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Comparative Analysis of Snapper (Chrysophrys auratus) Otolith Microchemistry to Ascertain Early Life Fine-Scale Movement Patterns

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Date

2023

Authors

Raby, Harrison

Supervisor

Sabetian, Armagan
Zhang, Jingjing
Lilkendey, Julian

Item type

Thesis

Degree name

Master of Science

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Publisher

Auckland University of Technology

Abstract

Understanding the early life habitat interactions and movements of fish is vital for fisheries management because it provides vital information such as their post/pre-settlement and nursery habitat use. Currently, there is a lack of high-resolution information on early life habitat dynamics of snapper (Chrysophrys auratus) stocks around New Zealand. Snapper are one of the most abundant coastal reef fish in New Zealand belonging to the sea bream family Sparidae. Their prevalence in nearshore waters has been evident since human arrival in New Zealand, making up over 70% of fish remains found in Māori middens dating as far back as 700 years. Snapper also have significant economic and social value as they support one of New Zealand’s largest and most valuable inshore commercial and recreational fisheries. Otoliths, because of their accretionary nature can act as a biological chronometer and record valuable chemical information from ambient waters across the lifetime of an individual. As such, otolith microchemistry information can be used to provide high-resolution information on the ontogenetic growth and movement of fishes. Our objective was to use the recently developed otolith time-series analysis in Sabetian et al. (2021) to compare patterns in the temporal habitat use of early life stage snapper recorded in their otolith chemistry profile. We collected both contemporary and historical snapper otoliths from a variety of locations around the upper North Island of New Zealand. Our modern-day samples included assemblages from the Hauraki Gulf and Doubtless Bay, while our historical samples included an assemblage from 1975 Hauraki Gulf, and an archaeological midden from Long Bay (Hauraki Gulf) dated between 1430 and 1485 CE. Otoliths were sectioned and prepared for laser ablation inductively coupled mass spectrometry (LA-ICP-MS). The collected time-series data were then subjected to Behavioural Change Point Analysis (BCPA) coupled with k-means clustering in order to infer residency and migration behaviour between different environments based on the elemental concentrations of Barium (138Ba) and Strontium (88Sr). Our results for habitat residency times showed that all groups spent the most amount of time in the marine state, averaging 46.5%, followed by estuarine at 35.8%, and the least amount of time in riverine states, averaging 17.8%. There was no significant difference in the amount of time spent in different habitats between different sites and assemblages. The number of transitions between habitats showed the most common transitions were between estuarine and riverine across all groups with an average of 26.4 transitions. The lowest number of transitions between environments was between riverine and marine with an average of 2.6. There was no statistical difference in the number of switches in states between the sites. Results for movements between different aquatic habitats showed marine dominant signatures very early on, confirming hatching at sea, followed by a short period of estuarine residency which transitions into a riverine environment. The riverine habitat then becomes the predominant environment for a short period before the transition back to estuarine environment begins. The estuarine environment signatures start to become stronger with some minor riverine transitions. Marine signatures then become prevalent post-settlement, gradually becoming the dominating habitat after 1 year of age. These results show that time-series analysis using tools such as BCPA can unlock fine-scale information which can be used to infer pre- and post-settlement life-history movement patterns of snapper. The novel nature of our methodological approach has also uncovered essential information in the largely unexplored comparison of laser ablation technique, which will help the methodological advancement of otolith microchemistry.

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http://hdl.handle.net/10292/16310

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