| Summary: | The quantification of a species’ trophic niche is important to understand the species ecology and its interactions with the ecosystem it resides in. Despite the high frequency of long-finned pilot whale (<i>Globicephala melas edwardii</i>) strandings on the Aotearoa New Zealand coast, their trophic niche remains poorly understood. To assess the isotopic niche of <i>G. m. edwardii</i> within New Zealand, ontogenetic (sex, total body length, age, maturity status, reproductive group) and spatiotemporal (stranding location, stranding event, and stranding year) variation were investigated. Stable isotopes of carbon (<i>δ</i><sup>13</sup>C) and nitrogen (<i>δ</i><sup>15</sup>N) were examined from skin samples of 125 <i>G. m. edwardii</i> (67 females and 58 males) collected at mass-stranding events at Onetahua Farewell Spit in 2009 (<i>n</i> = 20), 2011 (<i>n</i> = 20), 2014 (<i>n =</i> 27) and 2017 (<i>n =</i> 20) and at Rakiura Stewart Island in 2010 (<i>n =</i> 19) and 2011 (<i>n =</i> 19). Variations in <i>δ</i><sup>34</sup>S values were examined for a subset of 36 individuals. General additive models revealed that stranding event was the strongest predictor for <i>δ</i><sup>13</sup>C and <i>δ</i><sup>15</sup>N values, whilst sex was the strongest predictor of <i>δ</i><sup>34</sup>S isotopic values. Although similar within years, <i>δ</i><sup>13</sup>C values were lower in 2014 and 2017 compared to all other years. Furthermore, <i>δ</i><sup>15</sup>N values were higher within Farewell Spit 2017 compared to any other stranding event. This suggests that the individuals stranded in Farewell Spit in 2017 may have been feeding at a higher trophic level, or that the nitrogen baseline may have been higher in 2017 than in other years. Spatiotemporal differences explained isotopic variation of <i>G. m. edwardii</i> in New Zealand waters better than ontogenetic factors.
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