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Documented distribution of Gulf Sturgeon in North America, determined from acoustic and archival telemetry projects. 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. 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 100 m isobath is shown as the light blue areas near the coast. doi:10.1371/journal.pone.0071552.g002
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Worldwide, sturgeons (Acipenseridae) are among the most endangered fishes due to habitat degradation, overfishing, and inherent life history characteristics (long life span, late maturation, and infrequent spawning). As most sturgeons are anadromous, a considerable portion of their life history occurs in estuarine and marine environments where they...
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... hydrograph of a sturgeon-bearing river). In some areas, introduction of non-native sturgeons and hybridization between species (e.g. Scaphirhynchus) due to habitat alteration and/or unintentional release from aquaculture (e.g. in Europe) makes understanding the movement and life history of introduced sturgeons or hybrid populations an important conservation consideration [12], [13]. 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. Sturgeon species and/or populations with an anadromous life-history strategy may require assessment models that account for the seasonal movement patterns of different life-history stages exploited by fisheries [14], [15]. 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 [14], [16]. 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 [17], [18]. 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. 1.2.1. Gulf Sturgeon. 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 [19]. 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. Early information about Gulf Sturgeon distribution and migration came primarily from commercial fishing [20]. 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. More detailed information came from surveys in the 1980s conducted in response to declining catches and the species’ listing by the state of Florida as ‘‘threatened’’ [21], [22]. Marking with conventional tags mostly showed the range and extent of migration (e.g. recaptures of tagged fish by anglers below a dam or by commercial shrimp trawlers in Gulf of Mexico waters), whereas the first use of electronic tags (and manual/mobile tracking) provided insights about holding, staging, and spawning areas [22]; the use of radio tags in this study allowed the authors to characterize occupied riverine habitats in the Apalachicola River and to relate the timing of upstream and downstream migrations to environmental cues. 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 1980s a telemetry study was conducted wherein Gulf Sturgeon were tagged with both radio and sonic tags [23]. 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 [23]). The listing of Gulf Sturgeon in 1991 as a threatened species under the U. S. Endangered Species Act provided a further boost to research activity. For example, radio tracking studies in the Choctawhatchee River were initiated to identify potential spawn- ing sites, with confirmation through the use of artificial substrates to collect the adhesive eggs of Gulf Sturgeon [24]. Deployment of artificial substrates in a grid design provided fine-scale information about spawning habitat in the Suwannee River [25]. 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 [26–29]. The fish occupying these marine habitats were often from multiple river systems; for example, [27] reported that Gulf Sturgeon from the Yellow, Choctawhatchee, and Apalachicola rivers were located within a 25-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 [29] 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 [30]. 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. Genetic results showed strong natal river fidelity, so critical habitat was defined in each of the seven river systems containing currently reproducing populations (Pearl, Pascagoula, Escambia, Yellow/Blackwater, Choctawhatchee, Apalachicola, and Suwannee). This resulted in designation of nearly 2,800 river km as critical habitat for conservation of the species. 1.2.2. Green Sturgeon. In contrast to the relatively well- studied Gulf Sturgeon, the North American Green Sturgeon was little studied until 2002, when the US National Marine Fisheries Service received a petition to list it under the US Endangered Species Act. A severe lack of demographic and basic life-history information hampered the subsequent status review [31]. 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 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 [32]. Tagged sturgeon returned to the river to spawn every two to four years [33]. 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 [34]. 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 overwintering areas in the coastal ocean, with many individuals using areas around northern Vancouver Island [35], [36]. 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 [36]. 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 [37]. Habitat data associated with tag detections was used to gain further insight into freshwater [38] and fine 2 [39] and coarse- scale [40] marine habitat preferences and seasonal patterns of distribution. 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 [41–46]. In summary, the application of electronic tag technology to study Green Sturgeon revealed novel, reliable, and useful/relevant information ...
