Anadromous Adults Research Articles

Distribution and straying of minijack Chinook Salmon released from a captive broodstock hatchery program

AbstractObjectiveProduction of Chinook Salmon Oncorhynchus tshawytscha in hatcheries can unintentionally produce large numbers of age‐1 males, termed "minijacks," which pose ecological and genetic risks to target and nontarget populations. We evaluated the postrelease distribution of minijacks produced in a hatchery captive broodstock program targeting the White River in the Columbia River basin between 2010 and 2015.MethodsFish were passive integrated transponder (PIT)‐tagged in the hatchery (n = 218,555), and databases were searched to determine movement behavior and final detections on fixed PIT tag antenna arrays during the year in which they were released.ResultTwo main movement behaviors were detected: (1) residuals, which moved solely within the subbasin of release; and (2) migrants, which moved downstream into the Columbia River and then reascended the Columbia River in the year of release. Minijacks that reascended fish ladders in the Columbia River were most often detected at Rock Island and Bonneville dams, the nearest and furthest detection locations downstream of the Wenatchee River. Minijacks were last detected in all locations where spring Chinook Salmon spawn in the Wenatchee River subbasin (seven tributaries and one main‐stem area) and also in the Entiat River (an adjacent watershed); minijacks in eight of the nine locations were considered strays. Estimates of minijacks that strayed outside of the White River were between 61% and 100% annually and were influenced by release location. Minijacks were also more abundant than males of all older ages in some of the tributaries during some years. In addition, they were detected in these tributaries during periods when anadromous adults migrate into spawning areas and when spring Chinook Salmon spawn.ConclusionThe large amount of minijack production and the spatial and temporal overlap could pose genetic and ecological risks to both target and nontarget populations and particularly high straying poses risks to the maintenance of between‐population genetic variability.

Migratory behavior and maternal origin of anadromous brown trout in the Baltic Sea

In the Baltic Sea, brown trout have been shown to make extensive use of the marine ecosystem; however, little is known regarding their movements between freshwater and marine environments or the interactions between individuals at different life history stages within a population. First, we analyzed the otolith structure and chemistry of hatchery origin (n = 26) anadromous brown trout with known life history and maternal origin to evaluate the efficacy of otolith microchemistry to distinguish between freshwater habitat in northern Sweden and marine rearing in the northern Baltic Sea. We then described the maternal origin and migration patterns of wild anadromous brown trout (n = 59) originating from the Ume and Vindel River catchment in Northern Sweden. Otolith microchemistry revealed that the majority (73%) of fish made 3 or more (up to 5) migrations to the marine environment prior to capture, presumably to feed. We observed a high degree of life history diversity, where trout first migrated to sea from age-1 to age-4 and either migrated back to freshwater once each year (presumably to spawn) or spent more than 1 yr in the marine environment before returning to freshwater. While 42% of the wild anadromous trout were judged to be the progeny of a resident mother, sex ratio, age, and inter-habitat migrations were similar for resident and anadromous progeny, highlighting the role of resident life histories in producing anadromous adults. Results reported here provide managers with new information to support the protection and enhancement of brown trout populations in places where they have declined.

Anadromy efficacy of native kokanee in Alturas Lake, Idaho

Eaton KR, Tardy KA. 2022. Anadromy efficacy of native kokanee in Alturas Lake, Idaho. Lake Reserv Manage. XX:XX–XX. Partial migration is a complex process that can have profound impacts on ecosystems and populations. Oncorhynchus nerka ecotypes in the Sawtooth Valley include migratory and resident populations, with each exhibiting partial migration. Kokanee can exhibit anadromous behavior and therefore are valuable for O. nerka recovery. In the Sawtooth Valley, Alturas Lake supports a native kokanee population for which the ability to produce outmigrants could influence conservation decisions. In this study, we used contemporary genetic tools to identify the life history origin of Alturas Lake O. nerka outmigrants. Additionally we use population and survival estimates to determine the extent and success of any present kokanee migration. We found that in Alturas Lake, all juvenile outmigrants are progeny of native kokanee. We also found that increased population abundance is related to a higher number of outmigrants. Furthermore, juvenile survival estimates of Alturas kokanee outmigrants were similar to juvenile Redfish Lake sockeye salmon survival estimates. These similar survival estimates and return of anadromous kokanee adults throughout program history indicate that the Alturas Lake kokanee population is successful in exhibiting anadromous behavior. While kokanee are not a focus for O. nerka recovery, this study shows the importance of partial migration in a native kokanee population in preserving the anadromous life history strategy. Our results highlight that in locations with no sockeye salmon population, like Alturas Lake, native kokanee populations are vital to O. nerka recovery and should be monitored and protected accordingly. Supplemental data for this article is available online at https://doi.org/10.1080/10402381.2022.2026541.

