bluuebunny/crossref_metadata_2025 huggingface dataset:
Prediction and the aquatic sciences
Authors: Pace Michael L
Published: April 2011

The need for prediction is now widely recognized and frequently articulated as an objective of research programs in aquatic science. This recognition is partly the legacy of earlier advocacy by the school of empirical limnologists. This school, however, presented prediction narrowly and failed to account for the diversity of predictive approaches as well to set prediction within the proper scientific context. Examples from time series analysis and probabilistic models oriented toward management provide an expanded view of approaches and prospects for prediction. The context and rationale for prediction is enhanced understanding. Thus, prediction is correctly viewed as an aid to building scientific knowledge with better understanding leading to improved predictions. Experience, however, suggests that the most effective predictive models represent condensed models of key features in aquatic systems. Prediction remains important for the future of aquatic sciences. Predictions are required in the assessment of environmental concerns and for testing scientific fundamentals. Technology is driving enormous advances in the ability to study aquatic systems. If these advances are not accompanied by improvements in predictive capability, aquatic research will have failed in delivering on promised objectives. This situation should spark discomfort in aquatic scientists and foster creative approaches toward prediction.
Impacts of acid mine drainage on juvenile salmonids in an estuary near Britannia Beach in Howe Sound, British Columbia
Authors: Barry Karen L , Grout Jeffrey A , Levings Colin D , Nidle Bruce H , Piercey G Elizabeth
Published: April 2011

The abandoned copper mine at Britannia Beach, British Columbia, has been releasing acid mine drainage (AMD) into Howe Sound for many years. To assess the impacts of AMD on juvenile salmonids in the Britannia Creek estuary, we compared fish abundance, distribution, and survival at contaminated sites near the creek with uncontaminated areas in Howe Sound. Water quality near Britannia Creek was poor, particularly in spring when dissolved Cu exceeded 1.0 mg·L-1 and pH was less than 6. Beach seine surveys conducted during April-August 1997 and March-May 1998 showed that chum salmon (Oncorhynchus keta) fry abundance was significantly lower near Britannia Creek mouth (0-1.2·100 m-2) than in reference areas (11.5-31.4·100 m-2). Laboratory bioassays confirmed that AMD from Britannia Mine was toxic to juvenile chinook (Oncorhynchus tshawytscha) and chum salmon (96-h LC50 = 0.7-29.7% in freshwater and 12.6-62.2% in 10 ppt water). Chinook salmon smolts transplanted to surface cages near Britannia Creek experienced 100% mortality within 2 days. These results demonstrated that juvenile salmonids are vulnerable to AMD from Britannia Creek: their abundance peaks during spring when Cu concentrations are highest and toxicity is greatest in surface freshwater, which matches their preferred vertical distribution.
Cultivation/depensation effects on juvenile survival and recruitment: implications for the theory of fishing
Authors: Walters Carl , Kitchell James F
Published: April 2011

Large, dominant fish species that are the basis of many fisheries may be naturally so successful due partly to "cultivation effects," where adults crop down forage species that are potential competitors/predators of their own juveniles. Such effects imply a converse impact when adult abundance is severely reduced by fishing: increases in forage species may then cause lagged, apparently depensatory decreases in juvenile survival. Depensatory effects can then delay or prevent stock rebuilding. Cultivation effects are apparently common in freshwater communities and may also explain low recruitment success following severe declines of some major marine stocks such as Newfoundland Atlantic cod (Gadus morhua). Risk of depensatory effects should be a major target of recruitment research, and management policies should aim for considerably higher spawning abundances than has previously been assumed necessary based on recruitment data collected during adult stock declines associated with fishery development.
Effects of freshwater hyperoxia and hypercapnia and their influences on subsequent seawater transfer in Atlantic salmon (Salmo salar) smolts
Authors: Brauner C J , Seidelin M , Madsen S S , Jensen F B
Published: April 2011

Atlantic salmon (Salmo salar) presmolts, smolts, and postsmolts compensate for a respiratory acidosis associated with 96 h of exposure to hyperoxia (100% O2; hO2), hypercapnia (2% CO2and 98% air; hCO2), and combined hO2/hCO2in freshwater (FW) by increasing strong ion difference, predominantly through a reduction in plasma [Cl-] (presumably via branchial Cl-/HCO3-exchange). In smolts, compensation during hO2or hCO2occurred within 24 h, whereas that in combined hO2/hCO2was much slower, resulting in 33% mortality by 96 h. FW hO2and combined hO2/hCO2appeared to impair gill function, likely through oxidative cell damage. This resulted in reduced hypoosmoregulatory ability following subsequent transfer to seawater (SW), as indicated by changes in plasma ion levels, osmolality, and muscle water content, resulting in considerable mortalities. Interestingly, FW hCO2appeared to enhance hypoosmoregulatory ability during subsequent SW transfer. Smolts are often transported from FW to a subsequent SW release site, and these data indicate that care should be taken to minimize the degree of hyperoxia experienced by the smolts. Hypercapnia, which results from metabolic CO2production and inadequate water aeration, does not impair SW transfer, provided it does not occur in conjunction with hyperoxia.
Development and validation of numerical habitat models for juveniles of Atlantic salmon (Salmo salar)
Authors: Guay J C , Boisclair D , Rioux D , Leclerc M , Lapointe M , Legendre P
Published: April 2011

