Growth Of Juvenile Coho Salmon Research Articles

Juvenile salmon habitat use drives variation in growth and highlights vulnerability to river fragmentation

AbstractWidespread stream network fragmentation from dams and culverts has altered habitat connectivity in river ecosystems and presents an acute threat to migratory fish. To support watershed management for an iconic migratory fish group, we assessed juvenile salmon growth outcomes across habitat use strategies and characterized how these life histories may be impacted by stream connectivity loss. Juvenile coho salmon (Oncorhynchus kisutch) in the Big Lake drainage, Alaska, USA, were individually tracked over 2012–2013 and categorized into habitat use behaviors, with fish either remaining in streams throughout freshwater residency or migrating seasonally to overwinter in lake habitats. Size, growth rate, and body condition of smolts (n = 1113) were compared across habitat use strategies. Juvenile coho salmon that moved seasonally to lake overwintering habitats, the most frequently observed strategy, grew faster and were significantly larger as smolts compared to their counterparts who remained in streams exclusively (spring Age 1 fish: 18% larger by weight, 9% faster growth rate; spring Age 2+ fish: 26% heavier, 11% faster growth). Environmental data from a subset of overwinter lakes indicate that greater foraging opportunity and lower energy costs may be implicated in growth advantages conferred by lentic overwintering strategies. Habitat use strategies requiring seasonal migrations, however, increased exposure to stream connectivity loss, and fish blocked from accessing a potential overwinter headwater lake by a culvert and dam had lowest body condition among study groups. Stream network fragmentation restricts access to preferred overwinter habitats, and our findings suggest this may constrain freshwater rearing strategies associated with strong juvenile coho salmon growth. As size at smolt has been implicated as a driver of salmon survival through ocean residency, reduced freshwater habitat connectivity during juvenile stages may have deleterious impacts on later marine life stages. Consequently, conservation of stream connectivity across lentic and lotic habitats represents an important watershed management priority for juvenile salmon.

Effects of experimental flow manipulations on water quality, hypoxia, and growth of Threatened Salish sucker (Catostomus sp. cf. catostomus) and juvenile coho salmon (Oncorhynchus kisutch)1

The Salish sucker (Catostomus sp. cf. catostomus) is a federally Threatened species in Canada, inhabiting small lowland streams along with juvenile coho salmon (Oncorhynchus kisutch) in southwestern British Columbia and adjacent Washington State. Experiments were conducted in two ponds to determine the effects of reduced flow on dissolved oxygen, growth of stocked Salish sucker and juvenile coho salmon (Oncorhynchus kisutch), and fish movement using passive integrated transponder (PIT) tags. Sequential flow reduction in the first experiment resulted in a significant decrease in dissolved oxygen (9.1 to 3.1 mg·L−1) and Salish sucker growth (23% decline), although lower dissolved oxygen and growth were confounded with decreased temperature. Flow reduction in a second split-pond experiment including coho salmon resulted in significantly lower dissolved oxygen (6.9 to 2.9 mg·L−1), a 51% reduction in growth of coho salmon, but no detectable change in Salish sucker growth. PIT tag detections demonstrated increased use by both species of a well-oxygenated refuge in the flow reduction treatment, indicating sublethal effects of hypoxia on fish behaviour and habitat use. These experiments demonstrate the induction of severe hypoxia by reduced flows under eutrophy, with the potential for negative impacts on Salish sucker and juvenile coho salmon growth and habitat use.

