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）是开展水肺潜水（SCUBA）鲨鱼生态旅游的热门看点。该物种被《2008年濒危物种红色名录》（IUCN）列为“全球易危（Vulnerable）”等级（来源：www.iucnredlist.org/）。悉尼玛鲁布拉近海的魔力角（Magic Point）深受希望观测这类鲨鱼的休闲水肺潜水爱好者青睐。本研究的目标是通过实验探究休闲水肺潜水活动对鲨鱼行为的影响程度。本研究评估了鲨鱼对以下三类变量的响应：潜水员群体规模（4人、8人、12人）、时段（上午、正午、下午）以及潜水员与鲨鱼的间距（3米、6米）。研究发现，本观测点的潜水活动确实会对鲨鱼的聚集、游动及呼吸行为产生影响，尽管该影响仅为短期效应。潜水员群体规模对鲨鱼的聚集行为无显著影响，但潜水员与鲨鱼的近距离接触是关键影响因素。当潜水员距离洞穴3米时，洞穴内的鲨鱼分布会发生显著变化；而当间距为6米时，鲨鱼分布则保持不变。当12名潜水员组成的大群体在3米距离处开展活动时，该现象尤为明显：此时鲨鱼的游动速度提升，换气方式从“主动换气”转为“RAM式换气（RAM ventilation）”，且该行为变化同时伴随着换气频率的骤然下降。本研究结果表明，上述影响均为短期效应，一旦潜水人员撤离，鲨鱼便会恢复原有行为模式。若潜水人员遵守本观测点现行的潜水操作守则，则从长期来看，其活动不太会对灰护士鲨造成实质性影响。