bluuebunny/crossref_metadata_2025 huggingface dataset:
Habitat-dependent interactions between two size-classes of juvenile steelhead in a small stream
Authors: Harvey B C , Nakamoto R J
Published: April 2011

The presence of small steelhead (Oncorhynchus mykiss; averaging 55 mm fork length) influenced the growth of larger juvenile steelhead (90 mm fork length) during a 6-week experiment conducted in North Fork Caspar Creek, California, in summer 1994. In fenced replicate deep stream sections in this small stream, growth of the larger steelhead was greater in treatments in which small steelhead constituted half of the total biomass of fish than in treatments with an equal biomass comprised entirely of larger fish. In shallow habitats, growth of larger fish was lower in the presence of small fish. The growth of small fish was unaffected by the presence of larger juveniles and also was independent of habitat. Survival of both size-classes was high (70-90%) and unrelated to habitat or the presence of the other size-class. The advantage of large body size in intraspecific interactions among steelhead does not exist in all types of habitat, and interactions between the two size-classes may contribute to lower abundance of large juveniles in streams where aggradation reduces water depth.
Impact of crayfish predation on exotic zebra mussels and native invertebrates in a lake-outlet stream
Authors: Perry W L , Lodge D M , Lamberti G A
Published: April 2011

To test the hypothesis that Orconectes spp. crayfishes could be a significant source of zebra mussel (Dreissena polymorpha) mortality in streams, we conducted a laboratory experiment and a field experiment. In the laboratory experiment, maximum zebra mussel size consumed increased with increasing crayfish size for Orconectes rusticus, Orconectes propinquus, and Orconectes virilis. Slopes differed among crayfish species but not between O. rusticus sexes. To quantify crayfish impacts on seminatural zebra mussel populations, we placed 16 enclosures (0.2 m2) lined with artificial cobble substrata in a midwestern lake-outlet stream (mean width 17 m). Zebra mussels were stocked in each cage (20000 individuals/m2) 14 days before male O. rusticus (20 individuals/m2) were stocked in each of eight enclosures. Densities of all sizes of zebra mussels were reduced in enclosures, with a total density reduction of 31% over the 28 days of the experiment, relative to the exclosures. Crayfish also reduced gastropod densities by 54%, but did not significantly affect other invertebrates. Laboratory and field results suggest that predation by Orconectes crayfishes may significantly reduce zebra mussel populations in streams.
Optimal harvesting of fish populations with nonlinear rates of predation and autocorrelated environmental variability
Authors: Spencer P D
Published: April 2011

A common surplus production model incorporating a nonlinear rate of predation yields multiple, stable equilibria and, when forced with autocorrelated variability, has been invoked to qualitatively describe rapid ``flips'' in marine fish abundances. In this paper, I used optimal control theory and stochastic dynamic programming to obtain optimal harvesting policies for populations described by this model. Multiple, locally optimal stock sizes may exist with a management goal of sum of discounted yield, whereas a single optimum occurred with the goal of sum of discounted economic rent. The optimal policy for a population forced with autocorrelated variability and fluctuating between high and low equilibria required conservative (exploitative) behavior during poor (good) environmental conditions with high stocks and rebuilding of low stocks. Simulation of various harvest strategies applied to such a population revealed that, with a management goal of sum of discounted yield and a discount rate of 2.5%, the optimal policy provided more than twice the mean annual benefits as a constant fishing rate policy. The large differences in optimal policies for the management goals of sum of discounted yield and sum of discounted economic rent provide motivation to consider carefully what objectives should be sought from highly fluctuating fish stocks.
Population structure, growth, and sexual maturation of short-finned squid (Illex illecebrosus) at Newfoundland
Authors: Dawe E G , Beck P C
Published: April 2011

We describe size at age, growth, and population structure of short-finned squid (Illex illecebrosus) from Newfoundland waters during 1990. Ages were estimated from statolith increment counts and used to back-calculate hatching dates. Hatching ranged between December and June with the hatching months of March to May predominating. Constant interchange of individuals in the inshore population was evident in that the modal month of hatching progressed from March within the earliest (July) sample to May within the latest (November) sample. Within the mantle length range available, growth was adequately expressed by a linear model. Females grew faster than males, and during the March to May months of hatching, length at age and growth rate increased with hatching month. This positive effect of late time of hatching was also seen in growth in mass and in gonad development and sexual maturation.
Settlement timing, distribution, and abundance of Dover sole (Microstomus pacificus) on an outer continental shelf nursery area
Authors: Toole C L , Markle D F , Donohoe C J
Published: April 2011

