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Start date: 2022Subject: search.filters.subject.310305 Marine and estuarine ecology (incl. marine ichthyology)

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    Studies of the life history of school sharks (Galeorhinus galeus) : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy (PhD) in Ecology at Massey University, Albany, New Zealand
    (Massey University, 2025-09-26) Burton, Alex J. C.
    The school shark (Galeorhinus galeus) is a globally distributed, migratory species that was recently reclassified, globally, as Critically Endangered due to all but the New Zealand population having collapsed due to overfishing. Effective management and recovery of these populations is currently limited by a lack of accurate biological information, which is increasingly difficult to obtain due to the scarcity of school sharks throughout their range. By studying the last stable school shark population, located in New Zealand, the aim of this thesis is to provide accurate information on the biology of school sharks to better inform their management worldwide. Specifically, this thesis examines allometric relationships, inter-population variation in life-history stage transitions, intra-population variation in juvenile growth rates, extent of the transfer of elements from mother to pups, and the spatio-temporal connectivity of habitats important to life-history. To enable better standardisation of length data when combining datasets, the optimal model for converting between different length measurements of school sharks was first identified. After standardising length and life-history stage data, a novel Bayesian generative classifier model suggested that length at life-history stage transitions varied among several, globally distributed, school shark populations. A study of juvenile school shark growth across several regions in New Zealand (i.e., Kaipara Harbour, Tasman and Golden Bays, and the Canterbury Bight) revealed that somatic (increase in body length with age) and hepatosomatic (increase of energy stores in the liver with age) growth was consistent among regions, but body condition was generally greater in the Canterbury Bight compared to other two regions. Tracking the year-long, three-dimensional movements of large female school sharks tagged in the Kaipara Harbour with satellite tags showed these sharks dispersed to several potentially important reproductive and feeding habitats around New Zealand. Finally, nutrients and essential and non-essential elements maternally provided to developing young were likely sourced from those assimilated from the mother’s diet during vitellogenesis. This thesis has national and international implications for school sharks and other elasmobranch species, as it provides information and techniques crucial to better understanding the biology of species that is needed to inform more effective management and recovery efforts.
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    Foraging ecology and habitat suitability of the critically endangered New Zealand fairy tern or tara iti (Sternula neresis davisae) in Northland, New Zealand : a thesis present in partial fulfilment of the requirements for the degree of Master of Science in Conservation Biology at Massey University, Albany, New Zealand
    (Massey University, 2023) Ball, Jacob John
    This thesis aimed to improve scientific knowledge of the critically endangered New Zealand Fairy Tern/Tara iti (Sternula nereis davisae) (hereafter; NZFT) foraging ecology, measuring three key elements; (1) Behavioural time budget analysis; (2) Spatial interactions; (3) Dietary analysis through stable isotopes. Current knowledge of NZFT behaviour has been limited to observational and ad-hoc approaches. Coordinated behavioural observations occurred on 13 individuals (21% of population) throughout the 2021/22 breeding season in Mangawhai, New Zealand. A mean foraging trip length of 17 ± 1 min was determined for adult provisioning NZFT, during which they spent 97% of their time performing foraging related behaviours. I observed 17 flight paths and 25 dive locations outside of the estuary in coastal marine environment. Estuarine habitats accounted for less foraging trips than expected, suggesting the importance of other habitats. With the human population of Mangawhai predicted to increase over the next 30 years, I aimed to understand the current spatial use of Mangawhai estuary and surrounding areas by NZFT and people providing a baseline to support future management. Spatial data collection on dive and resting locations, and activities of humans were undertaken using GIS over the 2021/22 breeding season. Kernel density maps were compared through visual analysis and supported territorial foraging theory. Peak human presence occurred during the fledging period of NZFT chicks, highlighting need for management of human activities within Mangawhai estuary. This study used stable isotopes δ¹³C and δ¹⁵N to provide analysis into NZFT diets using chick feathers. Thirty-one feathers were obtained from four breeding seasons and analysis undertaken following previous methods (Ismar et al., 2014). Reference fish samples (n = 52) were obtained from Mangawhai estuary and Bream Bay, New Zealand. I found a higher proportion of marine prey in 2022 than other years, however, this was not statistically significant. Marine foraging was not shown to influence chick survival. Findings from my thesis highlight the role of the marine environment as an integral part of NZFT foraging habitat during breeding, complementary to estuarine foraging territories. Furthermore, my thesis results provide key baseline data for this species, emphasizing potential impact of increased human pressure.
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    Variation in corallite morphology and Symbiodiniaceae communities of corals at the Rangitāhua archipelago : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Conservation Biology at Massey University, Albany, New Zealand
    (Massey University, 2022) Gibson, Claudia
    Anthropogenic activity is causing climate change, exposing corals to intolerable conditions. The depletion of corals can severely degrade reef-associated species. Therefore, a greater understanding of corals’ responsiveness to environmental conditions is needed, especially near their tolerance limits. Here, we examined the corallite morphology and Symbiodiniaceae community of corals at Rangitāhua (the Kermadec Islands), New Zealand. Due to the high latitude of Rangitāhua, corals and their symbionts experience light conditions near their lower tolerance limit, therefore we expected to find morphological signatures of adaptation to low-light conditions indicative of a trophic shift, Symbiodiniaceae depth zonation (5-30m), and a high abundance of the physiologically diverse coral symbiont Cladocopium. We also expected that environments might differ among islands, and therefore corallite morphology and symbiont communities would vary among locations. We found a high abundance of Cladocopium, and a much lower abundance of Symbiodinium, Breviolum, and Fugacium. At Napier Island, Symbiodiniaceae communities of Astrea curta, Hydnophora pilosa, and Montipora spongodes had the fewest unique Symbiodiniaceae types and were most compositionally dissimilar to the communities at the more sheltered Meyer Islands. Furthermore, corals at Napier Island had small, densely arranged corallites, with few, short septa, suggesting low water flow. Over depth, shallow corals (5m) had high tissue coverage (i.e., large, close corallites of M. spongodes and greater corallite coverage of H. pilosa) presumably to optimise autotrophic feeding in energy-rich waters. The greater corallite spacing seen over depth could be a mechanism to alleviate self-shading but could also be indicative of poor health. The Symbiodiniaceae communities at intermediate depths (10-20m) were taxonomically richer and compositionally dissimilar from communities at the edges of the depth gradient (5-10m and 20-25m). Although there were general trends, the corallite morphology and Symbiodiniaceae community of Goniastrea favulus, Montipora capricornis, and Turbinaria frondens were relatively consistent across the depth and locations sampled. Nearly half of the Symbiodiniaceae types identified (22/42) were undocumented, highlighting the significance of marginal populations to our understanding of how environmental conditions can influence corals. Our examination of the coral population at Rangitāhua further supports the well-documented trends of a high abundance of Cladocopium symbionts at high latitudes, specialised corallite morphology to increase the light-gathering abilities of shallow corals, and increased corallite spacing over depth, as well as Symbiodiniaceae depth zonation and diversity among nearby locations. Overall, we provide insights into the morphological and symbiont diversity of marginal coral populations in low light conditions, helping us to understand how corals may persist, and perhaps refuge, in high latitudes.