Showing papers in "Canadian Journal of Zoology in 1998"
TL;DR: The existence of strikingly divergent prey preferences of resident and transient killer whales is revealed, which are reflected in distinctive foraging strategies and related sociobiological traits of these sympatric populations.
Abstract: Two forms of killer whale (Orcinus orca), resident and transient, occur sympatrically in coastal waters of British Columbia, Washington State, and southeastern Alaska. The two forms do not mix, and differ in seasonal distribution, social structure, and behaviour. These distinctions have been attributed to apparent differences in diet, although no comprehensive comparative analysis of the diets of the two forms had been undertaken. Here we present such an analysis, based on field observations of predation and on the stomach contents of stranded killer whales collected over a 20-year period. In total, 22 species of fish and 1 species of squid were documented in the diet of resident-type killer whales; 12 of these are previously unrecorded as prey of O. orca. Despite the diversity of fish species taken, resident whales have a clear preference for salmon prey. In field observations of feeding, 96% of fish taken were salmonids. Six species of salmonids were identified from prey fragments, with chinook salmon (Oncorhynchus tshawytscha ) being the most common. The stomach contents of stranded residents also indicated a preference for chinook salmon. On rare occasions, resident whales were seen to harass marine mammals, but no kills were confirmed and no mammalian remains were found in the stomachs of stranded residents. Transient killer whales were observed to prey only on pinnipeds, cetaceans, and seabirds. Six mammal species were taken, with over half of observed attacks involving harbour seals (Phoca vitulina). Seabirds do not appear to represent a significant prey resource. This study thus reveals the existence of strikingly divergent prey preferences of resident and transient killer whales, which are reflected in distinctive foraging strategies and related sociobiological traits of these sympatric populations. 1471
489 citations
TL;DR: Evidence of decreased raccoon density is found during and after the appearance of the mid-Atlantic States (Mid-Atlantic) rabies epizootic, a pattern similar to that seen in other carnivores and in rabies models.
Abstract: Density and survival of a raccoon (Procyon lotor) population in Rock Creek Park, an urban national park inWashington, D.C., were estimated using markrecapture and radio-tracking over an 8-year period following the appearance ofthe mid-Atlantic States (Mid-Atlantic) rabies epizootic. Raccoon density ranged from 333.3 to 66.7/km2 , with an overall parkestimate of 125/km2 . This density places the Rock Creek population within the range of other urban and suburban populationsand is many times greater than raccoon densities reported from other habitats. Density was particularly high in one thin spur ofparkland with the smallest ratio of area to urban edge. Raccoon survival rates were high except among juveniles during therabies epizootic. Data on rabies prevalence from Washington, D.C., indicate a cycle with peaks in 1983 during the initialepizootic and again in 1987 and 1991, a pattern similar to that seen in other carnivores and in rabies models. We found evidenceof decreased raccoon density during and afte...
226 citations
TL;DR: The diets of 41 moose in northern coastal Sweden contained 75% Scots pine (Pinus sylvestris) and willow and the remaining proportion equally divided among five deciduous browse species and common juniper (Juniperus communis).
Abstract: Understanding how large herbivores select their diet requires accurate measurements of the nutritional costs and benefits of food items and the composition of plants in the diet relative to the com...
187 citations
TL;DR: In this paper, the authors introduced repeat swimming performance as a particularly sensitive means to assess fish health and the effects of environmental stressors, and found that the recovery of fish pre-exposed to between 0.12 and 0.77 mg·L-1 dehydroabietic acid (DHA) for 8-14 h, and swimming in either hypoxia or normoxia, was impaired.
Abstract: Measurements of swimming ability, such as critical swimming speed (Ucrit), have commonly been used as indicators of the effects of environmental challenges on the general health of fish. In this study, we introduce repeat swimming performance as a particularly sensitive means to assess fish health and the effects of environmental stressors. Adult sockeye salmon (Oncorhynchus nerka) performed two Ucrit tests separated by a 40-min recovery period. When recovery ability was expressed as a ratio of Ucrit values in the first and second swim challenges (Ucrit,2/Ucrit,1), control fish exhibited recovery ratios of unity (0.98 ± 0.01 (mean ± SEM)). In contrast, the recovery of fish pre-exposed to between 0.12 and 0.77 mg·L-1 dehydroabietic acid (DHA) for 8-14 h, and swimming in either hypoxia or normoxia, was impaired. These fish had recovery ratios significantly lower than unity (0.92 ± 0.02) despite swimming to a similar initial Ucrit as control fish. The effect of pre-exposure to DHA was also evident in measure...
