Important target species for industrial fishing
The commercial importance of a fish species does not depend on how well-known it is, nor on how often it ends up on our plates. This is shown by the example of the sand eel, which hardly any consumers know or eat. These small fish play an extraordinarily important role in many marine ecosystems, and are also almost indispensable as a raw material for the European fishmeal industry.
The name is deceptive, since sand eels are not eels at all, despite their moniker. The name probably refers to the long, eel-like, almost cylindrical shape of their bodies as well as their unusual lifestyle – like eels, sand eels spend many hours of their day buried in sand. Sand eels form their own family (Ammodytidae), comprising 18 species (some authors even believe there are up to 30 species), which are primarily benthic (sea floor dwelling) and live in shallow coastal waters of the Atlantic, Pacific and Indian Oceans. The typical features of these small shoaling fish include deeply forked tail fins in addition to their body shape and long dorsal fin ridge, which extends over almost the entire length of their body.. These fish do not have pelvic fins or swim bladders. Their high fat content means that sand eels make nutritious food for many predatory fish, seabirds and marine mammals, and also most sand eel species remain comparatively small and easy to catch. Almost every nature lover has seen images of puffins carrying multiple sand eels in their colourful beaks at once. The most important defence for these small fish that are so highly prized by predators is, above all, how they conceal themselves in sediment, in addition to forming shoals which confuse attackers by pretending to be a much bigger ‘super-organism’. Fleeing sand eels can dive into loose sand or seashell fragments in an instant, making them invisible and inaccessible to most predators. However, this does not always work, because some predators have adapted to this game of hide-and-seek. They can target, track down and dig up their concealed prey.
However, sand eels do not just hide in sediment when fleeing from predators, they camouflage this way for protection all the time whenever they are not feeding. Some species even bury themselves in wet sand in intertidal areas during the ebb tide and only come out again when the water returns with the next high tide. Then they often form large shoals which move around within their area looking for food, but still remain relatively close to their original location. Sand eels spend the first weeks of their lives in open water before switching to a sea floor-based lifestyle when they are approximately five centimetres long, and then they remain in the same area almost constantly.
Half a dozen sand eel species with similar biology
Sand eels are represented by six species in the North Atlantic, five of which living along European coasts have commercial significance for industrial fishing, including in the North Sea and the Baltic Sea. Apart from their different maximum sizes, which range from 20 to 40 cm, these species are so similar in their appearance and way of life that precise differentiation between them is seldom done in the fishing industry in practice. Information on populations and distribution should therefore be treated with some caution.
The greater sand eel (Hyperoplus lanceolatus), which is said to reach up to 40 cm in length, is usually cited as the largest species. It can be identified by a dark spot on the side of its snout. Corbin’s sand eel (Hyperoplus immaculatus) reaches a maximum length of 30 cm. The lesser sand eel or sand lance (Ammodytes tobianus), which only reaches 20 cm in length, is the most common species in the North Sea. At 25 cm, Raitt’s sand eel (Ammodytes marinus), which is also known as the Raitt’s lesser sand eel, is only slightly larger. The fifth species in the family is the smooth sand eel (Gymnoammodytes semisquamatus), which, with its maximum length of 23 cm, lies between the two Ammodyte species. The taxonomic status of the Mediterranean sand eel (Gymnoammodytes cicerellus), which is said to be no larger than 16 cm, is currently disputed. Some biologists believe that G. cicerellus simply replaces the smooth sand eel (G. semisquamatus) in the Mediterranean, others are of the opinion that the Mediterranean sand eel is perhaps a synonym for the lesser sand eel.
Since the different species of sand eel are largely similar in their biology and way of life, the key data for all of the species is processed together centrally using the example of the greater and lesser sand eel, all the more so as these species often occur in shoals together. Typical of both species and all sand eels without exception is their softly radial fins and uniform body colouration with green-blue backs, silvery sides and white bellies. While the tip of the pectoral fin in greater sand eel ends before the beginning of the dorsal fin, in the lesser sand eel it extends to the beginning of the dorsal fin. The long and noticeably pointed head has a relatively deep mouth, and the lower jaw clearly protrudes. The protractile mouth, which forms a kind of tube when catching prey, is characteristic of sand eels. Both species occupy the same habitat, which extends from the coast until the water reaches a depth of 30 m. In winter, however, the shoals move further out to sea. There they prefer sand banks at deeper locations which provide them with especially good hiding opportunities. The distribution range of the greater sand eel in the North Atlantic extends from the eastern Murmansk coast over Spitsbergen, Iceland and the British Isles to Portugal and on through the English Channel into the North Sea. This fish can also regularly be found in the Baltic Sea. This distribution area is almost identical to that of the lesser sand eel.