Settlement timing, distribution, and abundance of Dover sole (Microstomus pacificus) were compared with depth and environmental variables off Oregon, U.S.A. Surveys were made every 2 months from January to November 1989 on three 50-400 m depth transects and every March from 1990 to 1994 on one transect. Annual March age-1 catch per unit effort (CPUE) estimates did not support Hayman and Tyler's (R.A Hayman and A. Tyler. 1980. Trans. Am. Fish. Soc. 109: 54-70) hypothesis that strong year-classes are associated with offshore convergence during the settlement season, despite a similar distribution of oceanographic conditions during the two studies. High March CPUE was correlated with high bottom temperature in the primary nursery area (100-119 m depth) and an increase in the proportion of larvae in deeper strata. Seasonal and annual observations support Hayman and Tyler's assumption that the primary postsettlement nursery area is bathymetrically restricted. Otolith increments indicated that larvae at 50-159 m had been on the bottom longer than larvae from greater depths, suggesting postsettlement inshore migration. Sediment size and bottom temperature do not explain the high CPUE in the primary nursery area. A negative size-depth relationship and a change in depth distribution with increasing density suggest that biological interactions may influence the spring distribution.
Thyroid function and olfactory responses to L-alanine during induced smoltification in Atlantic salmon, Salmo salar
Authors: Morin P -P , Hara T J , Eales J G
Published: April 2011

For 5 weeks starting in mid-February we examined developmental correlations between external smolt features, plasma thyroid hormone levels, and olfactory responses in Atlantic salmon transferred from 0.9 to 11°C and exposed to a 16 h light : 8 h dark (16L) or an 8 h light : 16 h dark (8L) photoperiod. In 16L fish, external smolt features developed to 80% of full state, plasma L-thyroxine (T4) surged at week 3, but there were no changes in plasma 3,5,3 prime -triiodo-L-thyronine, olfactory bulb electroencephalographic (EEG), or olfactory epithelium electro-olfactographic (EOG) activities in response to nasal stimulation with L-alanine (10-9 to 10-5 M). In 8L fish, external smolt features were arrested at 40% of full state, plasma T4 showed no surge, EOG activity increased modestly, but EEG activity increased markedly at weeks 3 and 4. Thus, under the particular photoperiod and temperature conditions imposed in this study in February and March, enhanced olfactory activity can develop in premigratory Atlantic salmon independently of external smolt features or a significant surge in plasma T4.
Effect of stream acidification and inorganic aluminum on mortality of brook trout (Salvelinus fontinalis) in the Catskill Mountains, New York
Authors: Baldigo B P , Murdoch P S
Published: April 2011

Juvenile brook trout (Salvelinus fontinalis) were exposed in cages to fluctuating chemical conditions in four Catskill Mountain streams during the spring and fall of 1989 and the spring of 1990. Specific chemical constituents and characteristics of acidic episodes that correlated with increased fish mortality were identified. Mortality increased during acidic episodes in one poorly buffered stream when inorganic monomeric aluminum (Alim) concentrations increased; mortality was low in three other streams during acidic episodes of shorter duration and smaller magnitude than measured in the poorly buffered stream. Variation in mortality was attributed primarily to differences in concentrations of both Alim and dissolved organic carbon. Linear and logistic regression analyses indicate that either mean or median Alim concentrations could account for 73-99% of the variability in mortality. Regression analyses suggest that mortality was highly related (in order of importance) to Alim, pH, dissolved organic carbon, calcium, and chloride concentration. Brook trout mortality was also highly related to durations of exposure above 0.225 and 0.250 mg/L Alim during test periods. Characteristics of acidic-Alim episodes that are critical to mortality of caged brook trout appear to be (i) Alim concentrations of at least 0.225 ± 0.025 mg/L and (ii) exposure to these toxic Alim concentrations for at least 2 days.
Climatic and hydrological determinants of year-class strength of St. Lawrence River lake sturgeon (Acipenser fulvescens)
Authors: Nilo P , Dumont P , Fortin R
Published: April 2011

From 1991 to 1993, juvenile lake sturgeon (Acipenser fulvescens), mostly aged between 1 + and 12 + , were sampled with experimental gill nets in the St. Lawrence River and in two of its major tributaries (Des Prairies and l'Assomption rivers) to determine population age structure and year-class strength. A ratio of 1:7 was observed between the weakest (1980) and the strongest (1989) year-classes. Positive, significant correlations were observed between year-class strength and daily rate of increase in St. Lawrence River water temperatures in May and June, and mean June water flows in the Des Prairies River (the major spawning tributary in the system). The results suggest that year-class strength is determined in the first few months of life and that climatic and hydrological conditions in June, during which larvae drift from the spawning grounds and exogenous feeding begins, are critical determinants of year-class strength in St. Lawrence River lake sturgeon.
In situ activity metabolism of rainbow trout (Oncorhynchus mykiss): estimates obtained from telemetry of axial muscle electromyograms
Authors: Briggs C T , Post J R
Published: April 2011

Activity metabolism of free-swimming rainbow trout (Oncorhynchus mykiss) was estimated using electromyogram telemetry of the axial muscle. Estimates were obtained for five fish for temperatures ranging from 3 to 22°C. Activity metabolism was divided by standard metabolism to produce a relative metabolic cost of activity (RMA). The average diel pattern of RMA was predominantly crepuscular. RMA increased at dawn and then slowly increased to an average maximum peak of 1.8 at dusk. After dusk, RMA slowly declined to a minimum value of 1.4 just prior to dawn. The diel pattern was similar over most of the temperature range studied, but became less distinct at the upper and lower limits of the range. Changes in mean daily RMA were strongly correlated with changes in mean temperature. Mean RMA of the five fish sampled over three seasons was 1.5, with very little variation among fish. The results of this study indicate that the activity metabolism of free-swimming rainbow trout is less than twice standard.
Accumulation of total mercury and methyl mercury in insect larvae of hydroelectric reservoirs
Authors: Tremblay A , Lucotte M
Published: April 2011

