Investigating variation in the diet and foraging ecology of the long-finned pilot whale (Globicephala melas edwardii) in Aotearoa New Zealand waters: A thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Zoology at Massey University Albany, New Zealand
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2023-12-20
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Massey University
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Abstract
Knowledge of foraging ecology is essential to understanding how species interact with the ecosystem they inhabit. Foraging variation due to ontogenetic and/or anthropogenic factors can affect individual body condition, which could have implications for reproductive fitness and survivorship. Despite a high stranding frequency, limited knowledge is available on the foraging ecology of long-finned pilot whales (LFPWs; Globicephala melas edwardii) within New Zealand waters. To address these knowledge gaps, multiple methods of dietary analysis (stomach content analysis, n = 283; stable isotope analysis, n = 125; and fatty acid analysis, n = 15) were performed on samples collected from carcasses of LFPWs stranded along the New Zealand coast between 2009 and 2017. Six new taxa contributed to LFPW diet, including the first report of fish consumption for this population. Whilst arrow squid Nototodarus spp. was determined to be the most important prey, both ontogenetic and spatiotemporal variation were noted in prey consumption. Stomach content, stable isotope and fatty acid investigations all supported a preference for pelagic feeding. However, both stomach content and stable isotope investigations also documented occasional benthic/coastal foraging, especially for mature male LFPWs and in the year 2017. Biochemical dietary tracers examined in five of the top prey species to LFPW diet at Farewell Spit suggested that prey investigated were not chemically similar and/or at least one key prey species was missing from analysis. Initial insights gained from morphometric body condition measurements signalled that axillary girth may explain some variation in the proportion of saturated, polyunsaturated fatty acids and dietary fatty acid C20:1n9 in the inner layer of dorsal blubber, though sample sizes were small. Given the sustained reliance on arrow squid in the diet of this species, monitoring of overlap between regions of commercial fisheries and LFPW foraging in these waters, in part through continued support of long-term data sets, is recommended. Furthermore, the importance of accurate body condition measurements and their potential for use in welfare assessment and strandings situations is discussed. Recommendations for future research, include telemetry studies, further investigation of fatty acid and body condition biomarkers in LFPWs and prioritisation of analysis of LFPW dietary samples collected during the austral winter.