bluuebunny/crossref_metadata_2025 huggingface dataset:
Use of eelgrass beds (Zostera marina) by juvenile Atlantic cod (Gadus morhua)
Authors: Gotceitas Vytenis , Fraser Sandra , Brown Joseph A
Published: April 2011

Two field surveys were conducted in Newfoundland, Canada: (1) SCUBA surveys at four sites differing in bottom type and the presence/absence of vegetation and (2) beach seining at three sites containing eelgrass (Zostera marina) and no-eelgrass locations. Results indicated that eelgrass is used as a nearshore habitat by age 0 + Atlantic cod (Gadus morhua). A subsequent laboratory experiment compared the use of patches of bottom substrates (sand, gravel, cobble) and artificial eelgrass (three densities) by age 0 + cod when in the absence and presence of a predator (an age 3 + conspecific). Before exposure to a predator, age 0 + cod associated with sand and gravel. With a predator present, in substrate combinations with cobble, age 0 + cod hid in the interstitial spaces of this substrate or in the patch of eelgrass when stem density was >=>720 stems/m2. In combinations with no cobble, age 0 + cod hid in the eelgrass regardless of stem density. Latency to capture an age 0 + cod was highest and the total number of age 0 + cod captured lowest in combinations with cobble or the patch of vegetation with 1000 stems/m2. In the remaining combinations, latency until an age 0 + cod was captured increased with both the presence and density of vegetation.
Cycles of abundance among Fraser River sockeye salmon (Oncorhynchus nerka)
Authors: Ricker W E
Published: April 2011

In some but not all populations of sockeye salmon (Oncorhynchus nerka) that mature mainly at age 4, there has been a persistently ``dominant'' line, a ``subdominant'' line about 10-25% as large, and two weak lines having less than 1% as many fish as the dominant one. Suggested causes of this phenomenon that have been shown to be wrong or inadequate are the presence of a few sockeye of ages 3 and 5 in the spawning stocks and a somewhat larger rate of harvest of the nondominant lines. The only plausible type of explanation that has been suggested so far involves interaction between the dominant line and the others, and the only specific example involves a 4-year cycle of abundance of a predacious fish at Shuswap Lake, described by F.J. Ward and P.A. Larkin. Other types of interaction are possible, but have not been documented. The magnitudes of the instantaneous interaction mortality rates at Shuswap Lake are estimated as about 0.78 per generation for the subdominant line out of a 7.65 total, and 1.11 out of 7.94 for the weak line 3, line 4 being similar.
Predation on fish by cormorants and pelicans in a cold-water river: a field and modeling study
Authors: Derby C E , Lovvorn J R
Published: April 2011

We studied diets of double-crested cormorants (Phalacrocorax auritus) and American white pelicans (Pelecanus erythrorhynchos) collected on the North Platte River, Wyoming, from May to August. Rainbow (Oncorhychus mykiss) and cutthroat (O. clarki) trout 10-16 cm long were stocked in late June - early July. Cormorants ate mainly suckers (Catastomus spp., 61% of numbers, 85% of fresh mass) before trout stocking; but trout consumed increased from 17% (12% of mass) in samples before stocking to 60% (82% of mass) after stocking. Pelicans ate mostly suckers (64% of numbers, 84% of mass) and minnows (Rhinichthys cataractae, Pimephales promelas; 21% of numbers, 1% of mass) throughout the study; trout were 1% (0.1% of mass) of the pelican diet before stocking, and 22% (14% of mass) after stocking. A bioenergetics model estimated that these birds consumed up to 80% of trout stocked in 1994. In August 1993, cormorants ate mostly trout (86% of numbers, 98% of mass), suggesting that many stocked trout survived until autumn. However, the much smaller fraction of trout eaten by cormorants in spring 1994 before stocking (mean 17% of numbers, 13% of mass) than after stocking (60% of numbers, 82% of mass) suggests that stocked trout declined substantially during winter. Because overwinter survival might have limited trout recruitment between years, it is unclear whether bird predation was additive or compensatory.
Phylogenetic relationships among Coregonus species inferred from the DNA sequence of the first internal transcribed spacer (ITS1) of ribosomal DNA
Authors: Sajdak S L , Phillips R B
Published: April 2011

Phylogenetic analyses based on morphometrics, data on protein electrophoresis, and mitochondrial DNA have given conflicting phylogenetic hypotheses for the subfamily Coregoninae (Prosopium, Coregonus, and Stenodus). To resolve these conflicts, phylogenetic analysis of 13 taxa of Coregoninae was done using a nuclear gene, the first internal transcribed spacer (ITS1) of the ribosomal DNA (rDNA). ITS1 sequences of all North American ciscoes were identical. In agreement with analyses based on other molecular data, the genus Stenodus was included in Coregonus, and there was no support for the monophyly of the ciscoes. The analysis based on rDNA also placed C. peled as the sister species to C. lavaretus, but this may represent a case of hybridization and introgression. A length polymorphism involving a repeating unit of 65-67 base pairs was found in the ITS1. All ciscoes except C. peled had one copy of the repeat. Coregonus peled, C. lavaretus, and Eurasian and Beringian C. clupeaformis had two copies of the repeat, while the other North American C. clupeaformis had three copies, suggesting that C. clupeaformis of northwestern North America is a form of C. lavaretus.
Influence of errors in natural mortality estimates in cohort analysis
Authors: Mertz G , Myers R A
Published: April 2011

