Zander

(Pikeperch)

(Sander lucioperca)

Order: Perciformes Suborder: Percoidei Family: Percidae

Description: The zander has spiny fins, sharp teeth and, like the perch (Perca fluviatilis), two separate dorsal fins. Its back is brownish green and grey and its underside white with a silvery sheen. The mouth of the zander is bigger than that of the perch, its upper jaw extending almost to the back edge of the eye.

Distribution: The zander is widely distributed in rivers flowing into the Baltic Sea, Caspian Sea and Black Sea. The southern limit of its range extends from south of the Alps to the Pyrenees. It does not occur in any rivers entering the Arctic Ocean. Owing to hatchery releases, the range has spread westwards, and in Finland the zander occur in southern and central parts of the country. The most northerly lakes in the world supporting a population of zander are in Finland, that is, Kemijärvi and the lakes of the river Tengeliönjoki. On the coast, the zander occurs in the Gulf of Finland, the Archipelago Sea, the eastern Åland Sea and in the Lumparn sea area. In the Gulf of Bothnia, it occurs mainly in river estuaries. The breeding ground of the zander found in the archipelago of Maksamaa, north of the city of Vaasa, for instance, is in the estuary of the Kyrönjoki. Since the warm summer of 2002, catches have been good in coastal waters of the Gulf of Bothnia up as far as southern Ostrobothnia, which is rare. The zander is a demanding species that thrives in warm freshwater, but it also tolerates brackish water if the salinity is not too high and warm spawning waters are available. Large, turbid lakes have been considered the optimal environment. It is not disturbed by low eutrophication. In Finland, the species lives at the northernmost limit of its range and is thus well adjusted to water in which the temperature rises rapidly in the spring and remains warm for a long time.

Reproduction: The male zander reaches maturity at an age of 4 years and a length of 35−40 cm, the female at an age of 5−6 years and a length of 40−50 cm. Spawning begins once the water temperature exceeds +10 °C and, in southern Finland, commonly lasts from mid-May to the end of June or even the beginning of July. The male first cleans out a nest-like spawning place mostly in shallow water, into which the female may lay one million eggs or more. These are then fertilized by the male, which stays near the nest to guard it and take care of the eggs. After hatching at a length of 4−5 mm, the larvae spread into the pelagic area.

Food, growth and migrations: When 5−6 mm long, zander larvae start to feed on zooplankton. They become predatory after their first growing season or, at the latest, at the beginning of their second summer. The adult zander is an omnivorous predator that feeds mostly on fish about 10 cm long. Zander grow relatively fast, depending on the food available and water temperature. In their first summer, larvae usually reach a length of 6−11 cm. A five-year-old zander commonly weighs anything from 0.2 to 1 kg and is about 30−45 cm long. Growth is fastest in eutrophic lakes in southern Finland, and slowest in northern Finland and in the Archipelago Sea. Zander usually migrate to their spawning grounds in shallow waters in spring. After spawning, they migrate offshore for feeding, and in the autumn move into deep water for the winter.

Fishing and catches: Zander are among Finland's most economically valuable fish and are important for both commercial and recreational fishermen. Recently, zander have fetched a higher price per kg than any other fish with the exception of eel. According to catch statistics, the annual zander catch exceeded 3 million kg at the end of the 1990s, and over half or even two-thirds of that was taken in Finnish coastal waters. Since then, catches have occasionally fallen to below 2 million kg. Recreational fishermen take about 70−90% of the total catch. The bulk of the commercial catch is taken with gillnets in late autumn, late winter and spring, whereas the catches by recreational fishermen are mainly taken with lures and gillnets in the summer. Recent years have seen an increase in the popularity of ice-fishing for zander.

Vulnerability, threats and management: Finnish zander stocks decreased heavily in the 1960s and 1970s, even becoming extinct in some places. Now, however, improved water quality, extensive releases and, in particular, the occasional strong year-classes resulting from warm summers have strengthened stocks in many areas, to such an extent that the zander comes second only to the whitefish (Coregonus lavaretus) as a release species. In 2003, over 9 million one-summer-old zander larvae were released into Finnish waters. In many places, these releases have caused mixing of native stocks, as in the early years no attention was paid to the origin of the released fish. Because the ecological and genetic differences between zander stocks are still unknown, it is nowadays recommended that stocks for release should be as close to the original stock as possible. The type of gear used, nets in particular, plays a key role in the management of zander stocks, as only too often undersized fish are caught with small-mesh nets. In order to let as many females as possible reproduce before being caught, mesh sizes of at least 50 mm and, for fast growing stocks, even 55 mm should be used. In addition, removal of the spawning closure has increased the amount of rod angling for spawning females and egg guarding males.

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