ALBERT

Notes: Swimming speed and activity costs of dace (Phoxinus eos × P. neogaeus) were estimated in the field using underwater video cameras. Activity costs were estimated by converting swimming speeds and the number of movements into swimming costs. Average swimming speed ranged from 6.7 to 12.2 cm.s−1 across 2 h periods and varied significantly among dates and time of day. The time spent swimming by dace ranged from 616 to 17 640 s 2 h−1. Activity costs per 2h period ranged from 2.1 to 4O.2J 2h−1 and were strongly correlated to the time spent swimming. Daily activity cost estimated using the cameras averaged 128.9J day−1 and was equivalent to 1.7 times the standard metabolic rate. Activity cost predicted using a bioenergetic model in conjunction with independent estimates of consumption and growth rates averaged 138.8J day−1. This study indicated that swimming characteristics and activity costs of dace varied significantly both within and among days. These analyses also indicated that equally valid activity costs for fish in the field can be estimated using video cameras and the difference between Consumption and growth rates.

Notes: Domestication has been shown to have an effect on morphology and behaviour of Atlantic salmon (Salmo salar). We compared swimming costs of three groups of juvenile Atlantic salmon subject to different levels of domestication: (1) wild fish; (2) first generation farmed fish origination from wild genitors; and (2) seventh generation farmed fish originating from Norwegian aquaculture stocks. We assessed swimming costs under two types of turbulent flow (one mean flow velocity of 23 cm s−1 and two standard deviations of flow velocity of 5 and 8 cm s−1). Respirometry experiments were conducted with fish in a mass range of 5–15 g wet at a water temperature of 15° C. Our results confirm (1) that net swimming costs are affected by different levels of turbulence such that, for a given mean flow velocity, fish spent 1·5-times more energy as turbulence increased, (2) that domesticated fish differed in their morphology (having deeper bodies and smaller fins) and in their net swimming costs (being up to 30·3% higher than for wild fish) and (3) that swimming cost models developed for farmed fish may be also be applied to wild fish in turbulent environments.

Notes: The feeding behaviour of juvenile Atlantic salmon Salmo salar in the Sainte-Marguerite River, Quebec, Canada, varied with the characteristics of turbulent flow. Simulations indicated that juveniles would decrease their swimming costs during attacks by 19·8% in low and by 31·1% in high turbulent conditions by initiating movements in low-speed flow events. The real swimming costs did not differ from the swimming costs estimated for a situation where fish initiate their movements at randomly selected flow velocities. The juvenile Atlantic salmon did not seem to prefer low-speed flow events when initiating their movements. The proportion of time used for movements by fish decreased with an increase in the mean and the s.d. of the flow velocity.

Notes: No significant differences were found in the time budget (time spent in feeding, moving and stationary), attack rate (number of feeding bouts min−1), and microhabitat use of juvenile (1+ years) littoral and pelagic brook charr Salvelinus fontinalis at 2 and 4 m depth, when restricted to feeding in pelagic enclosures. In contrast, fish of the littoral form allocated significantly more time than pelagic ones to feeding, moving and in total activity at 3 m depth. No significant differences were found in attack rate between the two forms at any given depth. Based on the mean for the water column (all depths pooled), however, fish of the littoral form executed a significantly higher attack rate than fish of the pelagic one. In multiple regressions analyses, the best predictors of time allocated to feeding and attack rate were the dummy variable ‘form’ (littoral individuals spend significantly more time in feeding than pelagic ones), light intensity at the surface (negative) and water temperature (positive), and explained 48 and 55% of these variations, respectively. Time allocated to moving was only explained by water temperature (negative) and explained 43% of the variation. Time in a stationary position was best explained by water temperature (negative) and light intensity at the surface (positive), explaining 52% of the variation. The results of this study support the hypothesis that littoral brook charr spend more energy in foraging than pelagic ones when restricted to feeding in the pelagic habitat, and thus that trophic diversification is adaptive in this species.

Notes: SUMMARY 1. The objective of this study was to evaluate the effects of zooplankton biomass (as a measure of density), fish biomass, light intensity and water temperature on the attack rate and swimming characteristics (i.e. swimming speed and angle of turn) of juvenile (1+) brook charr (Salvelinus fontinalis) in field enclosures. We used a portable underwater camera system in a series of pelagic enclosures to quantify the feeding behaviour of brook charr over a gradient of natural conditions.2. In simple linear or non-linear regression models we found (i) that attack rate and angle of turn were positively related to water temperature, (ii) that attack rate and swimming speed were positively related to zooplankton biomass and light intensity and (iii) that attack rate was positively related to swimming speed. In multiple regression models, fish biomass, light intensity and variance of the angle of turn accounted for 87% of the variation in attack rate. Light intensity and water temperature accounted for 86% of the variation in swimming speed. Fish gut fullness and attack rate accounted for 83% of the variation in the variance of the angle of turn executed by fish.3. The increase in the number of attacks as zooplankton biomass increases conforms to the general positive functional response observed in other fish species. Our results also support the hypothesis that swimming speed increases with prey biomass. We did not observe a plateau in attack rate as zooplankton biomass increased. As our experiments were performed under natural biotic and abiotic conditions, factors other than zooplankton biomass might affect or limit this response, such as water temperature and light intensity.4. Because zooplankton biomass was correlated with water temperature and light intensity, it was not possible to evaluate the independent contribution of these factors on the attack rate and swimming characteristics (swimming speeds and angle of turn) of brook charr. However, this study highlighted the impact of these factors on the feeding behaviour of juvenile brook charr when feeding in the pelagic habitat under natural conditions, and their importance in future models of optimal foraging and fish habitat quality.

