In severely depleted zones, the only way to restore stocks is by introducing protected reserves where all fishing is banned. In other areas, quota compliance needs to be properly monitored – fishing vessels could be licensed and fitted with tracking devices to ensure they don’t stray into illegal areas, spot-checks on fish could be carried out to ensure size and species, and fish could even be tagged, so that the authorities and consumers can ensure its sustainable source.
The other option is to take humanity's usual method of dealing with food shortages, and move from hunter-gathering to farming.
Already, more than half of the fish we eat comes from farms – in China, it’s as high as 80% – but doing this on an industrial scale has its problems. Farms are stocked with wild fish, which must then be fed – larger fish like salmon and tuna eat as much as 20 times their weight in smaller fish like anchovies and herring. This has led to overfishing of these smaller fish, but if farmed fish are fed a vegetarian diet, they lack the prized omega-3 oils that make them nutritious, and they do not look or taste like the wild varieties. Scientists are working to create an artificial version of omega-3 – current synthetic omega-3 versions are derived from fish oils.
Fish farms are also highly polluting. They produce a slurry of toxic run-off – manure – which fertilises algae in the oceans, reducing the oxygen available to other species and creates dead zones. Scotland's salmon-farming industry, for example, produces the same amount of nitrogen waste as the untreated sewage of 3.2 million people – over half the country's population. As a result, there are campaigns to ban aquaculture from coastal areas.
Farmed fish are also breeding grounds for infection and parasites that kill off large proportions of fish – escapees then frequently infect wild populations. Farmers try to control infestations with antibiotics, but usually only succeed in creating a bigger problem of antibiotic resistance.
Humanity is not limiting its impacts to fish most commonly found on menus. Exotic sea creatures from turtles to manta ray to marine mammals are being hunted to extinction. Shark numbers, for example, have declined by 80% worldwide, with one-third of shark species now at risk of extinction. The top marine predator is no longer the shark, it’s us.
A decline in shark numbers has a significant impact on the marine ecosystem: it can lead to an increase in fish numbers further down the food chain, which in turn can cause a crash in the population of very small marine life, such as plankton. Without the smallest creatures, the entire system is threatened.
One of the repercussions, which I have discussed before, is an increase in jellyfish numbers, but overfishing, pollution, climate change and acidification also affect the marine ecosystem. Warmer waters are pushing species into different habitats, causing some to die off and others to adapt by creating entirely new hybrid species. Meanwhile, trawlers are netting bycatch that include marine mammals and even seabirds – as many as 320,000 seabirds are being killed annually when they get caught in fishing lines, pushing populations of albatrosses, petrels and shearwaters to the edge of extinction.
Some solutions are easier than you might think. Seabirds can be protected by using weighted lines and scaring off birds with lines that have flapping streamers attached – these methods alone have reduced seabird deaths by more than 85-99% where they are used.
Strengthening and expanding protected marine reserves would also go a long way to conserving species. Currently, less than 1% of the ocean is protected, although by 2020, the international community has agreed to raise this to 10%. Reserves, when properly patrolled and monitored, do protect marine life, and nation after nation is stepping up to the plate. The tiny Pacific islands have banded together to create a giant protected area of 1.1 million square kilometres, for example. Not to be outdone, Australia has created the world’s biggest protected area, and countries around the world from Britain to New Zealand are joining the effort.