Sturgeon

Sturgeon(fromOld Englishstyrġaultimately fromProto-Indo-European*str̥(Hx)yón-) is thecommon namefor the 28 species of fish belonging to the familyAcipenseridae. The earliest sturgeon fossils date to theLate Cretaceous, and are descended from other, earlieracipenseriform fish, which date back to theEarly Jurassicperiod, some 174 to 201 million years ago. They are one of two living families of the Acipenseriformes alongsidepaddlefish(Polyodontidae). The family is grouped into four genera:Acipenser(which isparaphyletic, containing many distantly related sturgeon species),Huso,Scaphirhynchus,andPseudoscaphirhynchus. Two species (A. naccariiandA. dabryanus) may beextinct in the wild, and one (P. fedtschenkoi) may be entirely extinct.Sturgeons are native to subtropical, temperate and sub-Arctic rivers, lakes and coastlines ofEurasiaandNorth America.AMaastrichtian-age fossil found inMoroccoshows that they also once lived inAfrica.
Sturgeons are long-lived, late-maturing fishes with distinctive characteristics, such as aheterocercal caudal finsimilar to those ofsharks, and an elongated, spindle-like body that is smooth-skinned, scaleless, and armored with five lateral rows of bony plates calledscutes. Several species can grow quite large, typically ranging 2–3.5 m (7–12 ft) in length. The largest sturgeon on record was abelugafemale captured in theVolga Deltain 1827, measuring 7.2 m (23 ft 7 in) long and weighing 1,571 kg (3,463 lb). Most sturgeons areanadromousbottom-feeders, migrating upstream to spawn but spending most of their lives feeding inriver deltasandestuaries. Some species inhabit freshwater environments exclusively, while others primarily inhabit marine environments nearcoastalareas, and are known to venture into open ocean.
Several species of sturgeon are harvested for theirroe, which is processed into theluxury foodcaviar. This has led to seriousoverexploitation, which combined with other conservation threats, has brought most of the species tocritically endangeredstatus, at the edge ofextinction.
Acipenseriformfishes appeared in the fossil record some 174 to 201 million years ago, during theEarly Jurassic, making them some of the earliest extantactinopterygianfishes.True sturgeons appear in the fossil record during the UpperCretaceous, with amongst the oldest known remains being a partial skull from theCenomanian(100–94 million years ago) of Alberta, Canada.In that time, sturgeons have undergone remarkably littlemorphologicalchange, indicating their evolution has been exceptionally slow and earning them informal status asliving fossils.This is explained in part by the long generation interval, tolerance for wide ranges oftemperatureandsalinity, lack ofpredatorsdue to size and bony plated armor, or scutes, and the abundance of prey items in the benthic environment. They do, however, still share several primitive characteristics, such as heterocercal tail, reduced squamation, more fin rays than supporting bony elements, and unique jaw suspension.
Despite the existence of afossilrecord, full classification andphylogenyof the sturgeon species has been difficult to determine, in part due to the high individual andontogenicvariation, including geographicalclinesin certain features, such as rostrum shape, number of scutes, and body length. A further confounding factor is the peculiar ability of sturgeons to produce reproductively viablehybrids, even between species assigned to differentgenera. While ray-finned fishes (Actinopterygii) have a long evolutionary history culminating in the most familiar fishes, past adaptiveevolutionary radiationshave left only a few survivors, such as sturgeons andgars.
The wide range of the acipenserids and their endangered status have made collection of systematic materials difficult. The factors have led researchers in the past to identify over 40 additional species that were rejected by later scientists.Whether the species in theAcipenserandHusogenera aremonophyletic(descended from one ancestor) orparaphyletic(descended from many ancestors) is still unclear, though  the morphologically motivated division between these two genera clearly is not supported by the genetic evidence. An effort is ongoing to resolve the taxonomic confusion using a continuing synthesis of systematic data andmolecular techniques.
The phylogeny of Acipenseridae, as in thecladogram, shows that they evolved from thebony fishes.Approximate dates are from Nearet al., 2012.