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... and/or unintentional release from aquaculture (e.g. in Europe) makes understanding the movement and life history of introduced sturgeons or hybrid populations an important conservation consideration [12], [13]. 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. Sturgeon species and/or populations with an anadromous life-history strategy may require assessment models that account for the seasonal movement patterns of different life-history stages exploited by fisheries [14], [15]. 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 [14], [16]. 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 [17], [18]. 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. 1.2.1. Gulf Sturgeon. 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 [19]. 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. Early information about Gulf Sturgeon distribution and migration came primarily from commercial fishing [20]. 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. More detailed information came from surveys in the 1980s conducted in response to declining catches and the species’ listing by the state of Florida as ‘‘threatened’’ [21], [22]. Marking with conventional tags mostly showed the range and extent of migration (e.g. recaptures of tagged fish by anglers below a dam or by commercial shrimp trawlers in Gulf of Mexico waters), whereas the first use of electronic tags (and manual/mobile tracking) provided insights about holding, staging, and spawning areas [22]; the use of radio tags in this study allowed the authors to characterize occupied riverine habitats in the Apalachicola River and to relate the timing of upstream and downstream migrations to environmental cues. 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 1980s a telemetry study was conducted wherein Gulf Sturgeon were tagged with both radio and sonic tags [23]. 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 [23]). The listing of Gulf Sturgeon in 1991 as a threatened species under the U. S. Endangered Species Act provided a further boost to research activity. For example, radio tracking studies in the Choctawhatchee River were initiated to identify potential spawn- ing sites, with confirmation through the use of artificial substrates to collect the adhesive eggs of Gulf Sturgeon [24]. Deployment of artificial substrates in a grid design provided fine-scale information about spawning habitat in the Suwannee River [25]. 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 [26–29]. The fish occupying these marine habitats were often from multiple river systems; for example, [27] reported that Gulf Sturgeon from the Yellow, Choctawhatchee, and Apalachicola rivers were located within a 25-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 [29] 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 [30]. 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. Genetic results showed strong natal river fidelity, so critical habitat was defined in each of the seven river systems containing currently reproducing populations (Pearl, Pascagoula, Escambia, Yellow/Blackwater, Choctawhatchee, Apalachicola, and Suwannee). This resulted in designation of nearly 2,800 river km as critical habitat for conservation of the species. 1.2.2. Green Sturgeon. In contrast to the relatively well- studied Gulf Sturgeon, the North American Green Sturgeon was little studied until 2002, when the US National Marine Fisheries Service received a petition to list it under the US Endangered Species Act. A severe lack of demographic and basic life-history information hampered the subsequent status review [31]. 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 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 [32]. Tagged sturgeon returned to the river to spawn every two to four years [33]. 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 [34]. 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 overwintering areas in the coastal ocean, with many individuals using areas around northern Vancouver Island [35], [36]. 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 [36]. 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 [37]. Habitat data associated with tag detections was used to gain further insight into freshwater [38] and fine 2 [39] and coarse- scale [40] marine habitat preferences and seasonal patterns of distribution. 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 [41–46]. In summary, the application of electronic tag technology to study Green Sturgeon revealed novel, reliable, and useful/relevant information regarding marine migrations and habitat use, spawning locations and periodicity, and both marine and freshwater life history attributes. While tagging revealed clear overall ...
