Diel movements of out-migrating Chinook salmon (Oncorhynchus tshawytscha) and steelhead trout (Oncorhynchus mykiss) smolts in the Sacramento/San Joaquin watershed

We used ultrasonic telemetry to describe the movement patterns of late-fall run Chinook salmon (Oncorhynchus tshawytscha) and steelhead trout (O. mykiss) smolts during their entire emigration down California’s Sacramento River, through the San Francisco Bay Estuary and into the Pacific Ocean. Yearling hatchery smolts were tagged via intracoelomic surgical implantation with coded ultrasonic tags. They were then released at four upriver locations in the Sacramento River during the winters of 2007 through 2010. Late-fall run Chinook salmon smolts exhibited a nocturnal pattern of migration after release in the upper river. This is likely because individuals remain within a confined area during the day, while they become active at night and migrate downstream. The ratio between night and day detections of Chinook salmon smolts decreased with distance traveled downriver. There was a significant preference for nocturnal migration in every reach of the river except the Estuary. In contrast, steelhead smolts, which reside upriver longer following release, exhibited a less pronounced diel pattern during their entire migration. In the middle river, Delta, and Estuary, steelhead exhibited a significant preference for daytime travel. In the ocean Chinook salmon preferred to travel at night, yet steelhead were detected on the monitors equally during the night and day. These data show that closely related Oncorhynchus species, with the same ontogenetic pattern of out-migrating as yearlings, vary in migration tactic.     

Holding behavior of Chinook salmon (Oncorhynchus tshawytscha) and steelhead (O. mykiss) smolts, as influenced by habitat features of levee banks, in the highly modified lower Sacramento River, California

Using acoustic telemetry methods on large numbers of tagged fish, we studied how the holding behavior of Chinook salmon and steelhead smolts could be related to habitat features and spatial and temporal variables on a highly altered section of the Sacramento River. We viewed downstream migration as a process in which fish transition between moving and holding states, and used a binomial and negative binomial Generalized Linear Model to analyze two aspects of holding: 1) probability of holding, and 2) holding time. For Chinook salmon, the probability of holding increased as wood size and fine substrates increased; holding time increased as overhead shade increased. For steelhead, holding behavior was only weakly related to habitat variables, in contrast to the strong relationships with spatial and temporal variables. For both species, the probability of holding increased when distance from the release location decreased and instream flows decreased. We found support for three main findings: 1) spatial and temporal factors have considerably greater influence on Chinook salmon and steelhead smolt holding behavior than nearshore habitat features; 2) holding behaviors of Chinook salmon smolts are influenced more strongly by habitat features than steelhead smolts; and 3) incorporation of habitat features such as large woody material and overhead shade should be considered when conducting nearshore bank rehabilitation projects to increase cover from predators and provide velocity refuge, improving holding habitat during downstream migration.     

Interspecific habitat associations of juvenile salmonids in Lake Ontario tributaries: implications for Atlantic salmon restoration

Diel variation in habitat use of subyearling Chinook salmon (Oncorhynchus tshawytscha), subyearling coho salmon (O. kisutch), yearling steelhead (O. mykiss), and yearling Atlantic salmon (Salmo salar) was examined during the spring in two tributaries of Lake Ontario. A total of 1318 habitat observations were made on juvenile salmonids including 367 on steelhead, 351 on Chinook salmon, 333 on Atlantic salmon, and 261 on coho salmon. Steelhead exhibited the most diel variation in habitat use and Chinook the least. Juvenile salmonids were generally associated with more cover and larger substrate during the day in both streams. Interspecific differences in habitat use in both streams occurred with Atlantic salmon (fast velocities) and coho salmon (pools) using the least similar habitat. Chinook salmon and Atlantic salmon used similar habitat in both streams. These findings should help guide future management actions specific to habitat protection and restoration of Atlantic salmon in Lake Ontario tributaries.     

Oxygen consumption in unfertilized salmonid eggs: an indicator of egg quality?

