Scale dependence of sex‐specific movement in a small‐bodied stream fish

Abstract

Animal movement at localised scales is often modulated by competing pressures such as avoiding predators while acquiring resources and mates. The relative magnitude of these trade‐offs may affect males and females differently, often resulting in sex‐specific differences in movement. Sex‐biases in movement have been linked to mating systems (e.g. monogamy or polygamy) in birds and mammals; however, this relationship has received less attention among fishes. Using passive integrated transponder tags and a series of stationary antennas, we evaluated the movement dynamics of a small‐bodied, sexually dimorphic stream fish Fundulus olivaceus over a 30‐day period in a fourth‐order tributary to the Pascagoula River in Mississippi (U.S.A.). We documented dissimilar sex‐specific movement behaviours at different spatial scales that were likely to be facilitated by differential resource demands and competitive pressures. Females exhibited an increased propensity to engage in longer, exploratory moves (>30 m); whereas most males remained active within an established territory, making few long‐distance longitudinal movements. Local activity levels (proportion of individuals moving) were positively related to density (manipulated during the study), and density was found to affect the magnitude of sex‐specific movement. In contrast to females, males increased local activity and movement distance at the reduced density, presumably to expand territory size or mate‐searching behaviours, suggesting local mate competition may suppress the movement distance of males. Despite some evidence substantiating a relationship between movement and mating system, our results suggest that the documented sex‐specific differences may be related to traits that co‐evolve with mating systems, rather than the mating system per se. Our findings also highlight the importance of spatial scale when evaluating patterns of sex‐biased movement tendencies.

Complex effects of body length and condition on within‐tributary movement and emigration in stream salmonids

“…Stream fish movement varies temporally (Albanese et al, 2004; Schlosser, 1995), spatially (Letcher et al, 2015) and individually due to body length (Young, 2011), condition (i.e. body weight relative to length) (Gowan & Fausch, 1996) and sex (Clark et al, 2019; Koizumi et al, 2006). In addition, we argue that our synthetic understanding of stream fish movement has been hampered because movement is not always defined and measured consistently across studies.…”

“…pool) and among adjacent meso‐habitats (i.e. 10–100 m) (Clark et al, 2019; Gowan & Fausch, 2002; Pennock et al, 2018). Other studies measured movement distance to elucidate abiotic and biotic factors that explain why some individuals moved longer distances than others (Skalski & Gilliam, 2000; Terui et al, 2017; White & Wagner, 2021).…”

“…survival) declines in their current local habitat (Railsback et al, 1999). Consequently, stream fish are more likely to depart from their local habitat when food resources become scarce or fish density increases (Clark et al, 2019; Olsson et al, 2006). Thresholds of when fish depart from their local habitat vary individually in size‐structured populations, in which competitive outcomes are determined by body size (Werner & Gilliam 1984; Fausch et al, 2020).…”