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Archived PDF from the original on July 14, Archives of Biological Science, Belgrade. Mims February However, according to the CITES Secretariat and Interpol, the data available on poaching and smuggling in the Caspian are limited and existing legislation does not facilitate enforcement. The Secretariat believes that, despite improved communication between importing and exporting countries, more needs to be done. It emphasised the following requirements:.
The Iranian sturgeon industry seems to be the healthiest in the Caspian Sea area. It is still a state monopoly, held by the powerful Shilat , even if discussions for its privatization have been ongoing for some years. Over the last ten to fifteen years, Shilat has been investing in the future sustainability of its sturgeon fisheries by:. As a result of this extensive programme, the adult population of A.
The export quota for A. This figure represents some 73 percent of the total caviar quota in Iran see Table 3 while in caviar from this species represented some 23 percent of total production Hosseini In , exports of 72 MT of caviar and caviar substitutes generated some The aim of the Shilat is to generate revenues of The other producing areas in the world, in Europe, Asia, and North Ameria are affected by similar problems concerning their sturgeon populations.
These areas are:. In the Black Sea and Sea of Azov, the situation has been aggravated by a decrease in the production of fingerlings needed for restocking Hochleithner and Gessner In the Amur River, Chinese catches  have, historically, been higher than Soviet catches, which were limited to MT per year since the sixties. During the eighties and the beginning of the nineties, Chinese catches averaged MT annually, with an annual production of MT of caviar Hochleithner and Gessner According to some sources, illegal catches are believed to make up some 50 percent of the total Hochleithner and Gessner In , China committed itself to catch quotas of 42 MT A.
Chinese caviar is mainly sold to Japan and the United States, but is also consumed domestically Hochleithner and Gessner In North America, sturgeons and paddlefish have been subject to large-scale exploitation over time. Total sturgeon catches in the United States amounted to MT in They surpassed the threshold of MT in , , and then fell from 1 MT in to MT in In , catches amounted to MT. Wild stocks of North American sturgeons and paddlefish are now under strict management regimes, and benefit from measures such as size limits, maximum catches, closed seasons or total bans on some fisheries Hochleithner and Gessner The sturgeon farming industry is now a large-scale initiative.
Its objective is not to release in the wild as for the Caspian Sea hatcheries but the marketing of meat, caviar and live specimens for ornamental trade. The Acipenser species more suitable for aquaculture are the sterlet A. Other species, such as Adriatic sturgeon A. Out of these species, the most successful results concern the White sturgeon A.
Figure 8 shows the trend of the sturgeon aquaculture industry. The company Agroittica Lombarda is behind the success of sturgeon production in Italy. The species farmed is the White sturgeon A. Agroittica is currently marketing some 3 MT per annum of a new variety of caviar called Calvisius , which is sold fresh and pasteurised. Agroittica also markets several other sturgeon products, such as fresh and smoked sturgeon meat Agroittica Lombarda, Pers. In France, sturgeon culture is widespread in the Aquitaine region. The Gironde Estuary in Aquitaine used to be one of the habitats of A.
Nowadays, fish farmers in the Gironde successfully breed Siberian sturgeon A. Another interesting development is in South Korea. Stolt also produces sturgeon meat, whole fish and fillets. Its sturgeon farms are located in the Sacramento Valley of California. This is a Californian brand also producing caviar from farmed white sturgeon A. The species meeting criteria for listing include beluga H. The Conference of the Parties accompanied the listing with additional conservation and management requirements as described in Resolution In particular, the Conference recommended the Secretariat, in consultation with the Animals Committee, to explore the development of a uniform marking system for sturgeon parts and derivatives and aquaculture stocks .
Conference Decision Failure to do so would result in a zero quota for each non compliant party. Quotas for endemic species exploited by a country within its territorial waters and quotas for specimens bred in captivity are voluntary CITES b. In , the catch and export quotas for shared stocks of Acipenseriformes included in the Review of Significant Trade, such as the Caspian Sea stocks, were the result of an agreement between the CITES Standing Committee and the range states.
In the Caspian basin, the Review of Significant Trade led to, inter alia , the suspension, from spring to the end of , of all harvesting operations of four sturgeon species in Azerbaijan, Kazakhstan and Russia. In and , the catch and export quotas for Caspian Acipenseriformes were endorsed by the Secretariat within the framework of a coordinated sturgeon management system proposed by range states. The quotas per country are presented in Table 3 below, which includes both mandatory quotas for shared sturgeon resources and voluntary quotas for endemic species exploited by a country within its territorial waters and aquaculture stocks CITES Table 2: Retail prices of Caspian caviar.
Prices for 1. Azerbaijan informed the Secretariat of specimens obtained for export in or previous years, but that will be authorized for export in Details on these specimens can be obtained from the Secretariat. Bulgaria informed the Secretariat of specimens obtained for export in or previous years, but that will be authorized for export in China informed the Secretariat of specimens obtained for export in or previous years, but that will be authorized for export in The Islamic Republic of Iran informed the Secretariat of specimens obtained for export in or previous years, but that will be authorized for export in Kazakhstan informed the Secretariat of specimens obtained for export in or previous years, but that will be authorized for export in Caviar including kg allocated to Turkmenistan and 1 Meat including 12 kg allocated to turkmenistan and 36 kg from the export quota for Caviar including kg allocated to Turkmenistan and 3 Romania informed the Secretariat of specimens obtained for export in or previous years, but that will be authorized for export in Note: Romania has established a maximum number of individuals that may be caught, in addition to the maximum weight that may be caught.