Mean total mercury (Hg) and methyl mercury (MeHg) concentrations in insect larvae from hydrolelectric reservoirs were 3-5 times (up to 10 times) higher than in their counterparts from natural lakes. Taxonomic differences, which may be related to feeding behavior, and substrate type (lake sediment or flooded soils) together explained a large part of the total variability of total Hg (r2 = 0.64) and MeHg (r2 = 0.79) concentrations in insects. MeHg concentrations in flooded soils increased from 0.3-2 ng Hg cdot g dry weight-1 after 1-2 years of flooding to 15-2 ng Hg cdot g dry weight-1 after 16 years of impoundment. Total Hg and MeHg concentrations in insect larvae followed a similar pattern, but only weak correlations of both total Hg and MeHg concentrations were found between flooded soils and insect larvae, suggesting that factors other than MeHg content of flooded soils also affect the accumulation of these compounds in insects. Our results indicate that suspended particulate matter eroded from flooded soils by wave and ice action and bacterial activity enhanced by the release of labile carbon and nutrients from the flooded soils may indirectly transfer MeHg from flooded soils to insect larvae.
Contribution of suspended particulate matter and zooplankton to MeHg contamination of the food chain in midnorthern Quebec (Canada) reservoirs
Authors: Plourde Y , Lucotte M , Pichet P
Published: April 2011

Suspended particulate matter (SPM) retained by continuous-flow centrifugation, suspended matter of 20-150 mu m diameter, and zooplankton exceeding 150 mu m were sampled in the LG-2 and LA-1 reservoirs and in four natural lakes in northern Quebec during June, August, and September 1992 and 1993. Inorganic Hg concentrations in the three compartments did not differ significantly between the reservoirs and natural lakes, but methyl mercury (MeHg) concentrations in SPM (mean of 0.05 ppm) and zooplankton (up to 0.84 ppm) from LG-2 were 7 and 5 times higher, respectively, than in the natural lakes. The MeHg bioamplification factors between SPM and zooplankton ranged from 4 to 9 in the reservoirs and natural lakes. MeHg concentrations in SPM reached a maximum during August and were positively correlated with organic matter content. High MeHg concentrations were observed in the SPM and zooplankton sampled in August in a small impoundment separated from LA-1 by the LA-40 dike, which had been flooded for about 1 year. These data suggest that methylation and transfer of MeHg from flooded soils to SPM and zooplankton are rapidly accomplished. The process involves the bioaccumulation of MeHg by phytoplankton and (or) the ingestion of suspended soil-derived organic particles by zooplankton.
Seasonal and spatial variation in the abundance and size distribution of fishes associated with a petroleum platform in the northern Gulf of Mexico
Authors: Stanley D R , Wilson C A
Published: April 2011

Stationary dual-beam hydroacoustics and visual point count surveys were used in tandem to measure the density, target strength, and species composition of fishes associated with a petroleum platform in the northern Gulf of Mexico. Fish densities ranged from 0 to 10.5 fish · m-3 during monthly sampling trips from January 1991 to May 1992. Density and target strength were spatially and temporally variable. Target strengths varied significantly with side of the platform, month, and east and north current vectors. Density varied significantly with platform side, month, east current vector, and depth. Density and target strength did not change over 24 h periods or with water temperature. Fish densities were highest adjacent to the platform and decreased significantly beyond 16 m. Approximately 1990 - 28<|>100 fish were associated with the platform depending on the month. A total of 19 species were observed at the platform, with Chaetodipterus faber, Caranx fusus, Seriola dumerili, Balistes capriscus,Lutjanus campechanus, andArchosargus probatocephalus constituting 97% of observed fishes. Based on our results, we conclude that the fishes associated with a petroleum platform conform with the open nonequilibrium hypothesis proposed for fishes in coral reef habitats.
Marine zooplanktonic and benthic community respiration rates at Resolute, Canadian high Arctic
Authors: Welch H E , Siferd T D , Bruecker P
Published: April 2011

Benthic community respiration rates and macrozooplankton (>202 µm) biomass and respiration rates were measured throughout a calender year at Resolute (74°42 prime N, 94°50 prime W). The plankton averaged 7.2 g dry weight · m-2 with no seasonal pattern and respired 82 g O2 · m-2 · yr-1. Gelatinous and chaetognath predators made up 10% of macrozooplankton biomass and respired 6.4% of planktonic respiration. The lipid content of the nongelatinous fraction fluctuated seasonaly from 64% of dry weight in midwinter to 46% in early summer. The benthic soft-bottom community inside Resolute Bay respired about 125 g O2 · m-2 · yr-1, with a twofold rate increase in late summer. Offshore on hard bottom the few measurements we obtained suggested a respiration rate of about 75 g O2 · m-2 · yr-1. The macrozooplankton and benthos were therefore approximately equal in energy flow. The total ecosystem respiration of 157 g O2 · m-2 · yr-1 corroborated a previous independent estimate of photosynthesis of 60 g C · m-2 · yr-1 for the region. Microplankton respiration appeared to be relatively low. Our results are consistent with the hypothesis that the proporion of primary production exported to the benthos increases with decreasing water temperature and depth, increasing latitude, and increasing cell size.
Relationships between body mass, population density, and the self-thinning rule in stream-living salmonids
Authors: Dunham J B , Vinyard G L
Published: April 2011

