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.     

Coastal sea surface temperature and coho salmon production off the north-west United States

A time series of mean weekly sea surface temperature (SST) images was used to investigate the relationship between fluctuations in the marine survival of hatchery-reared coho salmon and coastal ocean dynamics off the north-western United States (51° to 37°N) between 1985 and 1996, using univariate and nonlinear bivariate regression analysis. Ocean conditions were matched against survival for a number of different annual time frames according to the sum of negative or positive weekly SST anomalies. From the univariate analyses, the sum of negative anomalies from April to June, when the juvenile salmon first enter the ocean, was found to have an R ² of 0.88 against survival with 1991 excluded as an outlier. The bivariate multiple regressions used the sum of negative anomalies from April to June as the first independent variable. When the sums of positive anomalies from the following periods during the fishes' second calendar year in the ocean were each used as the second independent variable, the R ² values were all greater than or equal to 0.92 (with no data points excluded): January to June, February to June, April to June, March to June. These results are discussed within the context of coastal ocean processes. It is concluded that the analysis of SST image time series might allow management to make reasonable forecasts of hatchery-reared coho salmon survival.     

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.     

Temporal and spatial responses of British Columbia steelhead (Oncorhynchus mykiss) populations to ocean climate shifts

The pattern of temporal change in recruitment of steelhead trout ( Oncorhynchus mykiss ) entering the ocean between 1963 and 1990 was geographically coherent in all regions of British Columbia. A major increase in recruitment was evident for smolts entering the ocean after 1977. Subsequently, an out-of-phase response occurred after 1990, indicating that the effect of a possible 1990 regime shift had both temporal and geographical structure. Steelhead entering northern regions had increasing recruitment, while steelhead entering southern BC coastal regions had sharply decreasing recruitment. The evidence clearly indicates that the overall recruitment response since 1977 was primarily shaped by changes in marine (not freshwater) survival. Similar sudden changes in adult recruitment also appear to be occurring for other species of Pacific salmon in BC and Oregon, such as coho ( O. kisutch ), which appear to occur suddenly and show considerable persistence. A possible explanation for the change is that ocean productivity declined in coastal regions of southern BC after 1990, reducing the marine growth of juvenile salmon. The Bakun upwelling index shows a pattern of geographical coherence along the west coast of North America that could in principle explain the observed pattern of changes in recruitment. However, no evidence for a temporal shift in this index occurring around 1977 and 1990 is apparent. The reason for the sudden and persistent decline in ocean survival is therefore uncertain.     

不同光照强度对花鲈幼鱼摄食的影响

研究结果表明,花鲈幼鱼为白昼中照度型鱼类,在10^3-10^0lx范围内,以10^2lx时摄食较好;为准确了解其最适摄食光照强度,进行10^3-10^2lx摄食强度实验,结果为在400lx照度下对蒙古裸腹Sou的摄食强度达最大值。     

The Fraser River plume: some preliminary observations on the distribution of juvenile salmon, herring, and their prey

Zooplankton and fish densities in the southern Strait of Georgia were observed to coincide with variations in surface salinities resulting from the outflow of the Fraser River. Vertical net hauls in the euphotic zone revealed that copepods, amphipods, and euphausiids were significantly more abundant per m³ in the brackish estuarine plume (surface salinities - 10–15 ppt) when compared to the area covered by the freshwater of the Fraser River plume (0–10 ppt) and the region of the Strait of Georgia (25–30 ppt) unaffected by the outflow of the Fraser River.
The estuarine and riverine plumes had significantly higher fish densities (adult and juvenile herring, and juvenile salmonids [excluding chinook]) than the Strait of Georgia region, with no significant differences in densities of juvenile chinook salmon observed between regions. The highest catches of juvenile salmonids were at the boundary between the estuarine plume and the Strait of Georgia. Zooplankton found in the stomach contents of both adult and juvenile herring suggested that the herring were filter-feeding on the zooplankton in the estuarine plume. Juvenile salmonids fed primarily on small unidentifiable juvenile fish. The existence of increased densities of prey items in the estuarine plume is proposed to be the primary mechanism resulting in increased residence time in this region by outmigrating juvenile salmonids. Utilization of aggregated zooplankton could lead to increased salmonid growth rates and therefore to enhanced survival of individuals utilizing the Fraser River plume environment.     

