bluuebunny/crossref_metadata_2025 huggingface dataset:
Bioeconomic Model of the Lake Michigan Alewife (Alosa pseudoharengus) Fishery
Authors: Hanson Floyd B.
Published: June 2008

A stochastic bioeconomic model is developed for the Lake Michigan alewife (Alosa pseudoharengus) fishery. This theoretical model possesses an intermediate degree of complexity and realism. Other Lake Michigan fish stocks are included in a simplified way as an aggregate, to account for interspecific predation by salmonids, but competition could be treated as well. Both alewife and aggregate fisheries are modeled by modifications of Beverton–Holt single-cohort models with growth in weight and interspecific interactions. The alewives are also subjected to large random disasters and it is demonstrated that these are density independent. The methodology is stochastic, feedback, optimal control using dynamic programming. Stochastic terms are used to represent random disasters in the alewife population. The computational results are given in terms of the maximal, expected economic values of the combined fishery and the optimal rates of harvest for both the alewives and aggregate fisheries. These results are new in the sense that continuous dynamic programming has been applied to a model for several interacting species undergoing occasional random shocks. The expected, optimal economic value of the combined fishery is much less sensitive to the initial recruitment of alewives than to that of the salmonid aggregate. Comparison with a deterministic model that does not include the random disasters shows that the disasters reduce the economic value of the combined fishery by 10–15%. The results are sensitive to reasonable data estimates and confirm the overexploitation of alewives by both the alewife fishery and salmonid predation. The need for reliable data with a common basis is emphasized with regard to comparing commercial and sport fisheries.
Multispecies versus Single-Species Assessment of North Sea Fish Stocks
Authors: Daan Niels
Published: June 2008

Development of multispecies virtual population analysis (MSVPA), which assesses interspecific and intraspecific predation through an analysis of stomach contents, has verified the hypothesis that predation among exploited fish species contributes significantly to their natural mortality and that predation, and thus natural mortality, is inherently variable from year to year. In single-species virtual population analysis (SSVPA), natural mortality is assumed to be constant. MSVPA also suggests that natural mortality among young fish after recruitment is much higher than previously thought. Although catch quotas based on predictions of short-term catches from multispecies assessments would appear to differ little from those derived from single-species assessments, and certain problems remain to be resolved before multispecies assessments can be accepted for fish stock management, the method has considerable implications for management. For instance, it suggests that effects of mesh sizes and bycatch on fisheries need reevaluation and that year class strength may not be as fixed as previously assumed.
Yield and Dynamics of Destabilized Chub (Coregonus spp.) Populations in Lakes Michigan and Huron, 1950–84
Authors: Brown Jr. Edward H. , Argyle Ray L. , Payne N. Robert , Holey Mark E.
Published: June 2008

Deepwater ciscoes (Coregonus spp.) or "chubs" of Lake Michigan far surpassed those of Lake Huron in yield, population density, and resilience following severe depletion in the 1960s and 1970s, when the bloater (C. hoyi) composed more than 90% of the stocks. The population decline of bloaters in recent decades was mainly attributed to exploitation, to the depression of chub recruitment (e.g. from inferred predation on early life stages) by nonendemic alewives (Alosa pseudoharengus) and rainbow smelt (Osmerus mordax), and to complications arising from extreme female predominance that was best documented for Lake Michigan. The various interactions between bloaters and the nonendemic species, which were intensified after the loss of large predators to sea lamprey (Petromyzon marinus), would help to explain why a stock–recruitment relation was not shown for the Lake Michigan bloater. We hypothesize that reproductive inefficiency caused by a shift to strong female predominance in the bloater depresses recruitment and thus helps to regulate abundance. However, the low resilience that sex imbalance seems to impart makes the stock unstable when exploited. It should therefore be exploited conservatively during such periods. Also, the sex ratio and its direction of change appear to be important qualifiers when surplus production is estimated from stock size.
Problems Associated with Fisheries Assessment Methods in the Great Lakes
Authors: Christie W. J. , Goddard Chris I. , Nepszy Stephen J. , Collins John J. , MacCallum Wayne
Published: June 2008

This paper presents a review of Great Lakes fishery assessment problems and addresses the variety of fisheries, the special circumstances created by rehabilitation, the emergence of joint strategic planning among fishery agencies, and convergence of water quality and fishery management. The inferences that emerge are that (1) continuing observation series are essential, (2) the variety of needs calls for a variety of assessment approaches, and (3) assessment objectives need to be clearly defined in order to protect the ongoing monitoring series. It is suggested that more attention should be given to fish community monitoring, to sport fishery statistics, and to gear calibration. On the other hand, improved coordination of human and material resources and focus on integration of water quality and fisheries assessment can achieve much, without great funding increases.
Meeting Future Information Needs for Great Lakes Fisheries Management
Authors: Christie W. J. , Collins John J. , Eck Gary W. , Goddard Chris I. , Hoenig John M. , Holey Mark , Jacobson Lawrence D. , MacCallum Wayne , Nepszy Stephen J. , O'Gorman Robert , Selgeby James
Published: June 2008