We evaluated the ability of numerical habitat models (NHM) to predict the distribution of juveniles of Atlantic salmon (Salmo salar) in a river. NHMs comprise a hydrodynamic model (to predict water depth and current speed for any given flow) and a biological model (to predict habitat quality for fish using water depth, current speed, and substrate composition). We implemented NHMs with a biological model based on (i) preference curves defined by the ratio of the use to the availability of physical conditions and (ii) a multivariate logistic regression that distinguished between the physical conditions used and avoided by fish. Preference curves provided a habitat suitability index (HSI) ranging from 0 to 1, and the logistic regression produced a habitat probabilistic index (HPI) representing the probability of observing a parr under given physical conditions. Pearson's correlation coefficients between HSI and local densities of parr ranged from 0.39 to 0.63 depending on flow. Corresponding values for HPI ranged from 0.81 to 0.98. We concluded that HPI may be a more powerful biological model than HSI for predicting local variations in fish density, forecasting fish distribution patterns, and performing summer habitat modelling for Atlantic salmon juveniles.
Seasonal reproduction, multiple spawning, and fecundity in northern krill, Meganyctiphanes norvegica, and Antarctic krill, Euphausia superba
Authors: Cuzin-Roudy Janine
Published: April 2011

Both northern krill, Meganyctiphanes norvegica, and Antarctic krill, Euphausia superba, release eggs seasonally in multiple spawning events. Fecundity estimates were determined based on counts of mature oocytes in the ovary of females in preserved field samples. Principal components analysis and allometry were used to analyze the covariation of egg-batch size with female characteristics. In both krill species, egg-batch size scaled isometrically with ovarian weight but showed a positive allometry with body size. Predicted egg-batch size ranged from 200 to 4000 eggs for M. norvegica of 25.5-35 mm body length and from 1500 to 6000 eggs for E. superba of 36-55 mm. Allometric relationships can be used to predict annual fecundity from size structure data of krill populations. In this study, the effect of temperature on the duration of molting and spawning cycles was used to infer a number of reproductive cycles per year, taking into account climate and seasonal variation.
Krill: a possible model for investigating the effects of ocean currents on the genetic structure of a pelagic invertebrate
Authors: Zane Lorenzo , Patarnello Tomaso
Published: April 2011

This paper reviews the information available on the population genetics and systematics of krill (Euphausiidae, Crustacea), integrating the published data with new data collected in our laboratory. Phylogenetic analysis of several Antarctic and sub-Antarctic Euphausia species indicates the importance of dispersal in determining the present-day geographic distribution. Dating speciation events suggest that the formation of the Antarctic Convergence, the oceanographic barrier isolating the Southern Ocean, may have played a role in separating the ancestral Antarctic and sub-Antarctic lineages. Intraspecific data show that the Antarctic krill (Euphausia superba) is characterized by weak genetic differentiation, whereas the northern krill (Meganyctiphanes norvegica) is more structured showing discrete genetic pools. This difference can be explained, at least partly, by the oceanographic conditions in the areas inhabited by the two species.
Metabolic and enzymatic adaptations in northern krill,Meganyctiphanes norvegica, and Antarctic krill,Euphausia superba
Authors: Buchholz Friedrich , Saborowski Reinhard
Published: April 2011

The Antarctic krill, Euphausia superba, is restricted to the Antarctic Ocean. The northern krill, Meganyctiphanes norvegica, is extremely widely distributed from the arctic North Atlantic to the warm Mediterranean. Respiration measurements showed no seasonal differences in rates determined in krill from the thermally stable Clyde Sea (Scotland) and the cooler but variable Danish Kattegat. In the warm Ligurian Sea, where temperatures are stable, krill showed higher rates in April than in September, indicating reactions to the short but intensive productive season. Krill can passively benefit from enhancements of overall metabolism when ascending into upper, warmer water strata during their pronounced diel vertical migration. Michaelis-Menten constants (Km) of citrate synthase (CS) were compared. In terms of respiration and enzyme regulation, krill from the Ligurian Sea stand apart: temperature and nutrition appear to be of different influence, relatable to genetic differentiation in the species. In contrast, Kmof CS in E. superba is temperature independent, highlighting the species' stenothermal physiology. A basal level of activity of digestive enzymes ensures immediate utilization of patchy food sources. Specific induction, including that of chitinases, indicating omnivory in both species, underlines krill's exceptional capacity to adapt to highly variable trophic environments. Processes of moult, growth, and reproduction are locally and seasonally adjusted.
Lipids, trophic relationships, and biodiversity in Arctic and Antarctic krill
Authors: Falk-Petersen Stig , Hagen Wilhelm , Kattner Gerhard , Clarke Andrew , Sargent John
Published: April 2011

