Publications

Many anthropogenic stressors broadly inflict mortality or reduce fecundity, including habitat destruction, pollution, climate change, invasive species, and multispecies harvesting. Here, we show—in four analytical models of interspecies competition—that broadly inflicted stressors disproportionately cause competitive exclusions within groups of ecologically similar species. As a result, we predict that ecosystems become progressively thinner—that is, they have progressively less functional redundancy—as broadly inflicted stressors become progressively more intense. This may negatively affect the temporal stability of ecosystem functions, but it also buffers ecosystem productivity against stress by favoring species less sensitive to the stressors. Our main result follows from the weak limiting similarity principle: species with more similar ecological niches compete more strongly, and their coexistence can be upset by smaller perturbations. We show that stressors can cause indirect competitive exclusions at much lower stressor intensity than needed to directly cause species extinction, consistent with the finding of empirical studies that species interactions are often the proximal drivers of local extinctions. The excluded species are more sensitive to the stressor relative to their ecologically similar competitors. Moreover, broadly inflicted stressors may cause hydra effects—where higher stressor intensity results in higher abundance for a species with lower sensitivity to the stressor than its competitors. Correlations between stressor impacts and ecological niches reduce the potential for indirect competitive exclusions, but they consequently also reduce the buffering effect of ecosystem thinning on ecosystem productivity. Our findings suggest that ecosystems experiencing stress may continue to provision ecosystem services but lose functional redundancy and stability.

Coral reef social-ecological systems worldwide face major impacts from climate change, and spatial variation in vulnerability is driven by differential exposure to climatic threats, ecological and socio-economic sensitivity to those threats, ecological recovery potential, and socio-economic adaptive capacity. We assess variation in social-ecological vulnerability to climate change-induced coral bleaching, specifically for reef-based fisheries and tourism, of islands throughout the insular Caribbean, thus providing the first region-wide quantitative analysis of island-scale social-ecological vulnerability to coral bleaching. We show that different components of vulnerability have distinct spatial patterns and that variability in overall vulnerability is driven more by socio-economic than ecological components. Importantly, we find that sovereign islands are less vulnerable on average than overseas territories and that the presence of fisheries management regulations is a significant predictor of adaptive capacity and socio-economic sensitivity, with important implications for island-level governance and policies to reduce climate vulnerability.

Aquaculture surpassed wild fisheries as the largest supplier of fish for human consumption in 2014 and is expected to supply the majority of seafood for future increases in demand. Marine and coastal aquaculture, collectively referred to as mariculture, currently represents just 36% of aquaculture production but is poised to expand in the decades ahead. One of the most commonly cited concerns regarding this likely expansion is ecological and socioeconomic interactions with wild-capture fisheries. While attention has largely been drawn to high-profile negative externalities from fed finfish and crustacean mariculture, not all marine-based practices are equivalent. Empirical evidence for the different interactions between mariculture and wild fisheries is often sparse. While negative consequences can arise, positive synergies can also occur. By considering mariculture development in the context of fisheries interactions, we suggest that it is possible to minimize conflicts and maximize positive connections between the two sectors. We provide the first comprehensive synthesis of the interactions between mariculture and wild fisheries, characterizing the types of interactions, evaluating available empirical evidence and identifying where management (sector-specific and cooperative) can play an important role. We highlight potential effects of mariculture on the efficiency, sustainability, and equity of seafood production and identify remaining knowledge gaps.

Offshore mariculture could enable increased seafood production and economic development while alleviating pressure on coastal ecosystems and wild fisheries. In the Caribbean, however, an integrated assessment of the ecological and economic potential for mariculture in the region is lacking. We assess site suitability and develop a spatial bioeconomic model to predict yields and profits for offshore cobia (Rachycentron canadum) mariculture across 30 jurisdictions in the Caribbean. We find that (1) approximately 1.4% of the study area may be technically feasible; (2) the model could avoid conflicts with other uses and sensitive habitats and protected areas; and (3) the model could be economically profitable, with the potential to produce almost half the amount of seafood that is currently harvested from wild fisheries globally. Here, we show that potential farm-scale production and profitability vary across and within countries and that accounting for the foreign investment risk associated with a country will impact estimated farm profitability.