The Russian Federation informed the Secretariat of specimens obtained for export in or previous years, but that will be authorized for export in Caviar including 1 kg allocated to Turkmenistan and 15 kg from the export quota for Food and canned products including 8 kg allocated to Turkmenistan and 47 kg from the export quota for Food and canned products including 4 kg allocated to Turkmenistan and 20 kg from the export quota for The following sub-sections will include analyses of the economic and social importance of the sturgeon and caviar industry for major producing and exporting countries.
The main source for fishery landings, trade and employment data is FAO, which relies on data provided by its Member States and Observers. Azeri catches declined from MT in to 61 MT in No data on this entry was available for the year Figure Exports of caviar and caviar substitutes from Azerbaijan, value Therefore, it may be estimated that some 60 fishers are dependent on the sturgeon industry in Azerbaijan. However, employment data are far too outdated to ensure a reliable estimate.
Number of fishers: full-time, of which 14 aquaculture farmers, 19 inland fishers and marine coastal fishers FAO FIDI data. In the following years they increased progressively reaching the record peak of 3 MT in In the nineties they decreased again to 1 MT in and Figure Exports of caviar and caviar substitutes from Iran have been grouped together in statistics from onwards. Figure Exports of caviar and caviar substitutes from Iran, value By comparing the last data available on inland fisheries landings in Iran, MT in , of which 1 MT were sturgeons with employment in the sector 19 inland fishers in , it is possible to give a rough estimate of some people being employed in the sturgeon fishery.
Iranian authorities appear to be positive about the contribution of CITES to the sturgeon and caviar industry. According to a Shilat representative, smuggling decreased dramatically as a consequence of the CITES listing and the tightening of controls on exports of caviar and other sturgeon products Shilat , Pers. Aquaculture production and value: 1 est. No data was available for and Figure This suggests an estimated fishers are dependent on sturgeon fisheries in Kazakhstan. Number of fishers: in , of which 1 aquaculture farmers, 62 inland fishers and marine fishers FAO FIDI data.
Gender breakdown: women employed as part-time aquaculture farmers, 30 women employed as inland fishers, 4 women employed as marine coastal fishers and 8 women employed as marine deep-sea fishers in FAO FIDI data. Sturgeon farming in Russia appears to be a viable activity with production reaching 2 MT in Figure Figure Exports of caviar and caviar substitutes from Russia, value This suggests fishers would be dependent on sturgeon fisheries in Russia.
Sturgeon stocks are seriously depleted, especially in traditional producing basins such as the Caspian Sea. The main factors behind the depletion of Caspian stocks include illegal fishing and habitat degradation. However, in some countries, such as Iran, the strict implementation of the CITES regime and tightening of controls on poaching and smuggling have had a beneficial impact against illegal activities. At the same time, aquaculture is gaining momentum as an alternative to sturgeon capture fisheries. Environmental groups advocate increased production of caviar and sturgeon meat from aquaculture to reduce pressures on wild stocks.
However, a decline in the demand for Caspian caviar may also entail negative consequences for employment in the Caspian sturgeon industry and, paradoxically, negative consequences for Caspian sturgeon stocks. Moving fishing effort away from the commercially exploited sturgeon species would lead to a reduction in investments in hatcheries and re-stocking programmes, which have been essential to preserve Caspian sturgeon stocks over time.
Without them these stocks would be more prone to threats like pollution and habitat disruption. Thus an effective global conservation programme for sturgeons is necessary to promote sustainable management of both wild and farmed sturgeon as complementary and not alternative options. However, due to the implementation of stricter management measures and the ban on international trade in caviar in , data for that year may show a significant decline.
This suggests that the entry included more sturgeon caviar than caviar substitutes. In they amounted to 75 percent of total revenues from exports of fishery products. However, the relatively large quantity involved suggests a significant component of caviar substitutes. The limited data available concerning the industry in the case countries does not allow a credible analysis of its social importance. In addition it has not been possible to make any estimate on employment in caviar processing and marketing.
The social estimates of this study are limited to:. The very rough estimates on employment in fishing and the lack of data on employment in processing and marketing make these figures largely under-representative of the social importance of the sturgeon industry in the Caspian region. Table 4: Economic and social aspects of the sturgeon and caviar industry in the Caspian Sea data, source FAO except when explicitly stated. Beluga Caviar Pricing Guide. List price comparison. Bolourchi, M. Caviar, the perfect pearls of nature. Caviar Emptor.
American caviar: an eco-friendly way to celebrate special Occasions. Convention on international trade in endangered species of wild fauna and flora. The 16 marine-oriented species species that spend a significant portion of their life history in marine environments occur on all of the continents to which sturgeons are endemic, including North America, Europe, and Asia. Sturgeons are generally long-lived fishes that exhibit late onset of maturity, slow growth, and infrequent reproduction .