In food and (or) space-limited populations, increases in average body size may be accompanied by increases in per capita space and (or) energy requirements. Thus, as body size increases in time or space, the equilibrium number of individuals that can be supported in a given environment should decrease. This relationship, referred to as self-thinning, produces a negative linear relationship between log body size (mass) and log population density. We studied body mass - population density relationships in stream-living populations of several trout species from the intermountain western United States. Our analyses of relationships between body mass and population density demonstrated that self-thinning can be manifested through both temporal and spatial variability in fish population characteristics. Several populations did not show self-thinning, possibly due to species-specific traits, temporal and spatial environmental variation, or both. Thinning lines may not reveal specific causal mechanisms, but they appear to be real, density-dependent responses and thus offer a potentially useful method for studying fish populations. Experimental studies of self-thinning under more controlled conditions are needed, however, to identify causal mechanisms and eliminate alternative explanations for body size - abundance relationships.
Trade-off between reproductive effort and adult survival in oviparous and viviparous fishes
Authors: Gunderson D R
Published: April 2011

An interspecific analysis of life history characteristics for 28 stocks of fish showed that age at maturity ( alpha ), natural mortality (M), and reproductive effort (gonadosomatic index, GSI) were weakly (r2 = 0.18-0.33) but significantly correlated with body size. Viviparity was associated with reduced reproductive effort, reduced age at maturity, and low M relative to oviparous species of a corresponding size. The allometric relationships of alpha , M, and GSI with Linf showed a high degree of scatter but were in agreement with predictions from models based on metabolic and ecological constraints on assimilation rate. In addition, however, residuals around the GSI-Linf and M-Linf relationships showed a strong positive correlation (r2 = 0.64), consistent with previous intraspecific manipulation experiments that indicated that reproductive effort and M are genetically linked. A strong positive correlation (r2 = 0.75) was found between GSI and M, and this relationship did not differ significantly between oviparous and viviparous species.
Toxicity and accumulation of zinc and copper in Hyalella azteca exposed to metal-spiked sediments
Authors: Borgmann U , Norwood W P
Published: April 2011

The relationship between zinc and copper toxicity in Hyalella azteca and accumulation from metal-spiked sediments was determined for future use in identifying sites where these metals contribute to sediment toxicity. Both zinc and copper accumulation increased rapidly with increasing sediment concentrations, showing no evidence of saturation as seen in waterborne exposures. Zinc accumulation from zinc spiked sediments was substantial, even at concentrations below those causing chronic toxicity, and body concentrations can readily be used to infer chronic toxicity. Chronic toxicity in spiked sediment exposures occurred at excess (above background) body concentrations twice as high as in waterborne exposures, possibly as a result of zinc in gut contents. In contrast, chronic copper toxicity occurred at body concentrations lower than those observed in waterborne exposures. Furthermore, body copper at low sediment exposures was independent of copper in sediment. Body copper concentrations can be used to infer short-term (1-week) toxicity but not chronic toxicity. Copper, but not zinc, caused a reduction in growth, even at concentrations below the 4-week LC25. Reduced growth can, therefore, be used to differentiate between chronic copper and zinc toxicity in sediments.
Discrimination of field-collected juveniles of two introduced dreissenids (Dreissena polymorpha and Dreissena bugensis) using mitochondrial DNA and shell morphology
Authors: Claxton W Trevor , Martel André , Dermott Ronald M , Boulding Elizabeth G
Published: April 2011

We developed molecular markers to distinguish two species of exotic bivalves, the zebra mussel (Dreissena polymorpha) and the quagga mussel (Dreissena bugensis sensu lato). Restriction analysis of a 710 base pair fragment of the COI mitochondrial gene showed a single restriction pattern for zebra mussels and a single restriction pattern for quagga mussels for each of the enzymes ScrfI, Csp6I, and Sau96I. This molecular analysis also confirmed that there were no sex-specific restriction patterns for either species. We then used our molecular markers to confirm the species identity of postmetamorphic and early juvenile stages (>=>300 µm shell length) of zebra and quagga mussels from Lake Erie and the Rideau River (Ottawa, Ont.). Useful shell characteristics to discriminate between postmetamorphic and early juvenile stages (>=>300 µm shell length) of zebra and quagga mussel included (i) overlap of valves at the posterior region, (ii) position of the dorsal point of curvature, (iii) angle of shell at the dorso-anterior region (hinge), and (iv) level of flatness of the ventral region (>2 mm shell length). Juveniles of approximately 300-700 µm shell length can be identified using the valve overlap criterion alone.
Changes in life history parameters in a naturally spawning population of chinook salmon (Oncorhynchus tshawytscha) associated with releases of hatchery-reared fish
Authors: Unwin M J , Glova G J
Published: April 2011