Long-term monitoring of a brown trout (Salmo trutta) population reveals kin-associated migration patterns and contributions by resident trout to the anadromous run

BackgroundIn species showing partial migration, as is the case for many salmonid fishes, it is important to assess how anthropogenic pressure experienced by migrating individuals affects the total population. We focused on brown trout (Salmo trutta) from the Guddal River in the Norwegian Hardanger Fjord system, which encompasses both resident and anadromous individuals. Aquaculture has led to increased anthropogenic pressure on brown trout during the marine phase in this region. Fish traps in the Guddal River allow for sampling all ascending anadromous spawners and descending smolts. We analyzed microsatellite DNA markers from all individuals ascending in 2006–2016, along with all emigrating smolts in 2017. We investigated (1) if there was evidence for declines in census numbers and effective population size during that period, (2) if there was association between kinship and migration timing in smolts and anadromous adults, and (3) to what extent resident trout were parents of outmigrating smolts.ResultsCensus counts of anadromous spawners showed no evidence for a decline from 2006 to 2016, but were lower than in 2000–2005. Estimates of effective population size also showed no trends of declines during the study period. Sibship reconstruction of the 2017 smolt run showed significant association between kinship and migration timing, and a similar association was indicated in anadromous spawners. Parentage assignment of 2017 smolts with ascending anadromous trout as candidate parents, and assuming that unknown parents represented resident trout, showed that 70% of smolts had at least one resident parent and 24% had two resident parents.ConclusionsThe results bear evidence of a population that after an initial decline has stabilized at a lower number of anadromous spawners. The significant association between kinship and migration timing in smolts suggests that specific episodes of elevated mortality in the sea could disproportionally affect some families and reduce overall effective population size. Finally, the results based on parentage assignment demonstrate a strong buffering effect of resident trout in case of elevated marine mortality affecting anadromous trout, but also highlight that increased mortality of anadromous trout, most of which are females, may lower overall production in the system.

Stray Rates of Natural‐Origin Chinook Salmon and Steelhead in the Upper Columbia River Watershed

AbstractDespite the importance of straying in understanding the ecology of Pacific salmon Oncorhynchus spp. and steelhead O. mykiss, most of what is known about salmon and steelhead straying comes from tagged hatchery fish. We provide estimates of donor straying by natural‐origin spring, summer, and fall Chinook Salmon O. tshawytscha and summer steelhead at three spatial scales in the upper Columbia River watershed by using PIT tags. In total, 823,770 natural‐origin Chinook Salmon and steelhead were PIT‐tagged as juveniles in the Wenatchee, Entiat, Methow, and Okanogan River subbasins and tributaries and the upper Columbia River between 2002 and 2017. Anadromous adults with PIT tags (n = 2,611) were detected at a variety of antenna arrays in the Columbia River basin between 2004 and 2018. Mean donor stray rates of each population were less than 1% at the basin scale (range = 0.0–0.7%), less than 10% at the subbasin scale (range = 0.0–9.8%), and less than 15% at the tributary scale (range = 0.0–14.3%). Many of the populations (11 of 28) that were evaluated across all spatial scales did not have any strays detected, and the mean of means for both species’ stray rates at all spatial scales was generally less than 5% (range = 0.2–4.0%). Chinook Salmon and steelhead strayed at similar rates when originating from the same subbasins and tributaries. Most straying occurred in an upstream direction at the subbasin (84%) and tributary (94%) scales. Variation in stray rates was most consistently associated with spatial scale and location and was less than 15% for both species at all spatial scales.

