bluuebunny/crossref_metadata_2025 huggingface dataset:
Predicting the effects of rainbow smelt on native fishes in small lakes: evidence from long-term research on two lakes
Authors: Hrabik Thomas R , Magnuson John J , McLain Ann S
Published: April 2011

We assessed predictability of negative interactions between native fishes and exotic rainbow smelt (Osmerus mordax) through field experiments and long-term data analysis for two lakes in Wisconsin. Predictions were made based on thermal preferences, diet characteristics, and published accounts of interactions between smelt and yellow perch (Perca flavescens) and smelt and cisco (Coregonus artedii). Our results indicate predation is the most likely cause for the extirpation of cisco from Sparkling Lake in 1990. In Crystal Lake, native yellow perch experienced significant overlap in distribution and diet with smelt. The condition of adult perch was negatively correlated with smelt abundance indicating competition was occurring. Smelt feed on a wide size range of prey items making this species a threat to native fishes, especially when spatial overlap is high. Information on spatial and temporal overlap and diet enable useful predictions about the effect of smelt invasions on native fishes.
Stable carbon isotope variations in otoliths of Atlantic cod (Gadus morhua)
Authors: Schwarcz H P , Gao Y , Campana S , Browne D , Knyf M , Brand U
Published: April 2011

Stable carbon isotope ratios (13C) were measured in annual layers of otoliths of Atlantic cod (Gadus morhua) from the northeastern Scotian Shelf, Atlantic Canada. Layers deposited during the first 4-6 years of otolith growth increased in 13C from minimum values between -5 and -2.5 to a maximum near 0. This pattern of increase was independent of the years in which the fish was collected. Layers formed after reaching the maximum 13C value displayed decreasing or nearly constant isotopic ratios. Early rise in 13C may be a combined result of (i) decrease in the fraction of metabolic oxidized carbon in the fishes' blood as they mature, relative to the proportion of seawater-derived carbon, and (ii) dietary shift to higher trophic-level foods with higher 13C values. Age of maximum in 13C may be indicative of age of maturity of cod. The maximum 13C value attained by otoliths decreased steadily between 1983 and 1993, while cod stocks in Atlantic Canada were declining. Drop in age of attainment of maximum 13C between 1984 and 1985 coincides with changes in population dynamics of the 4Vs stock. This decrease, as well as the post maximum decrease in 13C values of the mature cod otoliths may represent movement of the fish to deeper waters of the shelf, where 13C of dissolved inorganic carbon is lower.
Is spawner biomass a sensitive measure of the reproductive and recruitment potential of Northeast Arctic cod?
Authors: Marshall C Tara , Kjesbu Olav Sigurd , Yaragina Nathalia A , Solemdal Per , Ulltang Øyvind
Published: April 2011

The assumption that spawner biomass is directly proportional to total egg production by fish stocks underlies most spawner-recruit relationships. Despite its importance, this assumption is largely untested. Data describing the reproductive potential of Northeast Arctic (NEA) Atlantic cod (Gadus morhua) were used to test the proportionality assumption for a period showing strong variation in condition and abundance of spawners. At the individual scale, relative fecundity varied with length and condition. This decreases the likelihood that the proportionality assumption is valid. At the stock level, total egg production was estimated (1985-1996) using acoustic estimates of total abundance and demographic information from trawl sampling in combination with year-specific fecundity-length relationships. For NEA cod, spawner biomass estimated by virtual population analysis (VPA) was not proportional to total egg production. Compared with VPA-based estimates of spawner biomass, total egg production is an improved index of recruitment potential because (i) the magnitude of variation observed in total egg production was closer to that observed in recruitment and (ii) the relationship between recruitment at age 1 and total egg production approaches the origin. The results suggest that further progress in explaining recruitment variation will be achieved using more sensitive measures of the true reproductive potential of the stock.
DNA and allozyme markers provide concordant estimates of population differentiation: analyses of U.S. and Canadian populations of Yukon River fall-run chum salmon (Oncorhynchus keta)
Authors: Scribner Kim T , Crane Penelope A , Spearman William J , Seeb Lisa W
Published: April 2011

Although the number of genetic markers available for fisheries research has steadily increased in recent years, there is limited information on their relative utility. In this study, we compared the preformance of different "classes" of genetic markers (mitochondrial DNA (mtDNA), nuclear DNA (nDNA), and allozymes) in terms of estimating levels and partitioning of genetic variation and of the relative accuracy and precision in estimating population allocations to mixed-stock fisheries. Individuals from eight populations of fall-run chum salmon (Oncorhynchus keta) from the Yukon River in Alaska and Canada were assayed at 25 loci. Significant differences in mitochondrial haplotype and nuclear allele frequencies were observed among five drainages. Populations from the U.S.-Canada border region were not clearly distinguishable based on multilocus allele frequencies. Although estimates of total genetic diversities were higher for the DNA loci (Ht= 0.592 and h = 0.647 for nDNA and mtDNA, respectively) compared with protein allozymes (Ht= 0.250), estimates of the extent of population differentiation were highly concordant across marker classes (mean theta = 0.010, 0.011, and 0.016 for allozymes, nDNA, and mtDNA, respectively). Simulations of mixed-stock fisheries composed of varying contributions of U.S. and Canadian populations revealed a consistent bias for overallocation of Canadian stocks when expected Canadian contributions varied from 0 to 40%, due primarily to misallocations among genetically similar border populations. No single marker class is superior for differentiating populations of this species at the spatial scale examined.
Ammonium and phosphate retention in a Mediterranean stream: hydrological versus temperature control
Authors: Butturini Andrea , Sabater Francesc
Published: April 2011