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... 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 [9]. 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. River movement can be complex and include multi-step migrations [10] and include movement between and among rivers suggesting a meta-popula- tion structure [11]. 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. Directed migrations from overwintering locations to feeding habitats, in some cases timed to intercept specific, localized prey species, may be a population- based behaviour; other populations of the same species may exhibit an entirely different food-related migration pattern based on the abundance/timing of localized prey. 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. There may be sex-specific differences in the timing of movements (often males arrive at the spawning grounds before females) so harvest/interception regimes may need to be sensitive to this in order to maintain the male:female sex-ratio balance within the population. 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 [11]. 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.g. changes to the annual hydrograph of a sturgeon-bearing river). In some areas, introduction of non-native sturgeons and hybridization between species (e.g. Scaphirhynchus) due to habitat alteration and/or unintentional release from aquaculture (e.g. in Europe) makes understanding the movement and life history of introduced sturgeons or hybrid populations an important conservation consideration [12], [13]. 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. Sturgeon species and/or populations with an anadromous life-history strategy may require assessment models that account for the seasonal movement patterns of different life-history stages exploited by fisheries [14], [15]. 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 [14], [16]. 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 [17], [18]. 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. 1.2.1. Gulf Sturgeon. 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 [19]. 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. Early information about Gulf Sturgeon distribution and migration came primarily from commercial fishing [20]. 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. More detailed information came from surveys in the 1980s conducted in response to declining catches and the species’ listing by the state of Florida as ‘‘threatened’’ [21], [22]. Marking with conventional tags mostly showed the range and extent of migration (e.g. recaptures of tagged fish by anglers below a dam or by commercial shrimp trawlers in Gulf of Mexico waters), whereas the first use of electronic tags (and manual/mobile tracking) provided insights about holding, staging, and spawning areas [22]; the use of radio tags in this study allowed the authors to characterize occupied riverine habitats in the Apalachicola River and to relate the timing of upstream and downstream migrations to environmental cues. 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 1980s a telemetry study was conducted wherein Gulf Sturgeon were tagged with both radio and sonic tags [23]. 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 [23]). The listing of Gulf Sturgeon in 1991 as a threatened species under the U. S. Endangered Species Act provided a further boost to research activity. For example, radio tracking studies in the Choctawhatchee River were initiated to identify potential spawn- ing sites, with confirmation through the use of artificial substrates to collect the adhesive eggs of Gulf Sturgeon [24]. Deployment of artificial substrates in a grid design provided fine-scale information about spawning habitat in the Suwannee River [25]. 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 [26–29]. The fish occupying these marine habitats were often from multiple river systems; for example, [27] reported that Gulf Sturgeon from the Yellow, Choctawhatchee, and Apalachicola rivers were located within a 25-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 [29] 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 [30]. 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. Genetic results showed strong natal river fidelity, so critical habitat was defined in each of the seven river systems containing currently reproducing populations (Pearl, Pascagoula, Escambia, Yellow/Blackwater, Choctawhatchee, Apalachicola, and Suwannee). This resulted in designation of nearly 2,800 river km as critical habitat for conservation of the species. 1.2.2. Green Sturgeon. In contrast to the relatively well- studied Gulf Sturgeon, the North American Green Sturgeon was little studied until 2002, when the US National Marine Fisheries Service received a petition to list it under the US Endangered Species Act. A severe lack of demographic and basic life-history information hampered the subsequent status review [31]. 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 ...
Citations
... Reliance on a narrow gene pool from captive broodstock increases the likelihood of loss of fitness and introduction of undesirable characteristics into the population [139,141]. Moreover, the routes and timing of natural sturgeon migrations in the Caspian basin are not yet fully understood; new methods to monitor fish movements are available, but the scarcity of residual Caspian sturgeon populations has made it difficult to exploit them to increase our understanding of sturgeon biology and behavior [30,106,142,143]. The release of juveniles into wild populations characterized by depleted gene pools may also lead to undesirable interspecific hybridization [19,144,145]. ...
... The uncertainties associated with insufficient information about the hydrology of the Ural River, IUU fishing, and the consequences of stocking are well known, as is the bottleneck imposed by inadequate environmental monitoring data [28,83,152,170,171]. The lack of fundamental knowledge about structural changes in populations of Ural sturgeon species due to anthropogenic and other pressures [143] also generates ambiguity. These issues are compounded by a dearth of knowledge about the Ural's hydrobiology, which includes natural predators of sturgeon eggs and larvae, as well as the more than 50 native (and 3 non-native) fish species that coexist with sturgeon in the riverine ecosystem [27,31]. ...