Description of information needs for management of Great Lakes fisheries is complicated by recent changes in biology and management of the Great Lakes, development of new analytical methodologies, and a transition in management from a traditional unispecies approach to a multispecies/community approach. A number of general problems with the collection and management of data and information for fisheries management need to be addressed (i.e. spatial resolution, reliability, computerization and accessibility of data, design of sampling programs, standardization and coordination among agencies, and the need for periodic review of procedures). Problems with existing data collection programs include size selectivity and temporal trends in the efficiency of fishing gear, inadequate creel survey programs, bias in age estimation, lack of detailed sea lamprey (Petromyzon marinus) wounding data, and data requirements for analytical techniques that are underutilized by managers of Great Lakes fisheries. The transition to multispecies and community approaches to fisheries management will require policy decisions by the management agencies, adequate funding, and a commitment to develop programs for collection of appropriate data on a long-term basis.
Concepts and Methods of Community Ecology Applied to Freshwater Fisheries Management
Authors: Evans D. O. , Henderson B. A. , Bax N. J. , Marshall T. R. , Oglesby R. T. , Christie W. J.
Published: June 2008

In this paper we review selected theory, hypotheses, and methods of community ecology with reference to fisheries management. Community ecology is concerned with theoretical and empirical studies of the behavior of species assemblages over space and time. Ideas that have evolved from these types of studies concerning hierarchical organization, resource partitioning, food webs, structural integration, stability, complexity, and production and their relevance to fisheries management are discussed. One main conclusion confirmed by the ASPY Symposium is that the productivity of fish communities is determined by energy inputs, nutrients, edaphic factors, and habitat variables but that the distribution of the production by species is strongly influenced by interactions between species. A related conclusion is that species interactions are size dependent because of morphological, physiological, and behavioral constraints on predator–prey relationships, resulting in a hierarchical organization. Further, density-dependent interactions (predation, competition) within and between species influence growth rates, size distributions, and age-specific mortality and reproductive rates, and vice versa. Anthropogenic factors such as fishing, nutrient enrichment, introduction of exotic species, and chemical contaminants tend to act differentially at the level of species, but due to interdependencies between species their effects are propagated at the community level by disrupting its size- and niche-structured organization. Fish communities can be managed as relatively discrete functional units, but dependency on whole system dynamics ultimately necessitates an ecosystem perspective. Development of a more quantitative theory of fish community dynamics will require improved descriptions of species interactions (food web structure, ontogenetic histories, resource partitioning, and body size dependency), better characterization of complexity, stability, and successional change in fish communities, additional knowledge of energy transfer through aquatic ecosystems, and improved methods of estimating biomass distributions in fish communities. Comparative studies over space and time and experimental and adaptive management are appropriate ways for fishery scientists and managers to acquire this knowledge.
A Perspective on Great Lakes Fish Community Rehabilitation
Authors: Christie W. J. , Spangler G. R. , Loftus K. H. , Hartman W. L. , Colby P. J. , Ross M. A. , Tashelm D. R.
Published: June 2008

Review of the ASPY syntheses suggested that destabilization and subsequent fish community recovery in the Great Lakes are compatible with a model in which postglacial succession, and the structure and persistence of the fish communities, were governed by piscivores. Recent advances in the areas of particle size distribution, ontogenetic niche theory, and ecosystem stability contributed to a broader understanding of fishery management alternatives. Species succession in Great Lakes aquatic communities is characterized as a cyclic repetition of maturation followed by seasonal, annual, or periodic setbacks. These are termed "enjuvenation events" and are attributed to any cultural or climatic factors which induce flux in energy–matter delivery to the system. The extent of enjuvenation is dependent upon the magnitude of the perturbation and maturity of the community and is predictable to some degree by the age and biomass distributions of the species present. The time course of rehabilitation to any arbitrary prior condition of the community is closely related to the enjuvenation–maturation cycle and to the life span and reproductive characteristics of the species present. The principal homeostatic mechanism is perceived to lie with variations in the durations of life history stanzas as affected by fish growth rates. The "biomass storage" function of larger organisms in the system is thought to be a major determinant of the "biotic inertia" or sensitivity of the community to perturbations. We are convinced that trophic linkages from the piscivores downwards must be maintained as biological feedback pathways to ensure that moderately excessive fishery yields can be self-limiting. Without these linkages (vulnerable to intensive exploitation or other catastrophic reductions in predators), biomass capture of nutrient inputs by algae will vector to waste as planktivore density limits secondary production. The extent to which the fish community can be maintained or driven to a particular species composition is dependent upon the degree of external control of all sorts that can be applied to the system. The rehabilitation continuum ranges from a self-sustaining assemblage of native species requiring little external control to a completely artificially supported community of non-native species requiring extensive controls for both water quality and fish community maintenance.
Experimental Mesocosm Study of the Separate and Interaction Effects of Phosphorus and Mosquitofish (Gambusia affinis) on Plankton Community Structure
Authors: Lancaster Holli F. , Drenner Ray W.
Published: June 2008