The role of discharge and temperature changes in controlling the ammonium (NH4-N) and phosphate (PO4-P) uptake length (Sw) was studied for 9 months in a second-order stream affected by riparian tree logging in northern Spain. Over the study period, PO4-P Sw values ranged from 110 to 2793 m, and NH4-N Sw ranged from 67.5 to 693 m. Changes in discharge (for PO4-P) and discharge plus temperature (for NH4-N) explained about 98% of the variance in nutrient retention efficiency. Before logging, NH4-N and PO4-P Sw did not show any seasonal trend, and discharge explained only 31 and 37% of total variance, respectively. After logging, NH4-N and PO4-P retention efficiency was lower than before logging when discharge increased above the basal level (46 L·s-1). The results suggest that riparian trees and associated detrital compartments may buffer the influence of seasonal changes in discharge and physical conditions on the ability of the stream to retain nutrients. Results from the intersite comparison of nutrient Sw compiled from the literature indicate that PO4-P retention has a good fit with a hydrodynamic model that states that Sw increases approximately as a square root of discharge. This suggests a strong link between PO4-P Sw and processes related to discharge. On the other hand, NH4-N Sw does not fit well with this model, suggesting that NH4-N Sw is less sensitive to discharge changes and that other mechanisms (such as biotic processes linked with seasonal variation, or abiotic adsorption) may explain the NH4-N Sw results.
Temperature mediation of competitive interactions among three fish species that replace each other along longitudinal stream gradients
Authors: Taniguchi Yoshinori , Rahel Frank J , Novinger Douglas C , Gerow Kenneth G
Published: April 2011

Competitive ability changed across a range of 3-26°C among three fish species that show longitudinal replacement in Rocky Mountain streams: brook trout (Salvelinus fontinalis) at high elevations, brown trout (Salmo trutta) at middle elevations, and creek chub (Semotilus atromaculatus) at low elevations. Competitive ability was measured by food consumption and aggression in a stream tank. At 20°C, the trout species were competitively equal, and both were competitively superior to creek chub. Creek chub began to have competitive success against brook trout at 22°C and brown trout at 24°C, temperatures stressful but not lethal for the trout. Creek chub became competitively dominant over brook trout at 24°C and brown trout at 26°C, temperatures lethal to a portion of each trout species. We examined whether reduced food consumption was due to appetite loss or the presence of other species. For brook trout, interactions influenced feeding behavior at 22°C, but appetite loss became important at 24°C. For brown trout, interactions influenced feeding behavior at 24°C, but appetite loss became important at 26°C. For creek chub, there was an interaction between behavioral interactions and appetite in determining food consumption. Field data support a transition from trout to non-trout fishes at 22-25°C.
Comparison, using minisatellite DNA profiling, of secondary male contribution in the fertilisation of wild and ranched Atlantic salmon (Salmo salar) ova
Authors: Thompson C E , Poole W R , Matthews M A , Ferguson A
Published: April 2011

Secondary males, either subdominant adults or, more usually, parr which mature in freshwater, are known to successfully fertilise Atlantic salmon (Salmo salar) ova. This study has estimated the reproductive success of such secondary males in redds formed by pairs of wild and sea-ranched adults. Eight wild and 11 ranched redds were sampled from the Burrishoole system, western Ireland, in two consecutive years. Representative samples of fertilised ova were screened at three minisatellite loci to reconstruct the genotypes of putative anadromous parents and to estimate the proportion of eggs fertilised by secondary males. Multiple paternal genotypes were detected in 18 of the 19 samples, and of the 1484 progeny examined, 593 could not have been derived from the primary adult male genotype. The level of secondary male contribution detected among wild redds from Burrishoole (mean 28.9%) was similar to that found in previous published studies. The level among ranched redds was significantly higher (mean 48.2%) (P = 0.042). The difference was greater when data from 1995 were considered alone, with the average level of secondary male contribution in ranched redds being almost twice that in wild redds. Minimum numbers of secondary males were not significantly different between wild (mean 2.6) and ranched (mean 2.7) redds.
Respiratory metabolism and swimming performance in growth hormone transgenic Atlantic salmon
Authors: Stevens E Don , Sutterlin Arnold , Cook Todd
Published: April 2011

