Abundance and residency patterns of common bottlenose dolphins (Tursiops truncatus) in freshwater-influenced estuaries of the northern Gulf of Mexico

Multiple stressors are affecting common bottlenose dolphins in the northern Gulf of Mexico, including two embayments in Alabama, Mobile Bay (MOB) and Perdido Bay (PER), where no comprehensive abundance estimates and residency data are currently available.

This study provides the first seasonal abundance estimates and residency patterns for bottlenose dolphins in MOB and PER and discusses the effects of seasonal entry of large volumes of freshwater on dolphin abundance.

In MOB, abundance estimates were larger in summer, with the highest abundance recorded in summer 2022 (1,712 dolphins, 95% CI: 1,520-1,928) and the lowest in winter 2019-20 (518 dolphins, 95% CI: 260-1,032). The opposite pattern was found in PER, where abundances were larger in winter, with the highest abundance in winter 2021-22 (191 dolphins, 95% CI: 157-232) and the lowest in summer 2020 (100 dolphins, 95% CI: 81-122).

Stronger residency patterns were found in PER, with 28% (n = 52) encountered in more than three seasons compared to MOB where only 9% (n = 57) were encountered in more than three seasons.

The two studied embayments support a larger number of dolphins than previously documented and likely provide seasonally different resources, indicating high and potentially complex use of these estuaries. Combined with other data concurrently collected in this area, this study will inform conservation management and strategies for these highly impacted dolphin stocks.

多重压力因素正影响着墨西哥湾北部的普通宽吻海豚，其中包括美国阿拉巴马州的两个海湾——莫比尔湾（Mobile Bay, MOB）和佩尔迪多湾（Perdido Bay, PER），这两个区域目前尚未有全面的种群数量估算与居留数据。

本研究首次提供了MOB和PER区域宽吻海豚的季节性种群数量估算与居留模式，并探讨了季节性大量淡水输入对海豚种群数量的影响。

在MOB区域，夏季的种群数量估算值更高，2022年夏季记录到最高数量（1712头海豚，95%置信区间（95% Confidence Interval, CI）：1520-1928），而2019-2020年冬季数量最低（518头海豚，95% CI：260-1032）。PER区域则呈现相反模式：冬季种群数量更高，2021-22年冬季数量最高（191头海豚，95% CI：157-232），2020年夏季数量最低（100头海豚，95% CI：81-122）。

PER区域的海豚居留模式更为稳定：在三个以上季节中被观测到的个体占比达28%（n=52），而MOB区域该比例仅为9%（n=57）。

研究结果显示，这两个海湾的海豚种群数量高于此前记录，且可能提供季节性差异资源，表明这些河口湾被海豚高度且潜在复杂地利用。结合该区域同期收集的其他数据，本研究将为受影响严重的海豚种群保护管理与策略制定提供参考。