We examined community impacts of phosphorus and mosquitofish (Gambusia affinis) in an experimental mesocosm study of factorial design in which two levels of phosphorus addition were cross-classified with two levels of fish. Total phosphorus (TP), chlorophyll, cryptomonads, unicellular green algae, unicellular blue-green algae, colonial blue-green algae, filamentous blue-green algae, chironomid tube length, cladocerans, fish density, and fish biomass were significantly enhanced in the presence of phosphorus addition. Total nitrogen (TN), TN:TP ratio, Secchi depth, chrysophytes, and periphytic diatoms were suppressed in the presence of phosphorus addition. Diatoms, filamentous blue-green algae, chrysophytes, periphytic unicellular and colonial green algae, periphytic filamentous blue-green algae, and rotifers were enhanced in the presence of mosquitofish. Secchi depth, TN:TP ratio, cyclopoid copepodids, nauplii, cladocerans, and chironomid tubes were suppressed in the presence of mosquitofish. We found significant phosphorus × mosquitofish interaction effects for TN:TP ratio, chrysophytes, dinoflagellates, periphytic colonial green algae, cladocerans, and chironomid tubes. These results show that nutrients and fish do not act as independent regulators of plankton communities but instead have effects which can only be predicted from an understanding of their combined impacts.
Lake Dynamics and the Effects of Flooding on Total Phosphorus
Authors: Kenney Bernard C.
Published: June 2008

The concentration of total phosphorus in Lake Washington before and after the sewage diversion project was simulated using first-order linear dynamics. Fluctuation in total phosphorus in the lake occurred as a forced response to changes in inflow phosphorus concentration. The dynamics of total phosphorus in Lake Washington was adequately represented by two independent time scales based on water renewal and sedimentation. The water renewal time scale was modelled as a time dependent process. Sedimentation of total phosphorus, on the other hand, appeared constant over the 16-yr period that data were available. A marked increase of total phosphorus in the lake occurred during two flood periods when high concentrations of total phosphorus corresponded to small values of the water renewal time scale (i.e., high flows). At other times, peak concentrations of total phosphorus in the inflow coincided with large values of the water renewal time scale and the lake was dynamically unable to respond to these peaks.
A Comparison of the Growth of Vertically-Migrating and Nonmigrating Kokanee (Oncorhynchus nerka) Fry
Authors: Johnston N. T.
Published: June 2008

A comparison of the growth of vertically-migrating kokanee (Oncorhynchus nerka) fry and nonmigrating fry confined to the epilimnion in thermally-stratified Kootenay Lake, British Columbia rejected the bioenergetic efficiency hypothesis for the adaptive significance of vertical migration. Growth rates were higher for nonmigrating fry than for vertically-migrating fry. Geometric mean wet weights in early October were 2.88 g for non-migrating fry and 1.40 g for vertically-migrating fry of the same stock. The geometric mean weight of fry of a second stock rearing in the isothermal West Arm, in which behavioural thermoregulation by vertical migration was not possible, was 8.54 g in early October.
Plant Pigments as Tracers of Emergent and Submergent Macrophytes from the Hudson River
Authors: Bianchi Thomas S. , Findlay Stuart
Published: June 2008

Ratios of photosynthetic pigment concentrations in aquatic macrophytes can provide a useful way to differentiate between inputs of emergent versus submergent macrophytes into aquatic food webs. Using reversed-phase HPLC we examined the distribution of carotenoid and chlorophyll pigment markers in eight macrophytes from the tidal freshwater portion of the Hudson River. Lutein was the most abundant carotenoid in all macrophytes, and concentrations in the emergent forms were significantly higher. Chlorophyll-b showed significantly higher concentrations in the submerged macrophytes than in the emergent forms. The chlorophyll-b/lutein ratio may be a useful marker to distinguish between organic inputs of submergent and emergent forms of macrophytes in aquatic ecosystems.
Recruitment Mechanisms of Bloater in Lake Michigan: an Analysis of the Predatory Gauntlet
Authors: Luecke Chris , Rice James A. , Crowder Larry B. , Yeo Steven E. , Binkowski Fred P.
Published: June 2008

Laboratory experiments were used to evaluate the potential importance of size-dependent predation on bloaters through the first 1–2 mo after hatching. Of the potential predators encountered by bloater eggs and larvae during their hypolimnetic phase, only scuplins appear important. Sculpin feeding rate on eggs increased when egg or larval density was high. The presence of amphipods as alternative prey enhanced predation on eggs when on cobble but reduced predation when eggs were on sand. Sculpin feeding rate on larvae decreased when amphipods were present. All three epilimnetic predators, yearling alewife, smelt, and bloaters, readily ate bloater larvae. The presence of zooplankton as alternative prey reduced predation on larvae by smelt and bloaters, but not by alewives Capture success was strongly size-dependent for all three predators. All three species exhibited the same exponential decline in handling time with increasing predator:prey ratio. Computer simulations using results from these experiments show that when mortality is size-dependent, small changes in growth rate can have dramatic effects on survival. Sculpins and alewife are likely to be the most important predators in determining bloater recruitment in Lake Michigan.
Mitochondrial DNA Variation among Anadromous Populations of Cisco (Coregonus artedii) as revealed by Restriction Analysis
Authors: Bernatchez Louis , Dodson Julian J.
Published: June 2008

