bluuebunny/crossref_metadata_2025 huggingface dataset:
Interactions in North-Temperate Lake Fish Communities
Authors: Colby Peter J. , Ryan Philip A. , Schupp Dennis H. , Serns Steven L.
Published: June 2008

Several species interrelationships influenced by actural or preceived disturbances were described which managers should consider when manipulating fish populations and communities. For example, factors controlling homeostasis of adult northern pike (Esox lucius) and white suckers (Catostomus commersoni) in northern lakes may still operate despite walleye reductions, suggesting less niche overlap than we previously expected. In more northern centrarchid type communities, percid abundance and condition depend on how well northern pike and other predators control both white sucker and bluegill (Lepomis macrochirus) abundance. Evidence from walleye (Stizostedion vitreum vitreum) fry and fingerling plantings suggest that when intense interactions between species determine their abundance, these interactions occur during the very early life stages. Climatic changes may also be influential in determining abundance of several fish species common in north-temperate lakes. Rehabilitation of preferred species by removal of less desirable fishes can be successful in some ecosystems, but we warn that an undesirable compensatory response may also occur.
Increased Catchability of the Deep Monofilament Nylon Gillnet and Its Expression in a Simulated Fishery
Authors: Collins John J.
Published: June 2008

During 1979–81, Lake Huron fishermen changed from using 36-mesh monofilament nets to deeper (50-mesh) nets in the commercial fishery for lake whitefish (Coregonus clupeaformis). Simultaneous catch comparisons between the two gears showed that overall, deep nets were 1.7 times more efficient (but varied seasonally) for whitefish. The increase in efficiency exceeded that expected from the increase in area of the deeper nets. Simulation modeling demonstrates that the expression of enhanced catchability of deep nets is inversely proportional to the intensity of the fishery and thus total mortality rates (Z). Further, the temporal distribution of yield to the fishery would be advanced within the fishing period. This most recent change in catchability has introduced further bias in commercial catch and effort statistics.
Models on the Slope of, and Biomass Flow up, the Biomass Size Spectrum
Authors: Borgmann Uwe
Published: June 2008

A comparison is made between the different models of the biomass size spectrum proposed by a number of authors. Though superficially dissimilar, the models are all mathematically compatible if the differences in their underlying assumptions are taken into account. The simplest model does not consider the complexities of food webs over food chains, somatic growth, or the continuous nature of the size spectrum. Comparison with the more complex models, however, shows that these omissions do not seriously affect the slope of the size spectrum. For example, one model predicts that the effects of somatic growth and reproduction cancel if cohort biomasses remain relatively constant as the cohorts mature. If growth rate is related to body size in an allometric relationship and reproduction is ignored, then another model gives a slightly different slope (higher by roughly 0.03). If the same assumptions are used in both models, however, they give compatible results. Some simple equations are suggested for routine application in size spectrum analysis of biomass and production data.
Understanding Recruitment of Lake Michigan Fishes: The Importance of Size-Based Interactions Between Fish and Zoopiankton
Authors: Crowder Larry B. , McDonald Michael E. , Rice James A.
Published: June 2008

Mechanisms controlling recruitment of fishes appear to be strongly size dependent. It is now established that size-selective predators can dramatically reduce zooplankton size, but little is known about the effects of zooplankton size on growth and recruitment of fish through the post-larval stage. As fish grow, their optimal prey size increases; if large zooplankton are uncommon, growth rates may be reduced, prolonging vulnerability to predation or other size-dependent mortality sources and thus reducing recruitment. Most Lake Michigan fishes, including offshore species such as bloater (Coregonus hoyi) and nearshore species such as yellow perch (Perca flavescens), shift from feeding on zooplankton in their early years to feeding on benthic prey or to piscivory. Predation mortality on many larval and juvenile fishes including bloater and yellow perch has been shown to be size or growth rate dependent. As alewife (Alosa pseudoharengus) increased in abundance in Lake Michigan in the 1960s, large zooplankton declined and both bloater and perch recruitment was poor. In the late 1970s and early 1980s, alewife declined, large zooplankton increased, and strong year classes of bloater and perch were formed. Based on these dynamics and recent research on resource use, foraging behavior, and recruitment dynamics of larval and juvenile fishes, we suggest two hypotheses. First, young-of-year and juvenile pelagic fishes may have the major size-structuring effects on epilimnial zooplankton in Lake Michigan. And second, if large zooplankton are uncommon, as they were in Lake Michigan in the 1960s, growth rates and recruitment of native fishes will be reduced. Size-based interactions between fish and zooplankton appear to have important implications for growth and recruitment success of fishes.
Production and Biomass Size Spectra in the Bay of Quinte, A Eutrophic Ecosystem
Authors: Minns C K. , Millard E. S. , Cooley J. M. , Johnson M. G. , Hurley D. A. , Nicholls K. H. , Robinson G. W. , Owen G. E. , Crowder A.
Published: June 2008