Chinook salmon (Oncorhynchus tshawytscha) spawning runs in Glenariffe Stream, New Zealand, exhibited significant changes in life history traits following supplementation releases of hatchery-reared juveniles. Total run strength did not change but the proportion of naturally produced fish declined to 34%. Attempts to separate spawners of natural and hatchery origin were unsuccessful, and 31-48% of natural spawners are now of hatchery origin. Hatchery males were smaller at age 2 and 3 than males of natural origin, and more often matured as jacks, producing an 86-mm decrease in mean fork length over 28 years. There was no change in length at age or age at maturity for female spawners. The proportion of jacks entering Glenariffe Stream each year was positively correlated with the proportion of jacks in the ensuing cohort. Most differences between fish of natural and hatchery origin were related to hatchery rearing practices, but the decline in age at maturity among naturally produced males appears to reflect traits inherited from parent stock of hatchery origin. Hatchery releases may also favour the survival of ocean-type fry over stream-type fry, possibly reversing a tendency for stream-type behaviour to evolve in response to the lack of estuaries on most New Zealand chinook salmon rivers.
Fry-to-adult survival of natural and hatchery-produced chinook salmon (Oncorhynchus tshawytscha) from a common origin
Authors: Unwin M J
Published: April 2011

Fry-to-adult survival rates for chinook salmon (Oncorhynchus tshawytscha) from Glenariffe Stream, a tributary of the Rakaia River, New Zealand, were estimated for fish of both natural and hatchery origin. Survival of naturally produced fry, most of which leave Glenariffe Stream within 24 h of emergence, averaged 0.079% (range 0.013-1.17%). For hatchery fish released at 8-12 months, standardised to a mean weight of 38 g, survival covaried with weight at release consistently across all brood years and averaged 0.34% (range 0.008-3.28%). Survival rates for hatchery fish were four times higher than for naturally produced fry, but were extremely poor relative to their size at release. Survival rates for fish of natural and hatchery origin were positively correlated, suggesting that recruitment of both stocks is primarily controlled by common influences within the marine environment, probably during the first winter at sea. Stock-recruitment analysis for the natural population showed little tendency for recruitment to increase with stock size, suggesting that marine survival rates may be density dependent. Although the reasons for the relatively poor survival of hatchery fish are unclear, the results provide a case study in which hatchery fish appear to have a poorer ``fitness to survive'' than their natural counterparts.
Diet diversity of Steller sea lions (Eumetopias jubatus) and their population decline in Alaska: a potential relationship
Authors: Merrick Richard L , Chumbley M Kathryn , Byrd G Vernon
Published: April 2011

We examined the diet of Steller sea lions (Eumetopias jubatus) during June-August 1990-1993 from six areas in the Aleutian Islands and Gulf of Alaska and related these diets to sea lion population changes that occurred during the period. Seven general prey categories were identified, but either walleye pollock (Theragra chalcogramma) or Atka mackerel (Pleurogrammus monopterygius) dominated in every area. The diversity of prey consumed varied among sites. Only the eastern Aleutian Islands area had all seven categories in the diet, and there, walleye pollock and Atka mackerel each made up around 30% of the diet. The remainder was composed mostly of small schooling fish (e.g., Pacific herring (Clupea pallasi) and salmon (Oncorhynchus spp.)). The diet in the Gulf of Alaska included mostly walleye pollock whereas the central and western Aleutian diet was composed mostly of Atka mackerel. Populations in the six areas decreased up to 49% during 1990-1994. A strong positive correlation (r = 0.949, P = 0.004) was found between diet diversity and the amount of decline in an area: as diet diversity decreased, populations decreased. This suggests that sea lions need a variety of prey available, perhaps to buffer significant changes in abundance of any single prey.
Effects of base addition and brook trout (Salvelinus fontinalis) introduction on the plankton community of an acidic Adirondack lake
Authors: Bukaveckas Paul A , Shaw William
Published: April 2011

Calcite was added to Woods Lake in 1985 and 1987, and to its watershed in 1990, to restore and maintain water quality conditions suitable for reestablishing brook trout (Salvelinus fontinalis). Juvenile and adult brook trout were introduced following the first chemical treatment and were stocked annually thereafter from 1985 to 1989. In response to the combined chemical and biological manipulation, phytoplankton abundance increased whereas production per unit of biomass decreased. We attribute the increase in phytoplankton abundance and the reduction in biomass turnover rates to a decrease in zooplankton grazing. Zooplankton densities and estimated community grazing rates were lower during the posttreatment period despite a shift from small-bodied taxa (Diaptomus minutus, Bosmina longirostris) to a more diverse assemblage that included four species of daphnids. We attribute reductions in zooplankton abundance to planktivory of introduced brook trout. The changes we observed in phytoplankton and zooplankton species composition were consistent with trends observed during whole-lake acidification experiments, but functional responses in our experiment (decreased zooplankton abundance, increased phytoplankton abundance) were not. Our functional responses were consistent, however, with those observed previously in food webs manipulated to increase planktivore abundance.
Fatty acid signatures and classification trees: new tools for investigating the foraging ecology of seals
Authors: Smith Stephen J , Iverson Sara J , Bowen W D
Published: April 2011

