Tarpon! Cool fish, cool science questions.
Half of the work for this project is to understand the movement of Atlantic tarpon. So, why is it that tarpon are even interesting scientifically?
Tarpon are interesting to me partly because they are just incredible fish. There is a reason tarpon are known among fishermen as an incredible game fish. They are strong swimmers, vicious predators, and put up a huge fight when hooked. In the US alone the recreational fishery for tarpon is valued at as much as $5 billion dollars!! People like to catch tarpon.
But tarpon are more interesting than just their appeal to fishermen. They are also just cool fish, period. We still have a lot to learn about how tarpon live their lives, but those lives are long and involve long-distance migrations. Adult tarpon have been shown to migrate as much as 1,000 miles (1,600 km), and they live a really long time. They can live to older than 50 years, which for a fish is a really long time. In that time they grow to enormous sizes. I personally have seen tarpon whose length rivaled my height and whose mouth would comfortably encompass my head. They get BIG!!!
But more than that, tarpon are incredibly flexible. There are not that many species who can survive and thrive in both fresh and salt water. Tarpon are one of them. Young tarpon larvae drift inshore and settle into brackish and even fresh water (did I mention we really don't know anything about where or how they breed...except that it seems to be far offshore?). They love places like mangrove swamps where there are plenty of other little fish to eat, and protection from bigger fish. Unfortunately these mangrove swamps are disappearing, mostly because people like to build houses on the ocean and mangrove swamps are muddy and therefore seen as something that has to go if coastal property is going to be "improved". So, saving this habitat is crucial to saving tarpon as well.
But more about tarpon. Aside from having an incredible ability to adjust to multiple salinities tarpon also have the ability to breath air. Their air bladders have specialized structures that allow them to take in oxygen...this gives them a big boost in low oxygen environments where other fish would have trouble staying active. Juvenile tarpon are "obligate" air breathers and actually must surface to breathe air in order to survive.
In fact, the video below shows a tarpon that we found who had somehow decided to stay in a tide pool along the shore near Salinas, Pará just south of the mouth of the Amazon river. The water was HOT and the only reason this guy could possibly have survived was the ability to breathe air.
Tarpon in Brazil are even less well studied than Tarpon in the United States or the Caribbean. But, they make up a big portion of the fishery during certain parts of the year. And, the fishery appears to be overfished. So, understanding more about the population is important in order to maintain the population in the future.
But, more than that, we have the opportunity to understand more about how tarpon populations are different across their range from North America to Southern Brazil. This kind of large-scale knowledge is important for fish that make big migratory movements. Because tarpon make these incredibly long migratory movements it's likely that all of these populations are connected to their neighbors. Knowing how well connected the populations are, and whether different populations have different local behaviors, is important in order to know how best to conserve populations.
The scales of these fish store incredible amounts of chemical information about where individual fish travelled during their life. These signatures are stored in the outer calcium layer of the scale. They also store information about where these fish are in the food chain at different parts of their lives. This information is stored in the inner layer of the scale that is made of keratin (the same material that makes up our fingernails).
You can see in the photo above that tarpon scales grow in rings that record the growth of the fish. The isotope chemistry in those rings record what that fish was doing at that point in its life. By analyzing this chemistry we can tell whether a fish was in fresh, brackish, or salt water. We can tell how long it was there. We can also tell when it transitioned from eating plankton to eating other fish, and when it went from being a juvenile to being an adult.
We still have so much to learn about tarpon. I'm excited about the potential for this project and I hope you'll stick around to hear more about how our project is progressing. If you have questions, ask! I'd love to hear from all of you in the discussion section of the website.
Additional Photos
I've been lucky to be able to do this work in an incredible location, the Amazon Coast of Brazil. Here are some photos from my tarpon sampling trips. Enjoy!
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