Plenty of Fish in the Sea?

Worldwide, countless people depend on fishing for food, culture, and economic well-being.  From local subsistence fishermen in small coastal communities to large industrial-sized operations, oceans contribute to societies and economies at all scales.  To keep pace with demand, fishing rates have greatly accelerated, to the extent that over 77 billion kilograms of seafood are harvested each year.

Harvested fish on ice to be sold at a market
Fisheries around the world capture large harvests of fish to sell at markets.

At such high rates, many fish populations cannot reproduce quickly enough to replenish their depleted numbers, thereby classifying them as overfished.  Currently, 90 percent of fisheries around the world are burdened with or on the brink of over-exploitation beyond sustainable yields.

Due to the strategies used in harvesting fish, it is usually not just the target populations and species that suffer.  Typically fishermen strive to catch the largest and most profitable fish first, often the top predators—such as the Atlantic bluefin tuna.  As these stocks are depleted, their prey—species like sardines and herring—become more plentiful in the ecosystem.  Because larger fish generally live longer and require more time to become reproductively mature, their populations are more adversely affected by overfishing, and it can take years or even decades for their numbers to recover.  In the meantime, fishermen will likely redirect their efforts towards the more abundant smaller fish, which can in turn affect the populations of sea birds that rely on them for food.

The effects experienced by other species can vary depending on the method of fish capture used.  Among the worst methods in terms of environmental degradation are dredging and bottom trawling. These techniques involve dragging either a metal basket (in the case of dredging) or a net (used in trawling) along the sea floor—in the process destroying entire habitats—in pursuit of bottom-dwelling fish like halibut and sole.  Other methods, like purse seine or seine net fishing, use massive nets to catch large schools, though these approaches often also collect large amounts of unintended bycatch—non-target fish species that are accidentally caught in the fishing gear or captured and then later discarded back to the sea.  After being caught and discarded, most bycatch do not survive.

Sardines caught in a fishing net
Seine net fishing involves using giant nets to trap many fish at once.

But what alternatives are there to industrial fishing techniques?  Aquaculture—farmed fishing—has become an increasingly common solution, with over 40 percent of consumed seafood—including Atlantic salmon and shrimp—being reared in aquafarms.  Typically, these farms are net-enclosed areas of the ocean in which the fish of interest are raised.  While fish farming reduces the need to harvest from wild stocks, it can still have fairly devastating effects for ocean ecosystems.  As with terrestrial livestock farming, aquaculture requires chemical inputs in the forms of vaccines, antibiotics, and pesticides.  Since the enclosures are made of nets or cages that allow water to flow freely between the fish farm and the surrounding ocean, chemical contaminants, faecal matter, and excess nutrients can easily pass through the cage walls and pollute the neighbouring environment.  Additionally, fish often escape from their enclosures, which poses a risk to wild populations due to increased competition and disease transmittal.  Another important consideration is the food supply required to support the captive fish. As previously mentioned, carnivorous fish are among the most sought after for fishermen.  This means that in managing aquafarms, the stock has to be fed with other fish.  Due to metabolic inefficiencies between different trophic levels, only about 10 percent of the energy consumed by an organism from a higher level in the food chain is available for use by that organism.  In other words, if a fish eats 1,000 kilocalories-worth of food, it only has 100 kilocalories available to it for doing work.  Because of the large inputs required to operate fish farms, wild fish still have to be caught to produce fishmeal, which accounts for roughly a third of all wild harvests worldwide.

So what can we do about it?  Is the only sustainable option to cut fish out of our diets altogether? Of course not. With over 50 million people employed in the fishing and aquaculture industries and the importance of fish both culturally and economically, it is impractical and unreasonable to expect people to give up such a staple of their livelihoods.  Certain fishing operations, however, are focusing efforts to become more sustainable.  With regard to wild-caught fish, fishing nets can be designed to reduce bycatch by manipulating the size of the mesh. Further, targeted line-and-bait techniques are also considered to be more environmentally responsible by better selecting for specific species of fish. The Marine Stewardship Council certifies fisheries that employ sustainable and less ecologically damaging harvest practices.  In terms of aquaculture, a more environmentally-friendly approach might be to use land-based farms—like those being developed by the University of Maryland’s Dr. Yonathan Zohar —that filter and recycle water to avoid contaminating ocean ecosystems with farm-based pollutants.

Healthy school of fish
Over time and with sustainable fishery management, fish populations will start to recover.

We as consumers can make a difference by educating ourselves and others about different seafood options and their respective environmental impacts. There are several easily accessible online tools to help guide sustainable fish consumption.  The Marine Conservation Society’s Good Fish Guide as well as the Monterey Bay Aquarium’s Seafood Watch Assessment Tool (available in the United States) make it easy for users to look up commercially available types of fish to check which species are typically sustainably caught or farmed according to defined standards.  By caring about where our seafood comes from and the environmental toll of our consumption choices, we can join in the push towards sustainability and ensure that in future generations there will still be plenty of fish left in the sea.

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