Behavioral interactions between coho (Oncorhynchus kisutch) and chinook salmon (Oncorhynchus shawytscha) and prey fish species

Abstract— The predator-prey behavioral interactions between two salmon species, coho salmon ( Oncorhynchus kisutch ) and chinook salmon ( Oncorhynchus tshawytscha ), and their prey species were examined under laboratory conditions. These behaviors were studied to determine the bases for prey selection by salmon in Lake Michigan and ultimately facilitate predictions on shifts or changes in salmon diets. Chinook and coho salmon captured all prey items in the open water portion of the aquarium, and they had similar attack behaviors. Average attack swimming speeds varied from 2.6 to 3.6 m/s, and average escape swimming speeds varied from 2.6 to 2.9 m/s. There were no significant differences in attack swimming speeds and escape swimming speeds. There was a significant difference in median reactive distances between the prey captured and those that escaped. There was no reactive distance (0.00 m) for 96% and 98% of the successfully captured prey by chinook and coho salmon, respectively. Only 4% and 10% of the unsuccessful attacks by chinook and coho salmon, respectively, had no reactive distance (0.00 m). Salmon would repeatedly attack a school and capture individuals separated from the school. Alewives, bloaters and fathead minnows were easy prey because they remained in the open water portion of the aquarium and stayed in schools until only a few individuals remained. The schooling behavior of spottail shiners and emerald shiners was an effective anti-predation tactic against salmon attacks. After some experience with yellow perch, salmon were reluctant to attack them and would often break off attacks on them. When coho salmon were presented with different proportions of bloaters and yellow perch, they significantly attacked and captured bloaters in preference to yellow perch.     

Homing behaviour of juvenile coho salmon (Oncorhynchus kisutch) within an off-channel habitat

Abstract – Although homing behaviour has been observed in juvenile Atlantic salmon, brown trout and resident cutthroat trout, this behaviour has not been well studied in juvenile Pacific salmon. We examined the site fidelity and homing behaviour of juvenile coho salmon ( Oncorhynchus kisutch ) by marking and relocating them within an off-channel habitat. Over 80% of displaced fish returned to the area from which they were originally collected. The proportion of fish that returned to the original location did not vary significantly among three sampling dates. However, we found that this proportion decreased over time in a brackish lagoon when we statistically analysed the data reported by Day (1966) . Our results suggest that juvenile coho salmon exhibit strong site fidelity and are able to return to their home ranges after displacement. These behaviours are likely to be important for the winter survival of juvenile coho salmon.     

Marine environment‐based forecasting of coho salmon (Oncorhynchus kisutch) adult recruitment

Generalized additive models (GAMs) were used to investigate the relationships between annual recruitment of natural coho salmon (Oncorhynchus kisutch) from Oregon coastal rivers and indices of the physical ocean environment. Nine indices were examined, ranging from large‐scale ocean indicators, e.g., Pacific Decadal Oscillation (PDO), to indicators of the local ecosystem (e.g., coastal water temperature near Charleston, OR). Generalized additive models with two and three predictor variables were evaluated using a set of performance metrics aimed at quantifying model skill in short‐term (approximately 1 yr) forecasting. High explanatory power and promising forecast skill resulted when the spring/summer PDO averaged over the 4 yr prior to the return year was used to explain a low‐frequency (multi‐year) pattern in recruitment and one or two additional variables accounted for year‐to‐year deviations from the low‐frequency pattern. More variance was explained when averaging the predictions from a set of models (i.e., taking the ensemble mean) than by any single model. Making multiple forecasts from a set of models also provided a range of possible outcomes that reflected, to some degree, the uncertainty in our understanding of how salmon productivity is driven by physical ocean conditions.     

银鲑(oncorhynchus kisutch)形态性状测量

通过对银鲑的形性状测量 ,初步进行了银鲑的种质研究。结果表明银鲑的形态性状如下 :全长 /体长为 1 1 2± 0 0 2 ,头长 /眼径为 4 46± 0 45 ,体长 /体高为 4 49± 0 32 ,尾柄长 /尾柄高为 2 2 9± 0 30 ,体长 /头长为 4 0 4± 0 2 1 ,体长 /叉长为 0 94± 0 0 3 ,头长/头高为 1 2 8± 0 0 8,体长 /尾柄长为 5 2 3± 0 30 ,头长 /吻长为 3 33± 0 2 7,头长 /眼间距为 2 68± 0 2 0 ,背鳍 1 0～ 1 3 ,腹鳍 1 0～ 1 1 ,胸鳍 1 3～ 1 6 ,臀鳍 1 2～ 1 7,侧线鳞 1 2 1～1 4 4 ,幽门盲囊 45～ 83 ,鳃耙 1 9～ 2 3,脊椎骨 58～ 66。     

