Captive Breeding as a Component of Endangered Fish Recovery

Kristen D. Arkush, PhD

Captive breeding is becoming accepted as one component of species enhancement (Gipps 1991, Johnson and Jensen 1991; Olney et al. 1994). Just like programs for the black-footed ferret and California condor, captive breeding is one strategy in the fight against extinction of fish species at risk. Today, the U.S. Fish and Wildlife Service uses captive propagation to enhance populations of nearly 30% of the non-anadromous North American fish species listed under the federal Endangered Species Act (USFWS 1990, Johnson and Jensen 1991). Indeed, captive breeding may provide the only mechanism to prevent extirpation of a fish stock, especially before or during the early implementation of an environmental recovery program (Arkush and Siri 2001). Often, these programs are undertaken on an emergency basis to provide a stop-gap measure or “insurance” against genetic loss in an imperiled stock.

At the Bodega Marine Laboratory (BML), researchers and staff have been involved in captive breeding programs for endangered salmonid fish since 1992.

Figure 1. Winter-run Chinook salmon (Oncorhynchus tshawytscha) reared to adulthood in a captive broodstock program at Bodega Marine Laboratory.

From 1992-2004, we participated in a captive broodstock program for the Sacramento River Winter-Run Chinook salmon (WRCS). Since 1994, WRCS have been listed as endangered under the Endangered Species Act (59 Federal Register 440) due to a declining population trend (Figure 2).

Figure 2. Population abundance estimates for Sacramento River winter Chinook salmon from 1967-2003. Estimates were determined from counts made at the Red Bluff Diversion Dam, California.

In 1989, the US Fish and Wildlife Service began propagating WRCS by trapping returning adults and spawning them in captivity and subsequently releasing their progeny. This program was intended to supplement natural production. Concurrently, a captive broodstock program was initiated to provide a further measure of protection against extinction, with fish reared in captivity for their entire life span. BML was an active partner in this recovery effort, serving as a site for the captive broodstock program. Annual monitoring by the US Fish and Wildlife Service and the California Department of Fish and Game (CDFG) have shown that the number of WRCS returning to the upper Sacramento River have increased in recent years, with population abundance estimates of 8,120, 7,360, and 8,133 fish for the years 2001, 2002, and 2003, respectively. Given this upward trend, the US Fish and Wildlife Service, NOAA Fisheries, and the CDFG have recommended the withdrawal of captive rearing component of the draft winter-run recovery plan. Consequently, the WRCS captive broodstock program at BML was ended on December 31, 2004. The draft recovery plan for WRCS specifies delisting criteria that require a mean annual spawning abundance of 10,000 females and a cohort replacement rate greater than one over 13 consecutive years. While these levels have not yet been met, there has been a general trend toward increasing population size. Supplementation activities will continue for the near future to continue to boost the wild population, but the formal withdrawal from the captive broodstock component of the program is an encouraging step, and one indicator of “success” in the recovery of this endangered species.

More recently, we have begun participating in a restoration program for coho salmon of California’s Russian River in Sonoma County. The Central California Coast (CCC) Coho salmon ESU, or evolutionary significant unit, was listed as threatened under the Federal Endangered Species Act on October 31, 1996 by the National Marine Fisheries Service. Coho salmon was listed as endangered under the California Endangered Species Act in August of 2002. Goals of the Russian River Coho Salmon Captive Broodstock Program (RRCSCBP) include conservation of the genetic resources of Russian River fish populations, using captive propagation methods. In addition, the program is intended to provide opportunity for research on the effective use of artificial propagation (NOAA Fisheries 2004). In 2004, faculty and staff at BML began actively participating in this restoration effort. Initially, we provided advice on several aspects of broodstock management, including training in the use of ultrasonography to assess gender and maturation status in adult fish (Figures 3, 4) and methods of gamete cryopreservation. A more formal collaboration is now underway, with financial support from separate contracts with the Sonoma County Water Agency and the California Department of Fish and Game. A key component of this effort is to improve upon current rearing conditions to increase spawning success in captive coho salmon. At BML, we have begun initial studies to evaluate the effects of photoperiodic manipulation and water temperature on reproduction of captive broodstock. Other parameters can influence sexual maturation and spawning, including nutritional status of the adult broodstock, and the amount of time spent in both freshwater and seawater phases during rearing. We are uniquely positioned to address new husbandry or animal health issues as they arise, providing a responsive, research-based mechanism for adaptive management.

Figure 3. Below. Anatomic features of a maturing female Chinook salmon (Oncorhynchus tshawytscha) as seen in gross and ultrasonographic images of the same fish.

Figure 4. Below. Stages of sexual maturation in a female Chinook salmon (Oncorhynchus tshawytscha) as seen by ultrasonographic examination of the same fish over time.

The salmon rearing facilities at BML consist of two buildings containing various 4-foot, 6-foot, and 12-foot circular tanks and a hatchery system, a separate food preparation building, and specialized laboratories for conducting fish health diagnostics and research (Figure 5). High quality fresh water or saltwater (or mixed salinity water) can be delivered to the systems at controlled temperatures, using either single pass or recirculating flows. Life support systems may be alarmed for flow, temperature or salinity and monitored in real-time (data also recorded for archival purposes) using programmable logic computers and customized software. In addition to visual checks, all alarmed systems are monitored throughout the day via computer and can be accessed remotely by technical staff using their home computers. These systems are redundantly monitored by an external alarm company (Honeywell) for 24-hour surveillance.

Figure 5. Pathogen containment facility at Bodega Marine Laboratory.