Mitochondrial DNA (mtDNA) restriction analyses were done to test the hypothesis that river populations of anadromous cisco from James-Hudson Bays that exhibit life-history variations are reproductively isolated. MtDNA variation among 141 cisco (Coregonus artedii) from eight rivers was studied with eight hexameric, four multihexameric and one multipentameric restriction enzymes which generated a mean of 78 fragments per fish. Pair-wise sequence divergence estimates among the 19 mtDNA clones resolved were generally low but highly variable (mean: 0.52%, range: 0.08 to 1.03%). UPGMA and Wagner parsimony analysis revealed two major clonal groups which differed in diversity and geographic distribution; the more diversified (nucleon diversity index; 0.70) and less diversified (0.31) groups were twice as abundant in James and Hudson Bays, respectively. This suggests that cisco of James-Hudson Bays are derived from two glacial refugia and that they recolonized the area by two major postglacial routes. The frequency distribution analysis of all defined clones revealed significant stock discreteness among Hudson Bay populations and a lack of population subdivision in James Bay. The genetic structuring and diversity of anadromous cisco in James-Hudson Bay is discussed in relation to historical biogeographical events and to interactions of various life-history stages with the physical oceanographic environment.
Transport and Storage of 137Cs and 210Pb in Sediments of Lake St. Clair
Authors: Robbins John A. , Mudroch Alena , Oliver Barry G.
Published: June 2008

In 1985 cores were collected by diver from areas with fine-grained sediments in Lake St. Clair. Although the lake is shallow, rapidly flushed, and possesses only a thin layer of postglacial sediment (ca. 30 cm max.), 8% of the estimated, 137Cs loading from atmospheric nuclear testing in the mid-1960s and 13% of the potential standing crop of excess 210Pb were retained. A sediment column transport model including eddy diffusive mixing, advection and resuspension, acceptably described the vertical distribution of these radionuclides as well as stable lead and implied that such efficient retention may be of recent origin, occurring with the onset of net sedimentation about 100 yr ago. The model showed that, at selected sites, the history of lake loading by particle-associated contaminants can be reconstructed from sediment profiles. Horizontally averaged characteristics of the deposit indicate a surface mixed layer mass of 5 g∙cm−2 and tracer residence time of 3 yr in accord with residence times of surficial Hg, PCBs, and DDT. Trap-collected materials from two sites show markedly contrasting seasonal variations in,137Cs activity reflecting differing proportions of particles derived from inflow (ca 300 mBq∙g−1) and resuspension (< 30 mBq∙g−1).
Storage and Dynamics of Subsurface Detritus in a Sand-Bottomed Stream
Authors: Metzler Glenn M. , Smock Leonard A.
Published: June 2008

Annual mean storage of buried detritus (0–20 cm depth) in a first-order, sand-bottomed stream was 4.8 kg AFDM/m2, approximately one order of magnitude greater than surface storage. Forty percent of the buried detritus was wood > 8 mm; much of the remainder was 1–8 mm particles. Exchange of detritus between surface and shallow sediments occurred throughout the year; exchange between surface and deep sediments occurred only during spates Heavy rainfall during a September hurricane caused a mean scour depth of 6 cm (range = 0–27 cm) and contributed to a 0 94 kg/m2 reduction of buried detritus. Buried leaves were processed slower than leaves on the sediment surface (25% of initial buried leaves remained after 1 yr). Particles < 8 mm were processed faster from January to March (19% mass reduction) than at other times (8–9% mass reduction). Except during the September spate burial was approximately offset by decomposition. About 21% of estimated autumnal leaf input to the stream became buried. Given the large quantity of detritus stored in the subsurface, its slow processing rate and the episodic nature of its release from deep storage, the hyporheic area of this stream has an important effect on the stream's carbon spiralling length, energetics, and trophic dynamics.
Ranking Loci for Genetic Stock Identification by Curvature Methods
Authors: Gomulkiewicz Richard , Brodziak Jon K. T. , Mangel Marc
Published: June 2008

Measures of the utility of loci in genetic stock identification problems are usually not based on the method of maximum likelihood, which is the actual statistical procedure used to estimate stock contributions. We present a general procedure, derived from the likelihood method, for assessing the utility of baseline data. The method depends on the curvatures of potential likelihood surfaces and can be used prior to mixture sampling. We also develop a real time implementation of a curvature measure and apply it to simulated mixture samples. The error in likelihood estimation depends on the amount of variation in genotype frequencies between reference samples as well as the location of the center of that variation. The curvature measure accounts appropriately for both factors and, in addition, is able to quantify the synergistic interaction of multiple loci. The curvature approach and simulation results are also applied to the problem of sampling allocation.
A Genetic Mixture Analysis for use with Incomplete Source Population Data
Authors: Smouse Peter E. , Waples Robin S. , Tworek Joseph A.
Published: June 2008

While anadromous salmonids reproduce in fresh water, most harvests occur at sea. Effective genetic management requires knowledge of the stock (source population) composition of the harvest. This is accomplished with genetic stock identification (GSI), which compares the genotypes of harvested fish with those of freshwater stocks, assuming that all candidate stocks are identified and that their allele frequencies are known exactly. We develop methods that: (1) allow for sampling error in allele frequencies of candidate stocks, and (2) evaluate the possibility of unsampled contributing stocks. Composition analysis for chinook salmon (Oncorhynchus tshawytscha) collected for the Bonneville Dam egg bank program in 1980 and 1981 shows that about 10% of both harvests were from the Deschutes River and about 90% from the Hanford Reach area. Contributions from lower Columbia and Snake River stocks or from unidentified sources were limited.
Determination of Fish Movement Patterns from Tag Recoveries using Maximum Likelihood Estimators
Authors: Hilborn Ray
Published: June 2008

