Comparison of two passive methods for sampling invasive round goby (Neogobius melanostomus) populations at different depths in artificial lakes

Sampling of benthic fish is complicated, especially in deep inland water bodies with a structured bottom. The catches were compared of rapidly spreading round goby (Neogobius melanostomus) using small fykes nets and benthic gillnets in three artificial lakes in The Netherlands over a two year period. Round gobies were captured at all depth layers in each sampled lake. Significantly larger individuals were captured in gillnets compared to fyke nets. Reference sampling in littoral areas captured a wide range in size of round gobies with beach seines. With fyke nets, the highest catches were usually achieved in the shallowest and deepest depth strata. Gillnets catch decreased at deeper layers. Both methods are passive sampling tools and did not provide the absolute catch per bottom area, however relative density estimates of round gobies at different depths or habitats are possible. Round gobies showed a significant size bias associated with capture method. Because it is important to understand the biology and ecology of invasive species like round goby, the combination of small fyke nets and gillnets appears to be a good solution to sample a variety of ranges in deep or/and structured benthic habitats.