From the 1940s on, the Bay of Quinte was subjected to increased point-source phosphorus loading. This and other stresses (exploitation, fish species invasion, and perhaps climate fluctuation) altered the productivity of the ecosystem and community structure. In the late 1970s, point-source loading was greatly reduced. At the same time, walleye (Stizostedion vitreum vitreurn) produced the largest year class ever recorded and surged to abundance greater than those seen in the 1950s before its collapse. Also, the dominant invader white perch (Morone americana), which had flourished in the 1960s and 1970s, was almost eliminated by a low-temperature kill. Studies of the bay ecosystem before and after these events indicated that while nutrients and algae responded to changes in nutrient loadings, changes in secondary producers hinged on the changes in the fish community. Use of Borgmann's biomass size spectrum model provides a focus for the interpretation of nutrient- and predator-related changes in biomass distribution. Deviations of the biomass spectrum are interpreted. The biomass and production spectra are linked to both phosphorus concentrations, observed and predicted, and to fishery exploitation rates. The results suggest that while nutrients control the overall biomass of the ecosystem and the slope of the biomass spectrum, trophic interactions and perturbations (e.g. exploitation) determine the degree to which a smooth biomass spectrum is achieved.
Nonstationarity of Production Relationships in Exploited Populations
Authors: Walters Carl J.
Published: June 2008

Stock assessment usually proceeds from the assumption that there are time-invariant relationships between stock size and rate processes such as recruitment, although such relationships are difficult to discern due to noise caused by factors other than stock size. There are good biological reasons not to trust this assumption in exploited populations, where persistent environmental changes and shifts in stock structure may cause various parameters to change. Graphical and statistical procedures can be used to detect this nonstationarity in historical data sets for which stock size has varied so as to repeatedly sample a range of sizes. The policy implications of nonstationarity depend on whether the changes are clearly observable as deviations from known, Song-term baseline responses. If the changes are observable, it is usually best to pretend that the current deviation will persist unless strong constraints on policy change make it necessary to plan for changes that may occur far into the future. If the changes are not observable (the usual case), then it is necessary to make a difficult policy choice between passively waiting for informative stock responses versus actively experimenting with harvest rates so as to quickly get information about responses over a range of stock sizes.
Multivariate Time Series Analysis of the Canadian Fisheries System in Lake Superior
Authors: Cohen Y. , Stone J. N.
Published: June 2008

Data for the Canadian fisheries system in Lake Superior were organized into monthly time series of catch and effort from January 1963 through December 1976 for six fish species. Multivariate, autoregressive (ARMA) models were identified for the system based on data for the first 140 mo. Forecasts were compared to data for the last 28 mo. The structure of the models indicate that (1) within the system, AR processes, as opposed to MA processes, were of overriding importance, (2) intraspecific interactions (inferred from data on catch-per-unit-effort, CPUE) were more prevalent than interspecific interactions, (3) interactions within the system occurred with lags of 1, 4, 12, 24, 25, 28, and 36 mo, (4) some of the trophic relationships among the fish species were revealed by the models, and (5) CPUE time series of lake trout (Salvelinus namaycush) affected, but was not affected by, the CPUE time series of other species. The models were used to forecast catch and CPUE for the last 28 mo, and the data were generally within one standard error of the forecasts. The models may help policy decision makers to explore the effects of inputs (e.g. quota regulations) and feedbacks within the fisheries' system on outputs (e.g. production, CPUE).
Changes in the Multispecies, Winter Angling Fishery of Lake Simcoe, Ontario, 1961–83: Invasion by Rainbow Smelt,Osmerus mordax, and the Roles of Intra- and Interspecific Interactions
Authors: Evans David O. , Waring Peter
Published: June 2008

Winter creel surveys revealed major changes in the abundance of five fish species (lake trout, Salvelinus namaycush, lake whitefish, Coregonus clupeaformis, lake herring, Coregonus artedii, yellow perch, Perca flavescens, and rainbow smelt, Osmerus mordax) in Lake Simcoe (1961–83). Variations in abundance were in part caused by intra- and interspecific factors. Catches in alternate years for both lake herring and rainbow smelt were inversely correlated, suggesting negative interactions between their young-of-the-year and yearlings. Similarly an inverse relation between parental stock size and recruitment explained a significant component of the catch variation of lake herring and yellow perch. Natural recruitment of lake trout declined during the 1950s (associated with eutrophication effects), and in the early 1960s, rainbow smelt invaded the fake. Lake whitefish abundance declined in the early 1970s as smelt abundance increased; the decline in whitefish recruitment was probably caused by interaction between smelt and whitefish young-of-the-year. Catches of yellow perch were positively correlated with rainbow smelt and negatively correlated with lake whitefish. Lake herring also increased when lake whitefish density was low. Increased abundance of lake trout after 1975 (due to stocking) appears to have resulted in lower densities of lake herring, rainbow smelt, and yellow perch and the reestablishment of lake whitefish recruitment at a low level. These results suggest that a large predator (lake trout) can have a major influence on the structure of a fish community, by direct and indirect effects.
Optimal Use of Creel Survey Data in Assessing Population Behaviour: Lake Opeongo Lake Trout (Salvelinus namaycush) and Smallmouth Bass (Micropterus dolomieui), 1936–83
Authors: Shuter B. J. , Matuszek J. E. , Regier H. A.
Published: June 2008

