bluuebunny/crossref_metadata_2025 huggingface dataset:
Ecological and Genetic Effects of Salmonid Introductions in North America
Authors: Krueger C. C. , May B.
Published: April 2011

Stocking of non-native Salmoninae into North American waters began around 1870. Brown trout (Salmo trutta) from Europe established populations across North America and is the only successful inter-continental introduction. Introductions of native salmonids within North America but outside their native ranges have been common. Ecological effects of salmonid introductions. include competition, predation on native salmonids and other fishes, environmental modification through digging of redds in stream bottom substrates during spawning, and introduction of parasites and disease to native fish. Direct genetic effects from stocked salmonids are caused by interbreeding with native species. Indirect genetic effects may result through selective forces and/or a reduction of effective population size, genetic drift, and inbreeding. Management actions used to remove non-native salmonid populations include chemical reclamation and construction of barriers to movement. Salmonid stocking as a management practice is appropriate for species or population rehabilitation. Continued stocking of non-native salmonids should cease where viable native salmonid populations exist. New introductions of Eurasian species should not be made because effects are unpredictable. Aquaculture and the creation of transgenic fish pose special threats to North American salmonids. The era of widespread, intentional introductions of salmonids by man justifiably is drawing to a close.
Rapid mtDNA Sequence Analysis of Fish Populations Using the Polymerase Chain Reaction (PCR)
Authors: Beckenbach Andrew T.
Published: April 2011

The polymerase chain reaction (PCR) is a relatively new technique allowing the enzymatic amplification of selected genes to produce quantities sufficient for the determination of nucleotide sequences. We have compared sequences of several genes from the mitochondrial genome of six salmonid species. PCR analysis of protein coding genes provides sufficient resolution for determining relationships among species, or among isolated populations. Examination of more variable regions, such as the control region of the mitochondrial genome, will be required for other intraspecific comparisons.
Selective Diversification of Aquaculture Stocks: A Proposal for Economically Sustainable Genetic Conservation
Authors: Doyle R. W. , Shackel N. L. , Basiao Z. , Uraiwan S. , Matricia T. , Talbot A. J.
Published: April 2011

The genetic diversity of aquaculture stocks can be maintained, and their genetic impact on wild stocks minimized, by breeding programmes that deliberately generate genetic diversity. Current animal breeding practices are likely to reduce the diversity of domestic stocks if they are extended to aquaculture. It is proposed that national breeding programmes for aquaculture should, instead, try to develop numerous breeds specially adapted to local environments and aquaculture systems. An economic model is presented of decision-making by individual farmers who, in choosing which breed to produce, determine the "fitness" of the breeds in a meta-population that includes all breeds. As long as strong genotype-environment interaction for production traits is maintained by artificial selection, the economic self-interest of farmers should ensure the stability of genetic polymorphisms among breeds. Genetic variation would be conserved (in the among-breed component of genetic diversity) but not the primordial distribution of gene and genotype frequencies. Economic benefits to farmers, plus a high return on investment at the national or supra-national level, makes breed diversification an attractive conservation strategy even though it is admittedly a compromise from a purely genetic viewpoint.
U.S. State's View and Regulations on Fish Introductions
Authors: Wingate Paul J.
Published: April 2011

A survey of the poiicy of 50 U.S. states on transplanted fish introductions and stocking fish of different genetic strains indicates that all 39 responding states control exotic introductions. While 67% of the responding states restrict in-state movement of fish species, more attention is being given to restricting in-state strain movement. More needs to be done. Native species are stocked on top of reproducing populations and moved among watersheds; exotic species are introduced. In some cases, these stockings have appeared to benefit all interested parties, while in other circumstances exotics have totally disrupted ecosystems and become pests. These introductions and stockings are a combination of the fish being available, misunderstanding by managers of possible effects, and strong political pressure to satisfy anglers in more and more waters. Many times, little attention is given to the effect of these introductions on the native biota and fauna as it is perceived that stocking fish is a good thing. It is not until problems develop or anglers want another species added that the wisdom or success of these stockings is questioned. Minnesota's policy is that fish are not moved between watersheds until genetic similarities of the various species in the different watersheds are demonstrated.
Redescription of Myxobolus rhinichthidis (Myxosporea) parasitizing Rhinichthys cataractae, with a revised taxonomic list of species of Myxobolus known from North American freshwater fishes
Authors: Cone David K. , Raesly Richard L.
Published: April 2011

Myxobolus rhinichthidis Fantham, Porter and Richardson, 1939 (Myxosporea) is redescribed from longnose dace (Rhinichthys cataractae) in Maryland. Large round plasmodia occurred in the connective tissue of the skin covering the head and opercular regions. Fixed spores are oval in front view and measure 11.5–14.5 μm long, 9.0–10.5 μm wide, and 6.0–7.0 μm thick. The polar capsules are 5.5–7.0 μm long and 3.0–3.5 μm wide. Photomicrographs of formalin-fixed spores document variation in spore size and shape. The report is the first for M. rhinichthidis since the species was described from blacknose dace (Rhinichthys atratulus) in Quebec. An updated list of species of Myxobolus Bütschli, 1882 reported from freshwater fishes in North America is provided. Myxobolus jahnricei Landsberg and Lom, 1991 is considered a junior synonym of Myxobolus filamentus Grinham and Cone, 1990; and Myxobolus lii Desser, 1993 and Myxobolus gibbosus Li and Desser, 1985 are junior synonyms of Myxobolus uvuliferus Cone and Anderson, 1977.
Some pathways and factors of monogenean microevolution
Authors: Gusev A.V.
Published: April 2011

