UIC Biologists Use DNA to Study Migration of Threatened Whale Sharks

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UIC Biologists Use DNA to Study Migration of Threatened Whale Sharks
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News Release

 

[Writer] This is research news from U-I-C – the University of Illinois at Chicago. Today Jennifer Schmidt, associate professor of biological sciences, talks about genetic techniques being used in her lab to study the inter-ocean migration of whale sharks.

Here’s Professor Schmidt:

[Schmidt] My lab has been working on whale sharks for about eight years now. Whale sharks are the largest fish in the sea. They’re also the largest shark. They are quite a mystery to science – there really isn’t much known about whale sharks. They’ve only been studied for about the last 10-15 years and we really don’t know much about their biology, we don’t know much about their ecology and we don’t know much about their conservation status. We are trying to understand more about the biology of whale sharks to help to protect and conserve these animals.

One of the main questions that our lab has been trying to answer has to do with the relationship between whale sharks that are found in different parts of the world. Whale sharks occupy a geographic band around the equator in what are typically referred to as tropical waters. We find whale sharks in aggregations in many different countries within these latitudes. What we don’t know is if the whale sharks in these different geographic
locations are actually related to each other. In other words, are these isolated populations that don’t interact, or is there one large population of whale sharks that migrates and interbreeds between different geographic areas?

This question is important not only for understanding the biology of whale sharks, but also for helping to conserve these animals. If whale sharks are migrating and interbreeding, this can affect their conservation status.

Whale sharks are protected in many parts of their range, but they’re also actively fished in many countries in the world. There is evidence that in some parts of their range whale sharks are actually declining in number and they are declining in size. There have been studies done that have shown that the numbers of whale sharks in certain aggregations is decreasing and that these aggregations are made up of more immature animals, rather than mature animals of breeding age. This has a significant impact for the population — if larger animals are being selectively fished, which is what we believe.

The inter-connectedness of whale shark populations is important for their conservation because of the active fisheries that are open in certain parts of the world. If whale sharks remain in the areas where we study them – in protected waters – those animals are relatively safe and have little chance of being fished. However, if the animals are more migratory, then they can move to areas where there are more active fisheries, and those animals are in danger of being killed. So this is a very important question for knowing how to properly conserve whale sharks.

Our laboratory is a genetics lab and genetics can be used to answer conservation
questions. We’ve decided to use genetics then to try to understand the relationship between different populations of whale sharks. This can be done genetically by comparing DNA sequences between these different populations of whale sharks. Animals that are more closely related will have more similar DNA sequences and animals that are less closely related will have less similar DNA sequences.

We’ve worked with field biologists in a number of countries to obtain tissue samples from whale sharks. We studied approximately 68 whale sharks. We genetically analyzed these animals and compared the sequences of certain small DNA elements called microsatellites. These microsatellites are quite variable between different animals so we can compare them and use this to determine how related different populations are.

The conclusion from these experiments was that whale sharks found in different oceans are actually quite similar, genetically. We studied animals in the Indian Ocean, the Pacific Ocean and the Caribbean Sea and we find that these animals are quite similar genetically. What this means is that at some level, these animals actually migrate between populations and they interbreed between populations. This is reflected in the genetics that we were able to study.

These data have significant implications for conservation of whale sharks. They tell us that whale sharks from protected areas can not necessarily be assumed to stay in those areas. They can and do move between oceans and between populations. So animals that exist in a protected area may well move into areas where they’re actively being fished. These data provide strong support for the need to close active whale shark fisheries and to establish worldwide conservation guidelines for whale sharks.

[Writer] Jennifer Schmidt is associate professor of biological sciences

For more information about this research, go to www.today.uic.edu, click on “news releases” and look for the release dated April 7. 2009.

This has been research news from U-I-C – the University of Illinois at Chicago.

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