Posted by: leahbiery | June 13, 2010

Movin’ On Up (The Food Chain)

Mangroves provide important habitat for shark pups.

I’m moving to Vancouver this Fall to begin grad school at the UBC Fisheries Centre. I had plans to study the delicate mangrove trees that line our coast, providing nursery habitat for important commercial species and producing energy for nearby ecosystems, but my plans came to a skidding halt and did a 180 this week. My adviser just secured funding to study global shark fisheries, so he asked if I would like to take on that project instead. I love sharks, and I’m always up for a new challenge, so I said yes – and took the giant leap from primary producers to apex predators in one day.

I can’t wait to start getting a handle on the global status of shark populations (after one more fabulous summer at Sanibel Sea School of course), but I have to admit that I am in need of a crash course in cartilaginous fishes before I begin. While perusing the internet to get the scoop on sharks, I was reminded of some basics – they are cartilaginous fishes, have a great sense of smell, can detect vibrations, and have skin covered in dermal denticles. I also learned a few new things about sharks, and I wanted to share some interesting facts:

  • Sand tiger shark pups developing inside their mother will eat each other until only one survives. This is called intrauterine cannibalism. And you thought the sibling rivalry in your family was intense.
  • Last year, there were 61 shark attacks worldwide. Only 5 were fatal. Humans killed approximately 100 million sharks. It makes me rethink who should be more scared.
  • Like Bluefin tuna, Great White, Mako, and Thresher sharks are warm-blooded. Their ability to regulate temperature keeps their eyes and brain warm, allowing them to hunt efficiently at high speeds even in very cold water.
  • Cookiecutter sharks eat by gouging round sections out of large fish, whales, dolphins, seals, manatees, and sometimes humans.

This pilot whale was bitten by a cookiecutter shark.

  • Tiger sharks are adventurous eaters and have a diverse diet of fish, other sharks, sea turtles, shellfish, and many other marine organisms. They will apparently taste just about anything; iguanas, beer bottles, handbags, deer antlers, and license plates, which have all been found in tiger shark stomachs.
  • Some shark species can survive on a large meal for up to three months!

There’s no doubt that sharks are fascinating – but they are also in danger. If you asked a shark to name its biggest fears, it would probably say “bycatch” and “shark fin soup.”  Each year, millions of sharks are caught accidentally by fishermen and do not survive – the tuna industry is especially notorious for its high rate of shark bycatch.

The Chinese have a taste for shark fin soup, which is prized as a delicacy and eaten during celebrations. When fishermen catch a shark, they cut off the dorsal fin, which they hang to dry, then throw the rest of the shark back into the ocean. Unable to swim without its dorsal fin, the shark can’t move water across its gills and suffocates quickly. Fishermen do not keep the entire body because it is expensive to transport and only the fin is worth significant money at market. The per-pound price of shark fin is comparable to that of Bluefin tuna ($40-$400/lb. depending on quality).

I spent some time reading shark fin soup recipes, and I was sad to find out that the soup is usually chicken-based. The shark fin is basically a garnish, and many recipes call for a splash of bourbon or other alcohol to “enhance the flavor” – which I interpret to mean “cover up the fishiness.” Shark fin soup is a wasteful, destructive tradition like the use of tiger bones to treat arthritis.

Sharks grow slowly, mature late in life, produce few offspring, and only live for 20-30 years, so when their populations are damaged it is hard for them to recover. Currently, 244 out of about 450 shark species are on the IUCN Red List, meaning they are at risk of becoming endangered or extinct. Nobody is monitoring shark fisheries internationally at the moment – they are hard to study because of their highly migratory nature. That’s where I come in – I will join the Sea Around Us Project to compile all of the shark research that has been done since the 1950s into one big interactive map that shows global trends. Hopefully, it will help scientists figure out how we can manage shark fisheries to give these creatures a brighter future.

Of course I want to keep sharks around for the sake of sharks, but also because I hope that someday my kids will be just a little bit scared to swim in the ocean. There’s something meaningful about plunging into the water with the knowledge that a giant powerful creature that could eat you (but in all likelihood won’t) might be lurking nearby. As humans, we are used to being in charge. There is important perspective to gain from being in “someone else’s territory” –  and I want to share it with future generations.

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Responses

  1. Nice information.

    Isn’t is great that one of our attractions of being in the ocean is entering foreign territory, where we might not reign supreme. After many years in the ocean, it is always in the back – and sometimes the forefront of my mind.


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