Valuing impacts of the invasive alga Didymosphenia geminata on recreational angling

Recent global spread of the freshwater alga Didymosphenia geminata (Didymo) has caused major biosecurity and freshwater management concerns. Didymo degrades river esthetics, alters ecosystems, negatively impacts recreation experiences and may require strict containment measures. This paper assesses the impact of Didymo on nonmarket values for recreational angling using a case study from New Zealand, where Didymo is extraordinarily prolific. Choice experiment data are used to fit a latent class model, identifying five distinct angler preference profiles. For the largest class of anglers the presence of Didymo had no significant effect on angling benefits. However, other classes were negatively affected. Overall, Didymo reduced fishing values by about NZ$44 per visit. Anglers were sensitive to the scale of Didymo infestation, suffering significantly higher costs when more water bodies are affected. Closure of Didymo-infected mainstem-rivers to prevent spread of Didymo resulted in a significant reduction in angler net benefits, even if the policy were 100% effective. The latent class model identified distributional implications. While three angler classes would not have significantly different benefits if mainstem-rivers were closed to prevent the spread of Didymo, two classes of anglers would be highly impacted by such a policy, particularly those who regularly fish mainstem-rivers for salmon. ► Invasive Didymo alga negatively affects recreational fishery values. ► A stated preference model predicts fishers' behavioral responses to Didymo. ► Fishing water closures to prevent further spread of Didymo are inefficient.