A negative correlation between oxygen consumption and fertility was observed in both steelhead and chinook salmon eggs. However, this relationship was attributed to bacterial growth. Elimination of samples with bacterial growth resulted in no significant relationship between the rate of oxygen consumption (VO2) and fertility. VO2 of unfertilized eggs of both steelhead and chinook salmon was measured over a storage period of up to 24 days (d). Despite declines in fertility during storage, VO2 did not significantly change throughout storage. The average respiration rate for steelhead eggs was 3.4 nmol O2 per egg per h, and was 4.3 nmol O2 per egg per h for chinook salmon eggs. Treatment of chinook salmon eggs with uncouplers of mitochondrial respiration, 2,4-dinitrophenol (2,4-DNP) and carbonyl cyanide 4-trifluoro-methoxyphenylhydrazone (FCCP), resulted in an increase in VO2 to 12.9 and 11.5 nmol O2 per egg per h, respectively. Treatment with the putative uncoupler, clove oil, resulted in no change in VO2, while KCN, an inhibitor of oxidative phosphorylation, reduced oxygen consumption to zero. Copper caused an increase in oxygen consumption, even in the absence of eggs, suggesting a need for caution in interpreting changes in respiration rates as a result of metal exposure. Thus, unfertilized salmonid eggs demonstrated submaximal VO2, which was not correlated with fertility.     

Evaluating Stocking Efficacy in an Ecosystem Undergoing Oligotrophication

Oligotrophication has negatively affected fisheries production in many freshwater ecosystems and could conceivably reduce the efficacy of stockings used to enhance fisheries. In Lake Michigan, offshore oligotrophication has occurred since the 1970s, owing to reductions in total phosphorus (TP) inputs and nearshore sequestration of TP by nonindigenous dreissenid mussels. We evaluated simultaneous effects of stock enhancement and oligotrophication on salmonine species (Chinook salmon Oncorhynchus tshawytscha, lake trout Salvelinus namaycush, and steelhead O. mykiss) that support valuable recreational fisheries. We employed a novel application of an Ecopath with Ecosim model by conducting a full factorial simulation experiment. Our design included multiple levels of salmonine stocking, consumption by invasive quagga mussels (Dreissena bugensis), and TP that were informed by manager interests. Under all levels of TP and quagga mussel consumption, our results showed that stock enhancement could still increase salmonine biomass, but positive responses were stronger for lake trout and steelhead than Chinook salmon. Simulations showed that quagga mussel consumption has deleterious effects on pelagic-oriented prey fishes and Chinook salmon, which feed almost exclusively on the pelagic-oriented alewife (Alosa pseudoharengus). In summary, results from our simulation experiment suggested that lake trout and steelhead are better suited to the current ecosystem than Chinook salmon, and therefore, stock enhancement provides the highest gains for these two species. Furthermore, simulated biomass of all recreational salmonine species increased with increasing TP, indicating the need for managers to consider how potential future oligotrophication will limit the carrying capacity of salmonine biomass in Lake Michigan.     

Warming Ocean Conditions Relate to Increased Trophic Requirements of Threatened and Endangered Salmon

The trophic habits, size and condition of yearling Chinook salmon (Oncorhynchus tshawytscha) caught early in their marine residence were examined during 19 survey years (1981–1985; 1998–2011). Juvenile salmon consumed distinct highly piscivorous diets in cold and warm ocean regimes with major differences between ocean regimes driven by changes in consumption of juvenile rockfishes, followed by several other fish prey, adult euphausiids and decapod larvae. Notable, Chinook salmon consumed 30% more food in the warm versus cold ocean regime in both May and June. Additionally, there were about 30% fewer empty stomachs in the warm ocean regime in May, and 10% fewer in warm June periods. The total prey energy density consumed during the warmer ocean regime was also significantly higher than in cold. Chinook salmon had lower condition factor and were smaller in fork length during the warm ocean regime, and were longer and heavier for their size during the cold ocean regime. The significant increase in foraging during the warm ocean regime occurred concurrently with lower available prey biomass. Adult return rates of juvenile Chinook salmon that entered the ocean during a warm ocean regime were lower. Notably, our long term data set contradicts the long held assertion that juvenile salmon eat less in a warm ocean regime when low growth and survival is observed, and when available prey are reduced. Comparing diet changes between decades under variable ocean conditions may assist us in understanding the effects of projected warming ocean regimes on juvenile Chinook salmon and their survival in the ocean environment. Bioenergetically, the salmon appear to require more food resources during warm ocean regimes.     