Some species have life spans of well over years, and sexual maturity may be attained as late as 20—25 years of age or more in females . These life-history characteristics are linked to low maximum rates of population growth and underlie intrinsic vulnerability to exploitation-induced decline and a low recovery capacity  , . Human activities such as dredging, channelization, dyking, bank stabilization, in-river construction, and shoreline development can affect important juvenile rearing habitats .
Other prominent impacts to sturgeon include hybridization, pollution, introduced species, reduced food supply, water diversions, and saltwater intrusion into important spawning and rearing habitats  , . Their value as the source of black caviar the unfertilized roe of female sturgeon has led sturgeons particularly in the Black and Caspian seas to be the target of intensive legal and illegal fisheries  , . This has resulted in the collapse of several species and stocks of sturgeon . The combination of inherent life-history challenges, habitat degradation, and exploitation has reduced sturgeon abundance to such low levels that the sturgeons are now considered one of the most endangered groups of animals in the world according to the International Union for Conservation of Nature IUCN.
Sturgeons are also some of the least-well-known of the major taxa of concern in terms of spatial distribution and abundance, particularly for oceanic and nearshore phases of their life history. Almost all of the sturgeons that enter into saltwater have been understudied with respect to where they go and why Table 1 and many endangered species have received relatively little scientific attention and study .
Researching these information gaps is extremely important for conservation of habitats and distinct populations. Here, we explore these issues while providing case studies and tools for examining movement and distribution of these ancient fishes. Sturgeons may move from one location or habitat type to another to feed, reproduce, or overwinter.
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River movement can be complex and include multi-step migrations  and include movement between and among rivers suggesting a meta-population structure . Within a species, populations can differ on the timing of migrations into river systems, time spent within the river holding , and the distance upstream from the marine environment where spawning occurs. Protecting the genetic heritage and diversity of a species requires an understanding of these complexities at both the species and population levels, and an understanding of specific life-stage habitat requirements.
Species and populations subject to harvest typically benefit from well-managed harvest regimes that incorporate respective migration information. Preserving the evolutionary potential of a species and its ability to respond to environmental change requires understanding the number of distinct populations within a species. Natal homing fidelity is thought to be strong and thus in many cases rivers, or sections of a watershed between natural barriers, often define populations.
On the other hand, metapopulations may also exist . If individual populations differ in terms of abundance and reproductive capacity, researchers and fishery managers may want to minimize mortality of individuals from certain river systems while they are in marine environments. Movement studies can provide the necessary information at both population and species levels and can provide the basis for protective schemes under national and international legislation.
Characterizing environmental parameters that correlate with behaviour is further useful in evaluating the potential impact of habitat alteration e. In some areas, introduction of non-native sturgeons and hybridization between species e. Knowledge about movement and the spatial distribution of populations can also improve population assessments and help in specifying suitable management or recovery plans.
Population assessments are still lacking for most species and are often hindered by an insufficient understanding of spatial distribution. Tagging data can be incorporated into spatially explicit models to allow more accurate estimation of fishing mortality rates experienced by different age classes where fishing intensity varies by area  , . Insufficient data for parameterisation of models for migratory species with complex life histories can lead to large uncertainties in resource assessment and the likely effects of alternative management actions.
The lack of data for key parameters of population dynamics has been identified as a contributor to the depleted and endangered status of many sturgeon populations throughout their range  , . Below, we present recent studies of the Gulf and Green Sturgeon to show how the information gained from these representative studies has been used to direct subsequent activities toward species conservation and the protection of key habitats. The anadromous Gulf Sturgeon, Acipenser oxyrinchus desotoi , a subspecies of the Atlantic Sturgeon, Acipenser oxyrinchus , occurs in most Gulf of Mexico river systems from the mouth of the Mississippi River to the west coast of Florida Figure 2.
Both mature and immature Gulf Sturgeon undergo freshwater migrations, typically entering coastal rivers in March or April and outmigrating to the ocean in September or October . The cool-water period of estuarine or marine residency is critical for growth and reproduction, as Gulf Sturgeon do not feed during their freshwater residency.
The orange asterisks mark the easternmost and westernmost locations of confirmed detections of acoustic-tagged Gulf Sturgeon. Gulf Sturgeon spawn in coastal rivers including the eight shown on this map.
Sturgeon - Wikipedia
Spawning and non-spawning Gulf Sturgeon typically remain in coastal rivers until fall and occupy estuarine and nearshore marine waters during winter. Yellow triangles indicate winter concentration areas for Gulf Sturgeon from two or more river systems. The m isobath is shown as the light blue areas near the coast. Early information about Gulf Sturgeon distribution and migration came primarily from commercial fishing .
Fishing operations in individual rivers were mostly short-lived due to overharvest and subsequent fishery closures, as is typical for many in-river sturgeon fisheries , but the catches did provide some insights into the timing and extent of migration. Marking with conventional tags mostly showed the range and extent of migration e. Radio transmitters worked well for manual tracking of Gulf Sturgeon over long distances in rivers, but these transmitters cannot be detected in brackish or marine water.