This paper discusses probable causes for the origin and evolution of groups of monogenean congeneric sibling species infecting one fish host species, with special reference to freshwater fishes. These causes comprise strict specificity, topological differentiation of parasite micropopulations in microniches (microhabitats), ecological and geographic isolation of various parasite and host populations, paleogeographic or geomorphologic (but not paleogeologic) changes during the late Tertiary and Quaternary periods, with alternating marine transgressions and regressions acting upon continents which, after the Miocene, have been less affected by continental drift, orogenesis, and climatic fluctuations. Co-evolving with their hosts, Monogenea usually diverge faster than their hosts.
A population-phenetic analysis of morphological polymorphism in Polystoma integerrimum (Monogenea)
Authors: Malashenko A.A. , Roytman V.A.
Published: April 2011

The analysis of population phenetics to study some of the polymorphic characters in Polystoma integerrimum (Froelich, 1791) from two populations in the Moscow and Novgorod regions, Russia, revealed discrete variations of these characters, defined as phenes, which are discrete, usually alternative, simple features reflecting the peculiarities of a given genotype. The studies demonstrate that the frequencies of phenes B1, B2, and B3, characterized by peculiarities of the serrations on the lower basal part of the marginal hooks, define the differences in genetic structure of the populations studied. Besides these structural differences, the two populations of Polystoma differ in intrapopulational phenetic diversity, whose index was higher in the Novgorod population. It is suggested that variations in the number of chitinous hooks of the copulatory organ i.e., 5, 6, 7, 9, and 10 hooks, characterize the complex of East-European populations of P. integerrimum.
Relationship of parasites (Trematoda: Spirorchidae) and their eggs to the occurrence of fibropapillomas in the green turtle (Chelonia mydas)
Authors: Dailey Murray D. , Morris Robert
Published: April 2011

The prevalence of green turtle (Chelonia mydas) fibropapillomatosis is increasing in Hawaii, raising the possibility of long-term negative effects on the breeding population. As the etiology of this disease is unknown, our objective was to determine if any relationship exists between fibropapillomas and trematode eggs from the family Spirorchidae, whose presence in tissue sections has been noted for years. A process for tumor digestion and egg extraction was developed and a total of 61 tumors of all sizes was examined to determine the total numbers of eggs present and the species of spirorchid involved. Twelve samples of normal turtle tissue were also examined. Eggs of one to three spirorchid species (Leardius learedi Price, 1934; Haplotrema dorsopora Dailey, Fast and Balazs, 1993; and Carettacola hawaiiensis Dailey, Fast and Balazs, 1991) were recovered from all tumors and nontumored tissues digested. Five turtles were injected with spirorchid eggs and observed for 12 months. New tumors developed on two of the turtles at noninjected sites. Although attempts to induce fibropapillomas through injection were not successful, the presence of spirorchid eggs in every tumor examined raises additional questions regarding the relationship between these parasites and fibropapillomas in sea turtles.
A new species of Megalophallus (Digenea: Microphallidae) from the clapper rail, other birds, and the littoral isopod Ligia baudiniana
Authors: Overstreet Robin M. , Heard Richard W.
Published: April 2011

Megalophallus reamesi n.sp. infected the clapper rail, ruddy turnstone, black-bellied plover, and the isopod Ligia baudiniana. This precociously developed digenean occurred in the mid-Florida Keys, Florida, and in Pine Cay, Turks and Caicos, British West Indies, but not in numerous other examined localities from New York to Texas. It is most similar in body size (1.0–1.6 vs 1.0–1.1 mm) and structure of its copulatory organ to M. diodontis Siddiqi and Cable, 1960, but its copulatory organ has 23–39 micropapillae rather than 12–19, the species has rudimentary intestinal ceca rather than short fully developed ones, and an isopod rather than a portunid crab serves as the second intermediate host. The encysted metacercaria, occurring in the hemocoel of the isopod, was typically encapsulated with host connective tissue incorporating several host chromatophores.
Identification of larval Contracaecum osculatum s.l. and Phocascaris sp. (Nematoda: Ascaridoidea) from marine fishes by allozyme electrophoresis and discriminant function analysis of morphometric data
Authors: Brattey John
Published: April 2011

Biochemical markers (allozymes) were used to identify third-stage larvae of nematodes from the Contracaecum osculatum s.l. – Phocascaris sp. complex found in five marine fish species (Hippoglossoides platessoides, Gadus morhua, Mallotus villosus, Myoxocephalus scorpius, Pleuronectes americanus) collected off Newfoundland and Labrador. Three taxonomic groups, genetically identical to adult C. osculatum A, C. osculatum B, and Phocascaris sp. previously reported from North Atlantic seals, were found. Among the 859 larvae examined, C. osculatum B was most common (74.2%), particularly in H. platessoides (79.4% of 501 larvae), G. morhua (88.8% of 160), M. scorpius (87.5% of 32), and P. americanus (100.0% of 20), but Phocascaris sp. was more numerous in M. villosus (66.4% of 146). Contracaecum osculatum A was found only in H. platessoides (15% of 501). Discriminant function analysis revealed differences in shape among the nematode species. Larvae of Phocascaris sp. and C. osculatum B can generally be distinguished using three measurements and classified according to coefficients for quadratic discriminant functions, but larvae of C. osculatum A could not be reliably distinguished from the other two species. A simpler, more rapid method of screening biochemical markers, employing a cellulose acetate support medium, is also described.
Two new copepod species of the genus Pseudotaeniacanthus Yamaguti and Yamasu, 1959 (Poecilostomatoida: Taeniacanthidae), parasitic on moray eels in the Red Sea
Authors: Johnson S.C. , Kabata Z.
Published: April 2011