Short-lived plankton feeders with high fertility
Sand eels become sexually mature at the age of two years, when they have reached a length of approximately 10 cm. Considering their huge distribution area, spawning is taking place almost all year round in one place or another, depending on the water temperature. Sand eels in the North Sea mainly reproduce from April to September, i.e. in spring and summer. The females attach their eggs at a depth of 20 to 100 m in small heaps on sandy ground or gravel banks made of shellfish fragments. The fertility depends on the species of sand eel, the size of the fish and its condition. For the lesser sand eel, the number of eggs varies between 3,000 and 20,000, and the greater sand eel lays up to 35,000 eggs. The eggs are 0.8 to 1.0 mm large, and the larvae are 4-8 mm long. They ascend to the upper levels of the water for several weeks, where they feed on plankton organisms of a suitable size. The maximum documented age of the sand eel is approximately 10 years, which few animals reach, because they have a very large number of predators. Sand eels are part of the prey spectrum of almost all larger marine fish species, from sea trout and salmon to cod, shellfish, pollock and whiting, and mackerel and numerous flatfish species. Marine mammals and seabirds also prey on them. For their part, sand eels feed on the lower trophic levels of plant and animal plankton such as copepods, cladocera and small fish.
Humans are another major exploiter of the sand eel, catching these fish mainly for use as bait for longline and sports fishing and as an important target species for so-called industrial fishing. These comparatively small fish are only very rarely used for culinary purposes, although experienced cooks will attest that they are tasty and simple to prepare. What probably stops fish lovers from consuming them, in addition to the lack of a culinary tradition and scarcity of these fish in the retail trade, is primarily their limited size and the fact that they are relatively bony. However, there is nothing really standing in the way of putting these fish on our table every now and then. Fried sardines and anchovies, which are not much bigger, have after all conquered the Mediterranean kitchen, where they are very popular, and the annoying bones are said to become so tender when the fish is fried that they are hardly noticeable when eating. Although sand eels are one of the most underestimated edible fish species, with average weights per fish between 15 and 40 grams, many interesting and tasty-sounding recipes can be found on the Internet. For example, grilled sand eel in lemon butter or – like the widely loved fried herring – coated in rye flour and fried in melted butter. One recipe even recommends placing the fish, gutted and with heads removed, in a pan so close to one another that they stick to each other when frying and can be eaten almost like an omelette.
Enormous ecological and commercial significance
From a nutritional perspective, sand eels have a lot to offer. In addition to high-quality protein with all essential amino acids, they contain plenty of vitamins, above all A, D and B12, and are also an excellent source of EPA and DHA omega-3 fatty acids. However it should be noted in this context that the quantity of omega-3 fluctuates throughout the year along with the fat content of the fish. This is especially noticeable for sexually mature sand eels over 10 cm long. They have only 2 to 6 percent fat at the beginning of the spawning season in April, while this figure usually rises to 6–13 percent in June at the end of the reproduction period. For initial culinary experiences with these fish, catches from the second half of the year should therefore be used if possible.
Depending on the intended use, various methods are used to catch sand eels. Sports fishers, who need sand eels for angling bait, often turn to local fishers, who occasionally catch these small fish as bycatch in trawl nets. Some anglers also try to dig sand eels hidden in tidal flats out of the ground. The success of these methods, however, requires quite precise knowledge regarding the preferred hiding places of the sand eels. The third method for individual catching of limited quantities is the use of paternoster angling, which is familiar from herring and mackerel angling. This works very well in dense shoals, although the small fish are seldom hooked properly by the mouth, but usually somewhere in the body instead. When it comes to larger catches, whether for use as bait fish for longline fishing industry or for industrial uses, close meshed trawl nets or seine nets are used.