172 citations
TL;DR: Appetit inhibition in subordinate fish can be reversed by rearing in isolation, an effect that may be related to the reversal of a stress-induced activation of brain serotonergic neurones accompanying social subordination.
Abstract: We investigated the relationship between social interactions, brain serotonergic activity, and two behavioural patterns in juvenile Arctic char (Salvelinus alpinus): feeding and spontaneous swimming activity. Dominant and subordinate individuals were observed during rearing in pairs, followed by rearing in isolation. Throughout the experiment, levels of both food intake and swimming activity remained high in dominant fish. When they were in pairs, food intake was completely inhibited in subordinate fish; thus, dominant fish were able to monopolise food. At the same time, brain serotonergic activity, as indexed by the ratio of 5-hydroxyindoleacetic acid (5-HIAA) to serotonin (5-hydroxytryptamine, 5-HT) was elevated in the hypothalamus and brain stem of subordinate fish compared with dominants. During subsequent rearing in isolation, food intake, but not spontaneous locomotor activity, gradually increased in previously subordinate fish, while serotonergic activity fell to near that of dominants. Thus, appetite inhibition in subordinate fish can be reversed by rearing in isolation, an effect that may be related to the reversal of a stress-induced activation of brain serotonergic neurones accompanying social subordination. Reduced swimming activity is either a long-lasting response to social subordination or reflects permanently different behavioural strategies of subordinate and dominant individuals. Resume : Nous avons etudie la relation entre les interactions sociales, l'activite serotonergique du cerveau et deux types d'activite, l'alimentation et la nage spontanee, chez des Ombles chevaliers ( Salvelinus alpinus) juveniles. Des individus dominants et subordonnes ont ete observes, d'abord en groupes de deux, puis isoles. Pendant toute la duree de l'experience, les deux genres d'activite ont ete intenses chez les individus dominants. Lorsque les poissons etaient en groupes de deux, l'alimentation etait completement inhibee chez les poissons subordonnes et le poisson dominant avait alors le monopole de la nourriture. Pendant ce temps, l'activite serotonergique du cerveau, telle qu'evaluee par le rapport entre l'acide hydroxy-5-indoleacetique (5-HIAA) et la serotonine (hydroxy-5 tryptamine, 5-HT) etait elevee dans l'hypothalamus et le pedoncule cervical des poissons subordonnes comparativement a celle enregistree chez les poissons dominants. Apres l'isolement des poissons, l'alimentation, mais pas l'activite locomotrice spontanee, a augmente graduellement chez les poissons subordonnes et l'activite serotonergique de ces poissons est redevenue semblable a celle des poissons dominants. L'inhibition de l'appetit chez les poissons subordonnes peut donc etre inversee par l'isolement des poissons, sans doute par renversement de l'activation des neurones serotonergiques sous l'action du stress qui accompagne la subordination sociale. La diminution de l'activite natatoire peut etre interpretee comme une reaction de longue duree a la subordination sociale, ou alors elle reflete les strategies comportementales differentes qui prevalent en permanence chez les poissons dominants et les poissons subordonnes.
165 citations
TL;DR: Based on serum progesterone levels, first conception by females occurred at 16 months and the overall pregnancy rate was 94%, and in addition the minimum parturition rate was 86%, all of which indicate adequate nutrition, which is comparatively low, though similar to results from other studies on woodland caribou.
Abstract: Woodland caribou (Rangifer tarandus caribou) in central Saskatchewan are aggregated into several spatially disjunct populations. Historical data indicate that some local populations were eliminated and that the regional metapopulation declined during the 1970s. Proximate causes of decline may have included hunting, severe winter weather, and the end of predator control, though the ultimate causes may relate to road construction and logging activity, which expanded after 1966. There has been no sport hunting since 1987, yet the caribou populations in the region appear to be declining. Based on serum progesterone levels, first conception by females occurred at 16 months and the overall pregnancy rate was 94%, and in addition the minimum parturition rate was 86%, all of which indicate adequate nutrition. The annual survival rate of adults was 84%, which is comparatively low, though similar to results from other studies on woodland caribou. We observed a low rate of calf recruitment (28 calves : 100 cows), wh...