Two new species of Pseudotaeniacanthus, P. margolisi n.sp. and P. septemsetigerus n.sp. (Copepoda, Poecilostomatoida, Taeniacanthidae), described and illustrated herein, are parasitic on the gills of unidentified species of moray eels (family Muraenidae) in the Gulf of Aqaba, Red Sea. Pseudotaeniacanthus margolisi differs from its closest congener in armature of the terminal segment of its fourth exopod and unique sexually dimorphic armature of its second leg. Pseudotaeniacanthus septemsetigerus is distinguished by the armature of its endopods, as well as by the proportions and armature of its caudal rami. A revised key to the species of the genus is appended.
The ontogeny of salinity tolerance in the American shad, Alosa sapidissima
Authors: Zydlewski J , McCormick S D
Published: April 2011

Larval and juvenile American shad (Alosa sapidissima) raised from eggs in the laboratory were subjected to biweekly 24-h seawater (35 ppt) challenges. There was no survival in seawater before 36 days post-hatch, and most mortalities occurred within 2 h of transfer. Twenty-four hour survival reached 89% in seawater at 45 days post-hatch (when larval-juvenile metamorphosis occurred), 96% at 58 days post-hatch, and 92-100% from 58 to 127 days post-hatch. Survival in seawater for 24 h was a good indicator of long-term survival and growth. Seawater tolerance was associated with gill development and increased gill Na + ,K + -ATPase activity, which occurred at the onset of the larval-juvenile metamorphosis (3 months prior to the peak of migration). Gill Na + ,K + -ATPase activity increased threefold in juvenile shad acclimated to 35-ppt seawater, reached peak levels 5 days after transfer, and remained elevated with respect to controls. Plasma sodium and chloride increased 12 and 11%, respectively, within 48 h of seawater exposure. Plasma sodium recovered to initial levels and plasma chloride stabilized at a level 10% higher than initial levels after 5 days. Ionic perturbations that occurred at elevated salinities stabilized when gill Na + ,K + -ATPase activity increased.
Oxidation of nitrite to nitrate in isolated erythrocytes: a possible mechanism for adaptation to environmental nitrite
Authors: Doblander C , Lackner R
Published: April 2011

Rainbow trout (Oncorhynchus mykiss) were exposed to nitrite (0.007 mmol NO2-· L-1) for 48 days. During the first 14 days, the methaemoglobin concentration in the blood as well as the NO2-and NO3-concentrations in the plasma increased whereas further days of exposure led to a decrease in the nitrite, nitrate, and methaemoglobin concentrations in the blood. Isolated erythrocytes from rainbow trout have the ability to detoxify nitrite by oxidation to nitrate, thus removing this compound from the blood. This process is dependent on oxygen loading of haemoglobin and on the nitrite concentration in the medium. In anoxic erythrocytes the oxidation of nitrite to nitrate is drastically reduced. Assuming Michaelis-Menten kinetics, the uptake for nitrite in our investigation was estimated between 1.06 and 2.21 µmol NO2-· h-1· kg fish-1. After 14 days of exposure approximately 20% of the total NO2-taken up will be detoxified by erythrocytes in fish. We hypothesize that rainbow trout have the capacity for adapting to nitrite exposure by increasing the rate of oxidation to nitrate.
Variation in adult life history and morphology among Lake Washington sockeye salmon (Oncorhynchus nerka) populations in relation to habitat features and ancestral affinities
Authors: Hendry A P , Quinn T P
Published: April 2011

Body size, age composition, and male body depth were compared among five Lake Washington sockeye salmon (Oncorhynchus nerka) populations. Two of the populations (Bear and Cottage creeks) were indigenous to the watershed and three (Cedar River, Issaquah Creek, and Pleasure Point) were non-native (from Baker Lake, Washington). To isolate the relative contributions of habitat type and ancestral relatedness to phenotypic variation, we compared populations with (i) the same origin and similar habitats, (ii) different origins and different habitats, (iii) the same origin and different habitats, and (iv) different origins and similar habitats. Spawning salmon in the Cedar River were older and larger than those in the native populations, a result consistent with their origin (contemporary Baker Lake fish were also large and old) and with habitat variation (the Cedar River is much larger than Bear and Cottage creeks). Body size and age composition did not differ among the three non-native populations, but the body depth of males spawning on the lake beach (Pleasure Point) was greater than that of males in the Cedar River, suggesting adaptive divergence. Adaptive convergence may also have occurred because the population in Issaquah Creek (intermediate-sized creek) did not differ appreciably from those in Bear and Cottage creeks.
Spawning of Atlantic cod (Gadus morhua) in the northern Gulf of St. Lawrence: a study of adult and egg distributions and characteristics
Authors: Ouellet P , Lambert Y , Castonguay M
Published: April 2011

