The Sawshark Redemption
Published: Jul 18, 2018Paignton Zoo's collection of animal artefacts are being used to help with genetic research...
The thing that sets a zoo apart from almost all other places is its animals. These animals come in many shapes and sizes. What many people may not realise, however, is that as well as our living animals, we also house a large collection of animals (and animal parts) that are, well, dead…
Before things get too morbid, I should point out that these items make up our artefact collection. They’re the various bones, skulls, teeth and shells that we use for educational purposes in our classroom sessions and around the Zoo. A quick read through our artefact inventory reveals such treasures as an elephant’s tooth, a giraffe vertebra, a hummingbird’s egg and even a range of snakeskin bags and alligator shoes. Some of these items came from our animals here at the Zoo, but many were donated to us for educational purposes by HM Customs and Excise, having been seized as part of ongoing efforts to clamp down on the illegal global trade in animal products.
One of our most popular artefacts is our sawfish rostrum. Sawfish are, without any question, one of nature’s true marvels. Imagine a ray that looks like a shark with a chainsaw blade stuck on its nose and you’ll have a good idea of what they look like. If you can’t imagine this, just Google them – they’re incredible looking fish.
The ‘saw’ (or rostrum) is used to incapacitate fish – they swim into a shoal and thrash around before hoovering up the injured fish for dinner. The saws are also used to detect prey; like all sharks and rays, they can use electroreception to locate food and the sensors are clustered on the rostrum. Unfortunately, this amazing adaptation is also their downfall and sawfish are one of the world’s most threatened marine species. They have been hugely overfished both for their fins (which are used for shark fin soup) and also for their amazing saws. The reason we have sawfish rostra in our collection is because a number of illegal saws were confiscated by Customs and given to us to look after.
This year, our sawfish rostra are being used as part of an international research project which aims to help understand how wild populations have declined. Researchers from Louisiana State University and the University of Southern Mississippi will be taking DNA samples from our specimens in an effort to understand patterns in trade and whether the drop in numbers is linked to a drop in genetic diversity. Genetic diversity is an important part of conserving populations (it’s why zoo breeding programmes are so carefully managed), so the results will hopefully inform future conservation efforts for the remaining wild sawfish. It’s a great example of how zoos can use their animals (both alive and otherwise) and work with other organisations to contribute towards conservation.
Why is genetic diversity important?
In order to conserve species effectively, we need to understand how populations change over time. Although it stands to reason that small populations have fewer individuals than large populations, it isn’t just the number of animals that is important - we also need to look at the genetic diversity of the individuals. Genetic diversity allows a population to cope with changes to the environment and as a result, a diverse population tends to have a better chance of surviving for a longer period.
Some species are naturally uncommon, and even though the number of individuals is low, they survive because they have high genetic diversity. With many species, however, populations have decreased very suddenly (ie due to hunting) and this can cause a rapid drop in genetic diversity (known as a bottleneck). Understanding how a population has changed over time allows conservation scientists to decide on the best course of action for trying to reverse a decline. Comparing the DNA from our sawfish rostra with DNA from living sawfish gives us a glimpse into the past. We can then discover whether the diversity today is the same as, or less than, in the past.
Steve Nash, Head of Education