159 citations
TL;DR: The reproductive performance of female Steller sea lions was examined in order to evaluate the hypothesis that low pup production was associated with nutritional stress and to assess the response of males to nutritional stress.
Abstract: We examined the reproductive performance of female Steller sea lions (Eumetopias jubatus) in order to evaluate the hypothesis that low pup production was associated with nutritional stress and to assess whether reduced birth rates could have been a factor in a recent large-scale decline in numbers. Nearly all (97%) sexually mature females were pregnant during early gestation. However, by late gestation, pregnancy rates had declined to 67 and 55% in the 1970s and 1980s, respectively, owing to reproductive failures. We found that body condition, as depicted by mass index and blubber index, had a positive effect on the probability that a female would be pregnant during late gestation. Age, age2, and lactation were also associated with pregnancy status during late gestation. These findings support the hypotheses that reproductive failures were associated with lowered nutritional status and that the resulting low birth rates were a proximate factor in the decline. We speculate that abortion is a part of the re...
137 citations
TL;DR: Estimates of mean body mass were derived for 106 living species of marine mammals from generalized survival models applied to growth curves published for 17 species of cetaceans and 13 species of pinnipeds.
Abstract: Generalized survival models were applied to growth curves published for 17 species of cetaceans (5 mysticetes, 12 odontocetes) and 13 species of pinnipeds (1 odobenid, 4 otariids, 8 phocids). The mean mass of all individuals in the population was calculated and plotted against the maximum body length reported for each species. The data showed strong linearity (on logarithmic scales), with three distinct clusters of points corresponding to the mysticetes (baleen whales), odontocetes (toothed whales), and pinnipeds (seals, sea lions, and walruses). Exceptions to this pattern were the sperm whales, which appeared to be more closely related to the mysticetes than to the odontocetes. Regression equations were applied to the maximum lengths reported for 76 species of marine mammals without published growth curves. Estimates of mean body mass were thus derived for 106 living species of marine mammals.
135 citations
TL;DR: Changes in distribution and terrain use of calving barren-ground caribou with increasing density of roads in the Kuparuk Development Area, an oil-field re-development area, are investigated.
Abstract: We investigated changes in distribution and terrain use of calving barren-ground caribou (Rangifer tarandus granti) with increasing density of roads in the Kuparuk Development Area, an oil-field re...
129 citations
TL;DR: The results suggest that aggression is less useful as a mode of competition in habitats with greater structural complexity, and Manipulating the structural complexity of the habitat may be a practical way of controlling the intensity of aggression and resource monopolization in groups of animals.
Abstract: We tested the predictions that an increase in the structural complexity of a habitat causes both a decrease in aggression and the monopolization of resources. Groups of three zebra fish (Danio rerio) were allowed to compete for food in a complex habitat with simulated vegetation and in a simple habitat with no vegetation. As predicted, both the levels of aggression by the dominant fish (P = 0.050) and the coefficient of variation of the amount of food eaten within a group (P = 0.020), a measure of food monopolization, were lower in the complex habitat than in the simple one. Fish that chased competitors more frequently ate more food in both habitats, but the relationship was stronger in the simple than in the complex habitat. Our results suggest that aggression is less useful as a mode of competition in habitats with greater structural complexity. Manipulating the structural complexity of the habitat may be a practical way of controlling the intensity of aggression and resource monopolization in groups of animals.
127 citations
TL;DR: The abundance of all small mammals combined was lower in forest patches isolated by logging than in contiguous forest or farm woodlots surrounded by agricultural land, and this pattern was consistent in all years, despite significant annual fluctuations in numbers of the boreal red-backed vole.