In the late s a telemetry study was conducted wherein Gulf Sturgeon were tagged with both radio and sonic tags . This was also the first Gulf Sturgeon study to use stationary receivers to detect and log passage events in this case, to detect sonic tags as fish moved through barrier island passes . The listing of Gulf Sturgeon in as a threatened species under the U.
Endangered Species Act provided a further boost to research activity. For example, radio tracking studies in the Choctawhatchee River were initiated to identify potential spawning sites, with confirmation through the use of artificial substrates to collect the adhesive eggs of Gulf Sturgeon . Deployment of artificial substrates in a grid design provided fine-scale information about spawning habitat in the Suwannee River . Marine habitat studies using sonic tags and more recently, archival temperature-logging and pop-up archival tags showed that Gulf Sturgeon sometimes moved long distances along the shoreline and primarily used shallow nearshore areas  — .
The fish occupying these marine habitats were often from multiple river systems; for example,  reported that Gulf Sturgeon from the Yellow, Choctawhatchee, and Apalachicola rivers were located within a km stretch of coastline eastern winter concentration area shown on Figure 2. The co-occurrence of Gulf Sturgeon from the Pearl and Pascagoula rivers has been documented  in the concentration area off Mississippi western area shown on Figure 2.
Thus, marine and estuarine threats and management efforts may affect more than one population. Genetic studies have also aided in understanding Gulf Sturgeon migration patterns. For example, it has been shown that within a basin, genetic structure exists at least at the drainage level and possibly at the level of tributary rivers within the basin .
The genetic analyses were helpful in interpreting telemetry results since some fish were tagged outside their natal drainage and others were captured or detected in multiple drainages. These research results formed the basis for the Gulf Sturgeon recovery plan and led to the designation of critical habitats. These important habitats included upper-basin spawning sites with limestone bluffs and outcroppings, estuarine and marine feeding sites with preferred substrates and benthic fauna, and summer resting areas. This resulted in designation of nearly 2, river km as critical habitat for conservation of the species.
A severe lack of demographic and basic life-history information hampered the subsequent status review . A particularly troubling unknown was the population origin s of Green Sturgeon that form dense aggregations in certain estuaries during summer months. Green Sturgeon were known to use just three rivers for spawning the Sacramento and Klamath rivers in California, and the Rogue River in Oregon , and to spend much of their lives in marine waters between Alaska and Baja California Figure 3.
The purpose of the summertime estuarine aggregations was unknown, as was the proportion of Green Sturgeon exhibiting this aggregation behaviour. Green Sturgeon in these aggregations are vulnerable to capture in gillnet fisheries that target White Sturgeon and Pacific salmon species, and face environmental threats from activities associated with shellfish aquaculture and industrial activities in the estuaries where they aggregate. The orange asterisks mark the northernmost and southernmost locations of confirmed detections of acoustic-tagged Green Sturgeon.
They spend summers in estuaries and bays in California, Oregon, and Washington, and utilize the coastal ocean between southern Alaska and Baja California, Mexico, generally remaining in water less than m deep. Summer aggregation areas are shown as yellow triangles. The recent development of new telemetric tagging systems made it feasible to rapidly close some of these information gaps. Initial work focused on Green Sturgeon in the Rogue River, using radio and acoustic tags to learn that Green Sturgeon migrate into rivers in the early spring for spawning in up-river areas, and then hold in deep pools over the summer prior to emigration in the fall when flows rise with the onset of the rainy season .
Tagged sturgeon returned to the river to spawn every two to four years . Rogue River fish were also tagged with pop-off archival tags PAT , which revealed that they remain in fairly shallow water 50—80 m when in the coastal ocean, and showed that they migrate north to the west coast of Vancouver Island in the fall . A broader study using acoustic tags showed that Green Sturgeon make extensive seasonal migrations among spawning areas, over-summering in various estuaries and bays, and over-wintering areas in the coastal ocean, with many individuals using areas around northern Vancouver Island  , .
Further PAT work, using longer tag deployments, also showed this seasonal migration pattern, and fairly constrained depth and temperature distributions during the winter. Acoustic tags also revealed extensive use of and movement among non-natal estuaries. Green Sturgeon from different populations mixed together in common estuaries, but at different rates. Natal estuaries were used almost exclusively by fish from the associated natal river . Green Sturgeon were also shown to have diverse patterns of migration within and among populations.
Within the Sacramento River, acoustic tags revealed that a seasonal water diversion dam was a serious impediment to the spawning migration of Green Sturgeon . Captive rearing of Green Sturgeon is providing important information on salinity tolerance and the timing for successful transition to marine waters, as well as optimal temperature for egg hatching, embryogenesis, and larval and juvenile survival  — . While tagging revealed clear overall migration patterns, it also revealed a diversity of migratory behaviours that are likely important to consider in the conservation and protection of this species.
Complementary genetic studies have determined that two distinct population segments exist within Green Sturgeon that correspond to northern and southern populations, and that estuarine aggregations contain individuals from multiple populations . Data acquired from electronic tagging has already been the basis of many of the conservation regulations put in place after the listing of the southern distinct population segment of Green Sturgeon by the US federal government. Critical habitat for Green Sturgeon was designated in along the continental shelf of the US from southeast Alaska to central California out to a depth of m, as well as in a number of estuaries and bays in Washington, Oregon, and California.
