Utilisation of vertebral microchemistry techniques to determine population structure of two inshore shark species along the east coast of Queensland, Australia

Schroeder, Ron (2011) Utilisation of vertebral microchemistry techniques to determine population structure of two inshore shark species along the east coast of Queensland, Australia. Masters (Research) thesis, James Cook University.

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Abstract

As apex predators, sharks have a controlling influence on the marine ecosystem. However, their life history traits of being slow growing, late maturing and slow reproducing make them vulnerable to overfishing. The East Coast Inshore Finfish Fishery on Queensland, Australia's east coast produces 1800 tonnes per year, of which 35% are sharks. Current management is based on quantitative data, largely focused on teleosts. A need exists to include stock structure and population connectivity to more effectively manage the fishery over the long term. The stock structure of two species commonly taken in this fishery was investigated to determine possible patterns of structuring. Rhizoprionodon acutus is a small, fast growing, and short lived species that demonstrates limited movement throughout their life. Sphyrna lewini is a larger, slower growing species that has some site attachment as juveniles, but travels widely as adults. Several techniques exist to determine stock structure, including genetics, life history variation, and various tagging methods. For teleosts, otolith microchemisry analysis using inductively coupled plasma mass spectrometry (ICPMS) is often utilised to infer stock structure. This project developed a method to utilise ICPMS on shark vertebra to determine stock structure. Upon confirmation of the method, twelve to twenty samples of S. lewini and R. acutus were collected from each of six locations on the Queensland and northern NSW Australian coast. Vertebrae were analysed by laser ablation ICPMS for Ba, Ca, Cu, Mg, Mn, Sr, and Zn. This data was then used to determine stock structure among both species.

Both solution based and laser ablation ICPMS were applied to shark samples for method development. Microchemical variation between individuals was greater than the inherent variation in the ICPMS processing for both solution and laser ablation methods. The corpus calcareum or intermedalia of vertebral centra gave similar results on the separation of individuals, but their microchemical compositions differed significantly. Difficulty in polishing the soft vertebrae sections led to surface contamination of sections, but this was isolated in the data analysis stage. Microchemical composition was also not affected by vertebral column position or size of the individual from which the sample was drawn. While either approach can be used to determine geographic population structure in sharks, laser ablation provided greater versatility by allowing isolation of various stages of life in the analysis.

Analysing the whole life mean and end of life mean microchemical signatures in both species, principal components analysis (PCA) demonstrated some separation, but with heavy overlap, between six regions along the Queensland coast. MANOVA confirmed separation and Hotellings T₂ pairwise comparisons demonstrated significant differences between all adjacent regions, except Townsville – Mackay. Lack of separation between these two sites may infer significant migration or may be indicative of similar environmental parameters influencing microchemical signature of animals in those two regions. This study supports existing knowledge of S. lewini showing some site attachment as juveniles, and R. acutus demonstrating limited migration throughout life. From a fishery standpoint, limited connectivity among metapopulations may exist, allowing for some replenishment capability. However, it would be prudent to manage these species on a regional basis.

Several areas exist to expand this innovative method. Development of a vertebra standard that more closely approximates a shark would improve sensitivity drift correction capabilities. Tuning the ablation parameters such as scan speed, sample frequency and power may improve utility of laboratory time and data resolution for analysis. Improvements may be made by gaining further insight as to the environment from which animals are collected. This may include water sampling of elemental concentrations, temperature or salinity. Collection of these data would also require intensifying fishing effort to minimise overall time window of sample collection in order to maximise benefits from the knowledge. Further method advancement could be made by analysing vertebrae from animals with known histories, particularly those tagged with GPS or acoustic telemetry devices.

Item ID: 32088
Item Type: Thesis (Masters (Research))
Keywords: microchemistry; shark vertebrae; Sphyrna lewini; Rhizoprionodon acutus; inductively coupled plasma mass spectrometry (ICPMS)
Date Deposited: 29 Apr 2014 05:57
FoR Codes: 07 AGRICULTURAL AND VETERINARY SCIENCES > 0704 Fisheries Sciences > 070403 Fisheries Management @ 50%
07 AGRICULTURAL AND VETERINARY SCIENCES > 0704 Fisheries Sciences > 070405 Fish Physiology and Genetics @ 50%
SEO Codes: 83 ANIMAL PRODUCTION AND ANIMAL PRIMARY PRODUCTS > 8302 Fisheries - Wild Caught > 830204 Wild Caught Fin Fish (excl. Tuna) @ 50%
97 EXPANDING KNOWLEDGE > 970105 Expanding Knowledge in the Environmental Sciences @ 50%
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