Age at Release, Size, and Maturation Status Influence Residualism in Hatchery Steelhead

AbstractSteelhead Oncorhynchus mykiss that fail to emigrate seaward after release from hatcheries, commonly referred to as “residuals,” can have negative impacts on natural populations ranging from competition and predation to interbreeding with returning anadromous adults. We investigated how age at release, size, and maturation status influenced the rate of residual production in hatchery summer‐run steelhead released from the Winthrop National Fish Hatchery (Methow River, Washington) between 2010 and 2015. Migration data from 21,598 individuals implanted with PIT tags identified 1,783 residual steelhead expressing two distinct phenotypes: immature male and female parr; and precociously mature males. We found that age at release significantly affected the predominant residual phenotype. Age‐1 steelhead residuals (S1 rearing strategy) were dominated by smaller parr of both sexes (fish < 146 mm FL), while age‐2 residuals (S2 rearing strategy) were dominated by mature males, although both phenotypes were present in both S1 and S2 residual groups. Collections of residual steelhead in the Methow River indicated that parr phenotype residuals grew as well as natural‐origin juvenile O. mykiss, suggesting potential competition for food resources and habitat. Detections of PIT tags within the Methow River basin indicated that precocious male residuals may overlap both spatially and temporally with previously documented spawning anadromous adults, posing a potential genetic management risk. Both residual phenotypes had poor overwinter survival, and only 1 of the 1,783 residual fish eventually returned to the Methow River as an anadromous adult. We conclude that the ecological and genetic consequences of residual steelhead far outweigh their potential contribution to anadromous production, and measures should be taken to reduce their production by changing hatchery rearing practices.

Adult Atlantic salmon have a new freshwater predator.

The Atlantic salmon (Salmo salar) is one of the world’s most emblematic freshwater fish. Despite conservation and rehabilitation plans, populations of this species are dramatically declining due to human impacts such as habitat fragmentation, overfishing and water pollution. Owing to their large body size, anadromous adults were historically invulnerable to fish predation during their spawning period migration. This invulnerability has disappeared in Western Europe with the introduction of a new freshwater predator, the European catfish (Silurus glanis). Here we report how adults of Atlantic salmon are predated in the fishway of a large river of SW France, where the delayed and narrow passage created by the structure increases the probability of predator-prey encounter. We assessed predation risk by monitoring salmon and catfish in one fishway of the River Garonne, using video fish-counting from 1993 to 2016. We analysed the predation strategy of catfish using observations made with acoustic camera and RFID telemetry in 2016. Our results demonstrate a high predation rate (35%—14/39 ind.) on salmon inside the fishway during the 2016 spawning period migration. Our results suggest that a few specialized catfish individuals adapted their hunting behaviour to such prey, including their presence synchronized with that of salmon (i.e, more occurrences by the end of the day). Such results suggest that the spread of European catfish will potentially impact migration of anadromous species through anthropized systems.

The Entrainment and Screening of Returning and Postspawning Adult Salmonids at Irrigation Canals of the Umatilla River, Oregon

Abstract Anadromous salmonids can be vulnerable to entrainment at diversion intake structures on streams, effectively trapping fish in irrigation canals and removing them from a population. Currently little is known about how the differences in timing and direction of movement among adult salmonids contribute to their risk of entrainment and how successful they are at escaping irrigation canals. Potential routes of escape include passing against water currents and through the headgate of an irrigation canal intake or by navigating through screen and bypass infrastructure primarily designed to return juvenile fish to a stream. In this study, passive integrated transponders (PIT tags) were used to track the movement of adult Chinook Salmon Oncorhynchus tshawytscha (n = 573), Coho Salmon Oncorhynchus kisutch (n = 39), and anadromous Rainbow Trout Oncorhynchus mykiss (steelhead, n = 853) as they entered areas of the Umatilla River basin (Oregon) with irrigation canals and as they attempted to escape irrigation canals after entrainment. Although adult steelhead and spring Chinook Salmon often encountered diversions at similar times, the vast majority of entrained adults were steelhead (94%). Between 2% and 8% of adult steelhead observed entering the area were entrained. The entrainment of steelhead was strongly associated with downstream movements and Umatilla River discharge below 40 m3/s. Many downstream-moving steelhead were postspawning fish (kelts). As a result, vulnerability of anadromous adults to entrainment differed by species due to the direction of their movements and how these movements coincide with canal operations and river flows. It is unlikely that the screened irrigation canals acted as an ecological sink; the majority of adult salmonids approached the screen and bypass infrastructure (≥88%) and later river detection confirmed that many had used that infrastructure to return to the river (≥47%). However, half of steelhead appeared to experience bypass delays at fish screens. Adult steelhead that approached the canal headgate after becoming trapped in the canal did not successfully return to the Umatilla River using this route. Unscreened irrigation canals elsewhere may disproportionally trap downstream-moving steelhead, like postspawning kelts, due to their propensity for entrainment and their difficulties escaping through the water intakes of irrigation canals. In streams with anadromous salmonids, fish screen and bypass infrastructure primarily designed to eliminate the permanent entrainment of juvenile fish can also prevent the removal of adult fish that may reproductively contribute to the population.