Interactions between endangered wild and hatchery salmonids: can the pitfalls of artificial propagation be avoided in small coastal streams?

Hatchery and wild juvenile populations of steelhead Oncorhynchus mykiss and coho salmon Oncorhynchus kisutch , in a small coastal watershed in central California, were sampled throughout the year in a stream and at a hatchery. Both species grew faster in captivity than in the wild. Hatchery fish of both species had elevated gill Na⁺, K⁺‐ATPase activity, and thus were ready to enter sea water when planted during the wild fish migration. Downstream migrant trapping and stream surveys indicated that hatchery smolts went to sea soon after planting, consequently avoiding the effects of competition and predation that commonly occur when hatchery‐bred juveniles are released. Adult steelhead were also sampled throughout the watershed. The return of hatchery steelhead was highly synchronized with that of wild steelhead, indicating that hatchery propagation had no adverse effects on the timing of the run. A disproportionate number of hatchery steelhead returned to the tributary where the hatchery was located, despite being planted throughout the watershed. Hatchery steelhead did not differ in mean age or size from wild steelhead. Observations of spawning indicated that hatchery and wild steelhead interbreed. Competition for mates or spawning substratum was rarely observed between hatchery and wild steelhead. Many of the problems commonly associated with artificial propagation can be avoided in small coastal watersheds when wild broodstock are used and fish are released as smolts.     

Ephemeral floodplain habitats provide best growth conditions for juvenile Chinook salmon in a California river

We reared juvenile Chinook salmon for two consecutive flood seasons within various habitats of the Cosumnes River and its floodplain to compare fish growth in river and floodplain habitats. Fish were placed in enclosures during times when wild salmon would naturally be rearing in floodplain habitats. We found significant differences in growth rates between salmon reared in floodplain and river enclosures. Salmon reared in seasonally inundated habitats with annual terrestrial vegetation experienced higher growth rates than those reared in a perennial pond on the floodplain. Growth of fish in the non-tidal river upstream of the floodplain varied with flow in the river. When flows were high, there was little growth and high mortality, but when the flows were low and clear, the fish grew rapidly. Fish displayed very poor growth in tidally influenced river habitat below the floodplain, a habitat type to which juveniles are commonly displaced during high flow events due to a lack of channel complexity in the main-stem river. Overall, ephemeral floodplain habitats supported higher growth rates for juvenile Chinook salmon than more permanent habitats in either the floodplain or river. Variable responses in both growth and mortality, however, indicate the importance of providing habitat complexity for juvenile salmon in floodplain reaches of streams, so fish can find optimal places for rearing under different flow conditions.     

Variability in Migration Routes Influences Early Marine Survival of Juvenile Salmon Smolts

Variability in animal migratory behavior is expected to influence fitness, but few empirical examples demonstrating this relationship exist. The initial marine phase in the migration of juvenile salmon smolts has been identified as a potentially critical life history stage to overall population productivity, yet how fine-scale migration routes may influence survival are unknown. Large-scale acoustic telemetry studies have estimated survival rates of outmigrant Pacific salmon smolts through the Strait of Georgia (SOG) along the British Columbian coastline to the Pacific Ocean, but these data have not been used to identify and characterize fine-scale movements. Data collected on over 850 sockeye salmon (Oncorhynchus nerka) and steelhead (Oncorhynchus mykiss) smolts detected at an array in the Strait of Georgia in 2004–2008 and 2010–2013 were analyzed to characterize migration routes and link movements to subsequent survival at an array 250 km further along the marine migration pathway. Both species exhibited disproportionate use of the most eastern route in the Strait of Georgia (Malaspina Strait). While many smolts moved across the northern Strait of Georgia acoustic array with no indication of long-term milling or large-scale east-to-west movements, large proportions (20–40% of sockeye and 30–50% of steelhead) exhibited a different behavior, apparently moving in a westward or counterclockwise pattern. Variability in migratory behavior for both species was linked to subsequent survival through the Strait of Georgia. Survival for both species was influenced by initial east-to-west location, and sockeye were further influenced by migration timing and duration of time spent near the northern Strait of Georgia array. Westward movements result in a net transport of smolts from Malaspina Strait to the Strait of Georgia, particularly for steelhead. Counterclockwise movements may be due to the currents in this area during the time of outmigration, and the higher proportion of steelhead smolts exhibiting this counterclockwise behavior may reflect a greater exposure to wind-altered currents for the more surface-oriented steelhead. Our results provide an empirical example of how movements can affect migration survival, for which examples remain rare in movement ecology, confirming that variability in movements themselves are an important part of the migratory process.     

