bluuebunny/crossref_metadata_2025 huggingface dataset:
Estimating trends in fishing mortality at age and length directly from research survey and commercial catch data
Authors: Sinclair Alan F
Published: April 2011

Relative fishing mortality (R) is estimated directly as the ratio of commercial catch divided by a research vessel survey index of relative population abundance. If the survey is conducted near the middle of the fishing year, its catchability is constant, and the rate of catch reporting remains constant, R will be proportional to the actual fishing mortality (F). Trends in R will reflect trends in F. A case study is presented where R at age and length are compared with estimates obtained with sequential population analysis (SPA). They were found to be of similar magnitude and trend. This new method would be useful for stocks where SPA is not possible. It would also be a useful addition to analytical assessments where SPA is used; it provides estimates of relative F at length, it is insensitive to changes in natural mortality provided the research survey occurs close to the middle of the fishing year, and it provides useful diagnostics for interpreting SPA results.
Changes in the quantity and characteristics of large woody debris in streams of the Olympic Peninsula, Washington, U.S.A. (1982-1993)
Authors: McHenry Michael L , Shott Eric , Conrad Robert H , Grette Glenn B
Published: April 2011

We assessed the changes in large woody debris (LWD) abundance and composition at 28 sites in 27 low-gradient Olympic Peninsula streams between 1982 and 1993. The average number of pieces of debris was virtually identical (P = 0.98) in both years (50.7 versus 50.6). However, we found a significant (P <= 0.01) reduction in the total volume of LWD material in the stream sites surveyed (51.7 m3 ·100 m-1 in 1982 to 38.2 m3 ·100 m-1 in 1993). While the mean volume of second-growth derived LWD increased from 3.6 to 10.9 m3 ·100 m-1 (P < 0.01), the increase was insufficient to offset the loss of old-growth derived LWD. The mean volume of old-growth derived LWD for all sites decreased from 48.1 to 27.4 m3 ·100 m-1 between sample years (P < 0.01). The mean diameter of second-growth derived LWD was significantly larger in 1993 than in 1982, although still smaller than old-growth derived pieces. We measured a significant increase in the percentage of LWD pieces rated as highly decayed from 1982 to 1993. The results indicate that the loss of old-growth derived LWD following the removal of old-growth riparian forests is initially very rapid, followed by a slower rate of depletion associated with watershed destabilization. Inputs of LWD from second-growth riparian forests up to 73 years old were characterized by small diameter, high mobility, and high decay rates.
Dietary effects on the fatty acid signature of whole Atlantic cod (Gadus morhua)
Authors: Kirsch Penny E , Iverson Sara J , Bowen W Don , Kerr Stephen R , Ackman Robert G
Published: April 2011

Understanding the influence of dietary fatty acids on whole fish is necessary to evaluate the degree to which fatty acids may be used for understanding foraging patterns in fish, as well as in marine mammals that consume their prey whole. Adult Atlantic cod (Gadus morhua) were fed two prey items that differed significantly in fat content and fatty acid compositions. Cod were first fed squid (Illex illecebrosus, 2.0% fat) for 6 weeks, followed by Atlantic mackerel (Scomber scombrus, 15.7% fat) for 8 weeks. Twenty whole cod were individually analyzed at each of 0, 3, 6, 11, and 14 weeks. Despite being on a low-fat squid diet, in only 3 weeks, cod fatty acid patterns changed significantly to reflect the patterns found in squid and did not further change at 6 weeks. When switched to a high-fat mackerel diet, total body fat of cod increased and the fatty acid composition of cod changed significantly in the direction of patterns found in mackerel. Despite changes in cod fatty acid signatures, cod were readily distinguished from the fatty acid signatures of their diets. Our results provide support for the use of fatty acids as indicators of diet at upper trophic levels.
Incubation temperature, developmental biology, and the divergence of sockeye salmon (Oncorhynchus nerka) within Lake Washington
Authors: Hendry Andrew P , Hensleigh Jay E , Reisenbichler Reg R
Published: April 2011

Sockeye salmon (Oncorhynchus nerka) introduced into Lake Washington in the 1930s and 1940s now spawn at several different sites and over a period of more than 3 months. To test for evolutionary divergence within this derived lineage, embryos that would have incubated in different habitats (Cedar River or Pleasure Point Beach) or at different times (October, November, or December in the Cedar River) were reared in the laboratory at 5, 9, and 12.5°C. Some developmental variation mirrored predictions of adaptive divergence: (i) survival at 12.5°C was highest for embryos most likely to experience such temperatures in the wild (Early Cedar), (ii) development rate was fastest for progeny of late spawners (Late Cedar), and (iii) yolk conversion efficiency was matched to natural incubation temperatures. These patterns likely had a genetic basis because they were observed in a common environment and could not be attributed to differences in egg size. The absolute magnitude of divergence in development rates was moderate (Late Cedar embryos emerged only 6 days earlier at 9°C) and some predictions regarding development rates were not supported. Nonetheless our results provide evidence of adaptive divergence in only 9-14 generations.
Gear-independent patterns of variation in catch of juvenile Atlantic cod (Gadus morhua) in coastal habitats
Authors: Methven David A , Schneider David C
Published: April 2011