Dosage-dependent differences in the effect of aromatizable and nonaromatizable androgens on the resulting phenotype of coho salmon (Oncorhynchus kisutch)

This study was conducted to investigate whether aromatization to estrogen could be the cause for the paradoxical feminization of gonads of sexually-undifferentiated fish after treatment with androgen at either high doses or for long periods. The aromatizable androgen 17-methyltestosterone (MT) and the nonaromatizable androgen 17-methyldihydrotestosterone (MDHT) were administered to groups of newly hatched coho salmon (Oncorhynchus kisutch) in a single 2h immersion at concentrations ranging from 6.25 to 6,400µg/l. The effects of treatment were evaluated by determining the resultant proportion of males in each experimental group. The effects of steroid administration on the final mean weight, length and condition factor were also determined. An increase in all these three variables was observed in the groups treated with the higher doses of MT. Regarding the resultant sexual phenotype, the response to both androgens was similar at the majority of doses tested. However, at the highest dose, the proportion of females increased with respect to that of males for MT, but not for MDHT. Since the major difference between the two androgens tested is their capacity to be aromatized, it seems that aromatization to estrogen, rather than inhibition of the biosynthesis of endogenous androgen, may explain the paradoxical feminization encountered.     

Climate variability and marine survival of coho salmon (Oncorhynchus kisutch) in the Oregon production area

Time series of adult recruitment for natural runs of coho salmon from the Oregon coastal region (1970–94) and marine survival of hatchery-reared coho salmon from California to Washington (1960–94) are significantly correlated with a suite of meteorological and oceanographic variables related to the biological productivity of the local coastal region. These variables include strong upwelling, cool sea surface temperature (SST), strong wind mixing, a deep and weakly stratified mixed layer, and low coastal sea level, indicating strong transport of the California Current. Principal component analysis indicates that these variables work in concert to define the dominant modes of physical variability, which appear to regulate nutrient availability and biological productivity. Multiple regression analysis suggests that coho marine survival is significantly and independently related to the dominant modes acting over this region in the periods when the coho first enter the ocean and during the overwintering/spring period prior to their spawning migration. Linear relationships provided good fits to the data and were robust, capable of predicting randomly removed portions of the data set.     

Estimates of genetic and phenotypic parameters for length and weight of marine net-pen reared coho salmon (Oncorhynchus kisutch Walbaum)

Heritabilities and genetic and phenotypic correlations were estimated for length and weight of two brood years (BY 1977 and BY 1978) of coho salmon [Oncorhynchus kisutch (Walbaum)] during the marine net-pen phase of rearing. The estimates were calculated from length and weight measurements on progeny resulting from a nested mating design and measurements at approximately 4 and 7 months after entering sea water. Point estimate for heritabilities based on the sire component for BY 1977 were low to moderate (0.02–0.19) and did not differ significantly from zero. On the other hand, BY 1978 estimates ranged from 0.31 to 0.62 and, with two exceptions, were significantly different from zero. The latter estimates may have been inflated by inclusion of variances from non-additive sources, but still indicated that differences in the genetic potential for increased growth between the two year classes may be substantial. Genetic correlations between length and weight within sampling periods were consistently high (0.95–1.00), indicating that pleiotropic gene action or close linkage among genes affects length and weight. Genetic correlations between body size traits (length and weight) between sampling periods varied considerably but suggested a potential for indirect selection gains. Genetic correlation approximations derived using family means or ranks appeared to provide reliable estimates and may be useful when environmental influences cause a significant deviation from normality.     

Ocean distribution and habitat associations of yearling coho (Oncorhynchus kisutch) and Chinook (O. tshawytscha) salmon in the northern California Current

