Diel vertical and offshore-inshore movements of anchovies off the central Baja California coast

During the night anchovies were observed in the deep offshore oceanic and intermediate slope zones off the Baja California coast, Mexico, in high abundance. Anchovies moved towards the shallow inshore neritic zone in low density groups, returning at dawn to deeper depth strata. During the day, abundances were reduced drastically and those observed were forming compact and discrete schools at deeper depth strata. Anchovy and euphausiid abundance, as recorded by the echosounder, Were positively correlated.     

Lateral migrations of fishes between floodplain lakes and their drainage channels at the Lower Rhine: diel and seasonal aspects

Although the total migratory activity of fishes from floodplain lakes in the Lower Rhine (Germany) into the connected drainage channels, estimated using electrofishing, fyke nets and visual observations, was low during summer 1997, conspicuous diel migrations of adult bream Abramis brama in June and July were recorded in one of the channels studied. A considerable proportion of the population of the floodplain lake immigrated into the channel at dusk and left it at dawn. During two winters (1994–1995, 1997–1998) the abundance of fishes increased considerably in the channels. The winter migrations, studied in detail in one of the channels in 1997–1998, started in late October, when the water temperature dropped below 10° C. In contrast to the mean of 500 fishes per 100 m channel length between May and October, >5000 fishes were found from November to March, with maximum values of >50 000 fishes per 100 m channel length in February 1998. More than 90% of these shoals were 0+ year fishes, dominated by roach Rutilus rutilus , bream, perch Perca fluviatilis and rudd Scardinius erythrophthalmus . These shoals entered the channel at sunrise and left it around sunset. Generally, the 0+ year fishes in the shoals swam separately from the older fishes, and different reactions towards the attack of predatory fishes were observed. The migrating shoals of juvenile fishes during the winter were interpreted as a strategy to minimize predation risk.     

No sibling odor preference in juvenile three-spined sticklebacks

Laboratory-bred juvenile three-spined sticklebacks from 11 sibshipsdid notprefer to shoal with their siblings when they were offeredthe choice betweenodor from unfamiliar siblings and non-kinin a fluviarium, although the powerfor finding a significantpreference was very high (0.99). The test fishpreferred theside where odor from the heavier shoal was supplied; this showsthatthey could appreciate odor cues from conspecifics in our apparatusandshould have preferred their siblings if such a preferenceexists. Our resultsare compatible with theoretical predictionsbut are at variance with previousfindings by other authors.We used independent replicates in a blind protocolwith strictrandomization of fish and procedures.     

Schooling preferences for familiar fish in the guppy, Poecilia reticulata

Although schooling behaviour is an important antipredator response of guppies ( Poecilia reticulata ) in Trinidad it is not known whether fish elect to school with particular individuals. Familiarity is a simple mechanism that could lead to non-random associations within schools. In this paper we test the idea that prior experience of particular individuals influences the choice of partners during schooling. We show (in a laboratory study) that female guppies prefer to associate with familiar individuals. However, we are unable to detect any schooling preference for unfamiliar females from the same population.     

Diel activity patterns of juvenile Atlantic salmon in rivers with summer water temperature near the temperature‐dependent suppression of diurnal activity

Direct day and night underwater observations of juvenile Atlantic salmon Salmo salar during summer and autumn showed a duality in response to temperature between 7 and 11° C for young‐of‐the‐year (YOY) Atlantic salmon. They were predominantly diurnal in early summer and nocturnal in late summer although water temperatures were similar. Post‐YOY Atlantic salmon did not show a strong response to temperature as they were mostly nocturnal during the study period. It is suggested that the difference in activity patterns between YOY and post‐YOY Atlantic salmon can be explained by size‐dependent trade‐off between growth and predation risk.     

Laboratory studies on the effects of thermal change on the behaviour and distribution of juvenile chum salmon in sea water

Schooling chum salmon Oncorhynchus keta were biased towards the water surface (median position <1 m) under isothermal conditions (10° C) in a water column simulator (WCS). Thermal stratification (24/10° C) inhibited upward movement with fish congregating at the thermocline and displaying a clear avoidance of potentially lethal surface waters. A tri-phase model based on piece-wise nonlinear regression was used to describe the distribution shifts of chum salmon during a change from isothermal to thermally stratified conditions. Fish distribution was consistent with thermoregulatory behaviour and exhibited 'attraction', 'preference' and 'avoidance' phases. The thermal preference of 50% of the fish lay between 12·2 and 20·2° C, however, >83·5% of the fish occupied a 'preferred' temperature range of 13·7–17·9° C. The mean temperature at which 50% of chum salmon avoided rising temperature by shifting deeper in the water column and using the cooler thermocline was 20·2° C, and 90% avoidance occurred at 22·9° C. Behavioural responses to thermal stratification were consistent amongst underyearling fish of differing size and age.     

On the diel rhythms in metabolism and activity of post-hatching lesser spotted dogfish, Scyliorhinus canicula

The diel rhythms in metabolic rate ( M_R ) and activity level ( A_L ) were measured for single post-hatching dogfish (weight range, 2.76–10.61 g) at 15° C by the indirect calorimetric method of rate of oxygen consumption ( V O₂) and by video-observation respectively, over a period of 72 b. The mean VO ₂ increased from 62.0 (s.e. 2.9) mg O₂ kg⁻¹ h⁻¹ in the daylight hours to 85.5 (s.e. 3.1) mg O₂ kg⁻¹ h⁻¹ during the dark (light regíme, 12 h L: 12 h D). The simultaneous measurement of A _L also showed mean night elevation from 0.6 (s.e. 0.2) min h⁻¹ in the light phase to 14.5 (s.e. 1.6) min h⁻¹ during the darkness. Bimodal nocturnal activity (BNA) was exhibited by the post-hatching dogfish within the 12 h dark period, with V O₂ increasing from 71.4 (s.e. 2.8) mg O₂ kg⁻¹ h⁻¹ before 01.00 hours to 99.5 (s.e. 4.2) mg O₂ kg⁻¹ h⁻¹ after 01.00 hours. Similarly, A _L also increased from 8.9 (s.e. I.7)min h⁻¹ before 01.00 hours to 21.1 (s.e. 2.8) min h⁻¹ after 01.00 hours. The importance of the results presented to the natural behavioural ecology of the hatching dogfish are discussed.     

Archival Tagging Of School Shark, Galeorhinus Galeus, in Australia: Initial Results

Archival tags were used to study the movement and depth behaviour of school sharks, Galeorhinus galeus, in southern australia. Thirty fish were tagged in late 1997, and to date there have been nine recaptures (30% recapture rate). Periods at liberty varied from 8 days to 18 months. The sharks spent about 80% of their time on the continental shelf, and appeared to swim close to the bottom during the day. At night they often ascended for periods of up to several hours, except at times around the full moon. When in deep water, the sharks typically descended at dawn to depths of up to 600m, before ascending at dusk. It was not possible to use the light data from the tags to estimate position when the sharks were in deep water, because they were often at depths beyond the sensitivity of the tag. In shallower water, longitude was estimated from the light data but latitude was estimated from the maximum daily depth, assuming the fish were on the bottom. The timing of the dives in deepwater appeared sufficiently regular to offer the prospect of using it to estimate longitude. We propose future research using archival tags on this species should address questions about female reproductive migrations, pelagic behaviour and vertical movements.