We show that growth hormone enhanced transgenic salmon have a higher oxygen uptake during routine culture conditions and during forced swimming activity relative to similarly sized control fish. They also have a slightly higher critical oxygen level that limits oxygen uptake. However, they do not differ in regards to critical swimming speed. Growth hormone transgenic Atlantic salmon, Salmo salar, at 12-13°C were an F2 generation using eggs from a transgenic F1 female and milt from a nontransgenic male. They grew two to three times faster than control fish throughout the study period. Under routine culture conditions, both transgenic and control fish exhibited a diurnal cycle in oxygen uptake. However, oxygen uptake of transgenic fish was 1.7 times that of control fish at all times of the day. Oxygen uptake was independent of oxygen concentration above 10 mg/L in both groups of fish; critical oxygen uptake level was 6 mg/L in transgenic fish and 4 mg/L in control fish. During the oxygen decrease, transgenic fish and control fish lost equilibrium at the same low oxygen concentration levels. In the swim tunnel, oxygen uptake of transgenic fish was 1.6 times that of control fish at all swimming speeds. Critical swimming speeds did not differ between transgenic and control fish and were similar to literature values for salmonids.
Molecular evidence from short interspersed elements (SINEs) that Oncorhynchus masou (cherry salmon) is monophyletic
Authors: Murata Shigenori , Takasaki Nobuyoshi , Okazaki Toshio , Kobayashi Takanori , Numachi Ken-ichi , Chang Kun-Hsing , Okada Norihiro
Published: April 2011

The genome of salmonid species contains numerous short interspersed repetitive elements (SINEs), which are known as members of the Hpa I family of SINEs. We have isolated and characterized eight loci at which Hpa I SINEs have been inserted in a species-specific manner in the genome of Oncorhynchus masou (cherry salmon). All of these SINE units were fixed in each of the local populations examined. This observation suggests that the SINE insertion events must have occurred in the genome of the single ancestral species of all the subspecies of O. masou and that the SINEs must have spread throughout the various populations before the divergence of subspecies. This provides unequivocal evidence that O. masou is monophyletic. These species-specific SINE units provide a very convenient and reliable tool for identification of O. masou by the polymerase chain reaction.
Spatial and temporal factors affecting survival in coho salmon (Oncorhynchus kisutch) in the Pacific Northwest
Authors: Coronado Claribel , Hilborn Ray
Published: April 2011

Survival rates for coho salmon (Oncorhynchus kisutch) were estimated for all coded wire tag release groups in the Pacific Northwest between 1971 and 1990. The spatial and temporal patterns show considerable geographic variation, with most regions south of northern British Columbia showing declining survival since 1983, while northern areas have shown increasing survival during that period. The number of years of operation explained very little of the variation in survival, and many hatcheries showed major increases in survival after several years of operation. Survival of marked wild fish generally showed the same trend as hatchery fish. We conclude that the dominant factor affecting coho salmon survival since the 1970s is ocean conditions and that there are major geographic differences in the pattern of ocean conditions. The decline in survival seen in British Columbia and south over the last decade suggests that a major reduction in exploitation rates is necessary to maintain the populations.
Response of juvenile coho salmon (Oncorhynchus kisutch) and steelhead (Oncorhynchus mykiss) to the addition of salmon carcasses to two streams in southwestern Washington, U.S.A.
Authors: Bilby Robert E , Fransen Brian R , Bisson Peter A , Walter Jason K
Published: April 2011

Availability of organic matter and nutrients transported from the marine environment to streams by spawning salmon was increased in two small streams in southwestern Washington, U.S.A., by adding salmon carcasses from a nearby hatchery. Response of juvenile coho salmon (Oncorhynchus kisutch) and steelhead (Oncorhynchus mykiss) rearing at these sites was compared with nearby streams where few salmon spawned. Densities of age 0+ coho salmon and age 0+ and age 1+ steelhead increased following carcass additions to the treated streams. A similar increase in density was not observed at the reference sites. Condition factors in treated streams increased following carcass addition and remained at high levels while carcasses were present whereas no similar pattern was observed at the reference sites. Stomach contents of fish in streams to which carcasses had been added consisted primarily of salmon eggs and carcass flesh when carcasses were present in the stream. Stable isotope analysis indicated that the proportion of marine-derived nitrogen in the muscle tissue of juvenile salmonids increased as much as 39% following carcass placement. Results suggest that eggs and carcasses of adult salmon provide a very important resource during a period when other food items are often scarce.
Synergistic effects of nutrient loading and omnivorous fish on phytoplankton biomass
Authors: Drenner Ray W , Gallo Kirsten L , Baca Robert M , Smith J Durward
Published: April 2011

To examine how nutrient loading interacts with omnivorous fish to regulate the biomass of phytoplankton of lakes, we conducted a 1-month summer mesocosm experiment and a 1.5-year pond experiment. For the mesocosm experiment, we used a 2 × 2 × 2 factorial design in which two levels of nutrient loading were cross-classified with two levels of omnivorous fish and two levels of clay. We found a significant nutrient-fish interaction effect for chlorophyll biomass with the effects of fish being greater in the presence of nutrient loading. Clay did not affect the nutrient-fish interaction effect for chlorophyll. In the pond experiment, we used a 2 × 2 factorial design in which two levels of nutrient loading were cross-classified with two levels of omnivorous fish. We did not detect a significant nutrient-fish interaction effect for chlorophyll except at the end of the second summer of the experiment when the biomass of omnivorous fish was high and the cumulative effects of nutrient loading were greatest. Chlorophyll was suppressed by dense populations of Eurasian watermilfoil (Myriophyllum spicatum), which developed in some ponds during the experiment. The role of the nutrient-fish synergism in regulating phytoplankton biomass may be reduced in lakes with Eurasian watermilfoil.
Effects of habitat isolation on the recovery of fish assemblages in experimentally defaunated stream pools in Arkansas
Authors: Lonzarich David George , Warren, Jr. Melvin L , Lonzarich Mary Ruth Elger
Published: April 2011

