Does Sustainable Seafood Exist?
The first sustainable seafood guide was published in 1998 to inform consumers and encourage them to make purchasing choices that are less environmentally costly . At present, possibly the most well-known organisation for the certification of sustainable seafood is the Marine Stewardship Council (MSC), having certified over 100 fisheries as of 2012 . The practices of organisations such as the MSC seem to have a common goal to “promote the best environmental choice in seafood”, but over the years their evaluation methods have been thrown into question .
To become certified, fisheries pay between $15,000-150,000 to a chosen consultancy who then assess the sustainability of the fishery . This has raised concerns as it means it`s beneficial for certifiers to be over-generous in their assessments in order to receive more business . This could be concealing the true environmental cost of seafood products and may mislead consumers into supporting practices that are threatening the health of our oceans.
So, what kind of measures are used to determine sustainability? How can consumers choose sustainable products if these certifications may be unreliable?
Sustainable Fishing Practice
Organisations like the MSC determine the sustainability of fisheries based on reference points given by the United Nations Convention on the Law of the Sea (UNCLOS) and the United Nations Fish Stock Agreement (UNFSA) . One of these reference points describes how fish stocks should be “maintained at or rebuilt to a size that can support the Maximum Sustainable Yield (MSY)” . The MSY is modelled by estimating the relationship between fishing effort, fish yield and population carrying capacity (the number of fish the ecosystem can support without breaking down) .
Within these fishery assessments, size is another important reference point. This is because removing a large number of juveniles that have not reached sexual maturity may result in population declines, as there are fewer remaining individuals capable of counteracting the effects of fishing [6-7]. On the other hand, the selective fishing of large individuals often removes the most dominant and reproductively successful fish and thus decreases the reproductive potential of the population . Similarly, many larger species of fish take a longer time to reach sexual maturity, and so are slower to recover from fishing activity .
There are also typically fewer individuals in the population the further up the species sits in the food chain, i.e., there are fewer large fish than there are small fish . This means that large species such as cod, salmon and tuna may be more vulnerable to overfishing and it takes the removal of fewer individuals to cause population declines.
Although the Maximum Sustainable Yield is a good measure of how sustainable fish stocks are, UNCLOS and UNFSA also use fishing method as an indication of fishery sustainability . This is because the method employed by fishers can have major impacts on marine ecosystems; most notably through habitat degradation and bycatch.
Structural complexity is incredibly important for marine species. The presence of complex structures such as corals, saltmarshes and mangroves can provide organisms with both food and shelter, as well as changing the flow of water such that dispersal, nutrient availability and larval recruitment increase . Each of these factors are necessary to maintain healthy, balanced, diverse ecosystems and prevent the loss of marine species [10-11].
In the fourteenth century, the very first accounts of trawling described how destructive and wasteful the practice was . Bottom trawling uses a large net, often held open with a beam, that is dragged along the seafloor to scare fish into the net from their habitat .
Along with large quantities of fish, this method removes such vast amounts of habitat structure that previously trawled ecosystems are significantly less able to recover from the effects of fishing . Recent research has also discovered that due to the amount of carbon stored within marine sediments, trawling releases as much carbon dioxide into the ocean as all terrestrial farming releases into the atmosphere . Given that 1.3% of the global ocean is trawled annually, this could be having devastating impacts on the already threatening degree of ocean acidification taking place . Structures such as corals and oyster reefs often take thousands of years to grow, but as this catch is undesirable to fishers, it is usually thrown back overboard to join the rubble on the seafloor .
Despite being particularly destructive, trawling is not the only wasteful fishing practice threatening our marine ecosystems.
The incidental catch of non-target species is known as bycatch, and it is one of the largest problems facing fisheries today, occurring in all fishing fleets [13-14]. Although bycatch can be sold, it is usually simply thrown overboard as there are many economic or regulatory reasons the catch is unusable or undesirable . For example, while out at sea it may make economic sense to dispose of the dead or dying animals that may be less valuable in order to increase the space available for more valuable species.
Davies et al.  estimated that 38.5 million tonnes of bycatch are caught every year, making up an astonishing 40.4% of the annual global marine catch. This enormous estimate gives an idea of the scale of the issue, however it does not demonstrate the degree of damage that is reflected in our marine ecosystems. A large proportion of bycatch is composed of juvenile fish, which although weighing less, have greater ecological importance when removed from populations, as discussed above [6,13]. This highlights one of the main concerns of indiscriminate fishing practices, as the potential for a species to recover from fishing activity relies heavily on its life-history strategies. Traits such as growth rate, fecundity (fertility) and the time taken to reach maturity can make populations especially vulnerable to fishing activity, putting large marine predators such as sharks, dolphins and seabirds at particular risk of extinction .
How do we eat seafood sustainably?
Sustainable seafood guides go some way to informing consumers about which species may be more, or less resilient to the effects of commercial fishing, however inherent biases lie in the methods used to label fisheries as ‘sustainable’. The issues related to fishery sustainability come down to the complex interactions between life-history strategies of individual species and multi-level effects caused by the chosen fishing methods and practices.
Many models have been produced to try and find a healthy level of fishing. For example, in his book ‘The Unnatural History of the Sea’, Professor Callum Roberts discusses the advantages of removing certain individuals from a population and even suggests that some fishing is more beneficial to fish stocks than no fishing at all. The designation of Marine Protected Areas (MPAs) that ban the removal of any species from within their boundaries is supposed to improve fish populations outside the MPA itself by something called the ‘spillover effect’ .
Despite suggestions such as these, it seems that the most effective way to influence sustainability within the oceans is to eat less seafood. The cheapness of the seafood products available often fails to reflect how valuable these products are to our marine ecosystems and when the subsidies paid to struggling fishing fleets are considered, we are likely making up for this inexpensive food in how our taxes are spent [2,14].
Given the research that is currently available, it seems unlikely that we will reach a ‘sustainable’ solution until we as consumers, ease the pressure on fish stocks and our marine environment as a whole.
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