Reef sharks are an important species that aid in the ecosystem surrounding reefs. As the top predators as an indicator species in which their decline or abundance shows a direct correlation with the state of the reef ecosystem, they are important in regards to the understanding and sustainability of reefs all over the world. However, due to poaching and increased human interactions/strains with the environment in which reef sharks live in as well as the sharks themselves, many species of reef sharks such as the blacktip and grey reef sharks are facing near threatening conditions of population decrease according to the International Union for the Conservation of Nature. To best understand the implications of humans on reef shark behavior, Jean-Baptiste Juhel and her colleagues have studied the extent of Grey Reef shark behavior by comparing Grey Reef shark feeding habits and activity in New Caledonia, an archipelago composed of a 400 km long main island with a series of smaller islands. They choose Grey Reef sharks as their model organism due to Grey Reef sharks being common and widely distributed across the Pacific region, are vulnerable to overfishing and prone to location extinction, and exhibit high curiosity/association to new and unusual occurrences as well as disturbances and show intimidation behaviors.
Jean-Baptiste and her team experimented with the Grey Reef sharks in different regions of New Caledonian archipelago in which they varied in human shark interactions: opened regions allowed for fishing, no-take regions which are allowed for traveling to but no fishing, and no entry regions which prohibited human involvement/interaction with the reserve; to see the impact of human involvement on the Grey Reef sharks feeding behavior. They aimed to record the behavior response of the sharks to bait in the different regions by using a video camera (stereo-BRUVs) and bait and categorize the shark’s response. They indicated that a “zero” was a repulsive or neutral response in which they didn’t approach and eat the bait, a “one” was a twisted approach in which they would turn toward the bait showing cautiousness to the bait, and a “two” in which they showed the highest level of motivation for the bait with no wariness towards the bait or the camera. They also set up stereo-BRUVs and bait in increasing increments from the capital region of the archipelago (where there is the most human density) to see the effects of feeding behavior in increasing increments of travel time between where the sharks were feeding and the distance to the capital (main island) of the archaeological with the highest human density. The final experiment that they wanted to test was the effects of differing abundance of competitors (other species of reef sharks) on the feeding behavior of Grey Reef sharks. They recorded the body size and sex of the first shark to arrive at the site and the number of other sharks as well as the time in which it took for a shark to approach the bait and bite it.
Using the data of the total of 379 Grey Reef sharks and 367 stereo-BRUVs recorded, they found that bite occurrence was significantly increased when more grey reef sharks were recorded in the area yet the number of competitors (different shark species) had no significant effect on the rate in which Grey Reef sharks bite the bait, neither did Grey Reef shark body size or sex in the rate in which Grey Reef sharks bite the bait. The other important result found was that increased bait biting occurred in regions further from the capital (main island) and regions prone to human exclusion (no entry regions). In regions to the other regions, open regions have the lowest bait biting rate, then came no-take regions followed by no entry regions with the highest bait biting rate. Also, sharks showed that travel time from the capital (main island) affected how they approached their bait, sharks were more prone to approach the bait in a straight line in regions further from the capitol (main island) than regions closed to the capital in which they were more prone to approach the bait with a cautious approach as signaled by twisting turns or not approach the bait at all.
These results help understand the feeding behavior of Grey Reef sharks and aid in the removal of the stigma of shark behavior and assumptions towards their feeding nature. With the conclusions made by Jean-Baptiste Juhel and her peers, we can better understand the requirements and conditions to mitigate and prevent the disruption of these sharks feeding behaviors which result in their decrease fitness and reproductive success which in turn leads to their decreasing numbers and lack of ability to control the coral reef ecosystems in which they dwell in. With this in mind, cities and countries can better assess their policies regarding human interactions with species of reef sharks to prevent the degradation of their coastlines and ecosystems which impact them in other aspects besides ecological such as economical as coral reefs and the sustainability of them bring in money for tourists and the fishing industry. By using this information and establishing proper zone to prevent the extinction of reef sharks, both humans and these aquatic ecosystems and species that live in them can benefit and be sustainable in the future.
References
Juhel, J., Vigliola, L., Wantiez, L. et al. Isolation and no-entry marine reserves mitigate anthropogenic impacts on grey reef shark behavior. Sci Rep 9, 2897 (2019). https://doi.org/10.1038/s41598-018-37145-x