We removed fish from pools in two Arkansas streams to determine recolonization rates and the effects of isolation (i.e., riffle length, riffle depth, distance to large source pools, and location), pool area, and assemblage size on recovery. To determine pool-specific recovery rates, we repeatedly snorkeled 12 pools over a 40-day recovery period. Results indicated the effects of isolation on percent numerical recovery, but no effects of pool area or assemblage size. Numerical recovery of assemblages in pools separated from neighboring pools by short riffles occurred by day 30 whereas more isolated pools had not reached 70% numerical recovery by day 40. Recovery also was more rapid in downstream pools and in pools that were closer to large source pools. Finally, recovery patterns differed among species and size-classes, with large fish (<100 mm total length) recolonizing pools more rapidly than small fish. This is the first study to quantify species- and assemblage-level recolonization rates at the scale of individual pools and the effects of isolation on recovery. The findings of this study have potentially important implications for research aimed at understanding the ecology of stream fishes and predicting the consequences of land-use activities.
Influence of settlement time and size on postsettlement growth in the American lobster (Homarus americanus)
Authors: James-Pirri Mary-Jane , Cobb J Stanley , Wahle Richard A
Published: April 2011

We investigated the size and timing of settlement of postlarval (fourth instar) American lobster (Homarus americanus) and the size attained by the end of the first growing season. Mean size and duration of benthic instars (IV-XI) were obtained from a field growth experiment. Lobsters settling in early- and mid-season were larger at each instar and had different growth profiles than late-season settlers. In particular, the rate of growth at the fifth and sixth instar transition was greater for early- and mid-season settlers than for late-season settlers. Postlarvae settling early reached the ninth instar sooner than mid- or late-season settlers. Estimates of size and intermolt duration of each instar for early- and late-season postlarvae were applied to planktonic postlarval data (1988-1995) to estimate growth trajectories during the first year. For all years, postlarvae present early in the season were 30-50% larger (carapace length) and two or three instars further developed than late settlers by the end of the growing season. Estimates of size attained by the end of the 1994 growing season matched field-collected benthic size frequency data for this same year. Although initial carapace length at settlement was important, the timing of settlement was more influential on the size attained by the end of the first growing season.
Estimators of stream residence time of Pacific salmon (Oncorhynchus spp.) based on release-recapture data
Authors: Lady James M , Skalski John R
Published: April 2011

The area-under-the-curve method is a widely used method for estimating salmon escapement. The method depends on obtaining an accurate estimate of stream residence time, or stream life. This paper develops two estimators of stream residence time based on release-recapture data: a nonparametric estimator and a parametric estimator. Monte Carlo simulations showed that with an adequate release size and number of sampling occasions, both estimators provide precise estimates of stream residence time. If there is significant right censoring, however, the parametric estimator is significantly less biased. If the data are too sparse, the parametric estimator performs poorly and often fails. The stream residence time of spawning sockeye salmon (Oncorhynchus nerka) in Iliamna Lake, Alaska, was estimated using the estimators developed here. Because the estimators also provide the variance of the estimates, the precision of the stream residence time estimate could be assessed, and we were able to test and reject the hypothesis that the stream residence time for females is equal to that of males. Both estimators are applicable to estimating the life expectancy of any fish or wildlife population with release-recapture techniques.
Larval Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) growth on Georges Bank: a model with temperature, prey size, and turbulence forcing
Authors: Leising Andrew W , Franks Peter JS
Published: April 2011

Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) on Georges Bank are subjected to a high degree of variability in temperature, turbulence, and prey densities, depending on when they are spawned and where they are advected. We have developed an individual-based model that includes the effect of varying prey density, turbulence, and temperature. Temperature effects were included by using a Q10-type adjustment to the standard metabolic rate as well as a second temperature-dependent term added to the overall ingestion ability of our model fish, a function of the swimming speed, capture efficiency, and "liveliness" of a fish. Three cases were analyzed: (i) constant food and temperature conditions, (ii) variable temperature cycles, and (iii) variable temperature cycles plus turbulence. We found that prey density, turbulence, and temperature ranges typical of the peak spawning season are variable enough to be limiting to larval growth. The timing and location of spawning are crucial to the survival of the larvae. Increasing the average temperature cycle by 1°C, as might occur due to climatological change or interannual variability, increased growth for larvae that were not growing well previously. The increased temperature failed to increase larval growth in areas where larvae were already growing at rates close to their maximum.
Bayesian stock assessment using a state–space implementation of the delay difference model
Authors: Meyer Renate , Millar Russell B
Published: April 2011