Environmental seasonality is a critical factor in structuring polar marine ecosystems. The extensive data now available on the lipids of Arctic and Antarctic euphausiids show that all species are characterised by a seasonally high lipid content, and neutral lipids, whether wax esters or triacylglycerols, are primarily accumulated for reproduction. The Arctic Thysanoessa inermis and the Antarctic Euphausia crystallorophias contain high levels of wax esters and higher concentrations of 18:4(n-3) and 20:5(n-3) and a lower ratio of 18:1(n-9)/(n-7) fatty acids in their neutral lipids than the Arctic Thysanoessa raschii and the Antarctic Thysanoessa macrura and Euphausia superba. Large amounts of phytol in the lipids of T. raschii and E. crystallorophias during winter suggest the ingestion of decaying algae originating in sedimenting material or in sea ice. Thysanoessa raschii, T. macrura, and E. superba have a high ratio of 18:1(n-9)/ (n-7) fatty acids, indicating animal carnivory. We conclude that T. inermis and E. crystallorophias are true high polar herbivores, while T. raschii, T. macrura, and E. superba are omnivores with a more boreal distribution. The Arctic species Thysanoessa longicaudata and Meganyctiphanes norvegica are carnivores feeding on Calanus, as indicated by high amounts of 20:1(n-9) and 22:1(n-11) fatty acids.
Precocial maturation of male sockeye salmon in the Fraser River, British Columbia, and its relationship to growth and year-class strength
Authors: Healey M C , Henderson M A , Burgetz Ingrid
Published: April 2011

We analyzed historical data on the age structure and abundance of males in 22 populations of sockeye salmon (Oncorhynchus nerka) in the Fraser River, British Columbia, to determine geographical and temporal patterns of precocial maturation, its relationship with growth and maturation at other ages, and the value of precocial males as indicators of year-class strength. Most Fraser sockeye males spend two winters at sea before maturing at 3-5 years of age. Precocial males return to spawn at 2, 3, or 4 years of age (ages 0.1, 1.1, and 2.1) and comprised <1 to >33% of male brood year returns among populations. Precocity was lowest among populations that spawned far upstream and highest among populations spawning to the west of the main Fraser River and was not correlated with migration distance. Precocial maturation was related to growth during the second summer in the ocean to brood line and to brood line abundance. The combination of brood line, abundance, and size of precocial males accounted for more than 75% of the variation in total returns in four populations, suggesting that these variables might be used to predict abundance 1 year in advance.
Interannual growth variation in fish and tree rings
Authors: LeBreton Gregory TO , Beamish F William H
Published: April 2011

Interannual growth variations were compared among neighbouring populations of lake sturgeon (Acipenser fulvescens) and white spruce (Picea glauca), white pine (Pinus strobus), and red pine (Pinus resinosa). Measures of growth were obtained by removing long-term trends from widths of rings in the hard tissues of both aquatic and terrestrial organisms and assembling these measures into growth chronologies. Interannual growth variations were negatively correlated (r) between sturgeon and nearby tree population chronologies for those fish populations that displayed strong interseries correlation (mean r). The three sturgeon population chronologies developed from individuals that displayed the lowest interseries correlation coefficients failed to display significant correlation with tree growth. The results of this investigation indicate that the negative relationships between fish and tree growth may be related to annual fluctuations in air temperature. In general, fish population chronologies displayed positive correlation with measures of air temperature during the current season of growth, while tree population chronologies displayed negative correlation with air temperatures from either the current or the previous season of growth.
Depth-dependent vertebral number of Atlantic cod (Gadus morhua) on the Magdalen Shallows and Scotian Shelf: stock mixing or microgeographic trends within populations?
Authors: Swain D P , Frank K T
Published: April 2011

We examined spatial variation in the vertebral number of Atlantic cod (Gadus morhua) during the summer feeding season in the southern Gulf of St. Lawrence and on the Scotian Shelf. Mean vertebral number increased significantly with depth in the southern Gulf and on the northeastern Scotian Shelf but not on the southwestern Scotian Shelf. In the southern Gulf, where sampling was most extensive, mean vertebral number increased steadily as depth increased from 25 m to over 175 m. Mean vertebral number was also strongly related to relative length within age-classes, with the larger fish at age having more vertebrae. However, the association between vertebral number and depth could not be attributed to confounding between depth and size at age. These results indicate either unexpected mixing between neighbouring cod populations or unexpected structure at fine spatial scales within cod populations.
"Essential fatty acids" in aquatic ecosystems: a crucial link between diet and human health and evolution
Authors: Arts Michael T , Ackman Robert G , Holub Bruce J
Published: April 2011