The Effects of a Prolonged Drought on Southern Steelhead Trout (Oncorhynchus mykiss) in a Coastal Creek, Los Angeles, California

Long-term lifecycle monitoring of federally endangered southern steelhead trout (Oncorhynchus mykiss) in Topanga Creek provides a unique opportunity to examine the health and abundance of a steelhead population before (2008--2011) and during (2012--2016) a prolonged drought. We found that the five-year drought resulted in a substantial and significant decline in available wetted habitat suitable for rearing and upstream migratory access for anadromous adults. The response of the steelhead population has been a significant reduction in anadromous spawning, distribution of rearing, and abundance of all life stages of anadromous and resident steelhead. After five years of drought a population that exceeded 325 individuals in 2008, now numbers fewer than 50 fish, and appears to be at extremely high risk of extirpation. Acknowledging the possibility of increased drought regionally and globally, the need to bolster southern steelhead resiliency to additional disturbance is paramount.

Demography of sea lamprey (Petromyzon marinus) ammocoete populations in relation to potential spawning‐migration obstructions

Abstract Recent advances in the understanding of lamprey migrations have led to concerns over the impacts of obstructions on the demography of many species. This study investigated sea lamprey (Petromyzon marinus) larvae (ammocoetes) in two adjacent but contrasting rivers, both designated Special Areas of Conservation under the EC Habitats Directive (92/43/EEC), one (the River Wye) with a small number of potential migration obstructions in its upper reaches and one (the River Usk) with obstacles along its course. The geographical distributions, densities and age structures of the ammocoete populations were examined in relation to the locations of potential obstructions to the spawning migrations of anadromous adults. A minimum of three age classes was recorded as far as 200 km upstream of the mouth of the River Wye (93% of the length of the mainstem), demonstrating that adults regularly migrate to the upper reaches of the catchment (downstream of a natural waterfall). By contrast, sea lamprey ammocoetes appeared to be absent (in suitable habitat) from 20 km (17%) of the River Usk, and there was a reduction in density, prevalence and the number of age classes upstream of two putative spawning‐migration obstructions. This study highlights some of the potential impacts of habitat fragmentation by obstructions on the spawning migrations of anadromous species, as inferred from ammocoete demography. When used in combination to compare contiguous reaches, ammocoete densities, prevalence and age structure may be a useful indicator of which structures are likely to be important migration obstructions, and where further studies or mitigation efforts should be focused. It is likely that passage past some obstructions is enhanced if high river levels occur during the spawning migration, but there is a need to facilitate passage during all conditions, to improve access to under‐exploited spawning and nursery areas.

The Genetic Relationship between Anadromous and Resident Oncorhynchus mykiss at a Putative Barrier with Implications for Habitat Improvement

AbstractBig Bear Creek in the Potlatch River system, Idaho, contains an Endangered Species Act‐listed wild population of steelhead Oncorhynchus mykiss (anadromous Rainbow Trout) that is the focus of extensive habitat restoration actions intended to increase population abundance. Both anadromous and resident O. mykiss populations occur in the Big Bear Creek drainage; however, anadromous individuals are known to spawn and rear only in the lower drainage, whereas putative resident fish occur in the headwaters. Big Bear Falls is a potential upstream migration barrier that is located between the two populations. Oncorhynchus mykiss of unknown origin are present within 1 km above the falls. We used analyses of genetic diversity, structure, and sibship reconstruction to determine whether Big Bear Falls limited the movement of steelhead to headwater areas. Known resident O. mykiss were sampled in headwater areas, known anadromous adults were sampled at a weir in the lower drainage, and juveniles of unknown life history were collected from areas below and above the falls. Allele frequency data indicated that anadromous and headwater resident populations were highly differentiated and that exchange of genetic material between populations was limited. However, juvenile O. mykiss in the above‐waterfall collection were found to be the offspring or recent descendants of steelhead that successfully navigated above Big Bear Falls, demonstrating that the falls is not a complete barrier. We also identified evidence of limited downstream gene flow, suggesting that resident fish contributed genetic material to the downstream anadromous population. This study documented the successful passage of adult steelhead above Big Bear Falls and the downstream movement of resident fish from the headwaters. However, uncertainties still exist regarding the annual variability in passage and the habitat limitations that impact O. mykiss utilization of areas immediately above the falls.Received March 14, 2015; accepted October 27, 2015