Functions of restored wetlands for juvenile salmon in an industrialized estuary

The Duwamish estuary is an industrialized waterway located in Seattle, WA, USA. Despite a history of habitat loss, naturally produced juvenile Chinook salmon use the estuary. In addition to experiencing degraded habitat in the estuary, wild salmon growth may be affected by competition with more than three million hatchery fish released yearly into the river. Restoring habitat to benefit salmon in the Duwamish River is a priority for trustees of public resources, and a number of wetland restoration sites have been created there. We tested the function of restored sites in the Duwamish estuary for juvenile Chinook salmon by comparing fish densities from enclosure nets or beach seines at three paired restored/un-restored sites and by applying environmental and diet data to a bioenergetics model. We also examined temporal and diet overlap of wild juvenile Chinook salmon with other salmon species and with hatchery-reared Chinook salmon using non-metric multidimensional scaling (NMDS). At a brackish upstream site with a relatively large opening to the river, we found higher densities of juvenile Chinook salmon at the restored site. NMDS results indicated that juvenile Chinook salmon fed on different taxa at the restored sites than at the reference sites. However, modeled growth was similar at restored and reference sites. Co-occurring juvenile chum and Chinook salmon fed differently, with chum eating smaller prey, and Chinook salmon eating larger prey. Co-occurring hatchery and wild juvenile Chinook salmon had similar diets, indicating that they may compete for prey. However, modeled growth was positive and did not differ between hatchery and wild fish, suggesting that food was not limiting. Bioenergetics models indicated that overall juvenile Chinook salmon growth potential at the brackish water site was consistently higher than at more saline sites. Our results suggest that restoration sites in the Duwamish estuary that have larger access openings and are located in brackish water may have increased function over other configurations.     

Spatial and trophic overlap of marked and unmarked Columbia River Basin spring Chinook salmon during early marine residence with implications for competition between hatchery and naturally produced fish

Ecological interactions between natural and hatchery juvenile salmon during their early marine residence, a time of high mortality, have received little attention. These interactions may negatively influence survival and hamper the ability of natural populations to recover. We examined the spatial distributions and size differences of both marked (hatchery) and unmarked (a high proportion of which are natural) juvenile Chinook salmon in the coastal waters of Oregon and Washington from May to June 1999–2009. We also explored potential trophic interactions and growth differences between unmarked and marked salmon. Overlap in spatial distribution between these groups was high, although catches of unmarked fish were low compared to those of marked hatchery salmon. Peak catches of hatchery fish occurred in May, while a prolonged migration of small unmarked salmon entered our study area toward the end of June. Hatchery salmon were consistently longer than unmarked Chinook salmon especially by June, but unmarked salmon had significantly greater body condition (based on length-weight residuals) for over half of the May sampling efforts. Both unmarked and marked fish ate similar types and amounts of prey for small (station) and large (month, year) scale comparisons, and feeding intensity and growth were not significantly different between the two groups. There were synchronous interannual fluctuations in catch, length, body condition, feeding intensity, and growth between unmarked and hatchery fish, suggesting that both groups were responding similarly to ocean conditions.     

Accumulation and clearance of orally administered erythromycin and its derivative, azithromycin, in juvenile fall chinook salmon Oncorhynchus tshawytscha

Fall Chinook salmon Oncorhynchus tshawytscha were fed practical diets medicated with azithromycin (30 mg kg(-1) fish for 14 d) or erythromycin (100 mg kg(-1) fish for 28 d) either 1, 2, or 3 times beginning 14 d after initiation of exogenous feeding (February) and ending at smoltification (June). Average tissue concentrations of azithromycin increased from 19.0 microg g(-1) in fry to 44.9 microg g(-1) in smolts, and persisted in the tissues > 76 d after treatment ceased. Tissue concentrations of erythromycin were comparatively low, ranging from 0.2 microg g(-1) in fry to 10.4 microg g(-1) in smolts. Erythromycin was not detectable 21 d post-treatment. Neither antibiotic caused histopathologically significant lesions in the trunk kidney or other organ tissues. The high tissue concentrations and prolonged retention of azithromycin in Chinook may be factors that increase the efficacy of the antibiotic against Renibacterium salmoninarum, compared with erythromycin, particularly in early life history stages before covertly infected fish show clinical signs of disease.     

