Caribbean Reef Shark
Photo Credit: Twan Stoffers
Scientific Frontline: Extended "At a Glance" Summary: Human Disturbance and Caribbean Reef Shark Populations
The Core Concept: High levels of human recreational activities, such as diving, and extensive coastal development correlate directly with a reduced presence of reef sharks on Caribbean coral reefs, even in areas maintaining good ecological health.
Key Distinction/Mechanism: Unlike bottom-dwelling species such as nurse sharks and southern stingrays, whose distributions are primarily dictated by natural habitat characteristics like water depth and reef structure, reef sharks actively alter their spatial distribution to avoid areas experiencing high non-extractive human disturbance.
Major Frameworks/Components:
- Baited Remote Underwater Video (BRUV) Systems: Employed to safely and non-invasively quantify marine life and shark occurrences across diverse, geographically separated reef environments.
- Social Media Data Proxies: The integration of geolocated underwater photographs shared on social media to map and quantify diving pressure and coastal tourist activity where traditional infrastructure data was lacking.
- Species-Specific Spatial Analysis: Comparative ecological modeling utilized to assess the varying behavioral and distributional responses of different marine species to anthropogenic versus environmental drivers.
Branch of Science: Marine Ecology, Conservation Biology, Marine Biology.
Future Application: The integration of non-extractive human activity data into predictive ecological modeling to optimize the zoning of marine protected areas, refine reef management strategies, and inform sustainable ecotourism policies globally.
Why It Matters: Reef sharks are crucial apex predators necessary for maintaining balanced and healthy coral reef ecosystems. Recognizing that supposedly "low-impact" tourism drives these apex predators away fundamentally shifts how conservationists must approach reef management and species protection.
Reef sharks are observed less frequently on Caribbean reefs with high levels of diving activity and greater coastal development. This is shown by new research published in Journal of Applied Ecology. Even recreational activities that are often considered low impact are associated with fewer sharks on these reefs. Reef sharks play an important role in maintaining healthy reefs by helping to keep the ecosystem in balance.
The study is based on 995 underwater video recordings made between 2012 and 2017 using so-called Baited Remote Underwater Video systems (BRUVs). The research covered seven reef systems across the Caribbean. Cameras were deployed around six inhabited islands in the Dutch Caribbean and on the Saba Bank, a large and remote reef area with minimal human disturbance.
“What stands out is that we observe this pattern even on reefs that are otherwise in good ecological condition,” says Twan Stoffers, fish ecologist at Wageningen University & Research and lead author of the study. “This suggests that human presence plays an important role in shaping where these animals occur.”
Differences between coastal reefs and a remote reef area
Around the inhabited islands, reef shark presence was strongly associated with diving activity and coastal development. A different pattern was found on the Saba Bank. On these remote reefs, shark occurrence was primarily linked to habitat quality, while along populated coasts sharks were more often found in areas with lower human pressure.
“On the Saba Bank, where human disturbance is minimal, natural factors such as water depth and reef structure mainly determine where reef sharks occur,” Twan Stoffers explains. “On populated reefs, these natural factors play a smaller role, and patterns are more closely linked to human activity.”
This means that the same species responds to different drivers depending on local conditions.
Species-specific patterns
The influence of human activity and environmental factors differed clearly between species. For Caribbean reef sharks, lower numbers were associated with both intensive diving activity and higher levels of coastal development. These sharks were more frequently observed farther offshore and on less disturbed reefs.
For nurse sharks and southern stingrays, bottom-dwelling species, natural reef characteristics were more important. Their presence was more strongly linked to water depth and reef structure than to human activity. Nurse sharks were mainly found on structurally complex reefs, while stingrays were more often observed on flatter, less structured seabeds.
Sensitivity to human presence therefore varies among species: reef sharks appear more responsive to disturbance, while other species are primarily influenced by natural environmental factors and therefore reef quality.
Social media as an indicator of diving pressure
To map human activity around the reefs, the researchers combined ecological field data with open data sources. Geolocations of underwater photographs shared on social media were used as a proxy for diving activity and shoreline activity by tourists, while publicly available spatial data provided information on the extent of coastal development.
“By combining underwater video data with spatial indicators of diving activity and coastal development, we were able to analyze patterns across a large region,” says Twan Stoffers. “This approach is especially valuable in areas where detailed data on recreational use and human-made infrastructure are not available.”
Implications for reef management
The findings show that, alongside natural habitat characteristics, human presence around reefs is associated with reduced reef shark occurrence. While previous research has largely focused on fishing and habitat destruction as the primary driver of shark declines, this study indicates that tourism and coastal development also influence where reef sharks are found.
According to the researchers, this underscores the importance of explicitly considering non-extractive human activities in ecological research and reef management, alongside traditional factors such as habitat quality and water depth.
Reference material: What is: Ecosystem
Published in journal: Journal of Applied Ecology
Title: Anthropogenic disturbance modifies spatial patterns of reef sharks
Authors: Twan Stoffers, Jimmy van Rijn, Martin de Graaf, Hendrik V. Winter, Tadzio Y. Bervoets, Mark E. Bond, Chris C. Duinmeijer, Michael Heithaus, Matthew Needle, Georgios Papageorgiou, Jan Jaap Poos, Stijn Schep, Koen Tieskens, and Leopold A. J. Nagelkerke
Source/Credit: Wageningen University & Research
Reference Number: eco040626_01