Analysis of the fatty acid composition of milk lipids in marine mammals offers a potential means of determining changes in diet and lactation stage. However, the large number of fatty acids routinely identified (over 60) relative to the number of animals usually sampled can limit the usefulness of standard multivariate statistical models for characterizing these patterns. Classification trees or tree-based models, which are not limited by the number of variables, were used here to study the fatty acid patterns in the milk of female harbour seals (Phoca vitulina) at parturition and during lactation. Tree analyses correctly classified 44 of 51 seals based on milk fatty acid composition to four stages of lactation, which corresponded to states of fasting versus increasingly intensive feeding. The fatty acid 16:2n-6 was quite effective in differentiating between seals at parturition and those 4 days or more later. Seals were grouped into early and late lactation by fatty acid 24:1n-9. A comparison between classification rules derived from classification trees and discriminant analysis showed that each gave similar rates of misclassification but that the latter required a method for the a priori choice of which fatty acids to analyze.
Ecosystem differences in the trophic enrichment of 13C in aquatic food webs
Authors: France R L , Peters R H
Published: April 2011

Data from 35 published studies were collated to examine patterns in the trophic enrichment of 13C of consumers. Because both delta 13C and delta 14N vary systematically across ecosystems, it was necessary to standardize for such differences before combining data from numerous sources. Relationships of these measures of ecosystem-standardized delta 13C to ecosystem-standardized trophic position ( DELTA delta 15N) for freshwater, estuarine, coastal, and open-ocean and for all aquatic ecosystems yielded regression equations of low predictive capability (average of 20% explained variance in delta 13C). However, differences were observed in the slopes between delta 13C and standardized trophic position when data were examined study-specifically: the average trophic fractionation of 13C was found to increase from + 0.2omicron for freshwater to + 0.5omicron for estuarine to + 0.8omicron for coastal, and to + 1.1omicron for open-ocean food webs. This ecosystem-specific gradient in 13C enrichment for consumers supports previous findings of a similar continuum existing for zooplankton - particulate organic matter differences in delta 13C. Possible mechanisms to explain these ecosystem-specific patterns in 13C enrichment may be related to the relative importance of detritus, heterotrophic respiration, partial reliance on alternative food sources, and lipid influences in the different ecosystems.
Spatial scales of interannual recruitment variations of marine, anadromous, and freshwater fish
Authors: Myers R A , Mertz G , Bridson J
Published: April 2011

We examine the spatial scale of variability in recruitment for 11 marine, three anadromous, and five freshwater species. Generally the spatial scale of recruitment correlations for marine species is approximately 500 km, compared with less than 50 km for freshwater; anadromous species fall between these two scales. The scale for marine species is comparable with (but less than) that of the largest-scale environmental variables (and is compatible with the idea that large-scale environmental agents influence recruitment). Our results are consistent with the hypothesis that predation is a more important factor in determining recruitment in freshwater than it is in the marine environment.
Genetic variation of microsatellite and mitochondrial DNA markers in broad whitefish (Coregonus nasus) in the Colville and Sagavanirktok rivers in northern Alaska
Authors: Patton J C , Gallaway B J , Fechhelm R G , Cronin M A
Published: April 2011

There has been concern that a causeway leading to oil production facilities in the Alaskan Beaufort Sea could affect the extent of emigration from, and immigration into, a population of broad whitefish (Coregonus nasus) in the Sagavanirktok River. To assess this, we analyzed the genetic relationships of the broad whitefish populations in the Sagavanirktok River, and the nearest adjacent population, in the Colville River. Three microsatellite loci from the nuclear genome, and the NADH-1 gene of mitochondrial DNA (mtDNA), were analyzed. Diploid genotypes were determined with PCR amplification of the microsatellite loci, and mtDNA genotypes were identified with PCR amplification followed by sequencing of 798 nucleotides. Several alleles were identified at each locus and both populations had high levels of genetic variation. There is significant differentiation of the Sagavanirktok River and Colville River broad whitefish stocks for the three microsatellite loci (FST= 0.031) but not mtDNA (FST< 0.001). Possible explanations for the lower level of differentiation of mtDNA than microsatellites include female-mediated gene flow between populations, skewed sex ratios, natural selection, or mutation. The results indicate that there is limited gene flow between the Colville and Sagavanirktok rivers, which represent semi-isolated spawning populations.
Individual variation in dispersal behaviour of newly emerged chinook salmon (Oncorhynchus tshawytscha) from the Upper Fraser River, British Columbia
Authors: Bradford M J , Taylor G C
Published: April 2011

