Tangled in the food web

Features

We go to the sea hoping to see birds swooping and diving, to watch them carve the wind, to turn and twist, skimming the sea as they search for food. Their dark images darting against the setting sun give flight to our imagination, conveying freedom, beauty, and grace.

The reality, however, is that watching seabirds increasingly means seeing scavenging gulls following fishing boats, waiting for handouts. Where are the beautiful shearwaters, the comic puffins, the terns? Many are gone now due to starvation or breeding failure brought about by pollution, habitat destruction, and climate change. And destructive fishing practices.

Seabird populations are changing in all our oceans, but the trend is best illustrated in the waters of the Northeast Atlantic, which consists of the North Sea, the Norwegian Sea, and the Barents Sea. Over the past 40 years, this incredibly fertile ecosystem has eroded at an alarming rate. The North Sea is the most heavily trawled fishing ground in the world, with some areas being trawled once a month on average. Some nets are so large they could capture a dozen jumbo jets. The fishery removes 25 to 30 percent of the total biomass of the North Sea each year, an exceedingly high and unsustainable rate of depletion.

The North Atlantic is the first major fishery where production peaked and then experienced a gradual decline. In a 2002 study, Dr. Reg Watson and associates at the University of British Columbia Fisheries Center found the North Atlantic holds only about one-sixth the number of comestible fish species it had in 1900, yet is now being fished eight times as intensively. Production peaked in the late 1960s at 3.5 million tonnes per year; even with the subsequent introduction of modern fish-finding technology and bigger and more powerful boats, annual production of fish has fallen to just over two million tonnes.

The Northeast Atlantic is a good model for many ocean areas in demonstrating that the fishery alters the balance of bird species, their distribution, and the total population. Today, the fishery affects seabirds through discards, industrial fishing, overfishing, longlining, gillnets, and driftnets.

Discards
When a trawler brings its nets up from the bottom, the pace is often so fast that the fish literally explode. On average one-third of the catch consists of undersized fish, of species that cannot be brought into port because of regulations, or of species without market value. These are discarded, and this entire discard, mostly dead, goes overboard. The amount of discard is considerable. In 1990, in the North Sea alone, the European Parliament estimated that 800,000 tons of fish, invertebrates, and offal (i.e., heads and entrails) were discarded, while the total fish that went to market was nearly 3 million tons. Forty percent of the discards was consumed by seabirds, supporting higher populations of some species than a natural system could sustain.

The enhanced populations of scavenging birds distort a natural distribution by perhaps five million to eight million birds in the Northeast Atlantic. Great black-backed gulls, great skuas, and northern gannets out-compete other birds for discard from boats. The smaller kittiwakes follow fishing boats even when there is no discard, so that they can be the first on the scene.

Too many scavenging seabirds means greater predatory pressure on fish stocks that other types of seabirds eat, more eggs stolen from nests, and so forth. A more natural balance could be achieved by reducing discards. Most discard is generated by the trawling fishery, so any solution must primarily address trawling. As juvenile fish make up a substantial portion of discards, one corrective step would be to require larger fishing net mesh sizes. Discard would also be reduced if the fishers were required to bring all fish, regardless of size or species, into port. (This last idea is very contentious.)

Increasing mesh sizes in all other fisheries would help to reduce discard. Mesh size should be increased sufficiently to raise by one year the average age of caught fish. This would allow another year for fish reproduction.

Vastly diminished stocks of cod or halibut, or other fish at the top of the food web, have two consequences for bird populations. One, obviously, is that there are fewer codfish eggs or juveniles for birds to prey upon. More importantly, with fewer adult codfish, for example, there is a much lower predation rate on those species they eat. Populations of those fish species explode, which favors expansion of seabird species that specialize in them.

Industrial fishing
When most people think of North Sea fishing, images come to mind of fishers confronting Arctic winds and waves to catch cod, herring, or salmon. This is only part of the total fishery. Over the last 40 years, a huge industrial fishery has developed to catch fish destined not for the table, but to be converted into animal and fish feed. This industrial fishery lands between 600,000 and1,300,000 tons of fish each year, often more than half of all fish taken from the North Sea.

