bluuebunny/crossref_metadata_2025 huggingface dataset:
Phytoplankton community composition in relation to water quality and water-body morphometry in urban lakes, reservoirs, and ponds
Authors: Olding Daniel D , Hellebust Johan A , Douglas Marianne SV
Published: April 2011

Distinct differences in observed summer phytoplankton communities in relation to maximum depth suggest that constraints posed by water-body morphometry may modify the trophic control of phytoplankton-community composition and structure in urban water bodies. In deep urban sites (Zmax [Formula: see text] 5 m), phytoplankton communities tended to be predictably related to trophic status (i.e., increases in trophy were associated with increased cyanobacterial dominance, a decreased proportion of Chrysophyceae-Synurophyceae and grazable-size algae, and a decrease in community richness), although exceptions existed, owing to factors such as human intervention, age of the water body, and flushing rates. In contrast, in shallow urban water bodies (Zmax < 5 m), trophic status was a poor predictor of phytoplankton communities. Across meso- to hyper-eutrophic conditions, shallow urban sites were rarely dominated by cyanobacteria and, when they were, the species composition differed from nutrient-rich deep urban sites. The key requirement for cyanobacterial dominance in shallow urban sites appears to be sufficiently long water residence times, viz., greater than 8-14 days. Further study should describe how the relationship between water body residence time and species-generation time may limit the development of specific nuisance algal species, aiding in the management and rehabilitation of urban water bodies.
Krill (Euphausiacea) life history and aspects of population dynamics
Authors: Siegel Volker
Published: April 2011

The present perspective summarizes information on the variability of krill population parameters, which can assist in interpreting fluctuations in euphausiid populations. This requires knowledge about potential longevity of an individual as well as the age composition of populations. Further key parameters of the life cycle are discussed for a number of euphausiid species from oceans around the world. In a variable environment, species may show variations in sex ratio, breeding season, larval development, as well as functional characteristics such as natural mortality and productivity. Conceptual models based on results for some krill species indicate that environmental disturbances create instability in populations by reducing the recruitment success, which finally can lead to a decreasing population size.
Heritability of fluctuating asymmetry for multiple traits in chinook salmon (Oncorhynchus tshawytscha)
Authors: Bryden Colleen A , Heath Daniel D
Published: April 2011

The heritability of fluctuating asymmetry (FA) as an indicator of developmental instability is of interest to evolutionary and conservation biologists and is the subject of ongoing controversy. This study examined the inheritance of FA in two groups of fish: domestic chinook salmon (Oncorhynchus tshawytscha) mated in a full-sib design and domestic and wild chinook salmon mated in a half-sib design. Eight traits were measured on the right and left sides of each fish: eye diameter, head length, maxillary length, branchiostegal ray number, pectoral and pelvic fin ray number, and upper and lower gill raker number on the first gill arch. Narrow-sense heritabilities were calculated from parent-offspring regressions for the first group and using sib analysis for the second group. Our data represent the largest breeding program designed to detect heritability of FA in fish reported to date. We found no significant heritability of FA for any of the individual traits examined or for a composite FA index. Our results indicate that FA estimates in chinook salmon will not be confounded by appreciable additive genetic contributions and thus can be reliably used as an environmental and genetic stress indicator.
Fishing down Canadian aquatic food webs
Authors: Pauly Daniel , Palomares Ma. Lourdes , Froese Rainer , Sa-a Pascualita , Vakily Michael , Preikshot David , Wallace Scott
Published: April 2011

The mean trophic level (TL) of fish landed in fisheries on the east and west coasts of Canada is declining by 0.030.10·decade1, similar to global trends. This finding is based on data from United Nations Food and Agriculture Organization and the Canadian Department of Fisheries and Oceans and other Canadian sources for the period 18731997. Significant rates of decline in mean TL were obtained even when key species  Atlantic cod (Gadus morhua) on the east coast and Pacific herring (Clupea pallasi) and Pacific hake (Merluccius productus) on the west coast  were omitted from the analysis. Fish taken in inland water fisheries did not exhibit a decline in mean TL. Two models were developed, based on length and age, respectively, for correcting TL estimates of individual species for the effects of changes in body size due to changes in fishing mortality. Both produced corrections that were small relative to changes in mean TL that resulted from changes in species composition of the catch over time. Overall, these results suggest that the mean TL of fish landed can be used as an index of sustainability in multispecies fisheries and that its reliability will depend on the quality of the data and length of the time series available for analysis.
Behavior of Antarctic krill (Euphausia superba): schooling, foraging, and antipredatory behavior
Authors: Hamner William M , Hamner Peggy P
Published: April 2011