Implications of interannual variability in euphausiid population biology for fish production along the south-west coast of Vancouver Island: a synthesis

This is a synthesis of published and unpublished research on euphausiid and fish populations using the south-west coast of Vancouver Island. Overall, the studies covered 1985–98, when there were two ENSO events and considerable variation in upwelling. The population biology of the dominant euphausiids ( Thysanoessa spinifera , Euphausia pacifica ) was monitored during 1991–98. The species abundance trends differed. Results of simple correlation analyses suggested that variations in temperature, salinity and upwelling do not explain variations in the abundance of larval or adult euphausiids, or in the abundance of portions of euphausiid populations on which fish feed. I found significant interannual variations in daily ration of the dominant planktivorous fish species, but euphausiids remained the most important prey. Pacific hake ( Merluccius productus ), the dominant planktivore, fed on larger (>17 mm) T. spinifera , even though the biomass of this part of the euphausiid biomass decreased by 75% between 1991 and 1997, but Pacific herring ( Clupea pallasi ) may have begun feeding on smaller E. pacifica . Therefore, any study of the relationship between fish production and krill biology must consider that part of the euphausiid biomass exploited by fish. In addition, some fish species and/or life history stages appeared to adapt to changes in euphausiid availability, while others did not. Such variation in adaptations also has to be described and considered to understand how changes in euphausiid biology affect fish productivity.     

Feeding habits of skipjack tuna Katsuwonus pelamis and other tuna Thunnus spp. juveniles in the tropical western Pacific

ABSTRACT: The feeding habits of skipjack tuna Katsuwonus pelamis juveniles (8.5–66.8 mm standard length) were examined, collected from the tropical western Pacific in October to December 1994, and their habits were compared with those of the other tuna Thunnus spp. juveniles (9.8–55.3 mm standard length). The indices, frequency of occurrence of each food item in the total number of stomachs examined (% F ), percentage of number of each food item to the total number of all food items identified (% N ), percentage of wet weight of each food item to the total wet weight of all food items identified (% W ), and relative importance of each food item ( IRI ) were estimated in the north equatorial current (NEC) and the north equatorial countercurrent (NECC) areas. The most dominant prey item of skipjack juveniles in the two areas was fish larvae. Other major prey items in the NEC area were Euphausiacea, Amphipoda, and Copepoda; whereas those in the NECC area were Copepoda, Cephalopoda, Euphausiacea, and Amphipoda. In the other tuna juveniles, the IRI of fish larvae in the two areas was remarkably high. Other prey, Euphausiacea and Cephalopoda in the NEC area only and Cephalopoda in the NECC area, were also found. These results indicate that the skipjack juvenile is primarily a piscivorous feeder although they also depend on various other prey organisms, whereas the other tuna juveniles are stronger piscivorous feeders.     

光照强度对暗纹东方鲀稚鱼摄食的影响

在0～1000lx光照范围内,对不同光照强度下暗纹东方鲀稚鱼摄食量进行了测定,稚鱼在500lx时摄食强度最大,其次为300、700lx,摄食率在500lx时最高,并在5min时达到最大值,40～60min时段摄食效率最低接近停食。     

Prey‐type‐dependent foraging of young‐of‐the‐year fish in turbid and humic environments

Abstract – Fish, which are generally visual foragers, experiences reduced reaction distance in visually degraded environments, which has consequences for encounter rates with prey. Small prey is detected at shorter distances than larger prey, and piscivores are therefore predicted to be more strongly affected by visual degradation. In experiments, roach (Rutilus rutilus) were fed two plankton prey types and pike (Esox lucius) were fed Daphnia and larval roach, in clear water, algal turbid water and water coloured brown by dissolved organic matter (DOM). Planktivorous foraging in roach was not affected by visual degradation, while pike foraging on both Daphnia and larval roach was. Pike showed increased reaction distance to Daphnia in visually degraded water, while it was severely reduced with roach as prey even if the visual range was not reduced below pike reaction distances in clear water. Pike foraging on Daphnia was not affected, but when foraging on roach, the reduced search efficiency was counteracted by increased attack rates. However, there was no increase in movement and no difference between turbid and DOM treatments. Effects on piscivores will likely become more pronounced at later life stages as prey size and the reliance on long‐distance detection increases at the same time as changing climatic conditions may further deteriorate the visual conditions in future.