The Common Sturgeon Acipenser sturio is a long-lived fish, surviving to well over 100 years of age, reaching more than 3.4m in length and growing to over 300kgs when conditions allow. They exhibit bony plates (scutes) covering the head and five longitudinal rows of similar plates along the body. The tail fin is heterocercal; the upper lobe being longer than the lower. The toothless mouth, on the underside of the snout, is preceded by four sensitive barbels.
Common Sturgeon is anadromous, meaning that it migrates from the sea into fresh water to spawn. Common Sturgeon are slow to reach sexual maturity; males reproduce for the first time at 10-12 years, females at 14-18. There are indications that this species reproduce bi-annually for males and every 3-4 years for females. The distance of the spawning migration is thought to be correlated with water level, and a distance of 1,000 km or more may be covered during years of high water. Following spawning fish immediately return to the sea.
Juveniles migrate downstream and are present in upper estuaries at one year old. They continue a slow migration and penetrate the sea at between two and three years of age, following which they leave the sea to enter the lower estuary during the summer time for the next 4-6 years. Whilst at sea, this species feeds on a variety of benthic molluscs, crustaceans and small fish.
The sturgeon was an important commercial fish until the beginning of the 20th century and was likely a common fish in Britain in times gone by. It was recorded by Fitz-Stephen that in the early 12th century a dish of sturgeon could be readily obtained in the city of London.
King Stephen, the successor to Henry I (who unfortunately succumbed to a surfeit of lampreys), who commanded an army of 80,00 soldiers based his army in London. He stated that they had no need to fast or go hungry for long as there was no need to search to find sturgeon, implying the Thames held sturgeon a-plenty.
This species is one of the UK, and Europe’s, most threatened fish. Its’ range extends along the coasts of Europe, except in the northernmost regions and the Baltics. However, despite its broad range, they have become so rare that they area only known to breed in the Garonne river basin in France were the population is declining and potentially now absent. Conservation projects involving this species include reintroductions based on specimens from aquaculture with the first releases in 1995.
It is included on Section 41 and 42 of the NERC Act, is a European Protected Species and is listed on Annex IV of the Habitats Directive. It is considered by the International Union for Conservation of Nature (IUCN) to be critically endangered and the Convention on International Trade in Endangered Species of Wild Flora and Fauna regulates the trade of this species. They are also classed as a ‘Royal Fish’, which means that any caught become the personal property of the monarch of the United Kingdom.
The Common Sturgeon is very rarely seen in British waters, however the reintroduction programme in France has increased the potential for sightings and bycatch, and a number of catches have been reported in the English Channel. Indeed, there have been a number of recent records, including a fish of 30-40lb found dead near the River Thames and one caught off the Pembrokeshire coast.
The species last spawned in 1994 in the Garonne, where dams, pollution and river regulation has degraded and destroyed spawning sites. The current population size is between 20-750 wild, mature individuals. There has been more than a 90% population decline in the past 75 years based mainly on loss of habitat, along with pollution and exploitation.
This species now remains in just one location, where 27 spawning grounds (less than 10 km²) remain potentially accessible. As this species continues to be caught as bycatch, the population is still decreasing.
Whilst its potential UK reintroduction has been suggested, the likely success of any such schemes would be low, due to anthropogenic impacts to our rivers.