Publications

Data sets providing repeated observations of land use at fine spatial scales have enabled a new generation of land-use studies. In the past decade, these analyses have put increasing emphasis on empirical research designs that provide more convincing causal estimates. I review the use of instrumental variables, matching, difference-in-differences, regression discontinuity design, and randomized controlled trials in the recent land-use economics literature, exploring how new data have made possible the use of these research designs. I show that these estimators have produced different results than were obtained with traditional approaches and have provided new insights into important land-use policy issues such as additionality and spillover effects.

The capacity for aquaculture to provide an alternative source of fish and seafood to capture fisheries was once promoted as a tool to reduce demand for wild fish and thus tackle overfishing. To date, there is little evidence to suggest that aquaculture growth has successfully reduced fishing effort on wild populations. Recent theory on “blue transitions” suggests that displacement may only occur as aquaculture production surpasses that of capture operations. Yet, there has been no systematic attempt to understand whether aquaculture-driven fisheries displacement has occurred in countries where aquaculture is now the dominant production form. We investigate the role of aquaculture on fisheries landings in these “aquaculture-dominant” countries using national-level production, trade, consumption and socioeconomic data from 1980 to 2017. Importantly, we find that aquaculture growth is associated with fisheries decline in aquaculture-dominant countries, but the marginal effects of aquaculture have a far weaker influence on wild-caught landings than other promoting factors, such as fish consumption and trade. Further, our qualitative analysis of the state of wild fisheries in aquaculture-dominant nations suggests that overexploitation continues to be pervasive and that any minimal displacement effects from aquaculture are unlikely to have offset the environmental impacts imposed by the growing sector. The rise of aquaculture as an alternative production form can provide valuable insights for growing industries developing sustainable new foods. Unless coupled with effective food consumption policy, such products may simply add to rather than displace the environmental impacts of human food production.

To help the State of California achieve its carbon neutrality goal, a team of researchers from the University of California Santa Barbara (UCSB) completed this study commissioned by the California Environmental Protection Agency (CalEPA) that examines options for reducing the state’s supply of transportation fuel in parallel with reductions in demand. The report also considers paths to promote health and economic equity in the process of decarbonizing the transportation sector.

Seaweed aquaculture is capable of removing large quantities of nitrogen and phosphorus from coastal ecosystems, yet seaweed has gained little traction for its potential role in targeted nutrient assimilation. Marine nutrient pollution is increasing around the world, contributing to expanding eutrophic conditions and co-occurring with other stressors that impact the state and stability of aquatic ecosystems. In the United States, climate change, legacy nitrogen, and nonpoint source pollution make it increasingly difficult to curb growing eutrophication and the associated effects, such as hypoxia (dissolved oxygen < 2 mgL^-1). Employing a synthetic semi-quantitative approach, we use the Gulf of Mexico as a case study – a U.S. priority area for aquaculture with substantial nutrient pollution and one of the largest hypoxic zones on the planet – to assess the potential for native seaweed aquaculture to augment upstream pollution control with downstream nutrient assimilation. Results from this analysis suggest that given growing market demand, new product pathways, and nutrient pollution markets, seaweed aquaculture may be a feasible tool for nutrient assimilation that could subsidize, if not pay for itself.

Cell-based seafood is an emerging novel food, with many start-up companies aspiring for ocean conservation benefits through expanded market share that displaces wild-caught seafood. However, the ability for cell-based seafood to achieve this conservation outcome is often oversimplified and will rely on an extensive, and we find somewhat tenuous, chain of events. Here, we outline the technological, behavioural, market and ecological changes that must occur along this pathway, and conclude that fisheries recoveries and collateral ocean benefits are unlikely to result from cell-based seafood technology. In particular, we detail nine necessary steps and argue that failure at any one step could hinder or even eliminate cell-based seafood's conservation effects. We additionally draw comparisons to aquaculture and share broader lessons for other demand-driven product interventions.