Regulatory biologists are using the acoustic tagging data in their assessments of permit applications for activities such as dredging and dredge spoil disposal, large construction projects within and along the shores of estuaries, and the management of groundfish trawl fisheries in the coastal ocean.
The Caspian Sea is one of the most important areas for sturgeons globally and has supplied much of the world's wild caviar. Five of the species that inhabit this region Stellate, Beluga, Persian, Russian and Ship Sturgeon; Table 1 , including those that produce the highly prized Beluga, Sevruga and Osetra caviar, are anadromous. Adult sturgeons move into river systems to reproduce in spring and sometimes winter and fall. Most adults that migrate into rivers in spring are thought to leave the river just after spawning, but those that migrate in the fall and winter may overwinter.
The patterns of spawning migrations of Caspian Sea sturgeons differ amongst species, and the damming of rivers has likely altered migration patterns . After hatching, larvae and fingerlings remain within the rivers for several months depending on the species: for some species e. Stellate and Russian , fingerlings may overwinter in river deltas while for others e. Beluga , fingerlings will migrate into the Caspian Sea for rearing.
Information regarding the behaviour and movement of juveniles as well as adults within rivers has been gathered through fisheries-dependant surveys and fisheries-independent studies using nets. While a few tagging studies have been attempted e. Such studies would be of further benefit in understanding the reproductive periodicity of the different species. It is unclear whether adult sturgeon in the Caspian Sea return to their natal rivers for reproduction.
Genetic studies using mitochondrial DNA have not shown differentiation amongst river populations  , but preliminary data from microsatellites suggest that natal homing does occur. Hatchery supplementation and stocking in rivers may be affecting the natural population structure that once existed because hatcheries do not always use broodstock collected in the river system where the hatchery-produced juveniles are released.
Detections of genetic haplotypes from the non-native Siberian Sturgeon in tissue samples taken from Caspian Sea Russian Sturgeon have raised questions regarding hatchery practices, non-native releases, and the life history of this potential hybrid see section 2. There is a great need to understand the species and population structure of Caspian Sea sturgeons so that management activities reflect and protect the various populations. Within the Caspian Sea environment, comprehensive information about the distribution of sturgeons is lacking .
Much of what is known has been collected through trawl surveys, which have been limited spatially and geographically. The vertical distribution of sturgeons in the Caspian has been examined through trawl and drift net surveys, but these studies have been similarly limited. Since at-sea trawl survey information is used to generate abundance estimates and harvest quotas, a better understanding of distribution and movement is important. Tagging and tracking studies would greatly complement available data from the trawl and net surveys see  for compiled information , allowing better fisheries management and design of protected areas around feeding and spawning areas.
In Western Europe, sturgeons have been heavily affected by historic fishing and habitat alteration as well as non-native release see section 2. The area is represented by small, sometimes relict populations such as the European Baltic Sturgeon A. For these critically endangered species, the emphasis is on recovery and restoration; distribution and movement data are extremely useful for identifying critical and important habitats. Restoration projects for European and Atlantic Sturgeon have released marked mostly tagged with external T-bar tags juveniles from captive breeding facilities to track subsequent movements and habitat use .
Acoustic telemetry has been used to study young European Sturgeon in the Gironde River estuary and the influence of tidal cycles on their movement . This study was important to the success of reintroduction efforts 2,—5, tagged fish released per year and in guiding planned restoration and habitat protection efforts. Tagging will eventually reveal whether reintroduced animals survive to adulthood and return to their rivers of release to reproduce. This study as well as  and  not only provide knowledge for species restoration but also insight on the migratory and habitat use patterns of juvenile sturgeon, the least studied life history stage in terms of movement and migration.
Rearing of European Sturgeon in captivity also provides information on life history parameters associated with light, temperature, and salinity that are useful for the purpose of inferring population preferences and requirements in the wild  , . The Black Sea is home to the same commercially important species of sturgeon as found in the Caspian Sea, with the Danube River supporting the largest populations.
Sturgeons in this region have also been impacted by fishing and habitat degradation and the focus of scientific research is often on restoration, recovery, and management. In the Black Sea, acoustic tagging studies have been used to examine spawning location and timing for Stellate A. The current tagging study may be more successful than the previous effort due to a moratorium on sturgeon fishing currently in place in the Romanian and Bulgarian portions of the Danube River.
New research that incorporates microchemistry techniques is focusing on the use of trace elements to understand migratory patterns . Future monitoring and assessment studies that incorporate tagging will be important in understanding whether fishing moratoria are being respected and if sturgeon populations are successfully recruiting and rebounding. The Russian Far East and China include little-known and under-studied anadromous sturgeon species  , . The Amur A. These species are thought to have complex population structures, undertaking considerable migrations within the river Amur Sturgeon , and marine environment Kaluga.
