Human-predator conflict in the South African fly-fishing industry: fish survival probabilities and stakeholder perceptions

Abstract

The aquaculture and fishing industries have a long history of human-wildlife conflict (HWC), involving a miscellany species ranging from birds to mammals, and fishes to reptiles. Effectively mitigating HWC requires research to focus on both wildlife management as well as the human-side of the conflict, for despite the variety of species and circumstance involved, human opinions and actions will ultimately decide the outcome of conflicts. South Africa has a well-established fly-fishing industry, mainly based on non-native fishes such as brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss). Some stakeholders in the industry have expressed their concerns that piscivorous predators, such as otters (Aonyx capensis and Hydrictis maculicollis) and cormorants (mostly Phalacrocorax carbo lucidus) are detrimentally impacting fish stocks. In order to obtain a more complete view on HWC in the South African fly-fishing industry my research consisted of two components. Firstly, I investigated countrywide stakeholder perceptions of HWC in the fly-fishing industry. Secondly, I studied the survival of fish stocks at a fly-fishing property near Dullstroom in Mpumalanga Province, and assessed predator preference of water bodies at this study site. A questionnaire indicated that an overlap of human- and wildlife interests certainly occurs in the South African fly-fishing industry, with all respondents (n = 22) reporting that they experience stock losses to predators. However, the perceived extent of predator-induced losses varied greatly between individual respondents. Otters, cormorants, African fish eagles, and herons were commonly reported piscivorous predators on fly-fishing properties. Cormorants and otters are the predators most likely to be involved in conflicts as they are seen to pose the highest threat and are most often targeted by mitigation measures. Respondents reported to employ mitigation measures in 55 % of responses with shooting (both lethal and non-lethal) being the most common measure. Catch-and-release angling was reported to be highly prevalent at fly-fishing properties in South Africa. Using a mark-recapture approach, I investigated the survival probabilities of rainbow trout stocked in a comparatively large water body, as well as trout stocked in two smaller water bodies. I found high short-term (weekly) apparent survival probability (Phi) of fish stocked in both large (Phi = 0.97) and smaller water bodies (Phi = 0.93), while annual survival probability was low for both sites. This likely indicates that C&R has limited effects on fish survival at this study site, as most mortalities attributable to C&R have been found to occur within 48 h post-release. Low long-term survival is likely due to factors including predation, water quality, food availability, temperature and rainfall. Fish stocked in the larger water body had nearly nine times the annual survival probability (Phi = 0.18) of fish stocked in the smaller water bodies (Phi = 0.02). Otters were most prevalent at the smaller water bodies and are potentially capitalizing on the easy foraging opportunity provided by high fish numbers in relatively small confines. In contrast, avian predators were most prevalent at the large water body, possibly due the location being more distant to areas of high human disturbance. Despite the negative impacts of trout introduced for fly-fishing purposes, the habitat that these properties provide to many indigenous species should be considered when environmental regulations pertaining to the fly-fishing industry are made. However, for these properties to provide a continuous habitat for piscivorous predators, ways of mitigating HWC that are both beneficial for fish predator conservation as well as the economics of the fishing property are needed.