The angled-web: recreational angling as an under-appreciated disruptor to the interconnectedness of terrestrial and freshwater food-webs.

Abstract

1. The interconnectedness of adjacent freshwater and terrestrial ecosystems results in ‘tangled-webs’, where the cross-boundary exchange of materials results in energy flows that provide critical resources for ecosystem productivity. However, these energy flows can be disrupted by anthropogenic activities, resulting in modified ecosystem functioning. 2. A ubiquitous anthropogenic activity in fresh waters is recreational angling. Five major angling activities can disrupt the structure of the ‘tangled-web’ to produce an ‘angled-web’ (a tangled food-web that is modified by angling activities). (1) Fish stocking increases the number and species available to exploit, but the increased fish abundances can have strong top-down effects and disrupt reciprocal prey subsidies. Following capture, fish are either (2) harvested or (3) released alive (‘catch-and-release0; both can both drive eco-evolutionary changes that can modify food-web structure. Where fish are exploited using baited hooks, (4) the release of ‘ground-bait’ is used as a fish attractant; its composition of novel protein and carbohydrate sources form novel trophic links in the food-web and can accelerate eutrophication. Some angling styles also require (5) riparian and in-stream vegetation to be cleared to minimise gear fouling, potentially modifying fish spawning and nursery areas. 3. We suggest that each of these angling impacts (and their interactions) can contribute to transforming the ‘tangled web’ into an ‘angled-web’, with the strength and direction of the transformation dependent on angling pressure, prevailing fishery practices, regulations and management, and the extent of the interaction effects of the activities. These interactions and their impacts will vary globally given angling methods, practices and regulations differ across the world. 4. We argue that, in this era of substantial environmental change driven by climate change, habitat loss and nutrient enrichment of fresh waters, the extent to which angling impacts food-webs should not be overlooked and underappreciated. We emphasise that when freshwater angling activities are poorly managed and / or unregulated, they can strongly modify the interconnectedness between terrestrial and freshwater food webs.