This paper presents a Bayesian approach to fisheries stock assessment using the delay difference model to describe nonlinear population dynamics. Given a time series of annual catch and effort data, models in the Deriso-Schnute family predict exploitable biomass in the following year from biomass in the current and previous year and from past spawning stock. A state-space model is used, as it allows incorporation of random errors in both the biomass dynamics equations and the observations. Because the biomass dynamics are nonlinear, the common Kalman filter is generally not applicable for parameter estimation. However, it is demonstrated that the Bayesian approach can handle any form of nonlinear relationship in the state and observation equations as well as realistic distributional assumptions. Difficulties with posterior calculations are overcome by the Gibbs sampler in conjunction with the adaptive rejection Metropolis sampling algorithm.
Assessing water quality changes in the lakes of the northeastern United States using sediment diatoms
Authors: Dixit Sushil S , Smol John P , Charles Donald F , Hughes Robert M , Paulsen Steven G , Collins Gary B
Published: April 2011

Diatom assemblages were selected as indicators of lake condition and to assess historical lake water quality changes in 257 lakes in the northeastern United States. The "top" (surface sediments, present-day) and "bottom" (generally from >30 cm deep, representing historical conditions) samples from sediment cores collected from lakes and reservoirs were analyzed for diatom assemblages. The distribution of diatom species was closely related to several environmental variables, primarily lake water pH, total phosphorus, and chloride. Using weighted-averaging calibration and regression approaches, we constructed predictive models to infer these variables from the diatom assemblages. The diatom-based inference models were then used to assess the current status of lake water quality and to assess historical changes in lake water conditions in natural lakes over the past 150 years. Changes were also assessed in reservoirs. Population estimates of historical changes in limnological variables were made for all lakes of the northeast United States and also for lakes in the Adirondacks, New England Uplands, and Coastal Lowlands/Plateau ecoregions. The extent of cultural impact has been quite variable among the ecoregions, with marked water quality deterioration occurring in hundreds of lakes. Chloride and phosphorus levels have increased, especially in lakes that currently have high concentrations. Low-pH lakes have become more common in all three ecoregions. The maximum abundance of low-pH lakes was recorded in the Adirondacks, an area receiving the highest acidic precipitation in the northeast. In the Coastal Lowlands/Plateau, there has been a clear increase in eutrophic lakes, as inferred by total phosphorus. This was accompanied by a marked increase in the number of lakes with high chloride levels.
Reduced chlorophyll to phosphorus ratios in nearshore Great Lakes waters coincide with the establishment of dreissenid mussels
Authors: Nicholls K H , Hopkins G J , Standke S J
Published: April 2011

The establishment of zebra and quagga mussels (Dreissena spp.) in the Great Lakes has coincided with dramatic decreases in chlorophyll a to total phosphorus (Chl/TP) ratios in nearshore waters of Lake Erie, western Lake Ontario, and the Detroit River, but not in Lake Superior, southern Lake Huron, central and eastern Lake Ontario, or the upper St. Lawrence River. May-October average Chl/TP ratios in samples collected weekly (1976-1995) from five Lake Erie municipal water supply intakes were two to six times higher during the pre-Dreissena time period than during the post-Dreissena period. The pre-Dreissena logarithmically transformed Chl and TP data (May-October averages at all Great Lakes sampling locations) were highly correlated, with 75% of the log-transformed Chl variance explained by log-transformed TP. The post-Dreissena regression of May-October average Chl on TP was statistically significant, but only 14% of the variance in the Chl data could be explained by TP. We suggest that this has important implications for Great Lakes basin P management because changes in lake water TP resulting from further changes in TP loading will (post-Dreissena) have far less impact on Great Lakes phytoplankton growth potential than during pre-Dreissena times.
Effect of maturation on parr growth and smolt recruitment of Atlantic salmon
Authors: Whalen Kevin G , Parrish Donna L
Published: April 2011

We determined the effect of maturation on parr growth and smolt recruitment of Atlantic salmon (Salmo salar) stocked in Vermont tributaries of the Connecticut River. Both among and within tributaries, mature parr ranged between 28 and 52% of the age-1 parr collected and up to 67% of the age-2 parr collected. Percent age-1 parr maturing in October-November was positively related to mean length the preceding June. In October-November, immature age-1 parr were greater in mean length than age-1 mature parr. Data from parr individually tagged in June and recaptured in October showed immature parr exhibited twofold greater individual growth than maturing parr. Smolt recruitment was highly dependent upon state of maturity the preceding fall; fewer individuals that matured as parr recruited to smolt compared with parr remaining immature. Our study shows, over a broad spatial scale, that variation in incidence of maturation is largely explained by parr size among tributaries and river reaches and, furthermore, empirically demonstrates a direct negative effect of maturation on parr growth and recruitment to smolt. Thus, parr maturation is an important consideration for the enhancement and (or) restoration of Atlantic salmon populations via stream stocking programs.
An otolith-based back-calculation method to account for time-varying growth rate in rainbow smelt (Osmerus mordax) larvae
Authors: Sirois Pascal , Lecomte Frédéric , Dodson Julian J
Published: April 2011