Fatty acids (FA) are inextricably linked with key physiological and biochemical processes and are thus integral to proper ecosystem functioning. FA not biosynthesized effectively by animals are termed essential fatty acids (EFA). These EFA are important "drivers" of ecosystem health/stability and are therefore highly conserved in aquatic food chains. Aquatic organisms have been and continue to be our primary source of readily available EFA. However, overfishing and our burgeoning population may be acting in concert to threaten our access to this source of EFA. Here, we review the marine FA synthesis/transport cycle and traditional and nontraditional sources of EFA. Our review suggests that, while some traditional sources of marine oils (e.g., tuna) are in steady decline, other sources (e.g., krill) and technologies (e.g., heterotrophic fermentation) hold great promise for maintaining our access to EFA. We provide a minireview which illustrates that EFA contribute to our health and well-being. Finally, there is growing evidence that EFA have been an important force in our past evolution, leading us and others to speculate that an unbroken link exists between EFA, our present health, and, in all likelihood, our continuing evolution.
Modelling the dispersal and mortality of Browns Bank egg and larval haddock (Melanogrammus aeglefinus)
Authors: Brickman David , Frank Kenneth T
Published: April 2011

An early life stage model is described with constant mortality for egg and larval stages. The model is used to simulate the stage 4 egg and larval data for haddock (Melanogrammus aeglefinus) in southwest Nova Scotia for the years 1983-1985. The model is initialized using published abundance and mortality estimates for these years, and its output is compared with field data. We find that the model does a systematically poor job of reproducing both the spatial-temporal and area-integrated versions of the data. To understand the discrepancy, we derive an integrated version of the model (integral model) and analyze its properties. This leads to a general method for determining whether sequential stage abundance data is consistent with a stage-dependent constant-mortality model. We use this method to show that a constant-mortality early life stage model is not consistent with the data. The integral model allows for year-day dependent mortality functions, which results in almost perfect fits to the abundance data. These functions can be transferred to the early life stage model with significantly improved model performance, although spatial differences remain. The implications of the integral-model analysis for sequential stage mortality estimation are discussed.
Conservation biology of marine fishes: perceptions and caveats regarding assignment of extinction risk
Authors: Hutchings Jeffrey A
Published: April 2011

Quantitative criteria used to assign species to categories of extinction risk may seriously overestimate these risks for marine fishes. Contemporary perception is that marine fishes may be less vulnerable to extinction than other taxa, because of great natural variability in abundance, high fecundity, rapid population growth, and an intrinsically high capability of recovering from low population size. Contrary to perception, however, there appears to be generally little theoretical or empirical support for the hypotheses that marine fish are more likely to experience large reductions in population size, to produce unusually high levels of recruitment, to have higher reproductive rates, or to recover more rapidly from prolonged population declines than nonmarine fishes. Although existing population-decline criteria may not accurately reflect probabilities of biological extinction, they do appear to reflect the converse-population recovery. Insufficient support for contemporary perceptions of their susceptibility to extinction, coupled with caveats associated with the assignment of extinction risk, suggest that significant increases in the population-decline thresholds used to assign marine fishes to at-risk categories would be inconsistent with a precautionary approach to fisheries management and the conservation of marine biodiversity.
What controls who is where in freshwater fish communities  the roles of biotic, abiotic, and spatial factors
Authors: Jackson Donald A , Peres-Neto Pedro R , Olden Julian D
Published: April 2011

We examine evidence for the structuring of fish communities from stream and lake systems and the roles of biotic, abiotic, and spatial factors in determining the species composition. Piscivory by fish is a dominant factor in both stream and lake systems whereas evidence for the importance of competition appears less convincing. Within small streams or lakes, the impact of predation may exclude other species, thereby leading to mutually exclusive distributions and strong differences in community composition. Within a geographic region, abiotic effects frequently dictate the relative importance of piscivory, thereby indirectly influencing the composition of prey species present. The spatial scale of studies influences our perceived importance of biotic versus abiotic factors, with small-scale studies indicating a greater importance of competition and large-scale studies emphasizing abiotic controls. The scale of the individual sites considered is critical because smaller systems have higher variability and wider extremes of conditions than larger lakes and rivers. The stability of physical systems and degree of spatial connectivity contribute to increased diversity in both larger stream and larger lake systems. We identify challenges and needs that must be addressed both to advance the field of fish community ecology and to face the problems associated with human-induced changes.
Does spawning stock affect recruitment of New England groundfish?
Authors: Brodziak Jon KT , Overholtz William J , Rago Paul J
Published: April 2011

We evaluated the effects of spawning-stock size on the recruitment abundance of 11 groundfish stocks in waters off New England. Empirical patterns of association between spawning biomass and recruitment were investigated using nonparametric approaches. For most stocks, higher recruitment occurred at high stock sizes and lower recruitment at low stock sizes. Survival ratios, indexed by recruitment per unit of spawning biomass, were higher at low stock sizes and lower at high stock sizes-as expected under density dependence. To assess assumptions about recruitment dynamics, we analyzed constant-recruitment and compensatory and overcompensatory stock-recruitment models with uncorrelated and autocorrelated error structures, using Bayesian methods of statistical inference. Although no single model was adequate for all stocks, most groundfish had better than even odds of having density-dependent dynamics, and most had better than even odds of having dynamics with uncorrelated environmental variation. While some geographic and taxonomic differences in potential productivity were apparent, all stocks exhibited compensation in survival ratio at low stock sizes, albeit with substantial variation. These results indicate that conservation measures intended to increase the spawning biomass of New England groundfish will, on average, result in higher recruitment and, eventually, in increased and more stable fishery yields.
Diel variation of stomach contents of North Sea cod (Gadus morhua) during a 24-h fishing survey: an analysis using generalized additive models
Authors: Adlerstein Sara A , Welleman Henny C
Published: April 2011