Habitat and size of juvenile Atlantic cod (Gadus morhua) change substantially during the first 3 years after settlement, and hence, cohort size cannot be followed using a single gear. We investigated whether catch could be calibrated across gear types by deploying pairs of gears repeatedly in the same habitat. As expected, size selectivity differed substantially among gears. Trawls and seines generally collected individuals <200 mm. Gillnets and jiggers collected individuals >150 mm. Size modes, corresponding to age-classes, were common to catches of most gears. Highest catches were taken by trawls and seines. Gillnet catches were orders of magnitude lower. Standardized catches could not be calibrated across pairs of gears deployed in the same habitat at approximately the same time. However, it was possible to identify spatial depth gradients and diel changes in catch that were independent of gear. Consistent spatial and temporal patterns across gears were interpreted as characteristic of fish populations, not just of gears. Density in coastal habitats was higher at night and was higher at 4-7 m than at greater depths. These results, in conjunction with other studies, establish that coastal depths of 4-7 m represent the centre, and not the edge, of the distribution of age 0 cod in Newfoundland during autumn. Hence nursery areas during the early 1990s, a time of historically low spawning stock biomass, must be identified as the coastal zone, not offshore.
Concentrations of trace elements in recent and preindustrial sediments from Norwegian and Russian Arctic lakes
Authors: Rognerud Sigurd , Skotvold Trond , Fjeld Eirik , Norton Stephen A , Hobæk Anders
Published: April 2011

Cu, Hg, Ni, Pb, Se, and Zn concentrations in surface and preindustrial freshwater sediments from 66 lakes in the Norwegian and Russian Arctic were used for studying modern atmospheric deposition of these elements. Statistical analysis showed that, after adjusting for the effects of scavenging factors in sediments (organic matter, Al, and Fe), there were, in general, significantly higher concentrations of Hg and Pb in surface sediments than preindustrial sediments. The differences decreased with increasing latitude and increasing longitude to the east, and in the lakes from arctic islands of Svalbard and along the the arctic coastline of Russia, only Hg concentrations were elevated in surface sediments. We attribute this pattern to modern anthropogenic atmospheric deposition. There were no such differences or regional gradients for the other trace metals. A multivariate analysis of the sediment data showed that Hg and Se were associated with organic matter, whereas Cu, Ni, and Zn were associated with inorganic matter (Al, Fe). There was a shift in Pb association from inorganic matter in the reference sediment to organic matter in the surface sediment, which we interpret as an historic change in importance of sources (from bedrock-derived to atmospheric deposition).
Distribution of hoki (Macruronus novaezelandiae) eggs, larvae, and adults off Westland, New Zealand, and the design of an egg production survey to estimate hoki biomass
Authors: Zeldis John R , Murdoch Rob C , Cordue Patrick L , Page Mike J
Published: April 2011

The winter spawning aggregations of hoki (Macruronus novaezelandiae) off the Westland coast, South Island, support New Zealand s largest trawl fishery. The distribution and abundance of hoki eggs, larvae, and adults from ichthyoplankton and acoustic surveys made during the period 1978-1993 were used to describe the location and timing of hoki spawning off Westland. Hoki spawned primarily in south Westland, around Hokitika Canyon, and south along the outer shelf and slope to Cook Canyon, although spawning biomass appeared to increase in north Westland later in the season. Older stage hoki larvae occurred shoreward of eggs and newly hatched larvae, suggesting onshore advection. The data were used to designate spatial and temporal egg sampling strata that significantly increased egg abundance estimate precision. The egg data were used to estimate annual egg production and, combined with data on fecundity and recruited proportion spawning, to estimate virgin biomass. The historical biomass estimate (1.48 million tonnes, CV = 29.4%) was probably biased down because the plankton tows were too shallow. It appears that a future egg production survey, using appropriate plankton sampling depths, could provide a biomass estimate of Westland spawning hoki sufficiently accurate and precise for management purposes.
Nutrient-chlorophyll-Secchi relationships under contrasting grazer communities of temperate versus subtropical lakes
Authors: Mazumder Asit , Havens Karl E
Published: April 2011

Published data for total phosphorus (TP), total nitrogen (TN), chlorophyll (Chl), and water transparency (Secchi depth) for 420 lake-years in temperate North America and Europe and subtropical Florida were analyzed to test the hypothesis that subtropical and temperate lakes produce similar nutrient-Chl-Secchi relationships regardless of regional contrasts in seasonal, physical, chemical, and biological characteristics. We also tested the hypothesis that similarities in nutrient-Chl-Secchi relationships between temperate and subtropical lakes are expected only when the size or community structure of zooplankton remains constant. TP-Chl relationships were not significantly different for small zooplankton dominated temperate and subtropical lakes, but large herbivore (LH) dominated temperate lakes exhibited significantly lower Chl yield to TP than either subtropical small herbivore (SH) or temperate SH lakes. Although both nitrogen and phosphorus were important in determining the patterns and strengths of nutrient-Chl relationships in subtropical and temperate lakes, no particularly different role of TN or TP in determining Chl yield in the subtropical versus temperate lakes was observed. Unlike the nutrient-Chl relationships, Secchi depth seemed to decline as a function of both Chl and TP from subtropical SH to temperate SH to temperate LH lakes. Overall, the subtropical and temperate lakes seemed to produce similar general patterns of nutrient-Chl-transparency relationships, although mostly under the dominance of small zooplankton communities.
A general, life history based model for regional management of fish stocks: the inland lake trout (Salvelinus namaycush) fisheries of Ontario
Authors: Shuter B J , Jones M L , Korver R M , Lester N P
Published: April 2011

