Diel Habitat Use Research Articles

Size-structured diel use of river banks by fish

We examined the role of body size in the diel use of river banks by fish and the abundance of piscivorous fishes to determine if predation pressure influences diel habitat use. We hypothesised that the mean standard length (SL) of non-piscivorous fish would decrease at night. Fish were sampled via point sampling by electrofishing every 3-4 h over three 24-h periods (late August 1992, early September 1993, late May 1994) along two adjacent stretches of bank (shallow sand, steep boulder) of the River Morava, Czech Republic. Gill netting in mid-channel adjacent to the sand bank was also used in 1993 to determine predator abundance. Analysis of variance and size-class ordination revealed higher numbers of smaller fish were captured at night along the banks than during the day, being in most cases significant. In almost all cases (all years and along all bank types), the standard length (SL) of non-piscivorous fishes was significantly lower during hours of darkness, in particular near midnight. Conversely, the SL of the non-piscivorous fishes in August 1993 was significantly higher in the gill nets during hours of darkness. Size class ordination and electivity indices revealed that bitterling Rhodeus sericeus in August 1992 were distributed according to size along the sand bank (smaller size classes) and the boulder bank (larger size classes); also, equivalent or adjacent size classes of Rutilus rutilus (41-50, 51-60, 61-70, 71-80, 81-105 mm SL), a large bodied species, and Gobio albipinnatus (26-50, 51-60, 61-70, 71-80, 81-90mm SL), a small-bodied species, co-exploited both types of river bank, moving to the sand bank at night, a possible example of recruitment bottleneck. In May 1994, smaller size classes of Leuciscus leuciscus (78-84, 85-90, 90-108 mm SL) and L. cephalus (63-99, 100-149, ≥ 150 mm SL) preferred the sand and boulder banks, respectively, with the largest sizes of the two species occurring together more often than expected along both banks. The results generally support our hypothesis, suggesting that shallow river shorelines represent important night-time refuges from predation for the smaller size classes of fish, thus constituting crucial life-history habitat important for the recruitment of many riverine fishes.

Habitat segregation and interactive effects of multiple predators on a prey assemblage

1. In a field experiment we examined the interactive effects of two common predators of zooplankton, bluegill sunfish (Lepomis macrochirus) and Chaoborus spp. on the growth rate and habitat use of three congeneric prey species (Daphnia). Bluegill and Chaoborus both consume Daphnia, but bluegill also prey on Chaoborus. The prey species, Daphnia pulicaria, D. rosea and D. retrocurva, differed in body size and vertical distribution. We expected the largest species, D. pulicaria, to be most vulnerable to fish predation and the smallest species, D. retrocurva, to be most vulnerable to Chaoborus predation.2. As we expected, the population growth rate of D. pulicaria was significantly reduced by fish. However, Chaoborus also significantly reduced the growth rate of this species. No significant interaction effect was detected, indicating that the effect of these predators was additive. The growth rates of D. rosea and D. retrocurva were significantly reduced by Chaoborus, but a significant interaction effect indicated that the effect of Chaoborus was stronger in the absence of fish than when fish were present. Therefore the impact of Chaoborus and fish on D. rosea and D. retrocurva was non‐additive. The interactive effect of the two predators on D. retrocurva was greater in magnitude than on D. rosea.3. In the absence of predators, the three Daphnia species showed no differences in mean habitat depth between day and night. Both predators significantly affected diel habitat use of D. pulicaria and D. rosea. Fish caused both of these Daphnia species to move deeper during the day, whereas Chaoborus caused Daphnia to move into shallower water at night. Daphnia retrocurva tended to migrate upwards at night in all predator treatments, but no significant differences in migration were observed among the predator treatments. The effects of predators on habitat use were not interactive for any prey species.4. Our results suggest that body size, habitat use and the diel migratory response to predators are important factors mediating the interactive effects of multiple predator types on zooplankton.

Diel Movement and Habitat Use of California Golden Trout in the Golden Trout Wilderness, California

I used radio transmitters to determine the diel habitat use and movement patterns of California golden trout Oncorhynchus mykiss aquabonita inside and outside cattle exclosures on the South Fork Kern River, Golden Trout Wilderness, California. Twenty-three golden trout were monitored from September 10 to 19, 1993, during 216 diel-tracking hours at four study sites in upper and lower Ramshaw Meadow. No differences in distances moved or home ranges were detected between golden trout inside and outside exclosures. Mean home ranges were 18.5–54.0 m inside the two exclosure sites and 36.0–68.7 m outside the two exclosures. Most golden trout were found within 5 m of their previously recorded location at both upper (93.5% of 521 observations) and lower (92% of 394 observations) Ramshaw Meadow sites. Movement of individual fish varied: five fish moved less than 5 m throughout the 10-d study period, whereas 12 fish moved 100–608 m. Golden trout were active both day and night, and I observed them feeding throughout the night, even when water temperatures were as low as 2°C. At all study sites inside and outside exclosures, golden trout used three macrohabitats (pools, runs, and riffles) but selected pools in higher proportions than the more available runs. Throughout the study, golden trout were associated with nine habitat features (undercut banks, willows, bare banks, collapsed banks, open channel, aquatic vegetation, sedge, boulders, or rootwads) but were most commonly found near sedge and undercut banks.

Size-Dependent Diel Foraging Periodicity of a Mayfly Grazer in Streams with and without Fish

We tested the hypothesis that predation risk from diurnal fish influences the diel foraging periodicity of the mayfly grazer, Baetis tricaudatus Dodds, in a size-dependent manner by examining habitat use and foraging activity of mayflies in streams with and without these fish predators. In each stream diel habitat use was determined by counting the number of small (3 mm total length) and large (6 mm total length) Baetis larvae foraging on the upper surfaces of replicate, natural cobble during 4-8 sampling periods within a 24-h cycle over three seasons. Additionally, larvae were collected and preserved so that the dial periodicity in gut fullness could be determined