Creel survey and independent assessment data on the lake trout (Salvelinus namaycush) and smallmouth bass (Micropterus dolomieui) populations of Lake Opeongo were evaluated. Annual estimates of total mortality, fishing mortality, and abundance were generated for each population over the period 1936–83. Large variations in survey efficiency, angler efficiency, fishing mortality, and abundance were identified over this period. We argue that a creel survey, which is expected to provide reliable information on fish population dynamics, requires an overall study design which includes collection of data on the number and relative efficiency of different kinds of anglers and periodic assessment studies aimed at providing independent checks on both survey effectiveness and population behaviour.
Mechanisms Affecting Public Acceptance of Resource Management Policies and Strategies
Authors: Peyton R. Ben
Published: June 2008

Managing the issues which arise from Great Lakes rehabilitation efforts will involve some expertise in psychology and sociology and in the administration of public involvement processes. The components of issues which must be managed include inadequacies in our science, incomplete and/or conflicting public beliefs, and conflicting public values. Decisions must often be made without the benefit of complete scientific information, and the public is poorly prepared to deal with this limitation. Even when scientific knowledge is adequate, segments of the public may be uninformed and create issues. Most issues result from conflicts between users with differing value priorities in a management decision. Public involvement strategies exist to increase representative and interactive participation by citizens needed to resolve or avoid many issues, but additional strategies must be developed to deal with the difficult dynamics of value conflicts. The response of management agencies should be to implement long-range programs to develop their own expertise in the dynamics of public perceptions, citizen skills to participate in the management process, and more effective strategies for involving citizens in the difficult, value-laden resource management process.
Biotic and Abiotic Determinants of Lake Whitefish (Coregonus ciupeaformis) Recruitment in Northeastern Lake Michigan
Authors: Taylor William W. , Smale Martin A. , Freeberg Mark H.
Published: June 2008

Comparisons of lifetime average per capita reproductive rates (R0) between stocks of lake whitefish (Coregonus clupeaformis) in Lake Michigan found higher estimates of R0 for rapidly growing exploited stocks than for a commercially unexploited stock. Earlier maturation was the prime cause of this increase. Exploited stocks, however, were dependent on fewer age-classes for reproduction and had a greater potential for instability due to annual variation in recruitment. Overwinter whitefish egg survival in Grand Traverse Bay was nearly fourfold higher during a cold winter with prevalent ice than during the preceding mild, ice-free winter. However, the higher densities of larvae produced during the cold winter experienced greater mortality, with starvation the likely cause. Factors found to influence a stock–recruitment relationship developed for year-classes from 1958 to 1980 included spawning biomass, winter severity (ice-cover), and spring temperatures. Periods of abnormally high and low whitefish catch corresponded to periods in which cold or warm winters were more frequent, respectively. Harvest strategies that dampen naturally caused fluctuations in the spawning stock are recommended.
An Indirect Rapid Methods Approach to Assessment
Authors: Hoenig John M. , Heisey Dennis M. , Lawing William D. , Schupp Dennis H.
Published: June 2008

Strategies and tactics are explored for increasing the usefulness of assessment information obtainable under manpower and budget restrictions. A concept of indirect rapid assessment is gradually emerging based on a collection of rapid methods of varying degrees of accuracy, sophistication, and data requirements. These tactics involve the use of statistics which are functionally related to parameters of interest. Stock composition, growth, mortality, population size, intrinsic rate of increase, and stock production may be efficiently estimated with these methods. Short-term forecasting is also possible. Tactics include group testing, correcting biased estimates, use of comparative studies, using length as a substitute for age, and remote sensing type assessments.
Optimal F0.1 Criteria and Their Relationship to Maximum Sustainable Yield
Authors: Deriso R. B.
Published: June 2008

There is a unique size of entry into the fishable population that maximizes yield per recruit when an F0.1 fishing criterion is applied to the simple theory of fishing developed by Beverton and Holt in 1957. I define such a pair of parameters (size of entry, F0.1 value) to be the optimal F0.1 criteria and show that they are characterized by the single quantity M/K. A quantitative relationship is established between maximum sustainable yield and the optimal F0.1 criteria for a model population where recruitment is governed by a Ricker stock–recruitment function. This new theory is applied to three fish stocks: Pacific halibut (Hippoglossus stenolepis), western Lake Erie walleye (Stizostedion vitreum vitreum), and Bering Sea Pacific cod (Gadus macrocephalus).
Vulnerability, Stability, and Coherence of the Fish Community in Lake Superior
Authors: Cohen Y. , Stone J. N. , Vincent T. L.
Published: June 2008