The accuracy of the estimation of cohort strength from catch data may be greatly degraded if a poor estimate of the natural mortality rate is entered into the calculation. A straightforward, exact formulation for the error in cohort reconstruction due to a misspecified natural mortality rate is presented. The special case of constant fishing mortality is particularly transparent, allowing the error to be segmented into easily interpreted terms. A change in the fishing mortality may result in a distinct hump in the transient behavior of the bias factor, rather than a simple monotonic adjustment. This implies a similar pattern in estimated cohort strength.
Effects of the exotic zebra mussel (Dreissena polymorpha) on metal cycling in Lake Erie
Authors: Klerks P L , Fraleigh P C , Lawniczak J E
Published: April 2011

This research demonstrated the impact of high densities of the zebra mussel (Dreissena polymorpha) on the cycling of copper, nickel, and zinc in a lake environment. Experiments with mussels on sedimentation traps in western Lake Erie and with mussels in flow-through tanks receiving Lake Erie water showed that zebra mussels remove metals from the water column, incorporate metals in their tissues, and deposit metals on the lake bottom. Removal of metals from the water column was estimated at 10-17% · day-1 of the amounts present. This material was largely deposited on the lake bottom; zebra mussels more than doubled the rate at which metals were being added to the lake bottom. Metal biodeposition rates were extremely high (e.g., 50 mg Zn · m-2 · day-1) in high-turbidity areas with elevated metal levels. Two factors contributed to metal biodeposition by zebra mussels. First, their production of feces and pseudofeces increased the rate at which suspended matter was being added to the sediment (accounting for 92% of the increased metal biodeposition). Second, the material coming out of suspension had higher metal concentrations when zebra mussels were present (constituting 8% of the increased biodeposition).
Demersal fish biomass size spectra on the Scotian Shelf, Canada: species replacement at the shelfwide scale
Authors: Duplisea D E , Kerr S R , Dickie L M
Published: April 2011

Three parameters were derived from annual biomass size spectra constructed for a 22-year time series of demersal fish data for the entire Scotian Shelf: (i) total sampled biomass density, (ii) modal body weight, and (iii) the shape of the various biomass size spectra. Temporal variability of these parameters was compared among six species groups and between the species groups and their total. Species-group biomass varied more over the time series than did the total biomass, indicating the presence of a system factor. Conversely, modal body weight was as variable, and sometimes more variable, for the total than it was within species groups, indicating variability mainly at the species level. The shape of the biomass size spectrum showed annual differences in variability owing mainly to contributions of species groups. This variability was higher than variability in the combined species totals. We conclude that total biomass is limited at the combined species (systemwide) level because it depends on energy input to the system. Variability is greater at the species group (subsystem) level because the multiage species-group biomasses do not equally reflect a given energy limitation. Neither modal body weight nor the shape of the biomass spectrum is sensitive to the degree of taxonomic aggregation, suggesting that both measures are independent of energy input (primary production). We found no evidence of consistent species replacement trends on the shelfwide scale and conclude that diffuse replacement best describes species succession on the Scotian Shelf as a whole.
Internal phosphorus loading in Lake Mendota: response to external loads and weather
Authors: Soranno P A , Carpenter S R , Lathrop R C
Published: April 2011

We quantified summer internal phosphorus (P) loads and all the major P fluxes in Lake Mendota, Wisconsin, a deep stratified eutrophic lake, during two summers of contrasting external loads to determine (i) whether internal loading by entrainment (mixing at the thermocline) is a significant part of the epilimnetic P budget and (ii) what factors lead to interannual variability in internal loading. We estimated variables for the P budget weekly (standing stock, sedimentation) or daily (outflow, inflow, and entrainment) during a summer of average runoff (1992) and one of higher than average runoff (1993). Entrainment, estimated by calculating the amount of P transported into the epilimnion after the thermocline deepened following storms, was about 10 times higher than external loading during 1992, but was about equal to external loading during 1993. When entrainment was included, the epilimnetic P budget balanced. Interannual variability in internal loading appears to be due to a combination of water column stability, weather, and the P levels accumulated in the metalimnion. External loads to the epilimnion during summer 1993 were much higher than in 1992 (7.0 and 0.9 mg P ·m-2 ·day-1, respectively); however, total loads (internal + external) were more similar (12.5 and 7.8 mg P ·m-2 cdot day-1 in 1993 and 1992, respectively). Although summer chlorophyll concentrations were similar in the two summers, blue-green algal biomass in 1993 was about double that in 1992.
“Risk” in fisheries management: a review
Authors: Francis RICC , Shotton R
Published: April 2011

