Seasonal habitat use of three predatory fishes in a freshwater ecosystem

To understand the spatiotemporal overlap in the habitat use of sympatric predators, we studied longitudinal activity and reservoir section and depth use of pike (Esox lucius), pikeperch (Sander lucioerca) and catfsh (Silurus glanis) in the Římov Reservoir, using an autonomous telemetry system for 11 months. We found signifcant diferences among these species in studied parameters that varied considerably over tracked period. Pike consistently used the same sections of the reservoir, while pikeperch and catfsh frequently visited a tributary during the warm season (late spring and early autumn), and moved closer to the dam during the cold season (late autumn to early spring). Pike longitudinal activity was highest in the cold season, pikeperch in the warm season, and catfsh activity peaked in both seasons. Overlap in the depth use among species was higher in the warm season, when all species used the upper layer of the water column, and lower in the cold season, when pikeperch and catfsh used deeper areas. These results demonstrated overlay and temporal variation of habitat use among these predators, as well as potential spatiotemporal space for their direct ecological interactions. Acoustic telemetry · Predators · Habitat use · Movement ecology · Winter ecologypublishedVersio

Diel vertical migrations of age 0+ percids in a shallow, well-mixed reservoir

The distribution of age 0+ percids (perch, Perca fluviatilis and pikeperch, Sander lucioperca) was investigated in a shallow, wellmixed reservoir during a 24-h period in late May, using acoustic and netting methods. Diel vertical migrations (DVMs) were acoustically recorded between the layers close to the bottom and the whole water column. The netting data showed a high abundance of larvae and juveniles at night (nearly 1 ind m-3, or 6 ind m-2), whereas negligible numbers of age 0+ percids were present in the water column during the day (3% of night abundance). Age 0+ percids remained during the day in the layer very close to bottom. Smaller pikeperch larvae dominated the pelagic age 0+ fish assemblage during daylight, while larger perch prevailed at night. A strong difference between day and night abundances along with a clear pattern discerned by acoustic methods revealed the DVM of age 0+ percids. Analyses of the fish digestive tract contents indicate that DVM was not governed by feeding behaviour, but rather a defensive strategy against predation. This is in agreement with the size distribution of age 0+ percids, since they were smaller in water column during the day as opposed to the night

Who Is Who: An Anomalous Predator-Prey Role Exchange between Cyprinids and Perch

<div><p>Piscivory in cyprinids (Cyprinidae) is extremely rare. Specifically, common bream (<i>Abramis brama</i>) and common carp (<i>Cyprinus carpio</i>) are zooplanktivorous fish in deep lentic waters. Nevertheless, we observed predation by these two cyprinids under natural conditions in the Vír Reservoir, Czech Republic. We conducted diet analysis for cyprinids caught by trawling and gillnets and the large amount of young-of-the-year (YOY) perch (<i>Perca fluviatilis</i>), with sizes of 37–52 mm standard length, were found in their digestive tracts. In 2010, a large amount of YOY perch caused a significant decrease in <i>Daphnia</i> spp. size and abundance in the reservoir. Hence, a food deficit was induced for the cyprinids, apparent also from the poor nutritional condition of common bream which was much worse than the condition of those in similar reservoirs. Common carp and common bream shifted to forced piscivory, and they utilized the YOY perch as an alternative food source. In contrast, smaller species, such as roach (<i>Rutilus rutilus</i>) and bleak (<i>Alburnus alburnus</i>), widely utilized planktonic cyanobacteria. In the following year, YOY perch occurred in significantly lower numbers and conversely, <i>Daphnia</i> spp. size and abundance were significantly higher. The forced piscivory was not observed. Our results indicate a switch to forced piscivory by cyprinids, which was caused by a shortage of their natural food source. Moreover, this phenomenon presents an effective mechanism for reduction in the numbers of YOY perch, ensuring the stability of the ecosystem.</p></div

Comparison of length-weight relationships of common bream (<i>Abramis brama</i>).

<p>Data of 179 individuals with standard length ˃ 260 mm were obtained by sampling from three reservoirs in 2010 and 2011. The comparison was performed by generalized linear model with a log link function. Legend: Vír Reservoir 2010 (designated with dots and solid line, y = 5.864 × e ^0.0092), Vír Reservoir 2011 (triangles and dashed line, y = 5.942 × e ^0.0090); Vranov Reservoir 2011 (crossed square and dotted line, y = 6.146 × e ^0.0086) and Římov Reservoir 2010 (asterisk and dash-dotted line, y = 6.252 × e ^0.0071).</p

Mean carapace size (± S.D.), mean abundance (± S.D.) and population percentage share (PPS; i.e., relative <i>Daphnia</i> abundance from the entire water column) of <i>D</i>. <i>longispina</i> complex in the Vír, Římov and Vranov Reservoirs.

<p>Mean carapace size (± S.D.), mean abundance (± S.D.) and population percentage share (PPS; i.e., relative <i>Daphnia</i> abundance from the entire water column) of <i>D</i>. <i>longispina</i> complex in the Vír, Římov and Vranov Reservoirs.</p

Abundance of YOY fish in pelagic water layer of the Vír Reservoir in 2010 and 2011.

<p>Mean abundance of YOY perch (grey colour)and other YOY fish (black colour)according to the fry trawl catches (Number of tows: 63, sampled water volume: 337.413 m³).</p

A map showing the location of the Vír, Vranov and Římov Reservoirs in the Czech Republic (a) and a detailed view of the bathymetric map of the Vír Reservoir (b).

<p>In (b), 0 corresponds to the surface level in late July 2010. The legend shows contour lines with relevant depths. The sampling design of the Vír Reservoir consisted of four sections (Tributary, Upper, Middle and Dam) along its longitudinal gradient.</p

Vertical profile of abundance (horizontal bars for epi-, meta- and hypolimnion) and carapace size (box and whisker plots) of <i>D</i>. <i>longispina</i> cp.

<p>Data were obtained in the dam section of the Vír Reservoir in 2010 for a) June and c) July, and in 2011 for b) June and d) July. Black lines with black dots show the vertical temperature profiles. Box and whiskers plots: median values, upper and lower quartiles (boxes), maximum and minimum values (whiskers), and all outliers (dots) are shown. Arrows with dotted line indicate the minimum carapace size needed for reproduction according to Petrusek <i>et al</i>. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0156430#pone.0156430.ref044" target="_blank">44</a>]. The triangle in the center indicates water transparency measured by Secchi disk.</p