In currently acceptedtaxonomy, the classActinopterygiiand the orderAcipenseriformesare bothclades. The family Acipenseridae is subdivided into 2 subfamilies;Acipenserinae, including the generaAcipenserandHuso, andScaphirhynchinae, including the generaScaphirhynchusandPseudoscaphirhynchus.However, multiple recent studies have recovered this arrangement asparaphyletic, instead findingA. oxyrhinchusandA. sturioto form the mostbasalclade among sturgeons, and all other species being in a separate clade, with the various other species ofAcipenser,Scaphirhynchus,Pseudoscaphirhynchus, andHusoto have varying levels of relationship with one another.
A potential taxonomy of Acipenseridae is shown here, based on Luoet al. 2019, Nedoluzhkoet al. 2020, and Shenet al.2020.Note the paraphyletic relationships among genera:
The exact placement ofScaphirhynchusvaries depending on the study and the methods used, with some placing it within the second-most basal clade comprising primarily Pacific species (shown above), whereas others place it in its own clade that is more derived than the secondmost basal clade but less derived than the most derived Atlantic and Central Asian clade. No studies have yet delineated a relationship between it andPseudoscaphirhynchus. In addition, the exact relationships of the members of the mostderived, primarily Atlantic clade vary, although most analyses at least find all the species in it to form a monophyletic clade. The placement ofA. sinensisalso varies by the study, with some placing it as the only Pacific member of the otherwise Atlantic-based most-derived clade, whereas others place it with the rest of the Pacific sturgeons as a sister toA. dabryanus.
The family contains 8 extinct fossil species and 28 extant species/subspecies (include 1 species ofSterletand 2 species of living fossils), in 4 genera. This list uses the original classification scheme:
FamilyAcipenseridae
Sturgeon range fromsubtropicaltosubarcticwaters inNorth AmericaandEurasia. InNorth America, they range along the Atlantic Coast from theGulf of MexicotoNewfoundland, including theGreat Lakesand theSt. Lawrence,Missouri, andMississippiRivers, as well as along the West Coast in major rivers fromCaliforniaandIdahotoBritish Columbia. They occur along the EuropeanAtlanticcoast, including theMediterraneanbasin, especially in theAdriatic Seaand the rivers ofNorth Italy;in the rivers that flow into theBlack,Azov, andCaspianSeas (Danube,Dnepr,Volga,UralandDon); the north-flowing rivers of Russia that feed theArctic Ocean(Ob,Yenisei,Lena,Kolyma); in the rivers ofCentral Asia(Amu DaryaandSyr Darya) andLake Baikal. In the Pacific Ocean, they are found in theAmur Riveralong the Russian-Chineseborder, onSakhalinIsland, and some rivers in northeast China.
Throughout this extensive range, almost all species are highly threatened or vulnerable to extinction due to a combination ofhabitat destruction, overfishing, and pollution.
No species is known to naturally occur south of the equator, though attempts at sturgeonaquacultureare being made inUruguay,South Africa, and other places.
Most species are at least partiallyanadromous,spawningin fresh water and feeding in nutrient-rich, brackish waters ofestuariesor undergoing significant migrations along coastlines. However, some species have evolved purely freshwater existences, such as thelake sturgeon(Acipenser fulvescens) and theBaikal sturgeon(A. baerii baicalensis), or have been forced into them by human or naturalimpoundmentof their native rivers, as in the case of some subpopulations ofwhite sturgeon(A. transmontanus) in theColumbia RiverandSiberian sturgeon(A. baerii) in the Ob basin.
Sturgeons retain several primitive characteristics from the bony fishes. Along with other members of thesubclassChondrostei, they are unique among bony fishes because their skeletons are almost entirelycartilaginous. To maintain structure, sturgeons are one of few organisms to retain a post-embryonicnotochordthat acts like a soft spine running through the body. Notably, however, the cartilaginous skeleton is not a primitive character, but a derived one; sturgeon ancestors had bony skeletons.They also lackvertebral centra, and are partially covered with five lateral rows of scutes rather thanscales.They also have fourbarbels—sensory organs that precede their wide, toothless mouths. They navigate their riverine habitats traveling just off the bottom with their barbels dragging along gravel, or murky substrate. Sturgeon are recognizable for their elongated bodies, flattenedrostra, distinctive scutes and barbels, and elongated upper tail lobes. The skeletal support for the paired fins of ray-finned fish is inside the body wall, although the ray-like structures in the webbing of the fins can be seen externally.