Although Eurasia’s Caspian basin once supported the world’s richest and most diverse complex of sturgeon species, recent human activities have decimated populations of these ecologically and economically important fish. All five anadromous Caspian sturgeon species are critically endangered, and the potamodromous sterlet is also threatened. The precipitous decline of these species is due to a combination of factors that includes illegal, unreported, and unregulated (IUU) fishing; destruction of feeding and spawning habitat; water pollution; and the environmental consequences of climate change. International efforts are currently underway to re-establish sustained naturally reproducing sturgeon populations in the basin. Here, we update and review the status of sturgeon in the Caspian Sea with emphasis on the northern basin and the inflowing Volga and Ural rivers. We then focus on efforts to restore sturgeon in the Ural, which originates in Russia and flows through Kazakhstan before entering the Caspian Sea. With nearly ideal hydrological conditions for sturgeon, the Ural is the basin’s sole remaining river that allows migrating sturgeon unimpeded access to potentially productive spawning grounds. The challenge of re-establishing sturgeon in the Ural River exhibits the classical characteristics of wicked problems: ambiguous definitions, changing assumptions and unanticipated consequences, tradeoffs and economic dependencies, an incomplete and contradictory knowledge base, and no straightforward pathway toward a final solution. This challenge is examined here for the first time from the perspective of its wicked dynamics, with consideration given to approaches that have proven effective elsewhere in resolving wicked environmental problems.
... Alternatively, hatchery and wild origin individuals can be distinguished based on the geochemical analyses of calcified structures that form throughout the life of a fish and incorporate the naturally occurring differences in the geochemical makeup of different watersheds (Campana 1999;Nelson et al. 2013;Willmes et al. 2016a;Sellheim et al. 2017). The 87 Sr/ 86 Sr isotope signal is passed from water into the fish exchanging in trace amounts for calcium in calcified structures such as otoliths reflecting a chronological record of geochemistry (Kalish 1989;Hegg et al. 2013;Coelho et al. 2017). ...
Largemouth bass Micropterus salmoides, a popular warm water sport fish, is routinely stocked in reservoirs throughout the USA to augment wild populations. Evaluating if these supplementations are successful requires distinguishing hatchery-sourced fish from their wild counterparts. From 2011 to 2019, over 467 000 largemouth bass fingerlings were stocked from multiple hatchery sources into a large southwestern reservoir (Elephant Butte Reservoir, New Mexico, USA) to supplement the sport fish population. To identify hatchery-sourced largemouth bass, we measured strontium isotope ratios (87Sr/86Sr) and determined ages using otoliths and dorsal spines. Otolith analysis of 169 fish classified 92.9% (n = 159) to the reservoir with few fish of hatchery origin (2 from Arkansas, 1.2%, and 1 from Montana, 0.6%). While stocking over 467 000 fingerlings across 8 years appears to reflect negligible stocking success, it is likely that low and variable stocking densities (average 3.0, range 0.29–7.77 fish·ha−1) contributed to the low stocking success in Elephant Butte Reservoir. Dorsal fin spines did not yield accurate age reconstructions and their 87Sr/86Sr values were affected by matrix interferences preventing source assignments.
... In Africa, the negative ecological effects of dams have been reported on rivers Zambezi (Arthur et al., 2017), Tana in Kenya (Hughes, 1984), Aswa in Egypt (White, 1988), and Senegal in West Africa (Adams, 1985;Hughes, 1984 (Bassa et al., 2020;Nelson et al., 2013;Witte et al., 1992). Some studies have observed that the UVN is the faunal refugia to critically endangered fish species such as L. victorianus (Chapman, Chapman, Kaufman, Witte, & Balirwa, 2008;NaFIRRI, 2017) and is habitat to a rare haplochromine species, Neochromis simotes (Chapman et al., 1996;Greenwood, 1976;Ogutu-Ohwayo, 1988;Wilmsen & Van Hulten, 2017;Witte et al., 1992;Witte et al., 2008). ...
