We know that numbers of sharks and rays are declining for various reasons. Some are direct threats where sharks are killed by people – as through fishing – and others are indirect, like habitat loss. When an area of ocean or coastline is changed or degraded beyond the point that it can serve as a home for the species that live there, or is even destroyed entirely, that’s habitat loss.
There are various ways that the habitats used by sharks are altered or destroyed. Again, some are direct, like cutting down mangroves or trawling fishing nets over reefs, and others are indirect, such as pollution, which might affect water quality to the extent that the water becomes uninhabitable. Coastal development has accelerated over time as the human population grows and more and more people move to the coast, and it has been the driver of a lot of degradation in marine areas. Mining and aquaculture are other culprits.
The areas that are most accessible to people are the ones most degraded, so broadly in descending order the most affected are terrestrial areas, freshwater habitats, estuaries, coastal areas, the inshore region and the open ocean. This means that sharks that live in fresh or brackish waters are likely to be the most affected by habitat degradation. The Ganges shark Glyphis gangeticus, for example, has almost completely disappeared from its small range in the lower reaches of the Ganges–Hooghli river system in India, due to the degradation of its habitat.
Many shark species use coastal and estuarine areas as safe places away from predators to feed, give birth, mate and grow. The sharks that live in coastal areas for all or part of their lives are likely to be more affected by habitat loss than those that live in the open ocean. The lemon shark is one example of a shark that moves inshore to give birth. But scientists have found that dredging in The Bahamas for a new coastal development has negatively affected the survival of young lemon sharks there. Coral reefs and mangroves are also important for various shark and ray species, and both of these habitats have been in decline in terms of their extent and health.
Through research projects, such as those funded by the Save Our Seas Foundation, we can understand the effects of habitat loss on sharks and rays. What activities have the greatest and the least impact? Which species face the biggest threat from habitat loss? Where are sharks and rays affected (or unaffected) by habitat loss? The answers to these questions can guide the people who manage ocean resources, marine environments and the activities that impact on marine habitats by