Life history characteristics of 54 Ontario lake trout (Salvelinus namaycush) populations vary with differences in lake area (range 25-450 000 ha) and total dissolved solids (TDS) (range 15-180 mg·L-1). Populations from large lakes exhibit greater maximum sizes, greater ages and sizes at first maturity, lower natural mortality rates, and lower sustainable yields. Populations from high-TDS lakes exhibit higher growth rates in early life, lower ages at first maturity, larger sizes at first maturity, and higher natural mortality rates. Angler catchability increases significantly at low population densities. With these relationships included in an age-structured population model, we found that the fishing mortality rate at maximum equilibrium yield ranges from 0.12·year-1 for a 100-ha, low-TDS lake to 0.37·year-1 for a 10 000-ha, high-TDS lake; the fishing effort level at maximum equilibrium yield ranges from 6.6 angler-h·ha-1· year-1 for a 100-ha, low-TDS lake to 4.0 angler-h·ha-1·year-1 for a 10 000-ha, high-TDS lake. Populations from small, low-TDS lakes are more sensitive to overexploitation than populations from large, high-TDS lakes. Easily measured, environmental correlates of life history characters may be common among fish species and are useful in developing exploitation guidelines for populations that are not well studied.
Estimation of fishing and natural mortality from tagging studies on fisheries with two user groups
Authors: Brooks Elizabeth N , Pollock Kenneth H , Hoenig John M , Hearn William S
Published: April 2011

We present generalizations of fishery models that allow for the separate estimation of fishing mortality when more than one user group is present (e.g., a commercial and a recreational fishery). This model also allows for the fisheries to be in operation for any length of time whereas previously fisheries were generally considered to be pulse or continuous. Three cases are considered: (i) fisheries operate consecutively, (ii) fisheries overlap for a part of their seasons, and (iii) fisheries are in operation for the whole year. The results of a simulation study are included, which provide estimates of fishing and natural mortality along with their proportional standard errors (CVs). All scenarios had good precision, with most CVs < 25% and usually very little difference between the three cases. Coefficients of interaction, the potential gain by one fishery if another is closed down, are also given along with a method for calculating them. Factors affecting these coefficients of interaction were the order in which fisheries operated, amount of overlap in fishing seasons, and intensity of fishing effort by each fishery. We believe that these models could provide useful information for the management of fisheries with multiple user groups where allocation conflicts may arise.
A process for developing and evaluating indices of fish assemblage integrity
Authors: Hughes Robert M , Kaufmann Philip R , Herlihy Alan T , Kincaid Thomas M , Reynolds Lou , Larsen David P
Published: April 2011

We describe a general process for developing an index of fish assemblage integrity, using the Willamette Valley of Oregon, U.S.A., as an example. Such an index is useful for assessing the effects of humans on entire fish assemblages, and the general process can be applied to any biological assemblage and any region. First, a reference condition was determined from historical information, and then candidate metrics of ecological importance were listed. The variability of the candidate metrics in time and space was estimated and their responsiveness to independent measures of riparian and stream habitat quality assessed. Metrics were scored continuously from 0 to 10, producing an index of biological integrity (IBI) that was weighted to range from 0 to 100 regardless of the number of metrics. The index, developed from a set of 35 sites, was then tested on an independent set of eight urban sites sampled by the Oregon Department of Fish and Wildlife. Thirteen of the 16 candidate metrics were appropriate and produced an IBI with among-site variance triple that of revisit variance. The method distinguished sites with acceptable fish assemblages from marginally and severely impaired sites.
Planning programs to estimate salmon harvest with coded-wire tags
Authors: Bernard David R , Marshall Robert P , Clark John E
Published: April 2011

Methods are presented for planning individual catch-sampling, tagging, and field-sampling programs to estimate salmon (Oncorhynchus spp.) harvest in recreational and commercial fisheries from several hatchery-produced and wild cohorts through recovery of coded-wire tags. We show how to determine sample sizes sufficiently large to detect harvest and link sample sizes to expenditures through linear and allometric cost functions to determine optimal tagging and catch-sampling rates. Sample sizes that will minimize bias and variance are charted for field-sampling programs designed to estimate the fraction of a cohort with tags. We describe sampling strategies that can be used to detect or to minimize bias in harvest estimates from tag loss, tag-induced mortality, tag-induced straying, and nonrandom sampling. Methods are demonstrated with data on cohorts of chinook (O. tshawytscha) and coho salmon (O. kisutch) from Alaska.
Effect of animal and vegetal protein diets on feed intake and apparent digestibility of nutrients in rainbow trout (Oncorhynchus mykiss) infected by Aeromonas salmonicida, with and without chronic hypoxia stress
Authors: Néji H , de la Noüe J
Published: April 2011

