = 895 mm LT, k = 0.18 and t0 = -6.3, and for males L∞ = 832 mm LT, k = 0.44 and t0 = -2.6. From these models, age at 50 % maturity (A50) for females and males was 1.2 and 1.9 years, respectively. Overall, L. macrorhinus demonstrates similar life-history characteristics to other small-bodied carcharhinid sharks, and fast growth and early maturation when compared to larger-bodied carcharhinids.
Keyword Chondrichthyan
Hervey Bay
commercial fishery
Life History
Additional Notes Colour: 18, 19, 22, 35, 63, 70, 74, 76, 92, 94, 112, 116, 118, 120, 126, 129, 135, 161, 168, 170, 173, 178, 183 Landscape: 48, 51, 55, 57, 58, 59, 80, 148, 156, 158

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Created: Thu, 31 May 2012, 14:04:44 EST by Mr Adrian Gutteridge on behalf of Library - Information Access Service