Aspects of the behavior of pelagic euphausiids are reviewed, emphasizing the behavioral biology of Antarctic krill (Euphausia superba). Euphausia superba makes an abrupt behavioral transition after the last larval molt from an individualistic, planktonic lifestyle to that of a highly social, nektonic juvenile. Then and throughout the rest of its life, most aspects of krill behavior are expressed within the context of highly organized, polarized schools. A krill school is an integrated whole that displays properties greater than the sum of its parts. Emergent attributes of the aggregate evolve in response to a suite of positive and negative selective factors that act on entire schools as well as individuals. We evaluate the individual advantages and disadvantages of living within large schools of conspecific euphausiids primarily for foraging, antipredator behavior, and epidemiology. We review the history of research on krill behavior, comment on the current state of knowledge, and suggest new avenues for future investigations.
Competition among juvenile Atlantic salmon (Salmo salar) and steelhead (Oncorhynchus mykiss): relevance to invasion potential in British Columbia
Authors: Volpe John P , Anholt Bradley R , Glickman Barry W
Published: April 2011

Atlantic salmon (Salmo salar) are routinely captured in both freshwater and marine environments of coastal British Columbia (Canada). Recent evidence suggests that this species is now naturally reproducing in Vancouver Island rivers. Our objective was to quantify the performance of each species in intra- and inter-specific competition by assessing the competitive ability of Atlantic salmon sympatric with native niche equivalent steelhead  rainbow trout (Oncorhynchus mykiss). Significant behavioural differences, particularly with respect to agonism, were observed between species; however, the status of an individual as resident or challenger was the best predictor of performance. Resident fish always outperformed challengers, regardless of species. Thus, we suggest that Atlantic salmon may be capable of colonizing and persisting in coastal British Columbia river systems that are underutilized by native species, such as the steelhead.
Impact of elevated temperature on the growth, survival, and trophic dynamics of winter flounder larvae: a mesocosm study
Authors: Keller Aimee A , Klein-MacPhee Grace
Published: April 2011

Winter flounder (Pseudopleuronectes americanus) is a dominant commercial fish in Narragansett Bay, Rhode Island, and yet factors controlling its recruitment remain unclear. An experiment was conducted with six 13-m3 land-based mesocosms (5 m deep) from February to April 1997 to address the impact of increased temperature (+3°C) on growth, survival, and trophic dynamics of winter flounder larvae. Objectives were to determine if warmer winter temperatures result in lower survival of winter flounder as a result of increased predator activity or if temperature-induced alterations in the food web result in greater food availability, perhaps leading to increased survival. Analyses of variance revealed significant (P < 0.05) or near-significant (P < 0.10) differences in phytoplankton and zooplankton abundance and biomass between warm and cool mesocosms. Winter flounder egg survival, percent hatch, time to hatch, and initial size were significantly greater in cool systems (P < 0.05). Mortality rates were lower in cool systems and significantly related to the abundance of active predators (P < 0.05). The cumulative impact of decreased survival of eggs and larvae in warm systems may partially explain the decline of winter flounder in Narragansett Bay, which has experienced elevated winter water temperatures in recent years.
Dynamics of individual growth in a recovering population of lake trout (Salvelinus namaycush)
Authors: Fabrizio Mary C , Dorazio Robert M , Schram Stephen T
Published: April 2011

In 1976, the Wisconsin Department of Natural Resources established a refuge for a nearly depleted population of lake trout (Salvelinus namaycush) at Gull Island Shoal, Lake Superior. The refuge was intended to reduce fishing mortality by protecting adult lake trout. We examined the growth dynamics of these lake trout during the period of recovery by comparing estimates of individual growth before and after the refuge was established. Our estimates are based on an annual mark-recapture survey conducted at the spawning area since 1969. We developed a model that allowed mean growth rates to differ among individuals of different sizes and that accommodated variation in growth rates of individuals of the same size. Likelihood ratio tests were used to determine if the mean growth increments of lake trout changed after the refuge was established. Our results suggest that growth of mature lake trout (particularly wild fish) decreased significantly in the postrefuge period. This decreased growth may have been associated with a reduction in food availability. We also observed reductions in growth as wild fish grew older and larger, which suggests that the growth of these fish may be adequately approximated by a von Bertalanffy growth model if it becomes possible to obtain accurate ages.
Annual and interannual variability of nutrients and their estimated fluxes in the Scotian Shelf - Gulf of Maine region
Authors: Petrie Brian , Yeats Philip
Published: April 2011

Nitrate, silicate, and phosphate observations are used to determine their annual cycles for the Scotian Shelf and the Gulf of Maine. Concentrations increase from fall through winter, decrease rapidly at shallow depths in late winter, and remain at low levels through spring and summer. Deep layers exhibit a weak annual cycle with highest concentrations in summer. Winter nitrate concentrations (depth [Formula: see text] 50 m) are highest on the eastern Scotian Shelf, decreasing southwestwards into the Gulf of Maine. The Gulf of St. Lawrence is the primary source of nitrate (9300 mol· s-1) and silicate (7680 mol·s-1) during winter for the Scotian Shelf; in spring and summer, vertical diffusive fluxes, 1500-1000 mol·s-1 for the central Scotian Shelf, are as large as the horizontal advective ones and can provide the entire nitrate requirement. The 50-m vertical diffusive fluxes of nitrate and silicate vary by a factor of 4 in the Scotian Shelf - Gulf of Maine region. The interannual variability of nitrate and dissolved oxygen on the Scotian Shelf are coupled to water mass changes, with low (high) nitrate and high (low) dissolved oxygen concentrations corresponding to the dominance of Labrador (Warm) Slope water.
Designing and evaluating length-frequency surveys for trap fisheries with application to the southern rock lobster
Authors: McGarvey Richard , Pennington Michael
Published: April 2011