``Risk'' has appeared more frequently in the fisheries management literature in recent years. The reasons for this are partly internal (scientists seeking better ways to advise fishery managers) and partly external (e.g., adoption of the precautionary approach). Though terminology varies, there is consensus that there are two stages in dealing with risk. The first (here called risk assessment) is the formulation of advice for fisheries managers in a way that conveys the possible consequences of uncertainty. This advice is in the form of an evaluation of the expected effects of alternative management options, rather than recommendations. Risk assessment has been undertaken in many fisheries, and there is general agreement as to how it should be done (although technical details differ). The second stage (risk management) is the way fishery managers take uncertainty into account in making decisions. Much fisheries risk management is informal, i.e., nonquantitative, undocumented, and loosely linked (if at all) with a risk assessment. The major reason for this is that the objectives of fisheries management are often conflicting and are rarely stated in a way that provides explicit direction to managers or scientists.
Depensation in fish stocks: a hierarchic Bayesian meta-analysis
Authors: Liermann M , Hilborn R
Published: April 2011

The probability of different levels of depensation within four taxonomic groups was calculated using a Bayesian technique called hierarchical modeling. With this method we combined spawner-recruit data from many stocks within a taxon to estimate the distribution describing the variability of depensation within that taxon. The spawner-recruit model we use allows for both depensation (lower than expected recruits at low population levels) and hypercompensation (where recruits are higher than expected at low population levels). The end product of our analysis is a probability distribution that can be used as a Bayesian prior when analyzing a new data set. We examined four taxonomic groups (the salmonids, gadiforms, clupeiforms and pleuronectiforms) and found that, for all of the taxa, the most likely values fell close to or within the range of no depensation. However, because the distributions were very broad we suggest that analysis of stock recruitment data should incorporate spawner-recruit curves that include the possibility of depensation and hypercompensation.
Does fisheries science serve the needs of managers of small stocks in developing countries
Authors: Mahon R
Published: April 2011

Despite the prevalence and socioeconomic importance of small, low total-revenue stocks, predominantly in tropical, developing countries, most of the world's fishery science effort has been devoted to large stocks. Methods for assessing and managing large stocks, though applicable to small ones, are seldom feasible for them. Minimal attention has been paid to approaches that are specifically for small stocks. The tendency for managers of fisheries on small stocks in developing countries to believe that stock assessment is essential for successful fishery management, often leads to disproportionate allocation of resources to stock assessment rather than other critical components of management. This has been reinforced by several agencies that have made stock assessment methods and software available for use in developing countries, while paying little attention to other dimensions of fishery assessment and management. Hence, management efforts for small stocks are often stock assessment driven (SAD), rather than management objective driven (MOD), as they should be. The sequence of actions typical of these two approaches is contrasted. Managers of small stocks in developing countries need international programs that will develop and promote formal methodological approaches with broad emphasis on management objectives and process.
Aggregation of euphausiids and Pacific hake (Merluccius productus) along the outer continental shelf off Vancouver Island
Authors: Mackas D L , Kieser R , Saunders M , Yelland D R , Brown R M , Moore D F
Published: April 2011

From spring through autumn, euphausiids and Pacific hake (Merluccius productus) form dense aggregations off the outer coast of British Columbia along regions of steeply sloping bathymetry such as the continental shelf break. Their spatial overlap is ecologically significant because of their very strong prey-predator interaction. We analyze high-resolution measurements of shelf-edge spatial distributions of euphausiid and Pacific hake biomass (by echo integration), water properties (from surface measurements and conductivity-temperature-depth (CTD)/Rosette profiles), and current patterns (from acoustic Doppler current profiler, CTD profiles, and nearby current meter moorings). Both euphausiids and hake share similar horizontal distributions, although separated vertically by tens of meters during daylight hours. Bathymetric and water property patterns provide good coarse-scale prediction of aggregation location. However, details of patch location are better explained by flow-field indices such as cross-shore position of the shelf break current, intensity of cross-isobath flow and upwelling at the depth of the euphausiid scattering layer, and doming of isopycnals. Under prevailing summer oceanographic conditions along the British Columbia coast, likely ecological consequences of aggregation in and beneath upwelling water include access to high food density in the overlying surface layer, reduced alongshore transport, and horizontal segregation between adult and larval euphausiids.
Improving the precision of the daily egg production method using generalized additive models
Authors: Borchers D L , Buckland S T , Priede I G , Ahmadi S
Published: April 2011

