Conservation Genetics of
North American Green Sturgeon
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Conservation Genetics of North American Green Sturgeon |
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Funding
This research has been funded as tasks and independent research projects through numerous federal and state agencies including:
CALFED, Project # 98-C15 (B8178).
CALFED Science Program. “Biological assessment of green sturgeon in the Sacramento-San Joaquin watershed” (P.I.s: J. Cech, S. Doroshov, P. Klimley, B. May)
NOAA-Fisheries. “Examination of Juvenile Green Sturgeon Genetic Samples from Natal Rivers.” (P.I.: B. May)
Washington Department of Fish and Wildlife. “Mixed Stock Analysis of Washington State Estuarine Aggregations of Green Sturgeon.” (P.I.: B. May)
Sampling Protocols
We have funding in 2007 and 2008 to analyze and identify the population of origin for agencies, NGO, and individuals who are able to provide us with tissue samples. We are particularly interested in samples from rivers, estuaries, or the ocean!
Please see this protocol for taking tissue samples that will be useful for us.
Thanks for any assistance you may provide.
Research Emphasis
Our work has included many objectives and continues to develop in new directions:
1) We developed a genetic markers to distinguish green sturgeon from white sturgeon and use them to identify green sturgeon spawning sites
2) We developed and utilize microsatellite markers to study the population structure of green sturgeon. We are evaluating the inheritance patterns of these complex tetrasomic loci.
3) We described the population structure among natal population of green sturgeon in the Klamath, Rogue, and Sacramento rivers and have assessed the utility of this information for a genetic stock identification baseline.
4) We have utilized the genetic stock identification baseline to characterize the proportion of green sturgeon originating from the Southern and Northern Distinct Population Segments in coastal estuarine aggregations and identify the origins of green sturgeon encountered in ocean fisheries.
5) We developed a genetic-based methodology for estimating the number of breeding green sturgeon above collections sites. We use kinship coefficients among individuals in a cohort, assess the capture-recapture of full sibling genotypes, and construct estimates of spawning pairs of green sturgeon using accumulation functions.
7) We are evaluating mtDNA sequence of N. American green sturgeon and Sakhalin sturgeon in comparison with other Trans-Pacific sturgeon species to describe the evolutionary relationships among these species.
6) Disseminations of information concerning conservation genetics of green sturgeon and its potential role in recovery and restoration of this species.
Green sturgeon biology
Green sturgeon have successfully
persisted through periods when unfavorable conditions may preclude successful
recruitment for the last 2.2 million years (Brown et al. 1996). Traits like late
reproductive maturity, iteroparous reproduction, and wide physiological
preferences allowed them to periodically exploit favorable conditions. Green
sturgeon are benthic spawners, and presumably eggs are released in a single
spawning event over just a few days. Adult green sturgeon spawn annually in the
mainstem of the Sacramento, Klamath, Trinity, and Rogue rivers and spawning
females have a fecundity of between 59,000 and 242,000 eggs (Van Eenennaam et
al. 2006). Klamath River reproductive females range in age between 19-34 years,
while males are typically younger, ranging from 15-28 years old (Van Eenennaam
et al. 2006). On the Rogue River, Erickson and Webb (in press) observed green
sturgeon making a second spawning migration after 2-4 years following their
initial observed river migration.
Spawning site fidelity is documented in sturgeon (Bemis and Kynard 1997), and
this behavior likely reinforces reproductive isolation of breeding groups. Adult
green sturgeon will reside up to nine months in rivers during spawning years
(Benson et al. in press, Erickson and Webb in press), often entering freshwater
in March and April with a peak in spawning between late May and the beginning of
July. River habitats for spawning and holding are likely different and research
is continuing to identify, characterize, and distinguish these habitats. These
adult fish often hold in low-gradient, off channel habitats deeper than 5m
following spawning, although some proportion of them migrate out in the spring
(Benson et al. in press). Adult sturgeon appear to time their outmigration
according to temperature (< 10°C (50°F)) and hydrologic cues (following the
first fall rainstorm peak flows after oversummering, Erickson et al. 2002,
Benson et al. in press).
Green sturgeon eggs require cold, oxygenated waters. Experimental observations (Van Eenennaam et al. 2005) have found the hatching rate of eggs decreases when incubation temperatures are less than 11°C (51.8°F), with an upper limit of thermal optima at 17-18°C (62.6-64.6°F). Once through metamorphosis, post-larvae demersally remain associated with coarse substrate, and at about day 12 post-hatch initiated an approximately 12-day downstream nocturnal migration (Kynard et al. 2005). Green sturgeon fry feed diurnally with peak nocturnal activity until approximately day 84 post hatch in the river (Kynard et al. 2005). In the laboratory, Nguyen and Crocker (in press) demonstrated green sturgeon have significantly greater growth over bedrock substrate than sandy or cobble substrate. During the emigration period, when suboptimal water temperatures and limited food resources may stress green sturgeon juveniles, Allen et al. (2006b) found smaller juveniles had greater temperature tolerance than eggs, embryonic, larval, or larger juvenile fish. Green sturgeon were observed to continue nocturnal downstream migration until temperatures reach 8°C (46.4°F, Kynard et al. 2005). Based upon these observations, juveniles presumably overwinter in lower portions of rivers in deep pools with low light and some rock structure. Green sturgeon appear to display morphological (larger pectoral fin surface area) and behavioral (rostrum wedging and pectoral fin holding) attributes favoring station holding in these types of habitats (Allen et al. 2006a).