The industrial fishery began by processing offal from other fisheries into fertilizer and other products. By the 1950s, fishers realized it was profitable to catch fish specifically for industrial products. The industrial fishery expanded vigorously in the 1960s and remains huge to this day.

Industrial fishing first targeted mackerel and herring, already under pressure from conventional fishing. Fishmeal from these oily fishes is high in omega fatty acids for raising healthy poultry, swine, or farmed fish. Fishing pressure increased dramatically during the late 1960s, causing a collapse of mackerel stock in the North Sea in 1970. This fishery has never recovered. The herring fishery collapsed in the late 1960s in the Norwegian Sea and in the mid-1970s in the North Sea. Fishing in the Norwegian Sea was drastically curtailed, and the fishery there has partially recovered.

Having depleted mackerel and herring, the fishery was forced to turn to smaller species such as capelin and sandeel. Capelin and sandeel (also called sandlance) are critical components of the ocean food web in the Northeast Atlantic, serving as primary prey for cod, haddock, halibut, and other species at the top of the food web. The capelin, a small fish belonging to the salmon family, is found only in the Arctic. In summer, it grazes on the dense swarms of plankton at the ice edge. Larger capelin also eat krill and other crustaceans. Whales, seals, cod, and seabirds all prey on capelin. Capelin are key to bird populations in the Barents Sea. The sandeel, found throughout the Northeast Atlantic, is a finger-sized fish that prefers to burrow in the gravel-sand seabed sediment. It emerges to feed, often rising close to the surface. Sandeels can be extremely plentiful, especially now that many of the fish at the top of the food web are so depleted. The sandeel biomass in the Northeast Atlantic is estimated to exceed five million tons. But now, every year, more tons of sandeels are harvested from the North Sea than of any other species.

Sandeels are taken mostly offshore in the central North Sea or from banks off the east coast of Scotland. There is a comparatively small catch near the Shetland Islands that has become the focus of concern by environmentalists. Around Shetland, arctic terns and black-legged kittiwakes suffered a series of very poor breeding years in the 1980s. The cause of nesting failures is proven: there weren’t enough sandeels to feed the birds adequately. Professor Robert Furness at the University of Glasgow has studied the sensitivity of seabirds to reductions in sandeel abundance and found that terns are the most sensitive of all seabirds to reductions near rookeries. Low sandeel abundance near rookeries may mean a failed breeding season for terns. Kittiwakes, gulls, skuas, and puffins also have low breeding success if sandeels are scarce near rookeries.

The UK press concluded that the breeding failures of the 1980s and again in recent years are attributable to overfishing of sandeels near Shetland. However, research has since shown that local fishing was unlikely to be the direct cause of the decline in sandeel abundance: populations remained low even after the local fishery was closed. It may be that sandeels did not reproduce very successfully near Shetland for several years. Another possibility is that Shetland sandeels are actually born elsewhere, and were taken by the fishery before they reached Shetland waters.

Along the east coast of Scotland, south of the Shetland Islands, evidence of overfishing as the cause of the decline in a seabird population is more compelling. The expansion of the sandeel fishery there coincided with a decline in breeding success of black-legged kittiwakes on nearby coasts, a decline not seen elsewhere.

Overfishing also affects birds elsewhere in the Northeast Atlantic. In the 1980s, there were three especially good years for codfish spawn in the Barents Sea. But the large numbers of cod had little to eat because both herring and capelin stocks had been severely overfished. The young codfish grazed down all other prey species in the area, including other codfish. With approximately 20 million birds in the Barents Sea, a major food shortage forced the migration of millions. The puffin and guillemot populations there collapsed because of starvation.

Studies since the mid-1960s done in the Røst archipelago by Tycho Anker-Nilssen of the Norwegian Institute for Nature Research (and co-workers) show that the breeding success of the huge puffin population on Røst is strongly dependent on the number of young herring produced by the Norwegian spring-spawning herring stock. In 22 of the 33 years following the herring crash in the late 1960s, most puffin chicks starved to death in the nest. In some years, all of them starved. The number of puffins breeding in Røst dropped from almost 1.5 million pairs in 1979 to only about 500,000 pairs in 1988. There is still no sign of recovery.