Results show that the weight of cod (Gadus morhua) stomach contents sampled in the North Sea varies significantly within 24 h. To determine whether feeding varied with time, over 1100 cod stomachs were collected around the clock between 7 and 18 May 1984 in two areas in the central North Sea thought to be representative for feeding studies. Here we investigate temporal feeding patterns based on the analysis of stomach-content data, using generalized additive models (GAMs). Results show significant variation of content weight and indicate morning and evening peaks. The relative peak importance differed between and within areas. We propose that differences are due to diet composition, namely, prey size and diel availability. Cod fed primarily on molluscs, mainly ocean quahog (Cyprina islandica), crustaceans, sandeels (Ammodytes spp.), haddock (Melanogrammus aeglefinus), herring (Clupea harrengus), and several flatfish species. In one area, the diet was dominated by fish, relatively large prey that perform diel vertical migration, and in the other by invertebrates, smaller prey that are digested faster. The diel pattern was more pronounced where invertebrate prey were dominant. Generalisation of results and implications for predation-mortality estimates based on data from the North Sea Stomach Content Database, used to implement multispecies models in the region, are discussed.
Habitat-, season-, and size-specific variation in diel activity patterns of juvenile chinook salmon (Oncorhynchus tshawytscha) and steelhead trout (Oncorhynchus mykiss)
Authors: Bradford Michael J , Higgins Paul S
Published: April 2011

Juvenile salmonids that live in streams are sometimes nocturnal and may spend the day concealed in the stream substrate. We observed the diel activity patterns of juvenile chinook salmon (Oncorhynchus tshawytscha) and steelhead trout (Oncorhynchus mykiss) in two areas of the Bridge River, British Columbia, in all four seasons. In a reach with higher flows, most fish were nocturnal year-round, and they emerged from the substrate only at dusk to forage. In the reach with lower flows, some fish were active in the water column in the day in summer, but others remained concealed in the substrate until dusk. Parr and older fish were more nocturnal in summer than fry. All fish were nocturnal in winter. Because our study design controlled for temperature and photoperiod, we concluded that the differences in behaviour that we observed between reaches were due to habitat conditions that likely affected the trade-off between more risky daytime foraging and less efficient, but safer, nighttime foraging. Habitat-driven variation in activity patterns will likely affect the processes that regulate these populations and could make the prediction of the effects of ecosystem manipulations such as changes in flow very difficult.
Effects of turbidity on prey consumption and growth in brook trout and implications for bioenergetics modeling
Authors: Sweka John A , Hartman Kyle J
Published: April 2011

Brook trout (Salvelinus fontinalis) were held in an artificial stream to observe the influence of turbidity on mean daily consumption and specific growth rates. Treatment turbidity levels ranged from clear (<3.0 nephelometric turbidity units (NTU)) to very turbid water (> 40 NTU). Observed mean daily specific consumption rates were standardized to the mean weight of all brook trout tested. Turbidity had no significant effect on mean daily consumption, but specific growth rates decreased significantly as turbidity increased. Brook trout in turbid water became more active and switched foraging strategies from drift feeding to active searching. This switch was energetically costly and resulted in lower specific growth rates in turbid water as compared with clear water. Bioenergetics simulations were run to compare observed growth with that predicted by the model. Observed growth values fell below those predicted by the model and the difference increased as turbidity increased. Abiotic factors, such as turbidity, which bring about changes in the activity rates of fish, can have implications for the accuracy of predicted growth by bioenergetics models.
Nested analysis of genetic diversity in northwestern North American char, Dolly Varden (Salvelinus malma) and bull trout (Salvelinus confluentus)
Authors: Taylor Eric B , Redenbach Zoë A , Costello Allan B , Pollard Susan J , Pacas Charlie J
Published: April 2011

Partitioning within-species genetic diversity is fundamental to conservation of the bioheritage, current viability, and evolutionary potential of individual taxa. We conducted a hierarchical analysis of genetic diversity in Dolly Varden (Salvelinus malma) and bull trout (Salvelinus confluentus) involving analysis of hybrid zones between Dolly Varden and bull trout, analysis of phylogenetic structure within species across their native ranges using mitochondrial DNA, and a microsatellite DNA survey of population subdivision of bull trout within single watersheds. Our analyses documented hybridization and some introgression between Dolly Varden and bull trout across a geographically widespread zone of secondary contact between the two species. Both species were subdivided into two major mtDNA lineages, and one lineage in Dolly Varden may have arisen through introgression with bull trout. Bull trout have low levels of microsatellite diversity within populations, but there was substantial interpopulation variation in allele frequencies. Allele frequency distributions suggested that recent, severe bottlenecks occur frequently in bull trout populations. Our results illustrate partitioning of genetic variation at distinct levels of biological organization (species, phylogeographic lineages, local populations), and we address how such nested variation is fundamental to conservation of biodiversity.
A regional paleolimnological assessment of the impact of clear-cutting on lakes from the central interior of British Columbia
Authors: Laird Kathleen , Cumming Brian
Published: April 2011