This study was undertaken to investigate the effects of bacterial infection (Aeromonas salmonicida) and chronic hypoxia on mortality, feed intake, and apparent digestibility of each of two diets in rainbow trout (Oncorhynchus mykiss). The diets were isonitrogenous (gross basis); one was based mainly on animal protein and the other on vegetal protein. In each of two separate and successive experiments, where the first served as a control for the second, fish were immersed on day 0 (d0) in either a sterile phosphate buffer solution (first experiment) or a suspension of A. salmonicida (second experiment). Thereafter, the fish were either exposed on d2 for 12 days to hypoxic conditions (60% of water oxygen saturation) or maintained under normal conditions. Feed intake was measured daily, while apparent digestibility coefficients for gross energy, dry matter, and crude protein were measured on d0, d2, d5, d9, d11, and d14. Among all infected fish, feed intakes were reduced (P < 0.05), regardless of the source of dietary protein or the degree of water oxygenation. Also, regardless of infection, the feed intakes of hypoxic fish that were fed the vegetal protein based diet were significantly less than those of fish that were fed the animal protein based diet. This response, however, was transitory, since normal levels of feed intake in the former fish were found by d3. The apparent digestibility coefficients for all parameters were unaltered by hypoxia (P > 0.05), but they were significantly reduced (P < 0.05) by A. salmonicida infection, especially during the critical period of infection (d5 and d9).
Role of genetic markers in fisheries and aquaculture: useful tools or stamp collecting?
Authors: Ferguson Moira M , Danzmann Roy G
Published: April 2011

We comment on the role of genetic markers in fisheries and aquaculture with a view to the future. Our goal is to encourage researchers to evaluate the molecular markers they need to deploy and shift their thinking away from analyses of stock structure towards more aggressive pursuit of questions related to genome structure and function. Examples illustrate that no one marker type is appropriate for all applications. Choice should be based on the evolutionary genetic attributes of both the species and the marker loci themselves. We evaluate three relatively new marker types: mitochondrial DNA (mtDNA) sequences, randomly amplified polymorphic DNA, and hypervariable nuclear loci. We conclude that (i) sequences of mtDNA do not necessarily detect greater polymorphism than restriction endonuclease analysis, (ii) the technical ease of randomly amplified polymorphic DNA is offset by questionable repeatability, and (iii) simulations illustrate that even new marker systems with large numbers of alleles need not detect differences among closely related yet significantly differentiated populations. Increasing the number of alleles per locus did not increase the probability of detecting significant differences. Finally, we consider the roles of genetic markers in helping to determine family relationships in pooled lots of fishes and locate genes that control an organism's phenotype (quantitative trait loci). We discuss how knowledge of quantitative trait loci can help us to understand the basis of individual differences in performance.
Early survival and development of coastal cutthroat trout (Oncorhynchus clarki clarki), steelhead (Oncorhynchus mykiss), and reciprocal hybrids
Authors: Hawkins Denise K , Foote Chris J
Published: April 2011

We compared the survival and development of embryos from fertilization to emergence of two populations of coastal cutthroat trout (Oncorhynchus clarki clarki), one population of steelhead (Oncorhymchus mykiss), and their reciprocal hybrids under controlled conditions (10 ± 1°C). The egg weight of the steelhead (0.110 ± 0.008 (SE) g) was nearly twice that of coastal cutthroat trout (0.056 ± 0.003 and 0.051 ± 0.001 g for the two populations). Fertilization success, survival, duration of hatching and emergence periods, yolk absorption relative to total alevin weight, and yolk conversion efficiency were similar among the cross types. There was no evidence of reduced hatchability or viability of hybrids despite maternal and paternal species effects on size and development. Fish with cutthroat dams had lower percent hatch, were smaller at hatch and emergence, grew more slowly, used less yolk per day, reached 50% yolk absorption earlier, and had a smaller percent yolk at hatch than those fish with steelhead dams. Fish sired by cutthroat males hatched and emerged earlier and took less time between the two stages than fish sired by steelhead. As a consequence, hybrids with cutthroat dams emerged late and had little yolk, while hybrids with steelhead dams emerged early and had an abundance of yolk.
Genetic differentiation and introgression between putative subspecies of Leuciscus soufia (Teleostei: Cyprinidae) of the region of the Mediterranean Alps
Authors: Gilles André , Chappaz Rémi , Cavalli Laurent , Lörtscher Mathias , Faure Eric
Published: April 2011

