DataSheet_2_Pantropical spotted dolphin (Stenella attenuata attenuata) abundance estimates in Maui Nui, Hawaiʻi reveal small population in need of monitoring.pdf

IntroductionRecent minimum population estimates are critical for effective marine mammal conservation, yet such estimates are often lacking at the stock or management level. Throughout the Main Hawaiian Islands, pantropical spotted dolphins (PSD; Stenella attenuata attenuata) are comprised of a pelagic and three island-associated stocks (O‘ahu, 4-Islands, and Hawai‘i Island). The insular stocks, in particular, face multiple anthropogenic and natural threats such as vessel impacts, fisheries interactions, marine debris, climate change, and disease. Prior to this study, no abundance estimates of the 4-Islands (i.e., the Maui Nui region) PSD stock existed that were suitable for management use and inclusion in stock assessment report calculations.MethodsWe generated annual mark-recapture abundance estimates of naturally marked adults in a POPAN-framework using photo-identification data collected from small-boat surveys during 2014–2022 in the Maui Nui region. We extrapolated these estimates to the wider population using dorsal fin mark rates.Results and discussionWe collected data on 62 groups of PSD, throughout all months of the year, and with an average group size of 55.70 (SD = 17.31). We analyzed encounter histories of 174 distinct individuals. Annual recapture rate averaged 1.84 (SD = 1.32) with a maximum of 7. Individuals detected per year averaged 35.67 (SD = 21.16) with a maximum of 77 in 2017. Overall mark rate was 0.495 (SE = 0.010), resulting in total annual abundance estimates that averaged 154.87 (SE = 14.25) and ranged from 105 (SE = 13) in 2014 to 232 (SE = 31) in 2017. Although abundance estimates fluctuated, generally 250 animals or less used the study area each year and we found no overall evidence of a trend. Our benchmark results revealed a small population in need of monitoring given the numerous threats facing this stock, the uncertainty of their impacts, and the decreased resiliency and recovery potential of small populations to negative demographic and environmental stochastic events. Our findings, including documenting long-term site fidelity and year-round presence of PSD in Maui Nui, further signify this area as one of future research and conservation importance.

近年来，对海洋哺乳动物的有效保护迫切需要最新的最小种群估计数据，然而，在种群或管理层面，此类估计往往缺失。在主夏威夷群岛地区，泛热带斑纹海豚（PSD；Stenella attenuata attenuata）由一群浮游海豚和三个岛屿相关种群（包括欧胡岛、4岛群和夏威夷岛）组成。特别是岛屿相关种群，面临着多种人为和自然威胁，如船舶撞击、渔业交互作用、海洋垃圾、气候变化以及疾病。在本研究之前，4岛群（即毛伊努伊地区）的PSD种群尚未存在适用于管理目的且可用于种群评估报告计算的丰度估计。方法上，我们采用POPAN框架，利用2014年至2022年期间在毛伊努伊地区通过小型船只调查收集的照片识别数据，对自然标记的成年海豚进行了年度标记-重捕丰度估计。我们利用背鳍标记率将这些估计外推至更广泛的种群。结果与讨论中，我们收集了62组PSD全年各月的数据，平均每组群体大小为55.70（标准差=17.31）。我们分析了174个不同个体的遭遇历史。年度重捕率平均为1.84（标准差=1.32），最高为7。每年检测到的个体平均为35.67（标准差=21.16），2017年最高达77。总体标记率为0.495（标准误=0.010），导致总年度丰度估计平均为154.87（标准误=14.25），范围从2014年的105（标准误=13）到2017年的232（标准误=31）。尽管丰度估计存在波动，但通常每年有250只或更少的动物使用研究区域，我们没有发现整体趋势的证据。我们的基准结果显示，鉴于该种群面临众多威胁、其影响的不确定性以及小种群对负面人口和环境影响随机事件的抗逆性和恢复潜力下降，这一种群需要监测。我们的发现，包括记录了PSD在毛伊努伊长期对特定地点的忠诚度和全年存在的现象，进一步将该地区确定为未来研究和保护的重要区域。