The impact of forest harvesting on lakes within the central interior of British Columbia was examined in a paleolimnological study of six lakes that had 2882% of their watersheds clear-cut (impact lakes) and four lakes that had experienced no logging in their watersheds (reference lakes). Changes in diatom species composition and percent organic matter in210Pb-dated sediment cores were compared over the last 80 years in each of the impact lakes before and after the onset of forest harvesting and, in the reference lakes, before and after 1960 (the average onset of logging in five of the six impact lakes) and before and after 1975 (the onset of logging in one impact lake). Significant changes in species composition of diatoms following forest-harvesting activities were detected in four of the impact lakes and three of the reference lakes; however, the changes in diatom species composition were small, with changes in the relative abundance of the most common species being at most 11%. Significant increases in the percent organic matter after 1960 were found in one impact lake and three reference lakes; again these changes were small, with increases of 25%.
Permutation tests for univariate or multivariate analysis of variance and regression
Authors: Anderson Marti J
Published: April 2011

The most appropriate strategy to be used to create a permutation distribution for tests of individual terms in complex experimental designs is currently unclear. There are often many possibilities, including restricted permutation or permutation of some form of residuals. This paper provides a summary of recent empirical and theoretical results concerning available methods and gives recommendations for their use in univariate and multivariate applications. The focus of the paper is on complex designs in analysis of variance and multiple regression (i.e., linear models). The assumption of exchangeability required for a permutation test is assured by random allocation of treatments to units in experimental work. For observational data, exchangeability is tantamount to the assumption of independent and identically distributed errors under a null hypothesis. For partial regression, the method of permutation of residuals under a reduced model has been shown to provide the best test. For analysis of variance, one must first identify exchangeable units by considering expected mean squares. Then, one may generally produce either (i) an exact test by restricting permutations or (ii) an approximate test by permuting raw data or some form of residuals. The latter can provide a more powerful test in many situations.
Effects of fishing on a protogynous hermaphrodite
Authors: Armsworth Paul R
Published: April 2011

Population dynamic models and simulations are analysed for a harvested reef fish species that is a monandric, protogynous hermaphrodite. The models are applied to data for the coral trout Plectropomus leopardus (Pisces: Serranidae) on the Great Barrier Reef. One model examines the situation where sexual transition is induced by some exogenous behavioural mechanism, and another considers the case where transition is determined by some endogenous developmental schedule. The conclusions regarding the effects of fishing are common to both models, and the implementation of more efficient harvesting practices may not require a precise understanding of the mechanisms governing sexual transition.
Laboratory testing of a growth hypothesis for juvenile squid Loligo pealeii (Cephalopoda: Loliginidae)
Authors: Hatfield Emma MC , Hanlon Roger T , Forsythe John W , Grist Eric PM
Published: April 2011

Growth modeling in squid has been hampered by a paucity of raw growth data on live individuals. We reared wild juvenile squid Loligo pealeii, for up to 97 days post capture, to determine the form of growth and to test the hypothesis that a 5°C difference in temperature would significantly affect growth rates. Precapture growth rates (the instantaneous relative growth rate or percent increase in body mass per day (IRGR)) of 811% were estimated using statolith age data. Laboratory growth rates over a maximum of 97 experimental days fell into two phases in which most L. pealeii grew exponentially, albeit at a slower rate in phase 2. In both phases, the values of IRGR were significantly higher for L. pealeii reared at 20°C than for those reared at 15°C, being respectively, 4.36 and 2.69 in phase 1 and 2.57 and 1.63 in phase 2. This study provides strong evidence of phase-specific temperature sensitivity in squid growth. The IRGR values obtained were used to simulate the growth of squid hatched in nature from May to September in a simple predictive model. The growth simulations indicated that, by the end of phase-1 growth, squid hatched in June and July were two and three times the weight, respectively, at the same age, as squid hatched in May, owing to their exposure to warmer temperatures.
Impact of mussel (Mytilus galloprovincialis) raft-culture on benthic macrofauna, in situ oxygen uptake, and nutrient fluxes in Saldanha Bay, South Africa
Authors: Stenton-Dozey Jeanie , Probyn Trevor , Busby Alistair
Published: April 2011