This study develops a new back-calculation method, based on the larvae of rainbow smelt (Osmerus mordax), that takes into account the variation of growth rate over time. Known-aged larvae were reared in four 60-L microcosms during 49 days in order to obtain a large range of individual growth trajectories. We first validated the daily nature of the otolith increment deposition rate. The proposed time-varying growth (TVG) method weights the contribution of each increment in the length calculation using a growth effect factor. A small growth increment contributes less to the length increase of larvae than its relative importance in total otolith growth. On the other hand, a large growth increment contributes more to the length increase of larvae in comparison with its relative importance in total otolith growth. This method provided significantly better estimates of previous length-at-age than the biological intercept (BI) method at the individual level. In addition, the TVG method tended to provide more accurate estimates of previous length-at-age than the BI method at the population level, but the difference was not significant. The importance of using the TVG method instead of the BI method to back-calculate individual and population growth trajectories increases with the magnitude of the growth effect and the variation in growth rates over time.
Histopathology of adult Pacific herring in Prince William Sound, Alaska, after the Exxon Valdez oil spill
Authors: Marty Gary D , Okihiro Mark S , Brown Evelyn D , Hanes David , Hinton David E
Published: April 2011

Pacific herring (Clupea pallasi) sampled from oiled sites in Prince William Sound, Alaska, U.S.A., 3 weeks after the 1989 Exxon Valdez oil spill had multifocal hepatic necrosis and significantly increased tissue concentrations of polynuclear aromatic hydrocarbons (PAH). By comparison, Pacific herring from reference sites in 1989 and from all sites in 1990 and 1991 did not have hepatic necrosis or increased PAH concentrations. Adult Pacific herring were sampled for histopathology of liver, spleen, and kidney from oiled and reference sites in April (1989 and 1991) and October (1990 and 1991). Increased scores for macrophage aggregates contributed to significant differences in 1990, but these differences probably resulted from sampling older fish from the oiled site. Naphthalenes were the predominant PAH in all tissue samples. The development of hepatic necrosis and the predominance of naphthalenes in samples from 1989 is consistent with recent laboratory study in which crude oil exposure resulted in dose-dependent expression of viral hemorrhagic septicemia virus (VHSV). We conclude that Pacific herring were exposed to Exxon Valdez oil in 1989 and that development of hepatic necrosis in exposed fish probably was a result of VHSV expression.
Interactions between individual feeding behaviour, growth, and swimming performance in juvenile rainbow trout (Oncorhynchus mykiss) fed different rations
Authors: Gregory T Ryan , Wood Chris M
Published: April 2011

Aerobic swimming performance (critical swimming speed, Ucrit), food consumption per meal (by X-ray radiography), specific growth rate (SGR), haematocrit, and fin condition were monitored in individual juvenile rainbow trout (Oncorhynchus mykiss). The fish were held in groups over a 9-week period and fed daily group rations (dry food) of 2.0, 1.5, 1.0, and 0.5% wet body mass (BM)·day-1. SGR declined and competition increased at lower ration levels, as reflected by greater fin damage, reduced haematocrits and condition factors, and, at 0.5% BM·day-1, a substantial increase in the coefficient of variation among individual meals. Absolute Ucrit also declined at lower ration levels. However, there was no relationship between Ucrit and haematocrit, fin damage, or condition factor in any of the ration groups. A negative correlation was found between Ucrit and SGR in individual trout fed a group ration of 2.0% BM·day-1, but a positive correlation was seen at 0.5% BM·day-1 and no relationship at 1.0 and 1.5% BM·day-1. There was a positive relationship between individual SGR and food consumption only among fish fed a ration of 2.0% BM·day-1. A significant negative relationship between Ucrit and individual food consumption was also found among fish in this ration group.
Is solar radiation responsible for declines in marine survival rates of anadromous salmonids that rear in small streams?
Authors: Walters Carl , Ward Bruce
Published: April 2011

There have been profound declines in marine survival rates of steelhead trout (Oncorhynchus mykiss), coho salmon (O. kisutch), chinook salmon (O. tschawytscha), and Atlantic salmon (Salmo salar) since the mid-1980s, and these declines have been particularly acute in sunny regions. We suggest that the problem may originate in freshwater with radiation (e.g., UV-B) damage to metabolic machinery that is expressed during stressful periods of smolting and ocean entry and that progressively worse damage may soon appear as reduction in freshwater survivals as well. This hypothesis can be tested quickly by management agencies by comparing survival rates of hatchery-reared fish with and without radiation protection during rearing.
Changes in subcellular metal partitioning in the gills of freshwater bivalves (Pyganodon grandis) living along an environmental cadmium gradient
Authors: Wang Dacheng , Couillard Yves , Campbell G C , Jolicoeur Pierre
Published: April 2011

To test the response of the freshwater bivalve Pyganodon grandis to increased metal exposure in the field, specimens were collected from 10 lakes located along a known metal gradient in a mining area in northwestern Québec. Total gill concentrations of metallothionein (MT) were determined by the 203Hg saturation method for molluscs from each lake, and the distribution of Cd among various cytosolic ligands, including MT, was determined by size-exclusion chromatography. Gill MT concentrations responded to environmental exposure to Cd but not to Cu or Zn exposure; these spatial variations along the Cd gradient were more important than the seasonal summer variations in gill MT concentrations. Bivalves exposed to concentrations of dissolved free Cd2+ higher than ~1 nM in the external medium exhibited a marked increase of Cd in the low relative molecular mass ligand pool. Symptoms of toxic effects at different levels of biological organization were associated with this biochemical anomaly.
Infection with low numbers of the sea louse Lepeophtheirus salmonis induces stress-related effects in postsmolt Atlantic salmon (Salmo salar)
Authors: Nolan D T , Reilly P , Bonga SE Wendelaar
Published: April 2011

