Estimates of nocturnal home-range size of the adult Japanese fluvial sculpin, Cottus pollux (Pisces: Cottidae) in relation to bottom topography and sampling intervals

Abstract

I have estimated nocturnal home-range size for 24 individuals of the adult Japanese fluvial sculpin, Cottus pollux (large-egg type) by direct observation on a single night. On average, sculpin used 10.5 focal points (where they executed ambush predation) at night and stayed for 93.1 min at each point. Home-range size (mean 9.8 m2, range 0.3–79.9 m2), which was calculated by use of the minimum convex polygon method, was positively correlated with the number of focal points. The swimming paths and focal points used by each sculpin often depended on the configuration of rocks on the streambed, suggesting the importance of bottom topography to home-range use by the sculpin. More than one-third of the sculpins returned to within 1 m2 of the point of original capture and release; this provided evidence of their homing ability. Comparison of nocturnal home-range size and Schoener’s ratio (the amount of temporal autocorrelation) with the length of sampling intervals suggested that sampling intervals of 2 h through the dark period, which resulted in a 70% match with real home-range measurements and approximately half of the data sets became independent, provide the most accurate information for predicting the nocturnal home-range size of the sculpin.