From 1993 to 1995, Atlantic cod (Gadus morhua) egg abundance and distribution, fisheries acoustic surveys, and analysis of trawl catches provided evidence of spawning for the northern Gulf of St. Lawrence cod stock at the same location off Newfoundland's west coast. From the relative proportion of spent fish and various developmental stages of cod eggs, spawning could not have started before the end of March or early April. Spawning started while cod were in dense shoals following a prespawning migration from Cabot Strait. Larger cod started to spawn earlier than smaller cod. In May 1994, cod dispersed soon after spawning began, and most of the spawning activity probably occurred as the fish migrated and scattered within the northern Gulf. Stage I cod eggs were distributed throughout the water column but higher concentrations were observed within the cold (<0°C) layer of the Gulf each year. We propose that water temperature could have a dominant influence on determination of year-class strength in the northern Gulf via its effect on egg development and survival.
Does intense fishing on males impair mating success of female Dungeness crabs
Authors: Hankin D G , Butler T H , Wild P W , Xue Q -L
Published: April 2011

Commercial capture of female Dungeness crabs, Cancer magister, is prohibited and minimum size limits for commercial harvest of male crabs are designed to allow most males to mate at least once before capture. Annual exploitation rates often exceed 90%, however, and the resulting scarcity of large males might reduce mating success among large females. We present new data regarding (i) sizes of male and female crabs collected in premating embraces, (ii) carapace width frequencies of female Dungeness crabs, (iii) presence of sperm plugs and sperm, and (iv) fecundity. Minimum carapace width of hard-shelled mating males typically exceeds postmolt carapace width of soft-shelled females (i), but female Dungeness crabs exceeding the minimum legal size of males usually account for less than 5% of mature adult female crabs (ii), and sublegal-sized males actively participate in mating (i). Remnants of sperm plugs, definitive indicators of mating, were found in 97.5% of recently molted large females (iii), suggesting that virtually all molting females mate regardless of size. On the basis of (ii) and (iv), hypothetical worst-case calculations, assuming that no large females could find mates, suggest that total egg production would be reduced by no more than 2-25% among molting female crabs.
Acute physiological effects of zebra mussel (Dreissena polymorpha) infestation on two unionid mussels, Actiononaias ligamentina and Amblema plicata
Authors: Baker S M , Hornbach D J
Published: April 2011

Our laboratory studies of the physiological effects of zebra mussel (Dreissena polymorpha) infestation on the freshwater mussels Actinonaias ligamentina and Amblema plicata (Unionidae) show that (i) zebra mussel infestation causes stress and symptoms of starvation in unionid mussels, (ii) unionid species are affected unequally, and (iii) symptoms of starvation are greater when initial condition is low. Nutritive stress in infested unionid mussels was indicated by shifts to lower metabolic rates, more protein-based metabolism (lower O:N ratios), and compensatory increases in grazing rates. Starvation may be the result of local food depletion and (or) increased metabolic cost. Actinonaias ligamentina (subfamily Lampsilinae) was more sensitive to infestation than Amblema plicata (subfamily Ambleminae), as indicated especially by changes in oxygen uptake rate and grazing rate. The effects of infestation were greater in mussels that were already in low condition. Our results indicate that the decline in diversity of unionid mussels since the introduction of zebra mussels is due to species-specific rates of starvation.
The effects of ultraviolet radiation on respiration and photosynthesis in two species of microalgae
Authors: Beardall J , Berman T , Markager S , Martinez R , Montecino V
Published: April 2011

The effects of ultraviolet (UV) radiation (310-400 nm) on respiratory activity and photosynthetic carbon assimilation of the cyanobacterium Aphanizomenon flos-aquae and the green alga Selenastrum capricornutum were examined. When exposed for 2 h to 100 or 550 µmol · m-2 · s-1 photosynthetically active radiation (PAR) supplemented with UV-A + UV-B radiation, the two organisms differed in their responses. Photosynthetic rates were depressed by 33-81% in A. flos-aquae but never by more than 25% in S. capricornutum. Rates of oxygen uptake by A. flos-aquae following UV exposure were similar to or less than rates achieved without UV treatment. In contrast,S. capricornutum exhibited a stimulation of oxygen consumption immediately after exposure to UV + high PAR compared with treatment with PAR alone. In A. flos-aquae, dark carbon losses were completely eliminated after the cells had been exposed to UV (irrespective of the levels of PAR). This effect was less marked in S. capricornutum. Respiratory electron transport chain activity in A. flos-aquae was initially stimulated following UV + PAR exposure but was slightly impaired in S. capricornutum. The results indicate that there is considerable interspecific variation in the response of autotrophic organisms to UV radiation and that these responses are modulated by the level of concomitant exposure to PAR.
Effects of large woody debris placement on stream channels and benthic macroinvertebrates
Authors: Hilderbrand R H , Lemly A D , Dolloff C A , Harpster K L
Published: April 2011