The Upper Victoria Nile (UVN) flows from Lake Victoria into Lake Kyoga, spanning 117 km and supports a diverse aquatic fauna that sustains livelihoods of riverside communities. The UVN is habitat to critically endangered (Labeo victorianus), near threatened (Oreochromis variabilis and Oreochromis esculentus), and rare species (Neochromis simotes). Four hydropower dams were built on the UVN to provide energy for industrial and socioeconomic development, notwithstanding consequential environmental and socioeconomic impacts. The impacts of Bujagali hydropower (BHP) dam on fisheries and livelihoods were assessed biannually (April and September) from 2006 to 2019, using fishing effort, species abundance, catch composition, and economic beach revenue at upstream, mid‐reservoir, and downstream transects. The fishing boats increased from 31 in 2009 to 293 in 2019 and fishers from 83 to 500 over the monitoring period. Maximum annual catch of 461.4 t was recorded in 2014 and lowest of 54.2 t in 2009. In all transects, Protopterus aethiopicus and Labeo victorianus were least in the commercial catches and the use of Mormyrus kannume juveniles as bait for Nile perch fishery corresponded with increased catches from 3.3 t in 2009 to 148.2 t in 2019. Women were mostly engaged in post‐harvest activities such as fish drying, smoking, and food vending. These observations suggest coupling effects of the hydropower dam and ineffective fisheries management. The harvest of M. kannume wild stocks for bait should be banned and research in possible domestication of the species undertaken. There is a need to strengthen fisheries enforcement to curb illegal effort and overexploitation and to implement conservation actions to mitigate potential biodiversity impacts from the hydropower dam operations.
... Receiver placement and environmental conditions can influence p (Mathies et al. 2014). Most studies of aquatic species, including this one, focus on placing receivers in riverine and estuarine habitats (Kocik et al. 2009, Melnychuk 2009, Welch et al. 2009, Nelson et al. 2013). Many of the receivers managed by this study's authors as well as those in the ACT and FACT Networks were predominantly inshore. ...
Survival estimates of animal populations provide managers with critical information on productivity, population stability, and demography. Telemetry-based survival estimates can be obtained remotely. Atlantic sturgeon Acipenser oxyrinchus oxyrinchus are a wide-ranging species whose populations overlap along the East Coast of North America, complicating survival estimation. The objective of this study was to estimate apparent annual survival of the York River population using a Cormack-Jolly-Seber model. In this study, 36 males and 24 females were telemetered and monitored between 2013 and 2019. We considered the fit of a variety of models, selecting the best fit using Akaike’s Information Criterion. The optimal model estimated survival in seasonal increments and detection probability by sex in monthly increments. Five transmitters failed to leave the river and another three stopped being detected within 21 months, but of those, recapturing fish confirmed two had been lost and three were technological failures (12.8% of 39 recaptured). Apparent adult annual survival was estimated to be 99.2% (95% CL, 97.9-99.7%). Addressing sex-specific detection probability and failed transmitters, while including a length covariate for each individual produced higher survival estimates than previously reported studies of Atlantic sturgeon. Four males and one female appear to have died with the location of last detection for four of the suspected mortalities in shipping channels near the mouth of the Chesapeake Bay, suggesting managers should focus on this area of increased risk. Such high survival estimates of the adult stage suggest Atlantic sturgeon survival may be more similar to other long-lived, late maturing species than to most fish species.
... In sturgeons, three types of life history have been suggested in regard to salinity, each with increasing levels of salinity tolerance (Nelson et al., 2013;Rochard et al., 1990). Stenohaline species such as lake sturgeon may have tolerance for a narrow range of salinities but typically inhabit a single salinity throughout their life. ...
... Chemical signatures are another way to "batch mark" large cohorts of fish and the utility of microchemical signatures deposited in the fish hard structures (e.g., fin ray or otolith) has received increasing attention over the last decade (Bakhshalizadeh et al., 2021;Loeppky et al., 2019;Loewen et al., 2016;Nelson et al., 2013;Smith and Whitledge, 2011). One important consideration for chemical signatures is the length of time a "mark" may persist within the hard structure of the fish. ...
