The threatened status of restricted-range coral reef fish species

Coral reefs are the most diverse ecosystem in the sea. Throughout the world they are being overfished, polluted and destroyed, placing biodiversity at risk. To date, much of the concern over biodiversity loss has centred on local losses and the possibility of global extinction has largely been discounted. However, recent research has shown that 24% of reef fish species have restricted ranges (< 800 000 km2), with 9% highly restricted (< 50 000 km2). Restricted-range species are thought to face a greater risk of extinction than more widespread species since local impacts could cause global loss. We searched for information on status in the wild and characteristics of 397 restricted-range reef fish species. Fish body size, habitat requirements and usefulness to people were compared with those of a taxonomically-matched sample of more widespread species. We found that on average species with restricted ranges were significantly smaller (mean total length 19.1 cm versus 24.4 cm), tended to have narrower habitat requirements and were less used by people. Greater habitat specificity will tend to increase extinction risk while, if real, more limited usefulness (equivalent to exploitation) may reduce risk. Fifty-eight percent of restricted-range species were considered common/abundant in the wild and 42% uncommon/rare. Population status and threats to 319 species for which data were available were assessed according to the categories and criteria of the IUCN red list of threatened animals. A number of species were found to be rare, were exploited and had highly restricted ranges overlapping areas where reef degradation is particularly severe, placing them at a high risk of extinction. Five species were listed as Critically Endangered, two of them possibly already extinct in the wild, one as Endangered and 172 as Vulnerable. A further 126 species fell into Lower Risk categories and 11 were considered Data Deficient. Given the intensity of impacts to reefs, the broad geographical areas affected and the large numbers of restricted-range species, global extinctions seem likely. Urgent management action is now crucial for the survival of several species of reef fishes. E-mail: [email protected]. undoubtedly the best studied group. Around 30% of the world’s marine fish species can be found on coral reefs (McAllister, 1991; Nelson, 1994). In view of the threats faced by reefs the World Conservation Union’s (IUCN) Species Survival Commission, Coral Reef Fish Specialist Group set out to document distribution, diversity and endemism among reef fishes on a global scale. Of 1677 coral reef fish species they examined, a remarkable 9.2% had ranges of less than 50 000 km2 (Roberts et al., in press b). On land these species would be considered to have a restricted range (ICBP, 1992). Applying a less stringent criterion of restricted range, of 800 000 km2 or less (roughly equivalent to the area of the Australian Great Barrier Reef, or two-thirds the length of the Red Sea), 24% of reef fishes would qualify as having a restricted range. Although such an area seems large, only 0.34% of the typical range consisted of coral reef (Roberts et al., in press b). To refine their analysis of threat, Roberts et al. (in press b) examined overlap of individual species ranges with areas of reef classified as critically endangered and threatened by Wilkinson (1992). One species in 13 (7.7%) had ranges totally overlapping critically endangered reefs, while nearly a quarter (23%) completely overlapped critically endangered and threatened reefs combined. A third of all species (34%) had less than one-fifth of their range overlapping regions where reef condition was considered stable. Of those species whose ranges entirely overlapped endangered and threatened reefs, 53.1% had restricted ranges. This study by Roberts et al. (in press b) suggests that many species of coral reef fishes, especially those with restricted ranges, could be at risk of extinction from human impacts. However, virtually nothing is known about the status of these fishes. The present study aims to: (1) compile information on the status of restrictedrange species in the wild; (2) determine whether these species possess characteristics other than small range that may render them vulnerable to extinction; and (3) assess restricted-range species against the IUCN red list criteria.