Generalized additive models (GAMs) are used to model spatial variation in egg density and increase the precision of biomass estimates from the daily egg production method. Application of GAMs to survey data from the western mackerel (Scomber scombrus) and horse mackerel (Trachurus trachurus) stocks result in a substantial reduction in coefficients of variation of egg abundance. In developing GAM methods for the daily egg production method, we generalize Pennington's method, in which presence-absence is modelled separately from nonzero observations, and use a new form of the bootstrap that accommodates clustered count data without requiring explicit modelling of the form of clustering. In addition to increasing estimation precision, the use of GAMs has several advantages over stratified sample survey methods. To a large degree they allow the data to determine the form of functional dependence of the response on explanatory variables; they accommodate a wide variety of forms of stochastic variation of the response; they provide maps of the predicted density within the survey area; they provide an objective means of interpolating into unsampled areas; and estimation does not assume random sampling with respect to location.
A classification scheme for marine organic colloids in the Adriatic Sea: colloid speciation by transmission electron microscopy
Authors: Leppard G G , West M M , Flannigan D T , Carson J , Lott JNA
Published: April 2011

Organic colloids from the Adriatic Sea, covering the full colloid size range, were characterized on a per-colloid basis by transmission electron microscopy applied to ultrathin sections of embedded colloids. To detect, assess, and minimize artifacts, a multimethod correlative approach to analysis was used. A colloid classification scheme was developed from the characterizations, with individual colloid species defined in the broad sense established by environmental analytical aquatic chemists. The basic scheme is related to derivative classification schemes in which abundant colloid species are listed according to activities known from the literature, with a focus on activities related to carbon transformations and transport. Morphological criteria show that abundant colloid species occupy broad size ranges, such that colloid fractionation protocols based on sizing alone are likely to be of questionable scientific utility. Image analysis revealed that small colloids, designated as humic substances, represented 91% of the total organic colloid burden of the bulk water during a summer period of high biological productivity. At this time, fibrils were rare in the bulk water while representing the most abundant colloid in marine snow.
Countergradient variation in growth of young striped bass (Morone saxatilis) from different latitudes 1
Authors: Conover D O , Brown J J , Ehtisham A
Published: April 2011

Common garden experiments were undertaken to test the hypothesis that the genetic capacity for growth of striped bass (Morone saxatilis) varies inversely with length of the growing season across a latitudinal gradient (i.e., countergradient variation (CnGV) in growth). Newly hatched larvae were obtained from six native anadromous stocks spanning most of the natural range of striped bass (Florida to Nova Scotia). Growth experiments were conducted under conditions of unlimited food at three temperatures (17, 21, 28°C) and commenced after larvae had exhausted maternal energy resources (i.e., yolk and oil) and had begun to metamorphose. Mixed-model nested ANOVA demonstrated that length and dry weight growth differed significantly among latitudes in most comparisons. South Carolina fish ranked consistently as the slowest growing group in virtually all comparisons, but the rank order of the other latitudes differed among trials. North Carolina and Gulf of Mexico fish generally had intermediate rates of growth whereas New York, Maryland, and Nova Scotia fish generally had the highest growth. Overall, the average growth rate of progeny from the 28 mothers tested in this study had a strong positive correlation with latitude of origin, strongly indicating CnGV in growth.
Deepwater population structure and reproductive state of quagga mussels (Dreissena bugensis) in Lake Erie
Authors: Roe S L , MacIsaac H J
Published: April 2011

Quagga mussel (Dreissena bugensis) population structure and reproductive status were assessed at deepwater (37 and 55 m) sites in eastern Lake Erie during July 1996. Mussels occupied ~70% of soft substrates at 37-m sites and between 63 and 90% at 55-m sites. Shell length and dry mass frequency distributions were similar at both sites, although recruits <<= 5 mm comprised a larger proportion of the population at the deeper site. The population surveyed here allocated disproportionately less mass to shell and more to soft tissues relative to zebra mussels (Dreissena polymorpha) from shallow-water sites in eastern Lake Erie and from Lake St. Clair. The population at 55 m was slightly skewed toward male mussels (58%). Female mussels that were examined for reproductive state contained mature oocytes (80%) or had spent gonads (20%). Because water temperature at the site was only 4.8°C, this survey provides the first evidence of gonadal development and spawning by quagga mussels at low temperature. These findings contrast with most reports of spawning by congeneric zebra mussels at temperatures >=>12°C but are consistent with distributions of the species in different basins of the lake.
A seasonal energy budget for zebra mussels (Dreissena polymorpha) in western Lake Erie
Authors: Stoeckmann Ann M , Garton David W
Published: April 2011

We constructed a balanced energy budget for zebra mussels (Dreissena polymorpha) from the western basin of Lake Erie during the active growth and reproductive season (May-October). We measured metabolic costs (oxygen consumption and ammonia excretion), body mass change, and feces production weekly and marked mussels to quantify shell growth. Costs of reproduction were measured by inducing spawning four times using serotonin and collecting gametes. After conversion to calories, all energy budget components were combined with published length-frequency distributions and mussel densities to estimate population consumption. We estimated that individual zebra mussel consumption averaged 3.16 cal ·day-1 (1 cal = 4.1868 J). Metabolic costs account for >90% of energy consumption. Mussels <15 mm increased in body mass whereas mussels >15 mm allocated energy to reproduction in lieu of somatic growth. Our estimates of population consumption were sensitive to mussel size distribution, with the most abundant size-class responsible for the greatest proportion of population consumption. Based on published estimates for primary production in western Lake Erie, our energy budget estimated that zebra mussels (10 000 - 50 000 mussels ·m-2) potentially consume an equivalent of 10-50% of summer primary production.
Colour - mass balances and colour - dissolved organic carbon relationships in lakes and streams in central Ontario
Authors: Molot Lewis A , Dillon Peter J
Published: April 2011

