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Please begin with an informative title:

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As a marine educator I’ve become acutely aware of the threat posed by overfishing. In fact, I’m rather distressed about it considering that continuing our current rate of depletion of this resource it’s entirely possible that the marine ecosystem as we know it may collapse by the middle of this century.

Years ago I decided to do my part and swore off seafood completely. Although I have no animosity towards commercial fishermen, and indeed I rely on them often to obtain hard to get specimens for my education center, I’d really like to see the industry regulated in an intelligent way to preserve and protect at-risk species and the ecosystem as a whole. And as I’ve learned more about fisheries science I’ve come to the realization that boycotting commercial fishing en masse isn’t necessary. But carefully choosing what we consume is. Not only which species we eat, but how and where they are harvested or cultivated.

Intro

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My first diary in this marine life series, which is here, aimed to identify those species that consumers should consider as good choices, acceptable but with problems, and those that should be off limits. But here I would like to focus primarily on shrimp. I love shrimp, and although I gave it up for years, I’d like to find a way to eat one of my favorite foods and still not contribute to the destruction of the environment.

Commercial grade shrimp are found all over the world.  Wild stocks are mainly dragged for using bottom trawling nets. Farm-raised shrimps are harvested from man-made coastal pools where the shrimp can be contained and fed highly nutritious foods to increase their growth rates. Both methods have their upsides and downsides, and my goal here to see which harvesting methods, on balance, are preferable as far as ecological consequences go.

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Wild Caught Shrimp

I’m thinking back to the shrimp boat scenes in the movie “Forrest Gump” and I seem to remember a few shots of the shrimp haul by his boat where this huge netfull of shrimp is dumped on board. How easy it seemed: Drag a net for a while along the bottom and pull up a few thousand pounds of ready to eat crustaceans. Sadly, in reality this is not the case.

Most shrimp fishing is done using an otter trawl. This is a fine-meshed net dragged behind a boat which skims the ocean bottom in hopes of scooping up as much shrimp as possible in each pass. An otter trawl may have an opening up to sixty feet wide as it scours the ocean bottom picking up anything in its path. The shrimp you eat are benthic animals that live among grass beds, coral reefs and sandy bottoms. They are not free-swimming animals like their relatives the krills, famous as the main staple of baleen whales.

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Otter trawl

Benthic otter trawling is perhaps the single most destructive type of fishing method when it comes to “bycatch”. This term refers to the unwanted fish and invertebrates that are caught along with the target species. You would think that bycatch would be easy to deal with since you could simply throw back what you don’t want and keep the rest. But this is not how it works. For several reasons.

First we have productivity. Boat owners depend on a certain tonnage of sellable catch to cover their costs and hopefully make a profit. When you consider that a shrimp boat’s haul may contain as much as ten pounds of bycatch for every pound of shrimp, no businessman in his right mind would pay his crew to take the time and energy needed to release the unwanted animals unharmed. Economics dictates that you freeze the targeted catch as soon as possible and get the net back in the water.

Second, although shrimp may be found in dense numbers in favorable habitats, they do not form schools as many commercial finfish do, nor do they live in colonies like many species of mollusks. To catch a worthwhile amount of an animal with behaviors like shrimp requires the boat to cover a lot of ground. Covering a lot of ground means that many, many non-target species get caught up as well.

Third, even if some ecologically-minded boat owner decided on a “catch and release” policy for all of the unwanted haul (he’d go broke), the time the bycatch spends out of water before the crew can pick out the valuable shrimp and then release the rest, as well as the injuries caused by being dumped onto a boat deck with thousands of pounds of other creatures, would make survival rates inconsequential.

So, what happens to the bycatch? In general, after all the shrimp have been picked out of the giant pile of biomass on the deck and quickly frozen to preserve them, the crew shovels or hose-sprays the rest of the catch overboard. Pretty much nothing survives. Of course, because the bycatch is left dead and dying at the bottom of the sea these animals are basically out of sight, out of mind. Imagine the outrage if a hunter searching for a deer killed nearly every bird, mammal, reptile and insect in his path. And simply left them lying dead on the ground. You get the picture.