Large woody debris (LWD) was added as an experimental stream restoration technique in two streams in southwest Virginia. Additions were designed to compare human judgement in log placements against a randomized design and an unmanipulated reach, and also to compare effectiveness in a low- and a high-gradient stream. Pool area increased 146% in the systematic placement and 32% in the random placement sections of the low-gradient stream, lending support to the notion that human judgement can be more effective than placing logs at random in low-gradient streams. Conversely, the high-gradient stream changed very little after LWD additions, suggesting that other hydraulic controls such as boulders and bedrock override LWD influences in high-gradient streams. Logs oriented as dams were responsible for all pools created by additions regardless of stream or method of placement. Multiple log combinations created only two pools, while the other seven pools were created by single LWD pieces. Total benthic macroinvertebrate abundance did not change as a result of LWD additions in either stream, but net abundances of Plecoptera, Coleoptera, Trichoptera, and Oligochaeta decreased, while Ephemeroptera increased significantly with the proportional increase in pool area in the low-gradient stream.
Adjusting for missed tags in salmon escapement surveys
Authors: Rajwani K N , Schwarz C J
Published: April 2011

One of the assumptions in mark-recapture studies is that all tags recovered are correctly identified. In some cases, tags are overlooked, and a subsample of fish previously classified as untagged is examined to look for missed tags. In this paper, a method for estimating the salmon escapement using a mark-recapture methodology after correcting for missed tags is developed. The variance of the revised estimator is derived and the loss of efficiency compared with a Petersen estimate, where no tags are overlooked, is found. Optimal allocation of effort between the initial and second examination is considered. Finally, a numerical example using actual data from the 1994 Fraser River sockeye salmon (Oncorhynchus nerka) season is used to illustrate the results.
Heartworm, Acanthocheilonema spirocauda (Leidy, 1858), infections in Canadian phocid seals
Authors: Measures L N , Gosselin J -F , Bergeron E
Published: April 2011

Heartworm, Acanthocheilonema spirocauda, was observed in four of six species of seals (19 seals of 701) examined from the Atlantic coast of Canada including the Canadian Arctic. Fourteen of 221 ringed seals (Phoca hispida), 2 of 18 harbour seals (Phoca vitulina), 2 of 186 harp seals (Phoca groenlandica) (new host record), and the only hooded seal examined (Cystophora cristata) were infected with A. spirocauda. Intensity of infection ranged from 1 to 31. Infected seals were age 0 to 14, but 8 of the 14 infected ringed seals were age 0. All worms were found in the right ventricle except in three cases. In one ringed seal and one harp seal, worms were found in the pulmonary artery, and in another ringed seal, worms were found deep within the lungs. No infections were found in grey seals (Halichoerus grypus) (N = 271) or bearded seals (Erignathus barbatus) (N = 4). Heartworm is primarily a parasite of young seals. Its apparent absence in grey seals examined to date suggests either that a much larger sample of young seals from a broad geographic area is needed or that grey seals are refractory to infection or do not survive infections.
Another exotic mollusc in the Laurentian Great Lakes: the New Zealand native Potamopyrgus antipodarum (Gray 1843) (Gastropoda, Hydrobiidae)
Authors: Zaranko D T , Farara D G , Thompson F G
Published: April 2011

In 1991, the hydrobiid snail Potamopyrgus antipodarum (Gray 1843), native to New Zealand, was found 1 km offshore Wilson, New York, in Lake Ontario. This is the first known occurrence of the snail in eastern North America. Densities of P. antipodarum have increased since its discovery, and the snail is expected to spread quickly throughout the Great Lakes area. The biofouling potential of P. antipodarum is probably low; however, its most serious threat may be resource competition with native molluscs. This species was probably introduced in ballast water from transoceanic vessels, thus increasing the list of nonindigenous aquatic organisms introduced into the Great Lakes since the 1800s to 140 different organisms. The risk of other species invasions into the Great Lakes is still possible, despite the now mandatory ballast water regulations.
Variability and capture efficiency of bongo and Tucker trawl samplers in the collection of ichthyoplankton and other macrozooplankton
Authors: Pepin P , Shears T H
Published: April 2011

We examined the sampling variability and capture efficiency of bongo nets and a modified Tucker trawl used in the sampling of ichthyoplankton and other macrozooplankton by taking seven replicate samples at each of two stations on two separate occasions. Sample variance was highly significantly related to sample mean for all major taxonomic categories (i.e., fish eggs, fish larvae, crustaceans, and medusae-chaetognaths). Sampling variability of the bongo nets was significantly greater than that of the Tucker trawl for both fish eggs and larvae. Sampling variability of macrozooplankton was significantly greater than that of ichthyoplankton. For larval fish of 5 mm or less, bongo nets generally yielded higher estimates of abundance than the Tucker trawl and the reverse was true for lengths above 10 mm, but there was a significant influence of species-specific morphological characters. The large sample volume of the Tucker trawl relative to the bongo nets resulted in significantly higher estimates of species diversity for fish eggs and larvae but not for crustaceans or medusae. Although bongo and Tucker samplers are efficient at catching a wide range of sizes of larval fish, the latter's lower variability may make it a more effective sampler.
Comparing trophic position of freshwater fish calculated using stable nitrogen isotope ratios (δ15N) and literature dietary data
Authors: Vander Zanden M J , Cabana G , Rasmussen J B
Published: April 2011