Although the biology of juvenile green sturgeon in estuaries is poorly described, it is known that they can osmoregulate in fresh or brackish water by 100 days post hatch (Allen and Cech in press). Juvenile green sturgeon have been found in the Sacramento River Delta and San Francisco Bay, and have been observed in estuaries of the Eel, Klamath, and Rogue rivers. Juveniles are believed to spend one to three years in rivers or estuaries, before making an initial coastal migration. Allen and Cech (in press) found juvenile green sturgeon were not physiologically adapted to saltwater until about 1.5 years (1.5 kg, 75cm). Subadult green sturgeon, characterized as large juveniles prior to the initiation of spawning, enter the ocean and make long distance migrations along the coastal shelf. In the ocean, green sturgeon were found in a narrow and shallow depth distribution (primarily <100m) over the nearshore shelf off the Oregon Coast, and they appeared to actively occupy shallower habitats by night (Erickson and Hightower in press). Presumably this distribution and behavior is characteristic of green sturgeon throughout their marine range between Baja Mexico and the Bering Sea. These coastal migrations punctuated by estuarine occupancy are a distinct behavior of North American green sturgeon. Green sturgeon are frequently encountered in estuaries during the summer along the Oregon and Washington coasts. These subadults often remained at shallower depths (less than 10m) in the estuaries with no detectable preference for temperature, salinity, or dissolved oxygen (Kelly et al. in press). Green sturgeon were found in Willapa Bay, WA, when estuarine water temperatures exceeded coastal water temperatures by at least 2°C (Moser and Lindley in press).
Green sturgeon management
Managing rare species is difficult because tremendous uncertainty exists about their biology, population status, and the potential value of management alternatives. The rarity of green sturgeon globally and the potential risks associated with human activities, led to it being listed as a Species of Special Concern in Canada in 1987 (COSEWIC 2004). In 2001, various environmental organizations petitioned the U.S. government to list the species as threatened or endangered under the Endangered Species Act (EPIC et al. 2001). In response, the National Marine Fisheries Service (NMFS) initiated a status review (Adams et al. 2002) to evaluate the discreteness of the species, significance of threats to the species across its spatial distribution, and assess the risks to green sturgeon. This status review was further updated (Adams et al. 2005), because of a 2004 court ruling, to reconsider whether the geographic scope of threats encompassed significant portions of their range.
Historically, management of green sturgeon has been incidental to management for white sturgeon. A commercial sturgeon fishery developed during the 1860’s in the San Francisco Bay estuary, and caused a crash in the populations returning to the Bay. An initial closure of the fishery occurred in 1901, and other than a brief reopening from 1909 until 1917, California has prohibited all commercial fishing for white and green sturgeon (Kohlhorst 2001). The white sturgeon population, and presumably the green sturgeon population, responded favorably to these closures and a sturgeon sports fishery was opened in 1954. At this time, the California Department of Fish and Game (CDFG) began a long-term monitoring effort for both white and green sturgeon in the Sacramento River and Delta. Between 1954 and 2001, CDFG measured 643 green sturgeon during biennial white sturgeon monitoring trawl surveys. Over this period, white sturgeon increased in frequency, and it was presumed this was an indication of a rebound in the Sacramento white sturgeon population from the overfishing that occurred at the beginning of the 20th Century. However, California white sturgeon landings currently appear at a historic low since the reopening of sports fishing in 1954 (M. Donnellan, CDFG, personal communication), and presumably green sturgeon show similar trends. In 2007, the California Fish and Game Commission adopted new regulations that made the landing or possession of green sturgeon illegal.
Conservation Genetics, a tool for precautionary management
Identification of threats impacting green sturgeon is critical for developing management alternatives that augment the life history strategies of green sturgeon to avoid further population declines, yet knowledge of the population biology of green sturgeon is limited. The genetic methods described in Chapters 2, 3, and 4 provide information and methods for managers that constitute a foundation upon which to integrate their management strategies for green sturgeon. Management should be evaluated on a case-by-case basis (Reisenbichler et al. 2003) and uncertainties concerning specific recovery actions can be clarified with population genetic information. Genetic information about population structure and the distribution of individuals from each DPS at temporal and spatial scales relevant to management strategies can reduce uncertainty.