Sturgeons are among the largest fish: somebeluga(Huso huso) in theCaspian Seareportedly attain over 5.5 metres (18 ft) and 2,000 kilograms (4,400 lb)while forkaluga(H. dauricus) in theAmur River, similar lengths and over 1,000 kg (2,200 lb) weights have been reported.They are also among the longest-lived of the fishes, some living well over 100 years and attaining sexual maturity at 20 years or more.The combination of slow growth and reproductive rates and the extremely high value placed on mature, egg-bearing females make sturgeon particularly vulnerable tooverfishing.
Sturgeons arepolyploid; some species have four, eight, or 16 sets of chromosomes.
Sturgeons are long-lived, late maturing fishes. Their average lifespan is 50 to 60 years, and their firstspawndoes not occur until they are around 15 to 20 years old. Sturgeons are broadcast spawners, and do not spawn every year because they require specific conditions. Those requirements may or may not be met every year due to varying environmental conditions, such as the properphotoperiodin spring, clear water with shallow rock or gravelsubstrate, where the eggs can adhere, and proper water temperature and flow foroxygenationof the eggs. A single female may release 100,000 to 3 million eggs, but not all will be fertilized. The fertilized eggs become sticky and  adhere to the bottom substrate upon contact. Eight to 15 days are needed for the embryos to mature intolarval fish. During that time, they are dependent on their yolk sacs for nourishment.River currents carry the larvae downstream into backwater areas, such asoxbowsandsloughs, where the free-swimmingfryspend their first year feeding on insect larvae andcrustacea. During their first year of growth, they  reach 18 to 20 cm (7 to 8 in) in length and migrate back into the swift-flowing currents in themain stemriver.
Sturgeons are primarilybenthicfeeders, with a diet of shellfish, crustaceans, and small fish. Exceptionally, bothHusospecies, thewhite sturgeonand thepallid sturgeonfeed primarily on other fish as adults. They feed by extending their siphon-like mouths to suck food from thebenthos. Having no teeth, they are unable to seize prey, though larger individuals and more predatory species can swallow very large prey items, including wholesalmon.Sturgeons feed non-visually. They are believed to use a combination of sensors, including olfactory, tactile, and chemosensory cues detected by the four barbels, andelectroreceptionusing theirampullae of Lorenzini.
The sturgeons' electroreceptors are located on the head and are sensitive to weak electric fields generated by other animals or geoelectric sources.The electroreceptors are thought to be used in various behaviors such as feeding, mating and migration.
Many sturgeons leap completely out of the water,usually making a loud splash which can be heard half a mile away on the surface and probably farther under water. Why they do this is not known, but suggested functions include group communication to maintain group cohesion, catching airborne prey,courtship display, or to help shed eggs during spawning. Other plausible explanations include escape from predators, shedding parasites, or to gulp or expel air.Another explanation is that it "simply feels good".There have been some incidents of leaping sturgeon landing in boats and causing injuries to humans;in 2015, a 5-year-old girl was fatally injured after a sturgeon leapt from theSuwannee Riverand struck her.
Globally, sturgeon fisheries are of great value, primarily as a source forcaviar, but also for flesh.Several species of sturgeon are harvested for their roe which is processed into caviar—adelicacy, and the reason why caviar-producing sturgeons are among the most valuable and endangered of all wildlife resources.
During the 19th century, the US was the global leader in caviar production, having cornered 90% of the world's caviar trade.Atlantic sturgeon once thrived along the east coast from Canada down toFlorida. They were in such abundance in theHudson Riverthat they werehumorously called"Albany beef" and sturgeon eggs were given away at local bars as an accompaniment to 5¢ beer.White sturgeon populations along the US west coast declined simultaneously under the pressure of commercial fishing and human encroachment. Within the course of a century, the once abundant sturgeon fisheries in the US and Canada had drastically declined, and in some areas had been extirpated under the pressure of commercial overharvesting, pollution, human encroachment, habitat loss, and the damming of rivers that blocked their ancestral migration to spawning grounds.
By the turn of the century, commercial production of sturgeon caviar in the US and Canada had come to an end. Regulatory protections and conservation efforts were put in place by state and federal resource agencies in the US and Canada, such as the 1998 US federal moratorium that closed all commercial fishing for Atlantic sturgeon.It was during the 20th century that Russia grew to become the global leader as the largest producer and exporter of caviar.As with the decline in sturgeon populations in the US and Canada, the same occurred with sturgeon populations in the Caspian Sea.