A survey design for estimating the length distribution of harvested southern rock lobsters (Jasus edwardsii) was developed for the South Australian fishery. Experimental sampling was carried out by volunteer fishers in spring 1996 and autumn 1997 to test three proposed survey designs. A variance components analysis indicated that it would be more efficient to sample one pot per trip from all trips rather than the previous design of sampling multiple pots from a few trips. The variation among licenses (fishers) accounts for most of the remaining sample variance. Onboard research sampling by scientists, who in the past measured from all pots on selected trips, was shown to be the least efficient design option in comparison with volunteer sampling by fishers. A sampling protocol where fishers measure one to three pots per trip has been adopted by the South Australian rock lobster fishers. Estimators, based on a three-level sampling hierarchy of pot, day, and license, are presented for estimating the mean and sample variance of the numbers harvested overall and within each length category.
Redside shiner (Richardsonius balteatus) shoals provide a behavioral competitive refuge for subordinate juvenile steelhead trout (Oncorhynchus mykiss)
Authors: Tinus Craig A , Reeves Gordon H
Published: April 2011

We examined the relative effects of zero, three, and nine redside shiner (Richardsonius balteatus) on the aggression-related damage among three juvenile steelhead (Oncorhynchus mykiss) in aquaria at 15 and 20°C. No steelhead died when in the presence of nine redside shiner. When redside shiner were not present, mortality among the smallest steelhead was 80%. Thus, the survival of smaller juvenile steelhead was significantly enhanced by the presence of redside shiner. A second experiment was conducted in 6800-L stream channels at 15°C with natural substrate. In separate trials, 10 and 7 steelhead were held either alone or with 20 redside shiner. In the absence of redside shiner, fin damage was significantly greater among smaller steelhead. In both experiments, if a redside shiner group was present, the smallest steelhead frequently took refuge within the shiner group, thereby avoiding attack by dominant steelhead. We have termed this phenomenon a behavioural competitive refuge.
Sampling stream invertebrates using electroshocking techniques: implications for basic and applied research
Authors: Taylor Brad W , McIntosh Angus R , Peckarsky Barbara L
Published: April 2011

We present a new technique using electrofishing equipment to collect and quantitatively sample stream invertebrates. We used an electrofishing machine with a small anode to produce a localized field of pulsed direct current to induce invertebrate drift. We quickly obtained large numbers of live invertebrates for experiments by passing the anode over the stream bottom upstream of sampling nets. We compared the results of five techniques: (i) electroshocking inside a modified Hess sampler, (ii) repeated electroshocking over a large area to estimate population size by depletion, (iii) traditional Surber, (iv) Hess, and (v) individual stone sampling. Electroshocking techniques provided estimates of invertebrate density comparable with those of traditional sampling techniques. The electroshocking depletion method that sampled a large area provided higher measures of Ephemeroptera, Plecoptera, and Trichoptera richness. Hess and area-restricted electrobug methods had similar density and diversity estimates, whereas the Surber sampler provided low density estimates, especially for mobile taxa. Density estimates from individual stones were inflated, were biased for mayflies, and had low richness. Samples taken with the electroshocking method were processed 40% faster because these samples contained little detritus. Electroshocking techniques can provide accurate estimates of population size and diversity, minimize disturbance to benthic habitats, and reduce processing time.
Linking shrimp assemblages with rates of detrital processing along an elevational gradient in a tropical stream
Authors: March James G , Benstead Jonathan P , Pringle Catherine M , Ruebel Mark W
Published: April 2011

We experimentally excluded freshwater shrimp assemblages (Atyidae, Xiphocarididae, and Palaemonidae) to examine their effects on detrital processing and benthic insect biomass at three sites along an elevational gradient in a tropical stream in Puerto Rico. We also determined which shrimp taxon was responsible for leaf decay in a subsequent laboratory experiment. At the high-elevation site, the shrimp assemblage was dominated by Atya spp. and Xiphocaris elongata, and leaf decay rates were significantly faster in the presence of shrimps than in their absence. Laboratory experiments showed that this was primarily due to direct consumption of leaves by Xiphocaris. Shrimps had no effect on leaf decay rates at mid- and low-elevation sites where there were higher proportions of Macrobrachium spp. shrimps (which prey on Xiphocaris). Laboratory experiments showed that Xiphocaris consumed significantly less leaf material and experienced significantly higher mortality in the presence of Macrobrachium. Shrimp exclusion resulted in significantly less and significantly more insect biomass at the high- and low-elevation sites, respectively; no difference was found at the mid-elevation site. Insects played a minor role in leaf decay. Results show a strong linkage between shrimp assemblages and rates of detrital decay and illustrate the importance of conducting experiments at multiple sites.
A regional paleolimnological assessment of the impact of clear-cutting on lakes from the west coast of Vancouver Island, British Columbia
Authors: Laird Kathleen , Cumming Brian , Nordin Rick
Published: April 2011

