The sad case of an “amputee sawfish” reported by scientists earlier this month provides new proof that these endangered and protected creatures continue to be exploited for their most distinctive feature – and the resulting injuries mean the animals suffer a lingering death.
Back in 2011, researchers conducting a routine survey in the waters off western Australia came across a green sawfish (Pristis zijsron) whose rostrum – that "tooth-covered" blade that gives the sawfish its name – had been removed. At the time of the sighting, the fish's wound was still raw and bleeding, a sign that the injury had been inflicted only recently.
Once abundant across the world's oceans, all sawfish species have suffered dramatic declines – not just due to habitat loss and entanglement in fishing gear, but also because humans have coveted their unique rostrums for centuries, as weapons, trophies and souvenirs. And the cruel practice of rostrum removal has sadly not been relegated to the past. Just like the Australian "amputee", sawfish across their range are still being taken for trade in their body parts.
Determined to learn something from this unfortunate case, the team of scientists, led by Murdoch University associate professor David Morgan, opted to tag, release and track the animal, despite not knowing how it would fare – or if it would survive for any length of time at all. Experts have long speculated what life might be like for a saw-less sawfish, but one had never been monitored in the wild.
"There have been a number of anecdotal reports of sawfish surviving following removal of their rostrum," writes the team. But the current study, published earlier this month, is the first to report on their ecology or behaviour.
The animal was tracked using an acoustic tag as it moved along the Ashburton River estuary and nearby mangrove creeks. And while the amputee did live for an impressive 75 days, its behaviour was notably erratic. And yet the fact that it survived at all shows just how resilient sawfish can be.
"Its brain cavity was exposed to seawater," explains IUCN Shark Specialist Group Co-Chair Dr Nick Dulvy, who has done extensive work on sawfish conservation. "How [it] survived more than minutes [is astounding]."
The rostrum-less ray spent 50 percent of its time in shallow water (less than 0.2 metres, or 0.6 feet, deep), and it also ventured beyond the borders of the known habitat, likely because it couldn't forage efficiently without its toothy extension.
When it comes to hunting down fish and fast-moving invertebrates, a sawfish's rostrum is like a multi-tool. A rapid zig-zag head motion turns the blade into a hacksaw, but with careful placement, the rostrum can also be used like a pitchfork. Without one, the animal has no choice but to feed on whatever is slow enough to be hoovered up off the seafloor. And without the vital electrosensory pores that sit along the rostrum, finding prey – even easy prey – is a challenge.
"Additionally, or alternatively, this wide home-ranging behaviour may have been a function of reduced capacity for this individual to defend itself from competitors and predators," adds the team.
And this sad story doesn't end here. Alarmingly, Morgan encountered yet another rostrum amputee a few years later, this time a large-tooth sawfish (Pristis pristis) in the nearby Fitzroy River. "That animal was severely emaciated," he recalls.
In both cases, the injured fish disappeared without a trace, leading Morgan and the team to suspect that they died far sooner than any healthy sawfish of comparable size and age in the area.
"This is tragic, gruesome, and clearly a source of post-release mortality for sawfishes," says Dulvy. "It shows that where sawfishes are taken that fishers need to be aware of the plight of sawfishes and of best practice handling and release guidelines produced by the Australian and US government agencies."
Thankfully, support for sawfish has been on the rise in recent years. New conservation plans have emerged, mainstream media has begun to cover sawfish stories, and even LEGO incorporated the unique animals into their ocean exploration sets.
But the tough reality is that these incredible animals are still at higher risk of extinction than any other group of marine fish. Though they once cruised the waters of over 90 countries, today they are found in only two remaining strongholds: along Florida’s Atlantic coast and in northern Australia. And with numbers dwindling, mates can be few and far between, so the loss of even a few individuals can have catastrophic effects on the animals' ability to rebound.
"The decline of sawfishes due to fishing pressure is exacerbated by humans removing sawfish rostra," says the team. "The conservation value of these unique species needs to be actively promoted, and the cruelty of taking rostra as trophies should be afforded the same attention as other endangered species that are similarly poached for their body parts, [like] rhinoceroses and elephants."
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Top header image: Rachel Patterson, Flickr
Endangered
Predator vs Prey
Endangered
