Dependence of beach seine net efficiency on net length and diel period

Abstract

-The aim of this study was to quantify the efficiency of different lengths of beach seine nets for each diel period in freshwater reservoirs. Only fish older than young-of-the-year were considered. Nets of 10, 20 and 50 m length ("in-nets") were tested in an enclosed area framed by a 200 m long net (block net). The net efficiency estimate was calculated as the ratio of fish catches with the in-net and block net divided by the ratio of their respective areas. The net efficiency estimate was significantly different between day and night catches. At night, the efficiency estimate of nets depended on the size of the fish. The efficiency estimate of a 10 m long net decreased significantly in reverse correlation with fish size. A similar trend was found when using a 20 m long net. The efficiency estimate of a 50 m long net was independent of fish size. The variance in efficiency estimate between samples with a given net length was high, but decreased with longer nets. Of five species tested, only the efficiency estimate for catching bream (Abramis brama) increased significantly with the length of net. The biomass and abundance of larger fish was generally higher at night, although especially short nets exhibited a spuriously high efficiency estimate during the day, probably due to the concentrating (chasing) effect of the hauling ropes. We therefore recommend the use of a 50 m long net, since its nighttime efficiency estimate was about 0.9 in terms of both sampling abundance and biomass. A model relating the efficiency estimate and net length was developed with the data acquired.

Patterns in diel habitat use of fish covering the littoral and pelagic zones in a reservoir

“…Trawling and EF are prone to density underestimation because of gear avoidance (Reynolds, 1996;Rakowitz et al, 2012). Beach seining, however, provides relatively unbiased estimates (Pierce et al, 1990;Ř íha et al, 2008) when the sampled area was fully enclosed by the net. This bias is particularly noticeable during the daytime when fish trawl avoidance is higher, which can lead to an underestimation of fish density (Rakowitz et al, 2012).…”

“…Such a combination of methods was chosen for several reasons. Beach seining gives very robust results with low biases in size/species selectivity (Pierce et al, 1990;Ř íha et al, 2008). The two years of sampling using a beach seine net (2009)(2010) provide solid data focusing on the temporal stability of migration to the unstructured littoral.…”

Sinusoidal swimming in fishes: the role of season, density of large zooplankton, fish length, time of the day, weather condition and solar radiation

“…light from the dam construction or a nearby village, in combination with eyes equipped with a tapetum lucidum (common bream; Kühne & Sewall, 1880) may improve optical conditions to an extent that during the first part of the night this foraging behaviour is still reasonable for some unsatiated individuals. Generally, the disappearance of sinusoidal swimming after sunset coincided with lower abundance and biomass of larger fish in the open water, a result of nocturnal inshore migrations (Schulz & Berg, 1987;Kubečka, 1993;Kubečka & Duncan, 1994;Ř íha et al, 2008).…”

Juvenile Winter Flounder (Pseudopleuronectes americanus) and Summer Flounder (Paralichthys dentatus) Utilization of Southern New England Nurseries: Comparisons Among Estuarine, Tidal River, and Coastal Lagoon Shallow-Water Habitats

“…1), and subsequently analyzed by grouping across habitat-types as described above. The abundance data were standardized to the number of flounder/m 2 assuming 30% seine efficiency (Pierce et al 1990; Steele et al 2006; Říha et al 2008). Mean differences in WF and SF % FO and abundance were analyzed with Chi-square tests of independence and two-way analysis of variance (ANOVA) models, respectively, using habitat (bay, river, lagoon) and year (2009–2013) as explanatory factors.…”