Influence of Water Clarity on the Catchability of Six Freshwater Fish Species in Bottom Trawls

Abstract

Bottom trawl surveys are carried out every autumn to estimate the relative abundance of six major fish species, especially that of pikeperch (Stizostedion lucioperca) and Eurasian perch (Perca fluviatilis), in the 182 000-ha Lake IJssel, The Netherlands. The catchability of these species is influenced by light intensity at the bottom and therefore by water clarity and water depth. In autumn, water clarity can differ greatly from day to day because of wind-mediated resuspension of sediments. Catchability of ruffe (Gymnocephalus cernua) and age 0 pikeperch showed a significant inverse relationship with light intensity at the bottom, and therefore, a correction should be made when catch data for these species are used to estimate population size or year-class strength. Results were not consistent for perch, while for smelt (Osmerus eperlanus), roach (Rutilus rutilus), and bream (Abramis brama) the influence of light intensity on catchability was not significant. Corrected and uncorrected estimates of the abundance of age 0 pikeperch, based on trawl samples, were compared to demonstrate the effect of water clarity on the estimation of year-class strength. Increased water clarity can lead to zero catches and consequently diminish the effectiveness of sampling programmes.

Comparative visual function in four piscivorous fishes inhabiting Chesapeake Bay

“…Data for red drum (Ai), Atlantic croaker (Aii) and spot (Aiii) are from a previous study (Horodysky et al, 2008 Optical conditions in coastal and estuarine waters are complex and have changed dramatically over the past century due to human activities (Kemp et al, 2005), with potentially large consequences for visually foraging piscivores. Characterizing visual function of nearshore fishes is a first step, but many questions remain on topics such as ambient light levels in specific light niches as well as light threshold effects on predator-prey interactions (Mazur and Beauchamp, 2003;De Robertis et al, 2003), reproduction (Engström-Östa and Candolin, 2007), and fishery gear interactions (Buijse et al, 1992). The effects of ambient light fields on the reflectance of conspecifics, prey and competitors, encounter and reaction distances, and the manner in which these change in space and time should also be investigated to gain insight into visual systems and tasks for a species (Levine and MacNichol, 1979;Johnsen, 2002).…”

“…Such foraging shifts may tip the competitive predatory balance in an ecosystem from visually feeding piscivores to tactile and chemoreceptive foragers, with potentially cascading effects (Carpenter and Kitchell, 1993;Aksnes and Utne, 1997). Additionally, degradation of the chromatic and luminous properties of light fields can affect the distribution and movements of predatory fishes (McFarland, 1986), interspecific and intraspecific communication , reproductive habits and speciation (Seehausen et al, 1997), as well as vulnerability to fishing gear (Loesch et al, 1982;Walsh, 1991;Buijse et al, 1992).…”

Comparative visual function in five sciaenid fishes inhabiting Chesapeake Bay

“…Comparative methods have provided novel insights into the form-function-environment relationships of the fish eye (Walls, 1942;Levine and MacNichol, 1979;Parkyn and Hawryshyn, 2000;Jokela-Määtä et al, 2007), the distributions and movements of fishes (McFarland, 1986), communication (Hart et al, 2006;Siebeck et al, 2006), predator-prey interactions (Browman et al, 1994;De Robertis et al, 2003), and even vulnerability to capture (Buijse et al, 1992;Weissburg and Browman, 2005). Few such comparisons exist for the commercially and recreationally important fauna that use mid-Atlantic coastal and estuarine waters as key juvenile nurseries (Levine and MacNichol, 1979;Beck et al, 2001).…”

The efficiency of three fry trawls for sampling the freshwater pelagic fry community

“…At this stage, juvenile fish can no longer be considered ichtyoplankton and are capable of sensing and avoiding the gear (Buijse et al, 1992;Tischler et al, 2000).…”