In Anker-Nilssen’s 2001 paper, “Food Consumption by Seabirds in Norwegian Waters,” he writes: “Key fish prey for seabirds in Norwegian waters are capelin, juvenile herring, and sandeel. Young life stages (1st-3rd year) of saithe (pollock), haddock, cod and whiting are also important, especially for European shags and great cormorants. Sprats (sometimes sold as sardines) are also important in the North Sea. Fish eggs are important prey for wintering common and king eiders (seaducks).”

Hjelsøy and Bjørnøya, the main common guillemot breeding areas in Norway, experienced a dramatic decline in both colonies due to the overfishing of capelin in the Barents Sea in 1985 and 1986. Populations are now half of 1985 levels. In 1994, over 75,000 seabirds (guillemots, razorbills, shags, cormorants, kittiwakes, puffins, gannets, and little auks) washed ashore in England alone, victims of starvation.

The European Union (EU) faces a dilemma. Fishers are truly having a difficult time making a living because there isn’t much to be taken from the North Sea. On the other hand, the impact on the environment of overfishing is proven. To the consternation of the fishers, some 20,000 square kilometers of the sandeel fishing grounds off the Firth of Forth (Scotland) and the Shetland Islands are closed during critical times of the year. These protections mainly affect Denmark, the largest harvester of North Sea sandeels, the fish destined for Denmark’s poultry and swine industries. More restrictions on fishers appear inevitable.

Overfishing in the Norwegian and Barents Seas is not nearly the problem now that it was a decade ago. Strong measures in the 1990s rebalanced the fisheries in the Norwegian and Barents Seas, so while the situation there today is not perfect, it is much improved.

The problem can be addressed, if not entirely solved, through two strategies. First, a broad study of the environmental impact of the fishery in the Northeast Atlantic should be performed. Studies by fishery management agencies are generally limited to maximizing sustainable fish yields, rarely considering the impact on other elements of the environment until problems are apparent. The reason for this is straightforward: a broad environmental impact study of the oceans is very expensive because the ecosystems are extraordinarily complex and difficult to measure. If such a study reveals that the catch of sandeels, for example, needs to be reduced, then an option might be to stop feeding fishmeal to poultry or pigs.

The second part of the solution is to protect critical habitat areas. This action would help to re-establish a more natural food web in the Northeast Atlantic. No-fishing (“no-take”) areas formed elsewhere in the oceans not only protect the habitat, but also allow fish to reach larger sizes and to produce more offspring. A typical cod caught today might be four to seven pounds, able to produce a few thousand eggs.

A 40-lb. codfish—reasonably common in 1900, but virtually unseen today—can produce over one million eggs. Because fish move around, they ultimately spill over from the no-take zones into fishing areas, thus increasing the average size of the fish caught. The establishment of no-take zones in critical habitat is an ocean management tool that thus far has always improved both the environment and ultimately the fishery.

Longlining
In the Northeast Atlantic, the fishing practice called “longlining” catches cod and other fish dwelling near the bottom. A longline is simply a fishing line that is as long as 30 kilometers and bears thousands of baited hooks. As the line is let out from the boat, the bait can float on the surface long enough for a bird to grab it, become hooked, and get dragged under. Most of the birds killed this way are fulmars, which glide over the waves, dip to the surface to scavenge bait, and get hooked in the process. Observers have recorded mortality rates as high as 1.75 birds per thousand hooks set. Just the Norwegian part of this fishery represents 476 million hooks set in 1996, so as many as 830,000 bird mortalities are caused each year by the Norwegian fleet alone. Iceland and the Faeroe Islands (between Norway and Scotland) also have sizable longlining fleets. Because fulmar populations are actually expanding due to the availability of discards, longlining mortality does not pose a serious threat to the survival of the species, but it represents an ugly fate for the birds.

Setting gear at night prevents most bird deaths. Observed mortality rates for the Norway fleet were as low as 0.02 birds per thousand hooks when they were set at night. During the summer, there is little darkness at these high latitudes, so night setting cannot be the sole solution. Using minimal lighting on the boat and dumping fish wastes away from the lines both help. Another solution is to have the boat equipped with a steel tube about four meters long, through which the line passes from the vessel to the water. It shields the bait from the birds and helps sink it. Low-cost methods such as these could largely solve the longlining bird bycatch problem.