The impact of forest harvesting on lakes within the temperate rainforest on the west coast of Vancouver Island was examined in a paleolimnological study of four lakes that had 3592% of their watersheds progressively clear-cut over a period of 1530 years (impact lakes) and four lakes that had experienced little or no known anthropogenic disturbance in their watersheds (reference lakes). Changes in diatom species composition and percent organic matter in the 210Pb-dated sediment cores were compared over the last 100 years in each of the impact lakes before and after the onset of forest harvesting, which began in 1950, and before and after 1950 in the four reference lakes. Only one impact lake showed significant changes in percent organic matter. Significant changes (p < 0.05) in species composition following forest harvesting were detected in all four impact lakes and in one of the four reference lakes. However, the changes in diatom species composition following clear-cutting in the impact lakes were small, with changes in the relative abundance of the most common species being maximally 20%, but more typically 310%.
Effects of anoxia and sulfide on concentrations of total and methyl mercury in sediment and water in two Hg-polluted lakes
Authors: Regnell Olof , Hammar Tommy , Helgée Anders , Troedsson Bo
Published: April 2011

Between May and December 1996, monthly samples of surface sediment (01 cm), settling matter, and water were taken at a shallow site and a deep site in each of two consecutive Hg-polluted riverine lakes. In the upper lake, the sediment was polluted also with cellulose fiber. Both hypolimnia turned anoxic, but sulfide was detected only in the upper lake. When sulfide appeared, hypolimnetic methyl mercury (MeHg) increased and reached 47 pM (9.4 ng·L1), whereas MeHg in the sediment below decreased. The increase in hypolimnetic inorganic Hg (IHg = total Hg  MeHg), which reached a peak of 40 pM (8.0 ng·L1), was slower, possibly because mobilized IHg was methylated. In the lower lake, hypolimnetic MeHg and IHg increased less dramatically during summer stratification, reaching only 5 and 24 pM (1.0 and 4.8 ng·L1), respectively. There was no detectable concomitant decrease in sediment MeHg. In both lakes, MeHg appeared to increase simultaneously with total Fe and Mn in the hypolimnion, as did IHg in the lower lake. Our observations suggest that the presence of hydrous ferric and manganese oxides decreased the mobility of Hg in both lakes but increased MeHg production in the upper lake.
A comparison of gamma and lognormal maximum likelihood estimators in a sequential population analysis
Authors: Cadigan Noel G , Myers Ransom A
Published: April 2011

We analyze the model used to assess most major commercial marine fish populations, namely, sequential population analysis (SPA). This model estimates population abundance by combining catch-at-age data with research surveys or commercial catch per unit effort indices of abundance. We examine two maximum likelihood estimators of SPA parameters. These estimators are based on assuming that the stock-size indices are from lognormal or gamma distributions. Using simulations, we find that both types of estimators can have significant biases; however, our results indicate that it is preferable to use the gamma model, because it tends to have lower bias and variability, even when the true distribution of the stock-size indices is lognormal.
II: THE EFFECTS OF DYNAMITE EXPLOSIONS ON FISH LIFE.: A PRELIMINARY REPORT
Authors: KNIGHT M.A., M.D. A. P.
Published: April 2011

not available
IV.: A FURTHER REPORT UPON THE EFFECTS OF SAWDUST ON FISH LIFE.
Authors: Knight M.A., M.D. A. P.
Published: April 2011

not available
Diatom-inferred dissolved organic carbon reconstructions provide assessments of past UV-B penetration in Canadian Shield lakes
Authors: Dixit Sushil S , Keller W (Bill) , Dixit Aruna S , Smol John P
Published: April 2011

Paleolimnological approaches have provided strong inference models for lake-water acidity and metal concentrations in Sudbury-area lakes, but calibration data have not yet been explored for inferring lake-water dissolved organic carbon (DOC). A review of available limnological data provided DOC values for 80 of our 105 calibration lakes, allowing us to examine the relative importance of DOC in determining the distribution of diatom assemblages in Canadian Shield lakes, such as those in the Sudbury region. Canonical correspondence analysis (CCA) indicated that lake-water DOC explained a significant proportion of variation in the diatom data. Our weighted-averaging DOC model showed a strong relationship (r2 = 0.63) between measured and inferred DOC. Using this model, we reconstructed historical DOC concentrations in three Sudbury-area lakes, and then estimated temporal changes in UV-B penetration. These reconstructions showed that lake water DOC concentrations and underwater UV-B penetration have changed markedly in two of the three lakes modeled. The close correspondence between inferred and measured DOC for the 1980s in all three lakes provides further evidence that we have accurately inferred DOC concentrations. Quantitative DOC reconstructions in Sudbury-area lakes offer an excellent technique for assessing past changes in DOC concentrations and UV-B penetration in Canadian Shield lakes.
XII: SAWDUST AND FISH LIFE.
Authors: KNIGHT A. P.
Published: April 2011

not available
Quasi-cycles in crappie populations are forced by interactions among population characteristics and environment
Authors: Allen Micheal S , Miranda Leandro E
Published: April 2011