Stable nitrogen isotope ratios ( delta 15N) are commonly used to represent the trophic structure of aquatic systems, yet the ability of delta 15N to indicate the trophic position of aquatic consumers remains untested using traditional dietary methods. Interpreting the delta 15N of aquatic consumers relative to large, long-lived primary consumers such as unionid mussels provides a continuous measure of an organism's trophic position that adjusts for among-system variation in baseline delta 15N. We used this method to estimate the trophic position of eight littoral fish species from 36 lakes in Ontario and Quebec. We validated these delta 15N measures of trophic position by compiling literature dietary data from 342 populations of these same fish species and calculated a continuous measure of trophic position for each population. Mean dietary trophic position estimates corresponded closely to 15N estimates, with mean trophic position ranging from 3.3 for pumpkinseed (Lepomis gobbosus) to 4.4 for walleye (Stizostedion vitreum). Both methods indicated approximately one trophic level of variation among populations of a species. This study confirms the ability of baseline-adjusted delta 15N to represent the trophic position of aquatic consumers.
Land water linkages: influences of riparian deforestation on lake thermocline depth and possible consequences for cold stenotherms
Authors: France Robert
Published: April 2011

The purpose of the present study was to determine if riparian deforestation would expose lake surfaces to stronger winds and therefore bring about deepening of thermoclines and resulting habitat losses for cold stenotherms such as lake trout (Salvelinus namaycush). Removal of protective riparian trees through wind blowdown and two wildfires was found to triple the overwater windspeeds and produce thermocline deepening in two lakes at the Experimental Lakes Area. A survey of thermal stratification patterns in 63 northwestern Ontario lakes showed that lakes around which riparian trees had been removed a decade before through either clearcutting or by a wildfire were found to have thermocline depths over 2 m deeper per unit fetch length compared with lakes surrounded by mature forests. Riparian tree removal will therefore exacerbate hypolimnion habitat losses for cold stenotherms that have already been documented to be occurring as a result of lake acidification, eutrophication, and climate warming.
Terrestrial invertebrates as salmonid prey and nitrogen sources in streams: contrasting old-growth and young-growth riparian forests in southeastern Alaska, U.S.A.
Authors: Wipfli Mark S
Published: April 2011

Terrestrial-derived invertebrate (TI) inputs into streams and predation on them by salmonids (40-180 mm fork length) were measured in six coastal Alaska stream reaches from April through October 1993-1994; riparian habitat of three stream reaches contained conifer-dominated old-growth (no timber harvesting) and three were alder-dominated young-growth (31 years postclearcutting). Data from pan-traps placed on stream surfaces showed that TI biomass and nitrogen inputs averaged up to 66 and 6 mg ·m-2 ·day-1, respectively, with no significant difference between habitats. Stomach contents from coho salmon (Oncorhynchus kisutch), cutthroat trout (O. clarki), and Dolly Varden (Salvelinus malma) revealed that TI and aquatic-derived invertebrates (AI) were equally important prey. Additionally, salmonids from young-growth systems ingested a greater TI proportion than those from old-growth systems. There were trends but no significant differences between habitats of TI and AI biomass ingested; however, statistical power was <0.30. These results showed that TI were important juvenile salmonid prey and that a riparian overstory with more alder and denser shrub understory may increase their abundance. Riparian vegetation management will likely have important consequences on trophic levels supporting predators, including but not limited to fishes.
Transfer of mercury from benthic invertebrates to fishes in lakes with contrasting fish community structures
Authors: Wong Allan HK , McQueen Donald J , Williams D Dudley , Demers Eric
Published: April 2011

We examined the flow of mercury (Hg) from benthic invertebrates to fishes in lakes with contrasting fish community structure. The study was carried out in two whole lakes in southcentral Ontario in 1992. Both were remote from direct sources of contamination and were chosen because of their physical and chemical similarities. Although the fish communities in the two lakes were qualitatively similar, the total number of fishes in Ranger Lake was an order of magnitude smaller than that in Mouse Lake. As a result of the lower net predation from benthivorous fishes, documented in earlier studies, Ranger Lake benthic invertebrate populations were significantly higher. However, benthic invertebrate taxa in Mouse Lake were generally larger and had higher Hg concentrations. This was partly attributed to the stunted growth of Mouse Lake fishes, which did not allow them to prey on larger benthos as a result of gape limitations. Despite the lower Hg concentrations in Ranger Lake benthos, total benthic invertebrate Hg pools were higher in this lake as a result of its higher total benthic invertebrate biomass. However, the transfer of total Hg from benthic invertebrates to fishes was higher in Mouse Lake due to the higher consumption rates of benthivorous fishes.
Juvenile masu salmon (Oncorhynchus masou) abundance and stream habitat relationships in northern Japan
Authors: Inoue Mikio , Nakano Shigeru , Nakamura Futoshi
Published: April 2011

Relationships between abundance of juvenile masu salmon (Oncorhynchus masou) and stream habitat were analyzed on two spatial scales, stream reach and channel unit, in northern Hokkaido, Japan. Reach-scale analyses revealed that high water temperatures limited the salmon population level and that the salmon abundance increased with cover availability. These two limiting factors were strongly associated with the presence of riparian forest, emphasizing its importance for the salmon population. Channel-unit scale analyses showed greater use of pools by the salmon, with greater depth and abundant cover underlying the patterns of habitat use. However, the relative importance of depth and cover varied among the reach types having different cover availability. In reaches that had abundant cover, cover itself was less important in determining patterns of habitat use within the reaches. In contrast, in reaches with poor cover, patterns of habitat use were strongly affected by cover. The results indicated that habitat characteristics at the reach scale affect not only the salmon abundance of the stream reaches, but also the determinants of local abundance patterns of the salmon within the reaches. It was suggested that larger-scale influences in a hierarchy of habitat scales should be considered for better understanding of fish-habitat relationships.
Mitochondrial DNA evidence of distinct glacial refugia for brown bullhead (Ameiurus nebulosus) in the Great Lakes
Authors: Murdoch M H , Hebert P DN
Published: April 2011