This paper designs a reciprocal dumping model to address the control of industrial pollution between two trading partners. Firms generate transboundary pollution from production and environmental taxes represent the pollution control instrument. We ask whether environmental taxes implemented in a non-cooperative setting are more stringent than the globally efficient level. Relative to the globally efficient case, we find in the linear Markov Perfect Nash Equilibrium (MPNE) context that the tax rate for both countries is smaller and individual emissions are larger. However, these results may not hold in the non-linear MPNE case depending on market structure and environmental conditions. Unlike the symmetric equilibrium case, the tax rates are always discontinuous under asymmetric MPNEs. The asymmetric equilibrium scenario can give rise to higher individual payoffs relative to the symmetric equilibrium case.

With nearly every country combating the 2019 novel coronavirus (COVID-19), there is a need to understand how local environmental conditions may modify transmission. To date, quantifying seasonality of the disease has been limited by scarce data and the difficulty of isolating climatological variables from other drivers of transmission in observational studies. We combine a spatially resolved dataset of confirmed COVID-19 cases, composed of 3,235 regions across 173 countries, with local environmental conditions and a statistical approach developed to quantify causal effects of environmental conditions in observational data settings. We find that ultraviolet (UV) radiation has a statistically significant effect on daily COVID-19 growth rates: a SD increase in UV lowers the daily growth rate of COVID-19 cases by 1 percentage point over the subsequent 2.5 wk, relative to an average in-sample growth rate of 13.2%. The time pattern of lagged effects peaks 9 to 11 d after UV exposure, consistent with the combined timescale of incubation, testing, and reporting. Cumulative effects of temperature and humidity are not statistically significant. Simulations illustrate how seasonal changes in UV have influenced regional patterns of COVID-19 growth rates from January to June, indicating that UV has a substantially smaller effect on the spread of the disease than social distancing policies. Furthermore, total COVID-19 seasonality has indeterminate sign for most regions during this period due to uncertain effects of other environmental variables. Our findings indicate UV exposure influences COVID-19 cases, but a comprehensive understanding of seasonality awaits further analysis.

While forced labor in the world’s fishing fleet has been widely documented, its extent remains unknown. No methods previously existed for remotely identifying individual fishing vessels potentially engaged in these abuses on a global scale. By combining expertise from human rights practitioners and satellite vessel monitoring data, we show that vessels reported to use forced labor behave in systematically different ways from other vessels. We exploit this insight by using machine learning to identify high-risk vessels from among 16,000 industrial longliner, squid jigger, and trawler fishing vessels. Our model reveals that between 14% and 26% of vessels were high-risk, and also reveals patterns of where these vessels fished and which ports they visited. Between 57,000 and 100,000 individuals worked on these vessels, many of whom may have been forced labor victims. This information provides unprecedented opportunities for novel interventions to combat this humanitarian tragedy. More broadly, this research demonstrates a proof of concept for using remote sensing to detect forced labor abuses.

Seafood companies rarely disclose what or where they are fishing. To provide a first overview of the fishing industry in the high seas—the area beyond national jurisdiction—we linked fishing activity in the high seas to vessel owners and corporate actors. We identified 1,120 corporate actors for 2,482 vessels (∼2/3 of high seas fishing vessels and effort in 2018) and found that the top 100 corporate actors account for 36% of all high seas fishing effort. As attribution for anthropogenic activities expands beyond a national framework, we demonstrate the feasibility of methods to identify the high seas fishing industry. These results provide a unique lens through which to view accountability for the use and protection of marine biodiversity.