Crappie (Pomoxis spp.) populations have been characterized as cyclic, with strong year-classes recurring at 2- to 4-year intervals. We evaluated the potential for cyclic trends in crappie populations using a population model that included a density-dependent stock recruitment function and random environmental variation. Slow, medium, and fast growth were simulated over 100 years. The model predicted highly variable recruitment that was strongly influenced by environmental fluctuation at low and intermediate stock densities. At high stock density, recruitment was low, even if environmental conditions were favorable. Significant quasi-cycles occurred, but they were not sustained throughout the time series due to random environmental fluctuation. Quasi-cycles occurred because intermediate stock density and favorable environmental conditions occasionally combined to produce a very strong year-class that greatly increased stock density in the following 13 years and produced low recruitment, even if environmental conditions were favorable. Empirical data from 32 years of sampling age-0 crappies at Ross Barnett Reservoir showed trends similar to the simulated fluctuations. We conclude that crappie populations likely do not exhibit true cycles but may show quasi-cycles as a result of the interaction between random fluctuations in environment and density-dependent mechanisms. The frequency of such quasi-cycles may be enhanced by rapid growth and high exploitation.
High variability in spawnerrecruit data hampers learning
Authors: Hinrichsen Richard A
Published: April 2011

Variability is a formidable opponent of experimental management aimed at detecting spawnerrecruit (SR) effects in a short time frame. I fitted Ricker SR models to 214 different SR data sets and found that high residual error variability was common. For each of these data sets, in an a priori power analysis, I estimated the power of experiments that used the change in Ricker a as the treatment effect and a temporal reference alone (no subpopulation references). Power was calculated using both bootstrap resampling and the usual normal theory methods. The analysis revealed that large residual variability severely limits the power to detect large changes in recruits per spawner (R/S). At the median level of error variability, achieving the design criteria of α = 0.05 and power = 0.8 required an experiment that doubled R/S to last about 20 years (assuming an equal number of treatment and control years). Several approaches to countering large error variability are discussed along with their limitations.
The interaction between shellfish culture and ecosystem processes
Authors: Smaal Aad , Stralen Marnix van , Schuiling Egbertha
Published: April 2011

The carrying capacity of the Oosterschelde ecosystem for the production of mussels (Mytilus edulis) was evaluated before and after completion of a large-scale coastal engineering project in 1987. This project caused hydrodynamic and water-quality changes; hence, phytoplankton-species composition changed and phytoplankton turnover increased, but primary production remained the same. In the prebarrier period (19801986), condition of mussels showed a significant negative correlation with the annual shellfish standing stock and a significant positive correlation with the annual primary production. The system was exploited at maximum capacity. In the postbarrier period (19871997), the significant correlation between mussel condition and primary production remained, but there was no longer a negative correlation between standing stock and condition. This indicates overstocking, but yields were maintained. This was explained by (i) feedbacks of the mussels in the Oosterschelde ecosystemthrough their large filtration and nitrogen-regeneration capacity, increased phytoplankton turnover was induced; and (ii) adaptation to the new conditions by the shellfish farmers in their management of the mussel stocks. It was concluded that feedbacks by filter feeders and farmers have to be addressed in estimating the exploitation capacity of ecosystems.
Contrasting larval transport in demersal fish and benthic invertebrates: the roles of behaviour and advective processes in determining spatial pattern
Authors: Bradbury Ian R , Snelgrove Paul V.R.
Published: April 2011

Many benthic invertebrates and demersal fish have planktonic larvae and must therefore balance dispersal to new habitat with the need to settle where survival and growth are possible. We review published studies to determine whether the discontinuity in the literature between these groups represents a real ecological difference. Specifically, we examine the roles of biological and physical processes and the scales at which these processes act in pattern formation in fish and invertebrates. For most of the physical mechanisms that influence larval transport at different scales, we find examples of fish and invertebrate studies that are important at each scale. A comparison of planktonic durations suggests that more invertebrate species have highly limited dispersal potential. Comparison of dispersal potential and geographic range suggests that planktonic duration may play a role in defining the geographic range of species in both cases. Fish larvae were generally faster swimmers than invertebrate larvae, suggesting that swimming may contribute to pattern formation at larger spatial scales. In contrast, the documented capacity to delay metamorphosis is more prevalent in invertebrates and may be related to the greater mobility of adult fish relative to invertebrates. Ultimately, similar processes operate in both groups, although sometimes at different scales.
A semiparametric model to examine stockrecruitment relationships incorporating environmental data
Authors: Chen D G , Irvine J R
Published: April 2011

A novel semiparametric model that can incorporate environmental and fishery data is developed to analyze stockrecruitment relationships. Unlike traditional stockrecruitment models that assume a log-linear relationship between recruitment and environmental and fishery variables, the new model uses a nonparametric smoothing algorithm, which helps quantify the underlying empirical relationships and enables more accurate parameter estimates. Bootstrap resampling is used to evaluate uncertainties in the model parameters. Distribution plots can be produced for stockrecruitment productivity and capacity parameters. This approach is applied to southeast Alaska pink salmon (Oncorhynchus gorbuscha) with sea surface temperature as the environmental variable and West Coast Vancouver Island herring (Clupea harengus) with sea surface temperature and hake biomass as two environmental variables. Results from diagnostic tests indicate that our model performed better than the traditional Ricker model and a Ricker model that was extended to include environmental effects.
Consequences of model specification for the determination of gut evacuation rates: redefining the linear model
Authors: Bochdansky Alexander B , Deibel Don
Published: April 2011