Feeding of wild and hatchery reared Atlantic salmon (<Emphasis Type="Italic">Salmo salar</Emphasis> L.) smolts during downstream migration

In general, hatchery salmonid smolts experience higher mortality during migration than wild smolts, which is suggested to be due to domestication effects and that hatchery fish lack experience of the natural environment. However, possible differences in feeding during smolt migration between hatchery and wild smolts have rarely been addressed. We compared the number of feeding smolts and stomach fullness among wild Atlantic salmon smolts, hatchery-reared smolts released as 1-year-old parr, and hatchery-reared smolts released as 2-year-old smolts during their descent to sea in River Tornionjoki. In addition, estimations of prey selection among the smolt groups were conducted. A high proportion of wild smolts and smolts stocked as parr actively fed during the smolt migration. A lower proportion of smolts stocked as smolts was feeding and their stomach fullness were much reduced in comparison with the two other groups. The study also indicated that the feeding of migrating smolts is selective rather than opportunistic. In conclusion, this study suggests that stocked 2-year-old smolts may enter sea with an inferior foraging behaviour and it is a possibility that this may contribute to the observed low post-smolt survival in the Baltic Sea.     

Survival of migrating salmon smolts in large rivers with and without dams

The mortality of salmon smolts during their migration out of freshwater and into the ocean has been difficult to measure. In the Columbia River, which has an extensive network of hydroelectric dams, the decline in abundance of adult salmon returning from the ocean since the late 1970s has been ascribed in large measure to the presence of the dams, although the completion of the hydropower system occurred at the same time as large-scale shifts in ocean climate, as measured by climate indices such as the Pacific Decadal Oscillation. We measured the survival of salmon smolts during their migration to sea using elements of the large-scale acoustic telemetry system, the Pacific Ocean Shelf Tracking (POST) array. Survival measurements using acoustic tags were comparable to those obtained independently using the Passive Integrated Transponder (PIT) tag system, which is operational at Columbia and Snake River dams. Because the technology underlying the POST array works in both freshwater and the ocean, it is therefore possible to extend the measurement of survival to large rivers lacking dams, such as the Fraser, and to also extend the measurement of survival to the lower Columbia River and estuary, where there are no dams. Of particular note, survival during the downstream migration of at least some endangered Columbia and Snake River Chinook and steelhead stocks appears to be as high or higher than that of the same species migrating out of the Fraser River in Canada, which lacks dams. Equally surprising, smolt survival during migration through the hydrosystem, when scaled by either the time or distance migrated, is higher than in the lower Columbia River and estuary where dams are absent. Our results raise important questions regarding the factors that are preventing the recovery of salmon stocks in the Columbia and the future health of stocks in the Fraser River.     

Inorganic pyrophosphatase: a new polymorphic allozyme locus in Pacific salmon

Genetic polymorphism of inorganic pyrophosphatase was investigated in 2799 individuals in four species of Pacific salmon: chinook salmon (Oncorhynchus tshawytscha), coho salmon (O. kisutch), kokanee (O. nerka), and steelhead (O. mykiss), using horizontal starch gel electrophoresis. This enzyme system appears to be an isolocus system with electrophoretically indistinguishable allozymes encoded by two loci (PP-1,2*) expressed in retinal tissue. Mendelian inheritance was observed with a breeding study in three family crosses. Population variability in four species was characterized in 44 populations from the U.S. Pacific coast. Three alleles were found in chinook salmon; two alleles each were found in coho salmon, kokanee, and steelhead. Chinook salmon and kokanee populations differed enough with respect to PP-1,2* frequencies that this isolocus is useful for genetic stock identification in these species.     

