Science Facing Aliens - Invasive Alien Species in Belgium - Belgian ...

Non-indigenous freshwater fishes in Flanders: status, trends and
risk assessment
Hugo VERREYCKEN * , Gerlinde VAN THUYNE & Claude BELPAIRE
Research Institute for Nature and Forest (INBO), Duboislaan 14, 1560 Hoeilaart
*Corresponding author; tel. 02 658 04 26 & e-mail: hugo.verreycken@inbo.be
Abstract
At least eighteen non-indigenous freshwater fish species were reported to occur in the wild
within the territory of Flanders. Nine are considered naturalized while the others are
acclimatized and do not form self-sustaining populations. Nine of the introductions occurred
prior to 1950, with the other nine species introduced since then. This contribution reviews the
available information on these introductions, and evaluates a decade of data from fisheries
surveys to assess the recent development of these non-indigenous populations. Gibel carp
Carassius gibelio and topmouth gudgeon Pseudorasbora parva are the most widespread of
the non-indigenous species in Flemish waters, and both continue to expand their ranges. A
reduction in range has been observed in brown bullhead Ameiurus nebulosus only. Only four
species occur in all eleven river basins while eight species are restricted to one or two basins
and often only one specimen was found during fish stock assessments. We also discuss nonindigenous
fish species that are likely to colonize Flanders inland waters in the near future.
For all non-indigenous freshwater fish species present and expected to appear soon, different
risk analysis tools (FISK and ISEIA) were used to screen these species for their possible
invasiveness. Although scores from FISK and ISEIA differ for some species, gibel carp and
topmouth gudgeon were in both assessments classified as ‘highest risk’ species in relation to
their potential invasiveness.
Introduction
In 1995, the Research Institute for Nature and Forest (INBO) (then Institute for Forestry and
Game Management) started a monitoring network on freshwater fishes. Fish stock
assessments were performed on a regular basis at more than 800 locations all over Flanders.
The data collected during these fish stock assessments were brought together in an online
database VIS or Vis Informatie Systeem (Fish Information System) which can be consulted at
http://vis.milieuinfo.be. At present, data of more than 200 000 native and non-native fishes
with their individual lengths and weights are in this database. All these data are
georeferenced.
This paper discusses the presence and status of the non-indigenous fish species in
Flanders (Belgium). Data of non-native fishes from the VIS-database were analysed for trends
in numbers and biomass over the period 1996 - 2005. Potential invasiveness of all nonindigenous
freshwater fish species present and expected to appear soon was assessed using
the FISK tool by Copp et al. (2005a) and the ISEIA protocol by the Belgian Forum on
Invasive Species (Branquart, 2007). Both tools classify the invasiveness of the species into
low, medium or high, and results from both methods were compared.
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