Effective management of aquatic resources, wild and farmed, has implications for the livelihoods of dependent communities, food security, and ecosystem health. Good management requires information on the status of harvested species, yet many gaps remain in our understanding of these species and systems, in particular the lack of taxonomic resolution of harvested species. To assess these gaps we compared the occurrence of landed species (freshwater and marine) from the United Nations Food and Agriculture Organization (FAO) global fisheries production database to those in the International Union for Conservation of Nature (IUCN) Red List and the RAM Legacy Stock Assessment Database, some of the largest and most comprehensive global datasets of consumed aquatic species. We also quantified the level of resolution and trends in taxonomic reporting for all landed taxa in the FAO database. Of the 1,695 consumed aquatic species or groups in the FAO database considered in this analysis, a large portion (35%) are missing from both of the other two global datasets, either IUCN or RAM, used to monitor, manage, and protect aquatic resources. Only a small number of all fished taxa reported in FAO data (150 out of 1,695; 9%) have both a stock assessment in RAM and a conservation assessment in IUCN. Furthermore, 40% of wild caught landings are not reported to the species level, limiting our ability to effectively account for the environmental impacts of wild harvest. Landings of invertebrates (44%) and landings in Asia (>75%) accounted for the majority of harvest without species specific information in 2018. Assessing the overlap of species which are both farmed and fished to broadly map possible interactions – which can help or hinder wild populations - we found 296 species, accounting for 12% of total wild landings globally, and 103 countries and territories that have overlap in the species caught in the wild and produced through aquaculture. In all, our work highlights that while fisheries management is improving in many areas there remain key gaps in data resolution that are critical for fisheries assessments and conservation of aquatic systems into the future.

Climate change poses unprecedented challenges for fisheries management systems. Increased environmental variability and uncertainty due to climate change are creating shifts in productivity and distribution of fished species, and subsequent social-ecological impacts that require timely implementation of adaptive management strategies. Yet many proposed “climate-ready” fisheries actions – such as integrating climate factors into stock assessments and increasing flexibility in decision-making – either complicate or add to existing responsibilities of fishery managers and strain existing institutions. In the United States, many fisheries management agencies have explicitly acknowledged certain capacity shortfalls and institutional limitations to addressing current and projected impacts of climate change on marine fisheries. Many resource and capacity gaps across the adaptive fisheries management cycle could be filled through more effective fishery partnerships among management agencies, fishing industries, private sector, and academia. Partnership approaches are key to unlocking capacity for achieving climate-ready fisheries yet expanded implementation may require a shift towards a model that empowers and obligates fishery stakeholders to take on expanded roles with appropriate guidelines and oversight, while establishing increased roles for agencies as facilitators and auditors for certain tasks. Building and institutionalizing more effective fishery partnerships to achieve climate-ready fisheries will require clear guidance and enabling conditions.

Rural economies in many developing countries are characterized by a lean season in the months preceding harvest, when farmers have depleted their cash and grain savings from the previous year. To identify the impacts of liquidity during the lean season, we offered subsidized loans in randomly selected villages in rural Zambia. Ninety-eight percent of households took up the loan. Loan eligibility led to increases in on-farm labor and agricultural output, driving up wages in local labor markets. Larger effects for poorer households suggest that liquidity constraints contribute to inequality in rural economies.

Contrary to most terrestrial organisms, which release their carbon into the atmosphere after death, carcasses of large marine fish sink and sequester carbon in the deep ocean. Yet, fisheries have extracted a massive amount of this “blue carbon,” contributing to additional atmospheric CO2 emissions. Here, we used historical catches and fuel consumption to show that ocean fisheries have released a minimum of 0.73 billion metric tons of CO2 (GtCO2) in the atmosphere since 1950. Globally, 43.5% of the blue carbon extracted by fisheries in the high seas comes from areas that would be economically unprofitable without subsidies. Limiting blue carbon extraction by fisheries, particularly on unprofitable areas, would reduce CO2 emissions by burning less fuel and reactivating a natural carbon pump through the rebuilding of fish stocks and the increase of carcasses deadfall.

