Publications

In the past decade, the study of dispersal of marine organisms has shifted from focusing predominantly on the larval stage to a recent interest in adult movement. Antitropical distributions provide a unique system to assess vagility and dispersal. In this study, we have focused on an antitropical wrasse genus, Semicossyphus, which includes the California sheephead, S. pulcher, and Darwin's sheephead, S. darwini. Using a phylogenetic approach based on mitochondrial and nuclear markers, and a population genetic approach based on mitochondrial control region sequences and 10 microsatellite loci, we compared the phylogenetic relationships of these two species, as well as the population genetic characteristics within S. pulcher. While S. pulcher and S. darwini are found in the temperate eastern Pacific regions of the northern and southern hemispheres, respectively, their genetic divergence was very small (estimated to have occurred between 200 and 600 kya). Within S. pulcher, genetic structuring was generally weak, especially along mainland California, but showed weak differentiation between Sea of Cortez and California, and between mainland California and Channel Islands. We highlight the congruence of weak genetic differentiation both within and between species and discuss possible causes for maintenance of high gene flow. In particular, we argue that deep and cooler water refugia are used as stepping stones to connect distant populations, resulting in low levels of genetic differentiation.

When sustainably managed, wild harvestsfrom the sea provide livelihoods and a vitalsource of protein for hundreds of millions ofpeople (1, 2). If managed well, these benefitsare perpetually renewable. However, numer-ous challenges can compromise the sustain-ability of this natural bounty. Ironically,a significant challenge arises because of thediversity of species caught in nearly all fish-eries. Although healthy diverse ecosystemscan provide resilience against some perturba-tions, fishing pressure in these ecosystems isalmost always geared to the strongest, mosteconomically valuable stocks. In the processof fishing, many other species are incidentallycaught including both (i) species that nobodywants to catch but are costly to avoid, com-monly called bycatch, and (ii) species withsubstantially lower economic value than tar-geted, highline stocks. Even when the targetstock is perfectly managed, these incidentallycaught stocks can collapse if their life historytraits make them more susceptible to a givenlevel of fishing effort than target species.Without regular monitoring and strong man-agement of all species, these weak stocks mayforce the closure of otherwise highly profit-able fisheries. One solution is to expand sci-entific assessments to all species affected byeach fishery, but this is prohibitively expen-sive. Fish are expensive to monitor, and asa result, even the majority of target speciesare currently not adequately assessed world-wide (3). Solving the weak stock problemrequires new innovation. In PNAS, Burgesset al. (4) offer a unique forecasting tool toinnovatively address this global challenge.If the looming collapse of overfished weakstocks could be foreseen well in advance, theenvironmental and economic costs of elimi-nating the problem before it occurs may be farless than the costs of restoring overharvestedspecies after the fact. Overharvesting weakstocks or bycatch species often triggers a reg-ulatory shutdown of the entire fishery to allowrebuilding (5). This rebuilding can last formany decades, because the life history traitsthat put the species at risk also mean that theirrecovery will be exceedingly slow. For exam-ple, weak stocks such as yelloweye rockfish inthe highly diverse rockfish assemblage alongthe west coast of the United States only standsa 50% chance of recovery by 2047, despitesignificant reductions in fishing pressure (6).

A recent highly cited paper from this journal develops a model predicting maximum sustainable yield (MSY) of a fishery using the historical maximum catch (MaxCatch). The model is parameterized with a small sample of fisheries from the United States, and is subsequently applied globally to estimate the benefits of fishery recovery. That empirical relationship has been adopted for many subsequent high-profile analyses. Unfortunately, the analysis suffers from two important oversights: (1) because the model is non-linear, it suffers from “retransformation bias” and therefore the results significantly understate MSY and (2) the analysis is parameterized from of a very limited data set and so generalizability of the fitted empirical relationship between MSY and MaxCatch to global fisheries is questionable. Here, we rectify both oversights and provide an updated estimate of the relationship between MSY and MaxCatch.