Eggs from anadromous adults provide marine-derived nutrients to Atlantic salmon and brown trout parr in late autumn – observations from a Swedish coastal stream

In this paper we demonstrate that eggs from anadromous salmonines can constitute a large proportion of the dietary intake of individual juvenile Atlantic salmon Salmo salar and brown trout Salmo trutta during the spawning period in late autumn. The majority of fish older than 1 year residing on a spawning ground were found to have ingested eggs from spawning salmonines (Salmo sp.). Young-of-the-year brown trout were also able to consume eggs, at least down to a minimum fork length of 68 mm. The smallest Atlantic salmon found to have consumed eggs had a fork length of 79 mm. Larger fish were more likely to consume eggs, and consumed more eggs, than smaller individuals. The eggs of anadromous salmonines provide a rich source of marine-derived nutrients to the freshwater residing juveniles at the onset of winter. Our study highlights that these eggs may constitute an important energy input for juvenile salmonines in European anadromous populations, and could possibly influence winter survival rates and subsequent smoltification in the following spring.

Puny males punch above their weight to preserve genetic diversity in a declining Atlantic salmon population

Many salmonid fish populations have anadromous (i.e. migratory) and nonanadromous individuals co-existing in sympatry. The nonanadromous individuals, frequently males, mature at a much smaller size in freshwater without undergoing marine migrations and often successfully fertilize many eggs laid by anadromous females. Because these small males do not recruit to fisheries, they are often not regarded in high esteem by fishers. In this issue of Molecular Ecology, Johnstone et al. (2013) demonstrate that by substantially contributing to reproduction, such males help maintain genetic diversity in a declining population of Atlantic salmon (Salmo salar). Their results show that estimates of effective population size (Ne), obtained by counting the number of anadromous adults returning from sea and correcting for unequal sex ratios, are lower than estimates generated from genetic markers. Many mechanisms are expected to reduce Ne below the adult census population size (N); the opposite pattern of Ne > N observed by Johnstone et al. (2013) is difficult to explain unless the reproductive effort of nonanadromous males is accounted for. The results have important implications for the conservation of small populations and highlight the challenges of relating Ne to N in organisms with complex life histories.

Relationship between metabolism, sex and reproductive tactics in young Atlantic salmon ( Salmo salar L.)

Atlantic salmon can differ markedly in their growth and in the timing of reproductive maturation, leading to the dramatic contrast between the large anadromous adults and the diminutive mature male parr. This study examined the growth rates, anatomical and physiological characteristics of parr during the adoption of their discrete life histories to ascertain whether these properties can explain tactic choice. To minimise the impact of habitat differences upon these attributes, salmon were reared in the laboratory until 1.5 years of age, when the “decisions” to undergo smoltification or to mature as parr had been taken. At 1.5 years, both males and females showed bimodal size-frequency distributions. Neither the population of origin nor the paternal reproductive tactic influenced the “decision” to mature or the growth trajectories. Growth rate (% mass day − 1 during their final 10 months) and the % male and female offspring in the upper modal group were strongly correlated and varied markedly among families. Mean growth rate per family was negatively correlated with mean metabolic rate per family at emergence. Growth rate decreased as a function of parr size in January and the growth rates of upper modal fish were displaced upwards relative to those of lower modal fish. Most males in the smaller size mode matured, whereas all other fish began smoltification. Mature male parr did not differ from similarly sized female pre-smolt in routine metabolic rate, but these smaller fish had higher metabolic rates than larger male and female pre-smolts. However, mature parr differed markedly from similarly sized females and from larger male and female pre-smolts in possessing higher oxidative and lower glycolytic capacities in muscle. Overall, these data are consistent with the interpretation that growth rates dictate the distribution of parr between upper and lower modal groups. Individuals from faster growing families would be more likely to pass the threshold for smoltification and to accelerate growth, whereas those from slower growing families would remain in the lower mode. The use of metabolic capacities, e.g. metabolic rate, was linked with modal group, whereas muscle oxidative capacity was linked with male maturity. Mean family metabolic rate at emergence was negatively linked with mean growth during the subsequent year, suggesting that metabolic efficiency facilitates growth and eventually smoltification.