The Sakhalin Sturgeon inhabits the Russian Far East and is believed to have a primarily marine life history; it is one of the least studied of the sturgeons and is also one of the most critically endangered, with spawning populations possibly reduced to a single river. The Chinese Sturgeon, A. As with the Caspian and European species, these species would benefit from studies of migration, movement, and distribution, so that appropriate recovery and management plans can be produced.
Subsequent recaptures of tagged fish can yield information on movement, time at large, growth, etc. Sturgeon are long-lived animals; thus, tags or marks that can be positively identified many years following release are ideal. Although not always feasible, determination of sex and maturational stage of individual sturgeon used in long-term tagging studies can provide greater insights regarding interpretation of subsequent movement and migration patterns.
If tagging involves tag implants in the body cavity typically electronic tags , the process should include visual determination of sex and stage or analysis of plasma concentrations to identify sex  ,  ; see section 2. The use of uniquely identifiable tags can provide comparative growth and condition information for long-term studies with adequate sample sizes .
Length data i. Marking sturgeon with traditional methods such as dye marking, tattoos, pigment implantation, or freeze branding is not recommended for studies that intend to report recaptured marks over a long time span i. Another more-permanent marking approach to be considered, with caution, is scute removal  , . Scutes are one of the few body parts of sturgeon that can be removed that will not grow back. A combination of scutes removed from pre-determined locations on the sturgeon can translate into information such as location, year, and month.
Since scute removal may induce high levels of stress, it is not recommended for use on sturgeon populations that are critically endangered. Other permanent marks that have been applied to sturgeon include barbel clipping and fin ray removal. Barbel removal is not recommended due to the importance of barbels to sturgeon sensory physiology and the reduction in fitness and increase in mortality it can cause .
The total or partial removal of the lead pectoral fin ray has gained popularity and utility for sturgeon aging fin ray cross sectioning and can also be used for genetic analyses fin tissue and microchemistry analyses fin ray composition analyses. The removal or clipping of a fin ray can also constitute a short-term less than 5 years mark, typically as a secondary mark to a tag application. However, care should be taken to clip the fin ray beyond the articulated base above the insertion point with the body wall or mortality rates could increase .
As with scute removal, fin ray removal may elevate levels of stress and reduce swimming performance short term and is not recommended for use on critically endangered populations. Tag types for sturgeon fall into three major categories: external tags, internal tags, and electronic telemetry tags. For the purposes of this paper, internal tags will be limited to Passive Integrated Transponder PIT tags, which are small, individually coded tags that are injected with a specialized tool into the body musculature or internal body cavity of sturgeon and are detected with a hand-held electronic tag reader.
The use of electronic tags that can be attached externally or internally and utility of associated telemetric tag types radio, acoustic, satellite is presented in section 2. External tags — External, non-telemetry tags are typically attached to dorsal or lateral locations on the sturgeon with the intention to minimize the impact or influence of the tag encourage natural behaviour and maximize tag retention.
External tags are typically labelled with information that includes a unique tag number, and may include contact information for tag reporting, such as an address or phone number. T-bar anchor tags can have especially good retention rates  , . Internal PIT tags — A popular and effective tag for sturgeon is the PIT tag, a small, uniquely coded electronic tag that is applied internally via a hand-held applicator syringe. Popular PIT tag insertion locations are in the body cavity, base of pectoral fin or dorsal fin or between base of dorsal fin and lateral line , and behind head plate left or right of dorsal line.
PIT tags used for sturgeon are typically 2 mm in diameter and 10—14 mm in length. PIT tag readers are typically battery powered, and display the tag number on a small screen. Tags can be detected with most hand-held tag readers from a distance up to about 20 cm, and the signal can be detected through water, flesh, etc.
The PIT tag is injected just beneath the skin, about 1 cm behind the head plate, on the left side of the dorsal scute line. PIT tags can also be detected with PIT tag antennas that are built into passive underwater apparatus such as tubes, loops, or mats; when a PIT tagged sturgeon passes through or near the antenna, the tag code is logged with time and date in the memory of a receiving unit connected by cable to the antenna apparatus or array that is later downloaded.
This application may be effective to gather recapture data for constricted locations where tagged sturgeon are forced to pass through a confined area. For some applications, remote PIT tag detection may provide information to calculate overall survival  ; however, without a secondary detection strategy to document the passage of non-tagged sturgeon such as a video camera, or test sampling to determine mark rates, the tag data alone will not allow sufficient data to produce abundance estimates.
Considerations for PIT tags — PIT tags are typically more expensive in the order of 5—10 times more expensive per tag than most external tag types but have high retention rates. PIT tag information is transmitted from the tag by way of a specific radio frequency; both the tag and tag reader must be compatible and using the same frequency. Thus, when committing to a long-term research project that uses PIT tags, it is important to determine the long-term availability of both the tags and the compatible tag readers.
Also, researchers should determine if other sturgeon researchers that have worked or are working on the target population or species have applied PIT tags to sturgeon. If so, new studies that include PIT tag applications may want to consider using the same tag frequency so that previously tagged sturgeon can be identified. The rapid advancement of electronic tag technology telemetry has facilitated an explosion of research on sturgeon life history, which in turn has generated novel insights into migratory behaviour, habitat use, and demographic processes.