Yearling juvenile coho and Chinook salmon were sampled on 28 cruises in June and September 1981–85 and 1998–07 in continental shelf and oceanic waters off the Pacific Northwest. Oceanographic variables measured included temperature, salinity, water depth, and chlorophyll concentration (all cruises) and copepod biomass during the cruises from 1998–07. Juvenile salmonids were found almost exclusively in continental shelf waters, and showed a patchy distribution: half were collected in ～5% of the collections and none were collected in ～40% of the collections. Variance‐to‐mean ratios of the catches were high, also indicating patchy spatial distributions for both species. The salmon were most abundant in the vicinity of the Columbia River and the Washington coast in June; by September, both were less abundant, although still found mainly off Washington. In June, the geographic center‐of‐mass of the distribution for each species was located off Grays Harbor, WA, near the northern end of our sampling grid, but in September, it shifted southward and inshore. Coho salmon ranged further offshore than Chinook salmon: in June, the average median depth where they were caught was 85.6 and 55.0 m, respectively, and in September it was 65.5 and 43.7 m, respectively. Abundances of both species were significantly correlated with water depth (negatively), chlorophyll (positively) and copepod biomass (positively). Abundances of yearling Chinook salmon, but not of yearling coho salmon, were correlated with temperature (negatively). We discuss the potential role of coastal upwelling, submarine canyons and krill in determining the spatial distributions of the salmon.     

Effect of thyroid-stimulating hormone on the physiology and morphology of the thyroid gland in coho salmon,Oncorhynchus kisutch

Activity of the thyroid gland of the coho salmon,Oncorhynchus kisutch, was assessed by physiological, histological and ultrastructural criteria after treatment with graded doses of bovine thyrotropin (bTSH) in January and March. Average plasma thyroxine (T₄) levels increased from about 0.8 ng/ml in saline-injected controls to about 15 ng/ml in fish treated with four intraperitoneal injections of 0.8 lU bTSH. Light-microscope observations of one m-thick sections stained with methylene blue and azure II, showed that bTSH treatment increased epithelial height in both presmolts and smolts. Ultrastructural manifestations of increased activity owing to bTSH treatment were also seen, along with evidence of follicle proliferation. Cytoplasmic organelles and secretory granules increased in numbers with increased dosage of bTSH.     

Infectious haemolytic anaemia causes jaundice outbreaks in seawater-cultured coho salmon, Oncorhynchus kisutch (Walbaum), in Chile

In the last 9 years, epizootics of an icterus condition has affected coho salmon, Oncorhynchus kisutch (Walbaum), reared in seawater cages in southern regions of Chile. At necropsy, fish from field cases exhibited signs of jaundice accompanied by pale light-brown livers and dark spleens. Histopathological and haematological results indicated that these fish presented haemolytic anaemia. After microbiological examination no bacterial or viral agents could be identified as aetiological agents of this disease. In an infectivity trial, coho salmon, Atlantic salmon, Salmo salar L., and rainbow trout, Oncorhynchus mykiss (Walbaum), were inoculated intraperitoneally with a filtrate of an organ homogenate (0.45 microm) from a diseased coho salmon and held for 60 days in tanks supplied with fresh water. The disease was only reproduced in coho salmon in which mortalities, beginning at day 23 post-inoculation (p.i.), reached a cumulative value of 24% at day 27 p.i. This condition was transmitted to non-inoculated cohabiting coho salmon suggesting that it is a waterborne disease. Thus, this icteric condition is caused by an infectious form of haemolytic anaemia, probably of viral aetiology, and coho salmon are more susceptible than either Atlantic salmon or rainbow trout.     

Survival of smaller sport caught chinook, Oncorhynchus tshawytscha (Walbaum), and coho, Oncorhynchus kisutch (Walbaum), salmon from Lake Michigan and its management implications

Abstract The survival of small-sized (<50.8 cm) chinook salmon, Oncorhynchus tshawytscha (Walbaum), and coho salmon, Oncorhynchus kitsutch (Walbaum), caught by sport fishing was determined to assess the potential for increasing the size limit for these fish. Fishermen were recently catching smaller salmon than in the 1970s, but salmon growth rates had not changed. To be an effective management option, the survival rate of hooked and returned fish must be high. The overall survival rates were high: 76% for chinook salmon and 70% for coho salmon. There was no significant difference in survival of the coho salmon with size of hook used ( P = 0.31). Any mortality among fish was generally acute; fish hooked deep in the mouth or gills generally bled and died shortly after capture. Fish hooked in the gills had a significantly greater mortality ( P = 0.0002). The overall high survival rate for these species was the result of a small proportion of fish being hooked in the gills or deep in the mouth. Since the survival rate of the salmon was high, the size limit could be increased to allow smaller fish to grow to sizes preferred by sport fishermen.     

