Abstract
BackgroundIn 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. Here we explore the contemporary distribution and sighting frequency of sharks on reefs in the greater-Caribbean and assess the possible role of human pressures on observed patterns.Methodology/Principal FindingsWe analyzed 76,340 underwater surveys carried out by trained volunteer divers between 1993 and 2008. Surveys were grouped within one km2 cells, which allowed us to determine the contemporary geographical distribution and sighting frequency of sharks. Sighting frequency was calculated as the ratio of surveys with sharks to the total number of surveys in each cell. We compared sighting frequency to the number of people in the cell vicinity 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.Conclusions/SignificanceHuman pressures in coastal zones have lead to the broad-scale absence of sharks on reefs in the greater-Caribbean. 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.
Highlights
Strong declines in the abundance of many large pelagic sharks have been described worldwide and repeatedly linked to industrial fishing [1,2,3,4,5]
Using an extensive database of fish surveys conducted by trained recreational divers we show that contemporary sharks, other than nurse sharks, are largely absent on reefs in the greaterCaribbean
Comparison with data on human population density suggests that such disappearance may have been related to anthropogenic pressures
Summary
Strong declines in the abundance of many large pelagic sharks have been described worldwide and repeatedly linked to industrial fishing [1,2,3,4,5]. This uncertainty, in combination with the high vulnerability of sharks to fishing [3,8] has motivated the use of alternative sources of data to shed light on temporal and spatial trends in shark populations These sources of data include historical fisheries and market records of sharks in the Mediterranean [9], trophy photographs of fishing tournaments in Florida [10], archaeological and historical records on coral reef ecosystem changes worldwide [11], and ecological surveys of fish communities across spatial gradients of exploitation [12,13,14], among others. We explore the contemporary distribution and sighting frequency of sharks on reefs in the greaterCaribbean and assess the possible role of human pressures on observed patterns
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