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Biological oceanography

Earth Week: Overview on Overfishing

We are a remarkable species capable of incredible ingenuity that has allowed us to successfully inhabit extreme reaches of the planet. Unfortunately, as the human population continues to grow and we continue to develop new technology, we systematically exploit natural resources. Although the oceans seemingly hold an infinite amount of fish, we have caused numerous populations to collapse through overfishing.

Figure 1: There are less fish in the sea then there were just a few decades ago. Image from World Wildlife Fund

Figure 1: There are less fish in the sea than there were just a few decades ago. Image from World Wildlife Fund

When explaining overfishing to my friends and family I am usually met with disbelief. I get it- it seems so contradictory when you can find seafood in almost every grocery store and restaurant and you never see labels suggesting that there are fish shortages. Well, you don’t see those warning labels because we are so good at catching fish. Too good. The fish can’t reproduce fast enough to keep up with how quickly we are fishing them. It is estimated that 90% of fisheries are already overfished, overexploited, or have already collapsed (meaning they were so drastically overharvested that they can no longer be commercially fished; Figure 1). Unfortunately, this overfishing doesn’t just spell disaster for our dinner plates; it also spills over and affects the entire ecosystem. So how did we get here?

The tragedy of the commons:

The tragedy of the commons is an economic theory used to describe the exploitation of common resources. It goes something like this: Say you have a giant cake. If it is all yours, you will probably cut it into small pieces, eat a little each day, and savor it slowly so it isn’t gone right away. But, if you are at a buffet with 100 of your closest friends, you can bet you are taking three slices and gorging on it so that the cake doesn’t disappear before you have had your fair share (I know I fall into this trap!).

For the most part, the ocean is the unregulated “shared cake” in our example. In order to keep others from overfishing, everyone amps up their fishing efforts to make sure they too can get a slice of the cake. Unfortunately, the ocean is not an all-you-can-eat buffet and there is a limit to how quickly and  to what extent the fisheries can rebound from being exploited in this manner. According to the World Wildlife Fund, our global fishing fleet is 2-3 times larger than our oceans can actually support. This systematic overexploitation has led to some unfortunate consequences, like fishing down the food web.

Fishing down the food web:

Figure 2: This graphic shows how we fish down the food web, preferentially picking off large, apex predators (like the sharks) first and keep moving towards the smaller fishes after we have removed the larger fish from the ecosystem (image from fishingdown.org)

Figure 2: This graphic shows how we fish down the food web, preferentially picking off large, apex predators (like the sharks) first and keep moving towards the smaller fishes after we have removed the larger fish from the ecosystem (image from fishingdown.org)

Fishing down the food web is a term used to describe how our fishing habits have forced changes in what we consume.  Here is how it works: we specifically target the tastier fishes first (these tend to be large predatory fishes like tuna, groupers, mahi mahi and sharks). Once those have been overexploited and they are harder to catch due to low population sizes, we are forced to move to less desirable fishes to put on our plate. These are the small, often times herbivorous fishes, crabs, and shellfish (Figure 2). We continue to pick our way through the food chain, moving to less and less desirable animals at the bottom of the food web.  Read one of the original articles on this topic in Science: Daniel Pauley et al., 1998

Not only are we moving into the area of exploiting undesirable species, but we are also beginning to exploit uncharted territory. As we overfish areas that are easy to reach (near coastlines and shallower water), we are forced to find new areas of the ocean to harvest. We have begun fishing in more remote and deeper waters.

Figure 3: The long lived deep-sea orange roughy. Image from orangeroughyinfo.tumblr.com

Figure 3: The long lived deep-sea orange roughy. Image from orangeroughyinfo.tumblr.com

This can be doubly harmful, however, because many of the animals inhabiting these areas are more vulnerable: they grow slower, live longer, and produce fewer offspring. All of these traits lead to a faster exploitation of these species, like orange roughy (Figure 3). This species of deep-sea fish aggregates near deep-sea sea mounds, making it easily caught. With a lifespan exceeding 100 years, orange roughy populations have been unable to keep up with the rate of human harvest.

There is another HUGE problem with fisheries that usually gets swept under the rug (or thrown overboard…).

Bycatch:

Although consumers can be quite picky,  fishing gear is not as discriminatory. As a result, while targeting a single species, fisheries haul in tons of bycatch — the unwanted, often unusable animals that come up in their nets. Fishermen usually cannot sell bycatch, either because of consumer preferences or because of fisheries regulations., When these undesired animals are pulled onboard, they are often just discarded (and not usually alive). And when I say fishing gear is equal opportunity, I mean for all animals- including endangered fishes, sharks, turtles, dolphins, and sea birds.