The identification and description of green sturgeon population structure and the utility of alternative approaches for mixed stock analysis permits an increasingly precautionary approach to understanding the impacts of fisheries on this species. Due to the restricted distribution of green sturgeon along the coast, this species is susceptible to bottom trawl fisheries along the continental shelf (Erickson and Hightower in press). Additional sampling of fisheries in Canadian and Alaskan waters would be useful for understanding the migration of each DPS into coastal marine waters. Additionally, the development of the genetic stock identification baseline allows managers to assess stock composition and adequately manage mixed stocks in estuaries where fish from the Southern DPS are found. Regular efforts aimed at characterizing spawning fish in each of the DPS’s reproductive stocks will be necessary to maintain the utility of this approach. Long-term, fisheries independent mixed stock analyses undertaken while green sturgeon aggregate in estuaries, where they are easily sampled, can be expected to detect changes in DPS relative abundances before it is too late to implement management changes, and thereby provide the basis for a precautionary management approach.
Conservation Genetics, a tool for population monitoring
Management of species, similar to green sturgeon, which exhibit strong year classes, long reproductive cycles, and whose annual recruitment may only be a fraction of the spawning stock, should aim to maintain an appropriate age-structure to the spawning stock (King and McFarlane 2003). A factor in the ESA listing of green sturgeon was a decline in the abundance of juvenile green sturgeon at the state and federal pump facilities in the Sacramento River Delta in the 1980s and 1990s (Adams et al 2003), which may indicate fewer potential adults being recruited into future older life history stages. Conservation and recovery planning require information about the number of adult green sturgeon breeding annually. This information is difficult to assess with green sturgeon due to their rarity. The lack of this information has hindered recovery planning and monitoring in other listed sturgeon species (i.e. Gulf sturgeon, Morrow et al. 1999). Genetic studies, coupled with biological and age data about extant individuals, can yield retrospective information about recruitment variability and pattern, as well as stock-recruitment relationship. Genetic methods, similar to those in Chapter 4, promise to yield information that can guide ranking fine- and coarse-scale physical and biological threats to green sturgeon for managers to consider when assessing the viability of a green sturgeon populations and the habitat required for persistence at the riverscape.
Green sturgeon year class strength is presumably determined in the first few months of life and hydrological conditions have been found to be determinants in lake sturgeon (Nilo et al. 1997) and white sturgeon (Kolhorst et al. 1991). Thus, the earliest stages of sturgeon life history, particularly at the onset of exogenous feeding, have been called the “critical age” because of its relevance to successful recruitment classes into the adult population (Hardy and Litvak 2004). Studies to assess the intensity and periodicity of fry recruitment and the survival and state transition rates among stages of this “critical age” are necessary. Biological monitoring of green sturgeon eggs, larvae, and fry at the riverscape scale can estimate the reproduction occurring in discrete freshwater habitats to establish indices of abundance. Genetic “capture-recapture” studies, coupled with these studies, may yield estimates of the abundance of reproducing fish relative to fry recruitment and the relative survival rates between early life history stages. The presence and absence of specific kin groups in green sturgeon egg, larval, and fry collections, together with spatial and temporal information, can be used to evaluate the relative survival rates between these early life history stages.
Genetic data evaluated at the riverscape scale have tremendous promise to understand the implications of green sturgeon life history strategy on population structuring and demographics. The synergy of genetic and field methods can provide the necessary information for assessing the relative distribution of juvenile and breeding green sturgeon in freshwater habitats. Also, the coupling of molecular and field data may reveal insight into differential behavior of distinct population segments, including the periodicity of their movements and site fidelity, which cannot be otherwise appreciated given the long-lived, slow maturing, complex life history of these fish.
Recent work products relating to these studies
Israel,
Joshua. Ph.D. Dissertation: Conservation Genetics of North American Green
Sturgeon: Advances for Precautionary Management and Population Monitoring.
Chapter 1. Applications for
conservation genetics in the management and recovery of North American green
sturgeon. [introduction]
Chapter 2. Geographic patterns of genetic differentiation among collections of green sturgeon. [abstract]
Chapter 3. Stock complexity in North American green sturgeon: the utility of polysomic markers in mixed stock fishery analysis. [abstract]
Chapter 4. A ‘capture-recapture’ framework for estimating spawner abundance using relatedness among green sturgeon fry. [abstract]
Israel, J.A., M. Blumberg, J. Cordes and B. May. 2004. “Geographic patterns of genetic differentiation among western U.S. collections of North American green sturgeon (Acipenser medirostris).” North American Journal of Fisheries Management 24: 922-931.
· Israel, J.A. and B. May. 2007. “Mixed stock analysis of green sturgeon from Washington state coastal aggregations ” Report to Washington Department of Fish and Wildlife. 22p.
Israel, J.A. 2007 “Update on Conservation Genetics in Green Sturgeon Management” Presentation to Upper Sacramento River Monitoring Project Work Team Meeting, Red Bluff CA.
Israel, J.A. and B.P. May. 2007. “Regulation and Conservation: Insight on the Southern green sturgeon DPS from Mixed Stock Analysis.” Presentation to Interagency Ecological Pogram, Monterey, CA.