A general method for analysis of movement data from tag returns is proposed which has four major components: (1) a population dynamics and movement model that describes how the number of tagged individuals in each spatial location changes over time; (2) an observation model which describes how the tags are recovered and reported; (3) a likelihood function that specifies the likelihood of observing a specific number of recoveries in each space/time stratum as a function of the number thought to be there under a specific set of parameters of the population dynamics, movement and observation models, and (4) a nonlinear function minimization computer algorithm. This approach is applied to movements of skipjack tuna (Euthynnus pelamis). When tagging and recapture take place in each spatial stratum, reliable estimates of movement rates can be obtained. The approach described is completely general and can be used in cases where movement takes place continuously, or only once in the life history. Methods for determining confidence limits and evaluation of residuals are presented and extensions that include tagging mortality, tag shedding, and size specific vulnerability are discussed.
An Evaluation of the Effects of Atmospheric Acidic Deposition on Fish and the Fishery Resource of Canada
Authors: Kelso J. R. M. , Shaw M. A. , Minns C. K. , Mills K. H.
Published: June 2008

In Canada, 7.6% of our nation's surface area is water, and approximately 38% of this is found in regions susceptible to acidic atmospheric deposition. We estimate that 390 000 lakes in eastern Canada are sensitive to acidification, and provide significant revenue through the sport fishery to the economy. Evidence indicates that Sudbury lakes and Nova Scotian rivers acidified in the 1950's, '60's, and probably early '70's. Well documented cases of loss of fish species or production due to acidification are restricted to these two regions. However, the documentation of low pH lakes in areas of high acid loading suggest that acidification is more widespread. Recent increases in pH in some Sudbury and Algoma lakes, concomitant with reestablishment of fish populations, indicates that chemical and biological recovery is possible. Evidence from diverse experimental approaches–surveys, bioassays, and whole lake manipulation – are supportive in identifying fish responses to acidification. Fish community response is dependent upon several factors: complexity of the community, stage of acidification, species sensitivity, and availability of tolerant species to invade. If replacement of extirpated species by tolerant ones occurs, total fish biomass may remain stable until critical depauperation. It is unlikely we will be able to directly document further losses due to acidification.
Role of Instream Rootwads as Juvenile Coho Salmon (Oncorhynchus kisutch) and Steelhead Trout (O. mykiss) Cover Habitat Under Varying Streamflows
Authors: Shirvell C. S.
Published: June 2008

Coho salmon fry (Oncorhynchus kisutch) and steelhead parr (O. mykiss) occupied previously infrequently-used mid-channel areas of Kloiya Creek, British Columbia, Canada, once artificial rootwads were placed there. Ninetynine percent of all coho salmon fry and 83% of steelhead parr occupied positions downstream of natural or artificial rootwads during artificially created drought, normal, and flood streamflows. Fish associated with rootwads regardless of distance from shore, but steelhead parr preferred rootwads away from shore while coho salmon fry preferred rootwads next to shore. Coho salmon fry increased their use of natural rootwads where currents were slow during floods, while steelhead parr increased their use of artificial and natural rootwads where light remained low during droughts. Young fish apparently selected areas having slower water 80% of the time because they provided shelter from adverse current, and areas having reduced light intensities 20% of the time because they provided protection from predators, juvenile coho salmon and steelhead in Kloiya Creek selected locations with slower water velocities and reduced light intensities irrespective of the physical structure that caused them.
Increased Juvenile Salmonid Growth by Whole-River Fertilization
Authors: Johnston N. T. , Perrin C J. , Slaney P. A. , Ward B. R.
Published: June 2008

Nutrient concentrations, periphyton standing crop and size of steelhead trout (Oncorhynchus mykiss) and coho salmon (O, kisutch) fry increased after the fertilization of a nutrient-deficient stream with inorganic phosphorus (P) and nitrogen (N). Whole-river fertilization of the Keogh River, British Columbia, during 1983–86 to increase summer average nutrient concentrations from < 1 μg P∙L−1 and 25 μg N∙L−1 to 10–15 μg P∙L−1 and 30–100 μg N∙L−1 resulted in five- to 10-fold increases in periphyton standing crops on artificial substrata and 1.4- to 2.0-fold increases in late-September salmonid fry weights. Diatoms and chlorophytes dominated the algal periphyton on artificial substrata at fertilized sites. Cyanophytes were unimportant despite low N:P ratios in some cases. Juvenile salmonids fed primarily on benthic insects. These results suggest that autochthonous primary production can be an important energy source in forested, middle-order streams, and indicate that the manipulation of autochthonous primary production can be a useful management tool to increase salmonid growth in nutrient-poor coastal streams.
Influence of Prey Abundance on Species and Size Selection by Young Yellow Perch (Perca flavescens)
Authors: Confer John L. , Mills Edward L. , O'Bryan Linda
Published: June 2008