Gillnets and drift nets
Imagine climbing into a submarine and going to the bottom of the North Sea. There you see net “standing” 10 or 12 feet high, extending for hundreds of yards: a fence at the bottom of the ocean. This is gillnet, used to catch codfish and other bottom dwellers. So how could a net 3,000 feet below the surface be considered a threat to birds? Danger to birds comes while the net is being hauled to the surface and into the boat, or when it is being returned to the water. Birds are attracted to fish scraps in the nets and then become entangled. Thousands of birds, especially shearwaters, die in this manner every year.

Some types of seabirds can even become trapped in nets on the ocean floor. Guillemots feed by diving to the bottom of the sea, where they may become entangled in gillnets. In the Barents Sea, an estimated 100,000 guillemots died this way between 1965 and 1985. Total annual losses of deep-diving birds over all of the Northeast Atlantic, including puffins, are unknown, but likely significant. A few areas around the UK are now closed to gillnet fishing because of bird bycatch.

Drift nets hang down from the water surface and are often set for salmon. Because they are nearly invisible, drift nets are a hazard to birds. When a bird sees a fish near the surface and swoops down to take it, it risks entanglement in the net. Drift nets set for salmon in the Barents Sea lowered the population of common guillemots at Hjelsøy from 220,000 in 1965 to 10,000 in 1985. This drift net fishery was closed in 1989 to preserve salmon stocks, but drift nets are still used elsewhere in the Northeast Atlantic.

Increased mortality of guillemots and other seabirds in all types of fishing gear is reported from several different areas. On the island of Helgoland (North Sea), 6,566 guillemot fledglings were banded from 1912 to 1994, of which 605 were recovered. The recoveries were analyzed for causes of death. Until 1945, hunting killed most guillemots (71 percent of all recoveries), whereas by 1994, less than 2 percent were recorded as hunted. But the percentage of birds killed in fishing gear increased to almost 42 percent. Mortality by oil pollution reached its highest percentage between 1970 and 1988 (24 percent).

Tests in Canada during 2000 and 2001 using gillnets dyed with a white pigment have shown bird deaths were reduced by 75 percent, probably for the simple reason that the birds could see the nets more easily. To date the nets have not been tested elsewhere. Equipping drift nets in California with a highly visible section also led to a dramatic reduction in bird deaths.

Conclusion
The EU should sponsor a comprehensive study of the effects of fishing on the environment of the Northeast Atlantic. From this should come a plan to address negative impacts, including the distortion of the seabird population distribution.

Mitigation measures must be accompanied by enforcement. Given the divergent national interests of EU member nations and the interests of nations outside the EU, especially Norway, reaching consensus will be challenging. Steffen Smidt, director of the EU Commission and a member of the EU’s Directorate-General Fisheries, was dismissed in April 2002 when he sought reforms of the Common Fisheries Policy. Smidt’s plans had the full support of Commissioner for Fisheries Franz Fischler, but did not satisfy Spain and France because the reforms would have cut the EU fleet and stopped state aid to Spanish fishers.

What is done in the Northeast Atlantic has broader implications. Production in each of the 15 major fishing areas of the oceans worldwide has peaked, and most are now in decline. As the Northeast Atlantic preceded other fishing areas in decline by a decade or more, it may now provide clues to future developments in other areas. Indeed, many issues of the Northeast Atlantic are already extant in other areas. Discards distort seabird populations in every ocean. Overfishing west of South America (Peru/Chile), coupled with El Niño events, has resulted in a population decrease of 15 million guano birds since the mid-1950s. Longlining in the Southern Ocean and the North Pacific kills albatrosses at a rate that threatens the very existence of these birds. Gillnets threaten birds—not to mention sea turtles and dolphins—in every ocean. To date, governmental regulatory agencies worldwide have shown little interest in correcting bird imbalances caused by the fishery. We can develop and learn from new fishing strategies in the Northeast Atlantic to preserve and protect seabird populations everywhere. To do otherwise threatens these magnificent flyers with extinction.