The mitigation hierarchy for sharks: A risk‐based framework for reconciling trade‐offs between shark conservation and fisheries objectives

Abstract

Sharks and their cartilaginous relatives are one of the world's most threatened species groups. The primary cause is overfishing in targeted and bycatch fisheries. Reductions in fishing mortality are needed to halt shark population declines. However, this requires complex fisheries management decisions, which often entail trade‐offs between conservation objectives and fisheries objectives. We propose the mitigation hierarchy (MH)—a step‐wise precautionary approach for minimizing the impacts of human activity on biodiversity—as a novel framework for supporting these management decisions. We outline a holistic conceptual model for risks to sharks in fisheries, which includes biophysical, operational and socioeconomic considerations. We then demonstrate how this model, in conjunction with the MH, can support risk‐based least cost shark conservation. Through providing examples from real‐world fishery management problems, we illustrate how the MH can be applied to a range of species, fisheries and contexts, and explore some of the opportunities and challenges hereto. Finally, we outline next steps for research and implementation. This is important in the context of increasing international regulation of shark fishing and trade, which must lead to reductions in shark mortality, while managing trade‐offs between conservation objectives and the socioeconomic value of fisheries.

A Mitigation Hierarchy Approach for Managing Sea Turtle Captures in Small-Scale Fisheries

“…Equation 1 of the mitigation hierarchy stipulates that avoidance measures ensure no spatiotemporal overlap occurs between the impacting risk and the species unit of management concern, thereby reducing E B (Milner-Gulland et al, 2018). Thus, true avoidance measures require that the impacting fishing activity in question does not overlap with the bycatch of management concern (or has a very low likelihood of occurring; Booth et al, 2019). Because of this, spatiotemporal area closures avoid only if they are large enough or dynamic enough to ensure that fishing impact on the assessed unit of the species of management concern does not occur.…”

“…These are (i) defining the problem (by characterizing the fishery and bycatch issue, and setting the goal, target, metric, and baseline), and (ii) exploring potential management options by systematically stepping through the mitigation hierarchy using a conceptual framing. Booth et al (2019) explore the potential for the application of the mitigation hierarchy to shark bycatch management. These authors subdivide the two steps in Milner-Gulland et al (2018) into five.…”

“…These include (i) defining the problem, (ii) exploring potential management measures using the mitigation hierarchy, (iii) assessing the hypothetical effectiveness of management, (iv) making an overall management recommendation or decision, and (v) implementing, monitoring, and adapting implemented management measures. Here we use the steps proposed in Booth et al (2019), in combination with data from a real-world fishery, to explore the advantages and disadvantages of the mitigation hierarchy framework. We further develop the framework by exploring its potential for integration with MSE to evaluate trade-offs between management scenarios.…”

Mitigation of Elasmobranch Bycatch in Trawlers: A Case Study in Indian Fisheries

“…It aims to balance conservation with economic development, by facilitating the sustainable use of natural resources with minimal or no net loss of biodiversity (Arlidge et al, 2018). Booth et al (2019b) expanded and adapted the mitigation hierarchy for shark fisheries management. They provide a risk-based framework which integrates biological and operational aspects of species and fisheries with socio-economic context to manage potential trade-offs between conservation objectives and human needs.…”

“…We used the mitigation hierarchy for sharks (Booth et al, 2019b) to assess options for shark and ray catch mitigation in an Indian trawl fishery. Our study was conducted at Malvan, a fishing town with a coastal, mixed species fishery, making this the first practical application of such an approach to managing elasmobranch bycatch for a data-limited, fisheries-dependent site.…”