Spatial and temporal trends of Tamanend’s bottlenose dolphin (Tursiops erebennus) strandings in South Carolina, USA, 2006–2020

Abstract

Marine mammal strandings data contribute towards overall assessments of cetacean populations, including seasonal, annual and life‐history trends which result from both natural and anthropogenic causes. We conducted spatial and temporal analyses of Tamanend’s bottlenose dolphin (Tursiops erebennus) strandings in the waters of South Carolina, USA, over a 15‐year period from 2006 to 2020, with the following objectives: (1) to determine spatial and temporal trends; (2) to analyse seasonal reproductive trends; (3) to determine life‐history parameters, such as sex ratio and age class; (4) to determine the extent to which human interaction contributed to strandings; and (5) to compare stranding patterns with historical data from 1992–2005. A total of 837 strandings occurred over the study period, with a mean of 55.8 strandings per annum. The season with most strandings was Spring (April–June), while March and April had the highest number of strandings. A relatively equal number of male and females dolphins stranded, and mortality was highest in neonates, first‐year calves and adults. Neonatal strandings comprised 22.1% of all strandings and were predominant in May. Ninety‐five human‐interaction (HI) cases were observed, representing 22.9% of strandings where HI or non‐HI could be determined. Confirmed crab‐pot buoy‐line entanglements were the predominant HI category (n = 31). Density maps and hot spot analysis showed most strandings, including live and neonatal strandings and HI cases, occurred in defined areas of Charleston and Beaufort Counties. While many trends were similar to historical data, some new trends emerged, particularly an increase of strandings in March and April. Neonatal strandings decreased in November and the historical spike during this month has essentially disappeared. The results of this analysis serve as a tool to predict stranding rates and inform conservation and management decisions to better protect bottlenose dolphins.