Because of interspecific hybridization, there is considerable controversy over the taxonomic status of many members within the family Cyprinidae. In this study, morphological and genetic characters of Leuciscus soufia, a cyprinid fish of southern France and northern Italy, were examined to verify the existence of three subspecies. Leuciscus soufia agassizi differs from Leuciscus soufia multicellus in morphology, in heterozygosity at two diagnostic allozyme loci, and by distinct mitochondrial lineages. Leuciscus s. soufia is morphologically similar to L. s. agassizi but exhibits decreased enzymatic polymorphism. However, two specimens of L. s. soufia from the Var River were found to have mitochondria of the subspecies multicellus, while four Bevera River specimens of L. s. multicellus possessed the mitochondria of the subspecies agassizi. These data argue in favour of introgressive hybridization between L. s. soufia and L. s. multicellus, rejecting the hypothesis that an ancestral population was fragmented, generating three "subspecies" that retained the original polymorphism. We propose that L. s. soufia and L. s. agassizi be regrouped within the soufia subspecies. A calibrated molecular clock dates the separation of the remaining subspecies back to the Messinian (5 million years ago). Sea level fluctuations likely mediated their secondary contact and subsequent introgressive hybridization.
Comparison of methods to account for autocorrelation in correlation analyses of fish data
Authors: Pyper Brian J , Peterman Randall M
Published: April 2011

Autocorrelation in fish recruitment and environmental data can complicate statistical inference in correlation analyses. To address this problem, researchers often either adjust hypothesis testing procedures (e.g., adjust degrees of freedom) to account for autocorrelation or remove the autocorrelation using prewhitening or first-differencing before analysis. However, the effectiveness of methods that adjust hypothesis testing procedures has not yet been fully explored quantitatively. We therefore compared several adjustment methods via Monte Carlo simulation and found that a modified version of these methods kept Type I error rates near . In contrast, methods that remove autocorrelation control Type I error rates well but may in some circumstances increase Type II error rates (probability of failing to detect some environmental effect) and hence reduce statistical power, in comparison with adjusting the test procedure. Specifically, our Monte Carlo simulations show that prewhitening and especially first-differencing decrease power in the common situations where low-frequency (slowly changing) processes are important sources of covariation in fish recruitment or in environmental variables. Conversely, removing autocorrelation can increase power when low-frequency processes account for only some of the covariation. We therefore recommend that researchers carefully consider the importance of different time scales of variability when analyzing autocorrelated data.
High rate of redd superimposition by brook trout (Salvelinus fontinalis) and brown trout (Salmo trutta) in a Minnesota stream cannot be explained by habitat availability alone
Authors: Essington Timothy E , Sorensen Peter W , Paron Dean G
Published: April 2011

This study was conducted to test the hypothesis that redd superimposition by salmonine fishes is a consequence of limited habitat availability. We monitored redd site selection by brook trout (Salvelinus fontinalis) and brown trout (Salmo trutta) for two spawning seasons in Valley Creek, Minnesota. Redd superimposition rates were high; over one half of the brook trout and one third of the brown trout superimposed redds. We tested the role of habitat availability in this process by characterizing microhabitat at sites with and without redds in four small sections of this stream and then determined whether superimposition could be explained by random dispersal of fish over available habitat. Brown trout preferred spawning sites with high flows whereas brook trout strongly preferred deep sites with upwelling groundwater. No relationship was observed between fish density and superimposition. Additionally, the observed frequency of superimposition was greater than expected by chance in six of eight instances for brown trout and in one of three instances for brook trout. Finally, a behavioral experiment provided direct evidence that females have a behavioral preference to spawn on existing redd sites, suggesting that factors other than habitat may determine redd site selection and hence superimposition.
Effects of growth and fatness on sexual development of chinook salmon (Oncorhynchus tshawytscha) parr
Authors: Silverstein Jeffrey T , Shearer Karl D , Dickhoff Walton W , Plisetskaya Erika M
Published: April 2011

The independent effects of size and fatness, 1 year prior to maturity, on male sexual development of chinook salmon (Oncorhynchus tshawytscha) were tested. Beginning in March 1995, ration size and dietary lipid were independently manipulated to produce four groups of spring chinook salmon differing in size and fatness. Size, growth rate, adiposity, liver triacylglycerol and glycogen contents, and plasma insulin and insulin-like growth factor I (IGF-I) levels were monitored to follow the metabolic states of fish in the different treatment groups and to observe whether plasma levels of these growth mediators predict sexual development. Differences in size and fatness were well established by the first autumn (September 1995), 1 year prior to sexual maturity, and common ration size groups were pooled for further rearing. Subsequently in winter-spring (February-March), 6 months prior to sexual maturity, there were no within-tank differences in size or fatness. Nevertheless, the effects of size and fatness, from 1 year earlier, on incidence of sexual maturity were significant. Overall, size appeared to have the primary effect, but for smaller fish, an effect of fat content was indicated. Plasma insulin levels, and in limited cases, IGF-I levels, were correlated with growth rate and size, but were not accurate indicators of sexual development.
Metal accumulation in American wild celery (Vallisneria americana Michx.) in the St. Lawrence River: effects of water depth and exposure to current
Authors: Hudon Christiane
Published: April 2011

