Common Sturgeon
Acipenser sturio – It is difficult to imagine that some European rivers can hide giant fish measuring up to 20 feet (6 m) long that are capable of producing many millions of eggs in a single spawning. Such a fish is the common sturgeon. In spite of its prolific breeding habits, the species is at risk. The common sturgeon usually grows to a length of 3.3 to 6.6 feet (1 to 2 m), but can be longer. At least one report indicates that the species can attain a length of 20 feet (6 m) and a weight of about 1,300 pounds (600 kg). Despite this report, probably the largest specimen actually on record was 11.3 feet (3.4 m) long and 705 pounds (320 kg). The female has the potential to deliver close to 2.5 million eggs in a single spawning episode. As with some 40 or so other sturgeon species, the common sturgeon is under severe threat. It was once found in large numbers along the coast of Europe, from the North Sea to the Mediterranean and Black Seas. Today it is scarce throughout its range. Sturgeons are famous primarily for their eggs, known universally as caviar. However, many species have also been fished for their flesh. All species are long-lived, with ages beyond 50 years being common.
Double Life
The common sturgeon is anadromous, which means that it spends its life at sea but migrates into freshwater habitats during the spawning season. One notable exception to the rule is the common sturgeon population that lives in Lake Ladoga in Russia. Another is the sterlet, which lives permanently in fresh water. Spawning migrations upriver occur in early or mid-spring, with actual breeding taking place during early summer. Spawning is usually in pools that are several feet deep and have a flow of water. Alternatively, it may occur along river banks covered by spring floods. The eggs-up to 2.5 million for a largish female-are scattered over a gravelly bottom and abandoned. By now the condition of the adults has deteriorated, since they do not feed during their migrations: Many, in fact, will not make it back to sea to resume feeding. In better days such losses would not have been a problem, owing to the large number of adults in the population, not to mention the high numbers of offspring. Today every adult that dies adds to the scarcity of the species as it struggles to survive in the modern world. Young common sturgeon stay fairly close to the spawning grounds at first, but gradually move downriver as they grow. Some reports suggest that by the fall of the same year they move out to sea; others state that this may be delayed for one to four years. Whatever the case, males mature at between seven and nine years (some estimates indicate later maturation between nine and 13 years), while females may take eight to 14 years (some estimate it to be between 11 and 18 years) to mature and return to their waters of birth to breed for the first time.
Overfishing and Habitat Destruction
Overfishing is usually cited as the main reason for the sharp decline in numbers. Undoubtedly, fishing has had a severe effect on natural populations, not just of the common sturgeon, but of many of its relatives. Some of the eastern populations and species in particular are still the focus of illegal trade in caviar. In some cases arguments have been put forward to ban fishing altogether. However, others argue that to do so would drive the market underground and into the hands of organized illegal groups, thus probably accentuating rather than solving the problem. The common sturgeon’s best hope for the future appears to lie in coordinated captive-breeding programs to rear stocks for commercial exploitation of the roe (caviar). Such farms are likely to produce more fish than may eventually be needed for harvesting purposes, thus acting as a potential source of fish for restocking former habitats. A beneficial spinoff from such programs is that they also reduce pressure on existing wild stocks. However successful such breeding projects may be, the survival of the species in the wild needs to be urgently addressed. One problem is the pollution of watercourses. While it presents a daunting challenge, there are other potentially more difficult pressures facing the common sturgeon, including the building of dams, water channeling, and allied habitat-altering developments that plague the waterways.
Statistic Common sturgeon (Baltic sturgeon)
Acipenser sturio
- Family: Acipenseridae
- World population: Unknown, but close to extinction in parts of its range
- Distribution: Atlantic Ocean from Norway south to North Africa and into the western Mediterranean; Baltic, and Black Seas
- Habitat: Relatively shallow, mainly coastal seas, usually over sandy or muddy bottoms; some specimens move to deeper waters
- Size: Length: on average 3.3-6.6 ft (1-2 m). Weight: a 10-ft (3-m) specimen may weigh about 440 lb (200 kg)
- Form: Elongated body with distinct snout and characteristic caudal (tail) fin in which upper lobe is larger than lower one. Five rows of large, stout scales down body. Underslung mouth has distinctive barbels (whiskers)
- Diet: Adults feed on bottom-dwelling marine invertebrates, but will also take small fish; juveniles feed mostly on bottom-dwelling freshwater invertebrates
- Breeding: Migrates up to 620 miles (1,000 km) upriver in early to mid-spring; spawning occurs over gravel or pebbles, usually in flowing water pools. Each female is usually accompanied by more than 1 male. Hatching takes about 7 days, and juveniles may stay in their river of birth for up to 4 years
- Related endangered species: Over 40 populations of the 25 species are under varying degrees of threat, including the ship sturgeon (Acipenser nudiventris)