Marine protected areas (MPAs) are conservation tools that are increasingly implemented, with growing national commitments for MPA expansion. Perhaps the greatest challenge to expanded use of MPAs is the perceived trade-off between protection and food production. Since MPAs can benefit both conservation and fisheries in areas experiencing overfishing and since overfishing is common in many coastal nations, we ask how MPAs can be designed specifically to improve fisheries yields. We assembled distribution, life history, and fisheries exploitation data for 1,338 commercially important stocks to derive an optimized network of MPAs globally. We show that strategically expanding the existing global MPA network to protect an additional 5% of the ocean could increase future catch by at least 20% via spillover, generating 9 to 12 million metric tons more food annually than in a business-as-usual world with no additional protection. Our results demonstrate how food provisioning can be a central driver of MPA design, offering a pathway to strategically conserve ocean areas while securing seafood for the future.

Overfishing and other anthropogenic impacts to ocean ecosystems have motivated widespread implementation of no-take marine reserves to protect biodiversity and fished resources. Fully protected marine reserves now comprise approximately 2.5% of the ocean and calls for enhanced protections abound. The benefits to marine biodiversity within reserve borders are clear, yet the contributions beyond borders remain the subject of continued scholarship. In this article, six co-benefits of marine reserves for fisheries are explored. Broadly, the six co-benefits fall within two categories 1) use of reserves as tools to adaptively learn, promote resiliency, and manage marine resources, especially in the face of a changing climate and 2) use of reserves to provide credit against uncertainty in management and sustainability criteria. Broader understanding and consideration of the benefits of marine reserves can further policy discussions and deepen conversations regarding social, ecological, and economic tradeoffs of implementing marine reserves.

The World Trade Organization (WTO) is in a unique position to deliver on Sustainable Development Goal (SDG) 14.6 by reforming global fisheries subsidies in 2020. Yet, a number of unanswered questions threaten to inhibit WTO delegates from crafting a smart agreement that improves global fisheries health. We combine global data on industrial fishing activity, subsidies, and stock assessments to show that: (1) subsidies prop up fishing effort all across the world’s ocean and (2) larger subsidies tend to occur in fisheries that are poorly managed. When combined, this evidence suggests that subsidy reform could have geographically-extensive consequences for many of the world’s largest fisheries. While much work remains to establish causality and make quantitative predictions, this evidence informs the rapidly-evolving policy debate and we conclude with actionable policy suggestions.

Bigeye tuna in the Western and Central Pacific Ocean were perceived as overfished for nearly 20 years, in large part due to incidental catch in the much larger skipjack tuna fishery. Efforts to halt the overfishing of bigeye stalled due to disagreements over the distribution of costs and benefits from reform. An alternative Coasean-style approach to setting both harvesting levels and the allocation of costs and benefits might offer a path forward. We calculate the costs and benefits of achieving bigeye conservation goals and describe an exchange through which benefits could be realized via removal of Fish Aggregating Devices (FADs). Through trade, aggregate benefits and costs are more apt to be in balance relative to mandated protection controls. The realities of bargaining costs in a multilateral setting are not underappreciated, but in light of existing stalemates in this and other fisheries, consideration of Coasean-style approaches is warranted.

Moored fish aggregating devices (MFADs) are promoted throughout global small-scale fisheries as tools to enhance livelihoods and shift fishing pressure onto offshore resources. A particularly large number of projects initiating and encouraging MFAD development have occurred in the Caribbean region. Despite ongoing promotion of MFAD fisheries in the region, there is limited understanding of their current extent, distribution, and management across Caribbean states. Here we integrate key informant surveys with a supporting literature review to generate the first comprehensive overview of MFAD fishery status and trends in the insular Caribbean and Bermuda. While regional growth has been substantial, we find wide diversity among states in terms of the number of MFADs deployed, MFAD ownership (private or public), fleet engagement, and the existence and enforcement of MFAD regulations. Our results suggest that despite the presence of regulations in some states, management limitations and private MFAD ownership may be associated with a rapid proliferation of deployed MFADs across the Caribbean. We discuss the critical role of management and monitoring in attaining the anticipated benefits of MFAD fisheries and reducing social and environmental risks. By documenting the diverse paths that MFAD fisheries have taken in different states, this study provides an opportunity for prospective and existing MFAD programs to better evaluate the risks and rewards associated with MFADs and to design appropriate management.