Freshwater protected areas (FPAs) are increasingly important for biodiversity conservation, given the intensive use of these systems for water, energy and food production. However, the fisheries benefits of FPAs are not well understood, particularly for indiscriminate fisheries typical of tropical systems. Here we report the results of a model that tests the fisheries effects of no-take protected areas in conditions unique to indiscriminate riverine/floodplain systems. The model has a generalized form applicable to a wide range of systems. We report the results of the general model, as well as those from a specialized form parameterized for the Tonle Sap lake, Cambodia. Both the general and Tonle Sap versions of the model show that FPAs can pay important fisheries benefits, especially where it is difficult to control fishing mortality through gear restrictions or other means. The harvest and profit benefit response curves have similar shapes, with additional FPAs paying high dividends at less than approximately 50% FPA coverage, and then truncating and declining thereafter. In the specific setting of the Tonle Sap of Cambodia, FPAs would pay a large increase in harvest because current FPA coverage is low. It may be counterintuitive to community fisheries managers in Cambodia that the best way to increase harvest is to restrict fishing, but at very high levels of fishing effort, reducing effort or area fished will improve both harvest and profit. In Cambodia, it may make sense to maximize harvest rather than profit because fishers living in poverty need to maximize protein offtake, but the benefits of FPAs remain. Similar considerations may apply in many freshwater and indiscriminate fisheries.

A primary goal of McDermott et al. (1) was to stimulate discussion of the “blue paradox” among proponents of marine reserves. We welcome the chance to engage with conservation experts and are grateful for the commentary provided by Hanich et al. (2). However, we are unconvinced by their arguments. Hanich et al. (2) do not offer a substantive critique of our methods or provide data that overturn our findings.

Hanich et al.’s (2) chief criticism relates to the El Niño Southern Oscillation (ENSO), which they claim drove the preclosure surge in fishing activity within the Phoenix Islands Protected Area (PIPA). There are two problems with this argument as it pertains to the findings in McDermott et al. (1). The first is that we already control for the confounding effects of ENSO in our original analysis. For example, model M1 shows that our results are unaffected by the inclusion of region-specific sea-surface temperatures. The same is true if we directly control for a standard ENSO index, as shown in Fig. 1. The second problem is that the 2015/16 El Niño event occurred after PIPA’s closure and thus well after the observed period of anticipatory fishing.

Wild capture fisheries produce 90 million tonnes of food each year and have the potential to provide sustainable livelihoods for nearly 40 million people around the world (http://www.fao.org/3/a-i5555e.pdf). After decades of overfishing since industrialization, many global fish stocks have recovered, a change brought about through effective management. We provide a synthetic overview of three approaches that managers use to sustain stocks: regulating catch and fishing mortality, regulating effort and regulating spatial access. Within each of these approaches, we describe common restrictions, how they alter incentives to change fishing behaviour, and the resultant ecological, economic and community-level outcomes. For each approach, we present prominent case-studies that illustrate behaviour and the corresponding performance. These case-studies show that sustaining target stocks requires a hard limit on fishing mortality under most conditions, but that additional measures are required to generate economic benefits. Different systems for allocation allow stakeholder communities to strike a locally acceptable balance between profitability and employment.

How will countries harvesting mobile natural resources react to the possibility of regime shift? We address the non-cooperative exploitation of a migratory renewable resource in the presence of possible regime shift that affects its movement. Motivated by the anticipated effects of climate change, we model a regime shift that will alter the spatial movement patterns of the resource at some point in the future. We develop a stochastic spatial bioeconomic model to address the effects of this class of regime shift on non-cooperative harvest decisions made by decentralized owners such as countries exploiting a migratory fish or other natural resource stock. We find that the threat of a future shift modifies the standard “golden rule”, and may induce more aggressive harvest everywhere, irrespective of whether the owner will be advantaged or disadvantaged by the shift. We also identify conditions under which the threat of regime shift induces owners to reduce harvest rates in advance of the shift. Our analysis suggests that different property rights structures (single ownership vs common property) or heterogeneous growth can give rise to previously unexplored incentives and can even reverse conventional wisdom about how countries will react to the prospect of future environmental change.

Shark sanctuaries are an ambitious attempt to protect huge areas of ocean space tocurtail overfishing of sharks. If shark sanctuaries are to succeed, effective surveil-lance and enforcement is urgently needed. We use a case study with a high level ofillegal shark fishing within a shark sanctuary to help motivate three actionable oppor-tunities to create truly effective shark sanctuaries by leveraging satellite technology:(1) require vessel tracking systems; (2) partner with international research organiza-tions; and (3) ban vessels previously associated with illegal fishing from shark sanctu-aries. Sustaining the level of fishing mortality observed in our case study would leadeven a healthy shark population to collapse to <10% of its unfished state in fewer thanfive years. We outline implementations pathways and provide a roadmap to pair newand emerging satellite technologies with existing international agreements to offernew hope for shark conservation successes globally.