Sturgeon are found circumglobally throughout the northern hemisphere. Longevity, late age to sexual maturation and infrequent spawning are typical life history strategies that have supported their evolution over millennia but at the same time have made them vulnerable to extirpation or extinction when population sizes have been reduced as a result of overharvest, habitat degradation and/or pollution. As a consequence sturgeons are among the most at risk species as listed by the International Union for the Conservation of Nature. Aquaculture has been used as a conservation strategy to arrest declines or maintain current population levels for several sturgeon species. Here we describe the development of this conservation strategy in sturgeons, examining the importance of understanding genotype and environment in development of appropriate rearing strategies toward improved conservation practice for this imperiled group of fishes. Recent research indicates a significant effect of environment on phenotype, with early life history being particularly relevant; evidence suggests that repatriation should be the preferred approach where possible. We suggest that while aquaculture can be a valuable conservation and recovery tool, it is particularly effective when the impacts on phenotypic development during early life history are considered and combined with effective post-release monitoring and implementation of additional restoration efforts.
... Migratory fish management is often limited by a lack of information about how environmental variability and management actions intersect with natural complexity in habitat use, movements, and population status of a species (Nelson et al., 2013). This knowledge gap is largely due to the difficulty in reconstructing spatial distributions and habitat associations throughout individuals' lifespans, especially for long-lived species that make large migrations between habitats (Grande et al., 2009;Blechschmidt et al., 2020). ...
... Sturgeons (Acipenseridae) are ancient chondrostean fishes that inhabit aquatic environments throughout the Northern Hemisphere (Birstein et al., 1997;Nelson et al., 2013). Individuals may live over 100 years, mature as late as age 20-25, and reproduce infrequently (Billard and Lecointre, 2001). ...
... While White Sturgeon have experienced marked declines over the past century, they continue to support an important recreational fishery throughout the west coast of North America (Moyle et al., 2015;National Marine Fisheries Service [NMFS], 2015). Thus, identifying key environmental stressors and how they intersect spatially or temporally with sturgeon life histories remains a key priority for resource managers (Nelson et al., 2013). ...
Understanding life-history diversity in a population is imperative to developing effective fisheries management and conservation practices, particularly in degraded environments with high environmental variability. Here, we examined variation in habitat use and migration patterns of White Sturgeon (Acipenser transmontanus), a long-lived migratory fish that is native to the San Francisco Estuary, CA, United States. Annual increment profiles were combined with respective geochemical (87Sr/86Sr) profiles in sturgeon fin rays to reconstruct annual salinity chronologies for 112 individuals from 5 to 30 years old. Results indicated a complex and diverse amphidromous life history across individuals, characterized largely by estuarine residence, a general ontogenetic trend toward higher-salinity brackish habitats, and high variability in habitat use across all age groups. Hierarchical clustering based on fin ray geochemistry during the first 10 years of life, prior to sexual maturation, indicated at least four distinct migratory phenotypes which differed largely in the timing and duration of juvenile to subadult movements between fresh- and brackish-water habitats. This study provides information regarding habitat use and migration in sub-adult fish that was previously lacking. Different migratory phenotypes vary in exposure to stressors across time and space and populations. Understanding White Sturgeon habitat distributions through space and time at different life stages can help identify areas where habitat restoration would be most effective and develop management actions to reduce stressors associated with specific areas where White Sturgeon are present.
... Finally, tagging studies can be useful to engage the public in research and raise awareness about the conservation status of a species (Nelson et al., 2013). Fish population monitoring and assessment programs in which people capture fish, report the presence of tags, apply tags to untagged fish, and collect basic information (e.g., fish length, location, date of capture) have proved to be successful (e.g., Comité ZIP du lac Saint-Pierre, 2008;Fortin et al., 1993). ...
... Acoustic telemetry (Bangley et al., 2020) and archival tags, like pop-up satellite archival tags, would provide a more complete picture of seasonal movement, migration patterns, and habitat selection (Erickson et al., 2011;Rothermel et al., 2020;Taylor et al., 2016). Because many of these advanced techniques require expensive equipment and specialized training, collaborative research involving multiple organizations and a variety of tagging techniques is likely the best approach for future studies on sturgeon movement at multiple temporal and spatial scales (Nelson et al., 2013). ...