Can non-native smallmouth bass, <Emphasis Type="Italic">Micropterus dolomieu</Emphasis>, be swamped by hatchery fish releases to increase juvenile Chinook salmon, <Emphasis Type="Italic">Oncorhynchus tshawytscha</Emphasis>, survival?

One of the strategies that can be used to reduce predation impacts to valued fish species is by swamping predators with more prey than they can eat. We examined whether this approach was viable by calculating the maximum bioenergetic consumption potential of non-native smallmouth bass Micropterus dolomieu on fall Chinook salmon Oncorhynchus tshawytscha juveniles in the Yakima River throughout the spring between 1998 and 2002 and comparing those estimates to previously published estimates of fall Chinook salmon consumption. We found that the smallmouth bass population consumed fall Chinook salmon well below their bioenergetic potential. However, individual smallmouth bass that were piscivorous were eating other food items at a level near satiation. Furthermore, the maximum consumption potential was relatively low prior to mid-April, and then increased substantially to a peak in May. Predation mortality to hatchery fall Chinook salmon could be reduced within a year by releasing hatchery fall Chinook salmon that will emigrate quickly prior to mid-April, when predation potential is still very low. However, attempting to swamp predators with hatchery Chinook salmon to benefit naturally produced Chinook salmon poses uncertain benefits to natural origin fish and likely unacceptable costs to hatchery fish. Considerable swamping is occurring by other naturally produced fish species in the Yakima River such as dace Rhinichthys spp., mountain whitefish Prosopium williamsoni, and crayfish Pacificastus spp. Therefore, it is important to consider impacts to these non-target species because they could have indirect predation impacts on Chinook salmon.     

Amino acid cues emanating from Pacific salmon eggs and ovarian fluid

The eggs of salmonid fishes are an important food source for many aquatic predators that detect eggs using olfaction. Moreover, chemicals from eggs and ovarian fluid aid sperm cells in detecting and locating eggs for fertilization, and ovarian fluid is attractive to conspecific males. Thus chemicals from eggs and ovarian fluid may facilitate reproduction but may also attract egg predators. The authors sampled mature females of three Pacific salmon species – Chinook (Oncorhynchus tshawytscha), coho (Oncorhynchus kisutch) and sockeye (Oncorhynchus nerka) – and determined the proportional representation of amino acids, potent fish odorants, from their eggs and ovarian fluid (Chinook and coho salmon only). They then tested juvenile coho salmon, an egg predator, for responses to ovarian fluid and egg odours using the electro-olfactogram (EOG) recording technique. The amino acid compositions of the salmon species were significantly and positively correlated with each other, and the interspecific differences were comparable to those between individuals of the same species. The egg water samples were, on average, dominated by lysine, alanine and glutamine (12.6%, 12.4% and 10.9%, respectively). The ovarian fluid samples were dominated by lysine (20.5%), followed by threonine (9.7%), glycine (9.2%) and arginine (8.8%). EOG recordings demonstrated the ability of juvenile coho salmon to detect the chemical traces of eggs and ovarian fluid. It is concluded that salmon eggs are a potent source of odours for potential predators but likely not highly differentiated among salmon species.     

Seasonal foraging and piscivory by sympatric wild and hatchery-reared steelhead from an integrated hatchery program

We compared the diet of hatchery-reared steelhead produced from an integrated hatchery program as emigrating spring smolts and non-migrating hatchery residuals to their sympatric wild counterparts. Our results suggest that there is a potential for hatchery fish to affect wild steelhead populations due to dietary overlap and subyearling salmonid predation; however, relative ecological risk did not increase as steelhead delayed or forwent emigration. Predation by hatchery smolts was related to release timing, but not experience with native fish. Diet composition appears to be more strongly affected by seasonal and yearly differences in prey abundance and presence rather than differences in rearing environments. Hatchery and wild steelhead showed small but important foraging differences. Hatchery smolts did not consume as many salmonids as wild fish and hatchery residuals showed relatively stronger surface oriented feeding behavior than wild parr. Because most hatchery smolts emigrated shortly after release and the overall number of residuals in the study creek was low, we speculate that in this case there is low dietary and predatory-based risk of hatchery steelhead in Abernathy Creek negatively impacting wild salmonids.