Spatial and interannual variability of juvenile coho salmon growth in the Strait of Georgia (2012-2015)

We conducted a 4 yr (2012-2015) study of regional growth of juvenile coho salmonOncorhynchus kisutchin the Strait of Georgia (British Columbia, Canada). Size (fork length) and growth (insulin-like growth factor-1 [IGF-1] concentration) varied both regionally and inter-annually. Additionally, we found a positive relationship between IGF-1 concentration and fork length that varied between years, with slopes andy-intercepts higher in 2012 and 2014, respectively, as compared to 2013 and 2015. An ordinal increase of IGF-1 concentration from the south to north in 2012 and 2014 was coupled with an increase in the prevalence of both juvenile herring and juveniles of other fish species in the diet. Across all years, there was a positive relationship between regional mean IGF-1 concentration and regional mean percent of juvenile herring in the diet. Our study demonstrates relatively small-scale spatial heterogeneity in juvenile coho salmon growth that in part, was attributed to regional variation in diet. These findings also demonstrate the utility of short-term growth measures (such as IGF-1) for assessing relatively small-scale spatial and temporal differences in growth.

Juvenile coho salmon growth and health in streams across an urbanization gradient

Expanding human population and urbanization alters freshwater systems through structural changes to habitat, temperature effects from increased runoff and reduced canopy cover, altered flows, and increased toxicants. Current stream assessments stop short of measuring health or condition of species utilizing these freshwater habitats and fail to link specific stressors mechanistically to the health of organisms in the stream. Juvenile fish growth integrates both external and internal conditions providing a useful indicator of habitat quality and ecosystem health. Thus, there is a need to account for ecological and environmental influences on fish growth accurately. Bioenergetics models can simulate changes in growth and consumption in response to environmental conditions and food availability to account for interactions between an organism's environmental experience and utilization of available resources. The bioenergetics approach accounts for how thermal regime, food supply, and food quality affect fish growth. This study used a bioenergetics modeling approach to evaluate the environmental factors influencing juvenile coho salmon growth among ten Pacific Northwest streams spanning an urban gradient. Urban streams tended to be warmer, have earlier emergence dates and stronger early season growth. However, fish in urban streams experienced increased stress through lower growth efficiencies, especially later in the summer as temperatures warmed, with as much as a 16.6% reduction when compared to fish from other streams. Bioenergetics modeling successfully characterized salmonid growth in small perennial streams as part of a more extensive monitoring program and provides a powerful assessment tool for characterizing mixed life-stage specific responses in urban streams.

A laboratory-calibrated model of coho salmon growth with utility for ecological analyses

We conducted a meta-analysis of laboratory- and hatchery-based growth data to estimate broadly applicable parameters of mass- and temperature-dependent growth of juvenile coho salmon (Oncorhynchus kisutch). Following studies of other salmonid species, we incorporated the Ratkowsky growth model into an allometric model and fit this model to growth observations from eight studies spanning ten different populations. To account for changes in growth patterns with food availability, we reparameterized the Ratkowsky model to scale several of its parameters relative to ration. The resulting model was robust across a wide range of ration allocations and experimental conditions, accounting for 99% of the variation in final body mass. We fit this model to growth data from coho salmon inhabiting tributaries and constructed ponds in the Klamath Basin by estimating habitat-specific indices of food availability. The model produced evidence that constructed ponds provided higher food availability than natural tributaries. Because of their simplicity (only mass and temperature are required as inputs) and robustness, ration-varying Ratkowsky models have utility as an ecological tool for capturing growth in freshwater fish populations.

Effects of solar ultraviolet radiation exposure on early ocean survival and fry-to-smolt growth of juvenile salmon

Marine survival rates of many juvenile salmon populations have declined in recent decades. Although several potential causes have been proposed, there has been little conclusive evidence for which factors are responsible or not responsible for these declines. We experimen- tally addressed the hypothesis that exposure of coho salmon Oncorhynchus kisutch or sockeye salmon O. nerka to solar ultraviolet-B radiation (UVB) during freshwater rearing of fry and parr life-history stages increases mortality at the time of smoltification and ocean entry. Juvenile coho and sockeye salmon were reared in outdoor hatchery tanks either exposed to full spectrum sun- light or shielded from UVB radiation by plastic screens for up to 9 mo prior to release. Smolts were tagged with acoustic transmitters and detected with hydrophone receivers during their downriver and early ocean migration. Survival of treatment groups was compared using Cormack-Jolly- Seber and Burnham mark-recapture models. While exposure to UVB resulted in decreased growth of juvenile coho salmon, survivorship during the early marine period was unaffected by the UVB treatment for both populations. This first attempt to experimentally address the hypo - thesis of impaired survival resulting from solar UVB radiation has shown that other factors are more likely responsible for observed declines in salmon marine survival rates.