Restriction fragment length polymorphisms were used to survey the mitochondrial genome of Ameiurus nebulosus for nucleotide sequence variation. Two hundred and forty-nine individuals were analyzed from 12 populations across the Great Lakes drainage and 3 populations in possible refugial drainages. Fifteen restriction endonucleases revealed 50 distinct haplotypes among these fish. Two major phylogenetic assemblages, A and B, were revealed with an average 3.22% sequence divergence. Both assemblages were themselves fragmented into two groups. Strong geographic patterning was observed in the frequency of assemblages and groups across the sampling area: assemblage A was predominant in fish from populations east of Lake Erie, while western populations were dominated by assemblage B. The distribution and phylogenetic divergence of mitochondrial haplotypes indicate that brown bullhead in the Great Lakes originated from two Pleistocene refugia and further provides genetic evidence of subdivision within these refugia. Pleistocene glaciations appear to have had a similar influence on the geographic distribution of mitochondrial DNA lineages of other North American fishes. In contrast with these other species, however, much of the mitochondrial DNA variation and divergence was retained in brown bullhead populations living south of the ice sheets and is represented in extant populations.
Defining and measuring species interactions in aquatic ecosystems
Authors: Seip K L
Published: April 2011

Based on synoptic values of observed biomasses of pairs of species in aquatic ecosystems, it is possible to distinguish types of interaction forms between the species (e.g., predation, competition, mutualism) and relate these to characteristics of their theoretical, prototype representations. For example, a distinguishing feature of observed predation was the counterclockwise rotation of time trajectories in phase space predicted by prey-predator theory. To characterize interactions, the phase portraits of the interactions were first constructed, i.e., sets of trajectories were identified by plotting biomass values for one species (or functional species group) on the x axis and the simultaneously observed value for the other species on the y axis. To characterize the phase portraits they were described by 14 ``form factors,'' each capturing particular features of the interaction patterns. In addition seven theoretical, or prototype, interactions were characterized. Comparisons, clustering, and multivariate calibration were performed with principal component analysis and partial least squares techniques.
Cyprinid distributions in Northeast U.S.A. lakes: evidence of regional-scale minnow biodiversity losses
Authors: Whittier T R , Halliwell D B , Paulsen S G
Published: April 2011

Fish assemblages were sampled in 195 randomly selected lakes in the northeastern United States during the summers of 1991-1994. Most lakes in northern Maine had three to seven minnow species, constituting 40-80% of species in each lake. Lakes in New Jersey, southern New York, and southern New England rarely had minnows, other than golden shiner (Notemigonus crysoleucas). Lakes in the Adirondacks and the remainder of northern New England had intermediate numbers. We examined minnow native ranges and autecology and evaluated species richness related to littoral predators and human disturbance. Sample data suggested alteration in the minnow assemblages over much of the region. The most consistent factor related to minnow species richness was the presence of littoral predators. Median number of minnow species was two in lakes lacking predators and zero in lakes with predators. Non-native predators, especially Micropterus spp., have been introduced throughout the Northeast; 69% of the sampled lakes had non-native predators. In the absence of predators, minnow species declined with increased human activity in the watershed and along lake shorelines. Only in northern Maine did lake minnow assemblages seem relatively intact.
Some properties of methane oxidation in a thermally stratified lake
Authors: Bédard C , Knowles R
Published: April 2011

Profiles of14CH4and14CO oxidation and concentrations of CH4, NH4+, and nitrogen oxides (N2O, NH2-, NH3-) were studied in Lake St. George, Ontario, during late summer stratification. Metalimnetic maxima of the nitrogen oxides occurred and high rates of oxidation of CH4and CO were limited to a narrow band (<1 m) below the nitrogen oxide peaks at the oxic-anoxic interface. Oxidation of CH4and CO was strongly inhibited by the nitrification inhibitor allylthiourea. The affinity of the oxidizers for CH4(approximate Km= 4.6 µM), their sensitivity to picolinic acid, and the ratio of CH4oxidation to allylthiourea-sensitive CO oxidation together suggest that methanotrophs were responsible for the observed CH4oxidation. Pure cultures of Nitrosomonas europaea, although less sensitive to picolinic acid than the CH4oxidizers of Lake St. George, were affected by the inhibitor (approximate Kifor inhibition of NH4+oxidation = 51 µM).
Ultraviolet radiation and photosynthesis by Georgian Bay phytoplankton of varying nutrient and photoadaptive status
Authors: Furgal J A , Smith REH
Published: April 2011

