Invasive Species Compendium

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Abstract

Reproductive strategies of three invasive Gobiidae co-occurring in the Lower Rhine (Germany).

Abstract

At the Lower Rhine, three congeneric, invasive Gobiidae constitute the major part of local fish assemblages. Reproduction strategies play an important role in biological invasion processes and help to predict future population development. Up to now, studies on the reproductive traits of the three species have led to contradictory findings in invaded areas, and studies on native populations are scarce, especially when regarding a co-occurrence of the three species. This study provides an overview over already existing knowledge of reproductive traits in native as well as invaded regions and describes the reproduction modes of all three species at the Lower Rhine. Based on intensive beach seine sampling in nursery habitats for three consecutive years, detailed information about the spawning habits of the bighead goby Ponticola kessleri, the round goby Neogobius melanostomus, and the monkey goby N. fluviatilis is provided. Spawning onset as well as length and intensity of the spawning season were determined by estimating growth rates and subsequent back-calculations of hatching and spawning events. Gonadosomatic index (GSI) analyses of adult gobies were used to cross-validate results and to assess validity of the used method. Growth rates for the first three months of all three species were highly variable and ranged between 0.3 mm and 0.95 mm total length per day. All three Gobiidae displayed different reproductive modes with bighead gobies spawning first in March/April, but probably only once a season. In contrast, round and monkey gobies started reproducing slightly later, but then continued spawning throughout the season until September, exhibiting temporal separation with varying intensities. High variation in spawning onset, length and reproductive output for all three species was observed over the years and no relationship between spawning onset and temperature could be detected. For the first time, highly resolvent information on spawning onset and spawning season length is obtained and the fine-tuned differences between the three species are highlighted.