Movement of Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) and lake sturgeon (A. fulvescens) in the St. Lawrence Estuary (Québec, Canada) are not fully understood. To assess the movement extent of both species, a mark–recapture study was conducted in collaboration with commercial fishermen operating in the St. Lawrence Estuary. Between 1981 and 2015, 3,367 Atlantic sturgeon (fork length 21.8–199.5 cm) and 3,180 lake sturgeon (fork length 17.8–190.8 cm) were tagged and released. Of these, 673 Atlantic sturgeon and 42 lake sturgeon were recaptured. The maximum distances traveled between capture and recapture locations were 1,307 km for Atlantic sturgeon (8 years after initial capture) and 252 km for lake sturgeon (less than 1 year after initial capture). Statistical analyses identified differences in the dispersal distance of both species as revealed by a first component characterized by individuals with short dispersal distances (98% and <35 km for Atlantic sturgeon; 58% and <1 km for lake sturgeon) and a second component characterized by individuals with longer dispersal distances (2% and >600 km for Atlantic sturgeon; 42% and >190 km for lake sturgeon). We suggest that the short dispersal distances detected in the vast majority of Atlantic sturgeon recaptures likely reflect strong site fidelity, highlighting the importance of the St. Lawrence Estuary as a preferred habitat for juveniles and subadults. Although recaptures were low for lake sturgeon because this species is only marginally targeted by commercial fishermen in the St. Lawrence Estuary, our results also showed that this species uses estuarine habitats and that half of the population seems to exhibit strong site fidelity (67% of individuals were recaptured within 2 km).
... Genetic information can help determine connectivity between individuals and populations, and provides critical information about life cycles and life histories, movement patterns, sex-specific contributions and reproductive systems at the individual, species and community levels (Broquet & Petit, 2009;Fraser, Lippe, & Bernatchez, 2004;Nelson et al., 2013;Rooker et al., 2007). Genetic approaches used in the LMB to study population structure have shown that closely related species can exhibit very different population structures, suggesting differences in migration patterns. ...
Despite their economic and ecological importance, migratory fishes of the Lower Mekong Basin (LMB) remain understudied, which hampers effective management to sustain valuable fisheries and address serious threats such as habitat degradation, development and overharvest. From a list of potential knowledge needs, a group of fisheries professionals most frequently identified six top priorities for managing migratory fishes in Cambodia: (1) population abundances and trends, (2) life cycles and life history, (3) migration timing and triggers, (4) migration routes and distances, (5) locations of key habitats and spawning areas, and (6) environmental and habitat requirements. These needs are discussed along with nine relevant methodologies for addressing them, including fisheries-dependent and fisheries-independent sampling, reproductive techniques and captive studies, otolith and genetic analysis tools, and tagging and imaging techniques. A suggested research framework is also presented to inform adaptive management of migratory fishes. While emphasis is given to Cambodia, the analysis is also applicable to other LMB countries, given that migratory fishes occur throughout the basin and migrate across borders. It is suggested that a robust research and monitoring agenda is required to prioritise knowledge needs and select appropriate methodologies to answer questions vital to inform sustainable migratory fish management in Cambodia.
... Worldwide there are approximately two dozen species of sturgeon; many exhibit a migratory life history that involves periodic long-distance movements in large river systems (Nelson et al., 2013). ...