The photosynthesis-irradiance responses of phytoplankton from Georgian Bay (Laurentian Great Lakes) were measured in 1993 to determine the influence of ultraviolet-B (UV-B, 290-320 nm) radiation and the interacting effects of natural changes in nutrient status and photoadaptive state. Silicate concentrations and phosphorus availability (inferred from32P incorporation) varied widely but had little direct influence on photosynthetic performance. UV-B caused up to 80% loss of photosynthetic capacity in 1-day simulated surface exposures (artificial light) and up to 40% loss in half-day exposures (natural light), quantitatively consistent with reported responses of marine phytoplankton. The widely varying nutrient status and photoadaptive state (as inferred from photosynthetic light responses) of the phytoplankton had no significant influence on their sensitivity to UV-B radiation, and midsummer communities were as sensitive as spring or fall communities. To a first approximation, the impact of UV-B was proportional to the seasonal variation in surface UV-B irradiance being maximal near the summer solstice.
A rapid method for estimating biomass size spectra of benthic metazoan communities
Authors: Ramsay P M , Rundle S D , Attrill M J , Uttley M G , Williams P R , Elsmere P S , Abada A
Published: April 2011

The construction of biomass size spectra in aquatic environments suffers from two main problems: (i) it is a labour-intensive process, and (ii) there is a lack of conformity in methodologies. This study evaluates a technique that produces biomass spectra for benthic metazoans from subsamples stratified using a geometric series of nested sieves. The technique was applied to metazoan communities from three sites, two freshwater and one brackish water, on a small river in southern Britain. Random subsamples of animals from each sieve size were measured using image analysis and showed significant differences in body size, as equivalent spherical diameter (ESD), among all but two sieves. There was no significant difference in ESD among sites. Despite the propensity for long thin animals to pass lengthwise through meshes, sieves contained a consistent range of individual body sizes. Mean individual body size and abundance data for each sieve were used to calculate total biomass. These size spectra were consistent with those from previous studies, and it is hoped that this method will encourage the wider application and more rigorous measurement of biomass size spectra in aquatic ecology.
Genetic variation and conservation of stream fishes: influence of ecology, life history, and water quality
Authors: Heithaus M R , Laushman R H
Published: April 2011

Three stream-dwelling fish species were used to investigate effects of ecology, life history, and water quality on genetic variation. We sampled Etheostoma caeruleum, E. blennioides, and Campostoma anomalum from six streams of varying water quality. Allozyme electrophoresis revealed that the most ecologically specialized species, E. caeruleum, was the least variable (P = 68.4%, Hobs= 1.2%). Etheostoma blennioides was intermediate in specialization and variation (P = 77.8%, Hobs= 7.8%), and the least specialized species, C. anomalum, had the most variation (P = 90.0%, Hobs= 12.1%). This pattern conforms to Willis' niche-variation hypothesis and Selander and Kaufman's adaptation model. Differences in ecology, life history, and amount of genetic variation are responsible for differences in how variation is apportioned within and among populations and within and among rivers. Populations in the river with the worst water quality (Huron River) had the lowest within-population variation for each species; therefore, genetic variation may be a useful indicator of water quality. Lower genetic variation may result from selection associated with specific loci, e.g., PGM-2, in stoneroller minnows. However, indirect effects on population size probably contributed to the erosion of genetic variation. Ecology, life history, and pollution tolerance data combine as predictors of species' risk of genetic erosion.
Salinity tolerance of Gyrodactylus salaris (Platyhelminthes, Monogenea): laboratory studies
Authors: Soleng A , Bakke T A
Published: April 2011

The salinity tolerance of the freshwater monogenean Gyrodactylus salaris, infecting Atlantic salmon (Salmo salar) parr, was studied experimentally. Following direct transfer of infected fish from fresh water to 5.0omicron salinity, parasite population growth increased at the same rate as in fresh water and was positively correlated with temperature (1.4, 6.0, and 12.0°C). In 7.5omicron salinity the populations declined and became extinct after a maximum of 56 days, without any significant difference between 6.0 and 12.0°C. However, some infrapopulations demonstrated short periods of growth. At higher salinities (10.0, 15.0, 20.0, and 33.0omicron) the survival time decreased, and there was a negative correlation between survival time and temperature (1.4, 6.0, and 12.0°C). When transferred directly to sea water (33.0omicron) the parasites became opaque and ceased moving after a few minutes. There was no difference in parasite survival time between direct and gradual transfer from fresh water to 7.5 and 10.0omicron, except for one infrapopulation which demonstrated population growth from day 22 after some fluctuations following gradual transfer to 7.5omicron. The present findings support the hypothesis of brackish water dispersal of G. salaris with infected fish migrating between rivers in fjord systems.
The response of the thermal stratification of South Bay (Lake Huron) to climatic variability
Authors: King J R , Shuter B J , Zimmerman A P
Published: April 2011

The 37-year record (1955-1992) of water temperature profiles and corresponding meteorology for South Bay (Lake Huron) provide an extensive empirical data set for the study of climate variability and corresponding alterations in lake thermal structure. Thermoclines became shallower over this period and epilimnetic temperatures increased. Canonical analyses correlated warm May-July air temperatures and high July-August solar radiation with warmer epilimnia, larger thermal gradients across the thermocline, and shallower thermoclines. Multivariate canonical scores indicate that these thermal responses have increased in parallel with the recent warming trend since the mid-1960s. Anomalous multivariate scores correspond to El Niño events, and an extreme low score corresponds to the Mount Pinatubo cooling effect of 1992.