If we think for a minute about species driven to extinction during the course of human history, chances are most of us will come up with names of large, terrestrial species like the dodo, the mammoth or the Aurochs. And there are good reasons for that: in the past 500 years alone hundreds of conspicuous terrestrial species – including at least 130 birds, 30 reptiles, 75 mammals, 60 insects, 100 plants – disappeared altogether from the surface of the Earth (1), a process duly noticed.
Now, thanks to the unmatched skills of our species for destroying what is left of our unique biodiversity (overfishing, seabed mining, massive forest clearing, sea bottom trawling, persistant contaminants, introduction of invasive species, are all doing a very good job!), scientists fear that an extinction crisis is in progress, predicting a further 10-fold increase in global extinctions before this century is over. Which would bring us at the tipping point of the sixth great wave (2) of mass extinctions in the history of life on Earth.
The oceans support an estimated 80% of the world’s biodiversity, most of it made of small, inconspicuous species of which we know very little. In the face of that, what can we say with some degree of certainty about modern marine extinctions? About the types and number of species having disappeared from the world ocean in recent centuries? About those next on the list? Well, at least two or three things of interest.
• One is that a species disappearance, which is hard enough to confirm in the jungles and in other remote corners of continents, is even harder to spot in the immensity of the open ocean and in the dark abyss. Only if a marine species is ‘cute’, or of major commercial importance, will its ‘disappearance’ be noted.
The powerful novel Cannery Row by John Steinbeck is there to remind us all of the dramatic collapse of the sardine fisheries, which hit the North American West Coast so hard in the 1930s. Today we have no Nobel Prize winner in literature to relate the collapse of northern cod fisheries off Newfoundland (1992) and now in Icelandic waters … As shown below (3), when a highly connected species such as cod disappears, this will affect in direct and indirect ways at least one hundred species, bringing down a few of them with it. Since we know from foodweb research that an oceanic species interacts on average with more other species than a terrestrial or a freshwater species, the cascading impacts of overfishing under the sea surface are vastly underestimated.
• A second observation is that mammals have fared so far better in the sea than on land. In the last 500 years roughly 100 species of mammals were driven to global extinction, three of them marine, all seals: the Steller’s sea cow, declared extinct in 1768, and closer to us the Japanese sea lion, and the Caribbean monk seal. But this picture is fast changing. Earlier this year, China announced the extinction of the baiji, a dolphin that used to thrive in the Yangtze River, and the first cetacean species to disappear in modern times. A sign of things to come? Surely. The next cetacean facing global extinction is likely the Mexican vaquita, which now survives in low, fast decreasing numbers in the northern Sea of Cortez.
The larger whales are slightly better off, thanks to the moratorium on commercial whaling set in place 25 years ago by the IWC (4) once it had become clear that the whaling industry had decimated most stocks worldwide. Today the whales’ problems are not over, as they face (a) large-scale uncontrolled industrial whaling operated by a couple of nations under the pretense of ‘scientific research,’ (b) the absence of legal protection in the High Sea (5) , and (c) increasing damages due to entanglement in fishing gear, submarine noise, and worldwide pollution. As for the hundred species of ‘small’ marine mammals, many of them are doing poorly, the seals in particular, due to their dependance on coastal waters where man’s impact is magnified. If nothing serious is done soon at an international level, a number of these species will risk global extinction in the course of this century.
• A third factor – data deficiency – concerns many small, inconspicuous marine species long considered common, but obviously not subject to the same level of attention as marine mammals. Upon closer inspection it turns out that many of them in fact have not been recorded or seen in decades. These species, which ought to be formally listed as ‘missing,’ can sadly disappear without being remarked upon. As information improves, a large number of them will end up in the column ‘Extinct.’
In the world ocean this problem concerns mostly, but not only, the invertebrate fauna. Who knows for sure that this mollusk or that polychaete, nicely illustrated in my field guide but not seen in 50 years, is not extinct by now? Surprisingly, as a recent workshop of the Mediterranean Science Commission (6) on marine extinctions concluded, many fish species are concerned by this under-reporting as well. In particular the popular sharks and rays. These are not target species in Mediterranean fisheries but increasingly threatened, as unreported bycatch, by highly intensive fishing and bottom trawl. The status of many of them is unclear, even for species as conspicuous as the sawfish Pristis pectinata (last seen in 1902), the mako shark Isurus oxyrinchus, or the sandtiger sharks Carcharias taurus and Odontaspis ferox, once abundant and now presumed locally extinct.
Clearly the time has come to carry systematic surveys – using networks of researchers, fishermen and the public at large – to draw a reliable catalogue of missing, ‘most wanted’ species, starting with our coastal waters and regional seas.
(1) See IUCN Red List
(2) The previous wave, which swept away the dinosaurs and many other forms of life, occured in the Cretaceous about 65 million years ago.
(3) Illustration taken from the 2011 RSA open lecture ‘The Power of Networks’ – download from http://www.thersa.org/events/video/animate/rsa-animate-the-power-of-networks
(4) International Whaling Commission
(5) see http://www.ciesm.org/news/mscience/090712.htm