Immediately after emergence from spawning gravels, fry of stream-type chinook salmon (Oncorhynchus tshawytscha) populations from tributaries of the upper Fraser River, British Columbia, distribute themselves downstream from the spawning areas, throughout the natal stream, and into the Fraser River. We tested the hypothesis that this range in dispersal distances is caused by innate differences in nocturnal migratory tendency among individuals. Using an experimental stream channel, we found repeatable differences in downstream movement behaviour among newly emerged chinook fry. Fish that moved downstream were larger than those that held position in the channel. However, the incidence of downstream movement behaviours decreased over the first 2 weeks after emergence. We propose that the variation among individuals in downstream movement behaviour we observed leads to the dispersal of newly emerged fry throughout all available rearing habitats. Thus, between- and within-population variation in the freshwater life history observed in these populations may be caused by small differences in the behaviour of individuals.
Spatial differences in the productivity of American lobster in Nova Scotia
Authors: Miller R J
Published: April 2011

Lobster production per unit area of habitat varies greatly from location to location. Several physical and biological variables have previously been offered as explanations. In this study the density of ovigerous females (a proxy for egg production), postlarvae, and recruits to the fishery were measured in seven adjacent areas spanning 190 km of Nova Scotia coast. The ranking of these densities among areas persisted from year-to-year, showing consistent spatial differences in productivity. A high spatial correlation between postlarvae and fishery recruits implicated postlarvae as the proximate regulator of lobster yields. Further correlation showed that egg to postlarval survival, and not egg abundance, was related to fishery recruits. Implications for fishery management are (i) enhancement of any life-history stage between postlarvae and fishery recruits should increase fishery yields and (ii) very different levels of egg production may be necessary to maintain an equal level of fishery recruits among areas. Larval survival was highest in areas where hatching occurred late in the season; this differs from previous suggestions that early hatching promotes survival.
Complex recruitment dynamics with Doppler-like effects caused by shifts and cycles in age-at-recruitment
Authors: Bell KNI
Published: April 2011

Even with constant production (N0) and constant time-specific mortality (Z, daily), recruitment can vary greatly. A new variable-lag phenomenon modelled here generates temporal variation in recruitment from temporal shifts in age-at-recruitment (AAR; here synonymous with stage duration). The phenomenon is due to two components, one being analogous to the Doppler effect and the other an interaction of dAAR/dt with Z, and is distinct from those identified in previous contributions not focusing on temporal structure. Recruitment can be predicted from N0, Z, and AAR, using either numerical simulation or, in many cases, the modified Doppler equation given here. Seasonal recruitment cycles predicted for a sinusoidal AAR function fitted to natural data, with constant larval production and constant Z (varied among, not within, model runs), were strongly peaked with a difference of 20% between maximum and minimum recruitments at Z = 0, to a difference of 2000% at Z approx 0.2. The model gives indirect access to parameters difficult to measure in the field: if temporal variation is adequately described in two of the three input variables (N0, Z, or AAR), differences (residuals) between predicted and observed recruitment can indicate an unaccounted pattern in the unknown.
Visualizing catch–age analysis: a case study
Authors: Richards L J , Schnute J T , Olsen N
Published: April 2011

Catch-age analysis has become a standard tool for modern stock assessment. Widely available graphical techniques can be customized to provide an intuitive framework for this complex procedure. We illustrate a graphical approach using data from a stock of Pacific ocean perch (Sebastes alutus). These data encompass typical problems in stock assessment, with missing data for some years and changes in age determination and survey methodologies midway through the time series. Preliminary visual inspection of the raw data reveals important features that must be accommodated in the model development. We tailor a state-space model to address these requirements and provide appendices that completely define the model and its statistical application. We suggest graphical methods for evaluating model output, including residuals and standard errors of population biomass. Such portrayals of uncertainty help define realistic limits to the information inherent in fishery data.
Patterns in fish assemblages from coastal wetland and beach habitats in Green Bay, Lake Michigan: a multivariate analysis of abiotic and biotic forcing factors
Authors: Brazner J C , Beals E W
Published: April 2011

From May to September in 1990 and 1991, 24 coastal wetland and beach sites in Green Bay, Lake Michigan, were sampled to investigate abiotic and biotic factors influencing fish assemblages; half the sites were modified by human developments, and half were relatively undeveloped. The greatest assemblage differences were observed among regions, but there also were strong differences among assemblages from different habitats. Degree of development had less of an effect on site differences, although assemblages at undeveloped wetlands were unique, and those from developed and undeveloped sites in the upper bay were relatively distinct. The most influential abiotic factors were turbidity, reflecting the trophic gradient in the bay, and a suite of variables associated with macrophyte coverage and diversity, which were critical components of nursery habitats for the primarily immature fishes we captured. The volatile and unpredictable nature of shoreline habitats in the Great Lakes apparently precluded competition and predation from having a strong organizing role. This study demonstrates that undeveloped wetlands are a valuable and intensely utilized fish habitat, particulartly as nursery areas, that should receive special consideration in ecosystem management plans for the Great Lakes.
Does taxonomic resolution affect the multivariate description of the structure of freshwater benthic macroinvertebrate communities?
Authors: Bowman M F , Bailey R C
Published: April 2011

