Underwater evaluation of habitat partitioning in a European river between a non‐native invader, the racer goby and a threatened native fish, the European bullhead

Abstract

We conducted underwater surveys using SCUBA gear to examine habitat and microhabitat competition between the Ponto‐Caspian racer goby Babka gymnotrachelus and native European bullhead Cottus gobio to assess the potential for competitive displacement of the native species by the invading species. In summer, 88 surveys were made in a tributary of the River Vistula within defined benthic areas across the entire width of the river bed. The occurrence of fish by total length class (small: <6 cm; large: >6 cm) and environmental conditions (depth, water velocity, substratum type, plant cover, shelter type) was recorded. We found a substantial separation between the species and size classes in relation to substratum, shelter type and water velocity. European bullheads were limited to lotic areas with stony bottoms, whereas racer gobies also occupied lentic areas over sand or mud. European bullheads usually took refuge under stones in contrast to a wider range of shelters used by racer goby, including tree roots and rubbish. In general, the breadth of habitat used by the racer goby was wider than that of the European bullhead, although habitat overlap between the species was not statistically significant except for the type of shelter occupied by small fish, selecting smaller stones. An inverse relationship was observed between small European bullheads and all racer gobies in areas where they co‐occurred, suggesting that invader may be having an adverse effect on the distribution and habitat use of small native bullheads, particularly in areas of moderate water velocities over small stones and gravel.

Feeding preferences of an invasive Ponto‐Caspian goby for native and non‐native gammarid prey

“…The Ponto‐Caspian gammarids occur in the entire River Vistula, including its upper part (Jażdżewski et al ., ) where gobies have not yet been recorded (own unpublished data). In turn, the gobies have recently colonised small tributaries (Jażdżewski et al ., ; Kakareko et al ., ), avoided by the non‐native gammarids and constituting refuges for the native gammarids (Grabowski et al ., ). In these situations, the gobies might benefit from the presence of native prey, which have turned out to be a preferred and higher quality food source than the Ponto‐Caspian species.…”

Can the presence of alien Ponto–Caspian gobies affect shelter use by the native European bullhead?

“…Throughout the year, monkey gobies were caught usually on sand except for the spawning season when they occupied artificial shelters (Kakareko 2011). Although habitat preferences of gobies differ somewhat from those of bullheads (Van Kessel et al 2011;Kakareko et al 2016), they tend to use crevice shelters, such as spaces between or under stones , especially during the most important period, the spawning season.…”

Occurrence of non‐native fishes in the Danube east of Vienna (Austria) and potential interactions of invasive gobiids with native fishes

“…Nevertheless, also Janáč et al () concluded that the invasive gobies had no identifiable negative effect on bullheads. Therefore, although members of the genus Cottus (bullheads and sculpins) have been frequently reported to be affected by gobies (Dubs & Corkum, ; Janssen & Jude, ; Kakareko et al, ; Kakareko, Kobak, Poznańska, Jermacz, & Copp, ; van Kessel et al, ), this does not seem to be the case for the Upper Danube (Janáč et al, ; Mueller, Pander, & Geist, ).…”