Prey selection by young yellow perch (Perca flavescens) (22–62 mm TL) was measured during 11 experiments over two summers, 1982–83. For each experiment fish were offered different densities of the same mixture of zooplankton from Oneida Lake, NY. As density of prey increased, several measures of selectivity for Daphnia either remained unchanged or declined, while all measures of selectivity for calanoids and cyclopoids increased. At all densities small to mid-sized Daphnia were preferred to large Daphnia. Reanalyses of other studies suggests this may be the general pattern for young planktivores, despite the contrary predictions of several models of prey selection. For young planktivores, differences in the nutritional quality of zooplankton prey, including resultant growth efficiency and speed of digestion, can account for these results.
Hydrogen Peroxide Decay in Waters with Suspended Soils: Evidence for Biologically Mediated Processes
Authors: Cooper William J. , Zepp Richard G.
Published: June 2008

Hydrogen peroxide decay studies have been conducted in suspensions of several well-characterized soils and in natural water samples. Kinetic and product studies indicated that the decay was biologically-mediated, and could be described by pseudo first-order rate expressions. At an initial H2O2 concentration of 0.5 μM, the hydrogen peroxide half-life varied from 1 to 8 h. The decay was inhibited by thermal and chemical sterilization of the soils. Peroxidase activity was inferred in several natural water samples, where the suspended particles catalyzed the oxidation of p-anisidine by hydrogen peroxide. The mass spectrum of the major reaction product indicated that it was the dimer, possibly benzoquinone-4-methoxyanil, a product that also was observed from the horseradish peroxidase-catalyzed oxidation of p-anisidine by hydrogen peroxide.
Temporal Changes of Allele Frequency in Pacific Salmon: Implications for Mixed-Stock Fishery Analysis
Authors: Waples Robin S.
Published: June 2008

The effects of temporal variation in allele frequency on mixed-stock fishery analysis of Pacific salmon (Oncorhynchus spp.) are examined. The concept of effective sample size (Se), which equates the precision obtained from a sample from a finite population with that from one with no temporal variability, is used to evaluate the magnitude of the problems introduced by genetic drift. Results from simulations modeling the overlapping year-class pattern typical of chinook salmon (O. tshawytscha) indicate that the ratio of effective to actual sample size (Se/S) is determined primarily by the ratio of sample size to the effective number of breeders per year (S/Nb). Unless Nb is large relative to S, effective sample size can be considerably less than the actual number of individuals sampled. Sampling in more than 1 yr results in a higher Se than does taking the same total number of individuals in 1 yr; furthermore, the advantages to multiple sampling are greatest in small populations, in which the effects of genetic drift are most pronounced. By choosing an appropriate sampling strategy, the sources of uncertainty in the analysis attributable to genetic drift can be reduced below any arbitrary level.
Recent Trends in the Abundance of Harbour Seals,Phoca vitulina, in British Columbia
Authors: Olesiuk Peter F. , Bigg Michael A. , Ellis Graeme M.
Published: June 2008

Aerial censuses of harbour seals (Phoca vituiina) were conducted in the Strait of Georgia (1966–88), the lower Skeena River (1977–87), off the southwest coast of Vancouver island (1976–87), off the northeast coast of the Queen Charlotte Islands (1986), in Jervis Inlet (1987), and at the entrance to Queen Charlotte Strait (1988). The estimated number of seals in the Strait of Georgia, the primary study area, increased from 2170 in 1973 to 15 810 in 1988; the number in the lower Skeena River from 520 in 1977 to 1590 in 1987; and the number off south western Vancouver Island from 210 in 1976 to 1130 in 1987. The trends indicated that populations throughout British Columbia had been increasing at a rate of about 12.5% ∙yr−1since 1973. Based on the density of seals in the areas surveyed, and the relative distribution of bounty and commercial kills, the total post-pupping population in British Columbia was estimated to have numbered 75 000–88 000 in 1988, compared with 9000–10 500 when the species was protected in 1970. Despite the recent increases, which probably reflect the recovery from historic kills, there was no evidence of density-dependent changes in the population growth rate.
Sampling Littoral Fish with a Seine: Corrections for Variable Capture Efficiency
Authors: Pierce Clay L. , Rasmussen Joseph B. , Leggett William C.
Published: June 2008

Capture efficiency of a beach seine varies greatly depending on aspects of the littoral zone habitat and fish community. To address this sampling bias, we quantified seine efficiency and several habitat and fish community variables at 26 littoral stations in 10 southern Quebec lakes. We then generated regression models predicting capture efficiencies for total, midwater, and benthic fish. Predictions from these models yield "sliding" correction factors for seine catches. Bottom snags and seine rolling generally reduced capture efficiencies, and higher proportions of benthic fish were associated with reduced capture efficiencies for total fish. Higher macrophyte biomass was associated with increased capture efficiencies. Fish size was a significant predictor of capture efficiency only for benthic fish; smaller fish escaped the seine more readily. Regression models explained 26–73% of the observed variation in capture efficiency. Use of our models will improve the accuracy of abundance estimates from littoral seining with little additional effort.
Urchin Foraging and Algal Survival Strategies in Intensely Grazed Communities in Eastern Canada
Authors: Himmelman John H. , Nédélec Henri
Published: June 2008