The combination of gut contents and evacuation rate is an important tool to determine in situ feeding rates of many organisms. Traditionally used equations of gut evacuation models, however, have made a systematic comparison among models difficult. We changed the notation of the linear gut evacuation model to provide an algorithm compatible with the commonly used exponential model. Using examples from the literature, we demonstrate that prolonged retention of food after a true linear pattern of gut evacuation can be mistaken for an exponential pattern. In many of these examples, use of an exponential gut evacuation model causes overestimation of food consumption by approximately twofold. In situations where the entire gastrointestinal tract is examined instead of the stomach only, the time course of the gut content is best described by a plug-flow reactor for which the "input = output" rule applies. In contrast, the assumption of a "proportional release" must be met rigorously for the exponential model to be valid, which requires more complex feedback mechanisms than the simple plug-flow reactor. The new algorithm for the linear model is also consistent with the empirical observation that the gut evacuation rate is proportional to the initial gut content.
Estimation and analysis of biological parameters in elasmobranch fishes: a comparative life history study
Authors: Frisk Michael G , Miller Thomas J , Fogarty Michael J
Published: April 2011

Published life-history parameters for sharks, skates, and rays over a wide geographic range were used to develop predictive models to estimate parameters that are difficult to measure or have not been previously estimated in elasmobranch species. We determined empirical relationships between body size (total length) and length at maturity (Lm) and age at maturity (Tm). The data used in determining these empirical relationships, the von Bertalanffy parameters asymptotic length (L[Formula: see text]) and growth rate (k), and natural mortality (M) and maximum age (Tmax) were used to describe the life-history strategies of elasmobranch fishes. M/k and Beverton's growthmaturitylongevity plots were used to make comparisons between teleost fishes, reptiles, and elasmobranchs. We found that the M/k ratio in elasmobranchs is significantly different from those for other fish and reptile taxa. We linked elasmobranch species fecundity (f) and Tm to potential vulnerability to population decline under exploitation. We found that larger species of elasmobranchs have lower growth rates (k) and potential population increases (r'). Elasmobranchs can be categorized by species maximum length to determine susceptibility of decline under exploitation. Generally, species greater than 100 cm are characterized by life-history and population traits that place them at greater risk of population decline.
Biotic influences on habitat selection by young-of-year walleye (Stizostedion vitreum) in the demersal stage
Authors: Pratt Thomas C , Fox Michael G
Published: April 2011

The influence of prey availability and predation risk on the distribution of young-of-year (YOY) walleye (Stizostedion vitreum) was investigated by comparing species associations with the relative abundance of YOY walleye across nine habitat types using an underwater visual assessment technique. During the early demersal period (mid-June to mid-July), YOY walleye were found primarily in areas of high macrophyte cover at 25 m depth. YOY walleye abundance was positively correlated with the abundance of prey fishes at this time. YOY walleye shifted to low-cover, shallow areas during the late demersal period (mid-July to late August), and the significant prey associations disappeared. Although the selected habitats are considered to have low predation risk, the distribution of YOY walleye was not related to our index of predator abundance in either time period. YOY walleye were not observed in three of the nine habitat types, suggesting that active habitat selection was occurring. High macrophyte cover and prey availability appear to be the major factors influencing habitat selection during the early demersal period. Although our results do not demonstrate the functional significance of the shift of YOY walleye into shallow water, we hypothesize that these habitats are selected as refugia from particular predators such as adult walleye.
Effects of acclimation to brackish water on tolerance of salinity challenge by young-of-the-year Adriatic sturgeon (Acipenser naccarii)
Authors: McKenzie D J , Cataldi E , Romano P , Taylor E W , Cataudella S , Bronzi P
Published: April 2011

The effects of a 24-h salinity challenge in water at 28 g·L1 on plasma osmotic and ion homeostasis, swimming performance, and exercise respirometry were compared in young-of-the-year Adriatic sturgeon (Acipenser naccarii) maintained in freshwater (FW) or acclimated to brackish water (BW) that was slightly hypertonic to sturgeon plasma at a salinity of 11 g·L1. Salinity challenge caused a significant increase in plasma osmolality and Na+ and Cl concentrations in both groups, but this was significantly less severe in the group acclimated to the BW as compared with FW. Salinity challenge elicited a significant and profound decline in maximum sustainable swimming speed (Ucrit) in sturgeon from FW, whereas there was no significant effect on Ucrit in the sturgeon acclimated to BW. A negative linear relationship was revealed between plasma osmolality, Na+ or Cl concentrations, and Ucrit. These variables appeared to influence Ucrit by increasing costs for locomotion while reducing the sturgeon's capacity for oxygen uptake and muscular work. The results indicate that prior acclimation to mildly hypertonic BW promoted osmoregulatory adaptations that improved the ability of the sturgeon to perform exercise following further increases in water salinity.
Zebra mussel (Dreissena polymorpha) selective filtration promoted toxic Microcystis blooms in Saginaw Bay (Lake Huron) and Lake Erie
Authors: Vanderploeg Henry A , Liebig James R , Carmichael Wayne W , Agy Megan A , Johengen Thomas H , Fahnenstiel Gary L , Nalepa Thomas F
Published: April 2011

