Canadian Journal of Fisheries and Aquatic Sciences
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Permutation tests for univariate or multivariate analysis of variance and regression The most appropriate strategy to be used to create a permutation distribution for tests of individual terms in complex experimental designs is currently unclear. There are often many possibilities, including restricted permutation or permutation of some form of residuals. This paper provides a summary of recent empirical and theoretical results concerning available methods and gives recommendations for their use in univariate and multivariate applications. The focus of the paper is on complex designs in analysis of variance and multiple regression (i.e., linear models). The assumption of exchangeability required for a permutation test is assured by random allocation of treatments to units in experimental work. For observational data, exchangeability is tantamount to the assumption of independent and identically distributed errors under a null hypothesis. For partial regression, the method of permutation of residuals under a reduced model has been shown to provide the best test. For analysis of variance, one must first identify exchangeable units by considering expected mean squares. Then, one may generally produce either (i) an exact test by restricting permutations or (ii) an approximate test by permuting raw data or some form of residuals. The latter can provide a more powerful test in many situations.
Canadian Journal of Fisheries and Aquatic Sciences - Tập 58 Số 3 - Trang 626-639 - 2001
Diet shift in fish following competitive release We determined the diet preference of roach (Rutilus rutilus), perch (Perca fluviatilis), and bream (Abramis brama) before and after a fish removal program in Lake Finjasjön, Sweden. The biomass of roach and bream was reduced to 33 and 10%, respectively, after the program. The predominate diet change following this major reduction in fish biomass was an increased use of benthic organisms by most size-classes of roach. Also, bream shifted to benthos at an earlier ontogenetic stage. These diet shifts were most probably attributed to the drastic reduction in biomass of the benthivorous bream, resulting in underexploited benthic invertebrates. In order to test if alterations in diet choice were reflected in the composition of stable isotopes of consumer tissue, we determined the temporal changes in the 15 N/14 N ratio (δN) of potential fish prey as well as in fish tissue. No temporal trends were found for δN of fish, possibly due to the high temporal variability in δN of zooplankton. However, minimum and maximum δN values of major food organisms (chironomids and zooplankton) were generally reflected in the δN of both small roach and perch one sampling occasion later (3 months) and in piscivorous perch (exclusively feeding on small fish) two sampling occasions later. Hence, the stable isotope composition could be followed through food links, providing that the consumer mainly fed on one specific food item. However, several other predictions regarding connections between diet and stable isotope composition were not corroborated. We conclude that stable isotope analysis of consumer tissue cannot replace traditional methods of diet determination, but might well provide complementary data.
Canadian Journal of Fisheries and Aquatic Sciences - Tập 56 Số 1 - Trang 70-78 - 1999
Trophic position and individual feeding histories of fish from Lake Okeechobee, Florida We used C and N stable isotope measurements to identify trophic position and feeding histories of fish from Lake Okeechobee, one of the largest lakes in North America. When δ15 N values were used to estimate trophic levels, analyses of about 500 individual fish collected in two seasons at five sites showed that trophic level varied from 2 (herbivore) to 4.3 (second-level carnivore) among the 29 fish species examined. Lower trophic levels predominated among small fish caught at a littoral marsh site, and highest trophic levels were found among larger offshore fish. Marsh fish showed about three times the C isotope variation than did offshore fish, consistent with the wider array of foods in the marsh versus offshore food web. In addition to these community-level results, there were often unexpected large isotopic differences between individuals in almost all fish species examined, suggesting large differences in individual feeding behavior. Isotopic analyses indicate long-term differences in feeding among individuals, in addition to the short-term differences often observed in stomach content studies. Long-term individual variation in fish foraging may be important in understanding variation in other biochemical parameters measured in fish, such as Hg or PCB contents.
Canadian Journal of Fisheries and Aquatic Sciences - Tập 56 Số 4 - Trang 590-600 - 1999
Using stable isotopes to monitor watershed influences on aquatic trophodynamics Stable C and N isotope measurements of the clam Potamocorbula amurensis were used to help identify watershed-level differences in food webs of San Francisco Bay. Potamocorbula amurensis has become widely distributed in San Francisco Bay since introduction from Asia in1986. Clam samples were collected from both the river-influenced northern arm of San Francisco Bay and the lagoonal southern arm of the Bay during 1990-1991. Carbon isotopic compositions of clams responded primarily to riverine inputs and provided an index of hydrologic mixing across the estuarine system. Nitrogen isotopic compositions of clams were more responsive to watershed nutrient loading, with higher δ15 N values found in South Bay, which receives stronger inputs of anthropogenic N. Routine monitoring of animal consumer isotopic compositions could be an effective way to detect long-term watershed-level changes in C and N dynamics important for secondary production in aquatic systems.
Canadian Journal of Fisheries and Aquatic Sciences - Tập 56 Số 11 - Trang 2167-2171 - 1999
Using bioenergetics models to predict stable isotope ratios in fishes To describe temporal dynamics of stable isotope ratios in fishes, we developed a bioenergetics-based model that links isotope ratios to growth, as influenced by fish size, temperature, diet, and prey quality. The model includes error terms for isotope ratios, diet proportions, and fractionation. The model accurately predicted temporal δ15 N dynamics of lake trout (Salvelinus namaycush) in a diet-switch experiment but was less successful for δ13 C, possibly because of variable fractionation. The model was then used in three heuristic applications. In a diet-validation scenario, a model derived from limited knowledge of rainbow smelt (Osmerus mordax) diet reasonably estimated δ13 C and δ15 N compared with a null model but inaccurately estimated prey consumption. In a scenario where adult lake trout briefly cannibalized stocked lake trout fingerlings, the detectability of a cannibalism-induced δ15 N increase depended on predator size, duration of cannibalism, and sample size. In a scenario where seasonal isotopic variability occurred at the base of a food web, variation propagated to higher trophic levels depended on consumer size and diet. Our approach is most valuable when used to examine multiple diet combinations that produce observed stable isotope ratios; one can then identify the most reasonable diets through field tests or other observations.