Effects of habitat and internal prey subsidies on juvenile coho salmon growth: implications for stream productive capacity

Abstract – To evaluate the effects of habitat, foraging strategy (drift vs. limnetic feeding) and internal prey subsidies (downstream transport of invertebrate drift between habitats) on fish production, we measured the growth of juvenile coho salmon confined to enclosures in flowing (pond inlets and outlets) or standing water (centre of pond) habitats in a constructed river side‐channel. The effects of habitat and foraging strategy on fish growth were mediated primarily through habitat effects on prey abundance. Invertebrate drift biomass was nearly an order of magnitude higher at pond inlets relative to outlets. Drift‐feeding coho in inlet enclosures grew 50% faster than drift‐feeding coho at pond outlets or limnetic feeding coho in the centre of ponds, suggesting that elevated drift at inlets was sufficient to account for higher inlet growth rates. Forty per cent of prey biomass in stomachs was terrestrial in origin. These results indicate that, in addition to dependence on external terrestrial subsidies, streams with alternating slow and fast water (i.e., pool‐riffle) sequences are also characterised by internal prey subsidies based on transport of drifting invertebrates from refuge habitats (high velocity riffles) to habitats more suitable for drift‐feeding predators (e.g., pools), which may result in higher maximum fish growth in systems where internal subsidises are large. Restoration of small streams to maximise productive capacity for pool‐rearing salmonids will require a better understanding of the length and interspersion of habitats that maximises both internal prey subsidies and available rearing habitat for juvenile salmon.

A top-down survival mechanism during early marine residency explains coho salmon year-class strength in southeast Alaska

Coho salmon (Oncorhynchus kisutch) are a vital component in the southeast Alaska marine ecosystem and are an important regional fishery resource; consequently, understanding mechanisms affecting their year-class strength is necessary from both scientific and management perspectives. We examined correlations among juvenile coho salmon indices, associated biophysical variables, and adult coho salmon harvest data from southeast Alaska over the years 1997–2006. We found no relationship between summer indices of juvenile coho salmon growth, condition, or abundance with subsequent harvest of adult coho salmon in the region. However, using stepwise regression, we found that variation in adult coho salmon harvest was largely explained by indices of juvenile pink salmon (Oncorhynchus gorbuscha) abundance (67%) and zooplankton abundance (24%). To determine if high juvenile pink salmon abundance indicates favorable ‘‘bottom-up’’ lower trophic level environmental conditions for juvenile coho salmon, we plotted abundance of juvenile pink salmon against growth and condition of juvenile coho salmon. No change in growth or condition of juvenile coho salmon was observed in relation to the abundance index for juvenile pink salmon. Therefore, we hypothesize that coho salmon year-class strength in southeast Alaska is influenced by a ‘‘top-down’’ predator control mechanism that results from more abundant juvenile pink salmon, which serve as a predator buffer during early marine residency. Published by Elsevier Ltd.

Summer Distribution and Growth of Juvenile Coho Salmon during Colonization of Newly Accessible Habitat

