The effect of SCUBA diver interactions on the aggregation and behavior of the Spotted Ragged-tooth Shark (Carcharias taurus) - Assessing human impact on the resting behavior of ragged-tooth sharks through remote underwater photo data analysis

Abstract

The urgent need for consorted efforts in the protection of marine ecosystems and species has been raised by natural conservation organizations all over the world. As predators, sharks maintain a vital balance in marine ecosystems, but are today threatened by extinction; a result of overfishing, habitat destruction, and being caught as bycatch in large-scale commercial fishing. Many species of sharks are slow to recover after disturbance and so protecting the habitats of natural populations is integral to maintaining their viability in the wild. This study examined the effects of SCUBA diver exposure on the behavior of the spotted ragged tooth shark (Carcharias taurus), as they migrate to the protected reefs of Sodwana Bay during a particularly vulnerable stage of their reproductive cycle. Using remote underwater cameras, long term monitoring of the sharks was made possible at two different reefs, one where diving was allowed and one within a Wildlife Sanctuary zone. Several metrics for shark behavior were devised to make use of the photographic data, and mixed effect linear models were created to model shark agitation levels and group behavioral differences between the reefs and in response to diver presence. Significant differences between the reefs were found for shark group size and swimming speed, indicating a higher level of agitation at the reef where divers frequently visit. Swimming speed was seen to further increase significantly on days where divers had visited the reef, but larger dive groups was not found to have greater impact than smaller ones. Sharks within the sanctuary zone were found to rely less on large groups to exhibit restful behavior, instead acting more independently. The findings of this study contribute to a larger body of research submitted in an annual report to iSimangaliso Wetland Park, informing future management decisions. As such, possible conservation measures and areas for potential future research is brought up in the discussion section of this report.