A video and photographic study of aggregation, swimming and respiratory behaviour changes in the Grey Nurse Shark (Carcharias taurus) in response to the presence of SCUBA divers

The Grey Nurse Shark (Carcharias taurus) is a popular attraction for shark eco-tourism using SCUBA. The species is also ‘globally Vulnerable’ (IUCN 2008. List of Threatened Species. www.iucnredlist.org/). Magic Point (off Maroubra) in Sydney is favoured by recreational SCUBA divers wishing to observe these sharks. The objective of this study was to experimentally test the level of the activities of recreational SCUBA divers on shark behaviour. This study assessed the shark responses to diver group size (4, 8 and 12), time of day (am, noon and pm) and diver distance from the sharks (3 m and 6 m). The study found that diver activity does affect the aggregation, swimming and respiratory behaviour of sharks at this site, albeit at short-term levels. Diver group size had no significant effect on shark aggregation, but the proximity of divers to the sharks was crucial. Shark distribution in the cave changed significantly in the presence of divers at 3 m distance from the cave, but stayed unchanged at 6 m. This was particularly apparent in the presence of large groups of 12 divers at 3 m distance when sharks increased their swim speed and ventilation mechanism from ‘active’ to ‘RAM’ ventilation. Such change coincided with a sudden decrease in ventilation frequency. Our research suggests that these effects are short-term and that sharks resume their behaviour once the divers retreat. If divers abide by the current code of practice for diving at this site, it is unlikely that their activities will substantially impact Grey Nurse Sharks in the long term.灰护士鲨（Carcharias taurus）是水肺潜水（SCUBA）鲨鱼生态旅游的热门观赏对象。该物种被列为“全球易危”物种（国际自然保护联盟（IUCN）2008年《濒危物种红色名录》，www.iucnredlist.org/）。悉尼马鲁布拉近海的魔力角深受希望观测此类鲨鱼的休闲水肺潜水爱好者青睐。本研究旨在通过实验量化休闲水肺潜水活动对鲨鱼行为的影响程度，考察了鲨鱼对三类变量的响应：潜水员群体规模（4人、8人、12人）、观测时段（上午、正午、下午）以及潜水员与鲨鱼的间距（3米、6米）。研究结果显示，潜水活动会对该区域鲨鱼的聚集、游动与呼吸行为产生短期影响；潜水员群体规模对鲨鱼聚集行为无显著影响，但潜水员与鲨鱼的间距是关键影响因素。当潜水员距离洞穴3米时，鲨鱼在洞穴内的分布会发生显著变化，而间距为6米时则无明显改变，这一现象在12人规模的潜水群体于3米间距处时尤为显著：此时鲨鱼游动速度提升，呼吸机制从“主动通气”切换为“RAM通气”，且伴随呼吸频率的骤然下降。本研究表明此类影响均为短期效应，潜水人员撤离后鲨鱼可恢复原有行为模式；若潜水人员遵守该区域现行的潜水操作规范，其活动从长期来看不会对灰护士鲨造成实质性影响。