Colour and dissolved organic carbon (DOC) concentrations and mass balances were measured for seven unproductive lakes and 20 tributary streams between June 1980 and May 1992. Individual observations of colour, which measures an unknown DOC fraction assumed to be principally humic, were not good predictors of discrete DOC concentrations for any of the study sites. Long-term mean colour was, however, strongly correlated with long-term mean DOC concentrations in streams and lakes. Colour behaved differently from the total DOC pool in lakes. Lake retention and loss coefficients for colour were always higher than corresponding values for the total DOC pool, and the mean annual colour/DOC ratios in lake outflows were always less than the corresponding ratios in lake inputs, indicating that the coloured fraction was preferentially removed or photooxidized. A steady-state mass balance model was used to estimate the upper bound for the average coloured fraction of DOC in each lake. The upper bound for the seven lakes ranged from 34 to 88%, increasing with increasing colour, DOC, and total phosphorus.
Effect of nonlinear predation rates on rebuilding the Georges Bank haddock (Melanogrammus aeglefinus) stock
Authors: Spencer Paul D , Collie Jeremy S
Published: April 2011

The collapse of several northwest Atlantic groundfish stocks, including Georges Bank haddock (Melanogrammus aeglefinus), necessitated new fishing regulations and generated interest in the role of predation on stock productivity. The sharp break between prolonged periods of high (pre-1965) and low (post-1965) haddock abundance suggests differing levels of stock productivity, consistent with a surplus production model incorporating a nonlinear predation rate (Steele and Henderson's (1984. Science (Washington, D.C.), 224: 985-987) model). This model and a Schaefer (1957. Inter-Am. Trop. Tuna Comm. Bull. 2: 245-285) model without a predation term were fit to haddock data to evaluate various rebuilding strategies with two performance measures: the sums of discounted yield and discounted revenue. Steele and Henderson's model provided plausible parameter estimates for the entire data set (1931-1993) whereas Schaefer's model provided plausible estimates only for years of low productivity (1976-1993). The presence of multiple equilibria in Steele and Henderson's model resulted in minor shifts of F, potentially producing large shifts in projected future biomass. For either model, levels of F that maximize either yield or revenue were lower than the recently adopted target level of F0.1 = 0.24. Recent low production provides impetus for managers to consider a variety of plausible stock production models, and the uncertainty of production dynamics, in choosing rebuilding strategies.
A comparison of several measures of genetic distance and population structure with microsatellite data: bias and sampling variance
Authors: Ruzzante Daniel E
Published: April 2011

Because of their rapid mutation rate and resulting large number of alleles, microsatellite DNA are well suited to examine the genetic or demographic structure of fish populations. However, the large number of alleles imply that large sample sizes are required for accurate reflection of genotypic frequencies. Estimates of genetic distance are often biased at small sample sizes, and biases and sampling variances can be affected by the number of, and distances between, alleles. Using data from a large collection of larval cod (Gadus morhua) from a single area, I examined the effect of sample size on seven genetic distance and two structure metrics. Pairs of samples (equal or unequal) of various sizes were drawn at random from a pool of 856 individuals scored for six microsatellite loci. ( delta µ)2, DSW, RST, and FSTwere the best performers in terms of bias and variance. Sample sizes of 50 <= N <= 100 individuals were generally necessary for precise estimation of genetic distances and this value depended on number of loci, number of alleles, and range in allele size. ( delta µ)2and DSWwere biased at small sample sizes.
Role of ecological factors and reproductive strategies in structuring freshwater mussel communities
Authors: Haag Wendell R , Warren, Jr. Melvin L
Published: April 2011

Freshwater mussel community composition within two drainage basins in Alabama, U.S.A., was better explained by patterns of variability in the fish community and the type of strategy used by mussels for infecting host-fishes than by patterns of variability in microhabitat. Mussel species richness increased in a downstream direction, and large-stream sites were characterized by a distinctive faunal assemblage that was similar between drainages. In contrast, faunal composition of headwater sites varied widely between drainages. Patterns of mussel community variation were correlated with patterns of fish community variation but not with habitat. Densities of host-specialist mussels with elaborate host-attracting mechanisms and host-generalist mussels were independent of host-fish densities, and these mussels were present throughout the drainages. Densities of host-specialist mussels without elaborate host-attracting mechanisms were correlated positively with host-fish densities and were absent or rare in headwater and midreach streams. We propose that mussel species dependent on host-fish density are restricted to sites with stable numbers of hosts, but mussels not dependent on host-fish density are able to persist in areas with more unstable fish assemblages, such as headwaters.
A simplified formulation for fish production
Authors: Mertz G , Myers R A
Published: April 2011