AbstractPacific salmon Oncorhynchus spp. are capable of exploiting vacant habitat, but most research has focused on straying and colonization by adults. However, dispersal of juveniles of stream‐rearing species, such as coho salmon O. kisutch, may also be an important component of colonization. Installation of fish passage structures on the Cedar River, Washington, and subsequent adult migration into the newly accessible habitat provided a rare opportunity to investigate colonization as coho salmon regained access to 33 km of habitat from which they had been excluded for more than a century. In this study, we describe the spatial distribution and growth patterns of the first two generations of juvenile coho salmon produced in the new habitat. Snorkel surveys in the Cedar River revealed patchy distributions of juvenile coho salmon that largely matched the distribution of adults spawning the previous fall, and higher densities occurred in lower reaches (i.e., those not far upstream from the dam). However, sequential surveys indicated that juveniles entered and moved upstream within a Cedar River tributary, Rock Creek, where few, if any, adults spawned. Juveniles captured in the Cedar River were similar in size to those in Rock Creek, but sizes differed between years and larger fish tended to occur farther upriver. We found no evidence for density‐dependent growth; there was no relationship between fish size and local density in either main‐stem or tributary habitat. Abundance estimates suggest that relatively few juvenile coho salmon dispersed long distances into reaches neglected by spawning adults. We were unable to find any clear evidence that juvenile dispersal would increase the number of adults returning in the next generation, but such movements could accelerate the spatial expansion of the colonizing population in philopatric species like coho salmon.

Food abundance and fish density alters habitat selection, growth, and habitat suitability curves for juvenile coho salmon (Oncorhynchus kisutch)

To understand how fish density and food availability affect habitat selection and growth of juvenile coho salmon (Oncorhynchus kisutch), we manipulated fish density (2–12 fish·m–2) and natural invertebrate drift (0.047–0.99 mg·m–3) in 12 experimental stream channels constructed in a side-channel of Chapman Creek, British Columbia. Increased food resulted in increased growth of both dominant and subdominant fish and a shift to higher average focal velocities (from 6.5 to 8.4 cm·s–1) with maximum growth in the range of 10–12 cm·s–1. Increased food appears to permit juvenile coho to exploit higher velocity microhabitats that might otherwise be bioenergetically unsuitable at lower food levels. Increased fish density resulted in lower growth of subdominant but not of dominant fish and a general displacement of fish to both higher and lower focal velocities. The shapes of habitat suitability curves were sensitive to food abundance, implying that differences in food availability may affect transferability of habitat suitability curves between streams of different productivity. While habitat suitability curves captured the change in extent of available habitat following prey enrichment, actual increases in growth rate with enrichment (i.e., changes in habitat quality) were poorly represented by habitat suitability values and better represented by bioenergetic model predictions.

Effects of Introduced Fishes on Wild Juvenile Coho Salmon in Three Shallow Pacific Northwest Lakes

AbstractDeclines in Pacific salmon Oncorhynchus spp. have been blamed on hydropower, overfishing, ocean conditions, and land use practices; however, less is known about the impacts of introduced fish. Most of the hundreds of lakes and ponds in the Pacific Northwest contain introduced fishes, and many of these water bodies are also important for salmon production, especially of coho salmon O. kisutch. Over 2 years, we examined the predation impacts of 10 common introduced fishes (brown bullhead Ameiurus nebulosus, black crappie Pomoxis nigromaculatus, bluegill Lepomis macrochirus, golden shiner Notemigonus crysoleucas, green sunfish L. cyanellus, largemouth bass Micropterus salmoides, pumpkinseed L. gibbosus, rainbow trout O. mykiss, warmouth L. gulosus, and yellow perch Perca flavescens) and two native fishes (cutthroat trout O. clarkii and prickly sculpin Cottus asper) on wild juvenile coho salmon in three shallow Pacific Northwest lakes, all located in different watersheds. Of these species, largemouth bass were responsible for an average of 98% of the predation on coho salmon in all lakes, but the total impact to each run varied among lakes and years. Very few coho salmon were eaten by black crappies, brown bullheads, cutthroat trout, prickly sculpin, or yellow perch, whereas other species were not observed to eat coho salmon. Juvenile coho salmon growth in all lakes was higher than in nearby streams. Therefore, food competition between coho salmon and introduced fishes in lakes was probably not limiting coho salmon populations. Largemouth bass are widespread and are present in 85% of lowland warmwater public‐access lakes in Washington (n = 421), 84% of those in Oregon (n = 179), and 74% of those in the eight northwesternmost counties in California (n = 19). Future research would help to identify the impact of largemouth bass predation across the region and prioritize lakes where impacts are most severe. Nevertheless, attempts to transplant or increase largemouth bass numbers in lakes important to coho salmon would be counterproductive to coho salmon enhancement efforts.