Vulnerability analysis and spectrum analysis were found useful in examining potential structural changes in fisheries systems influenced by large perturbations. In the 1950's the Ontario fisheries of Lake Superior experienced a major perturbation due to invasion by sea lamprey (Petromyzon marinus). Vulnerability analysis indicated that invasion by sea lamprey and the consequent shifting of the fisheries to more intensive fishing on lower trophic level species resulted in higher vulnerability of the predatory fish species; i.e. likelihood of extinction increased. Spectrum analysis was then applied to the yield series of five fish species from Lake Superior. Analysis of the data before and after invasion by sea lamprey indicated major structural changes in the fishery: (1) except for lake trout (Salvelinus namaycush), either the dominant amplitude, the dominant frequency, or both decreased; (2) partial coherencies between pairs of yield series changed after the invasion; (3) lake whitefish (Coregonus clupeaformis) and lake trout replaced lake herring (C. artedii) as the species whose fluctuations in commercial yield were most highly synchronized with those of the other species of commercial importance.
Partitioning Potential Fish Yields from the Great Lakes
Authors: Loftus D. H. , Olver C. H. , Brown E. H. , Colby P. J. , Hartman W. L. , Schupp D. H.
Published: June 2008

We proposed and implemented procedures for partitioning future fish yields from the Great Lakes into taxonomic components. These projections are intended as guidelines for Great Lakes resource managers and scientists. Attainment of projected yields depends on restoration of stable fish communities containing some large piscivores that will use prey efficiently, continuation of control of the sea lamprey (Petromyzon marinus), and restoration of high-quality fish habitat. Because Great Lakes fish communities were harmonic before their collapse, we used their historic yield properties as part of the basis for projecting potential yields of rehabilitated communities. This use is qualified, however, because of possible inaccuracies in the wholly commercial yield data, the presence now of greatly expanded sport fisheries that affect yield composition and magnitude, and some possibly irreversible changes since the 1950s in the various fish communities themselves. We predict that total yields from Lakes Superior, Huron, and Ontario will be increased through rehabilitation, while those from Lakes Michigan and Erie will decline. Salmonines and coregonines will dominate future yields from the upper lakes. The Lake Erie fishery will continue to yield mostly rainbow smelt (Osmerus mordax), but the relative importance of percids, especially of walleye (Stizostedion vitreum vitreum), will increase. In Lake Ontario, yields of salmonines will be increased. Managers will have to apply the most rigorous management strictures to major predator species.
Policy Making within an Adaptive Management Framework, with an Application to Lake Trout (Salvelinus namaycush) Management
Authors: Milliman Scott R. , Grima A. P. , Walters Carl J.
Published: June 2008

Using lake trout (Salvelinus namaycush) rehabilitation in the Laurentian Great Lakes as an example, we combine a policy design process known as "adaptive management" in biological circles with basic concepts found in natural resource economics. Emerging from this synthesis of biological and economic thought is a practical method for making policy choice in fisheries in the presence of biological uncertainty. We introduce this method by first reviewing key biotic uncertainties which impede the progress of lake trout rehabilitation. Drawing upon these uncertainties, a framework is proposed for developing a set of policy options. Included in these options are "actively adaptive" policies which are purposely experimental in hopes of both reviving the lake trout fishery and concurrently yielding data which may alleviate the nagging uncertainties. Using basic concepts from natural resource economics, we then outline how, in the presence of the key uncertainties, the policy which most likely maximizes socioeconomic gains can be chosen from the various options. We conclude with some brief policy implications for lake trout rehabilitation.
Direct and Indirect Estimation of Gillnet Selection Curves of Atlantic Herring (Clupea harengus harengus)
Authors: Winters G. H. , Wheeler J. P.
Published: June 2008

Length-specific selection curves for Atlantic herring (Clupea harengus) were calculated for a series of gillnets ranging in mesh size from 50.8 to 76.2 mm (stretched measure) using Holt's (1963) model (ICNAF Spec. Publ. 5: 106–115). These curves were than compared with direct estimates of length-specific selectivity obtained from a comparison of gillnet catch length frequencies with population length composition data as determined from acoustic surveys. Selection curves calculated indirectly using the Holt model were unimodal and congruent. The empirical selection curves however were multimodal and fishing power varied with mesh size. These differences in selectivities were due to the fact that herring were caught not only by wedging at the maximum girth but also at other body positions such as the gills and snout. Each of these modes of capture have different length-specific selectivity characteristics and, since the relative contributions of the different modes of capture varied both between nets and annually, the selection curve of herring for a particular mesh size is not unique. It can however be reasonably approximated when girth is used as the selection criterion. Direct empirical selectivities are therefore recommended when interpreting population parameters from herring gillnet catch data.
Filtering rates of Diaptomus minutus, Bosmina spp., Diaphanosoma sp., Holopedium gibberum (Crustacea), and Zooplankton Community Grazing Rates in Some Acidic and Circumneutral Ontario Lakes
Authors: Bleiwas Agnes H. , Stokes Pamela M.
Published: June 2008

