The Mediterranean’s Missing Sawfishes

In 1959, off the southern coast of France, a tuna boat hauled up a largetooth sawfish. The catch wasn’t particularly large. The razor-snouted fish only stretched about four feet long; still a baby by the standards of its species. But it was one of the last to be seen in those waters. Within a decade, the largetooth sawfish entirely disappeared from the Mediterranean Sea.

Such accidental catches and sightings in the Mediterranean have often been regarded as signs of largetooth and smalltooth sawfish migrating into the sea from the coast of Africa. When sawfish experts gathered in London in May 2012 under the auspices of the IUCN, they concluded that the Mediterranean gets too cold in winter to have hosted resident populations of the warm-water fish. Therefore all the historic accounts must have referred to “vagrant” animals, and sawfish blades in museums were brought to coastal museums by trade routes that have been in place for centuries. But after trawling through bibliographic records and museum displays, Hopkins Marine Station biologist Francesco Ferretti and colleagues have suggested a different interpretation. The Mediterranean is missing its native sawfishes.

Ferretti and coauthors cast a wide net. They searched everything from records on pre-dynastic Egypt through modern ocean biodiversity databases to find any sign of sawfishes in the Mediterranean. Being that the science of ichthyology didn’t get going until the 16th century, it’s not surprising that the earlier part of their timerange came up empty. But between the 18th and 20th century – when naturalists often kept track of who was landing what at the local docks – the researchers turned up 48 original accounts of sawfish in the Mediterranean, 24 of which could be verified in the literature or in museums. These verified records were split between largetooth and smalltooth sawfish, and the size of many of these fish hint that they were not migrants from the African coast.

Largetooth and smalltooth sawfish grow slowly. Largetooth sawfish, in particular, take between eight and ten years to reach maturity, at which time they’re about 10 feet long and start reproducing. But in their youth, sawfish typically stick very close to the place they’re born. Smalltooth sawfish, for example, have a home range of less than a half a mile. Ferretti and coauthors counted 15 sawfishes in their sample that fell within the juvenile category.

If those juvenile sawfishes were swimming from the nearest population centers to the Mediterranean, they must have journeyed more than 2,000 miles – over ten times the distance an adult sawfish has ever been observed to travel. Unless the historic populations of large and smalltooth sawfish undertook truly exceptional journeys, Ferretti and colleagues argue, it’s more likely that they had a resident population in the Mediterranean.

While lacking in as much detail as modern biologists wish for, the 18th and 19th century naturalist accounts of sawfishes also throw some support to the idea that sawfish had a home in the Mediterranean. Some accounts list them as relatively rare, and others as common, but there doesn’t seem to be any hint that it was strange to see sawfishes along Europe’s southern coastlines. It was only in the 20th century – when sawfish populations plummeted and totally disappeared – that sawfishes were regarded as especially rare and the idea of migration started to take hold.

Not all marine biologists are convinced by the historic evidence. In a paper published around the same time as the paper by Ferretti and coauthors, Nicholas Dulvy and colleagues argue that the Mediterranean gets too cold for sawfishes and that the past occurrences really do represent piscine vagrants. More than that, Dulvy and colleagues write, “Whether or not sawfishes were previously extant in the Mediterranean Sea has little bearing on current conservation priorities as any activities benefitting West African sawfishes can only restore migration and improve the likelihood of vagrancy to the Mediterranean Sea once again.”

Ferretti and colleagues disagree on both counts. Regarding temperature, the researchers suggest, past Mediterranean sawfish populations may have been better-adapted to cooler waters than others. If not that, then young sawfishes could have taken refuge in deeper water that maintains warmer, more constant temperatures than those at the surface during winter. There may not be a way to know for sure – the Mediterranean sawfishes are all gone – but temperature alone can’t be used to rule out the previous presence of resident populations.

And this question does have relevance for the future of the largetooth and smalltooth sawfish. If sawfishes previously had a home in the Mediterranean, perhaps they could live there again. Ferretti and colleagues even have a spot in mind – a national park in southern France near where the last recorded sawfishes were seen. What hopes sawfishes might have for survival in such a place are murky, but if restoration attempts are to be considered at all, the Mediterranean may be a place where these awkwardly charismatic fish may find a refuge.

How long the longtooth and smalltooth sawfish will survive is unknown, and their fate largely rests on the decisions we make. And in making those decisions we must be aware of our own history. The only good records of Mediterranean sawfishes we have come from a timespan when these vulnerable fish had already been coping with centuries of human disturbance to their nearshore haunts. Our species only started keeping track of what was “natural” when the sawfishes were already in decline. Marine biologists know this as “shifting baselines“, and it’s the same reason why many don’t feel the absence of ground sloths and mastodons in North America’s forests. The megamammals were already gone by the time naturalists started paying attention to the woods, and we don’t consider how empty the landscape is. We just don’t know what we’re missing.

References:

Dulvy, N., Davidson, L., Kyne, P., Simpfendorfer, C., Harrison, L., Carlson, J., Fordham, S. 2014. Ghosts of the coast: global extinction risk and conservation of sawfishes. Aquatic Conservation. doi: 10.1002/aqc.2525

Feretti, F., Verd, G., Seret, B., Šprem, J., Micheli, F. 2014. Falling through the cracks: the fading history of a large iconic predator. Fish and Fisheries. doi: 10.1111/faf.12108

Guilhaumon, F., Albout, C., Claudet, J., Velez, L., Lasram, F., Tomasini, J., Douzery, E., Meynard, C., Moupuet, N., Troussellier, M., Araújo, M., Mouillot, D. 2014. Representing taxonomic, phylogenetic, and functional diversity: new challenges for Mediterranean marine-protected areas. Diversity and Distributions. doi: 10.1111/ddi.12280