Interannual and interdecadal variability in juvenile coho salmon (Oncorhynchus kisutch) diets in relation to environmental changes in the northern California Current

The feeding habits of juvenile coho salmon, Oncorhynchus kisutch, in the northern California Current were examined using samples from two different time periods (1980–85 and 1998–2003) of highly contrasting oceanographic conditions. The goal was to test the influence of interannual and interdecadal changes in taxonomic composition of prey, feeding intensity, and size spectra of teleost prey. Analyses were done for samples taken both early in the summer (June) shortly after the salmon enter the ocean, and also in late summer (September) following some ocean residency. Fish prey dominated coho salmon diets by weight during most years, but this trend was more pronounced during the 1980–85 sampling period. In terms of numerical composition, the diets were more variable on an interannual basis, but decapod larvae and euphausiids were important prey in most years. Pteropods and copepods were important prey during weak upwelling or El Niño years, whereas euphausiids were important during strong upwelling or otherwise highly productive years. Hyperiid amphipods comprised a substantial proportion of the diets only in 2000. Coho salmon showed highly significant differences in prey composition among years or between decades both in weight and numerical composition. The percentage of empty stomachs was highly variable by year in both June and September, but was significantly different only for September between decades. In contrast, an index of feeding intensity did not show many significant changes in either comparison. However, the relative size ratios for fish prey consumed were highly variable by year, and larger than average fish prey were consumed during 1998, leading to the highest feeding intensity observed.     

Spatial distribution of ocean habitat of yearling Chinook (Oncorhynchus tshawytscha) and coho (Oncorhynchus kisutch) salmon off Washington and Oregon,USA

We determined the habitat usage and habitat connectivity of juvenile Chinook (Oncorhynchus tshawytscha) and coho (Oncorhynchus kisutch) salmon in continental shelf waters off Washington and Oregon, based on samples collected every June for 9 yr (1998–2006). Habitat usage and connectivity were evaluated using SeaWiFS satellite‐derived chlorophyll a data and water depth. Logistic regression models were developed for both species, and habitats were first classified using a threshold value estimated from a receiver operating characteristic curve. A Bernoulli random process using catch probabilities from observed data, i.e. the frequency of occurrence of a fish divided by the number of times a station was surveyed, was applied to reclassify stations. Zero‐catch probabilities of yearling Chinook and yearling coho salmon decreased with increases in chlorophyll a concentration, and with decreases in water depth. From 1998 to 2006, ～ 47% of stations surveyed were classified as unfavorable habitat for yearling Chinook salmon and ～ 53% for yearling coho salmon. Potentially favorable habitat varied among years and ranged from 9 856 to 15 120 km² (Chinook) and from 14 800 to 16 736 km² (coho). For both species, the smallest habitat area occurred in 1998, an El Niño year. Favorable habitats for yearling Chinook salmon were more isolated in 1998 and 2005 than in other years. Both species had larger and more continuous favorable habitat areas along the Washington coast than along the Oregon coast. The favorable habitats were also larger and more continuous nearshore than offshore for both species. Further investigations on large‐scale transport, mesoscale physical features, and prey and predator availability in the study area are necessary to explain the spatial arrangement of juvenile salmon habitats in continental shelf waters.     

Tracking environmental processes in the coastal zone for understanding and predicting Oregon coho (Oncorhynchus kisutch) marine survival

To better understand and predict Oregon coho (Oncorhynchus kisutch) marine survival, we developed a conceptual model of processes occurring during four sequential periods: (1) winter climate prior to smolt migration from freshwater to ocean, (2) spring transition from winter downwelling to spring/summer upwelling, (3) the spring upwelling season and (4) winter ocean conditions near the end of the maturing coho's first year at sea. We then parameterized a General Additive Model (GAM) with Oregon Production Index (OPI) coho smolt‐to‐adult survival estimates from 1970 to 2001 and environmental data representing processes occurring during each period (presmolt winter SST, spring transition date, spring sea level, and post‐smolt winter SST). The model explained a high and significant proportion of the variation in coho survival (R² = 0.75). The model forecast of 2002 adult survival rate ranged from 4 to 8%. Our forecast was higher than predictions based on the return of precocious males (‘jacks’), and it won't be known until fall 2002 which forecast is most accurate. An advantage to our environmentally based predictive model is the potential for linkages with predictive climate models, which might allow for forecasts more than 1 year in advance. Relationships between the environmental variables in the GAM and others (such as the North Pacific Index and water column stratification) provided insight into the processes driving production in the Pacific Northwest coastal ocean. Thus, coho may be a bellwether for the coastal environment and models such as ours may apply to populations of other species in this habitat.     