Abstract: To determine the effects of forest fragmentation on the abundance of small mammals, we livetrapped at edges and in the interior of forest patches in contiguous, logged, and agricultural landscapes in the southern boreal mixedwood forest of Saskatchewan. From 1994 to 1996, we captured 1548 small mammals (11 species) during 8172 trap-nights. The abundance of all small mammals combined was lower in forest patches isolated by logging than in contiguous forest or farm woodlots surrounded by agricultural land. This pattern was consistent in all years, despite significant annual fluctuations in numbers of the boreal red-backed vole (Clethrionomys gapperi), one of the most abundant species in our study area. Red squirrels (Tamiasciurus hudsonicus) and northern flying squirrels (Glaucomys sabrinus) were more abundant in farm woodlots. The abundance of deer mice (Peromyscus maniculatus) was significantly lower in forest patches surrounded by clearcuts, and we speculate that they may have used clearcuts more than forest patches. In contrast, the numbers of boreal red-backed voles were similar among landscapes. The only species showing a response to edge was the deer mouse, which was significantly more abundant at edges of farm woodlots than in interiors. We also found no significant difference in abundance of any species between small (10 ha) and large (>20 ha) farm woodlots. For most species, within-landscape attributes such as edge and patch size seemed to have little effect on their abundance. However, for a variety of reasons, small-mammal numbers seem to vary considerably among forest patches in different landscapes.
TL;DR: Sperm whale photoidentification data spanning 12 years of study around the Galapagos Islands were examined to investigate the size, variability, and stability of social units, suggesting that the benefits of remaining in a social unit usually outweigh selection for some optimal unit size.
Abstract: Sperm whale (Physeter macrocephalus) photoidentification data spanning 12 years of study around the Galapagos Islands were examined to investigate the size, variability, and stability of social units. Adult females and immature whales of both sexes have two types of associates: "constant companions," which are members of an individual's "stable" social unit, and "casual acquaintances," which are temporarily associating members of different units. We analysed long-term association patterns and calculated that individuals have a mean of 11.3 constant companions. Estimated social unit size ranged from 3 to 24 individuals. Evidence of splitting and merging of units and of transfer of individuals between units is presented. The estimated overall frequency of these unit-membership changes is 6.3% per individual per year. These forms of unit dynamics are rare in species with male dispersal and matrilineally related social groups, and cannot be easily explained in this species. There is considerable variation in unit size (perhaps caused by demographic processes), suggesting that the benefits of remaining in a social unit usually outweigh selection for some optimal unit size. However, the occurrence of merging and transfers suggests that the ecological or social cost/benefit of leaving one's matrilineal unit may sometimes outweigh the cost/benefit of staying. Resume : Des photographies individuelles de cachalots (Physeter macrocephalus), recouvrant une periode d'etude de 12 ans dans les Galapagos, ont servi a etudier la taille, la variabilite et la stabilite des groupes sociaux. Les femelles adultes et les individus immatures des deux sexes s'allient a deux types de compagnons : ils ont des « compagnons constants », qui sont des membres du meme groupe social « stable », et des « connaissances d'occasion » qui sont des membres d'autres groupes auxquels ils s'associent temporairement. Nous avons procede a une etude a long terme de ces associations et avons calcule qu'un individu a en moyenne 11,3 compagnons constants. Un groupe social contient de 3a2 4 individus. Nous avons observe des separations et des fusions au sein des groupes, de meme que des transferts d'individus d'un groupe a un autre. La frequence globale de ces changements d'appartenance a ete estimee a 6,3% par individu par annee. Ce type de dynamique au sein des groupes est rare chez des especes dont les mâles se dispersent et ou les groupes sociaux sont formes par affiliation maternelle, et il est impossible a expliquer chez cette espece. Il y a une variation considerable de la taille des groupes (peut-etre causee par des processus demographiques), ce qui semble indiquer que les benefices d'appartenir a un groupe social depassent generalement les benefices de la selection pour la taille optimale d'un groupe. Cependant, les fusions et transferts qui se produisent au sein des groupes indiquent que les couts/benefices ecologiques ou sociaux relies au fait de quitter son groupe d'affiliation maternelle depassent parfois les couts/benefices relies au fait d'y rester.
TL;DR: Six humpback whales tagged during March and April 1995 with satellite-monitored radio tags off Kaua´i, Hawai´i travelled independent, parallel courses toward the upper Gulf of Alaska on north-northeast headings, suggesting faster inter-island movement than had been previously thought.
Abstract: We examined inter-island movements and offshore migrations of six humpback whales (Megaptera novaeangliae) tagged during March and April 1995 with satellite-monitored radio tags off Kaua´i, Hawai´i...
