Size-dependent microhabitat use and intraspecific competition in Cottus gobio

• Published in: Journal of fish biology Vol. 67; no. 2; pp. 428 - 443
• Main Authors: Davey, A. J. H., Hawkins, S. J., Turner, G. F., Doncaster, C. P.
• Format: Journal Article
• Language: English
• Published: Oxford, UK; Malden, USA Blackwell Science Ltd 01.08.2005; Blackwell
• Subjects: Agnatha. Pisces; Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; body size; Cladophora; Cottus gobio; density-dependence; Fresh water ecosystems; Freshwater; Fundamental and applied biological sciences. Psychology; interference; intraspecific competition; microhabitat shift; stream fish; Synecology; Vertebrates: general zoology, morphology, phylogeny, systematics, cytogenetics, geographical distribution; British Isles, England; Microhabitat; Interference; Biology; microhabitat shift; Cottus gobio; Freshwater environment; Vertebrata; Pisces; Body size; density-dependence: interference; Intraspecific competition; Habitat; Stream; Density dependence; stream fish
• ISSN: 0022-1112; 1095-8649
• DOI: 10.1111/j.0022-1112.2005.00736.x

An electrofishing survey of daytime shelter microhabitat use of bullhead Cottus gobio in a southern English chalk stream revealed positive selection for moderate water velocity, vegetation cover and coarse substrata. Water depth, other forms of cover, shade and substratum embeddedness had no significant influence on the distribution of fish. Microhabitat use was size‐dependent, with patches occupied by adult fish containing coarser substrata and less blanket weed (Cladophora algae) than those occupied by smaller juvenile conspecifics. Differences in substratum use between size‐classes were less pronounced in parts of the stream shaded by the tree canopy. In laboratory tanks stocked at low fish density, both juveniles and adults favoured use of cobbles over pebbles. The response of fish to increased conspecific density was size‐dependent; juveniles reduced use of the coarse substratum whereas adults maintained their predominance in this habitat. An apparently greater shift by juveniles when in the presence of adults was significant at α = 0·10 only, as was an apparent reduction in interactions between size‐classes under low light intensity. The displacement of small juvenile fish from the preferred cobble substratum is consistent with the hypothesis that intraspecific competition contributes to the size‐related microhabitat shift observed in the field. Although there was a tendency for the strength of competition to be reduced at low light levels, the mechanism by which tree canopy cover affects microhabitat use remains uncertain.