Microcystis aeruginosa, a planktonic colonial cyanobacterium, was not abundant in the 2-year period before zebra mussel (Dreissena polymorpha) establishment in Saginaw Bay (Lake Huron) but became abundant in three of five summers subsequent of mussel establishment. Using novel methods, we determined clearance, capture, and assimilation rates for zebra mussels feeding on natural and laboratory M. aeruginosa strains offered alone or in combination with other algae. Results were consistent with the hypothesis that zebra mussels promoted blooms of toxic M. aeruginosa in Saginaw Bay, western Lake Erie, and other lakes through selective rejection in pseudofeces. Mussels exhibited high feeding rates similar to those seen for a highly desirable food alga (Cryptomonas) with both large ( >53 µm) and small (<53 µm) colonies of a nontoxic and a toxic laboratory strain of M. aeruginosa known to cause blockage of feeding in zooplankton. In experiments with naturally occurring toxic M. aeruginosa from Saginaw Bay and Lake Erie and a toxic isolate from Lake Erie, mussels exhibited lowered or normal filtering rates with rejection of M. aeruginosa in pseudofeces. Selective rejection depended on "unpalatable" toxic strains of M. aeruginosa occurring as large colonies that could be rejected efficiently while small desirable algae were ingested.
Thermal heterogeneity in the hyporheic zone of a glacial floodplain
Authors: Malard Florian , Mangin Alain , Uehlinger Urs , Ward J V
Published: April 2011

We examined the thermal regime of surface and hyporheic waters at three kryal sites and four krenal streams within the channel network of a glacial floodplain. Temperature was continuously measured for 1 year in the surface stream and at sediment depths of 30 and 80 cm. The vertical pattern of water temperature was strongly influenced by the direction and intensity of surface water  groundwater exchanges. At sites characterized by strong downwelling of surface waters, the thermal regimes of surface and hyporheic waters were virtually identical. In contrast, inputs of groundwater substantially increased mean summer temperatures in the hyporheic zone of the main kryal channel, decreased summer temperatures in the hyporheic zone of krenal streams, and elevated hyporheic temperatures of all stream types during winter. Groundwater from different sources had dramatically different effects on the seasonal regime of temperature in the hyporheic zone. Inflow of shallow alluvial groundwater had minimal effects on seasonal patterns of hyporheic temperature, whereas upwelling from deep alluvial and hillslope aquifers resulted in significant time lags and differences in seasonal amplitudes between surface and hyporheic temperatures. The unexpectedly high thermal heterogeneity of hyporheic waters presumably sustains biodiversity and stimulates ecosystem processes in this glacial floodplain.
Empirical relationships between watershed characteristics and coho salmon (Oncorhynchus kisutch) smolt abundance in 14 western Washington streams
Authors: Sharma Rishi , Hilborn Ray
Published: April 2011

We assembled data on coho salmon (Oncorhynchus kisutch) from 14 streams in western Washington, including annual smolt counts and annual escapement, either as absolute counts or as an index. We also compiled data on large woody debris (number·km%#150;1 of stream), road densities in the watersheds (km road·km%#150;2), gradient of the streams (%), valley slope adjacent to the stream (%), drainage area in the watershed (km2), and pool, pond, and lake areas (m2·km%#150;1). We explored the relationships between habitat variables and two measures of coho production, the maximum production of smolts in the stream (capacity) and the maximum smolts/spawner (productivity). Using the 11 streams with pool and pond counts, we found that pool and pond densities served as good predictors of smolt density (r2 = 0.85 for pools and 0.68 for ponds, independently). Pools produced 0.39 smolts·m%#150;2 and ponds produced 0.07 smolts·m%#150;2 in the multiple regression fit, accounting for 92% of the residual error. We also found that lower valley slopes, lower road densities, and lower stream gradients were correlated with higher smolt density.
Climate regimes and water temperature changes in the Columbia River: bioenergetic implications for predators of juvenile salmon
Authors: Petersen James H , Kitchell James F
Published: April 2011

We examined how climatic regime shifts may have affected predation rates on juvenile Pacific salmonids (Oncorhynchus spp.) by northern squawfish (Ptychocheilus oregonensis, also called northern pikeminnow), smallmouth bass (Micropterus dolomieu), and walleye (Stizostedion vitreum) in the Columbia River. During 19331996, oceanic, coastal, and freshwater indices of climate were highly correlated, and an index for the Columbia River Basin suggested that climate shifts may have occurred about 1946, 1958, 1969, and 1977. Summer water temperature varied as much as 2°C between climate periods. We used a bioenergetics model for northern squawfish, the most important piscivore, to predict that predation on salmonids would have been 2631% higher during two periods with relatively warm springsummer water temperatures (19331946, 19781996) than during an extremely cold period (19471958). Predicted predation rates of northern squawfish were 6896% higher in the warmest year compared with the coldest year. Predation rates of smallmouth bass and walleye on juvenile salmonids varied among climate periods similar to rates predicted for northern squawfish. Climatic effects need to be understood in both freshwater and nearshore marine habitats, since growth rates of salmon populations are especially sensitive to mortality during early life stages.
Testing the functional redundancy of Limnodrilus and Tubifex (Oligochaeta, Tubificidae) in hyporheic sediments: an experimental study in microcosms
Authors: Mermillod-Blondin Florian , Gérino Magali , Degrange Valérie , Lensi Robert , Chassé Jean-Luc , Rard Michael , Châtelliers Michel Creuzé des
Published: April 2011