Susceptibility of coho salmon, Oncorhynchus kisutch (Walbaum), to different toxins of Clostridium botulinum

Coho salmon Oncorhynchus kisutch (Walbaum), held at 15°C were tested for their susceptibility to toxins of proteolytic and nonproteolytic Clostridium botulinum types A, B, C₁, C₂, D, E, F, and G administered by the oral and intraperitoneal (i.p.) routes. By the oral route, the fish were most susceptibile to type E neurotoxin, which was lethal at a dose equivalent to 90 mouse intraperitoneal minimum lethal doses (MLDs). The oral lethal dose increased to 2000 MLD for nonproteolytic and proteolytic type F neurotoxins, but the toxin types A, B, and C₁ were not lethal to fish at 2000 MLD and type D was not lethal at 20 000 MLD (highest titre tested). The fish were not susceptible to 200 MLD (the highest titres tested) of type G neurotoxin or C₂ cytotoxin. By the i.p. route, all of the toxins except type G were lethal to coho salmon. Type E neurotoxin was the most toxic at a level of one‐half the mouse MLD. Coho salmon held at temperatures ranging from 1 to 20°C were sensitive to type E neurotoxin by both the oral and i.p. routes. As the temperature decreased the fish became more resistant to type E neurotoxin by the oral route, but the i.p. dose remained one‐half the mouse MLD at all temperatures.     

Prey selectivity and diel feeding chronology of juvenile chinook (Oncorhynchus tshawytscha) and coho (O. kisutch) salmon in the Columbia River plume

We studied salmon feeding selectivity and diel feeding chronology in the Columbia River plume. Juvenile chinook and coho salmon were caught by trawling at 2–3 h intervals throughout a diel period on three consecutive days (21–23 June 2000) at stations located 14.8 and 37 km offshore from the mouth of the Columbia River. A total of 170 chinook salmon were caught at the inshore and 79 chinook and 98 coho salmon were caught at the offshore station. After each trawl, potential prey were sampled at different depths with 2–3 different types of nets (1‐m diameter ring net, bongo net, neuston net). Despite the variability in zooplankton abundance, feeding selectivity was surprisingly constant. Both salmon species fed selectively on larger and pigmented prey such as hyperiid amphipods, larval and juvenile fish, various crab megalopae, and euphausiids. Hyperiid amphipods were abundant in the salmon diets and we hypothesize that aggregations of gelatinous zooplankton may facilitate the capture of commensal hyperiid amphipods. Small copepods and calyptopis and furcilia stages of euphausiids dominated the prey field by numbers, but were virtually absent from salmon diet. Juvenile chinook salmon, with increasing body size, consumed a larger proportion of fish. Stomach fullness peaked during morning hours and reached a minimum at night, suggesting a predominantly diurnal feeding pattern. In general, both chinook and coho salmon appear to be selective, diurnal predators, preying mostly on large and heavily pigmented prey items, in a manner consistent with visually oriented, size‐selective predation.     

Homing of coho salmon (Oncorhynchus kisutch) exposed to morpholine

Smolts of coho salmon (Oncorhynchus kisutch) were exposed to 5 × 10^?5 mg·l^?1 morpholine for 15 days and released into the Salmon River along with an unexposed control group. During the following two autumns, morpholine was introduced into the hatchery's fish ladder on various days and the return of experimental fish was recorded. The returns of morpholine-exposed and control fish were not statistically different. With morpholine present in the fish ladder, control fish were not repelled, and with morpholine absent from the ladder, morpholine-exposed fish returned as readily as control fish.     

Genetic variability in four hatchery strains of coho salmon, Oncorhynchus kisutch (Walbaum), in Chile

Coho salmon, Oncorhynchus kisutch (Walbaum), is intensively cultured in Chile. An increasing proportion of the eggs necessary to sustain the culture are locally produced by some hatcheries. However, there is no information about the origin or the genetic variability in these strains. The present study analysed allozymic variability and its distribution within and between some commercial strains of coho salmon in southern Chile. The genetic variability was estimated using horizontal starch gel electrophoresis. Samples of coho salmon were obtained randomly from four Chilean hatcheries. Twenty‐five enzymatic systems were examined, representing 51 enzymatic loci. Eight loci showed variability in at least one strain, which represented a total polymorphism (P) of 15.7%. Only the PGM‐1* locus was variable in all strains. The remaining loci were fixed in at least one strain. Total heterozygosity (H_T) and within population heterozygosity (H_S) were 0.35% and 0.36% respectively. The index of genetic diversity (G_ST) was 1.5%. The results confirm previous reports of low genetic variability in cultured strains of coho salmon in Chile, below that observed in their native range, which suggests loss of the genetic variability caused by genetic drift or other causes in these strains.