TL;DR: The temperature differences within the clutch were larger in loggerhead than in green turtle nests, and the mean temperature over the entire incubation period is not a good indicator of sex ratio but can be used to predict the duration of incubationperiod.
Abstract: Temperatures of green turtle (Chelonia mydas) and loggerhead turtle (Caretta caretta) nests on the beaches of northern Cyprus and Turkey were examined. Electronic continuous-temperature recorders programmed by computer were placed at the top, middle, and bottom of the nests. The sex of 3-7 hatchlings from each level was determined from gonadal histology. The maximum temperature increase during the incubation period was 9.6oC for both species. The mean temperature during the middle third of the incubation period is a good indicator of the sex ratio of the clutch. The percentage of female embryos increased with temperature, 50% being female at 29°C. The mean temperature over the entire incubation period is not a good indicator of sex ratio but can be used to predict the duration of incubation period. The temperature differences within the clutch were larger in loggerhead than in green turtle nests. Eggs at the top of the nest experienced generally warmer (up to 1.4°C) conditions than eggs at the bottom of t...
TL;DR: Poor nutritional conditions may affect reproductive success through failure to rear a pup, and pup production the following year may also be reduced, resulting in a lower rate of pregnancy.
Abstract: The relationships between female reproductive parameters (fertility, pregnancy, and lactation status) and body mass, body condition, and body length in South African fur seals (Arctocephalus pusillus) were investigated over 4 years. Ovulation rate in every year was 100% despite interannual differences in female body condition index (BCI). The overall pregnancy rate was 79%. The proportion of pregnant females was related to BCI but not to body mass or body length. In good years, BCI decreased through the first part of the reproductive cycle to a minimum at implantation and increased again through pregnancy. In 1989, BCI declined over the whole reproductive cycle, and there was a higher proportion of nonpregnant females and failures of lactation. Thus, poor nutritional conditions may affect reproductive success through failure to rear a pup, and pup production the following year may also be reduced. This lower rate of pregnancy is partly explained by an increase in the incidence of spontaneous abortions, but other parameters such as a lower implantation rate are also likely to be involved. Resume : Dans cette etude nous examinons les relations entre, d'une part, les variables associees a la reproduction (fertilite, taux de gestation et de lactation) et, d'autre part, la masse, l'indice de condition physique (ICP) et la longueur du corps, chez des femelles de l'Otarie du Cap (Arctocephalus pusillus). Pour l'ensemble de la periode d'etude, le taux d'ovulation a ete de 100% malgre les differences inter-annuelles d'ICP des femelles, mais le taux de gestation n'a ete que de 79%. La proportion de femelles en gestation s'est averee en correlation avec l'ICP des femelles, mais la masse ou la longueur n'ont pas influence cette variable. Les annees ou les conditions alimentaires ont ete bonnes, l'ICP des femelles a diminue pendant la periode de preimplantation pour atteindre des valeurs minimales en periode d'implantation puis augmenter de nouveau pendant la gestation. En 1989, une mauvaise annee, l'ICP des femelles a diminue tout au cours du cycle reproducteur et i lyae u uneplus forte proportion de femelles non reproductrices et non nourricieres cette annee-la. Il semble donc que de mauvaises conditions alimentaires affectent le succes de la reproduction en entravant le succes de l'elevage du petit et en diminuant le taux de gestation. La diminution du taux de gestation s'explique partiellement par l'augmentation du nombre d'avortements et par le taux probablement plus faible d'implantation.
TL;DR: Predictive equations of total body fat and body mass from ultrasonographic fat measurements for application in live animals detected a strong linear relationship between ingesta-free bodyfat and rump fat thickness measured by ultrasonography.
Abstract: Lipids are the primary energy store of the body and estimation of these reserves provides an indication of nutritional status in moose (Alces alces). Estimates of total body fat enhance our underst...
TL;DR: The swim bladder of the oyster toadfish, Opsanus tau, has a distinctive heart shape with two anterior protrusions separated by a midline cleft that represents a compromise between opposing tendencies toward an omnidirectional sound source that would optimize a male's opportunity to attract females from any direction.
