Courtesy: Pedasi consultant via Wikimedia Commons
Hi there. My name is Titus. I'm a yellowfin tuna. You're probably guessing this post is going to be all about me and my family, and you're justified in thinking that. But the truth is, this is all about you.
You see your species really, really loves to eat us. Well not so much yellowfin specifically, but my cousins bluefin and skipjack tunas. Bluefin are the most expensive food fish in the world. Someone bought a relative of mine for $1.8 million in 2013! That crazy price tag means most of you have probably never eaten a bluefin. If tuna's ever crossed your lips though, you've almost definitely eaten a skipjack. Skipjack gets sold in cans that say "chunk light" on them and that's about 70% of the tuna in the US. The problem comes when you go to catch skipjack, the way you catch them means you also catch my siblings, and a bunch of other animals in the process.
Now I want to be clear; I have no moral authority to say you shouldn't eat fish. From one apex predator to another; I totally get it. Many of you have probably seen a documentary where we tear through a bait ball like it was nothing. In fact my mom was there when the BBC filmed the original Blue Planet. The difference between the way we catch our fish, and the way you catch yours comes down to effort. We really earn it, you often make it too easy. To what see I mean I'll have to show you a little bit more about where I come from.
"Follow me."
Courtesy: Elias Levy via Flickr
My relatives and I live a pelagic (pronounced pel-aj-ick) lifestyle. That means that we're always swimming closer to the surface than to the bottom. Don't get me wrong though; we've been seen diving over 2,000m down. It's just that we live in the big part of the ocean, the part that makes your stomach drop when you look down and there's nothing but blue fading to black over the miles beneath your feet.
Courtesy: US Pacific Fleet via Flickr
It takes some really special adaptations to find food in this great azure emptiness. There's little phytoplankton to feed the ecosystem out here so prey are spread very far apart. That means we have to cross hundreds of miles of what's essentially desert to have opportunities to hunt. And we're not talking about pretty, cactus rich desert like the American Southwest here. The open ocean is more like the Dune Sea on Tatooine from Star Wars.
Even the way we're born is designed to help us get by in the vastness. My mom, carrying about 2 million of the eggs that would become me and my siblings, swam from the open Atlantic into the Gulf of Guinea off the West coast of Africa. Why there? Upwelling and river runoff. Nutrients from the bottom of the ocean and far inland travel into the surface waters of the Gulf and fertilize massive blooms of planktonic algae. Those plant-like plankton feed animal plankton, which are pretty much Gerber baby food for larval tuna.
Courtesy: K. Dale via NOAA
I hatched from my floating egg into this rich soup of life where I fed on all kinds of tiny and delicious animals. Seriously, you guys haven't lived til you've tried copepods. Anyway, chowing down on these energetically rich little buggers meant that it only took about a month for me to develop the muscles I needed for adulthood. High stamina "red muscle" in my sides allows me to continuously swim for hundreds of miles with no breaks. In fact, I can't actually breathe if I'm not always swimming so taking a break would be a terrible idea. Those stoic red muscles are the tissue that you eat as poke, or sashimi, or in sushi rolls, or seared, or on salads. You really like to eat our red muscle is my point. And like I said before, I totally understand wanting to eat delicious fish. That's basically my entire diet.
So my parents set us up in a great feeding ground and we grew quickly, but the ocean is a fickle place. Pretty soon the plankton blooms started to die back and the anchovies, herring, and other small fish my relatives and I were eating began to disappear. Luckily one part of the ocean's end of the bloom is another's beginning and I felt something deep inside me stir. This instinct drove me to join up with other tunas and pushed us all out into the formless wilds of the open sea.
And here's where we start to get to the larger point. I didn't school up with just yellowfin tuna. I joined with albacore, skipjack, bigeye, you name it. As long as we were about the same size none of us cared if we were the same species or not. My school doesn't even care if we're all fish; sometimes we work with dolphins. We even hang out with whale sharks every fall in the Gulf of Mexico, those dudes are super chill. While this embracing of diversity is awesome it poses a problem when you scoop up our whole school in nets. If you're fishing for skipjack, which are a stable fishery, but you use a big net you almost always catch a bunch of the rest of us. There are fewer of us yellowfin, and waaaay fewer bluefin than some of the other species. You could theoretically sort through and pick out the species you're not targeting, but remember we don't last long if we're not continually swimming, and to be honest we all look a lot alike when we're young.
The two on the left are skipjacks.
Courtesy: Stephanie Rogers and NOAA via Flickr
To make it worse, people catching tuna often use something called a FAD to lure us in. FAD stands for Fish Aggregating Device. That's a fancy sounding name, but it could be literally anything anchored to the bottom that provides something to hide on, under, or around. Old plywood, clumps of rope and sail, seaweed and branches, literal trash; all are shockingly useful to us pelagic creatures.
For animals that spend their lives travelling, floating debris is like a cute diner you stop at to pee and buy a slice of pie while on a road trip. Small fish are drawn to the piles because they think it will give them somewhere to hide from predators. Larger fish are attracted to the piles because we aren't dumb. There's literally nowhere else for you to hide anchovy! Anyway this is normal and good when it's natural debris, but when humans place the material on purpose....
Once every fish from miles around has come to your FAD you can efficiently dent the population with a single net haul.
Truthfully, I can't really get mad at you for such cleverness. Humans have used the adaptations they were given to survive challenging environments the same way we have. But the difference is that you have a choice. Your species is so smart that most of you have access to more calories than any of us in the ocean could dream of. So if you want to make sure me and my cousins don't disappear there are a couple things you can do.
Eating lower on the food chain is a great choice. Be like me and eat mackerel! Mackerel have nice, soft white meat like albacore, with none of that fishy taste that scares a lot of people off. Also if you're going to eat tuna make sure it comes from someone who's committed to ensuring we stick around on this planet. Since canned represents the vast majority of the tuna you eat, it's especially important to consider the health of our stocks when you're buying it. Thankfully some nice humans have produced this chart:
It's awesome! Open Nature, American Tuna, Whole Foods and Ocean Naturals all employ fishing boats that don't use FADs. They also catch us with individual hooks and lines so that it's nearly impossible to catch the entire school! I chase down prey at 30 miles per hour or more so I can understand the thrill of the hunt that comes with bringing a fish in on a single line too. Just know that if it's ever me you catch; I'm gonna fight hard. We're all just trying to live as best we can.
Editor's Note: The text of this post was dictated to a tuna researcher by Titus from his autumn home in the Gulf of Mexico and emailed to the Depth and Taxa team. It would be absurd to think that a fish could type. However tuna do in fact have a broad knowledge of human culture particularly: Star Wars, memes, and Star Wars memes.
References:
Allain et al., "Interaction Between Coastal and Oceanic Ecosystems of Western and Central Pacific Ocean through Predator-Prey Relationship Studies", PLOS One, Vol 7 Issue 5, May 2012
Arocha et al., "Update on the Spawning of Yellowfin Tuna, Thunnus albacares, in the Western Central Atlantic", Collective Volume of Scientific Papers, 52(1): 167-176, 2001
Gonzales-Andres et al., "Abundance and Distribution Patterns of Thunnus albacares in Isla de Coco National Park Through Predictive Habitat Suitability Models", PLOS One, December 14th 2016
Scutt Phillips et al., "Revisiting the Vulnerability of Juvenile Bigeye (Thunnus obesus) and Yellowfin (T. albacares) Tuna Caught by Purse-seine Fisheries While Associating with Surface Waters and Floating Objects", PLOS One, June 29th 2017