A new formulation for fish production is presented, one that clearly embodies the balance between aggregate somatic growth and losses due to natural and fishing mortality. The method permits simplified calculation of production over biomass and yield over production ratios; estimates of the latter can be used to investigate the reliability of yield as a proxy for production. Simple applications of the formulation indicate taxonomic variation in the yield to production ratio. Specifically, production is well approximated by yield for many piscivorous species, but yield seriously underestimates production for prey species.
Designing optimal estimators for fish stock assessment
Authors: Cordue Patrick L
Published: April 2011

Many estimation procedures are used in the provision of fisheries stock assessment advice. Most procedures use estimators that have optimal large-sample characteristics, but these are often applied to small-sample data sets. In this paper, a minimum integrated average expected loss (MIAEL) estimation procedure is presented. By its design a MIAEL estimator has optimal characteristics for the type of data it is applied to, given that the model assumptions of the particular problem are satisfied. The estimation procedure is developed within a decision-theoretic framework and illustrated with a Bernoulli and a fisheries example. MIAEL estimation is related to optimal Bayes estimation, as both procedures seek an estimator that minimizes an integrated loss function. In most fisheries applications a global MIAEL estimator will be difficult to determine, and a MIAEL estimator will need to be found within a given class of estimators. "Squared f-error," a generalization of the common squared error loss function is defined. It is shown that an estimator can be improved (for a given squared f-error loss function) by using its best linear transformation which is the MIAEL estimator within the class of linear transformations (in f space).
Fine-scale fishing strategies of factory trawlers in a midwater trawl fishery for Pacific hake (Merluccius productus)
Authors: Dorn Martin W
Published: April 2011

A Markov decision process model is developed to investigate the optimal scheduling of haul setting and retrievals on a factory trawler in the Pacific hake (Merluccius productus) fishery. The model was used to investigate changes in fishing behavior during a temporary ban on night fishing in 1992. The cycle of setting the net, fishing, and retrieving the net is modeled with different costs for each activity. The optimal controls generally consist of a bin threshold that signals the vessel to start fishing and a catch threshold that signals the vessel to stop fishing. A range of simple "rule of thumb" strategies generated nearly as much net revenue as the optimal control, indicating that the reward surface is flat in the region of the optimal control. A model with diel variation in catch rates caused the vessel to adjust bin and catch thresholds through the day to stockpile fish during the daylight hours and then to cut back on fishing at night when the catch rate is lower. With a ban on night fishing, vessels accumulated fish to a greater extent during the day, but daily net revenue did not decline significantly. Operational models of fishing have important applications in evaluating the consequences of management actions on the fishing industry. Regulations that ignore the constraints and trade-offs under which fishing vessels operate may fail to achieve their intended purposes, or may have unforseen adverse consequences.
Use of the stratified-Petersen estimator in fisheries management: estimating the number of pink salmon (Oncorhynchus gorbuscha) spawners in the Fraser River
Authors: Schwarz Carl James , Taylor Carolyn Gail
Published: April 2011

The simple-Petersen estimator is a well-known mark-recapture method to estimate animal abundance. Two key assumptions are equal catchability in both samples and complete mixing of tagged and untagged animals. If these are violated, severe bias can occur. The stratified-Petersen estimator can be used to account for some of the heterogeneity in catchability or mixing. In this paper, we first review recent developments in the stratified-Petersen experiment for fisheries audiences and demonstrate some of the practical problems that can occur that have not been discussed in the theoretical literature. Second, we present a case study to estimate the gross escapement of Fraser River pink salmon (Oncorhynchus gorbuscha) in 1991. The motivation for this study is a discrepancy of over 5 million fish between the estimates as derived by the Pacific Salmon Commission (PSC) (7.5 million fish based on a hydroacoustic method) and the Department of Fisheries and Oceans (DFO), Canada (13.0 million fish based on a mark-recapture method). One hypothesis put forward was that the discrepancy may be due to the use of a pooled-Petersen estimator when there is differential migration over time. The stratified-Petersen model suggests that little of this discrepancy can be explained by differential migration.
Prey fish exploitation, salmonine production, and pelagic food web efficiency in Lake Ontario
Authors: Rand Peter S , Stewart Donald J
Published: April 2011

