Recreation ecology: impacts of recreational angling and other water-based activities on freshwater biodiversity

Recreational activities at freshwater ecosystems have been increasing during the recent years. While water-based recreation is beneficial for human well-being, it can also have adverse effects on freshwater ecosystems. Recreational angling is considered to be a particular threat to freshwater ecosystems, due to long stays of anglers directly at the shoreline, even at night. As the biodiversity crisis is particularly pronounced in freshwater ecosystems, impacts should be mitigated by adequate nature conservation measures. At the same time, it is crucial to also minimize social costs of these measures. Therefore, a solid scientific evidence is needed to identify and quantify the impacts of all water-based recreational activities in a comparative way. First, I conducted a comprehensive literature synthesis to recapture the existing evidence about recreational impacts on freshwater ecosystems. I performed a global meta-analysis to compare the magnitude of impacts of shore-bound activities, shoreline angling, swimming and boating on different levels of biological organization. The recreational activities did not differ significantly in the magnitude of effects, although boating impacts were the strongest and most consistent. Effects were mainly reported on individual level, especially for individual birds, while impacts on higher levels such as population and especially community level should be more relevant for nature conservation. Although water fowl are known to be very sensitive towards human disturbance, impacts on water fowl were moderate and strongest impacts were found on invertebrates and plants caused by shore-bound activities and boating.
The narrative review on the impacts of non-motorized, non-consumptive activities in and around freshwater ecosystems further approved that the responses of sessile and mobile organisms to human disturbance differ, because plants were more strongly impacted than animals. The review highlighted the need of more studies on community level and underrepresented taxonomical groups and I considered these findings in my empirical analyses. In the first empirical study I compared the biodiversity of several taxonomic groups (water fowl, songbirds, dragon flies, damselflies, amphibians, fishes, aquatic macrophytes, riparian herbs and trees) of gravel pit lakes with different intensities and combinations of recreational activities. The results were in line with the results of the meta-analysis that human presence and general intensity of use were more relevant than the specific recreational activity, suchas angling. Although the presence of angling had positive impacts on the diversity of fishes it also showed negative impacts on amphibian diversity. This aspect was also verified by the second empirical study with the focus on impacts of angling management, in which I compared the biodiversity of angler-managed and unmanaged gravel pit lakes. With the last study I present a potential solution to mitigate impacts of angling and other recreational uses on freshwater ecosystems. Protected riparian areas installed by angling clubs in small gravel pit lakes can positively influence habitat quality and benefit biodiversity. Aside from the intended positive impact on the fish abundance, I also detected positive contributions of small-scale riparian protected areas on habitat structure, riparian vegetation, local fish abundance and abundance of sensitive songbirds at the lake-scale. Again, I did not find impacts on disturbance sensitive water fowl. The often-reported impacts on individual level of water fowl (e.g. flight reactions) do not necessarily transmit to higher levels of biological organization. All empirical studies have shown that recreational impacts are minor compared to other threats such as pollution, habitat loss and degradation as main threats of freshwater biodiversity represented by environmental variables related to eutrophication, lake morphology and land use. In conclusion, human use in general is the main driver of recreational impacts, while the specific activity itself is of less importance in regard to ecological impacts. Consequently, selectively banning or constraining one particular form of recreation may have high social costs at low benefits for conservation. Conservation measures are more promising if stakeholders are involved in decision making. Spatial zoning might be an effective tool in nature conservation to improve habitat quality and thus protect biodiversity. Other recreation management options are also discussed in this thesis.