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A sea turtle, along with hundreds of other
species, lies dead on the deck of a shrimp
boat. (Photo by NOAA)

Tropical shrimp live in much more diverse and fragile environments than those species found in the temperate Atlantic or Pacific. The damage that tropical trawling can do to bottom habitats can be summed up simply with a term some ecologists use for the destruction left behind in the wake of a passing shrimp boat: “Coral Decapitation”. Temperate shrimp, on the other hand, live in less vulnerable habitats that are able to rebound from the damage done by a trawl (assuming it is given the chance to recover, that is) much quicker than a tropical reef or grass bed.

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These Alaskan shrimp are caught
with smaller bycatch problems
than southern varieties.

Now, I’m not dismissing the bycatch issues associated with northern shrimp fishing, but consider this one truism of marine populations: In temperate oceans there is a smaller diversity of species than in tropical oceans, however these northern species occur in denser populations. In other words, a given area of tropical reef may have a thousand species on it but each species has a low population size. A temperate area of equal size may have twenty species living there but each species has many, many individuals.

This is important in two ways. Any deaths from bycatch in a tropical zone will result in a harder hit to the species’ small population. The bycatch of temperate animals will affect fewer species total, and because they inevitably will contain many individuals of each type, the bycatch will more likely be utilized as a marketable catch as opposed to being discarded back into the ocean.

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Mangrove forest

Shrimp Farming

With many types of fisheries, aquaculture is a very good way of bringing seafood to market while still protecting wild stocks of the species from dwindling. A perfect example of this is mussel and oyster farming, which uses the manipulation of these animals’ own environment to increase their numbers. This is done by creating floating “reefs” full of suitable substrate for the mollusks to grow on and avoid their natural predators by having these beds suspended above the ocean bottom.

But this is not the case when it comes to shrimp farms. There are two main problems with these. The first is the issue of eutrophication. This is the suffocating of coastal or inland waters by the introduction of large amounts of nutrients into the water body. This fertilizer causes plant growth to explode, and when the plants die the resulting explosion of decomposing bacteria depletes the oxygen levels and results in large fish kills (not to mention the smothering of valuable filter feeders by the algae growth to begin with). Eutrophication can be caused by manure runoff from farmland, or in this case, the huge amounts of nutrients added to the shrimp ponds to encourage growth.

The second problem with shrimp culture is the massive destruction of coastal estuaries, habitats which are perhaps the most biologically productive areas in the world, in order to make room for shrimp farms large enough to be economically profitable. Of particular concern are tropical mangrove forests which are being destroyed at alarming rates to make room for extensive shrimp farms in South America and Southeast Asia. Studies on Malaysian mangrove forests have discovered that they are vital habitats for the young of 80% of all commercial seafood species. These farms not only rob other species of their breeding grounds, but threaten the livelihood of people who make their living fishing for other types of seafood.

Rice paddy fields in some Southeast Asian countries (particularly Bangladesh and Vietnam) are sometimes converted into shrimp farms, however because of toxic sludge that accumulates at the bottom and the salinization of the surrounding soils, these ponds may only be viable for a few years. After that the paddies can no longer support shrimp, rice or any other crop. This has major impacts not just on wildlife habitats but on the local human population as well.

In Hong Kong there is now a method of responsible shrimp farming known as Gei Wai which employs smaller, enclosed ponds that support a variety of edible species (mini ecosystems). Not only do these ponds pose less risk to estuaries, but actually attract endangered coastal birds, which benefit from the pond’s life without depleting the crop. Once a year the pond is drained and the animals harvested. The Gei Wai is then used for grain crops for part of the year (absorbing the collective wastes as fertilizer) and then reverted back to shrimp/fish ponds. This method is so effective and unharmful environmentally that it has been endorsed by the World Wildlife Fund.

