Ocean zoning within a sparing versus sharing framework

Abstract

The land-sparing versus land-sharing debate centers around how different intensities of habitat use can be coordinated to satisfy competing demands for biodiversity persistence and food production in agricultural landscapes. We apply the broad concepts from this debate to the sea and propose it as a framework to inform marine zoning based on three possible management strategies, establishing: no-take marine reserves, regulated fishing zones, and unregulated open-access areas. We develop a general model that maximizes standing fish biomass, given a fixed management budget while maintaining a minimum harvest level. We find that when management budgets are small, sea-sparing is the optimal management strategy because for all parameters tested, reserves are more cost-effective at increasing standing biomass than traditional fisheries management. For larger budgets, the optimal strategy switches to sea-sharing because, at a certain point, further investing to grow the no-take marine reserves reduces catch below the minimum harvest constraint. Our intention is to illustrate how general rules of thumb derived from plausible, single-purpose models can help guide marine protected area policy under our novel sparing and sharing framework. This work is the beginning of a basic theory for optimal zoning allocations and should be considered complementary to the more specific spatial planning literature for marine reserve as nations expand their marine protected area estates.

Evidence-Based Guidelines for Prioritizing Investments to Meet International Conservation Objectives

“…Further, Runting et al 45 found greater biodiversity outcomes from improved management compared to shifting to a landscape-sparing strategy. Similar results were found by Kuempel et al 44 in the marine context where optimal budget allocations were split across enforcement or expansion, but the long-term allocations favored enforcement, and by McGowan et al, 46 who found that small management budgets favor marine protected area establishment, whereas larger budgets favor fisheries management strategies. Even restoration, one of the most extreme forms of management, has been found to produce greater outcomes when carried out alongside or even in place of protected area expansion, 47 which is in contrast to tradition orthodoxies.…”

“…Nearly all analyses that have modeled conservation actions based on different budget allocations have concluded that the optimal decision is largely dependent on three factors: the rate of habitat degradation, the relative costs of actions, and time lags between actions. 11,15,16,44,46,70 It is essential that these components are considered when making decisions, however, they are rarely explicitly and transparently included in the conservation decision process (e.g., costs 71 ) and are not recognized as important within international conservation objectives.…”

“…However, many modeling approaches aimed at increasing biodiversity, often using standing biomass as a proxy, also incorporate minimum harvest levels to ensure the optimal decision considers the need to provide food into the future. For example, McGowan et al 46 found that investing in no-take marine protected areas can reduce harvest to a point where it no longer becomes optimal, particularly for large budgets. By incorporating minimum harvest levels in this model, important trade-offs between protected area establishment and food security become apparent and can be used to guide the most cost-effective actions for these two potentially competing goals.…”

What Have We Learned from the Land Sparing-sharing Model?

“…The original formulation of the land sparing-sharing framework omits some complexities, but it can be and already has been modified to incorporate many of these, including spatial configuration and the influence of edge effects [60,61]; the influence of changing diets and reducing food waste [50]; inclusion of some ecosystem services [4,7,50,62]; prediction of the effects of specific public policies [63]; and application to forestry [64,65], urban planning [66][67][68][69] and marine conservation [70]. It is a model, and so all assumptions can be varied and tested.…”

Taking a landscape approach to conservation goals: designing multi-objective landscapes

“…The framework is now being used in a broader context to encompass issues about landscape design in general, and not just specifically about maximising yield, for example the design of cities and plantation landscapes, livestock production, and fisheries production (e.g. Lin & Fuller 2013; Edwards et al 2014; Law et al 2016; McGowan et al 2018). As its application moves into more general usage the issue of oversimplification becomes even more apparent, emphasizing that limiting landscape decisions to two states (shared or spared) is often too simplistic to produce viable landscape design options.…”