Culture of the mussel Mytilus galloprovincialis in a South African bay created organic enrichment and anoxia in sediments. Particulate organic matter (POM) was high under rafts versus the references, especially in the first 10 cm (C = 7.5 versus 0.4%, N = 0.7 versus 0.08%). Total reducible sulphides (TRS) increased threefold downcore (from 0.04 to 0.12%). High C:N ratios (1215) indicated accumulation of refractory POM, derived mainly from faeces and decaying mussels and foulers. Although O2 uptake by raft sediments was the lowest, rates could not conclusively be separated from the references. Ammonium dominated N efflux, the highest and most variable rates being under mussels (825 ± 500 µmol NH4·m2·h1). Phosphate efflux (25140 µmol·m2·h1) could not be ascribed to culture biodeposition, but there was an inconclusive trend for the molar N:P ratio to be highest in these sediments. Macrofauna biomass was reduced and trophic groups and taxa altered. Under rafts, macrofauna and organic debris were linked to O2 uptake rates, whereas at the reference sites, macrofauna appeared to be the major O2 consumer. It was concluded that POM and TRS in sediment as well as macrofauna biomass, and potentially molar N:P ratios, were more sensitive indicators of benthic impact from mussel culture than O2 uptake rates or nutrient fluxes.
Bioaccumulation and biomagnification of mercury in Lake Murray, Papua New Guinea
Authors: Bowles Karl C , Apte Simon C , Maher William A , Kawei Matthew , Smith Ross
Published: April 2011

The bioaccumulation of mercury in the food webs incorporating the major piscivorous fish species of Lake Murray, Papua New Guinea, has been characterised. Methylmercury concentrations increased with trophic level and the proportion of total mercury present as methylmercury increased from <1% in plants to 94% in piscivorous fish. Methylmercury bioaccumulation factors (BAFs) were similar to those found in temperate environments, with a typical increase of 1 log unit between planktivore and piscivore trophic levels. The greatest bioaccumulation of methylmercury occurred between seston and the water column (log BAF of 5.36). The bioaccumulation of mercury to levels of regulatory concern by the lake's piscivores was attributable to the biomagnification power of the plankton-based food chain comprising four trophic levels (phytoplankton, zooplankton, planktivore, piscivore) rather than any elevated concentrations of mercury in waters or sediments. The methylmercury concentrations of individual piscivores were positively correlated with both trophic position, as indicated by δ15N measurements, and fish size. Stable-isotope measurements were used to identify fish species where dietary changes occurring with age significantly augmented age-related bioaccumulation of mercury.
Isotopic turnover in aquatic predators: quantifying the exploitation of migratory prey
Authors: MacAvoy Stephen E , Macko Stephen A , Garman Greg C
Published: April 2011

In the tidal freshwaters of Virginia, U.S.A., the blue catfish (Ictalurus furcatus), an introduced piscivore, derives a significant proportion of its nutrition from spawning anadromous fish (genus Alosa, including blueback herring (A. aestivalis), American shad (A. sapidissima), and alewife (A. pseudoharengus)). Because the Alosa are not continually available to I. furcatus, there is an isotopic turnover, defined as change in isotope composition due to growth and metabolic tissue replacement, in I. furcatus tissues associated with the diet switch from freshwater to anadromous fishes. However, isotopic turnover rates for ictalurid fish are unknown. This study determined the maximum isotopic turnover rate of channel catfish (Ictalurus punctatus) tissues and compared this maximum rate with that of I. furcatus captured in the field over the 3-month Alosa spawning run. Maximum turnover rates for δ13C were 0.014 and 0.017 per day in muscle and blood. For δ34S, rates were 0.017 and 0.020 per day in muscle and blood, respectively. Isotopic turnover of muscle carbon reflected growth rate, but sulfur did not match growth as well. Ictalurus furcatus captured in the field showed no enrichment during the Alosa spawning run owing to slow turnover and variable diet. In aquatic ecosystems that have migrating prey, exploitation by predators may be underestimated using isotopes because of slow tissue turnover.
Effect of spawning day and temperature on salmon emergence: interpretations of a growth model for Methow River chinook
Authors: Beer W Nicholas , Anderson James J
Published: April 2011

A mechanistic temperature-dependent model for preemergent growth coupled with spawning and river temperature data is used to evaluate early life history strategies for chinook salmon (Oncorhynchus tshawytscha) in the Methow River, Washington, U.S.A. Since the model provides a predictable coupling between time of spawning and fry emergence, it helps explain the spatial and temporal patterns observed for the sympatric stocks. The model suggests that progeny of August-spawning chinook in upper river habitats emerge at button-up (no visible yolk sac) over a wide range of days in the early spring. The eggs grow efficiently, which maximizes fry mass. The progeny of October-spawning downstream chinook can exploit a wide range of habitats in the river because their emergence mass is not sensitive to location in the river, but the adults must spawn later in the season to avoid summer high temperatures. Late spawning forces fry to emerge prior to button-up to avoid scouring flows but synchronizes their emergence times. The trade-offs between the spawning strategies of these two salmon runs are complex and the seasonal and spatial distribution of temperatures plays a critical role in these trade-offs.
Response of the Cache Creek macroinvertebrates during the first 10 years following disturbance by the 1988 Yellowstone wildfires
Authors: Minshall G Wayne , Royer Todd V , Robinson Christopher T
Published: April 2011

