Eric Demers

Activity patterns of largemouth and smallmouth bass determined with electromyogram biotelemetry

Abstract Electromyogram (EMG) biotelemetry was used to assess activity patterns for adult free-swimming largemouth bass Micropterus salmoides and smallmouth bass Micropterus dolomieu. We first conducted laboratory respirometry trials and found a strong association between EMG signal and swimming activity which indicated that EMG biotelemetry could be used to assess activity of wild fish. A field study confirmed that both species exhibit diurnal activity patterns. When EMG activity was compared with estimates of swimming activity from location tracking, elevated EMG activity was often recorded for apparently stationary fish. These observations suggested that fish activity at spatial and temporal scales too small for detection by location tracking may account for a significant proportion of daily activity. We argue that EMG biotelemetry, combined with location tracking, may be a versatile tool for application to a wide variety of problems in fisheries biology, including the study of physiological energetics...

Prevalence of HIV and hepatitis C virus infections among inmates of Quebec provincial prisons

Background: To determine the prevalence of HIV and hepatitis C virus (HCV) infections and examine risk factors for these infections among inmates in Quebec provincial prisons. Methods: Anonymous cross-sectional data were collected from January to June 2003 for men (n = 1357) and women (n = 250) who agreed to participate in the study and who completed a self-administrated questionnaire and provided saliva samples. Results: The prevalence of HIV infection was 2.3% among the male participants and 8.8% among the female participants. The corresponding prevalence of HCV infection was 16.6% and 29.2%, respectively. The most important risk factor was injection drug use. The prevalence of HIV infection was 7.2% among the male injection drug users and 0.5% among the male non-users. Among the women, the rate was 20.6% among the injection drug users, whereas none of the non-users was HIV positive. The prevalence of HCV infection was 53.3% among the male injection drug users and 2.6% among the male non-users; the corresponding values among the women were 63.6% and 3.5%. Interpretation: HIV and HCV infections constitute an important public health problem in prison, where the prevalence is affected mainly by a high percentage of injection drug use among inmates.

Zooplankton spatial patterns in two lakes with contrasting fish community structure

Horizontal and temporal patterns in crustacean zooplankton communities were analyzed in two small, oligotrophic lakes which were morphologically and chemically similar, but had contrasting fish communities. Ranger Lake was dominated by two bass species and the planktivores numbered < 25 ind. ha−1. Mouse Lake had no large piscivores and planktivores numbered > 1200 ind. ha−1. There were significant differences in the distribution of zooplankton taxa and size classes between sampling stations. In Ranger Lake, the smallest size classes were more abundant at the deeper stations and the larger individuals were more abundant at the shallower stations. In Mouse Lake, the smaller individuals were more common at the shallow stations and the larger individuals were more common at the deeper stations. These differences suggest medium scale patterns induced by vectorial forces, but modified by species specific migration patterns. We tested the hypothesis that horizontal heterogeneity should be influenced by planktivore density and found that none of the taxa showed significant between-lake differences in the variance-mean regressions. We also tested the hypothesis that larger taxa should be more heterogeneous and we found that cladocerans were more heterogeneous than copepods and nauplii. In terms of sampling methodology our data suggest that the between-station variability was so high that a single mid-lake sample would certainly lead to completely unacceptable errors in the estimation of population densities and biomasses.

Stability of oligotrophic and eutrophic planktonic communities after disturbance by fish

The objective of our study was to investigate the relationship between resource availability and stability (resistance and resilience) in freshwater zooplankton communities and to assess their recovery after predation impact. We used 12 in-lake enclosures (3.8 m diameter x 3.5 m deep) treated with 6 combinations (replication n = 2) involving 2 nutrient concentrations and 3 fish densities. The experiment lasted 14 weeks and zooplankton and water chemistry were monitored throughout. The protocol involved 3 treatment-specific time periods: (a) the before fish treatment period comprising the first 2 weeks, (b) the during fish treatment period comprising the next 5 weeks, and (c) the after fish treatment period which lasted 6 weeks following fish removal. In terms of biomass and numbers, we found that the zooplankton in the fish treatments varied most and that the eutrophic biomasses were higher. In terms of stability, the zooplankton in the oligotrophic enclosures were more resistant to disturbance by fish and were more resilient after the fish were removed. Conversely, zooplankton communities in the eutrophic enclosures responded more strongly to fish predation and were less likely to return to the pre-disturbance community structure. Zooplankton at the top of the food web (top carnivores) were the most susceptible to planktivory, but recovered as quickly as the other zooplankton groups. Studies of trophic structure showed that the omnivorous, intermediate species group, had the highest species interaction levels and contributed most to community recovery in all of the treatments. Resource availability and disturbance magnitude are likely to determine post-disturbance biomass production. The stability of low productive systems seems to be maintained through strong food web links, while more productive systems are more loosely structured.

Cutaneous leishmaniasis in a returning traveller

An otherwise healthy 42-year-old man presented with a small erythematous nodule on the superior part of his right ear and substantial swelling of the entire pinna ([Figure 1A][1]), which he had first noticed 2 weeks before presentation. There were no other lesions, palpable lymphadenopathy or

Testing problem solving in turkey vultures (Cathartes aura) using the string-pulling test.

Abstract To examine problem solving in turkey vultures (Cathartes aura), six captive vultures were presented with a string-pulling task, which involved drawing a string up to access food. This test has been used to assess cognition in many bird species. A small piece of meat suspended by a string was attached to a perch. Two birds solved the problem without apparent trial-and-error learning; a third bird solved the problem after observing a successful bird, suggesting that this individual learned from the other vulture. The remaining birds failed to complete the task. The successful birds significantly reduced the time needed to solve the task from early trials compared to late trials, suggesting that they had learned to solve the problem and improved their technique. The successful vultures solved the problem in a novel way: they pulled the string through their beak with their tongue, and may have gathered the string in their crop until the food was in reach. In contrast, ravens, parrots and finches use a stepwise process; they pull the string up, tuck it under foot, and reach down to pull up another length. As scavengers, turkey vultures use their beak for tearing and ripping at carcasses, but possess large, flat, webbed feet that are ill-suited to pulling or grasping. The ability to solve this problem and the novel approach used by the turkey vultures in this study may be a result of the unique evolutionary pressures imposed on this scavenging species.

Density-Dependent Growth in Juvenile Sockeye Salmon (Oncorhynchus Nerka)

Data gathered over 77 lake-years from 4 coastal British Columbia sockeye salmon nursery lakes suggest that density-dependent growth reductions are only possible at exceptionally high fry densities. In Great Central Lake (n=33 years) and Sproat Lakes (n=30 years) there was no relationship between smolt weight and mean summer fry densities ranging from 760-3800 fry ha -1 . However, in two years when Sproat Lake fry densities were unusually high (1983=5183 ha -1 , 1996=4801 ha -1 ) smolt weights were among the lowest recorded. In Woss and Vernon lakes (n=14 lake-years), there were significant bottom-up relationships between fall-fry weights and zooplankton biomass, but no relationships between December-fry weights and average fry densities (range 331-1361 ha -1 ), nor were there significant top-down relationships between fry densities and average zooplankton biomass. Comparisons of zooplankton production with bioenergetic-based fry consumption, suggested that the carrying capacity for Vernon Lake which had the highest rate of zooplankton production, was 12,700 fry ha -1 , and for Sproat Lake which had the lowest zooplankton production, was 5200 fry ha -1 . We conclude that fry densities in the range commonly observed for British Columbia coastal lakes (i.e. 500-4000 ha -1 ) cannot cause density-dependent reductions in prey biomass or fry growth rates. Further research is necessary.