Filtering rates of several zooplankters and grazing rates of the zooplankton community were investigated in seven Ontario lakes ranging in mean pH from 4.6 to 7.1. Filtering rates of Diaptomus minutus, Diaphanosoma sp., and Holopedium gibberum were negatively correlated with lake pH and alkalinity; rates for these species averaged 89, 171, and 514 μL∙ind−1∙h−1, respectively in the circumneutral lakes, and 200, 374, and 1853 μL∙ind−1∙h−1 in acidic lakes. The filtering rate of Bosmina spp. was not correlated with lake pH; its average rates were 35 and 44 μL∙ind−1∙h−1 in circumneutral and acidic lakes, respectively. Other environmental parameters examined (temperature, light intensity, plankton biomass, chlorophyll a concentration) did not appear to influence the filtering rate of most species tested. Zooplankton community grazing rates were not correlated with lake pH; rates averaged 1.1 %∙h−1 in circumneutral lakes, and 1.5%∙h−1 in acidic lakes. This result does not support a previous hypothesis that the efficiency of energy transfer from primary to secondary trophic levels is reduced by acidification. There was no indication that grazing pressure on small versus large cells changed at low pH, based on comparisons of community grazing rates on the small alga Chlorella and the larger Cosmarium.
A Partial Bias Correction Factor for Stock–Recruitment Parameter Estimation in the Presence of Autocorrelated Environmental Effects
Authors: Walters Carl J.
Published: June 2008

Stock–recruitment time series often give a distorted picture of average recruitment rates, with high productivities per spawner being overrepresented at low stock sizes. This distortion is exaggerated by autocorrelation among years in environmental effects on productivity. The common procedure of fitting a stock–recruit curve and then analysing residuals from the curve will result in a substantial underestimate of the autocorrelation among environmental effects. Previous studies have recommended using Monte Carlo simulations to estimate the bias in stock–recruit model parameter estimates. These simulations can generally be avoided by using a simple correction equation. However, deviations from the corrected stock–recruit curve will not give better estimates of autocorrelation patterns in environmental effects, and hence will not help to provide better forecasts and stronger tests for factors that may be causing the effects.
Aggregations of Berried Lobsters (Homatus americanus) in Shallow Waters off Grand Manan, Eastern Canada
Authors: Campbell Alan
Published: June 2008

The relative abundance, size, and sex frequencies of trap-caught lobsters were determined from five areas near the northern end of Grand Manan during August–September 1982 and August 1983. Large numbers of berried (ovigerous) females (90/100 trap hauls) and few male or nonberried female lobsters were caught in shallow (1–22 m) depths close to the shoreline in one area. The sex ratio was near 50% males in deeper areas. In the shallow area SCUBA divers observed mature lobsters excavating bowl-shaped depressions in the sand-clay substrate and confirmed the high density of berried females indicated by the trap catches. Berried females may seek and congregate in areas favourable for egg development and larval dispersal. During summer, shallow areas provide warmer water than deeper areas and therefore allow faster egg development and egg extrusion. Also, the shallow waters with strong tidal currents would allow rapid dispersal of newly hatched larvae.
Pharmacokinetics and Tissue Disposition of the Off-Flavor Compound 2-Methylisoborneol in the Channel Catfish (Ictalurus punctatus)
Authors: Martin John F. , Plakas Steven M. , Holley Janis H. , Kitzman Joseph V. , Guarino Anthony M.
Published: June 2008

The tissue disposition of the off-flavor compound 2-methylisoborneol (MIB) was examined in market-sized channel catfish (Ictalurus punctatus). Purified MIB was intravascular administered to channel catfish at a dosage of 1 mg∙kg−1 body weight. Body tissues and fluids were collected at intervals following administration and were analyzed for MIB by microwave distillation and capillary gas chromatography. Plasma clearance of MIB was characterized by a two-compartment open model with half-lives of 0.14 and 3.62 h or distribution and elimination phases, respectively. MIB was more concentrated in peritoneal fat and subepidermal adipose tissue than in other tissues. The concentration in the edible flesh decreased from 0.107 μg∙g−1 at 2 h to 0.025 μg∙g−1 at 96 h. There was no evidence of biotransformation of MIB to the related compounds 2-rnethylenebornane and 2-methyl-2-bornene over the 96-h sampling period. The low recoveries of the administered dose in body fluids and tissues and the rapid clearance suggested significant gill excretion of this compound.
Metabolic Allometry of Larval and Juvenile Yellow Perch (Perca flavescens): In Situ Estimates and Bioenergetic Models
Authors: Post John R.
Published: June 2008

Measurements of in situ food consumption and growth rates of young-of-the-year (YOY) yellow perch, Perca flavescens, indicated that extrapolations of the metabolic allometry of adult perch to larval and juvenile perch were inappropriate. YOY active metabolism had the same weight dependent slope as adults but was 4.4 times adult standard respiration. Adult active respiration is typically 1–2 times standard. YOY consumption rates were also higher than predicted from adult allometry. Model simulations demonstrate that consumption and growth dynamics of larval and juvenile fish are more sensitive to variation in temperature and prey availability than are adults.
Age at Sexual Maturity and Pregnancy Rates of Harbour Porpoises Phocoena phocoena from the Bay of Fundy
Authors: Read Andrew J.
Published: June 2008

Age at sexual maturity and pregnancy rate were estimated from a sample of 108 female harbour porpoises Phocoena phocoena killed incidentally in a commercial gill net fishery in the Bay of Fundy during July–September, 1985–88. Estimates of sexual maturity ranged from 3.15 to 3.44 yr, depending on the method used; few individuals older than 7 yr of age were present in the sample. The mean age at first pregnancy was 3.76 yr. Pregnancy rate was estimated using two methods: (1) considering the entire sample and using the presence of a corpus luteum as indicative of pregnancy, and (2) by considering the sample collected after implantation and using the presence of a foetus as the criterion of pregnancy. Estimated pregnancy rates using these two methods were 0.86 and 0.74, respectively. Many young females failed to conceive in their first year or two of sexual maturity, but most older females in the sample were pregnant. These high pregnancy rates are indicative of annual reproduction in this population.
Use of Statistical Models for the Estimation of Abundance from Groundfish Trawl Survey Data
Authors: Smith Stephen J.
Published: June 2008

