1
How important are fish to the human population, and how do technology and the tragedy of the commons interact to jeopardize global fisheries?
INFOGRAPHICS 31.1 AND 31.2
True or False: It is not surprising that the cod fisheries collapsed in the North Atlantic because the cod population was historically small and easy to catch.
FALSE
The capture of fish, dolphins, turtles, and other nontarget species in a fishing net is known as ________________.
Bycatch
The collapse of the cod fishery is a tragedy of the commons because:
some fishers are not allowed to fish in the Grand Banks.
cod was the most common fish in the area.
the privatization of the fishery caused its collapse.
fishers would take as much as possible because if they didn’t, someone else would.
D
Why might bottom-trawling fishing techniques make it harder for the cod population to recover even after the ships have left the area?
No fish are left to breed.
The nets damage the seabed where cod spawn.
The cod leave the area once a trawler has come through.
The ships attract seabirds that eat the cod.
B
Why do we define a fishery in terms of human use? Does that diminish it as an ecological concept?
A fishery is an industry devoted to the catching, harvesting, processing, and selling of certain aquatic species. It only exists in terms of human use and is defined by our interests in using particular aquatic resources for food.
From an ecological perspective there is no such thing as fisheries; rather, any particular fishery is part of an aquatic ecosystem. But a focus on fisheries can diminish our consideration of oceans as an ecosystem because the narrow interest in a specific species allows us to disregard for the impact that fishing practices may have on the rest of the ecosystem. Ideally, we would use ecological principles in managing fisheries, from establishing harvest quotas to selecting fishing methods that reflect an understanding of where and how the species of interest fits into its ecosystem.
2
What is fishing down the food chain, and how does it jeopardize fish populations? What is the current status of the world’s fisheries?
INFOGRAPHICS 31.3 AND 31.4
True or False: Currently more than 60% of fisheries are sustainably fished, while around 29% are unsustainably fished.
TRUE
“Fishing down the food chain” refers to:
taking only higher-trophic-level species and throwing back lower-trophic-level species.
making sure equal numbers of individuals are taken from all the trophic levels.
current management techniques designed to restore a depleted fishery.
moving on to taking lower-trophic-level species once the higher levels are depleted.
D
Ecosystems like those found in the extreme environment of the Arctic have simple food webs, with only a few organisms at each trophic level, whereas ecosystems with more moderate climates have more robust food webs with many species. Why is a simple food web more vulnerable to collapse than a more complex one?
A simple food web means that even the loss of one species can have significant consequences for the entire ecosystem as there are fewer other species (or none) to fill in the role of the species in decline. This can be seen in the case of the cod fisheries where the loss of the higher trophic level cod is particularly disruptive and may be irreversibly changing the ocean ecosystem of the Grand Banks. Declines in cod and the fish they feed on have increased the population of small jellyfish-like organisms called hydroids. Ironically this increase in hydroids makes it harder for the cod population to recover because not only do the hydroids feed on the same food as the very young cod, but they also feed on the juvenile cod themselves.
3
What are some of the ways we are trying to protect our fisheries?
INFOGRAPHIC 31.5
True or False: Exclusive economic zones are areas where fishing is prohibited.
FALSE
Marine protected areas:
are found in every ocean.
offer a variety of levels of protection from no-take zones to restricted access.
appear to be effective at helping damaged areas recover.
all of the above.
D
Define sustainable fishery.
A sustainable fishery is one that is fished and managed in a way to ensure that fish stocks are maintained at healthy levels, the ecosystem is fully functional, fishing activity does not threaten biological diversity, and the fishery is managed effectively.
4
What is aquaculture, and how might it ease the strain on at-risk fisheries? What are the trade-offs of aquaculture?
TABLE 31.1
The rearing of aquatic species in tanks, ponds, or ocean net-pens (fish farming) is known as __________________.
Aquaculture
Why might aquaculture be considered the “future of fishing”?
Systems like recirculating aquaculture systems (RAS) are so affordable that more fishers will turn to them.