The sensitivity of Vallisneria americana Michx. as an indicator species of metal concentrations was assessed through the examination of its spatial (between- and within-site) and temporal (short- and long-term) variability. Eight macrophyte beds located in the St. Lawrence and Ottawa rivers were selected to contrast metal concentrations found in plants exposed to different types of waters, upstream and downstream of their confluence, in the Greater Montreal urban area. Comparisons among sites revealed higher metal concentrations, both in water and in plant tissues, at sites exposed to Ottawa River "brown" waters than at sites exposed to St. Lawrence River "green" waters. Within each site, samples represented a broad range in terms of water depths, exposure to current, incident light intensity, and total plant biomass. At all sites, metal concentrations in plant tissues were lowest in the shallow water found in sheltered, dense beds of submerged aquatic vegetation and increased in deep, open-water areas beyond the limits of dense vegetation. This persistent gradient may result from local differences in plant growth rates, exposure to currents, and (or) metal bioavailability. The use of a sampling strategy designed to control for within-site (depth-balanced) variability makes it possible to measure spatial and (or) temporal differences on the order of 20% whereas unbalanced sampling designs may lead to erroneous conclusions. Significant reductions in metal concentrations in plant tissue were observed both between 1994 and 1996 (Fe, Mn, Pb, Zn, N) and between 1976 and 1996 (Cd, Cr, Pb, Zn, N). Particular care must be given to sampling design if V. americana is to be used as a biological indicator of further long-term reductions in metal concentrations.
Stream phosphorus and nitrogen export from agricultural and forested watersheds on the Boreal Plain
Authors: Cooke Sandra E , Prepas Ellie E
Published: April 2011

We evaluated phosphorus (P) and inorganic nitrogen (IN) export from two agricultural and two forested watersheds on the nutrient-rich but relief-poor Boreal Plain. One agricultural stream was in a watershed that contained cropland, while the second consisted of mixed agricultural activities. Over the 2-year study, total dissolved phosphorus (TDP) concentrations were proportionately high, particularly in the agricultural streams. Flow-weighted TDP averaged 82% of the total phosphorus (TP) in the agricultural streams and 43% in the forested streams. In all watersheds, TDP was almost exclusively dissolved reactive phosphorus and most of the annual P export was in summer. The type of agricultural activity in the watershed influenced IN speciation; in the mixed agricultural watershed, 94% of IN export was ammonium, whereas 98% of IN load was nitrate from the cropland watershed. Disproportionately high TDP to TP export from agricultural watersheds suggests that, in areas of low relief and relatively high soil water P content, land clearing may influence dissolved more than particulate phosphorus export.
Modeling the effects of fish migration on bias and variance in area-swept estimates of biomass: a vector-based approach
Authors: McAllister Murdoch K
Published: April 2011

Estimates of fish abundance from trawl and acoustic surveys are typically imprecise and may often be biased because of uncontrollable factors such as fish migration. In this paper, I present a model for the bias in area-swept biomass estimates when fish migration occurs as the survey is conducted. Bias in acoustic and trawl survey biomass estimates is treated as a function of the direction and speed of the vessel and the fish in each survey transect and results mainly from distortions in the observed area across fish aggregations. I use the model to evaluate the magnitude and direction of bias and interannual variability in biomass estimates from fish migration in systematic transect survey designs. For even relatively low fish migration velocities (<0.5 m/s), bias in estimated fish biomass can be very large (>500%). Furthermore, relatively small interannual variability in fish migration rates and vessel speeds (e.g., CV = 0.1 for each) can result in very large interannual error variability in biomass estimates (e.g., CV > 0.5). Designs with the least bias and variance in biomass estimates had the fastest vessel speeds along transects, more survey vessels, shorter transects, and transects aligned roughly parallel to the direction of fish migration.
Changes to the runoff of Canadian ecozones under a doubled CO2 atmosphere
Authors: Clair Thomas A , Ehrman James , Higuchi Kaz
Published: April 2011

Increases in atmospheric greenhouse gases may change the hydrology of a number of Canada's regions. This will have an impact on aquatic and wetland ecosystems as well as municipal, industrial, and power generation uses. It is thus important to get an estimate of the potential changes to the Canadian hydrological cycle in order to make intelligent decisions concerning mitigation factors that society may be forced to undertake. We divided Canada into ecoclimatologically similar regions called "ecozones." We developed two month-stepped temperature-precipitation-runoff models for the country using an artificial intelligence neural network (ANN) approach. We modified input temperature and precipitation variables in the ANN models to match those predicted by the Canadian Climate Centre General Circulation Model II for a doubled CO2 atmosphere and calculated new monthly equilibrium runoff predictions. Our results predict that much of Canada will experience higher annual runoff than is currently the case. The timing of runoff will change significantly in a number of the ecozones, as we show that in many regions, peak runoff will occur approximately 1 month earlier than is currently the case. The ANN model did not work as well for basins in the Prairie ecozone, as we could not develop a good model with data from regulated rivers.
Effects of recent ecosystem changes on the recruitment of young-of-the-year fish in western Lake Erie
Authors: Gopalan Gouthaman , Culver David A , Wu Lin , Trauben Bruce K
Published: April 2011