Electronic tagging offers advantages over traditional tagging approaches requiring large sample sizes to overcome low recapture rates. Electronic tags can be categorized by several characteristics. One distinction is whether tags transmit data in real-time to receivers telemetry tags or store data to internal memory for transmission at some later date archival tag. Telemetry tags can be further differentiated by signal transmission mode: acoustic or radio. To date, telemetry tags have been most widely used in sturgeon research, although archival tags have been used with great success in studies of oceanic fish and marine birds.
Radio tags are similar, with differences related to signal transmission mode: radio waves propagate well through air and freshwater, but poorly in hard or saline water. Because acoustic or radio tagged fish need not be recaptured and can be detected at a distance, strategically placed receivers can collect large amounts of data on tagged fish.
Combined acoustic and radio tags CART combine both transmission modes, allowing radio receivers to be used in freshwater and acoustic receivers to be used in brackish and saltwater. For both kinds of tags, information about the tagged fish is only collected from fish within the detection area of receivers.
This shortcoming can be overcome by archival tags, which record signals from various sensors and store them internally. Typical information recorded by archival tags include pressure depth , temperature, and light level, which allows estimation of location based on sea surface temperature and the time of sunrise and sunset . Other sensors include electromyograms EMG that record muscle contractions, and accelerometers and tilt sensors that provide data on movement and orientation.
Data from archival tags can be recovered by recapturing the tagged animal and downloading data from the tag or by telemetric transfer of archived data to satellites after pre-programmed release from the tagged animal.
Sturgeons and Paddlefish of North America
Use and utility of telemetry tags — We searched the primary literature for sturgeon studies reporting the use of electronic tags, and found 55 relevant studies summarized in Table 2. To date, the most frequent application of electronic tagging has been to study habitat use and movement of wild sturgeon within rivers. A substantial fraction of these studies have identified the timing and location of spawning, a topic of obvious interest to those working on conservation of sturgeon. These studies have relied on both acoustic and radio tracking, often in combination, and typically have made use of mobile tracking to detect tagged sturgeon.
A related type of study examines the movement and habitat use of cultured sturgeon after release. The second most frequent use of electronic tags for sturgeon research has been to investigate large-scale migrations e. These studies have used all types of telemetry tags and tracking methods, and most have used acoustic tags, or a combination of acoustic and other tag types. The study of  is notable for its use of cross-shelf arrays of receivers to document annual migrations of Green Sturgeon individuals of which can cover more than kms per year.
This was possible because the continental shelf off the west coast of North America is narrow, and a number of studies were underway using compatible tags and receivers, including the Census of Marine Life's Pacific Ocean Shelf Tracking POST program . Lawrence River estuary that used mobile tracking and one fixed receiver .
The study by  used a combination of archival tags, radio tags, and sophisticated data analysis to determine if mature Shovelnose Sturgeon spawned successfully following tagging. The radio tags were used mainly to relocate individual sturgeon whose state of gonadal development had been determined bearing the digital storage tags that recorded temperature and depth. The analysis involved fitting a switching model to the depth histories of individual sturgeon; spawning was inferred by observing a period of reduced depth variability.
Data provided by electronic tags, especially from archival tags, can be a rich source of information on behaviour that can be analysed with appropriate models that connect behavioural modes to the tag data  — . Electronic tags have also been used to investigate the behaviour of cultured sturgeon following release  —  , the behaviour of sturgeon near potential fish passage impediments  ,  , experimental evaluations of habitat suitability  , and to identify spawning habitat  , .
Both acoustic and electromyogram EMG tags have been used to test the response of White Sturgeon to changes in dam operations . EMG tags transmit radio pulses when muscles contract, allowing researchers to measure the physical activity of fish at finer scales than can be determined from tracking techniques that only provide coarse changes in position over time, or in flow fields where swimming speed in water may differ substantially from speed over ground. The importance of sex determination in telemetry studies — Many biotelemetry studies have been conducted with juvenile and adult sturgeon without identification of sex and stage of maturity.
In certain cases, such as identification of general habitat use or spatial distributions of a population, it may not seem imperative to know the sex of individuals. However in many cases, such as when trying to understand why habitat is chosen, or when and why migrations are initiated or ceased, identifying the sex and, in adult populations, the stage of maturity provides greater insight into the behaviour of the animal . It often is stated in the literature that sex and stage of maturity were not determined to reduce stress; it is critical to reduce stress, but trained personnel can determine sex and stage of maturity with very little increased handling time during transmitter application, or blood plasma levels can be examined for retrospective analysis.
A review of methods is provided here . If transmitters are attached externally, ultrasonography or endoscopy may be used to determine sex and maturity  — . The primary limitation of these techniques is that it is often difficult to differentiate immature females from males; in addition, the stage of maturity in males cannot be determined as size of testicular lobe does not always confer stage of maturity. Ultrasound and endoscopy are useful tools in the identification of ripe females.
When transmitters are implanted surgically, a sterilized otoscope or pen light may be used to visually determine sex and stage of maturity. A larger incision than the incision for insertion of the tag is not required under these circumstances. However, as in the case with ultrasound and endoscopy, the stage of maturity in males cannot be determined visually, though a small biopsy may be collected for histological analysis and stage of maturity determination.
