Movers and stayers: Effects of fragmentation on brook trout movement dynamics

Background/Question/Methods

            Recent advances in technology and methodology question the restricted movement paradigm (RMP), which groups fish into “movers” and “stayers” within a population. Stayers are generally defined as those fish that remain in a home territory (approximately 20m section) with the exception of possible spawning migrations, while movers travel farther than their 20m home section. The movement and dispersal of brook trout, Salvelinus fontinalis, has important implications for conservation, management efforts, and for colonization of new habitats. Fragmentation and connectivity, both natural and anthropogenic, ultimately affect movement within and between populations. Over a long period of time, the effects of connectivity might even force artificial selection on a variety of traits. In this study, we describe movement patterns, distributions, and proportions of movers and stayers of brook trout across multiple temporal scales (weeks, months, and years) in a network of three headwater streams with varying connectivity. We used a long term passive integrated transponder (PIT) tag study and portable antenna to track the movement of brook trout within the site weekly over three to five month intervals from 2002 to 2010.

Results/Conclusions

            We analyzed movement as directional, characterizing upstream and downstream specific movement, and as non-directional absolute movement. Frequency distributions of distances moved by movers and stayers were moderately to extremely leptokurtic; however distributions for movers were far more likely to be normally distributed. Next, we found significant differences among streams in the distances individuals moved, with greater distances moved in streams of higher connectivity. Individuals in the tributary with no barrier to the main stem showed greater movement than either of the other two less connected tributaries. However, there were no consistent differences in the proportion of movers and stayers within the three streams or at various temporal scales. Interestingly, the results imply that while overall distances individuals move may be much greater in more connected streams, it does not appear that such differences in connectivity have caused artificial selection for more resident stayers in local populations.