Estimates of production and predation rates from bioenergetic models of chinook salmon (Oncorhynchus tshawytscha), coho salmon (Oncorhynchus kisutch), and lake trout (Salvelinus namaycush) suggest a long-term decline in their gross conversion efficiency (gross production/prey consumption) and the gross production to biomass ratio in Lake Ontario during 1978-1994. The former pattern was caused primarily by a declining trend in adult alewife (Alosa pseudoharengus) energy density during 1978-1985; the latter pattern resulted from reductions in growth rates (coho salmon) and a buildup of the older age-classes in the population (lake trout) over time. Model results suggest that over 100 and 25% of the annual production of adult alewife and rainbow smelt (Osmerus mordax), respectively, was consumed by salmonines during 1990 in Lake Ontario; hence, we claim that recent observations of reduced salmonine growth in Lake Ontario may be a result of prey limitation. Energy transfer from primary production to salmonines appeared to be more efficient in Lake Ontario than in Lake Michigan, probably due to higher stocking levels per unit area and higher densities of preferred prey fish in Lake Ontario. Through separate analyses, we arrived at conflicting conclusions concerning the sustainability of the food web configuration in Lake Ontario during 1990.
Multiyear tagging studies incorporating fishing effort data
Authors: Hoenig John M , Barrowman Nicholas J , Hearn William S , Pollock Kenneth H
Published: April 2011

The Brownie models for multiyear tagging studies can be used to estimate age- and year-specific annual survival rates and tag recovery rates. The latter are composites of the exploitation rates and rates of tag reporting, tag shedding, and tag-induced mortality. It is possible to estimate the exploitation rates if the other components of the tag recovery rates can be quantified. Instantaneous rates of fishing and natural mortality can be estimated if information is available on the seasonal distribution of fishing effort. The estimated rates are only moderately dependent on the timing of the fishing; consequently, the relative effort data can be crude. Information on the timing of the catch over the course of the year can be used as a substitute for the effort data. Fishing mortality can also be assumed to be proportional to fishing effort over years; consequently, if fishing effort is known then the tag reporting rate, natural mortality rate, and a single catchability coefficient can be estimated (instead of natural mortality and a series of fishing mortalities). Although it is possible in theory to estimate both the tag reporting rate and the natural mortality rate with all of these models, in practice it appears necessary to obtain some additional data relating to tag reporting rate to obtain acceptable results. The additional data can come from a variable reward tagging study, a creel or port sampling survey, or from tagged animals that are secretly added to the fishers' catches.
Relations between heavy metals in aquatic sediments and in Chironomus larvae of Belgian lowland rivers and their morphological deformities
Authors: de Bisthoven Luc Janssens , Postma Jaap F , Parren Peter , Timmermans Klaas R , Ollevier Frans
Published: April 2011

Levels of Cd, Pb, Cu, and Zn were measured in fourth-instar Chironomus gr. thummi and in three sediment fractions of Belgian lowland rivers, extracted with 1 M NH4-acetate, 1 M HCl, and 70% HNO3 - 30% H2O2. The percentages of deformed larvae and the mean population severities (MPS) of deformity for the head structures were compared by means of Pearson and linear and polynomial regressions against the metal concentrations in the different compartments. All correlations found were positive. Mentum deformities correlated with all lead fractions (MPS) and the larval copper fraction (percent deformed), while the pecten epipharyngis deformities correlated with the sediment lead fractions and the HCl fraction of copper. Premandible deformities correlated with the copper sediment HNO3-H2O2 fraction and with extreme values of cadmium and zinc. The study demonstrated a variety of deformity response curves to trace metals. At one site, higher lead concentrations were found in larvae with a deformed mentum, compared with normal larvae. Mentum deformities appeared to be potential predictors of lead levels in the sediments and the larvae, while pecten epipharyngis deformities may be an indicator of lead and copper in the sediments.
Environmental control of photosynthate allocation in the phytoplankton of Georgian Bay (Lake Huron)
Authors: Furgal J A , Taylor W D , Smith REH
Published: April 2011

Allocation of photosynthate by phytoplankton in Georgian Bay was measured from spring through fall of 1993 to test previous models for environmental control of allocation and to assess for the first time the effects on allocation of solar ultraviolet radiation. Ultraviolet-B radiation (UV-B, 280-320 nm) at near-surface levels significantly inhibited photosynthesis (by up to 82%) under both natural and artificial light. UV-B effects on allocation to protein, polysaccharide, low molecular weight materials, and total lipids were rarely significant, but the sensitivity of photosynthesis to UV-B increased directly with allocation to protein. UV-B exposure had more influence on allocation among lipid classes, but the effects were still statistically marginal. Allocation to protein and glycolipids varied directly with silicon availability, while allocation to total lipids and glycolipids varied inversely with phosphorus availability. Previously published models for predicting protein, polysaccharide, and total lipid allocation from temperature and daylength were unsuccessful. Lipid classes showed distinctive seasonal patterns and environmental correlates, consistent with differing functional roles and (or) taxonomic associations among the major lipid classes. The allocation of photosynthate, and thus the food quality and nutrient stoichiometry of the primary producers, appeared to be under complex control that could not be precisely predicted from any simple combination of environmental variables.
Particle retention by non-suspension-feeding cyprinid fishes
Authors: Sanderson S Laurie , Mort Mark E , Cech, Jr. Joseph J
Published: April 2011