Estimates of fish abundance from stratified random trawl surveys are highly variable and a number of estimators from various statistical models have been suggested to provide more precise estimates. However, model-based estimates of the survey finite population mean which are not based on the sample mean, can be biased and nonrobust to deviations from the model. This is demonstrated in particular for estimates based on the Δ-distribution. A criterion known as asymptotic design consistency (ADC) is presented for selecting those models that can provide estimates of the finite population mean which are asymptotically robust to deviations from the model. The concept of a predictive estimate is presented as a means of incorporating models into an estimate of the finite population mean which can provide more information than the sample mean. Predictive estimates use statistical models to relate the abundance measured in the sample to covariates measured over the whole survey area. This paper demonstrates that consistent relationships exist between the catch of age 4 cod (Gadus morhua) in the survey trawl and concurrently measured hydrographic covariates which can be used to construct model-based ADC predictive estimates of the finite population mean.
Validation of Corbicula fluminea Growth Reductions Induced by Copper in Artificial Streams and River Systems
Authors: Belanger Scott E. , Farris Jerry L. , Cherry Donald S. , Cairns Jr. John
Published: June 2008

Studies designed to evaluate impacts of copper (Cu) on Asiatic clams, Corbicula fluminea, in artificial stream and field environments were conducted. Adult and juvenile responses (survival and growth) to Cu, relevance to Cu bioaccumulation, site-specific comparisons, and the relation to observed densities of resident clams at an impacted site were assessed. Juveniles were more sensitive than adults; however, clam tissue and shell growth were significantly impaired (p < 0.001) for both juveniles and adults at 8.4–26.7 μg Cu/L in artificial streams. Tissue levels of Cu were 2.5–6 times greater at 8.4–26.7 μg/L exposure concentrations compared with background body burdens in unexposed clams. In studies conducted at the Clinch River, Virginia power plant, clam growth was reduced at 22.5–104.8 μg/L at a water hardness (180 mg/L) that was more than two times the hardness in artificial streams. Clam population densities in the river were well correlated with outcomes of field growth studies. Corbicula fluminea growth patterns are a clear and interpretable indicator of Cu contamination in natural and artificial streams and represent a viable alternative to contemporary chronic testing protocols.
Aggressiveness and the Foraging Behaviour of Young-of-the-Year Brook Charr (Salvelinus fontinalis)
Authors: Grant James W. A.
Published: June 2008

Individual young-of-the-year brook charr (Salvelinus fontinalis) were observed in the field to relate their aggressiveness to their body size, the size and quality of their foraging site, and their feeding rate. Aggressive charr were 13% larger than nonaggressive conspecifics observed on the same day in the same area. Aggressive fish had a lateral foraging radius 29% larger than nonaggressive fish and a 45% greater mean distance to neighbours, even when the effect of body size was removed by analysis of covariance. Aggressive fish of two size categories (20–29 and 40–99 mm) made 70 and 55% more feeding attempts per unit time, respectively, than nonaggressive fish of the same size. Number of prey items in stomachs was significantly and positively correlated with feeding attempt rate. In addition, aggressive fish appeared to occupy more preferred sites, since their sites were significantly more likely to be reoccupied after their removal than were sites occupied by nonaggressive fish. These results are consistent with the hypothesis that defence of a foraging site is a better tactic than ignoring conspecifics.
Reproductive Strategy in Yellow Perch (Perca flavescens): Effects of Diet Ontogeny, Mortality, and Survival Costs
Authors: Hayes Daniel B. , Taylor William W.
Published: June 2008

Factors influencing the theoretical optimal age at first reproduction for yellow perch (Perca flavescens) were explored for three different ontogenies including: zooplankton only; zooplankton and benthos; zooplankton, benthos, and fish. Under each of these diets, optimal age at first reproduction decreased as the decrease in mortality caused by reproduction increased. When adult yellow perch fed only on zooplankton, adult survival rate has little effect on optimal age at first reproduction. When fish and benthos are utilized, the optimal age at first reproduction varies strongly with adult survival. Growth rates were affected by both age at maturity and diet ontogeny, with diet ontogeny having a much greater effect. Maximal adult size was affected by reproductive strategy in each case, with larger terminal sizes obtained when maturity was delayed. Increases in size with delayed maturity were greatest when zooplankton, benthos, and fish were available as prey items.
Predictors of Relative Fish Biomass in Lakes and Reservoirs of Argentina
Authors: Quiros Rolando
Published: June 2008