Additional limitations of ultrasonography are the potentially high cost of equipment and the moderate level of training required in order to interpret sonograms. Measurement of circulating sex steroids may be used less invasively to determine sex and stage of maturity  ,  — . Under ideal circumstances, the misclassification rates of assigning fish to classes of sex and maturity i. Interestingly, when classification functions derived for White Sturgeon to predict sex and stage of maturity  were applied to a small number of Lake Sturgeon, comparable classification rates were found .
Special consideration for the use of this tool should be made in populations that may be exposed to environmental contaminants . Stress associated with capture and handling in telemetry studies — Less is known about the neuroendocrine control of the stress response and roles of allostasis and hormesis in chondrosteans compared to teleosts . However, the cortisol response has been described in several sturgeon species in response to a stressor  —  , and cortisol has been identified as the primary glucocorticoid in Pallid Sturgeon .
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Plasma cortisol concentrations basal and stressed in sturgeon vary by species  ,  ; variation in plasma cortisol concentrations may also be influenced by time of day, age, size, season, temperature, and capture and sampling techniques  ,  ,  , . It is essential to reduce stress i. In order to design a cost-effective and useful tagging program, researchers should compose an experimental design that considers sample size, the costs associated with tagging and recapture activities, and study duration .
With the exception of telemetry studies where data may be recovered remotely , consideration should be given to the potential number of tags that are expected to be recovered based on the number of tags deployed and the level of subsequent sampling effort to recover tags and reported. Low tag reporting rates can lead to low precision in estimates of rates of natural and fishing mortality .
Ideally, tagging and marking studies should aim to minimise tag loss and tagging-related mortality and be done in a way that the tag reporting rate is known or can be estimated  . Researchers should consider the statistical power of a planned tagging experiment, and whether their sample size will provide adequate power to detect the effect size of interest  . Further stratification by length, age, sex, or life-history stage may also be desirable  ; in this case, the number of releases will need to be scaled up by the number of classes or life-history stages for which parameters will be estimated to achieve the desired level of precision and accuracy .
In the context of exploitation rate estimation, tagged fish should be representative of the exploited population, such that each exploitable fish is equally likely to be tagged . Information from marking and tagging experiments can aid the design of subsequent surveys and the interpretation of the survey data. This is particularly relevant to Caspian Sea sturgeons as total allowable catch estimates are based upon population assessments derived from trawl survey data.
Spatially-structured mark-recapture models provide a suitable framework for estimation of rates of residency and movement using tagging data  — . Tagging data also allow inference about population abundance and exploitation rates  , providing that rates of tag loss and reporting are known or estimable  , . Electronic tags generate relatively new kinds of data, and methods for the analysis of these data are lagging behind the rapid development of the tags, and the increasing use of large release groups. In the early studies, when tags were more expensive and their utility unproven, typical studies tagged a handful of animals.
In this case, data arising from each tag could be presented separately and in full. Newer studies have tagged hundreds or even many thousands of fish e. Methods for analyzing the rich data streams from archival tags are relatively well-developed. Capture-recapture methods, such as the multi-strata robust design, would seem to be applicable to situations where sturgeon move among many different areas and experience different mortality rates according to their location or state e.
These include achieving large-enough sample sizes to reliably estimate the many parameters of such models, and dealing with the problem that detections of tagged sturgeon occur over the same time interval as the mortality process. Typical capture-recapture models assume that there is no mortality during the recapture process, which in some cases can be instantaneous. Using life-history traits to understand how populations may respond to perturbations such as harvest has been advocated as a useful approach to predicting extinction vulnerability and formulating management strategies  — .
The majority of population dynamics models for sturgeon species to date can be classified as simulation models, which can be applied to evaluate the sensitivity of population productivity and growth rates to changes in the survival rates of different life stages, or to estimate maximum sustainable yield harvest rates  — . Where a time series of historical catches is available, population dynamics models can be used to reconstruct unfished population abundance over time to estimate depletion the ratio of current to unfished abundance or biomass  — .
Applying genetic techniques allows a researcher to understand the species that are present in a given area i. An important question that can be addressed using genetics is that of where an individual animal reproduces. As a first step in answering this question, reproductively isolated populations of a sturgeon species must be identified through genetic analysis. By knowing the number of isolated populations, appropriate conservation schemes can be created that preserve the evolutionary and ecological potential of a species. The protection of multiple populations can serve to buffer against extinction due to environmental change.
Many sturgeons are thought to return to their natal river to reproduce and it is this behaviour that creates genetic structure and separate populations. It is unlikely, on the timescale of interest to managers, that animals from one river system would replace those in another if an individual population were to go extinct; thus, it is important to minimize individual population extinction since translocation of individuals from other populations should only be used as a last resort.
A related point is that of identifying the presence of non-native species or hybrids in an area as an important step in conservation planning. While information on the location of reproduction can be obtained through tagging studies, this approach does not answer the question of whether the animal effectively breeds in an area. Evidence of spawning can be gathered through biochemical means e.
Related Sturgeons and Paddlefish of North America: 27 (Fish & Fisheries Series)
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