Insectivorous Sacramento squawfish (Ptychocheilus grandis) and omnivorous benthic-feeding California roach (Hesperoleucus symmetricus) were exposed to suspended styrene microspheres (31-90 µm) or brine shrimp cysts (210-300 µm) in the presence of finely crushed Tetramin flakes or adult Artemia. These fish species retained small numbers of microspheres, and significantly more brine shrimp cysts than microspheres. During a 10-min period, they swallowed all of the brine shrimp cysts from a volume of water equivalent to 1-15 times their body volume. Squawfish and roach do not possess the morphological features of the branchial apparatus and palate that are associated with suspension feeding in confamilial Sacramento blackfish (Orthodon microlepidotus). The brine shrimp cysts could have been trapped between squawfish and roach gill rakers, while the microspheres as well as the brine shrimp cysts could have been retained on mucus-covered buccopharyngeal surfaces. These results suggest that non-suspension-feeding fish species may ingest small suspended particles routinely, with energetic and ecotoxicological implications that deserve further study.
Chronic exposure of rainbow trout (Oncorhynchus mykiss) to simulated climate warming and sublethal ammonia: a year-long study of their appetite, growth, and metabolism
Authors: Linton Tyler K , Morgan I J , Walsh P J , Wood Chris M
Published: April 2011

This study was conducted to assess, over the thermal cycle of an entire year, the effects (on appetite, growth, and metabolism) of a chronic small temperature increase (+2°C) and sublethal ammonia (70 µmol ·L-1) on rainbow trout (Oncorhynchus mykiss). Juvenile rainbow trout ( approx 11 g initially) were exposed for 14 months to four treatments: the natural water temperature cycle of the inshore region of Lake Ontario, this cycle +2°C to simulate a global warming scenario, and these temperature cycles in the presence of an additional 70 µmol total ammonia ·L-1(NH3range: 0.005-0.013 mg ·L-1). The additional +2°C substantially increased appetite over winter, significantly elevating specific growth rates. These gains were lost, however, over summer due to suppression of appetite and growth at high temperature. Ammonia alone tended to elevate growth, but the combination of +2°C and ammonia resulted in a general decrease in the activity of enzymes involved in nitrogen metabolism (alanine aminotransferase, aspartate aminotransferase, glutamate dehydrogenase, and glutamine synthetase). These results document the dramatic influence of a +2°C warming scenario on the growth and feeding metabolism of juvenile rainbow trout. Moreover, the data indicate that a chronic small temperature increase, together with low-level ammonia pollution, substantially alters protein dynamics, and hence growth, in juvenile freshwater fishes; juvenile rainbow trout without thermal refuge will experience an increase in t a warmer, more polluted environment.
Going against the flow: an examination of the propulsive movements made by young brook trout in streams
Authors: McLaughlin Robert L , Noakes David LG
Published: April 2011

We examined the propulsive movements and behaviour of young-of-the-year (YOY) brook trout (Salvelinus fontinalis) swimming in their natal streams. Our findings demonstrated that swimming performance was influenced by temporal and spatial heterogeneity in water flow. Pectoral fins were used commonly, even by individuals swimming in fast flowing water. There also was spatial variation in the speed attained for a given tail-beat frequency and amplitude. After controlling statistically for variation in spatial location, fork length, and tail-beat amplitude, the swimming speeds brook trout attained for a given tail-beat frequency were lower than values expected from laboratory studies of steady swimming but higher than values expected from laboratory studies of unsteady swimming in standing water. Trout holding station made short-term adjustments in tail-beat frequency also suggesting a degree of unsteady swimming. A field experiment demonstrated that introduction of a current-velocity refuge reduced swimming costs by 10%, on average, without affecting the frequency of foraging attempts made.
Trade-offs between herbivore resistance and competitiveness in periphyton of acidified lakes
Authors: Graham Mark D , Vinebrooke Rolf D
Published: April 2011

It was hypothesized that herbivores regulate periphyton succession in acidified lakes by suppressing loosely attached filamentous algae that otherwise persist and outcompete other growth forms for resources, such as dissolved inorganic carbon (DIC). This hypothesis was tested by conducting grazer-exclosure experiments over an ice-free season in acidified and circumneutral lakes that differed in DIC concentrations. In each lake, the two-factor experimental design had two herbivore (presence-absence) and five succession (early-late) treatments. Total periphyton biomass was greater and significantly suppressed by herbivores in the circumneutral lake. Here, acid-sensitive green frog (Rana clamitans) tadpoles suppressed loosely attached (i.e., zygnematacean taxa) while stimulating firmly attached (i.e., Coleochaete scutata) algae, causing succession towards a herbivore-resistant physiognomy. Conversely, a loosely attached and tall physiognomy persisted in the absence of significant grazing and greater resource limitation in the acid lake. Our findings suggest that trade-offs between competitiveness and herbivore resistance help predict changes in periphyton in recovering acidified lakes. During recovery, concomitant increases in herbivory and resources should favour a firmly attached and short periphyton physiognomy that is resistant to removal by herbivores, but that lacks the competitiveness of loosely attached and tall forms in DIC-limited acid lakes.