Beginning with the 1979 US embargo on Iran,poachingand smuggling sturgeon caviar was big business but an illegal and dangerous one.Officers with theWashington Department of Fish and Wildlife(WDFW) busted a poaching ring that was based inVancouver, Washington. The poachers had harvested 1.65 tons of caviar from nearly 2,000 white sturgeon that were poached from the Columbia River. The caviar was estimated to be worth around $2 million. WDFW busted another ring in 2003, and conducted an undercover sting operation in 2006–2007 that resulted in 17 successful attempts out of a total of 19.
In response to concerns over the future of sturgeons and associated commercial products, international trade for all species of sturgeons has been regulated underCITESsince 1998.
Sturgeons are threatened by the negative impacts of overfishing, poaching,habitat destruction, and the construction of dams that have altered or blocked their annual migration to ancestral spawning grounds.Some species of sturgeon are extinct, and several are on the verge of extinction, including theChinese sturgeon,the highly prized beluga sturgeon,and theAlabama sturgeon.Many species are classified as threatened or endangered, with noticeable declines in sturgeon populations as the demand for caviar increases.IUCNdata indicates that over 85% of sturgeon species are at risk of extinction, making them more critically endangered than any other group of animal species.
In addition to global restocking efforts, the monitoring of populations and habitat, and various other conservation efforts by national and state resource agencies as applicable to their respective countries, several conservation organizations have been formed to assist in the preservation of sturgeons around the world. On a global scale, one such organization is theWorld Sturgeon Conservation Society(WSCS) whose primary objectives include fostering the "conservation of sturgeon species and restoration of sturgeon stocks world-wide", and supporting the "information exchange among all persons interested in sturgeons."The North American Sturgeon and Paddlefish Society (NASPS)and Gesellschaft zur Rettung des Störs e.V.are WSCS affiliates. WSCS has been instrumental in organizing global conferences where scientists and researchers can exchange information and address the various conservation challenges that threaten the future of sturgeons.Conservation efforts at the grass roots level are also instrumental in helping to preserve sturgeon populations, such as Sturgeon For Tomorrowwhich was founded in 1977, consists of volunteers and a sturgeon guarding program to monitor known spawning sites. The organization has grown exponentially over the years and has become "the largest citizen advocacy group for sturgeon in the world", and has expanded with affiliate chapters in other states that have sturgeon populations.Other projects focus on specific local issues, such as the We Pass project, seeking a solution to the migratory impasse represented by theIron Gatesin the Danube River Basin.For example, currently all anadromousDanubesturgeon (all species except the predominantly freshwater sterlet) are now classed as Critically Endangered or extirpated from the upper and middle reaches of the Danube River above the dams.
Before 1800,swim bladdersof sturgeon (primarily Beluga sturgeon from Russia) were used as a source ofisinglass, a form of collagen used historically for theclarificationofwineandbeer, as a predecessor forgelatin, and to preserveparchments.
The Jewish laws ofkashrut, which only permit the consumption of fish with both scales and fins, forbids sturgeon, as they haveganoid scalesinstead of the permittedctenoidandcycloid scales. While allOrthodoxgroups forbid the consumption of sturgeon, someConservativegroups do allow it.The theological debate over its kosher status can be traced back to such 19th-century reformers asAron Chorin, though its consumption was already common in European Jewish communities.
Sturgeons were declared to be aroyal fishunder a statute dating back to 1324 by KingEdward II of England. Technically, the British monarchy still owns all sturgeons,whales, anddolphinsthat inhabit the waters aroundEnglandandWales.Under the law of theUnited Kingdom, any sturgeons captured within the realm are personal property of the monarch.
Similar laws reserving sturgeon for the king were enforced in late medieval Denmark. An archaeological example of sturgeon in a royal context comes from the wreck of the Danish-Norwegian flagship,Gribshunden, which sank in June 1495 while King Hans sailed from Copenhagen to Kalmar, Sweden for a diplomatic summit. Archaeologists recovered from the wreck a cask containing a butchered sturgeon, probably intended for the king's table during feasts in Kalmar.
In heraldry, a sturgeon is the symbol on the coat of arms for SaintAmalberga of Temse.