Abstract: The swim bladder of the oyster toadfish, Opsanus tau, has a distinctive heart shape with two anterior protrusions separated by a midline cleft. The lateral surfaces contain intrinsic muscles that meet at the caudal midline, but the rostromedial surface is muscle-free. We hypothesize that swim-bladder design represents a compromise between opposing tendencies toward (i) an omnidirectional sound source that would optimize a male's opportunity to attract females from any direction, and (ii) a directional sound source that would shield the nearby ears during sound production. To determine if the directionality of toadfish sound is consistent with this hypothesis, boatwhistle advertisement calls of individually identified males were recorded in the York River, Virginia, by means of two calibrated hydrophones and a waterproof recording system: one hydrophone was fixed 1 m in front of the fish and the second was roving. Boatwhistles in the horizontal plane propagated in a modified omnidirectional pattern that wa...
TL;DR: Sex and body size related differences in activity pattern and foraging range have important implications for the methodologies currently used to assess the population size, population energy requirements, and diet composition of coastal pinnipeds.
Abstract: Most pinnipeds disperse from centralised terrestrial sites to forage at sea, but the factors that result in variation in foraging-trip characteristics remain unclear. We investigated the influence of sex and body size on the summer foraging activit y of radio-tagged harbour seals ( Phoca vitulina) from Scotland. Mean foraging-trip duration (range 17-257 h) was strongly correlated with mean foraging range (range 4.3-55.0 km), but both were significantly shorter for females. The proportion of time spent at sea, mean trip duration, and mean foraging range were all positively related to body size. Comparison with data from other study areas suggests that both environmental and endogenous factors shape foraging characteristics in this species. These sex and body size related differences in activity pattern and foraging range have important implications for the methodologies currently used to assess the population size, population energy requirements, and diet composition of coastal pinnipeds.
TL;DR: The results of this study indicate that the presence of woody debris decreases intraspecific competition through visual isolation, allowing fish to reduce aggressive interactions and energy expenditure.
Abstract: We examined the effects of woody debris on the growth and behaviour of brown trout (Salmo trutta) in experimental stream channels. Two types of habitat were used in the study: a complex habitat created by placing woody debris on a gravel bed and a uniform habitat consisting of a gravel bed only. The experiment was run both outdoors with wild fish that fed on natural invertebrate drift and indoors with hatchery fish that were fed artificial food. In both treatments most of the fish lost mass. In all trials, however, the fish in the woody debris channel lost less mass than the fish in the control channel. Study of the fishes' behaviour revealed less swimming activity, less aggression, and less feeding activity in the woody debris channel than in the control channel. The results of this study indicate that the presence of woody debris decreases intraspecific competition through visual isolation, allowing fish to reduce aggressive interactions and energy expenditure.
TL;DR: Overall, high use of deer appeared to have been associated with increased vulnerability due to winter severity or, in the case of young fawns, inability to escape, and it is suspected that coyotes are forced to focus their hunting efforts on prey other than deer, regardless of density, owing to low vulnerability of deer.
Abstract: We investigated the influence of white-tailed deer (Odocoileus virginianus) and snowshoe hare (Lepus americanus) availability on the feeding habits of coyotes ( Canis latrans) in Nova Scotia from 1992 to 1997. We hypothesized that coyotes would switch from deer to hare as hare abundance increased. Based on the analysis of 2443 scats, deer and hare were the dominant food items. Other important food items included small mammals, and fruits during late summer. In areas where they were readily available, coyotes fed predominantly on hare during winter, with the use of deer declining as hare density increased. However, the functional response was not proportional to the changes in the relative densities of deer or hare. This was particularly evident at low deer densities, where coyotes continued to feed largely on deer, even in the presence of high hare densities. The consumption of deer fawns during June and July exceeded that of hare in all areas, despite high hare densities in some areas. Overall, high use of deer appeared to have been associated with increased vulnerability due to winter severity or, in the case of young fawns, inability to escape. During mild winters, we suspect that coyotes are forced to focus their hunting efforts on prey other than deer, regardless of density, owing to low vulnerability of deer. When severe winter conditions occur, coyotes switch to feeding mainly on deer.
TL;DR: The developmental rate, distribution on the host, and pathogenicity (skin damage) of salmon lice were tested on artificially infected sea trout post smolts, and skin damage became severe, especially on the preferred head and dorsal areas, causing mortality of the most heavily infected fish.
