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STATISTICS

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General

Small fish are forced to live in schools, in which the large number of potential prey hampers, in addition to other benefits, the hunting of predatory fish and other predators for an individual prey. This effect of predator desorientation is called confusion effect (Neill & Cullen, 1974; Gillett et al., 1979; Milinski, 1979; Landeau & Terborgh, 1986; Smith & Warburton, 1992; including theory Jeschke & Tollrian, 2005; Tosh et al., 2006; Ruxton et al., 2007; Ioannou et al., 2008). To avoid this effect, predatory fish use several tactics to hunt for schooling prey. One of them is eliminating in schools the so called odd prey that differ on their species belonging, shape, size, armour, color and behaviour from the school mates (Major, 1978; Ohguchi, 1981; Theodorakis, 1989; Ranta & Lindström, 1990; Krause & Godin, 1994; Peuhkuri, 1997; Mathis & Chivers, 2003; Almany et al., 2007; Jones et al., 2010; Rodgers et al. 2011).

Largemouth bass, Micropterus salmoides (powered by Joseph Tomelleri)

Landeau & Terborgh (1986) have conducted some experiments to clarify the roles of confusion effect and prey oddity as they interact to influence the hunting success of predators. Largemouth bass (Micropterus salmoides) quickly captured solitary silvery minnows (Hybognathus nuchalis), but performed many unsuccessful attacks as prey school size was increased. At school sizes of 8 and above, predators were effectively stymied demonstrating the confusion effect. An inclusion of 1 or 2 odd (blue dyed) minnows in the school of 8 members greatly increased the ability of bass to capture both normal and odd prey, but this effect disappeared at the school size of 15. The implications of the foregoing results for understanding the adaptive basis of mixed species flocks, herds and schools in various animals is discussed (Landeau & Terborgh, 1986).

The number of prey, rather than the density or area occupied by the group, has the greatest effect on the predator confusion (Tosh et al., 2006; Ruxton et al., 2007; Ioannou et al., 2008). In addition, it is shown (Tosh et al., 2006) that the confusion effect is U shaped with the strongest changes for 5-15 members of model groups.

Fishing practice

Umbrella rigs allow to imitate small groups of fish and other animals, with the number of lures ranged usually from 3-6 for casting rigs to several tens for trolling rigs. With this number of lures, the confusion effect may occur. To verify the occurrence of this effect, we have tested in the field commercial radially symmetric casting umbrellas equiped with 5 matched and 1 odd lures.


Figure 1. Umbrella rig with 6 radial arms, 5 matched and 1 odd lures (details are not shown)

An umbrella pattern with 5 matched and 1 odd lures is demonstrated schematically in Fg.1 (six arms and hooks are not shown). Commercial Curly Tail Grubs (1″) of Green Body & Lime Tail (LT) and White Body & Red Tail (RT) colors were used.

Abundant common perch, Perca fluviatilis, were selected as an usable fish model.

If the confusion and prey oddity effects do not occur, the total number of caught perch must be distributed on average with an equal probability between six lures, 1/6. During 2 test days, 71 perch were landed: 50 for LT and 21 for RT. The mean value is 11,8 perch per one lure, both matched and odd one. Because an odd lure attracted 21 perch instead of mean 11,8, it means that in the foregoing special conditions of multiple choice perch prefer to select lures on color oddity.

Basic References

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Category: Shoals & Sworms | Views: 1286 | Added by: nickyurchenko | Date: 2013-04-07

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