Infection of postsmolt Atlantic salmon (Salmo salar) with three, six, or 10 preadult and adult sea lice (Lepeophtheirus salmonis) per fish resulted in changes to epithelial structure and at sites in the skin and gill, distant from lice attachment and feeding. In the skin, increased apoptosis and necrosis occurred in the superficial epithelial cells and numbers of mucous cells decreased. In the gill, where no lice were found, uplifting of the epithelium, intercellular swelling, and infiltration by leukocytes occurred in filaments and lamellae. High cell turnover of chloride cells was associated with significantly elevated gill Na+/K+-ATPase activities. Serum chloride levels were elevated in the 3 and 6 lice/fish groups, and the serum Na to Cl ratio was lower in all parasitized groups at 5 days. The results indicate that infection with low numbers of the preadult and adult parasite induced changes characteristic of a stress response. In the low- and medium-infested groups, homeostatic recovery had occurred by 10 days, but recovery was incomplete in the highly infected group. Thus, 10 lice per fish, which is a low infestation level in nature, is stressful and creates a long period during which the overall condition of the skin and gill epithelia may render the fish susceptible to secondary infections.
Using 137Cs to measure and compare bioenergetic budgets of juvenile Atlantic salmon (Salmo salar) and brook trout (Salvelinus fontinalis) in the field
Authors: Tucker S , Rasmussen J B
Published: April 2011

Through the 137Cs mass balance method, annual consumption rates were estimated for juvenile Atlantic salmon (Salmo salar) parr and precocious males as well as for brook trout (Salvelinus fontinalis) at four sites in the Ste-Marguerite River system, Québec. With explicit age analysis, consumption rates and growth rates were derived on an individual fish and age-class basis. These represent the first consumption estimates for Atlantic salmon in the wild. Precocious males had consumption rates 1.5 times greater than nonmaturing parr, while Atlantic salmon parr consumption rates were 2.7 times greater than brook trout. There was a strong positive relationship between individual annual consumption and growth rates for Atlantic salmon and brook trout at all sites. Subsequently the concept of field maintenance ration was introduced as the intercept of consumption over growth. Maintenance rations for Atlantic salmon parr ranged from 0.010 to 0.016 g·g-1·day-1 between sites. Brook trout had maintenance rations approximately half those of Atlantic salmon at 0.0059 g·g-1·day-1. Precocious male growth efficiencies were half those of nonmaturing parr despite higher feeding and growth rates. Brook trout growth efficiencies were significantly greater than those of Atlantic salmon parr. The lower growth efficiencies observed for Atlantic salmon are likely due to increased metabolic costs associated with higher activity. On average, Atlantic salmon parr spent 2.4-fold more energy in activity than brook trout. Atlantic salmon precocious males spent 1.7 times more energy in activity than parr.
Effects of salmon carcass decomposition on biofilm growth and wood decomposition
Authors: Wold Amy K. Fisher , Hershey Anne E
Published: April 2011

Salmon carcasses from spawning migrations can be retained in stream ecosystems behind woody debris, boulders, and other substrata where they contribute nutrients and organic matter to the stream biota. We hypothesized that carcasses would enhance algal and microbial growth and wood decomposition. To test this, we placed wood and clay pot substrata directly downstream of decomposing salmon in the Little Knife River, Minn., U.S.A., and compared total biofilm biomass on substrata in the vicinity of decomposing salmon and upstream of salmon carcasses. After 335 days in the stream, there was a significant mass loss of wood but no apparent effect of carcass decomposition on wood mass loss. Significantly, more chlorophyll a was found on both wood and pots when carcasses were present (p < 0.05) compared with controls. Stable isotope analyses suggest that the fish-derived nitrogen was taken up by the periphyton and total biofilm. Biofilm on the pots and wood near fish showed a significant increase in ash-free dry mass (p < 0.05). We conclude that fish-derived nutrients enhanced algal and total biofilm growth but did not significantly influence wood decomposition.
Resource partitioning along three niche dimensions in a size-structured tropical fish assemblage
Authors: Piet G J , Pet J S , Guruge WAHP , Vijverberg J , Van Densen WLT
Published: April 2011

In Tissawewa, a tropical reservoir, the size-specific resource use of the 10 most important fish species was determined along three dimensions: trophic, spatial, and temporal. During this study, a drought occurred distinguishing two periods before and after the drought that differed markedly in availability of resources and fish biomass. In this study, differences in resource use between the two periods are presented together with their consequence on the partitioning of resources. A different approach is introduced into the calculation of niche breadth and niche overlap incorporating size-specific differences in resource use and interactions between resource dimensions. Comparison with conventional measures of niche breadth and niche overlap shows that conventional measures often misrepresent interactions between species. Condition and biomass were used as indicators of a species' fitness, and it is shown that fitness of most species is governed by the availability of resources and partitioning of these resources is an important mechanism allowing potential competitors to coexist. Resource partitioning along the trophic dimension was more important than along the spatial or temporal dimension.
Responses of rainbow trout (Oncorhynchus mykiss) and their prey to inorganic fertilization of an oligotrophic montane lake
Authors: Johnston N T , Stamford M D , Ashley K I , Tsumura K
Published: April 2011