Changes in Solar Input, Water Temperature, Periphyton Accumulation, and Allochthonous Input and Storage after Canopy Removal along Two Small Salmon Streams in Southeast Alaska

Changes in solar radiation, water temperature, periphyton accumulation, and allochthonous inputs and storage were measured after we removed patches of deciduous, second-growth riparian vegetation bordering two small streams in southeast Alaska that produce coho salmon Oncorhynchus kisutch. Solar radiation and leaf litter input were measured at the water surface at random locations dispersed through six alternating closed- and open-canopy stream sections. Water temperature, periphyton, and stored organic samples were collected near the downstream end of each section. Solar radiation intensity was measured with digital daylight integrators and pyronometers, periphyton biomass and chlorophyll a were measured on red clay tile substrates, allochthonous input was measured with leaf litter baskets, and benthic organic matter was measured with a Hess sampler. Average intensity of solar radiation that reached the water surface of open-canopy sections was significantly higher than in closed-canopy sections of two streams measured during daylight hours in summer 1988 and of one stream measured day and night in summer 1989. Average daily water temperature was similar in the two canopy types in summer 1988, but was higher in open- than in closed-canopy sections in 1989. Accumulation of periphyton biomass was significantly higher in open- than in closed-canopy sections of the two streams studied in the summer of 1988 and of the one stream sampled in 1989. Accrual of periphyton biomass on tiles placed in the stream for 30-d colonization periods during the summer months of 1989 was also significantly higher in the open than closed sections. Accumulation of chlorophyll a was significantly higher in the open- than in closed-canopy sections of the two streams in 1988 but did not differ significantly between canopy types in 1989. Thirty-day accrual of chlorophyll a was greater in open- than in closed-canopy sections of the one stream studied in 1989. Allochthonous input to the streams decreased after canopy removal, but the amount of organic material stored in the substrate did not differ significantly between open- and closed-canopy sections. Weather was predominantly overcast and rainy in summer 1988 and mostly sunny with infrequent rain in 1989. We speculate that advective heat transfer and high stream discharge from frequent rains moderated the effect of canopy removal and increased solar radiation on water temperatures in open-canopy stream sections in 1988. In 1989, solar radiation was a significant factor in regulating water temperature, especially when streamflows were low. Using a model, we predicted that water temperatures would change little in a 160-m open-canopy reach of Eleven Creek during any weather condition when flows were high. With low flows, however, stream temperatures in open sections of Eleven Creek were predicted to exceed the optimum for growth of juvenile coho salmon in about 20 m during clear sunny weather and in about 50 m when cloudy and overcast.

Summer Distribution, Survival, and Growth of Juvenile Coho Salmon under Varying Experimental Conditions of Brushy Instream Cover

Abstract Woody debris is an important feature of streams, and its presence and abundance have been correlated with the abundance, growth, and survival of juvenile salmonids. To investigate the proximate mechanisms linking brushy woody debris to salmonid fishes, we determined, over a 1-month period in summer, the spatial distribution of juvenile coho salmon Oncorhynchus kisutch introduced into an outdoor experimental stream containing riffle-pool units that had one of four different levels of instream brushy-debris complexity. We then equalized the fish density in each unit and monitored fish growth and survival over a 15-week period. Coho salmon distribution, growth, and survival varied greatly but were not consistently related to the complexity of brushy debris.