Ten data sets from published studies of freshwater benthic macroinvertebrates were used to deduce the necessary level of taxonomic resolution (from genus to phylum) for assessing variation in community structure. Quantitative data sets describing communities of benthic invertebrates identified to genus were aggregated to family, order, class, and phylum. Bray-Curtis distances between each pair of communities in a given study were calculated at each level of taxonomic aggregation. Also, quantitative data were converted to qualitative (presence-absence) data and aggregated in the same manner. Jaccard's distances between communities were calculated for these data matrices. Correlations between the resulting distance matrices, calculated at different taxonomic resolutions, were quantified using Mantel's test (N. Mantel. 1967. Cancer Res. 27: 209-220). Distance matrices for different taxonomic resolutions were highly correlated (r >> 0.64) when based on quantitative data for all except 1 of the 10 studies. Correlations were lower and more variable for qualitative data sets. For the data sets investigated, genus-level identification did not usually provide a strikingly different description of community patterns than higher levels (e.g., family, order) of taxonomic identification.
Greenland halibut (Reinhardtius hippoglossoides) in the North Atlantic are genetically homogeneous
Authors: Vis M L , Carr S M , Bowering W R , Davidson W S
Published: April 2011

Greenland halibut (Reinhardtius hippoglossoides) have become of great importance to the Canadian fishery since the moratorium on northern cod (Gadus morhua), and an understanding of stock relationships among populations at the northern and southern extremes of their commercial range is crucial for proper management. We compared mitochondrial DNA sequence variation among fish taken from thoughout the Northwest Atlantic (Flemish Pass, the Grand Banks, Davis Strait, and Northwest Greenland) with samples from the Gulf of St. Lawrence, Iceland, and Norway. Within a 401 base pair portion of the cytochrome b gene, 22 genotypes were identified. Three of these occur at frequencies >10% and in the same relative abundances in all samples (except the Gulf of St.Lawrence). Genotype proportions do not differ significantly among samples, and genetic subdivision among samples (measured by the coancestry coefficient theta ) is nil. Genetic distances among samples are not related to geographic distribution: pairwise differences between the Gulf sample and other western Atlantic samples exceed those for trans-Atlantic comparisons. These data suggest that there is sufficient mixing of Greenland halibut, not only within the NAFO regulatory area, but among sites in the North Atlantic generally, to prevent the development or maintenance of genetically independent stocks.
Late-summer distribution of phytoplankton in relation to water mass characteristics in Hudson Bay and Hudson Strait (Canada)
Authors: Harvey M , Therriault J -C , Simard N
Published: April 2011

Descriptive and multivariate analytical methods were used to analyze the early September (1993) abundance and species composition of phytoplankton in relation to water mass characteristics in Hudson Bay and Hudson Strait. Four groups of stations distributed along well-defined environmental gradients characterizing the distribution of physical and chemical variables were identified. The first group, located in the most southern region of Hudson Bay, was strongly influenced by freshwater runoffs from James Bay and from the other major rivers around the bay and was characterized by a relatively high phytoplankton biomass (chlorophyll a (Chl a) > 1.0 µg ·L-1) in the near-surface waters and by a phytoplankton assemblage equally dominated by small flagellates and dinoflagellates. The second group, located in an area northwest of the Belcher and Sleeper islands, was characterized by relatively well-mixed conditions where small diatoms composed about 50% of the phytoplankton assemblage. The third group occupied the upper part of the bay and the entrance of the strait and was characterized by the lowest surface nutrient concentrations encountered. A clear subsurface chlorophyll maximum dominated by small flagellates (>55% of the assemblage) was observed in this region. The fourth group was located in the central part of the strait where the highest surface nutrient concentrations and phytoplankton biomass values (Chl a > 2.0 µg ·L-1) were observed. The phytoplankton assemblage there was clearly dominated by small diatoms (>80%). These conditions are related to the presence of more intense tidal mixing in this region. The phytoplankton standing crop within this area was comparable with that observed during an autumn bloom situation in most temperate regions of the world's ocean.
Zebra mussel (Dreissena polymorpha) effects on sediment, other zoobenthos, and the diet and growth of adult yellow perch (Perca flavescens) in pond enclosures
Authors: Thayer S A , Haas R C , Hunter R D , Kushler R H
Published: April 2011

Zebra mussels (Dreissena polymorpha) in enclosures located in an experimental pond adjacent to Lake St. Clair, Michigan, increased sedimentation rate but had relatively minor effects on percent organic matter and percent nitrogen content of sediment. In contrast, sediment from Lake St. Clair adjacent to zebra mussels was significantly higher in carbon than that 0.5 m away. Zebra mussels increase the nutritional value of surficial sediment and provide greater structural heterogeneity, which is probably more important in causing change among zoobenthos. Zoobenthos and yellow perch (Perca flavescens) diet were dominated by dipteran larvae and leeches. Zoobenthos was significantly different between enclosures with and without zebra mussels. Treatments with zebra mussels had significantly more oligochaetes and tended to have more crustaceans (isopods and amphipods). In June, yellow perch without zebra mussels consumed significantly more zooplankton, and those with mussels had more crustaceans in their diet. Zooplankton density was greater in treatments without zebra mussels. Yellow perch with zebra mussels grew significantly more than those without mussels. Zebra mussels in the enclosures neither reproduced nor were eaten by yellow perch; hence. the observed growth differences were due to indirect effects involving zebra mussel induced changes in benthic structure and biota.