Patterns and ecosystem consequences of shark declines in the ocean

Area of Science:

• Marine Ecology
• Apex Predator Dynamics
• Fisheries Science

Background:

• Marine apex predators, particularly large sharks, are experiencing rapid population declines.
• Unlike terrestrial predators, the ecological roles of many marine predators are still being understood as they decline.
• Sharks are vulnerable to fishing pressure, impacting diverse marine habitats.

Purpose of the Study:

• To review documented changes in exploited elasmobranch communities.
• To synthesize the ecological effects of sharks on their prey and broader marine communities.
• To investigate the top-down impacts of large sharks in various marine ecosystems.

Main Methods:

• Literature review of exploited elasmobranch communities across coastal, demersal, and pelagic zones.
• Synthesis of studies documenting shark predation and behavioral effects on prey species.
• Analysis of evidence for trophic cascades and mesopredator release.

Main Results:

• High shark diversity and abundance are susceptible to even low fishing pressure.
• Shark decline leads to increased prey survival, altering abundance, distribution, and behavior of smaller marine life.
• Evidence suggests top-down effects from sharks cause cascading changes in coastal ecosystems and mesopredator release in pelagic/demersal systems.

Conclusions:

• Large sharks exert significant top-down control, shaping marine communities across large scales.
• Further empirical research is required to confirm the widespread ecological importance of sharks.
• Fishing pressure on sharks and mesopredators can mask or reverse ecosystem effects.