Large-Scale Absence of Sharks on Reefs in the Greater-Caribbean: A Footprint of Human Pressures

In recent decades, large pelagic and coastal shark populations have declined dramatically with increased fishing; however, the status of sharks in other systems such as coral reefs remains largely unassessed despite a long history of exploitation. The authors used REEF data to explore the contemporary distribution and sighting frequency of sharks on reefs in the greater-Caribbean, and assessed the possible role of human pressures on observed patterns. The analysis was based on 76,340 underwater surveys carried out by REEF volunteers between 1993 and 2008. The authors compared sighting frequency to the number of people in each area surveyed, and used population viability analyses to assess the effects of exploitation on population trends. Sharks, with the exception of nurse sharks occurred mainly in areas with very low human population or strong fishing regulations and marine conservation. Population viability analysis suggests that exploitation alone could explain the large-scale absence; however, this pattern is likely to be exacerbated by additional anthropogenic stressors, such as pollution and habitat degradation, that also correlate with human population. Preventing further loss of sharks requires urgent management measures to curb fishing mortality and to mitigate other anthropogenic stressors to protect sites where sharks still exist. The fact that sharks still occur in some densely populated areas where strong fishing regulations are in place indicates the possibility of success and encourages the implementation of conservation measures.