Notes: The number of visible Atlantic salmon Salmo salar parr in the Sainte-Marguerite River, Québec, increased between 2030 and 2230 hours then remained relatively stable until 0230 hours. Moon phase did not appear to influence the number of visible parr. There were more fish closer to the shore than to the middle of the stream.

Notes: Nocturnal underwater counts of Atlantic salmon Salmo salar parr were made on four consecutive occasions (two lunar cycles, samplings at both the full and new moon) at four 40 m long sites in the Sainte-Marguerite River, Québec, Canada, between 30 June and 14 August 2003. Atlantic salmon parr counts did not differ significantly between moon phases. Cloud cover ranged from 0 to 100% during the study, and had no significant effect on parr counts. There were significantly more Atlantic salmon parr in the near shore than in the midstream areas. The findings of this study suggest that the sampling strategy of summer studies aimed at assessing population abundance or developing habitat quality models can be designed without taking moon phase or cloud cover into consideration, but it should account for the higher relative abundance of Atlantic salmon parr in the near shore areas as compared to areas closer to the middle of streams.

Notes: We tested the hypothesis that the energetics of swimming in a flume accurately represent the costs of various spontaneous movements using empirical relationships between fish swimming costs, weight, and speed for three swimming patterns: (1) ‘forced swimming’ corresponded to movements adopted by fish forced to swim against a unidirectional current of constant velocity; (2) ‘directed swimming’ was defined as quasi-rectilinear movements executed at relatively constant speeds in a stationary body of water and (3) ‘routine swimming’ was characterized by marked changes in swimming direction and speed. Weight and speed explained between 76% (routine swimming) and 80% (forced swimming) of net swimming cost variability. Net costs associated with different swimming patterns were compared using ratios of model predictions (swimming cost ratio; SCR) for various weight and speed combinations. Routine swimming was the most expensive swimming pattern (SCR for routine and forced swimming =6.4 to 14.0) followed by directed (SCR for directed and forced swimming =0.9 to 2.8), and forced swimming. The magnitude of the difference between the net costs of forced and spontaneous swimming increases with movement complexity and decreases as fish weight increases.

Notes: The results of beach seining were compared with visual surveys, in habitats showing a gradient of macrophyte densities in Lake Drouin, Québec, Canada. Six community descriptors (species density, total fish density, relative abundance per species, presence or absence of given species, size structure of the fish community and total biomass of the fish community) were used to compare the sampling methods. Most of the fish community descriptors obtained by visual surveys were estimated with an accuracy similar to that of beach seining. Both methods sampled the same number of species (eight out of nine). Visual surveys assessed the relative abundance of the yellow perch Perca flavescens and white sucker Catostomus commersoni with an higher accuracy than the beach seine. The greatest discrepancies between the two sampling methods were for total fish density and the total fish biomass. Because of the sampling strategy, both descriptors were underestimated by visual surveys, notably in the higher macrophyte density. In a broad community survey to determine the relative importance of species abundance, the visual survey was effective and could be used to develop a within-lake regular and fine-scale sampling design of the spatial arrangement of fish communities and their habitats.

Notes: The validity of a hydroacoustic procedure was assessed using a combination of horizontal and vertical scanning to map the distribution of targets and to estimate target density in a shallow lake. Three distribution patterns were created using 37–50 artificial targets (metal hex nuts) anchored at known positions. Real and acoustic maps were qualitatively similar. Aggregation indices estimated by hydroacoustics were within 15% of the real values. Target density ranged from 1 to 8 targets per 100 m−3. Estimated target densities were within one target of the real values for 88% of our observations. The variable angle approach was used also to monitor daily and seasonal variations in fish distribution and relative abundance outside the littoral zone. Dace Phoxinus eos × P. neogaeus appeared to use the littoral as a refuge during the day and to migrate to the pelagic zone at dusk. The movements of dace outside the littoral zone were limited to the months of June-August. The variable angle acoustic approach can be useful to estimate fish distribution and relative abundance in shallow lakes.