Dams can impede access to habitats that are required for the completion of life history phases of many migratory fish species, including anadromous sturgeons. Various forms of fish passage have been developed to permit migratory fishes to move above dams, but many dams still lack such structures. Translocation of ripe, mature fish above dams has been used as a first step to determine the efficacy of potential fish passage systems. The anadromous Gulf sturgeon, Acipenser oxyrinchus desotoi, inhabits the Gulf of Mexico and coastal rivers from Florida to Louisiana, and requires upriver spawning habitats to complete its life cycle. Historic overfishing and other anthropogenic threats, including dam construction, led to species declines and subsequent listing as threatened under the Endangered Species Act. In the Apalachicola River, FL, the 1957 completion of Jim Woodruff Lock and Dam (JWLD) created Lake Seminole and blocked Gulf Sturgeon from accessing 78% of historic riverine habitat—including potential spawning habitat—in the Apalachicola‐Chattahoochee‐Flint River Basin. The objective of this pilot study was to determine the efficacy of passage around JWLD through the trap‐and‐transport of 10 male Gulf sturgeon from the Apalachicola River to the reservoir above the dam. Through the use of acoustic telemetry, we were able to assess the ability of these fish to navigate Lake Seminole, access potentially suitable spawning habitat in the Flint and River, and complete their seasonal outmigration to the Gulf of Mexico. In this study, 2 translocated sturgeon moved 69 km upstream into potential spawning habitat in the Flint River, but 6 fish fell back through the lock/spill gates at JWLD within days of translocation. Four sturgeon appeared to remain trapped in the reservoir, and their long‐term survival was deemed unlikely. Given our low sample size, and examination of male fish only, we cannot conclude that a trap‐and‐transport program would ultimately fail to restore spawning above JWLD, but our findings suggest that the risk of adult mortality is nontrivial. Alternatively, we suggest future studies examine the population level trade‐offs associated with translocation of adults or consider alternatives such as a head‐start program to rear and release juvenile sturgeon above JWLD to study viability of their passage in addition to effects on overall recruitment in the population.
... The delayed sexual maturity between male and female Chinese sturgeons (8-18 years for males and 14-26 years for females) increases the difficulties in their protection compared with that of fishes that have a short-span maturity (Yue et al., 2015). In addition, because of the lack of visible sexual dimorphism between male and female sturgeons, and no obvious secondary sexual characteristics, even in the breeding period (Pikitch et al., 2005;Nelson et al., 2013), it is necessary to know the sex of sturgeons for breeding management and for establishing effective breeding populations. To date, the sex identification techniques for sturgeons include minimally invasive surgery identification, endoscopy identification, B-ultrasound identification, blood biochemistry, and sex hormone detection (Doroshov et al., 1997;Kynard and Kieffer, 2002;Webb et al., 2002;Feist et al., 2004). ...
The Chinese sturgeon (Acipenser sinensis) is critically endangered in China. Owing to the lack of visible sexual dimorphism and effective DNA markers for sexing in this species, a novel non-invasive method for sex identification in Chinese sturgeons would be helpful for conservation management. The zona pellucida (ZP) gene and sex determining region Y-box 9 (Sox9) gene were considered as candidate genes involved in gonadal differentiation. Here, we first detected the differences in expression of the ZP3.2 and Sox9 genes in the gonads and ventral fins of 107 Chinese sturgeons aged 2, 3, 6, 7, and 9–11 years old, using quantitative real-time polymerase chain reaction (qRT-PCR) to develop non-invasive expression markers. The accuracy of the developed marker was confirmed using endoscopy in another 240 individuals in four different age groups (aged 5–8 years old).
The expression levels of the ZP3.2 gene in the ovaries and ventral fins at different ages were significantly (p < 0.05; p < 0.05, respectively) higher than those in the counterparts of males. The expression levels of the Sox9 gene in the testes at different ages were significantly (p < 0.05) higher than those in the ovaries, whereas the expression levels of the Sox9 gene in the male ventral fins were low, similar to those observed in the female ventral fins. Furthermore, a sex identification accuracy of 78.33% to 86.66% for the ZP3.2 gene in the ventral fin was confirmed by conducting endoscopies on individuals of four different age groups.
The differential expression of ZP3.2 in the ventral fins of female and male Chinese sturgeon can be used as an effective non-invasive sex indicator in individuals over 2 years of age. This work also provides a novel solution for non-invasive sex identification in other surgeon species.