We compared the variability in forage fish recruitment over the last 27 years against major ecological changes that occurred in Lake Erie over the same time period. During a period of high adult walleye abundance and declining phosphorus loading (1976-1982), we observed a decline in the abundance of later hatching forage fish species (e.g., July) and those species that did not shift their diets from zooplankton to benthos during the summer of their life. During years of high young-of-the-year (YOY) white perch abundance (1983-1990), forage fishes whose hatching dates and (or) diet overlapped with YOY white perch declined in abundance. When the zebra mussel (Dreissena polymorpha) became abundant (1991-1995), most forage fishes showed no change in abundances. Given a YOY's ability to switch to benthos during summer, the date on which this occurred was determined by a combination of zooplankton abundance and fish size. Hence, the dates individual taxa of fish hatch relative to seasonal cycles of zooplankton abundance and the size at which they can undergo an ontogenetic diet shift to benthos and (or) fish could be influencing fish growth and recruitment and need to be incorporated into YOY recruitment models.
Nutrient – sestonic chlorophyll relationships in northern Ozark streams
Authors: Lohman Kirk , Jones John R
Published: April 2011

We investigated relationships between sestonic chlorophyll (Chl), total phosphorus (TP), and total nitrogen (TN) at 23 sites on 13 streams in the Missouri Ozarks. There was a strong curvilinear relationship between mean sestonic Chl and both mean TP (R2 = 0.78) and mean TN (R2 = 0.70). Both models were improved when catchment area was included with either TP (R2 = 0.90) or TN (R2 = 0.84). Limited to 17 sites without point source nutrient additions, the relationship between sestonic Chl and both TP and TN was linear. Including catchment area strengthened linear models with either TP (R2 = 0.94) or TN (R2 = 0.84). Land use (percent row crop or percent forest), together with catchment size, was also a good predictor of sestonic Chl in Ozark streams without point sources. When catchment area and TP or TN were used to predict sestonic Chl on specific dates following catastrophic flooding, models were less accurate than those based on long-term averages, but still explained 55-74% of the variance in sestonic Chl. Our results demonstrate that sestonic Chl is closely associated with nutrients and catchment area in Ozark streams and that nutrient - sestonic Chl models may have broad application in running waters.
Evaluation of quota management policies for developing fisheries
Authors: Walters Carl
Published: April 2011

Losses can be measured as deviations from a desired reference trajectory of quotas that would be taken if there were no uncertainty and are highly dependent on assessments prior to and during development. Simulations of assessment and quota setting under various quota setting rules indicate that variability in relative abundance indices can cause substantial losses, especially considering cumulative effect of early quota errors on later departures of biomass from that needed to produce the desired quotas, even if optimum fishing mortality rate is known in advance. Conservative assessments (low biomass estimates for which there is only a small probability that biomass is actually lower) are favored during development when loss is measured as the relative departure from the best quota for each year. But if loss is measured as absolute departure from the best quota, it is generally better to base the quota on the biomass estimate for which there is nearly a 50% chance that the stock is smaller. Deliberate overfishing (probing) is not favored under either loss measure. Losses can be reduced with minimum biomass surveys and closed areas that directly cushion fishing mortality rates from being more than 50% too low or high.
Seasonal dynamics of carbon dioxide and methane in two clear-water lakes and two bog lakes in northern Wisconsin, U.S.A.
Authors: Riera Joan L , Schindler John E , Kratz Tim K
Published: April 2011

We investigated carbon dynamics in the water column and CO2 and CH4 exchange across the air-water interface in four closed-basin lakes in northern Wisconsin: two with clear, low dissolved organic carbon (DOC) waters and two bog lakes with stained, high-DOC waters. Clear-water lakes quickly became undersaturated following ice-out and remained undersaturated until fall turnover. Bog lakes were supersaturated in CO2 throughout the ice-free season, although surface CO2 concentrations dropped sharply following ice-out and increased again during autumn turnover. Differences in seasonal patterns of CO2 were attributed to morphometry and the timing and intensity of mixing events. Ice-free season fluxes of CO2 were 6.7 and 10.0 mol·m-2 in the bog lakes and 1.2 and 0.09 mol·m-2 in the clear-water lakes. Fluxes of CH4 were significant only immediately after ice-out and during autumn turnover and were <0.4 mol·m-2 in the bog lakes and <0.05 mol·m-2 in the clear-water lakes. Compared with changes in carbon pools in the lakes, our results indicate rapid carbon turnover rates in bog lakes, as opposed to clear-water lakes. We suggest that allochthonous inputs of CO2 may be responsible for this rapid turnover.
Slow growth and decomposition of mosses in Arctic lakes
Authors: Sand-Jensen Kaj , Riis Tenna , Markager Stiig , Vincent Warwick F
Published: April 2011

