Distributed at temperate latitudes throughout the northern hemisphere, sturgeon have been fished for meat, but primarily for the harvesting of caviar, for many centuries.
Exploitation of wild stocks has intensified over recent decades with the development of a global market for luxury foodstuffs and all major sturgeon fisheries are now in decline due to over-fishing (Pikitch et al., 2005). In parallel to this recent decline in wild stocks, efforts have been made to develop commercial aquaculture programmes to produce caviar, particularly in Europe and North America, but also now in Caspian Sea range states such as Russia and Iran (Raymakers and Hoover, 2002). At the present time it is estimated that 50% of caviar in trade is harvested from farmed stocks. The capacity to produce farmed caviar could theroretically alleviate pressure on wild stocks. However as has been observed with other rare wildlife species of high commercial value, farming may only serve to sustain a market in which fishermen are incentivised to catch every last fish available, in spite of increasingly stringent wildlife protection laws.
The genus Acipenser contains 17 of the 25 caviar-producing fish commonly termed sturgeon. All Acipenser species are listed under CITES Appendices I or II, with the intention of controlling international trade and promoting the implementation of sustainable management policies. Regulations within the EU, the world's largest caviar importer as well as a major producer, include a strict labeling system for all caviar products detailing the species name and country of origin. Such regulations are an attempt to restrict the caviar trade to products derived from CITES quotas, approved farms or licensed repackaging companies (EC, 2006). Despite such regulation, the value of caviar drives a multi-million euro black market economy in which caviar from non-sustainable sources is known to be widely traded under mis-labelled packaging.
To address the issue of illegal trade it is essential that there exists a robust, legally valid (forensic) method of authenticating the caviar labeling system, enabling customs officials and trade authorities to test products in trade on a routine basis or as part of intelligence led investigations. Ideally, such a testing system should allow traceability of a product to source, either the wild geographic origin, or the farm where caviar was produced. In the first instance, it is vital to be able to accurately determine the species of origin of traded caviar in order to assess the validity of the product label. A broad range of analytical tools have been examined for their utility in caviar identification (Rehbein et al., 2008), with the most promising technology for general application found to be DNA-based methods. In fact, DNA identification has been used for caviar identification at a species level for over a decade and is regularly employed to support enforcement action in countries such as Germany, the UK and the USA.
Nevertheless, the current method of identification, DNA sequencing of the mitochondrial cytochrome b gene, does not provide sufficient resolution to discriminate among certain species, in particular four species commonly found in Europe either as traded products or wild fish, namely: Russian (A. gueldenstaedtii), Persian (A. persicus), Siberian (A. baerii) and Adriatic (A. naccarii) sturgeon. Despite several attempts to identify mitochondrial genetic markers that can distinguish these species, they have so far proved unidentifiable, severely limiting the ability to enforce existing regulations concerning the caviar trade. There is therefore an urgent need to discover, test and validate new molecular markers capable of species identification in this group.
Beyond species identification, it is also becoming increasingly important to be able to verify whether caviar has been produced through aquaculture or was harvested from the wild. With wild stocks continuing to decline, it is possible that future trade will be completely restricted to aquaculture product. In order to be able to impose such constraints, any regulation must be enforceable and that would require the ability to trace back caviar to its farm of origin, or at least to enable caviar to be excluded from the source described on the packaging. Nuclear genetic markers are already being used in this context in Russia, as part of a "genetic passport" system to license caviar producing farms (N. Mugue pers comm.). However, more genetic markers across a broader range of species are needed if such a method is to ever be implemented throughout Europe.
The SturSNip project aimed at addressing these issues by undertaking research to discover SNP markers in Russian (A. gueldenstaedtii), Persian (A. persicus), Siberian (A. baerii) and Adriatic (A. naccarii) sturgeon. The SNP discovery method was enriched for markers that are polymorphic among species and candidate SNPs were tested to ensure their ability to authenticate parental inheritance. The research outputs represented the first major step in the development of a comprehensive suite of new DNA markers for the forensic identification of caviar products in trade within the European Union.
EC (2006) COMMISSION REGULATION (EC) No 865/2006 of 4 May 2006 laying down detailed rules concerning the implementation of Council Regulation (EC) No 338/97 on the protection of species of wild fauna and flora by regulating trade therein.
Pikitch E.K., Doukakis P., Lauck L., Chakrabarty P., Erickson D.L. (2005) Status, trends and management of sturgeon and paddlefish fisheries. Fish and Fisheries, 6: 233-265.
Raymakers C. and Hoover C. (2002) Acipenseriformes: CITES implementation from Range States to consumer countries. J. Appl. Ichthyology 18: 629–638.
Rehbein H., Molkentin J., Schubring R., Lieckfeldt D., Ludwig A. (2008) Development of advanced analytical tools to determine the origin of caviar. J. Appl. Ichthyology 24 (Suppl. 1): 65–70.