We examine relationships between food preferences of the urchin, Strongyhcentrotus droebachiensis, and such properties of fleshy macroalgae as dry mass, ash content, calorific value, and phenolic content. Grazing resistant algae characteristic of urchin dominated habitats rank low in attraction, reflecting the ability of urchins to detect and locate them in the field. They fall into two groups, (1) reds, Phycodrys rubens, Turnerella pennyi, and Ptilota serrata, with a high proportion of dry matter and low phenolic content, and (2) browns, Desmarestia viridis and Agarum cribrosum with low to intermediate calorific values. Algae susceptible to grazing fall into two additional groups, (3) algae with high dry mass which strongly attract urchins and are consumed at an intermediate rate (mostly annuals), and (4) readily eaten perennials which attract urchins to an intermediate degree and have high ash and low phenolic content. The susceptible algae survive through spatial and temporal escapes, mainly in shallow water where the effectiveness of urchin grazing is reduced. The urchin is a selective feeder and its ability to locate preferred algae promotes intake of foods (algae in the subtidal algal fringe and drift algae) that enhance fitness by favouring somatic and gonadal growth.
Heterotrophic Bacterial Production and Its Dependence on Autotrophic Production in a Hypertrophic African Reservoir
Authors: Robarts Richard D. , Wicks Richard J.
Published: June 2008

The incorporation of [methyl-3H]thymidine (TdR) into bacterial DNA in Hartbeespoort Dam, South Africa was measured over 16 mo and at nine depths. Bacterial numbers at the surface ranged between 2.45 and 32.20 × 106cells∙mL−1[Formula: see text] while bacterial production varied between 1.0 and 251 pmol TdR∙L−1∙h−1(0.01 to 1.9 mg C∙m−3∙h−1). At the bottom, production ranged between 0 and 26.7 pmol TdR∙L−1∙h−1(0–0.2 mg C∙m−3∙h−1). The fastest bacterial doubling time was 59 h. At the surface, bacterial production was dominantly correlated to chlorophyll a (6.6–6530 mg∙m−3) and phaeopigments (0.9–378 mg∙m−3) (r = 0.81) followed by primary production (26.6–8886 mg C∙m−3∙h−1) (r = 0.77) (n = 30–34, p < 0.001). However, below 5 m, water temperature and bacterial numbers were the dominant correlates. Bacterial production for the water column averaged 2% of daily, areal primary production. The data demonstrated a close coupling between autotrophic production and heterotrophic bacterial production. However, the low bacterial production compared with primary production, together with the small size of the bacteria (usually 0.09–0.25 μm width), suggest substrate supply was a major limiting factor of bacterial growth.
Toxicity of Cadmium, Copper, and Mercury to Isolated Trout Hepatocytes
Authors: Denizeau F. , Marion M.
Published: June 2008

Freshly isolated rainbow trout (Oncorhynchus mykiss) hepatocytes were put in culture and exposed to Cd, Hg, and Cu. Toxicity was evaluated by determining lactate dehydrogenase (LDH) release into the extracellular medium. The cellular response to each individual metal was assessed and the possibility of modulation of Cd effects by either Hg or Cu was tested, intracellular metal accumulation was measured by radioactive labelling (203Hg) or graphite furnace atomic absorption spectrophotometry (Cd and Cu). It was found that the cells were most sensitive to Cd, while Cu was the least cytotoxic metal; Hg exhibited intermediate activity. The greater cytotoxic potential of Cd over Hg was not attributable to a greater uptake of Cd in comparison to that of Hg. In dual-exposure experiments, Hg had no significant effect on Cd cytotoxicity, but increased sensitivity to Cd appeared when Cu was present. Metal uptake data showed that there was no significant change in the accumulation of Cd due to Cu and vice versa. Trout hepatocytes in culture represent a useful tool for investigating the cytotoxicity of individual metals as well as the effects of environmental metal mixtures.
Phytoplankton in Quebec Lakes: Variation with Lake Morphometry, and with Natural and Anthropogenic Acidification
Authors: Pinel-Alloul Bernadette , Méthot Ginette , Verrault Ghislain , Vigneault Yvan
Published: June 2008

Phytoplankton of 54 Québec lakes were studied to determine the effects of acidification, physico-chemistry, and lake morphometry on the community composition. The phytoplankton groups data matrix was submitted to a flexible linkage cluster analysis. The resulted six clusters of lakes are distributed along the northeast to southwest geographic axis and are related to an ascending density gradient in total phytoplankton, chlorophytes, cyanophytes, and microflagellates. Factor analysis produced five derived environmental factors (hardness-alkalinity, lake depth and transparency, dystrophy, lake size and salinity-sulphates loading), which explain 73% of the total variance of the abiotic data matrix. Alkalinity–acidity gradient is the most important factor related to phytoplankton groups and species distribution. Most of the cyanophytes taxa and some chlorophytes are positively related to the hardness-alkalinity and the sulphates loading factors. The abundances of pyrrophytes increases in alkaline lakes subjected to great sulphates loading. Lake morphometry and trophy also influence the phytoplankton distribution. Deep and clear lakes in eastern Quebec are dominated by chrysophycean species. Few species are related to the dystrophy factor. Phytoplankton distribution and relationships with environmental factors in Quebec lakes are compared with studies of the phytoplankton composition in Newfoundland and Labrador lakes.
Statistical Models for the Analysis of Ageing Error
Authors: Richards Laura J. , Schnute Jon T. , Kronlund A. R. , Beamish Richard J.
Published: June 2008

