SUBJECT: Recent marine extinctions
AUTHOR: Nicholas K. Dulvy, Centre for Environment, Fisheries, Aquaculture Sciences, Lowestoft, Suffolk, UK

SUMMARY: Here I review human impacts on the oceans and outline evidence for local, regional and global marine extinctions over the past 300 years.

KEYWORDS: Fishing, habitat loss, extinction.

Human impacts on the oceans are widespread and substantial and concern has been growing of the possibility of extinction of marine species. Fisheries exploitation has removed a high proportion of the abundance and biomass of species at the top of marine food chains and benthic disturbance of fishing gears has caused some degree of habitat degradation. Fishing also removes non-targeted species, including birds, aquatic mammals, reptiles, sharks and rays and other fishes and invertebrates. Habitat loss is a major cause of modern extinctions of mammals, birds, butterflies and plant on land; by comparison little is known of the extent of or the rate of change of major marine habitats. The only habitat for which loss rates are known at large spatial scales is coral reef, and recent estimates from the Caribbean and the Great Barrier Reef indicate a decline in hard coral cover of approximately 1% per year over the past 25 years. Finally, the occurrence of novel marine pathogens appears to be on the increase and diseases are associated with mass mortalities of a number of marine species.

Current evidence suggests few marine organisms have become globally extinct in the past 300 years, compared to on land where 100s of birds and mammals have disappeared. There is unequivocal evidence for the extinction of only three marine mammals, five birds and four gastropods. Another 18 taxa could be considered extinct if their status as a valid species can be confirmed. Most of these species were large bodied and presumably had low maximum population growth rates and little capacity to withstand the hunting pressures they were exposed to. It appears the gastropods were habitat specialists, and disappeared as a result of habitat loss. Three diadromous fishes have been exploited to extinction (New Zealand grayling, Adriatic beluga and Aral sea ship sturgeon). By contrast there is little good evidence for the global extinction of fully marine species. Though there are hints that Galapagos damselfish and the Mauritius green wrasse have become extinct throughout their small geographic ranges. If the definition of extinction is relaxed to consider local and regional disappearances then the list is much longer. It is estimated that a total of 133 marine species have undergone a local, regional or global extinction. Given the relatively high degree of fishing impact on marine fishes this could be interpreted to suggest the effect on fish biodiversity has been low. This would be consistent with arguments that marine organisms are more resilient to extinction and more able to recover than terrestrial species due to larger geographic ranges, wide larval dispersal and higher fecundity. Alternatively it could be that it is more difficult to detect extinctions of non-air breathing marine organisms. The latter hypothesis cannot be discounted for three reasons: most local and regional extinctions were detected retrospectively long after the date of last sighting, most (80%) were detected using retrospective methods and even the best marine monitoring surveys have very little power to detect declines and disappearances. If knowledge of marine extinctions were perfect there would be little time lag between the date of last sighting and reported date of disappearance. However there is typically a 53-year reporting lag. In summary, current evidence is consistent with the hypothesis that the number of marine extinctions is underestimated.