The effect of the size of the resampling areas (indicated by dashed lines) on the ability to detect marked fishes, relative to the distances that the fishes move. As determined by a modeling study, the largest resampling area (2,000 m) can detect 100% of fish movements up to 750 m upstream or downstream from the marking site (indicated by shading). The smallest sampling area (500 m and the same as the marking area) could only detect 100% of fishes that moved less than approximately 50 m. Based on Albanese et al. (2003).

      In theory, the probabilities of capture from distance weighting could be used to adjust the observed captures of fish (see Albanese et al. 2003). In actuality, outside of the zone of uniform sampling, the numbers of fish captured were so low that adjustments generally were not possible—adjustments are not possible if no fish are captured! The take-home message is that an understanding of distance weighting using PS_d values is most useful for the a priori design of the sampling study. The a posteriori application of correction factors generally cannot correct for a poor study design.

      In spite of the cautionary words by Gerking (1959) about the problem of experimental design and the presence of fish straying, and the suggestion by Funk (1955) about sedentary and mobile groups, the restricted movement paradigm became entrenched in the literature. One of the first to take issue with the restricted movement paradigm, specifically in regard to salmonids, was Gowan et al. (1994), who pointed out that although most tagging studies captured the majority of fish near the point of release, in 78% of the salmonid studies that they reviewed, over half of the fishes were never seen again after being marked. Whether these fish represented mortalities or fish that simply moved much greater distances is the crux to understanding the level of movement of fishes. Gowan et al. (1994) also suggested that the mobile fraction of fish populations had been downplayed through the use of such deprecating terms as “strays” and argued that more attention needed to be given to the experimental design of fish movement studies and to the underlying mechanisms involved in fish movement. The greater realization of the often high degrees of movement shown by freshwater fishes has had important consequences for the better understanding and management of fish populations (Fausch et al. 2002).

      A study of fish movement in a small Ouachita Highlands stream (Arkansas) involved four species of stream fishes (Creek Chub, Semotilus atromaculatus; Blackspotted Topminnow, Fundulus olivaceus; Green Sunfish, Lepomis cyanellus; and Longear Sunfish, L. megalotis) (Smithson and Johnston 1999). The study area was 500 m long and consisted of 10 pools, and the possibility of movement of fishes outside of the study area was determined to be unlikely. Most fishes were recaptured in the same pool where they were initially marked; however, there were differences among the species. Compared to the other three species, Blackspotted Topminnow moved significantly greater distances. For all species, there were some individuals that moved greater distances than others, although there were no apparent morphological correlates associated with greater movement and, in fact, the same individuals switched between static and mobile behaviors over the course of the study. This suggests that individual fish periodically engage in exploratory travel, perhaps assessing habitat quality in areas outside of their home pool.

      Field and theoretical approaches were used by Skalski and Gilliam (2000) to examine characteristics of movement of primarily four species (Bluehead Chub, Nocomis leptocephalus; Creek Chub; Redbreast Sunfish, Lepomis auritus; and Rosyside Dace, Clinostomus funduloides) in a small southeastern stream. In contrast to Smithson and Johnston (1999), species showed only weak differences in their degree of movement. However, within a species there was evidence for both “movers” and “stayers.” In addition, the distribution of distances moved tended to be leptokurtic, with more short and long movements and fewer intermediate movements compared to a normal distribution. Relationships between the propensity to move and morphological characteristics were complex and varied among species. Within Bluehead Chub, the probability of movement increased with size for individuals that had slow growth but decreased with size for those having fast growth. In Creek Chubs the probability of movement increased with body size but was not related to growth rate. There was no relationship between body size and the probability of movement in Redbreast Sunfish or Rosyside Dace. Correcting the movement data to account for distance weighting had little effect. However, this does not negate the strong potential effect of distance weighting but emphasizes the importance of an appropriate sampling design that, a priori, deals with the problem of distance weighting—a conclusion also reached by Albanese et al. (2003) (Box 5.2).