When and how should public agencies provide finance to the private sector in support of climate change mitigation and adaptation? We distinguish theoretically between pilot projects, whose main objective is to obtain information about the desirability of a climate-related project, and full projects, which are at-scale and are often quite risky. When a successful project has distinct private and public benefits, a publicly-funded subsidy may be warranted to induce a pilot project, a full project, or both. We draw on insights about the value of experimentation for entrepreneurship and raising private capital to derive insights about when subsidizing projects or pilots is more efficient. We find that pilot projects have many virtues not previously examined, and these often render them the optimal target of public subsidies to the private sector.

Use of data-limited methods for setting target catches is increasing in the Northeast U.S., but there remains considerable uncertainty over which methods may be suitable for stocks in the region. We retrospectively evaluated the ability of data-limited methods to set target catches close to the overfishing limit for data-rich stocks in the Northeast U.S. Methods explored include options that would be used in truly data-poor cases (i.e., catch-only methods), but we also evaluated methods with different data requirements for stocks that have information beyond a catch time series. The majority of options we explored that used average catches over some portion of the time period, or adjusted the recent catches based on trends in an index were sensitive to the level of historical exploitation. Such methods produced target catches above the overfishing limit for stocks that had a history of overfishing, or target catches that were overly conservative for stocks with a history of light exploitation. Careful consideration of the level of historical exploitation rates, if possible, is therefore needed if using such approaches are to be applied. Catch curve methods, which require catch-at-age information, were the only approaches not sensitive to the level of historical exploitation, and were largely effective at setting target catches close to the overfishing limit, even for stocks with intense historical exploitation rates. However, there were cases where catch curve methods produced unsustainable target catches, particularly for stocks with episodic recruitments, such that care is needed when implementing catch curve methods.

Many analyses of fishery recovery have demonstrated the potential biological and economic benefits of management reform, but few have compared these to the associated costs of management upgrades, which can be substantial. This study aims to determine if the projected economic benefits of management reform outweigh the increases in management costs required to achieve those benefits. To answer this question, we developed a database of country-level fisheries management costs and use those to estimate the country-level costs of management changes. We use this framework to compare estimates of future costs of management upgrades against their economic benefits in terms of profit. Results indicate that for most nations, including the top 25 fishing nations, management upgrades outweigh their associated costs. This result is robust to a number of alternative assumptions about costs. Results also suggest that stronger reforms such as rights-based management, although sometimes more expensive to implement, can lead to greater net economic benefits compared to alternatives.

The world’s oceans supply food and livelihood to billions of people, yet species’ shifting geographic ranges and changes in productivity arising from climate change are expected to profoundly affect these benefits. We ask how improvements in fishery management can offset the negative consequences of climate change; we find that the answer hinges on the current status of stocks. The poor current status of many stocks combined with potentially maladaptive responses to range shifts could reduce future global fisheries yields and profits even more severely than previous estimates have suggested. However, reforming fisheries in ways that jointly fix current inefficiencies, adapt to fisheries productivity changes, and proactively create effective transboundary institutions could lead to a future with higher profits and yields compared to what is produced today.

Most large-scale conservation policies are anticipated or announced in advance. This risks the possibility of preemptive resource extraction before the conservation intervention goes into force. We use a high-resolution dataset of satellite-based fishing activity to show that anticipation of an impending no-take marine reserve undermines the policy by triggering an unintended race-to-fish. We study one of the world’s largest marine reserves, the Phoenix Islands Protected Area (PIPA), and find that fishers more than doubled their fishing effort once this area was earmarked for eventual protected status. The additional fishing effort resulted in an impoverished starting point for PIPA equivalent to 1.5 y of banned fishing. Extrapolating this behavior globally, we estimate that if other marine reserve announcements were to trigger similar preemptive fishing, this could temporarily increase the share of overextracted fisheries from 65% to 72%. Our findings have implications for general conservation efforts as well as the methods that scientists use to monitor and evaluate policy efficacy.

