Alien species add to the pressureAlready weakened fish stocks in some maritime regions are faced with the additional threat of alien species. Predators which feed on the fish, eggs and larvae of weakened stocks are particularly problematic, and competitors for food can play further havoc with depleted stocks. The situation becomes critical when the alien species thrives under its new living conditions and begins to reproduce vigorously. For example, alien species migrate from the Red Sea and through the Suez Canal into the Mediterranean. Some of them are apparently supplanting the native species of the eastern Mediterranean. The anchovy and sprat stocks of the Black Sea collapsed in the 1990s. This was due partly to overexploitation and partly to a type of fist-sized comb jellyfish introduced in the ballast water from ship tanks further undermining the already low fish stocks. The swarms of jellyfish ate the fish eggs and larvae en masse, biologists believe. Stocks have still not fully recovered. They are considered either fully exploited or still overexploited.
A closer look at the different speciesTaking a closer look at the individual fishing areas of the world, it becomes clear that there is no simple response to the question of how the fish are faring. It’s a complex situation. Without doubt many stocks are overexploited or have collapsed. But others are recovering thanks to sustainable fisheries management regimes. By way of illustration, the following section describes some individual fish species and their status – including the most important species with the highest total catch volumes. These fish species make up about 25 per cent of the world’s total fish catch. Most of their stocks are considered fully exploited or overexploited.
- 3.10 > Tins of tuna generally contain the flesh of widespread species such as the skipjack tuna. Nonetheless, consumers should ensure that the products they buy are from sustainable fisheries.
The Peruvian anchovy – sometimes more, sometimes lessThe development of the Peruvian anchovy (Engraulis ringens) is interesting. In terms of catch, it is the most important fish in the world. Large amounts are processed into fishmeal and fish oil to be fed to larger farmed fish in aquaculture operations. The largest volume ever caught, around 13 million tonnes, was landed in 1971. Today this would equate to a quarter of the global fish catch – excluding catches of other marine fauna such as mussels and squid. In the 1980s, the stocks crashed to about a tenth of this record level, not only as a result of intensive fishing but probably also because of a lack of food caused by the El Niño climatic phenomenon. The stocks later recovered. A new annual record of 12.5 million tonnes was reached in 1994. Since 2004, catch volumes have been dropping again, once more mainly due to El Niño. This anchovy example clearly shows the extent to which stocks can fluctuate. It also illustrates the vast amounts of fish which humans are removing from the seas; when adverse environmental conditions are added to the equation even vast stocks can be decimated. This example also teaches us that a stock can regenerate rapidly due to the ability of the fish to reproduce profusely. Other species of fish and stocks, however, are not capable of recovering so quickly from overfishing. One example of this is the Northeast Atlantic mackerel.
- 3.11 > The ten most important ocean fish species and their worldwide catch totals. As a result of the El Niño climatic phenomenon, catches of the Peruvian anchovy in particular fluctuate from year to year.
The Northeast Atlantic mackerel – departure from the North SeaThe Northeast Atlantic mackerel (Scomber scombrus) fishery comprises three components: the western, the southern and the North Sea stock. Each has its own spawning grounds. The North Sea mackerel spawn along the east coast of Britain, the southern component in the Bay of Biscay and off the Iberian Peninsula and the western component to the west of the British Isles and Ireland. In spring, when the plankton proliferates in response to rising temperatures, the mackerel of all three stocks gather in large hunting schools and migrate to the region between the Shetland Islands and Norway. They later gradually leave this nutrient-rich summer feeding area to spawn in the three regions mentioned above. They display an amazing swarming instinct: by no means all the first-time spawners return to their traditional spawning grounds, but often follow the majority of the mackerel. The North Sea mackerel used to be the largest component, so many first-time spawners were attracted to the North Sea. However, stocks of this component collapsed in the 1970s due to overfishing.