We evaluated the effects of disturbance on stream benthic macroinvertebrates at the ecological scales of time, stream size, and burn extent in six segments of Cache Creek over the first 10 postfire years. Postfire changes in macroinvertebrate taxa richness, density, and dominant taxa in the burn streams were significantly different from those in the reference stream. Chironomidae and Baetis typically comprised 4060% of the macroinvertebrate assemblages of burned streams but only 1518% of the assemblage in the reference site. Coefficients of variation for the 10-year period indicated that richness, density, biomass, and Baetis abundance were more variable (1.23.5 times higher) in the burn streams than in the reference stream and that variability in Chironomidae abundance in burn sites increased with stream size. Fire effects were not attenuated progressively with increasing stream size, probably because the proportion of the catchment burned did not decrease. However, similar-sized streams in which 6871% of their catchments burned were more severely disturbed than those in which only 3947% burned. Long-term effects on the macroinvertebrate community were due largely to the loss of terrestrial vegetation and increased runoff, which caused severe alterations in stream channel conditions and large-scale bedload movement.
Reproductive potential of individual male blue crabs,Callinectes sapidus, in a fished population: depletion and recovery of sperm number and seminal fluid
Authors: Kendall Matthew S , Wolcott Donna L , Wolcott Thomas G , Hines Anson H
Published: April 2011

We evaluated the depletion and recovery rates of sperm number and vas deferens weight following mating for male Callinectes sapidus both below (<127 mm carapace width) and well above (>140 mm) the fishery size limit for hard crabs in Chesapeake Bay (127 mm). Large males had low sperm count and vas deferens weight immediately after mating and required approximately 920 days to fully recover. After mating, small males had significant reduction in sperm number despite no significant change in vas deferens weight. Furthermore, small males with completely recovered seminal stores had significantly lower vas deferens weight than fully recovered large males but did not differ significantly from large males in number of sperm. The changes in vas deferens weight and sperm count following experimental mating suggest that large males delivered 21 times as much seminal fluid and 2.25 times as much sperm as small males. Field collections in a subestuary of Chesapeake Bay revealed that the majority (5090%) of males had extremely low vas deferens weight relative to males with fully recovered sperm volume. Since the fishery targets males primarily, reducing both the number and average size of males in the population, many females may be mated with small or recently mated males that transfer less seminal material.
Impact of zebra mussels (Dreissena polymorpha) on the pelagic lower trophic levels of Oneida Lake, New York
Authors: Idrisi Nasseer , Mills Edward L , Rudstam Lars G , Stewart Donald J
Published: April 2011

We analyzed a data series on nutrients, phytoplankton, zooplankton, and young-of-the-year fish from Oneida Lake, New York, to test several hypotheses relating the response of the pelagic food web to grazing by zebra mussels (Dreissena polymorpha). System-wide grazing rates increased by one to two orders of magnitude after zebra mussel introduction. The most dramatic change associated with dreissenid grazing was increased water clarity and overall decrease in algal biovolume and Chl a. Contrary to predictions, primary production did not decline. We attribute the lack of whole water column decline in primary productivity to the compensating effect of increased water clarity resulting in deeper penetration of photosynthetically active radiation. We observed no change in total or dissolved phosphorus concentrations. Although algal standing crop declined, Daphnia spp. biomass and production did not, but dominance shifted from Daphnia galeata mendotae to Daphnia pulicaria. Consistent with our findings in the lower food web, we found no evidence that zebra mussels had a negative impact on young yellow perch (Perca flavescens) growth, biomass, or production. Thus, despite the order of magnitude increase in grazing rates and associated decrease in algal biomass, pelagic production at primary, secondary, and tertiary levels did not decline in association with zebra mussels.
Effects of individual quotas on catching efficiency and spawning potential in the Alaska sablefish fishery
Authors: Sigler Michael F , Lunsford Chris R
Published: April 2011

Individual fishery quota (IFQ) management eliminates the race for fish and may improve economic efficiency, conservation, and safety in fisheries. Empirical information documenting these effects is limited, even though IFQs have been used since the late 1970s. We analyzed fishery data from the Alaska sablefish (Anoplopoma fimbria) longline fishery, which came under IFQ management in 1995. We compared the fishery data with fishery-independent survey data, which acted as a control to separate annual changes in population demographics from changes due to IFQ management. We found that IFQ management increased fishery catch rate and decreased harvest of immature fish. Catching efficiency increased 1.8 times with the change from an open-access to an IFQ fishery. The improved catching efficiency of the IFQ fishery reduced variable costs to catch the quota from 8 to 5% of landed value, a savings averaging $3.1 million US annually. Decreased harvest of immature fish improved the chance that individual fish will reproduce at least once. Spawning potential of sablefish, expressed as spawning biomass per recruit, increased 9% for the IFQ fishery. Switching from the open-access fishery's race for fish to IFQs provided two clear benefits that should be considered when evaluating management options for other open-access fisheries.