Molecular Biotechnology Applications in Fishery Management

Molecular tools have been developed to enable salmonid run determination and gender identity. Many of these microsatellite markers were created and tested specifically to support the confirmation of winter-run Chinook salmon and to provide a means for discrimination of protected populations (Banks et al. 2000). Population genetic data are increasingly important in managing salmonid populations on the brink of extinction (Waples 1995). There is a need to identify protected stocks in mixed ocean harvests and in rivers and estuaries where dams or water diversions can harm out-migrating juveniles. Identification of broodstock in propagation programs is necessary to avoid admixture and hybridization among spawning runs. Finally, genetic markers are useful for confirming parentage and relatedness in hatchery-bred fish and for verifying models of hatchery impacts on genetic diversity of naturally spawning stocks (Hedrick et al. 1995, 2000a, 2000b).

The Impact of Infectious Diseases on Endangered Fish Propagation

Infectious diseases alone or in concert with adverse environmental conditions can largely determine the fitness and survival of fish populations. In the case of threatened or endangered stocks, populations may already be reduced and thus less genetically diverse, thereby increasing their vulnerability to disease. For example, diseases are viewed as one key factor in the unsuccessful efforts to restore coho runs to the Russian River in Northern California (personal communication Dr. Bill Cox, Statewide Fish Health Coordinator, CDFG). Host-parasite relationships should be evaluated and correlated to other monitored biologic components of ecosystem health. In the case of anadromous stocks that spend varying amounts of time in freshwater, estuarine, and nearshore marine environments, water quality parameters (e.g. flow and temperature) can have direct and negative influences on established fish host-parasite interactions. Further, restoration efforts that include artificial supplementation using either within-basin orout-of-basin stocks, risk the introduction of more virulent or even nonindigenous pathogens to the system.

During the winter-run Chinook captive broodstock program, we encountered pathogens common to salmonids such as the bacterial agents Renibacterium salmoninarum, Listonella (Vibrio) anguillarum, and Flexibacter maritimus. Infectious hematopoietic necrosis virus is established in three Sacramento River Chinook races, including Fall, late-Fall, and winter-run adults. Recent research at BML has demonstrated that adult Chinook salmon may contribute to the dissemination of this virus when they contract the disease as spawning adults (Arkush et al. 2004, Figure 6). BML researchers have also shown that a new and exotic protozoan parasite, Sphaerothecum destruens, formerly the “rosette agent” has caused morbidity and mortality in the winter-run Chinook salmon (Arkush et al. 1998, Arkush et al. 2003). A related parasite is gaining worldwide notoriety, having been implicated in the loss of European fish diversity (Gozlan et al. 2005). Molecular diagnostic tools have been developed to detect these and other fish pathogens, enabling improved broodstock management practices and providing methods to help protect our fisheries (Mendonca and Arkush 2004).

Figure 6. Bodega Marine Laboratory staff conducting fish health diagnostic testing.

Investigating the Molecular Basis of Disease Resistance in the Winter-Run Chinook Salmon

Among the major threats to endangered species are habitat alteration and destruction, overharvesting, and the biotic effects of introduced competitors and predators. In recent years, it has become widely recognized that endangered species may be also threatened by exposure to pathogens (see Lafferty and Gerber 2002), many of them exotic and novel to the endangered species. Disease resistance often has a significant genetic component. In particular, genes in the major histocompatibility complex (MHC) play an important role in pathogen resistance in vertebrates (Edwards and Hedrick 1998; Hedrick and Kim 2000). In endangered species, the level of genetic variation in the MHC, and other genes that may influence host resistance, may be lower because of past or present small population size, than more common species. Further, in the small populations of endangered species, there may also be a higher frequency of inbreeding, a factor that results in an increase in homozygosity for all loci. There is evidence that inbred animals within a population may have higher susceptibility to pathogens than outbred individuals (Coltman et al. 1999; Hedrick et al. 2001). Pathogens introduced from more common species, then, may result in final decline to extinction in an already imperiled species.

We have carried out the first major infectivity trial to examine differential genetic resistance in fish for pathogens (Arkush et al. 2002). We used captive-bred, endangered winter-run Chinook salmon to determine resistance to three pathogens: the bacterium, Listonella (Vibrio) anguillarum, infectious hematopoietic necrosis virus (IHNV), and Myxobolus cerebralis, the causative agent of whirling disease. We compared resistance to these three pathogens between inbred and outbred salmon and between siblings that were heterozygous or homozygous for a MHC class II gene. In two of these five different comparisons, we found significant genetic effects on disease resistance. First, MHC heterozygotes had a higher survival than MHC homozygotes when exposed to IHNV. Second, outbred fish had a higher resistance (or lower infection severity) than inbred fish when exposed to M. cerebralis . Overall, our study suggests that pathogen susceptibility in the winter-run Chinook salmon will increase if further genetic variation is lost in this endangered species.

References

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Arkush KD and Siri PA (2001). Exploring the role of captive broodstock programs in salmon restoration. Fish Bull. 179: 319-329.

Arkush KD, Giese AR, Mendonca HL, McBride AM, Marty GD, and Hedrick PW ( 2002). Resistance to three parasites in the endangered winter-run Chinook salmon (Oncorhynchus tshawytscha): effects of inbreeding and major histocompatibility genotypes. Can. J. Fish. Aquat. Sci. 59:966-975.

Arkush KD, Mendoza L, Adkison MA, and Hedrick RP (2003). Observations on the life stages of Sphaerothecum destruens n. g., n. sp., a mesomycetozoean fish pathogen formerly referred to as the rosette agent. Journal of Eukaryotic Microbiology 50(6): 430-438.

Arkush KD, Mendonca HL, McBride AM, and Hedrick RP (2004). Susceptibility of captive adult winter-run Chinook salmon Oncorhynchus tshawytscha to waterborne exposures with infectious hematopoietic necrosis virus (IHNV). Diseases of Aquatic Organisms 59:211-216.

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