Figure 4: Left- Bycatch from the Gulf of California being thrown overboard including fishes, rays and guitarfishes (a shark relative). Image taken by Brian J. Skerry, National Geographic Stock, from WWF.org (http://www.worldwildlife.org/media?threat_id=bycatch) and Right- a sea turtle caught in a fishing net is just another form of bycatch (image from seafoodwatch.org- http://www.seafoodwatch.org/ocean-issues/wild-seafood/bycatch)

Figure 4: Left– Bycatch from the Gulf of California being thrown overboard including fishes, rays and guitarfishes (a shark relative). Image taken by Brian J. Skerry, National Geographic Stock, from WWF.org and Right- a sea turtle caught in a fishing net is just another form of bycatch. Image from seafoodwatch.org

Pulling all of these animals out of the ocean at an unsustainable rate can have severe consequences on the marine habitat. By pulling out certain groups of fishes we take out key players in the ecosystem. For example, when we pull out all of the predators, the fish they would normally eat multiply unchecked, which can cause problems for the rest of the habitat. Likewise, as we fish down the food web and start removing herbivorous fishes, we run into issues like algae growing uncontrollably.

Figure 5: Fishing can have many unintended consequences, as shown in this infographic from the University of Walkato

Figure 5: Fishing can have many unintended consequences, as shown in this infographic from the University of Walkato

Fishing can also damage fragile environments (i.e. bottom trawling) and pollute the environment when fishing gear is lost (for example ghost nets are nets which have been lost at sea that continue to do their job, entangling animals as they drift through the ocean). These are just two consequences of overfishing that I want to bring to your attention. Broadly speaking, there can be a lot of strings attached to that fish fillet you buy at the store (Figure 5).

 

Farming fish (and other seafood):

To cope with the endless demand for seafood, there has been a move to farming fish (and other seafood) instead of catching stocks from the wild. While some of these techniques are decent alternatives, some can actually increase water pollution and add to the overexploitation of fish stocks. Here are the basics: whenever you are growing fish, they require food and produce waste. When these fish are being farmed, the systems are usually closed with other additives like antibiotics and fertilizers. Depending on the fishery, fish may be fed wild-caught feeder fish, increasing demands on natural fish populations. If the fish are not being raised in a closed system (as is the case for off shore tuna and salmon fishing and many coastal shrimp fisheries), the waste, antibiotics, and fertilizers pumped into the farmed system can escape into surrounding waters and contaminate and  pollute the environment.

Let’s look at an example: Shrimp tend to be farmed in open, coastal systems. The shrimp may be caught from wild populations to stock the pond (which is frequently more of a coastal area netted-off but still in contact with the open ocean ), further contributing to overharvesting of wild populations. The ponds are usually dosed with antibiotics to keep disease from spreading in the densely packed ponds. The waste produced by the shrimp and the antibiotics readily flow from the open ponds into the surrounding water, polluting the open ocean. Antibiotics may keep disease from ravaging the farmed population, but they also can kill important bacteria in the water, meaning this runoff can cause dead zones in affected areas. This type of farming alone, has led to the destruction of more than 3.7 million acres of mangroves. These mangroves are hugely important because they provide a lot of ecosystem services, including hosting large degree of biodiversity, acting as important nurseries for  many oceanic animals, and creating barriers that can lessen impacts of storms for inhabited areas.

What can you do?

Seafood watch app from Monterey Bay Aquarium can help you make healthier and more sustainable seafood choices

Seafood watch app from Monterey Bay Aquarium can help you make healthier and more sustainable seafood choices.

Make educated seafood choices! You do not necessarily need to stop eating seafood altogether, but be aware of the consequences of different fishing methods and try to base your consumer choices accordingly.

Monterey Bay Aquarium has fantastic resources to help you make smart seafood choices, including pocket guides to help you pick seafood based on where you live (they even have one for sushi!). Even better, There’s an app for that! You can easily check your seafood choices on your phone and be informed about safer alternative choices. The World Wildlife Fund has some great international guides to help you make smart decisions outside of the United States as well.

Want to become more educated on fishing practices, policies, and overfishing? Here are some good links to start your search:

Want to know about the current research in this area? Here are some links to other oceanbites posts on overfishing:

 

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