Abstract: The developmental rate, distribution on the host, and pathogenicity (skin damage) of salmon lice (Lepeophtheirus salmonis) were tested on artificially infected sea trout (Salmo trutta) post smolts. Male lice developed faster than females, taking approximately 29 and 38 days, respectively, to reach the adult stage at 10°C. During this time, infection intensity decreased. Less than 40% of the lice reached the adult stage, and their distribution changed from overdispersed towards a more random pattern. The chalimus larvae of the lice exhibited a preference for the gills and fins, especially the dorsal fin, and caused only minor skin damage. When the preadult and adult stages appeared, skin damage became severe, especially on the preferred head and dorsal areas, causing mortality of the most heavily infected fish.
TL;DR: No nucleotide differences were found, supporting the hypothesis that the profundal form of the quagga mussel is a phenotype of D. bugensis, not a separate species, and the presence of either a third dreISSenid mussel species in the Great Lakes or a previously unknown morphological phenotype of an existing dreissenid species is suggested.
Abstract: The discovery of a morphologically distinct dreissenid mussel in the profundal zone of Lake Erie suggests the presence of either a third dreissenid mussel species in the Great Lakes or a previously unknown morphological phenotype of an existing dreissenid species. We examined the morphometrics and molecular systematics of the zebra mussel (Dreissena polymorpha) and the profundal and epilimnetic forms of the quagga mussel (Dreissena bugensis) from Lakes Erie and Ontario. In an attempt to resolve the taxonomic status of the profundal form of the quagga mussel, we sequenced a 710 base pair fragment of the cytochrome oxidase subunit I mitochondrial gene of the two forms of the quagga mussel. No nucleotide differences were found, supporting the hypothesis that the profundal form of the quagga mussel is a phenotype of D. bugensis, not a separate species. In contrast, the second and third principal component scores from an analysis of the morphological variables shell length, shell width, shell height, and shell...
TL;DR: Dreissena polymorpha and Dreissena bugensis are two exotic species of dreissenid mussels introduced into the Great Lakes within the past decade.
Abstract: Dreissena polymorpha and Dreissena bugensis are two exotic species of dreissenid mussels introduced into the Great Lakes within the past decade. Dreissena bugensis profunda is a morphologically dis...
TL;DR: The aquatic stages of amphibians may be sensitive to increased levels of solar ultraviolet B radiation (UV-B) that have been observed at higher latitudes over the past several decades, but the effects on most species are unknown.
Abstract: The aquatic stages of amphibians may be sensitive to increased levels of solar ultraviolet B radiation (UV-B, 280–320 nm) that have been observed at higher latitudes over the past several decades, but the effects on most species are unknown. We exposed eggs and larvae of Hyla regilla and Rana aurora to three experimental treatments: (1) solar UV < 450 nm blocked (control), (2) ambient solar UV, and (3) solar UV-B enhanced 15 and 30% above ambient levels at midday to simulate conditions predicted for the next decades at midlatitudes. The rearing containers were covered with acrylic filters to provide the desired radiation regimes. Hatching success of H. regilla did not differ among the treatments and was 87.7, 71.8, and 87.1% in April 1995 and 94.0, 85.1, and 97.4% in May 1995 for the control, ambient, and enhanced UV-B treatments, respectively. In contrast, hatching success of R. aurora in the enhanced UV-B treatment (56.0%) was lower than in the ambient UV (89.8%) and control (81.0%) treatments. Larval s...
TL;DR: The echolocation calls of aerial-feeding bats at sites in Canada, Mexico, Brazil, and Zimbabwe were significantly dominated by frequencies between 20 and 60 kHz, although at the more tropicallocations some aerial- feeding bats used echlocation calls with most energy 60 kHz.
Abstract: Hunting aerial-feeding bats, species that take airborne prey (usually flying insects), use echolocation to detect, track,and assess targets. The echolocation calls of aerial-feeding bats at sites in Canada (British Columbia and Ontario), Mexico,Brazil, and Zimbabwe were significantly dominated by frequencies between 20 and 60 kHz, although at the more tropicallocations some aerial-feeding bats used echolocation calls with most energy 60 kHz. The impact of frequency-specificattenuation, perhaps combined with frequency-specific, hearing-based defenses of some insects, suggests that by usingecholocation calls 60 kHz would be less conspicuous to the insects. We found two patterns of echolocation-callbehaviour. Most adjacent echolocation calls, and all that were dominated by sounds >20 kHz, showed large (80%) overlap inbandwidth. The other pattern involved much less...