Effects of Leaf Litter on Survival and Growth of Juvenile Coho Salmon

Abstract Juvenile coho salmon (Oncorhynchus kisutch) were raised for a 6-week period from 2 weeks posthatching through yolk-sac absorption in oval tanks with or without a 5-cm layer of leaf litter. Each treatment was conducted in triplicate tanks; each tank initially contained 100 yolk-sac fry. The fish were fed at a reduced ration in order to discern nutritive effects (possibly from invertebrates) due to the presence of leaf litter. In each of the two consecutive years that the experiment was conducted, there was a third experimental condition – in year 1, a nylon screen was placed on top of the leaf litter to separate cover effects from nutritional effects; in year 2, a treatment group was fed full ration. Examination of total treatment mortality suggested that some factor in the leaf litter tended to improve survival, although the added leaf litter did not have any statistically significant effect on growth during the experiment. Thus, leaf litter, a component of the natural habitat of coho salmon fry,...

Effects of Fine Sediments on Growth of Juvenile Coho Salmon in Laboratory Streams

Juvenile coho salmon (Oncorhynchus kisutch) production (tissue elaboration) was monitored in 12 laboratory streams under six replicate treatment levels of fine sedimentation. Increasing sedimentation suppressed fish production. Our data confirm that habitats of salmonid juveniles, as well as spawning areas, should be protected against fine sediments. Substrate Score, a visual technique for evaluating stream substrate quality, correlated closely with both the geometric mean particle size of the substrate and fish production, and can be easily applied in the field.

Osmotic adaptation of Oncorhynchus kisutch Walbaum. III. Survival and growth of juvenile coho salmon transferred to sea water at various times of the year

Juvenile salmon from two successive broods (1974 and 1975 spawnings) were transferred to sea water of various salinities at different periods of the year in 1976 to determine the tolerance to sea water in terms of mortality and growth. Fish of the 0 + age group, transferred directly to sea water (35‰) on 23 June (19.5 ± 3.3 g) and 13 July (27.1 ± 2.4 g) very rapidly showed an extremely high mortality. Progressive adaptation performed at the same dates indicated a higher tolerance in June compared to the July transfer, but still with significant mortalities. Direct transfers made between September and December with subyearlings showed a better adaptability in September–October than later. Yearling fish put in sea water on 3 March (68.3 ± 0.8 g) and 14 April (98.0 ± 2.4 g) had a very low 30-days mortality after contact with sea water of various salinities (25–30–35‰). However, growth assessment indicated better osmotic adaptation in April whereas the fish transferred in March showed a much lower average growth. The results suggest that the 30-day survival criterion alone is not sufficient to characterize a good osmotic adaptation to the marine environment. The simultaneous examination of growth and mortality data gives a more precise estimation of the tolerance to sea water. This study provided information on the seasonal variations of this tolerance to high salinities, and defined the minimum sizes required for a satisfactory adaptation. It is interesting to note that the periods of highest euryhalinity (April–June and September–October) correspond to the phases of highest gill Na +K + ATPase activity described in an earlier paper.

Influence of Oxygen Concentration on the Growth of Juvenile Coho Salmon

Abstract Juvenile coho salmon, Oncorhynchus kisutch (Walbaum), were held at 20° C. in 12-gallon bottles, usually 10 to a bottle, in continuously renewed fresh water having various dissolved oxygen concentrations. Reduced oxygen concentrations were maintained by bubbling nitrogen through the inflowing water. In most of the experiments, the fish were fed beach hoppers (marine amphipods) to repletion twice daily so that food was available for 10 hours each day. Growth and food consumption rates of age-class 0 juveniles observed in the year 1956 declined slightly with reduction of oxygen concentration from a mean of about 8.3 to 6 and 5 mg/l, and declined more sharply with further reduction of oxygen concentration. Weight gains in grams per gram of food consumed (food conversion ratios) were slightly depressed at concentrations near 4 mg/l, and were markedly reduced at lower concentrations. At concentrations averaging 2.1 to 2.3 mg/l, many fish died and surviving fish consumed very little food and lost weight...