Development of the freshwater fish assemblage in the Mark watershed, the Netherlands

• Autor(a) principal: Fritz, Maarten
• Data de Publicação: 2016
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10400.1/13539
• topic: Água doce; Peixes; Rio Mark; Holanda; Domínio/Área Científica::Engenharia e Tecnologia::Outras Engenharias e Tecnologias

Effectiveness of recently applied management strategies on developments of the freshwater fish assemblages in the Mark watershed has been unclear. Therefore, the objective of this study was to identify developments within the freshwater fish assemblages of the Mark watershed. Furthermore, the identified developments in fish assemblages were analyzed for correlations with physical-chemical parameters and implementation of fish passages and habitat restoration in streams as explanatory variables. Fish assemblage data of 498 surveys have been collected between 1994 and 2014, and were analyzed to detect developments in diversity indices over time. Furthermore, 30 routine sampling stations for annual mean of physical-chemical variables, 8 fish passages and 5 remaindering projects were used to explain the differences in diversity indices. Finally, dominant proportions of guilds and fish communities in small streams of the Mark watershed were categorized and studied for correlations to the physical-chemical variables. Altogether 25 native and 6 exotic fish species were detected in the Mark watershed. Species number and diversity varied significantly between watercourses and year of sampling. The Bavelse Leij, Bijloop-Turfvaart, Chaamse Beken, Kleine Beek, Molenbeek and Merkske showed no significant differences in diversity indices over the period of 1994 till 2014. Small streams of the Galderse Beek and Strijbeekse Beek were characterized by a significant decreasing linear trend in average diversity. Diversity significantly decreased from 1.34 to 0.93 between 1994 and 2005 for the Galderse Beek and 1.56 to 0.82 between 1994 and 2006 for Strijbeekse Beek. Diversity at the Galderse Beek significantly decreased due to an exponential increase in the numbers of nine spined stickleback and stone loach, accounting for 83.5% of the total number of individuals. Decreased diversity for the Strijbeekse Beek was caused by an increase in the number of gudgeon, accounting for 77.1% of the total number of individuals. After 2006, average diversity decreased gradually further, however no significant differences were obtained anymore. Mark en Vliet was characterized by a significant linear decrease in average species richness and increase in average Pielou’s evenness over the studied period. Diversity at Mark en Vliet was characterized by a significant depression of 1.15 to 0.81 between 2005 and 2008. After 2008, diversity recovered to original values of approximately 1.20. Depression at Mark en Vliet could not be explained and the reason remain unclear. The Aa of Weerijs showed a significant gradual increasing linear trend in average diversity indices. The average species richness gradually increases over the period of 1994 to 2013. Together with an significant improvement of Pielou’s evenness in 2013, diversity significantly increases from 1.32 to 1.67 for the Aa of Weerijs between 2010 and 2013. The Boven Mark showed a fluctuating character in average diversity indices between 1994 and 2013, and a significant linear increase in average species richness was observed. Average species richness increased from respectively 6.06 species in 1994 to 8.08 species in 2013. However, diversity showed no significant differences due to variation in the distribution among species. Redundancy analysis and Pearson correlation analysis for the Aa of Weerijs and Boven Mark revealed a positive correlation between the construction of fish passages and diversity. However, it is assumed that the overall environmental conditions improved, allowing a greater diversity to exist, and increased connectivity by fish passages functions as a promoter. Habitat restoration projects showed no significant connection to the diversity indices. Furthermore, the physical-chemical variables conductivity, total phosphorus, total nitrogen, chloride and saturated oxygen concentration showed significant correlations to the diversity indices, where conductivity, total phosphorus, total nitrogen and chloride have a negative correlation and saturated oxygen concentration a positive correlation. Non-metric dimensional scaling for the Mark watershed revealed differences between the fish communities collected at different watercourses and by used fishing gear. Focus on the small streams of the Mark watershed, showed the distribution of dominant fish communities in the samples. The small streams are relatively well represented by the occurrence of characteristic stream fish species such as, stone loach, gudgeon, three-spined stickleback and nine-spined stickleback. However, undesirable fish communities of perch & roach and pike & rudd exist in the small streams, and indicate the points for future improvements. Pearson correlation analysis of the fish communities showed that the physical- chemical variables temperature, total nitrogen, total phosphorus, saturated oxygen concentration an conductivity have a significant correlation. The number of perch in the small streams negatively correlates to total nitrogen, total phosphorus, and saturated oxygen concentration, while the number of gudgeon positively correlates. Furthermore, the numbers of three-spined stickleback and stone loach respectively correlate positively and negatively to water temperature of the small streams. Finally, conductivity at the small streams showed a positive correlation to the numbers of nine-spined stickleback.