Sperm competition between alternative reproductive tactics of the Atlantic salmon in vitro

The maintenance of brood stock in appropriate conditions is an important requirement for the production of high quality offspring. In this study, we investigated fertility of the two life history forms of Atlantic salmon males, precocious parr, brought up in breeding tanks in the hatchery and anadromous, migratory sea-ranched males, caught when returning to the home river. The sperm quality was assessed by experiments between equal amount of sperm from one adult and one parr male in competition to fertilize eggs of a single female. The paternity was determined by a microsatellite analysis. Parr males achieved greater reproductive success than anadromous males under competition, and anadromous adults had greater fertility in controls as compared to the sperm competition situation. In total, parr males achieved 3.6 times greater fertilization success than anadromous males. Sperm ATP content contributed significantly to male fertility. Our results provide evidence that ejaculates of precociously mature Atlantic salmon parr are of increased quality as an adaptation to high sperm competition intensity due to better maintenance in the fish farm than in the wild.

Examining the Conflict between Smolting and Precocious Male Maturation in Spring (Stream‐Type) Chinook Salmon

AbstractPrecocious male maturation is a natural life history strategy for spring Chinook salmon Oncorhynchus tshawytscha. During spawning, precocious males employ a “sneaker” strategy to fertilize eggs in competition with full‐size anadromous adults. Hatchery rearing practices may increase the incidence of this phenotype beyond its natural levels. Previous research reported high rates (>40%) of precocious male maturation at age 2 (minijacks) in the Yakima River spring Chinook salmon supplementation program in Washington State. Minijack rates in wild populations are believed to be less than 5%. We compiled seasonal profiles for size, condition factor (K), gill Na+,K+‐ATPase activity, whole‐body lipid levels, plasma 11‐ketotestosterone (11‐KT), insulin‐like growth factor‐I (IGF‐I), and thyroxine (T4) in minijacks and immature smolts in the hatchery and during out‐migration. In the hatchery, minijacks were larger and had higher K, whole‐body lipid, plasma 11‐KT, and IGF‐I levels than smolts. Plasma T4 and gill Na+,K+‐ATPase activity increased in minijacks in spring, but the levels were slightly lower than those of smolts. Most minijacks are thought to remain resident in headwater streams throughout the summer in preparation for autumn spawning. A subset of these minijacks migrate hundreds of kilometers toward the ocean in the spring, only to reverse course later in the summer in an effort to return to their natal spawning grounds. These migrating minijacks had elevated plasma 11‐KT, IGF‐I, and T4 levels and gill Na+,K+‐ATPase activity. It is generally thought that smoltification and reproductive maturation are mutually exclusive life history events in salmonid fishes. This investigation examined the physiology of a unique phenotype in which smoltification and downstream migration appear to occur in fish that have already initiated the maturation process. These results suggest that hatchery programs with high minijack rates may produce significant numbers of fish that are maladapted for either smoltification or competing on the spawning grounds, and it is likely that they die in the freshwater environment before contributing to subsequent generations.

Die Off and Current Status of Southern Steelhead Trout (Oncorhynchus mykiss) in Malibu Creek, Los Angeles County, USA

A die-off of native and exotic fish and invertebrate species, including the endangered southern steelhead trout (Oncorhynchus mykiss) was observed in Malibu Creek, Los Angeles County, during the summer and fall of 2006. Death was preceded by a period of illness during which trout in particular exhibited a noticeable yellow coloration. Physical, chemical and biological variables, including temperature, dissolved oxygen, a variety of chemical contaminants, presence of toxin producing algae, and direct pathology were examined but results remain inconclusive. The first day of a 12-day high temperature event occurred on the same date yellow trout were first observed. This sustained event is different from shorter term temperature spikes recorded in other years. Recovery monitoring documented re-colonization by all exotic fish species and crayfish, but limited numbers of southern steelhead trout in 2007. Surveys in summer 2008 documented a record number of anadromous adults (five silvery fish over 50 cm total length) and young of the year (over 2,200 under 10 cm).