We present statistical models for estimating the true age distribution of a population, based on multiple readings from individual fish. There are two steps to this process. The first involves estimating a classification matrix that defines the probability of assigning an age a to a fish when its true age is b. Since true age is unknown, we require an assumption related to ageing error bias; we assume that the true age is the most probable value for the observed age. True age proportions, or alternatively, true ages of fish in the sample are then estimated in the second step. Our methods allow us either to conduct both steps simultaneously or to estimate true age proportions from a previously estimated classification matrix. We illustrate our methods with data on walleye pollock (Theragra chalcogramma). We recommend that multiple independent readings be obtained for a subset of structures in future ageing studies and that ageing error be considered in subsequent analyses. Sample sizes must be increased with increasing ageing error to achieve a specified precision in estimates of true age proportions.
Straying Patterns of Coho Salmon (Oncorhynchus kisutch) Stock from Southeast Vancouver Island, British Columbia
Authors: Labelle M.
Published: June 2008

Fourteen coho salmon (Oncorhynchus kisutch) stocks of wild and hatchery origin were tagged from 1985 to 1988 in nine streams within a 150-km coastal section of Vancouver Island. Tag escapements to natal streams were estimated from fence counts, stream surveys, and mark–recapture operations. On average, adult (age 3+) strays accounted for ~4.7% of escapements, but for > 40% of the adult escapements in some cases. Adult straying rate, averaged across all years and stocks, was < 2%. Straying rates tended to be lower for hatchery fish and highest for stocks subjected to certain enhancement practices. Adult strays escaped to streams 2–159 km from their home stream (average 15.7 km); over 50% escaped to streams < 7 km from their stream of release. Straying rates of jacks (age 2+) in a given year and that of their adult siblings during the following year were not related. Genetic makeup, age-at-return, run timing, and exposure to nonnatal water sources during the rearing stage did influence homing. Changes in natural straying patterns should be suspected where enhancement measures include flow controls, selective breeding, and exposure of fry to various water sources. Straying levels and stray contributions should be considered when estimating survival and exploitation rates
Genetic Protein Variation in Natural Populations of Atlantic Salmon (Salmo salar) in Scotland: Temporal and Spatial Variation
Authors: Jordan W. C. , Youngson A. F. , Hay D. W. , Ferguson A.
Published: June 2008

Levels of temporal and spatial genetic heterogeneity within and among Atlantic salmon (Salmo salar) populations in Scotland were assessed through starch-gel electrophoretic analysis of variation at 30 protein-coding loci. Over three year-classes the level of temporal variation within populations was generally nonsignificant, although significant heterogeneity among year-classes was found at some loci at some locations. Hierarchical analysis of gene diversity showed that 97.6% of the genetic diversity was found within single sites, with the remaining diversity distributed among sites. While there was no evidence of subpopulation differentiation among a number of samples of Atlantic salmon from the River Tweed system, significant genetic heterogeneity was observed among samples from different river systems within Scotland. Comparison of the levels of among-population heterogeneity in the Atlantic salmon with those found in the closely related brown trout (Salmo trutta) over a similar geographical area shows the Atlantic salmon to be relatively genetically homogeneous.
Effects of Grazer Community Composition and Fish on Algal Dynamics
Authors: Turner Andrew M. , Mittelbach Gary G.
Published: June 2008

We examined the effects of grazer community composition and fish on phytoplankton abundance by manipulating zooplankton community structure and the intensity of planktivory in a factorial experiment. Enclosures (1700-L bags) were treated with fish (present/absent) and two grazer communities (one a large-bodied community dominated by Daphnia and the other a small-bodied community dominated by Ceriodaphnia) in a 2 × 2 factorial design. We sampled zooplankton and algae every 4–8 d during the 5-wk experiment. Algal biovolume, chlorophyll a, total particulates, and light extinction were all significantly higher in the presence of fish. Further, the effect of fish on algal standing crop did not depend on which grazer assemblage was initially present. Fish enhanced algal standing crop to the same degree in both Daphnia and Ceriodaphnia treatments. We discuss these results in light of patterns reported in the literature, and the nature of size-structured interactions among fish, zooplankton, and algae.
Microbial Leaf Decomposition in Adirondack Streams Exhibiting pH Gradients
Authors: Osgood Marcy P. , Boylen Charles W.
Published: June 2008

The effects of water pH and related water chemistry parameters on microbial decomposition processes were studied in three small, low-order woodland streams located in the Adirondack region of New York State. These streams exhibited spatial and seasonal gradients in water pH ranging from pH values of 4.5 to 7.0. Measurements of microbial biomass (ATP), bacterial numbers, and bacterial production (thymidine incorporation) on leaves of Acer saccharum were made over a 9-mo period (fall to spring). Decomposition of A. saccharum leaves was significantly decreased at lower pH. The developing epiphytic microbial community was affected in a very specific way. Bacterial numbers were not related to water pH values, nor were ATP measurements significantly correlated with pH or any pH-related water chemistry variable. However, thymidine incorporation by bacteria on leaf material (used as a measure of bacterial productivity) was significantly decreased at lower pH. This was the only consistent indicator of reduced microbial activity in response to acidification of these streams.