Experimental Manipulation of Sculpin (Cottus cognatus) Populations in a Small Stream

Abstract

Abstract We examined movement and age distribution of experimentally manipulated natural populations of slimy sculpin (Cottus cognatus) in streams having open and closed vegetation canopies. Densities were estimated in three treatments: reference populations (no transfers), reductions (fish removed from the sites), and additions (fish added to the sites). Biweekly replenishment of addition sites raised sculpin densities to over 10/m2 in the open canopy, at least 3 times that of reduction and reference populations. In closed canopy habitats, densities of addition populations (6/m2) were twice as great as reference populations (3/m2), although reduction populations (41m2) did not differ from either. Addition sites showed a net increase of numbers of sculpin over four summer months, in spite of a decline in older sculpin (age III-V years). Reduction sites showed no differences from reference sites regarding sculpin numbers, indicating that recruitment of fish to reduction sites did occur. However, more than ...