TL;DR: The pathogenic protozoan that has caused high mortalities among cultured Japanese scallops, Patinopecten yessoensis, is described as a new species, Perkinsus qugwadi, which multiplication occurred in the intercellular spaces and haemolymph sinuses of all organs of the host.
Abstract: The pathogenic protozoan that has caused high mortalities among cultured Japanese scallops, Patinopecten yessoensis (introduced into British Columbia in 1983), is described as a new species, Perkinsus qugwadi. As in other species in the genus Perkinsus, vegetative multiplication occurred in the intercellular spaces and haemolymph sinuses of all organs of the host. Although the morphology of all developmental stages was similar to that of other Perkinsus spp., differences were observed in the ultrastructural morphology of some organelles in the biflagellate zoospore of P. qugwadi. Also, unlike all other Perkinsus spp., P. qugwadi multiplied and was pathogenic at low temperatures (8-15°C), the development of zoospores was found to occur only within the interstitial spaces of living hosts (and only in some heavily infected juvenile scallops that were less than 50 mm in valve height), and the thioglycollate culture technique that is a diagnostic test for all previously described Perkinsus spp. was negative fo...
TL;DR: To investigate the influence of temperature on the length of internesting periods in loggerhead turtles and green turtles, body temperature and water temperature and depth for free-ranging turtles were monitored using micro data loggers and Arrhenius' equation was used to describe the quantitative relationships.
Abstract: To investigate the influence of temperature on the length of internesting periods in loggerhead turtles (Caretta caretta) and green turtles (Chelonia mydas), body temperature and water temperature and depth for free-ranging turtles were monitored during internesting periods using micro data loggers. Body mass and clutch size were also measured. The experiments were conducted at nesting beaches in the Japanese archipelago from 1989 through 1996. Internesting interval was significantly negatively correlated with mean body temperature and mean water temperature. Internesting intervals for some turtles exceeded 21 d when they experienced low water temperatures. Arrhenius' equation was used to describe the quantitative relationships, and Q10 values of 3.1 for water temperature and 3.4 for body temperature were calculated. There was no significant relationship between either clutch size or body mass and internesting interval. Body temperatures were kept higher than water temperatures throughout internesting per...
TL;DR: Size at birth, growth, and early survival of northern fur seals from birth to weaning at Bering Island, Russia, over 8 breeding seasons from 1982 to 1989 was investigated and subsequent growth in mass and length was correlated with birth size.
Abstract: We investigated size at birth, growth, and early survival of northern fur seals (Callorhinus ursinus) from birth to weaning at Bering Island, Russia, over 8 breeding seasons from 1982 to 1989. One ...
TL;DR: Animals that scatter-hoard seeds frequently dig up and recache them at new locations, and the effect of the recaching of seeds on plant reproductive success was studied in the Sierra Nevada of western Nevada.
Abstract: Animals that scatter-hoard seeds frequently dig up and recache them at new locations. The effect of the recaching of seeds on plant reproductive success was studied in the Sierra Nevada of western ...
TL;DR: Incubation temperatures in loggerhead sea turtle (Caretta caretta) nests were examined as a method for predicting hatchling sex ratios and during the thermosensitive period, temperatures in the center of the egg mass were significantly higher than...
Abstract: Incubation temperatures in loggerhead sea turtle (Caretta caretta) nests were examined as a method for predicting hatchling sex ratios. Incubation temperatures were recorded in 40 nests that were laid on Hutchinson Island, Florida. Small temperature data loggers were placed directly in nests (in the center of the egg mass) and were programmed to record temperature every 1.2 h for the entire incubation period. Nests laid during the early, middle, and late portions of the peak nesting period (June and July) were examined. The nests were equally distributed on an untreated beach and a beach that had been artificially supplemented with sand to compensate for erosion. Three nests received multiple data loggers to assess temperature variation within the nest. The average daily temperatures within these nests varied from a maximum of 2.1°C at the top of the egg chamber to a minimum of 0.4°C at the bottom. During the thermosensitive period, temperatures in the center of the egg mass were significantly higher than...