Relationships between total fish biomass and chlorophyll, nutrient levels, and morphometric and climatic factors are shown for a set of 106 Argentinian lakes and reservoirs. The total data base is highly heterogeneous. Relative fish biomass (CPUE) was estimated from gill net catches. A data screening process was applied to the environmental data base to homogenize it. Nutrient, total organic matter content, and mean depth were most important in explaining relative fish biomass variability between lakes and reservoirs. In most heterogeneous sets total organic nitrogen (TON) explained most of CPUE variability. After screening for limnological anomalies (i.e. turbidity derived from inorganic sources, unsuitable conditions for fish, and TN/TP (total nitrogen/total phosphorus) < 37 (molar basis)), TP and TON were highly correlated with CPUE. Mean annual air temperature was significantly related to fish biomass, but the relationship was not significant after nutrients, morphometry, and environmental oxygen conditions had been accounted for. Several possible causes are discussed. The results support the hypothesis that fish/phytoplankton, and fish/zooplankton biomass ratios are inversely related to lake trophy.
Evaluation of Models Predicting Mixing Depth
Authors: Hanna Micheline
Published: June 2008

Since mixing depth affects many aspects of lake productivity, including nutrient recycling, I evaluated the predictive power of 17 empirical models that relate mixing depth to morphometric variables to identify the best predictor. These models were tested empirically by compiling data from 123 temperate lakes of differing morphometry, geometry, and trophy. Four statistical indices of precision and bias, indicate that the model published by Shuter et al. (1983) using maximum effective length of the lake was the best published model for predicting mixing depth, although it is slightly biased. I then examined the effect of alternate predictors, reflecting lake configuration, basin shape, and geographical indices, to formulate an improved model. The best single predictor of therrnodine depth (THER) was maximum effective length (MEL): Log THER = 0.336 Log MEL − 0.245. No improvement in predictive power was obtained by combining other variables. This model is statistically superior to that of Shuter et al. (1983) beause it is not biased, it represents a greater number of lakes, and it covers a broader range of lake sizes and shapes over a more extensive geographical region. Two other models, using lake area and length of shoreline are proposed as alternate predictive tools, if MEL is not readily available.
Growth of 0+ Roach (Rutilus rutilus) in Relation to Temperature and Size in a Shallow Eutrophic Lake: Comparison of Field and Laboratory Observations
Authors: Mooij W. M. , Tongeren O. F. R. van
Published: June 2008

The growth rates of larval and juvenile roach (Rutilus rutilus) were measured in the laboratory at different temperatures under conditions of excessive food supply. Using these data, the maximum growth rate of 0+ roach in relation to size and water temperature could be adequately described with an equation of the type: dW/dt = amax∙Wb∙(T−c) (W = weight, T = temperature, t = time). Using this equation the growth of larval and juvenile roach in Tjeukemeer was predicted for 12 successive years. The predicted growth rates were about 20% lower than the observed growth rates. Reasons for this bias are discussed. The results indicate that food is not limiting growth of roach in Tjeukemeer.
Mysis relicta in Lake Michigan: Abundances and Relationships with their Potential Prey, Daphnia
Authors: Lehman John T. , Bowers James A. , Gensemer Robert W. , Warren Glenn J. , Branstrator Donn K.
Published: June 2008

Mysis relicta were sampled at a 100-m reference staton in southeastern Lake Michigan (43°N 86°40′W) from 1985 to 1989, to quantify nighttime water column abundances and to compare vertical distributions with those of Daphnia. Diel vertical migration produced maximum concentrations in the thermocline at night of 1 to 10 mysids∙m−3. Variation among replicates averaged 28% with a 3-net Tucker trawl and 19% with Puget Sound vertical closing nets. Mean areal abundances over 5 yr averaged 110 mysids∙m−2 (SE = 20; n = 30; range = 25 to 645) based on nighttime vertical and oblique net tows at 1–3-wk intervals during summers at the reference station. Synoptic cruises from 43°N to 45°N during August indicated that densities were considerably greater offshore than inshore, and greater in the north than in the south. Hypothesized long-term changes in mysid abundances were not detected. Although Mysis is potentially an important predator on Daphnia, differences in nighttime vertical distributions reduce encounters between Mysis and Daphnia during summer in Lake Michigan, such that Mysis exert mortality rates on Daphnia of < 1.5% per day; the latter are in general less than 10% of the birth rates of Daphnia populations, estimated from fecundities.
Phylogenetic Relationships Among Members ofSalvelinusInferred from Mitochondrial DNA Divergence
Authors: Grewe Peter M. , Billington Neil , Hebert Paul D. N.
Published: June 2008

Mitochondrial DNA (mtDNA) was isolated from five species of the genus Salvelinus (alpinus, confluentus, fontinalis, malma, and namaycush) and from the closely related taxon, Hucho hucho. Restriction sites recognized by 14 endonucleases were mapped for each of the species and percent sequence divergence estimated between species pairs. A phylogeny of Savelinus based on restriction analysis of mtDNA, using Hucho as an outgroup, readily resolved the three subgenera: Baione, Cristivomer, and Salvelinus. Within Baione, no differences were detected between the mtDNA of brook (S. fontinalis fontinalis) and aurora (S. f. timagamiensis) trout. However, members of the subgenus Salvelinus were more variable such that two groups were resolved, one consisting of S. alpinus alpinus, S. a. oquassa, and S. malma, and the other of S. a. stagnalis and S. confluentus. A composite distance phenogram representing the phylogeny of the subfamily Salmoninae was constructed using the sequence divergence data obtained in the current study in conjunction with data from three other salmonid mtDNA studies. Estimates of divergence time between the major taxa of this group suggest that the salmonine genera originated in the late-Miocene to early-Pliocene, while extant species originated during the late-Pliocene to early-Pleistocene.
Thin Layer Interference may Reduce the Visibility of Transparent Phantom Midge Larvae (Chaoborus trivittatus) to Predators
Authors: Giguère Louis A. , Dunbrack Robert L.
Published: June 2008

