Effects of environmental parameters on the distribution of bullhead Cottus gobio with particular consideration of the effects of obstructions

Abstract

1.The bullhead Cottus gobio is a small-sized fish that occurs in stony streams and lakes in Switzerland. Its numbers have declined and its distribution has become narrower over the last 30 years, most probably due to chemical pollution and/or structural habitat deterioration, and at present it is classified as a potentially endangered species. 2. This study evaluated whether chemical parameters and/or structural habitat heterogeneity have an effect on the occurrence and density of bullhead in a river system, in order to assess the potential usefulness of this species as an indicator for these parameters. Ten sites were chosen, where chemical parameters were measured monthly over a period of 2 years. Habitat heterogeneity was assessed with respect to river width and maximum depth. Correlations were drawn between the density of bullhead, the chemical water constituents and the structural habitat diversity. The longitudinal distribution of bullhead in the whole river system was determined and all obstructions with a height of at least lOcm were investigated. In two sites, the total population density of bullhead older than O+ was assessed using both multiple removal collecting and a mark-recapture method. 3. Structural habitat diversity appeared not to be important for bullhead, and the only chemical parameter that correlated with the density of this species was dissolved organic carbon. 4. Obstructions with a height of 18-20 cm were impassable for upstream movement of bullhead and thus acted as migration barriers. The longitudinal connectivity of the main river was interrupted by 48 such obstructions, which were all human-made. 5.Multiple removal collecting of bullhead resulted in small catching probabilities of 0.1 7 and 0.34. The total estimated population densities of bullhead were high, with 118 and 327 in 100 m*. The mark-recapture method revealed even higher estimated densities, of 121 and 444 in loom'. 6. It is concluded that the bullhead is a useful indicator species for determining to what extent the longitudinal connectivity of a river is interrupted by obstructions. For restoration of rivers, it is recommended that any human-made obstructions with a height of 20cm or above are removed, starting at confluences with joining rivers and moving upstream.

Assessment of the conservation status of endemic sculpinCottus haemusi(Cottidae) in the river Vit (Danube Tributary), northwest Bulgaria

“…In contrast, one population showed substantially higher densities of 75 individuals·m -2 (Mann, 1971). Jansen et al (2000) and Utzinger et al (1998) found densities in the range of 1.8-14.7 individuals·m -2 . Appreciable differences in bullhead abundance from site to site were also found in the Garonne stream system (Legalle et al, 2005).…”

“…On the contrary, Perrow et al (1997) and Gosselin et al (2010) observed a positive correlation between bullheads and greater depths and slow velocity. In fact, there is an ontogenetic shift and seasonal changes in the preferences of sculpins for water depth, velocity and size of the substrata (Carter et al, 2004;Van Liefferinge et al, 2005) and the bullhead may be more flexible in its habitat requirements than generally assumed (Utzinger et al, 1998;Jansen et al, 2000). Most studies have found that bullheads avoid muddy bottoms and homogeneous areas and wider sections of the river (Legalle et al, 2005;Gosselin et al, 2010).…”

“…It has been reported that bullheads are capable of rapid recolonization of rehabilitated watercourses (Pretty et al, 2003). By tagging fish with PIT markers Knaepkens et al (2005) demonstrated that bullhead populations not only consist of stationary individuals but also of relatively mobile fish that cover distances of up to 270 m. However, bullheads have little ability to overcome natural or man-made obstructions, and anything with a height of 20 cm or more is impassable for bullheads moving upstream (Utzinger et al, 1998). The migration of bullheads above sampling site K3 is prevented by an artificial obstruction (weir) and numerous natural rock shoots.…”

“…Mann, 1971;Crisp et al, 1974;Welton et al, 1983;Waterstraat, 1992;Perrow et al, 1997;Fischer and Kummer, 2000;Jansen et al, 2000;Cowx and Harvey, 2003;Carter et al, 2004;Kotusz et al, 2004;Legalle et al, 2005;Van Liefferinge et al, 2005;Abdoli et al, 2007). The spread of local populations of bullhead has been hampered by the low migratory ability of the species, its specific ecological requirements and river fragmentation (natural and man-made), which have prevented significant dispersal (Utzinger et al, 1998;Fischer and Kummer, 2000;Knaepkens et al, 2005). The current distribution of Cottus species across Europe is a result of colonization and re-colonization processes during interglacial periods (Riffel and Schreiber, 1995;Hänfling and Brandl, 1998;Englbrecht et al, 2000;Kontula and Väinölä, 2001;Volckaert et al, 2002;Šlechtová et al, 2004).…”

“…Cottus petiti) (Persat et al, 1996;Kottelat and Freyhof, 2007). Some populations of Cottus species are becoming endangered as a result of water pollution and habitat deterioration (Pedroli et al, 1991;Utzinger et al, 1998;Fischer and Kummer, 2000;Knaepkens et al, 2005). The bullhead, Cottus gobio, was included in Annex II of the European Commission's Council Directive 92/43/EEC on the conservation of natural habitats and wild fauna and flora (Habitats Directive).…”