Land-use regulations can lower real estate prices by imposing costs on property owners, but may raise prices by restricting supply and generating amenities. We study the effects of the California Coastal Act, one of the nation’s most stringent land-use regulations, on the price and rental income of multifamily housing. The Coastal Act applies to a narrow section of the California coast, allowing us to compare properties just on either side of the jurisdictional boundary. The setting is advantageous for the study of land-use regulation: boundary location is plausibly exogenous, which we confirm with historical data on boundary placement, and orthogonal to other jurisdictional divisions. We decompose the effects of the regulation into (i) a neighbor effect, the value of restrictions on adjacent properties, (ii) a local effect, which reflects the net effect of own-lot restrictions and the neighbor effect, and (iii) an external effect, the value of amenities generated by restrictions on all properties within the regulated area. Our analysis of multifamily housing prices reveals local and external effects of approximately +6% and +13%, respectively. We use data on rental income to estimate a zero neighbor effect. Together with evidence on building ages and assessed building and land values, this suggests that property owners anticipate that the Coastal Act will provide protection from undesirable development on adjacent properties, even though material differences have not yet appeared.

I examine the estimated economic, ecological, and food security effects of future fishery management reform in Asia. Without climate change, most Asian fisheries stand to gain substantially from reforms. Optimizing fishery management could increase catch by 24% and profit by 34% over business-as-usual management. These benefits arise from fishing some stocks more conservatively and others more aggressively. Although climate change is expected to reduce carrying capacity in 55% of Asian fisheries, I find that under climate change large benefits from fishery management reform are maintained, though these benefits are heterogeneous. The case for reform remains strong for both catch and profit, though these numbers are slightly lower than in the no-climate change case. These results suggest that, to maximize economic output and food security, Asian fisheries will benefit substantially from the transition to catch shares or other economically rational fishery management institutions, despite the looming effects of climate change.

Low-probability, high-consequence climate change events are likely to trigger management responses that are based on the demand for immediate action from those affected. However, these responses may be inefficient and even maladaptive in the long term.

Climate change has impacted physical, biological and human systems, and many of its effects are expected to increase in severity and magnitude in coming decades¹. Some changes will happen gradually, such as sea-level rise and shifts in species ranges. Other impacts, such as floods, fires and disease outbreaks, are acute, low-probability events with widespread consequences. In light of recent social science research on the role of salience in decision-making, we argue that although the risk of episodic high-impact events can motivate planned adaptation, it is the occurrence of events that often leads to action.

Salience theory predicts that people experiencing low-probability, high-consequence events give those events disproportionate weight in subsequent decision-making because their attention is drawn to them as standing out from the norm². Because governments rely on public perceptions and input to allocate public goods that are intended to modify hazards, events that raise the salience of risk will make people and governments more likely to pay attention to that risk, act on that risk or demand action from others — regardless of whether such actions actually reduce risk. While salience-driven decision-making can facilitate action that reduces risk, it can also lead individuals and governments to respond in ways that are inefficient or even maladaptive — such that the allocation of resources could more effectively address future risks or the responses may actually increase future risks.

Here we describe examples of how salience provides a behavioural link between episodic climate impacts with substantial societal and ecological costs (wildfire, floods, disease outbreaks) and observed responses that can be inefficient or maladaptive (Table 1). Ignoring this behavioural link inhibits successful strategies for climate change adaptation planning.

Sustainable management of complex human–environment systems, and the essential services they provide, remains a major challenge, felt from local to global scales. These systems are typically highly dynamic and hard to predict, particularly in the context of rapid environmental change, where novel sets of conditions drive coupled socio-economic-environmental responses. Faced with these challenges, our tools for policy development, while informed by the past experience, must not be unduly constrained; they must allow equally for both the fine-tuning of successful existing approaches and the generation of novel ones in unbiased ways. We study ocean fisheries as an example class of complex human–environmental systems, and present a new model (POSEIDON) and computational approach to policy design. The model includes an adaptive agent-based representation of a fishing fleet, coupled to a simplified ocean ecology model. The agents (fishing boats) do not have programmed responses based on empirical data, but respond adaptively, as a group, to their environment (including policy constraints). This conceptual model captures qualitatively a wide range of empirically observed fleet behaviour, in response to a broad set of policies. Within this framework, we define policy objectives (of arbitrary complexity) and use Bayesian optimization over multiple model runs to find policy parameters that best meet the goals. The trade-offs inherent in this approach are explored explicitly. Taking this further, optimization is used to generate novel hybrid policies. We illustrate this approach using simulated examples, in which policy prescriptions generated by our computational methods are counterintuitive and thus unlikely to be identified by conventional frameworks.