Influence of water chemistry and migratory distance on ability to distinguish progeny of sympatric resident and anadromous rainbow trout (Oncorhynchus mykiss)

Otolith Sr:Ca ratios near primordia (Sr:CaCore) have been used to distinguish progeny of resident and anadromous Oncorhynchus mykiss and to estimate rates of exchange between the two forms; however, the influences of confounding variables on Sr:CaCore have not been quantified. We analyzed Sr:CaCore in juvenile O. mykiss produced at 13 California hatcheries that spawn primarily resident or anadromous broodstock. Mean Sr:CaCore of progeny of resident females increased with increasing Sr:Ca ratio of the stream (Sr:CaWater) in which the mother spawned (r2 = 0.71). Mean Sr:CaCore of progeny of anadromous females averaged 1.0 × 10–3 higher, also increased with Sr:CaWater, and decreased with increasing migratory difficulty (distance × elevation) of the mother (r2 = 0.96). Model results predict that discrimination of sympatric progeny is equally good among streams where Sr:CaWater is less than 5 mmol·mol–1, but limited at higher Sr:CaWater or when anadromous females return to freshwater 6 months or more before spawning (e.g., summer steelhead). The models also provide an alternative method of interpreting Sr:CaCore data that can improve discrimination between sympatric progeny. Analysis of adults from one stream and eight hatchery sites suggested that resident females made little or no contribution to populations of anadromous adults, but anadromous females contributed to populations of resident adults.

Increases in steelhead (Oncorhynchus mykiss) redd abundance resulting from two conservation hatchery strategies in the Hamma Hamma River, Washington

Conservation hatcheries for anadromous salmonids that aim to increase production and minimizing genetic, ecological, and demographic risks have not been experimentally tested for their ability to increase number of adults spawning in the natural environment. The conservation hatchery program for steelhead (i.e., sea-run rainbow trout, Oncorhynchus mykiss) evaluated in this study caused an increase in the number of redds in the supplemented Hamma Hamma River compared with the presupplementation period. Three control populations (nonsupplemented) either remained stable or declined over the same period. The increase in redds from hatchery-produced spawners did not reduce the redd production from natural-origin spawners. The strategy of rearing and releasing adult steelhead accounted for the greatest proportion of redd abundance increases. Environmentally induced differences in spawn timing between the adult release group and anadromous adults of hatchery and natural origin may explain why the adult release group and anadromous adults assortatively formed pairing combinations on the spawning grounds. Although captively reared adults produced the majority of redds in years they were released in substantial numbers, uncertainty regarding the relative reproductive success of this strategy suggests caution in recommending one strategy over the other. A demographic boost to the naturally spawning population was effected while managing to minimize negative ecological consequences.

A genetic evaluation of relatedness for broodstock management of captive, endangered Snake River sockeye salmon, Oncorhynchus nerka

The use of captive broodstocks is becoming more frequently employed as the number of species facing endangerment or extinction throughout the world increases. Efforts to rebuild the endangered Snake River sockeye salmon, Oncorhynchus nerka, population have been ongoing for over a decade, but the use of microsatellite data to develop inbreeding avoidance matrices is a more recent component to the program. This study used known genealogical relationships among sockeye salmon offspring to test four different pairwise relatedness estimators and a maximum-likelihood (M-L) relatedness estimator. The goal of this study was to develop a breeding strategy with these estimators that would minimize the loss of genetic diversity, minimize inbreeding, and determine how returning anadromous adults are incorporated into the broodstock along with full-term hatchery adults. Results of this study indicated that both the Mxy and RQG estimators had the lowest Type II error rates and the M-L and RR estimators had the lowest Type I error rates. An approach that utilizes a combination of estimators may provide the most valuable information for managers. We recommend that the M-L and RR methods be used to rank the genetic importance of returning adults and the Mxy or RQG estimators be used to determine which fish to pair for spawning. This approach provides for the best genetic management of this captive, endangered population and should be generally applicable to the genetic management of other endangered stocks with no pedigree.