The body wall of transparent aquatic animals is constructed of materials which have a higher refractive index than water. Because of this, light will reflect from their surface, making their body contours visible to predators. Electron micrographs of cuticle from the transparent pelagic stage of the phantom midge Chaoborus trivittatus reveal thin layers less than a wavelength of light thick which could alter the spectral composition of this surface reflection by acting as an interference filter. This hypothesis is supported by measurements of the reflectance of the body surface of C. trivittatus. Reflectance was lower than expected at the wavelengths which maximize contrast in aquatic environments and higher than expected at ambient background wavelengths, suggesting that interference may reduce the visibility of Chaoborus to its predators by improving the spectral matching of its body reflection to the visual background.
The Shape of Recruitment Distributions
Authors: Shelton Peter A.
Published: June 2008

The shape of recruitment distributions in marine fish is generally assumed to be lognormal on the basis of empirical evidence and theoretical argument. If recruitment is considered to be an outcome of the probability of survival of individuals or groups of individuals which may contribute to the year class, then it can be shown that the underlying distributional shape will depend on the degree of survival independence and may be nearly symmetrical for bet-hedging species. The underlying distributional shape may be obscured by estimation error, which may suggest a greater degree of positive skewness than actually exists.
Size of the South American Sardine (Sardinops sagax) Population in the Northern Part of the Peru Upwelling Ecosystem after Collapse of Anchoveta (Engraulis ringens) Stocks
Authors: Patterson K. R. , Zuzunaga J. , Cárdenas G.
Published: June 2008

New estimates of sardine (Sardinops sagax) biomass suggest that a change in state of the Peruvian upwelling ecosystem, previously thought to be from one of anchoveta (Engraulis ringens) dominance to one of equal abundances of sardine and anchoveta, has been a clear switch in dominance from anchoveta to sardine. The sardine stock inhabits the northern part of the Peru upwelling system and extends its distribution into waters off Ecuador. Virtual population analyses show the population to have been considerably larger than was previously thought, with a biomass in 1982 estimated at between 15 and 18 million tonnes. The anchoveta collapse appears to have allowed a large bloom in sardine abundance. Sardine stock size has declined in recent years, concurrently with estimated mortalities in excess of F0.1 and declining recruitment.
Allozyme Variation of Great Lakes Alewife, Alosa pseudoharengus: Genetic Differentiation and Affinities of a Recent Invader
Authors: Ihssen Peter E. , Martin G. William , Rodgers David W.
Published: June 2008

Allelic frequencies for six polymorphic allozyme loci (27 loci examined), as determined by starch-gel electrophoresis, were not significantly different for alewife, Alosa pseudoharengus, among the Great Lakes (Ontario, Erie, Huron, and Michigan). Alewife from one of the Finger Lakes (Cayuga Lake) had allelic frequencies similar to Great Lakes alewife, and the alleles of Great Lakes alewife form a subset of those found in Cayuga Lake. In contrast, Maritime Canada populations (Gaspereau, Miramichi, and St. John rivers) were distinct from each other and from the Great Lakes and Cayuga Lake populations. Highly significant allelic frequency differences were observed among the Maritime populations and between the Maritime populations and the Great Lakes or Cayuga Lake populations. Fifteen alleles were not shared between the Great Lakes and the Maritime populations. We concluded from these results that Great Lakes alewife and Cayuga Lake alewife form a contiguous stock and that Great Lakes alewife are a recent invader that probably originated from the Hudson–Mohawk rivers via the Erie Canal and the New York Finger Lakes rather than the previously suggested alternative origin from the Canadian Maritimes via the St. Lawrence River.
Effect of Female Size and Propagation Methods on Larval Production at a South Carolina Striped Bass (Morone saxatilis) Hatchery
Authors: Secor David H. , Dean John Mark , Curtis Thomas A. , Sessions Forrest W.
Published: June 2008

Larval production as a function of female size and hatchery propagation methods was examined for a South Carolina striped bass (Morone saxatilis) hatchery from 1988 to 1990. Female weight was not related to egg size or embryo survival among years or between source rivers of females. However, female weight was strongly related to number of hatched embryos due to its collinearity with fecundity. In 1988 and 1990, the offspring of 14 females contributed to 50% of hatchery production. In 1989, only six females contributed to 50% of larval production. In 1990, changes in propagation methods associated with improved female response to hormone injection resulted in more consistent rates of larval production among broods. While the deleterious effects of inbreeding on striped bass populations remain unknown, results indicate that extensive use of large females by hatcheries in fishery recovery programs could decrease effective population size.