We used two montane lakes (4.5 and 7.8 ha) in a before-after control-impact pair experimental design to measure the responses of rainbow trout (Oncorhynchus mykiss) and their prey to 5 years of inorganic phosphorus and nitrogen (liquid ammonium polyphosphate and urea ammonium nitrate) additions. Epilimnetic total phosphorus (TP) concentration, euphotic zone chlorophyll a concentration, limnetic macrozooplankton biomass, and annual trout yield increased significantly in the fertilized lake. Chlorophyll a concentration and zooplankton biomass varied directly with epilimnetic TP. Trout yield varied as TP0.5. Fertilization increased trout reproductive output, growth, and yield but did not alter yearling survival or the mean age of mature fish. Prey utilization by trout did not change. DeltaC data indicated that trout in the fertilized lake obtained 65% of their body carbon from benthic insects and 35% from zooplankton. Increased biomass of Hesperodiaptomus accounted for most of the zooplankton response. Benthic insect emergence decreased with increasing water depth but was greater at a given depth in the fertilized lake. Resources accounted for smaller proportions of the variance of consumer biomass with increasing trophic level.
Patterns of covariation in length and age at maturity of British Columbia and Alaska sockeye salmon (Oncorhynchus nerka) stocks
Authors: Pyper Brian J , Peterman Randall M , Lapointe Michael F , Walters Carl J
Published: April 2011

We examined patterns of covariation in age-specific adult body length and in mean age at maturity among 31 sockeye salmon (Oncorhynchus nerka) stocks from western Alaska to southern British Columbia. Positive covariation in body length was prevalent across stocks of all regions (e.g., correlations (r) from 0.2 to 0.6), suggesting either that growth periods critical to final body length of sockeye salmon occur while ocean distributions of these stocks overlap or that large-scale environmental processes influence these stocks similarly while they do not overlap. We also found stronger covariation among body length of stocks within regions (r from 0.4 to 0.7), indicating that unique regional-scale processes were also important. Mean age at maturity also showed positive covariation both among and within regions, but correlations were weaker than those for length. We also examined patterns of covariation between length and mean age at maturity and between these variables and survival rate. Although length and mean age at maturity were negatively correlated, there was little evidence of covariation between these variables and survival rate, suggesting that environmental processes that influence marine survival rates of sockeye salmon are largely different from those affecting size and age at maturity.
Modeling the size of snapper (Pagrus auratus) using temperature-modified growth curves
Authors: Millar Russell B , McArdle Brian H , Harley Shelton J
Published: April 2011

Age-length keys from RV Kaharoa trawl surveys in the years 1984-1990 and 1992-1994 were used to estimate mean lengths-at-age of snapper (Pagrus auratus) in the Hauraki Gulf of New Zealand. A von Bertalanffy growth curve fitted to these lengths-at-age exhibited poor fit, and when the fit was restricted to only cohorts since 1968 (those for which sea surface temperature data were available) the estimated maximum length parameter dropped 5 cm. A power curve provided a better fit without an increase in the number of parameters and was not sensitive to the restriction to younger cohorts. When water temperature was added to the power curve model the residual plots indicated unexplained year effects and temporal correlation. These features were included using a mixed-effects model for repeated-measures data, and temperature was found to be statistically significant (p < 0.0001). This conclusion was corroborated via a simple randomization test. The model predicts growth over a year to change by the equivalent of 8 weeks if the average annual water temperature changes by 1°C. This is sufficient to predict a 4-year-old snapper from the 1986 cohort as having the equivalent of 6 months more growth (at the growth rate corresponding to average water temperature) than a 4-year-old fish from the 1990 cohort.
Size-dependent predation in piscivores: interactions between predator foraging and prey avoidance abilities
Authors: Lundvall David , Svanbäck Richard , Persson Lennart , Byström Pär
Published: April 2011

Body size is known to play a crucial role in predator-prey interactions. For a given predator size, it has been suggested that prey mortality should be a dome-shaped function dependent on prey body size. In this study, we experimentally tested (i) the suggested mechanisms responsible for the dome-shaped prey vulnerability function and (ii) whether a prey refuge affected the form of this function. As prey, we used young-of-the-year Eurasian perch (Perca fluviatilis), and as predator, larger Eurasian perch. The prey mortality as a function of prey size was dome shaped for large and medium predators but decreased monotonically with prey size for small predators. Capture success of predators decreased monotonically with increasing prey size and was lower for small predators. In refuge trials, the mortality of prey declined monotonically with prey size for all predator sizes. Refuge use of prey increased with the sizes of both prey and predator. Our results suggest that the hypothesized dome-shaped relationship on prey vulnerability can be altered by the presence of an absolute prey refuge. Our results further suggest that the ability to perform more flexible foraging behaviors is of increasing importance when prey size increases.