- Although the fishery was completely closed, the component has still not recovered. The western stock component then became the most prominent. The repercussions are clear: many mackerel which today begin their lives in the North Sea follow the main flow of fish towards the west when they first spawn. This occurs even in good years. Even when there are plenty of young fish in the North Sea most of them migrate westwards to spawn. The fact that there are still mackerel in the North Sea presumably means that a certain proportion of them continue to frequent the spawning grounds on England’s east coast. The question is whether a major mackerel stock will ever again be able to establish itself in the North Sea. It is interesting that the Northeast Atlantic mackerel has apparently been increasingly orienting itself towards the west in recent years. The early-summer migration has been taking them more regularly into Icelandic waters. As a result, Iceland’s mackerel catches have soared from 4000 to 200,000 tonnes in only three years. Scientists are worried about the development because for years now too many mackerel have been caught. The reason is that the littoral states – the Faroes, Iceland, Norway, Russia and the European Union – cannot agree on lower catches. Each nation sets its own limits. When added together the total catch far exceeds the annual tonnage recommended by scientists. Fears that Northeast Atlantic mackerel stocks will be completely overexploited in the coming years are therefore justified.
The European hake (southern stock) – haggling over catch numbersThe future of the European hake (southern stock) in the Bay of Biscay and west of the Iberian Peninsula is also uncertain. This is a classic example of how difficult it is to accurately assess a stock. And it also shows that if in doubt, a fishing nation tends to continue fishing rather than protect a fish population. The hake debate is difficult, mainly because the species seems to have been proliferating more rapidly over the past two years than had been observed previously. Its spawning biomass levels are increasing. ICES scientists, however, believe that for some time now, probably since the turn of the century, the stock has been overfished. The ICES fish abundance estimates have revealed that three times more hake has probably been caught than the stock can sustain over the long term. After tough and protracted negotiations with Spain, the European Commission in 2005 finally succeeded in establishing a management plan. But the ICES experts consider this inadequate, because it aims to reduce catches very slowly. In purely arithmetical terms, the stock could, at some stage, recover. However, the scientists claim that such an increase in the hake population would be so minimal as to be scarcely perceptible. Accordingly, it would be impossible to predict any stock recovery within the next ten years. For this reason, many experts consider the management plan absurd, providing the hake with little protection. Nonetheless, Spain is persisting with it based on the evidence of the current increase in spawning biomass. The ICES believes that too many fish are still being caught, and it is simply a matter of luck that spawning stocks are expanding. They claim that hake numbers are growing in spite of and not because of the management plan. Spain is unlikely to back down. The data it has submitted to the ICES for 2012 is incomplete and is of little use in this form. This has led to the current heated debate taking place between the ICES and Spain.
- 3.12 > Resolute fisheries management can ensure the recovery of a fish stock. After the North Sea herring was overfished in the 1960s (as revealed by the drop in spawning biomass), the fishery was completely closed. The stock, particularly the numbers of sexually mature fish (spawners), regenerated. After renewed over-fishing in the 1990s a management plan was agreed in 1997, which once again limited catches. The spawning stock was able to recover. The reduction of spawning biomass since 2002 can presumably be ascribed to climatic changes.
The North Sea herring – recovery is possibleThe example of the North Sea herring shows that a stock can recover if it is given a chance. Within a few years of the introduction of seine fishing in the 1960s, the stocks collapsed. The herring fishery was therefore completely closed between 1977 and 1981 – a measure which was both logical and correct. The stock recovered. In the early 1990s the spawning biomass level reached a new high. The next crisis followed not long after. This time many juvenile fish were captured in the nets as bycatch, leaving fewer fish to grow to maturity and rebuild depleted populations. As a result the spawning biomass dropped markedly once again, and stocks reached another low point in the mid-1990s. But this time reaction was swift. In mid-season 1997 catch amounts were again cut back drastically, and stocks recovered.
Purse seine A purse seine is a net that is used to encircle a school of fish. The net is then drawn together to retain the fish by using a line at the bottom, allowing the net to be closed like a purse.
- This example shows that the development of a stock can be very specifically controlled by restrictions and bans on fishing, resulting in positive change. Since 2002 the spawning biomass has again been dropping – most probably due to natural climatic fluctuations. Apparently the reproduction of the herring is partially connected to the North Atlantic Oscillation (NAO), a large-scale fluctuation in atmospheric pressure which occurs at regular intervals. This is leading to more differences of opinion between the ICES which makes the recommendations, and the EU Council of Ministers which is responsible for fisheries management in the North Sea. The positive stock development prompted the Council of Ministers in 2011 to set higher catches than envisaged in the management plan and recommended by ICES. The ICES is urging that catches should remain as they were, in spite of the good spawning stocks. Especially in good times a management plan should be complied with, it claims, so that stocks can further regenerate and cushion years with poor reproduction.