Canadian Journal of Fisheries and Aquatic Sciences - Tập 59 Số 1 - Trang 115-124 - 2002
Plasma Cortisol Levels of Fingerling Rainbow Trout (<i>Salmo gairdneri</i>) at Rest, and Subjected to Handling, Confinement, Transport, and Stocking Fingerling rainbow trout, acclimated to hatchery raceways or laboratory aquaria, had low plasma cortisol levels (≤ 2 ng/mL), with no apparent daily cycle in levels. Netting of cohorts out of an aquarium, without agitation, did not cause a rise in plasma cortisol concentrations in remaining fish. However, following 90 s of handling and confinement by netting, fingerlings had a sharp rise in plasma cortisol to a peak at 15 min, and then a gradual decline to the basal level over 2 h. Gentle agitation and intermittent restraint with a dip net in the aquarium caused a gradual increase in plasma cortisol concentrations. Intense handling and severe confinement caused a rapid increase in plasma cortisol to a plateau, two to four times greater than the peak levels found in fingerlings subjected to the less vigorous stressors; high levels of plasma cortisol were maintained to the median tolerance limit. During a stocking operation, there was a rapid rise in plasma cortisol concentrations during the initial capture from the rearing ponds, and high levels were maintained through to stocking into the lake 6 h and 10 min later, although a small decrease occurred during transit while the fish were in the truck tanks. After stocking, plasma cortisol concentrations in caged fingerlings did not decrease to the basal level until 8 d poststocking.Key words: rainbow trout, fingerlings, plasma cortisol, cycles, handling stress, stocking stress
Canadian Journal of Fisheries and Aquatic Sciences - Tập 37 Số 5 - Trang 805-811 - 1980
Theory, Practice, and Effects of <i>Mysis relicta</i> Introductions to North American and Scandinavian Lakes Fisheries biologists have greatly altered the natural distribution of the crustacean Mysis relicta by introducing it into many lakes in both North America and Scandinavia to serve as a supplementary food source for fish. The original concept of Mysis as a deepwater benthic organism which remains isolated in the profundal zone of lakes needs to be modified to include its downstream dispersal capabilities. After introduction to a lake, Mysis will probably eventually reach all lakes in the downstream watershed. Recent studies indicate that rates of increase of introduced Mysis populations probably depend on available food and temperature. As well, introduced populations have been shown to modify benthic, phytoplankton, zooplankton, and fish communities. Most Mysis introductions have taken place without consideration of general criteria suggested for introduced species.
Canadian Journal of Fisheries and Aquatic Sciences - Tập 43 Số 6 - Trang 1277-1284 - 1986
Temperature-dependent allometric models to estimate zooplankton production in temperate freshwater lakes
Canadian Journal of Fisheries and Aquatic Sciences - Tập 54 Số 10 - Trang 2350-2360 - 1997
Predicting the vertical distribution of the opossum shrimp, Mysis relicta, in Lake Ontario: a test of laboratory-based light preferences Light and temperature strongly influence the vertical distribution of the mysid shrimp, Mysis relicta . We monitored the vertical movements and depth selection behavior of mysids exposed to different light intensities and light–temperature gradients in the laboratory and derived a mysid light preference function in units relevant to mysid vision: “mylux”. Mysids preferred light levels between 10−8 and 10−7 mylux (∼10−6 to 10−5 lux) and rarely moved into waters of 10−3 mylux (∼0.1 lux) and greater. A model that assumed equal weight and independence of mysid light and temperature preference functions successfully predicted the proportion of mysids found in two different temperature–light combinations in the laboratory. This model also predicted the depth of maximum mysid density to within 2 m on two spring nights and within 5 m on two summer nights of varying moon phase and thermal conditions in Lake Ontario. This study provides novel insights into how temperature and light interact to influence the vertical distribution of mysids. Our model may be used to predict mysid vertical distribution in any deepwater system inhabited by mysids in which the primary mysid predators are visual feeders.
Canadian Journal of Fisheries and Aquatic Sciences - Tập 66 Số 1 - Trang 101-113 - 2009
Predicting the identity and impact of future biological invaders: a priority for aquatic resource management The identification and risk assessment of potential biological invaders would provide valuable criteria for the allocation of resources toward the detection and control of invasion threats. Yet, freshwater biologists have made few attempts at predicting potential invaders, apparently because such efforts are perceived to be costly and futile. We describe some simple, low-cost empirical approaches that would facilitate prediction and demonstrate their use in identifying high-risk species from an important donor region: the Ponto-Caspian (Black, Caspian, and Azov seas) basin. This region is the source of several freshwater organisms already invading North America, including the zebra mussel (Dreissena polymorpha), quagga mussel (Dreissena bugensis), ruffe (Gymnocephalus cernuus), and round goby (Neogobius melanostomus). Based on a thorough literature review, we identify 17 additional Ponto-Caspian animals that have recent invasion histories and are likely to be transported overseas in ship ballast water; moreover, their broad salinity tolerance could allow them to survive an incomplete ballast-water exchange. These results suggest that, unless current vectors are more effectively controlled, the Great Lakes - St. Lawrence River system and other North American inland waterways will continue to receive and be impacted by invasive Eurasian species.
Canadian Journal of Fisheries and Aquatic Sciences - Tập 55 Số 7 - Trang 1759-1765 - 1998
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