Other methods of shrimp farming are being developed in the U.S. and Canada that are under strict regulations as far as nutrient run-off and habitat destruction goes. Unfortunately these operations require large startup costs and are only viable for industrialized countries. As technology improves in the aquaculture field these shrimp-growing plants will undoubtedly become more efficient, profitable and environmentally benign.

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(image by NOAA)

Conclusions

When I first started this diary I expected to be able to give you recommendations as to which type of shrimp harvesting method is more environmentally responsible. What surprised me is that it seems it is not the fishing method (wild caught vs farm raised), but the geographical locations the shrimp are found in (tropical vs temperate) that really matters.

The bottom line is if the shrimp is caught or farmed in temperate zones, there may be problems associated with harvesting the species, but they can still be considered an acceptable seafood choice, especially if used sparingly (like saving your shrimp meals for holidays and special occasions).

On the other hand, any tropical species of shrimp, whether wild caught or farm-raised, should be considered off limits. The human and ecological costs of harvesting these species of shrimp is unsustainable and frighteningly destructive to the marine and coastal environments.

How can you tell where a shrimp is native to, and whether or not it has been farmed? Most frozen and bagged shrimp should be clearly labeled. If you get your seafood from a real fishmonger, he will know where it originated from, so ask him. Large Stop and Shop type grocery stores will generally buy the cheapest species and these will no doubt be tropical (beware especially of those labeled “Tiger Shrimp” since these often come from the worst run shrimp farms). Also, the little peeled shrimp used in shrimp cocktail are usually northern so should be safe, but again, simply buying them from a reputable dealer that you trust should be your best guide. Oh, and when asking about the origin of your seafood, be sure to explain to the dealer why you want to know. It may influence his choice the next time he deals with a wholesaler.

So now that we’ve identified a relatively ecologically sound way of buying these crustaceans, you can now in fairly good conscience use them in your favorite recipe. Or you can try mine, called Cajun Barbecued Shrimp. You keep the shells on the shrimp, and because of the way it’s cooked you can actually eat the whole shrimp, shell and all (but not the tail. Just use that as a convenient handle). Also, during my vegetarian days I tried making this recipe using strips of tofu substituted for the shrimp and it is nearly as good. Especially when served over steamed rice. For the veggie version substitute bacon with soy-based bacon bits.

When using tofu you need to get rid of as much excess water as possible. Place the block of extra-firm tofu on a plate, put another plate on top of it and weigh that top plate down with something fairly heavy, like cans of tomato sauce or something. Drain the dish periodically of the water. This should take about a half hour or so. Then slice the block in two lengthwise and cut into one-inch strips.

Cajun Barbecued Shrimp

Ingredients:

1 1/2 lb large shrimp (responsibly bought)
4 slices bacon, chopped fine
1/4 lb butter
1/4 cup olive oil
2 tbl dijon mustard
1 1/2 tsp chili powder
1/4 tsp dry basil
1/4 tsp dry thyme
dash “liquid smoke” (Don’t overdo this. Just a dash.)
1 tsp ground black pepper
1/2 tsp dry oregano
2 cloves garlic, grated
3 tbl “Old Bay” crab boil (Your seafood store will have this.)
2 tsp tabasco sauce
Preheat the oven to 375 degrees. Saute bacon in a frying pan and then add all other ingredients except for the shrimp. Heat on medium and mix well for ten minutes, stirring constantly.

Place shrimp, with the shells on, in an open glass baking dish in a single layer. Pour the sauce over the shrimp and be sure all of them are coated.  Bake uncovered for 20 minutes and serve hot over rice. Shells can be eaten or peel the shrimp as you go.

Other diaries in this series can be found here.

Extended (Optional)

Originally posted to Mark H on Fri Jan 26, 2007 at 07:34 AM PST.

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