Today’s aquaculture techniques provide fish to consumers without damaging the environment.
It can produce large numbers of fish while reducing pressure on many wild stocks.
It will raise fish to be released into the ocean to support commercial fisheries.
C
A disadvantage of net-pen operations is:
fish that can be successfully raised this way are not popular food items.
these operations are expensive.
they release pollution into the surrounding water.
they cannot be done on a large scale.
C
Distinguish between pond, net-pen, and RAS aquaculture.
Pond aquaculture: freshwater species of fish like catfish and tilapia are raised in ponds.
Net-pen aquaculture: marine species are raised inside pens that are lowered into the ocean. The net pens are usually close to shore but large mobile pens can also be taken further offshore and brought back to shore when it is time to harvest the fish.
RAS rears marine species of fish indoors in large tanks. This is the newest aquaculture technique that is more expensive to set up but can rear large, marine species of fish that are popular with diners such as tuna and sea bass.
5
What are recirculating aquaculture systems (RAS), and how might using them address some of the problems facing fish populations today?
INFOGRAPHIC 31.6
In what way is the RAS waste-treatment plan an example of biomimicry?
It purifies the water with biodegradable filters.
It depends on bacteria doing what they normally do in nature.
It allows the waste to naturally sink to the bottom of the pool, where it remains out of the way.
It focuses on frequent water changes rather than on purification of water.
B
What are the advantages of RAS, and where (in what nations or regions) will these systems likely be adopted? If adopted in these areas, will they help lower the impact of eating fish? Explain.
RAS systems share some advantages that apply to all aquaculture systems, and have some additional advantages over open water systems like net pen or pond aquaculture. The following is a list of potential advantages:
(1) they can be sized as needed to feed a modern city, or even a country
(2) they can raise large marine species that are declining in the wild, and perhaps ones which are the most beneficial to human health, independent of location of the aquaculture operation
(3) the fish growing in RAS tanks require less food per pound and convert their food into flesh at a much higher ratio than the same fish grown in a net pen because aquaculturists can control food intake, and because salinity is always optimal, fish don’t have to invest as much energy in osmoregulation
(4) they reduce habitat loss
(5) the system is biosecure—there is no risk of the fish from RAS operations (especially if they are non-native) escaping into the wild and causing problems for wild stock
(6) no pollution is released as RAS employs carefully calibrated microbial communities to manage waste: in fact, bacteria convert some 96% of the solid waste into fuel-grade methane so an additional benefit is that the system produces energy that can offset some of the energy costs
One of the limitations of RAS systems is that the technology is more complex and it is more expensive to set up and operate, making it not feasible in the poorer regions of the world or in water-starved areas. But given that the type of fish grown can be chosen based on economic opportunity rather than location, such a system is potentially well suited for markets in developed countries like the United States where most of the fish consumed is imported and thus typically shipped long distances. Reducing the distance between the fishery and the consumer, RAS technology could make that environmental impact much smaller (less energy for transportation and cold storage) and the fish would be fresher and probably less expensive as well.
Consider the triple bottom line and propose (based on current technology) a low-impact way for people in developing nations to meet their need for fish.
Answers may vary but should account for economic, social and environmental concerns. Example:
Since net pen operations are a simpler technology as well as less expensive to set up and operate, the best way (environmentally and economically) for people in developing nations to meet their need for fish (a social concern) would be to address the specific problems associated with such operations:
• to reduce diseases, the associated use of antibiotics, as well as waste that is generated, it would help to decrease the density of fish in net pens
• to reduce loss of mangrove and other fragile coastal habitats, it would help to move outdoor fish farms farther from the coast
• to reduce the pressure on wild fish stock (that are used as a source of food), it would help to find alternative foods that do not rely on fully on wild caught fish, and also concentrate on fish lower on the trophic chain to increase efficiency of food conversion
• to reduce effects on wild stock from non-native fish escaping, it would help to only use native species of fish in net pen operations
31-19