Folks, I’d like to introduce you all to sawfishes (not to be confused with the similar looking but very distinct sawsharks). There are 5 recognised species that make up this family of rays (the Pristidae ), all of which are ‘of conservation concern’. And when I say concern, I really mean it. Three of the five species – smalltooth sawfish (Pristis pectinata) , largetooth sawfish (Pristis pristis) , and green sawfish (Pristis zijsron) are classified on the IUCN Red List as critically endangered. The remaining two species – narrow sawfish (Anoxypristis cuspidate) , and dwarf sawfish (Pristis clavata)_ are classified as endangered. These rather beautiful rays, argues Nick Dulvy from Simon Fraser University and collaborators from Australia and America, are probably “ the world's most imperilled marine fishes ”.
Like other rays, and indeed sharks, skates and chimeras – all of which are a class of fish called Chondrichthyes – the cartilaginous fish (their skeletons are made of cartilage not bones), sawfish conservation has not been much of a priority in most areas of the works. Fortunately for sawfish, not everyone thinks that this is right, so Nick and his team of collaborators have put together this neat paper summarising some key informationon sawfish to help get the ball rolling a ‘tad’ faster than it is already. In fact the information summarised in this paper has played a part in the Global Sawfish Conservation Strategy. So let’s take a peek into the world of the sawfish, and crucially what we can do to give them a chance.
If we want to be able to effectively conserve a species, we need to know something about them – their life history traits, and general ecology. Sawfish are pretty big critters. Green sawfish and dwarf sawfish and the two largest species coming in at 700 centimetres in total length (TL – this is the measurement from tip of the tail to the tip of their snout), and 318 centimetres respectively. These guys are only surpassed in size by the whale shark (Rhincodon typus) and basking shark (Cetorhinus maximus) . Life span is highly variable among the species. Whilst the smalltooth sawfish has an estimated lifespan between 30 and 50 years – and most likely even older, the narrow sawfish is thought to live only 9 years. Juvenile sawfish tend to hang around rivers and estuaries but as they reach maturity tend to move into shallow marine and estuarine areas, especially seagrasses and mangroves, though there are records of sawfish down to depths exceeding 100 meters. Historical records place sawfish in some 90 countries and overseas territories throughout the tropical Atlantic, Pacific, and Indian Oceans. The largetooth sawfish used to be the most widespread of the sawfish, with records in some 75 countries. By contrast, dwarf sawfish historical records place it in 47 countries. You will see that the word “historical” a lot. Since the beginning of the 20th century, the geographic range size for all 5 species has declined. The long lived smalltooth sawfish fairs the worse, with an 81% decline in geographic range size. The dwarf sawfish isn’t too far behind with a 70% decline. The largetooth sawfish follows with a 61% decline. The largest of the sawfish - green sawfish, has seen a 38% decline whilst the sort lived narrow sawfish has experienced a 30% decline in geographical range size. Out of the original 90 countries and overseas territories that used to have sawfish, only 70 presently do.
So what’s going on? Well the IUCN highlights a number of primary threats to this group. The first is related to their long, toothed rostrum. As marvellous a device as this is for hunting prey*, it also makes it super easy for the sawfish to get entangled in fishing gear, especially drift and gill nets. Unfortunately for the sawfish, many seagrass, mangrove, and estuarine areas, these sorts of fishing techniques are used. Bycatch – the accidental capture of a non-targeted species, or indeed subset of that species (like immature individuals) has been heavily implicated in the decline of sawfish in many areas. Sawfish however aren’t just declining because they are being accidentally ensnared in fishing gear, they are also deliberately targeted as a high value product. Sawfish fins are a delicacy for sharkfin soup (before anyone points it out, yes I said that these critters are rays and not sharks - I guess sometimes a fin is a fin). In fact so valuable are sawfish fins, that they are considered among the most valuable of all marine products. Of course we can’t forget all those teeth on the rostrum. In Central and South America, these are sold for cockfighting spurs, and not for a small sum either. In Brazil a whole sawfish can sell for more than U$1000….awfully tempting for many a fisher, especially those who may be struggling to make a living. Then there is a problem with the habitat itself. Since 1980 global mangrove cover has reduced by some 20 – 35%. As for seagrass, since the late 1800s this has declined by some 29% globally. But it doesn’t stop there. The habitat of sawfish tends to overlap with areas of high human density, from which pollution, litter, alterations of water flows and sediment movement from development is all too common. In short, what habitat they have left is also degrading in quality. With their long generation lengths (relative to their lifespan – generation length refers to the time between the birth of the parent and the birth of the offspring), and relatively small number of offspring contributing to low rates population growth, recovery from overexploitation – whether accidental or deliberate – is severely hampered. I don’t think anyone can argue that a global sawfish conservation strategy is needed.
The first thing any strategy needs is a vision. For this particular strategy, the vision is quite straight forward: “ a world where sawfishes are restored – through understanding, respect and conservation – to robust populations within thriving aquatic ecosystems “ The strategy aims to do this through two goals: “ Robust sawfish populations where threats are minimized through improved fisheries management, strategic research, species and habitat protection, and trade limitation “ And... “ Effective sawfish conservation and management enabled through capacity building, outreach and fundraising “ There are also 9 objectives, but I’ll leave you to read those in the paper. The real challenge, the researchers note, “ is to develop and implement effective actions at local and regional scales , particularly in countries where there is high incentive to retain sawfishes for their parts and little capacity to enforce regulations “.
So, given an effective strategy, can sawfishes recover? The researchers point us to what they call potential “lifeboat” areas – areas of hope – Florida USA, and northern Australia, primarily down to national and local protections offered. Of course good(ish) protection in two places is not enough to save all sawfish species, and it seems that in Australia in particular, critical habitat is still under constant threat from human activities like mining. It seems we have a choice. We can either focus on the sheer difficulty of the task of not just halting the decline of sawfish but also aiding their recovery, or we can start looking for solutions - and crucially - taking the steps needed to action these solutions out.
The paper, which is open access, appears in the Early View of the journal Aquatic Conservation: Marine and Freshwater Ecosystems . You can have a read of it here www.dx.doi.org/10.1002/aqc.2525
* Check out this cool video from Dr Barbara Wueringer for a captive sawfish using its rostrum http://news.sciencemag.org/2012/03/sawfishs-versatile-hunting-tool
Image: A Largetooth sawfish (Pristis pectinata) Taken by David Illiff at the Georgia Aquarium back in 2006. David has licensed this – and many other really nice images at Wikimedia Commons under a Creative Commons Attribution. You can check out more of his work by searching for his username Diliff.