Professor Callum Roberts exposes the rapacious fishing practices that lie behind much of the canned fish we see on our supermarket shelves
In the early 1920s, Zane Grey, a bestselling author of pot-boiler cowboy novels and an obsessive fisherman, described the frustrations of fishing Costa Rican seas: ‘It was a marvellous sight to peer down into that exquisitely clear water and see fish as thickly laid as fence pickets, and the deeper down the larger they showed …We saw yellow-tail and amberjack swim among the sharks as if they were all friendly. But the instant we hooked a poor, luckless fish he was set upon by these voracious monsters and devoured. They fought like wolves. Whenever the blood of a fish discoloured the water these sharks seemed to grow frantic. They appeared on all sides, as if by magic.’
Grey was not alone in discovering the exceptional abundance of sharks and other fish in Costa Rican waters. Travellers had remarked upon teeming hordes of predators since at least the late eighteenth century, when Captain Vancouver had passed by on his voyage of discovery. Costa Rica’s waters have many times been described as the ‘sharkiest’ on the planet.
Costa Rica’s Thermal Dome
All the more remarkable then – and worrying – that in 2017 a BBC Blue Planet II film crew could spend three weeks at sea there and not see a single shark, despite being surrounded by abundant prey fish.
The incredible fertility of Costa Rican seas is down to the unique oceanography of this region. Just offshore there is an upwelling of nutrients from the deep sea which feeds a prolific bloom of plankton. Upwelling is driven by intense offshore winds that push water away from Central America, pulling up deeper layers that have far more fertilising nutrients. Depending on the strength of the winds, the Costa Rica Thermal Dome, as it is called by oceanographers, ranges from a width of several hundred kilometres to more than a thousand. Satellite tracking devices attached to ocean-going megafauna such as sharks, whales, turtles, manta rays and dolphins shows that the Dome is Grand Central for a huge array of wildlife. These animals make a beeline from all over the Eastern Pacific to feast at the banquet.
The recent absence of sharks is perhaps explained by what the film crew did see: tuna purse seine and longline fishing boats.
In the pursuit of their target species, mainly tuna and mahi-mahi, the proponents of these fishing methods inflict astonishing collateral damage on other wildlife. Longlines, as the name suggests, are often tens of kilometres long and studded with thousands of hooks. One study estimated that from 1999 to 2010 Costa Rican longlines accidentally caught 700,000 olive ridley turtles! Another study recorded the bycatch from 43,000 hooks set for mahi-mahi. To capture just 211 mahi-mahi, they also hooked – and almost certainly killed – 468 olive ridley turtles, 20 green turtles, 408 pelagic stingrays, 47 devil rays, 413 silky sharks, 24 thresher sharks, 13 smooth hammerhead sharks, 6 crocodile sharks, 4 oceanic whitetip sharks, 68 Pacific sailfish, 34 striped marlin, 32 yellowfin tuna, 22 blue marlin, 11 wahoo, 8 swordfish and 4 ocean sunfish. This isn’t fishing – it’s wholesale annihilation.
Tuna purse seines are nets up to 2 kilometres long and 200 metres deep that are set like walls around shoals of tuna. The spinner dolphin pods filmed by Blue Planet II for their remarkable aerial pirouetting displays are fellow travellers with tuna. Fishing captains watch them closely. After the film crew left, on that occasion – as no doubt on many others – the fishers set their nets around both tuna and dolphins. Legal tuna boats are required to let the dolphins go, but their capture causes stress and some will die. Illegal fishing boats, of which there are many, couldn’t care less about the dolphins’ wellbeing.
Progressive on land
Costa Rica is a country well-known for progressive nature conservation on land. But in the ocean it has a long way to go. When I visited in 2017, I went to a leatherback turtle nesting beach. Numbers returning to lay their eggs had fallen from over 1,000 per year in the 1990s, to just 17 that season, a 98% decline.
Most were probably caught and drowned by longlines and gill nets.
Costa Rica has banned the highly destructive bottom trawling for prawns in its coastal waters. In addition, it urgently needs to reduce fishing offshore and establish extensive and highly protected marine parks. There are moves afoot, with a fully protected marine park around Cocos Island, where Zane Grey saw his sharks. But time is short and the fishing industry rapacious.
There is a further complication to protecting this region, however. The upwelling that enriches Costa Rican seas and feeds its fisheries straddles the waters of several neighbouring countries and a large chunk of international waters. One of the most spectacular scenes in the 2019 Netflix series Our Planet was also filmed off Costa Rica. Here the camera crew came across something none had ever seen, something so momentous it had never been filmed before. Ten thousand spinner dolphins churned the ocean surface into foam as they demolished a giant shoal of deep sea lanternfish. The lanternfish live in the ocean’s twilight zone between 200 and 1000 metres deep. If recent scientific findings are confirmed, twilight zone fish could make up nine tenths of all the fish in the sea. By day lanternfish seek safety in the darkness of the depths; by night they come to the surface to feed on abundant plankton and small fish. This shoal had probably been trapped at the surface by the dolphins, preventing retreat to the depths as morning broke over the Eastern Pacific. By the time the sun set, most had been eaten.
High seas fishing
This breathtaking abundance draws in the high seas fishing fleet. High seas fishing is governed by regional fisheries management organisations. Countries sign up to these bodies and agree to be governed by the regulations that members collectively set. In practice, these regulations are often weak, since consensus on rules that would guarantee sustainability is rarely achieved. To make things worse, countries that don’t wish to abide by any rules can fish as they wish by not joining the management organisation. The result is that overfishing is the norm rather than exception, and protection for threatened wildlife like turtles or dolphins is never sufficient. And soon, lanternfish may also be targeted by the high seas fleet, to the detriment of wildlife and the planet. These little fish are crucially important in shuttling carbon from shallow to deep water, locking it away from the atmosphere where it would otherwise contribute to global warming. Without these fish, it has been estimated there would be 50 per cent more carbon dioxide in the air, and so the world would be much hotter.
The high seas are no longer a place we can conveniently ignore while ships plunder their riches out of sight and beyond the law. The creatures that live there are too vulnerable and too important for us to allow mismanagement and poor governance to destroy it. This is why negotiations under way at the United Nations for a treaty to protect wildlife on the high seas are so critical.
Failure of these negotiations could cost the ocean, perhaps even the Earth.
Callum Roberts is Professor of Marine Conservation at the University of York and was series scientific advisor to Blue Planet. He is Chief Scientist of BLUE Marine Foundation. email@example.com.