As regards the ecological significance of sand eels for the marine ecosystem and their heavy use by the fishing industry, the question naturally arises as to how the stock situation is looking for these important species. When estimating stocks in fisheries biology, a distinction is not made between the individual species, instead all of them are recorded together as the Ammodytes-Hyperoplus group of species. Like the capelin (Mallotus villosus) or the Peruvian anchoveta (Engraulis ringens) and other relatively short-lived fish that feed planktiverously at low trophic levels and are very fertile, sand eel stocks are also subject to frequent strong fluctuations in natural stock levels. Stocks can also recover very quickly following weaker years if the external conditions are right and sufficient plankton food is available. In order to be able to precisely model and predict these developments, a particularly comprehensive and detailed database would be required, which cannot be achieved to a sufficient extent for the sand eel. It is generally assumed that none of the fished sand eel species are currently seriously endangered and stocks are not threatened, but the precise situation is unclear for the most part. This is why the precautionary approach is particularly valued when determining catch quotas (TAC). Nevertheless, some are of the opinion that sand eel stocks have been declining in recent years. This is particularly concerning for the ornithologists among the nature conservationists, who see the food supply of some seabird species becoming endangered as a result.
Danish industrial fishing is the main user of sand eels
Almost reflexively, Danish industrial fishing is then blamed for the situation, although it emphasises strongly that it complies with all legal provisions and with the catch quantities approved according to the TAC. During the 18-week sand eel fishing season in 2020, which began on 1 April and ended on 31 July, approximately 238,000 tonnes of fish were landed by Danish and foreign fishing vessels in Danish ports for the country’s fishmeal industry. 171,700 tonnes of this was landed by Danish fishing vessels, 39,700 tonnes by Norwegian and 23,500 tonnes by Swedish fishing vessels, as well as 3,100 tonnes by vessels of other nationalities. Sand eels are in fact only one of the fish species that are processed into fishmeal and fish oil in Danish factories. Without exception these are small, short-lived species such as the capelin, blue whiting, sprat, Norway pout (Trisopterus esmarkii) and boarfish (Capros aper), which have little or no commercial value for human consumption. Their fishing mortality is usually much lower than their natural mortality and the size of the stocks can fluctuate significantly from year to year. All fishing industries are strictly regulated and the catch quotas are based on the scientific recommendations of the ICES. Cutoffs, i.e. carcasses, cuttings, trimmings and other leftovers from fish processing are growing in importance as a raw material for the fishmeal industry. Depending on the fish species and product, often only one to two thirds of the body of the fish is used. Processing them into fishmeal is a sensible use for these remaining scraps. This also applies to undersized fish from bycatch that have been accumulating in EU countries since the landing ban. Fishmeal is therefore not a waste of valuable marine resources, but rather the exact opposite – it is making an indispensable contribution to their full use.
Denmark is the most important industrial fishing nation in the EU, and accounts for a large part of the catch quotas for the relevant pelagic species. In 2019, its share made up approximately 84% of the EU landings for this sector. Industrial fishing therefore makes up a significant portion of the Danish fishing sector. In 2019 it accounted for almost half of the value created at 43%. The significance of the sand eel for supplying raw material to the Danish fishmeal industry varies, however, due to the large fluctuations in stock from year to year. Measured against the Danish catch quotas, sand eel contributed almost half of fishmeal production in 2017, but only 10 to 15 percent in 2012 and 2016. The individual sand eel species are characterised by medium to high resilience, which for fishery biologists is a measure of the resilience of fish species. While the greater sand eel (Hyperoplus lanceolatus) takes approximately 1.4 to 4.4 years to double its population, the lesser sand eel manages to do the same in less than 15 months. These figures are reflected in strong fluctuations of the TAC and landing quantities, which is also confirmed by the official statistics from the Danish fishing authorities. From 2016 to 2017, for example, within only one year, sand eel landings increased by a whopping 900 percent. In 2018 and 2019, the two subsequent years, they halved again. These changes do not result from overfishing but are the logical consequence of a sustainable fishing industry where the catch quota always follows the development of stocks.
Similar developments can also be seen for other industrial fishing species. Since the turn of the millennium, EU landings of fish species intended for non-food purposes fluctuated between under 1.1 million tonnes (2000) and 433,000 tonnes (2012). In the past, sand eels and sprats were the two main industrial fishing species. Although sand eels could become very important in the future, they currently appear to be declining in relative importance. The proportion of blue whiting has increased; in 2019 it made up 20% of total landings. Despite its economic significance, industrial fishing is, however, a relatively small sector compared to other types of fishing. In 2019, the value of industrial fish made up only 3% of total EU landings. And this value will probably decrease further, because the demand for small pelagic species such as herring and mackerel for human consumption is growing. Danish fishmeal manufacturers are also feeling this, as their production declined by 39 percent between 2000 and 2019.