To see and not be seen:the visibility of predator and prey with respect to feeding behaviour

Abstract

ABSTRACT. The visibility of herring Clupea harengus and mysids Praunus flexuosus was studied in the shallow water of the Kiel Fjord (Baltic Sea). The apparent brightness contrast of the predator (hernng) and its prey (mysid) were measured from various visual angles with a n underwater video system. The camera looked at the prey from the predator's point of view and vice versa. During a head-on encounter, the contrast of the prey against the ocean background was very poor. With increasing visual angles (relative to a horizontal plane), the visibility of the prey unproved. The predator was most visible from below, but was excellently camouflaged when observed from above or from a horizontal line of vision. When the herring was located 30 to 90' below the mysid, the prey was fairly visible to the predator but the predator was nearly invisible to the prey. By incorporating these ocean optics and taking into account the limits of the maneuvering potential of cruis~ng herring, a n optimal attack angle can be postulated: a t oblique predator-prey configurations between 30 and 60°, herring are still capable of modulating their normal cruising to a n upward directed position while the preconditions of a successful attack -to see and not to be seen -are fulfilled. In Kiel Aquarium, adult herring attacked mysids from a n average angle of 48" from below. In sltu measurements from inside a feeding school of juvenile herring showed a mean attack angle of 43"

Fish or jellies—a question of visibility?

“…3) that the light flux in the basin waters will be several orders of magnitude lower in Lurefjorden, suggesting a severe reduction in the potential for visual feeding (Giske and Aksnes 1992; Aksnes and Giske 1993; Aksnes and Utne 1997). The importance of light flux and water optics for predator-prey relations has been well documented experimentally (Vinyard and O'Brien 1976;Wright and O'Brien 1984;Montgomery et al 1989;Gregory and Northcote 1993;Thetmeyer and Kils 1995;Utne 1997) and in the field (Kaartvedt 1996;Kaartvedt et al 1996). Hence, we cannot reject the hypothesis that a much higher light absorbance in the basin water of Lurefjorden (Figs.…”

Prey availability and selective foraging in shorebirds

“…Charnov et al 1976;Zwarts 1990;Ens et al 1993;Kalejta 1993;Anholt & Werner 1995;Skutelsky 1995;Luo et al 1996). The importance of viewing prey availability from the perspective of the prey has also improved our understanding of selective foraging (Zwarts & Wannink 1989;Wolda 1990;Kersten et al 1991;Ens et al 1993;Thetmeyer & Kils 1995). A particularly significant contribution was that of Ens et al (1993), who equated prey availability with the performance of risky behaviour by fiddler crabs.…”

Feeding mechanism and capture success of european whitefish (Coregonus lavaretusL.) larvae

“…Previous studies which investigated the benefits of searching and attacking the prey from below discerned different advantages for this strategy. On the one hand, planktonic organisms have higher contrast with the background and are more conspicuous when observed from below (Thetmeyer and Kils, 1995), especially when they are located outside the Snell's window (Janssen, 1981). On the other hand, the predator is hidden to its target prey when located below it (Thetmeyer and Kils, 1995).…”

“…Support for this hypothesis is given by the absence of binocular vision in larval fishes from the Coregoninae subfamily (Braum, 1978). Blueback herring (Alosa aestivalis) and herring (Clupea harengus) have been shown to mostly attack their prey from below (Janssen, 1981;Thetmeyer and Kils, 1995). Coughlin (1993) also reported that clownfish larvae detected more prey items in the upper half of their perception field.…”

“…On the one hand, planktonic organisms have higher contrast with the background and are more conspicuous when observed from below (Thetmeyer and Kils, 1995), especially when they are located outside the Snell's window (Janssen, 1981). On the other hand, the predator is hidden to its target prey when located below it (Thetmeyer and Kils, 1995). Finally, approaching from below could be a strategy of the predator to avoid casting a shadow that might warn the prey.…”