Aquatic mosses are often the exclusive form of macrophytic vegetation in Arctic lakes. Despite the cold nutrient-poor water and the short ice-free summer, the mosses form dense stands on the lake bottom down to great depths. The environmental conditions suggest that moss growth and decomposition are extremely slow, but logistical and methodological difficulties have so far precluded direct measurements of the processes. Here, we use temporal changes in the size and density of leaves along the axis of moss shoots collected from different depths in Char Lake and North Lake in the Canadian High Arctic to reconstruct the annual growth and decomposition of the mosses during the past 10-17 years. Our results show low but remarkably constant annual elongation rates (about 10 mm·shoot-1) in the long-lived shoots that carry green leaves for several years and decompose slowly. Cold temperatures and low nutrient supply in combination with the short Arctic growing season can account for the low growth rate, the low decomposition rates, and the unprecedented longevity of these moss communities relative to other submerged macrophytes.
Spatial and temporal differences in the diet of Great Lakes herring gulls (Larus argentatus): evidence from stable isotope analysis
Authors: Hebert Craig E , Shutt J Laird , Hobson Keith A , Weseloh DV Chip
Published: April 2011

Stable nitrogen (δ15N) and carbon (δ13C) isotope values were measured in lipid-free homogenates of herring gull (Larus argentatus) eggs collected from the Laurentian Great Lakes during 1974-1995. δ15N values provided an indication of adult gull trophic position during egg formation. After adjustment of egg δ15N values for interlake differences in baseline food web δ15N signatures, significant differences in gull trophic position were found among colonies. These results were attributed to differing proportions of fish in the diets of gulls from the various colonies. Aquatic foods available to gulls had greater δ15N values than terrestrial foods. δ13C measurements provided some support for our hypothesis that terrestrial foods, particularly garbage, were more enriched in 13C than aquatic foods. As the proportion of fish in the diet decreased, the fraction consisting of terrestrial food increased, resulting in an increase in δ13C values and a decline in δ15N values. Stable isotope values for gull eggs from Lake Erie changed significantly during the study period and may have reflected a decline in fish availability.
Influence of fishers’ behaviour on the catchability of surface tuna schools in the Venezuelan purse-seiner fishery in the Caribbean Sea
Authors: Gaertner Daniel , Pagavino Mauricio , Marcano Jesus
Published: April 2011

The influence of Venezuelan skippers' behaviour on the catchability of surface tuna schools was modelled using logistic regressions. Data obtained from observers onboard purse seiners indicated that fishers' fine-scale decisions, such as chasing and setting a school, were influenced by (i) the skipper's skill, (ii) the fishing equipment used (e.g., whether a bird radar was used or not), (iii) the features of the tuna school, and (iv) some environmental factors. The connections among the decisions related to the fishing process and these variables were synthesized in a causal network approach. Results clearly showed that schools (i) composed by fishes under 2 kg and (ii) where biomass was lower than 5 metric tons were disregarded by fishers. Because fishers used these thresholds to decide when to set the net, modifications in their behaviour over the years may introduce serious biases in the analysis of any catch rate and abundance relationship. An average daily activity record of a purse seiner shows the proportion of time spent in searching and in setting activities and highlights the impact that the use of new fishing equipment may have on fishing power.
Recent declines in the recreational catch of coho salmon (Oncorhynchus kisutch) in the Strait of Georgia are related to climate
Authors: Beamish R J , McFarlane G A , Thomson R E
Published: April 2011

Wild and hatchery-reared coho salmon (Oncorhynchus kisutch) from streams and rivers that flow into the Strait of Georgia are caught in the Strait of Georgia and off the west coast of Vancouver Island. The percentage of coho caught in either of these two areas varies from year to year. The variation is associated with the flow of freshwater from the Fraser River and became more extreme in the 1990's. In four of eight years in the 1990's and in the past three years, most coho have been caught outside the Strait of Georgia. The dramatic decline in the sport catch in the Strait is related to ocean conditions in the Strait. The change in ocean conditions is related to an increase in the number of days of zonal (westerly) winds in October, November, and December and to an increase in relative sea level height. The climate change about 1989 that affected the pattern of winter winds and the circulation in the Strait of Georgia was associated with changes in other global climate indices, demonstrating the impact that global climate events can have on the dynamics of regional salmon stocks.
The regime concept and natural trends in the production of Pacific salmon
Authors: Beamish R J , Noakes D J , McFarlane G A , Klyashtorin L , Ivanov V V , Kurashov V
Published: April 2011

Large fluctuations in the trends of Pacific salmon production in this century have been linked to trends in climate in the Pacific that are in turn associated with climate trends throughout the Northern Hemisphere. The close correspondence in the persistence of climate trends and the synchrony of the changes is evidence that a common event may cause the regime shifts. The trends or regimes can be characterized by stable means in physical data series or multiyear periods of linked recruitment patterns in fish populations. The regime concept is important in fisheries management because the natural shifts in abundance may be large and sudden, requiring that these natural impacts be distinguished from fishing effects. An equally important consideration is that biological and physical mechanisms may change when regimes shift, resulting in conditions that may not be characterized in the earlier part of the data series. Fluctuations in Pacific salmon abundance in this century were synchronous with large fluctuations in Japanese sardine abundance, which can be traced back to the early 1600's. The synchrony in the fluctuations suggests that Pacific salmon abundance may have fluctuated for centuries in response to trends in climate. The concept of regimes and regime shifts stresses the need to improve our understanding of the mechanisms that regulate the dynamics of fish and their ecosystems.