Most tubificid worms are classified in the same functional group by their similar bioturbation and feeding activities in fine sediments of lakes. The objective of this study was to test the functional redundancy of two genera of tubificids (Limnodrilus and Tubifex) at two densities in coarse sediments using slow filtration columns. We measured the effects of the worms on particle redistribution, organic matter processing, nutrient fluxes, and microbial characteristics. The results showed that Limnodrilus and Tubifex created the same stimulation of aerobic and anaerobic microbial activities in the sediment. However, 50 Tubifex had a greater effect than 50 Limnodrilus on microbial processes. Furthermore, at a density of 100 oligochaetes per column, only Tubifex significantly increased particle redistribution and oxygen consumption in the first centimetre of the sediment. In contrast, Limnodrilus more often modified microbial activity in the deeper layers of the columns. The functional redundancy of the two genera of tubificid worms was validated by most measured processes. However, the variability within functional groups cannot be neglected because each genus had its functional peculiarity in the ecosystem.
Influence of harvest refugia on penaeid prawn population dynamics and sustainable catch
Authors: Tanner Jason E
Published: April 2011

Harvest refuges have frequently been proposed as fishery management tools for species with sedentary adults and dispersive juveniles but less often for species with a highly mobile adult phase. In this paper, I use a population model to investigate the potential of using harvest refuges for managing species with both dispersive juveniles and mobile adults using the penaeid prawn Penaeus latisulcatus as a model. Maximum harvest occurred when only a very small proportion of the habitat (23%) was fished very heavily (F = 10). When only a small percentage of the habitat was trawled, harvest increased as fishing mortality increased, but when trawling was more extensive, harvest peaked with a relatively low fishing mortality. This supports recent contentions that by themselves, marine reserves are insufficient to manage a fishery effectively and that they need to be used in conjunction with effort restrictions. Sensitivity analyses indicated that adult, juvenile, and larval mortality are all near thresholds that qualitatively change model behaviour, but provided their values remain below the threshold, it is not important to know them accurately to determine the best harvest regime.
The use of marine reserves in evaluating the dive fishery for the warty sea cucumber (Parastichopus parvimensis) in California, U.S.A.
Authors: Schroeter Stephen C , Reed Daniel C , Kushner David J , Estes James A , Ono David S
Published: April 2011

Management of sustainable fisheries depends upon reliable estimates of stock assessment. Assessment of many stocks is based entirely on fishery-dependent data (e.g., catch per unit effort), which can be problematic. Here we use fishery-independent data on stock size, collected within and outside of no-take reserves before and after the onset of fishing, to evaluate the status of the dive fishery for warty sea cucumbers, Parastichopus parvimensis, in southern California. Long-term monitoring data showed that abundance decreased throughout the Channel Islands within 36 years after the onset of fishing. No significant changes in the abundance of P. parvimensis were observed at the two non-fished reserve sites, although densities tended to increase following onset of the fishery. Beforeafter, controlimpact (BACI) analyses of seven fished and two non-fished sites implicated fishing mortality as the cause of 3383% stock declines. In sharp contrast, stock assessment based on CPUE data showed no declines and a significant increase at one island. To date, most discussion on marine reserves has focused on the protection and enhancement of exploited populations. Our study demonstrates the critically important, but often overlooked, role that marine reserves can play in providing reliable information on stock assessment.
Exploitation trajectory of a declining fauna: a century of freshwater mussel fisheries in North America
Authors: Anthony James L , Downing John A
Published: April 2011

Freshwater mussels (Bivalvia: Unionidae) have been an economically valuable biological resource in North America since the mid-1800s. Although the industries based upon mussel harvest are quite distinct from one another, the trends apparent in harvest statistics are remarkably similar among each successive harvest era. Whether fished for freshwater pearls, button production, or cultured pearl production, market factors have driven commercial harvests while the life history and ecology of mussels have been largely ignored. Annual yields of freshwater mussels are declining throughout the United States and catch per unit effort (CPUE) has declined dramatically in some of the most important American mussel fisheries. Harvest statistics indicate that mussel populations are dangerously depleted due to the erosion of the latest industry based upon their harvest. It seems likely that the exhaustive harvests of both the distant and recent past, coupled with habitat loss and degradation, have left North American unionid mussel populations at levels insufficient to support the substantial harvests consistently demanded by industry. This century-long exploitation trajectory provides valuable lessons about the mechanisms of fisheries collapse that are necessary to ensure the sustainable management of aquatic resources.