While detrital material is recognized as an important food source on coral reefs, its role in reef food webs remains unclear. We quantified standing stock and input rates to the detrital resource pool in exposed forereef and protected backreef habitats of Palmyra Atoll National Wildlife Refuge and measured the trophic structure of the overlying fish assemblage. While detrital standing stock was 1.6 times higher on the backreef than on the forereef, detrital input rates were 1.7 to 2.9 times higher on the forereef. Planktivores were the most abundant guild in the forereef habitat, and stable isotope signatures of detritus reflected a greater input from pelagic sources (i.e. depleted in ¹³C). In contrast, herbivores and detritivores numerically dominated the backreef habitat and detrital stable isotope signatures appeared to be predominately of benthic origin (i.e. enriched in ¹³C). Through total organic carbon (TOC) and nitrogen analyses we found that benthic detritus may represent a significant nutritional source. Converting total nitrogen into maximum protein estimates, we found high benthic deposition of protein (104 to 124 mg m^-2 d^-1) and organic carbon (184 to 190 mg m^-2 d^-1), but very low standing stocks of these materials (protein: 5 to 6 mg m^-2, organic carbon: 46 to 63 mg m^-2). While high water flow rates may explain low standing stocks of detritus in forereef habitats, the lower flow rates in backreef habitats suggest that removal of this material is via consumption by abundant roving detritivorous fishes. Our results provide support for the hypothesis that reef fish detritivory represents a significant consumer-mediated energy pathway, promoting nutrient recycling by linking many elements of a complex food web.

Managers are moving from a model of managing individual sectors, human activities, or ecosystem services to an ecosystem-based management (EBM) approach which attempts to balance the range of services provided by ecosystems. Applying EBM is often difficult due to inherent tradeoffs in managing for different services. This challenge particularly holds for estuarine systems, which have been heavily altered in most regions and are often subject to intense management interventions. Estuarine managers can often choose among a range of management tactics to enhance a particular service; although some management actions will result in strong tradeoffs, others may enhance multiple services simultaneously. Management of estuarine ecosystems could be improved by distinguishing between optimal management actions for enhancing multiple services and those that have severe tradeoffs. This requires a framework that evaluates tradeoff scenarios and identifies management actions likely to benefit multiple services. We created a management action-services matrix as a first step towards assessing tradeoffs and providing managers with a decision support tool. We found that management actions that restored or enhanced natural vegetation (e.g., salt marsh and mangroves) and some shellfish (particularly oysters and oyster reef habitat) benefited multiple services. In contrast, management actions such as desalination, salt pond creation, sand mining, and large container shipping had large net negative effects on several of the other services considered in the matrix. Our framework provides resource managers a simple way to inform EBM decisions and can also be used as a first step in more sophisticated approaches that model service delivery.

Marine reserves are an effective tool for protecting biodiversity locally, with potential economic benefits including enhancement of local fisheries, increased tourism, and maintenance of ecosystem services. However, fishing communities often fear short-term income losses associated with closures, and thus may oppose marine reserves. Here we review empirical data and develop bioeconomic models to show that the value of marine reserves (enhanced adjacent fishing + tourism) may often exceed the pre-reserve value, and that economic benefits can offset the costs in as little as five years. These results suggest the need for a new business model for creating and managing reserves, which could pay for themselves and turn a profit for stakeholder groups. Our model could be expanded to include ecosystem services and other benefits, and it provides a general framework to estimate costs and benefits of reserves and to develop such business models.

Benefits humans rely on from the ocean – marine ecosystem services – are increasingly vulnerable under future climate. This paper reviews how three valued services have, and will continue to, shift under climate change: (1) capture fisheries, (2) food from aquaculture, and (3) protection from coastal hazards such as storms and sea-level rise. Climate adaptation planning is just beginning for fisheries, aquaculture production, and risk mitigation for coastal erosion and inundation. A few examples are highlighted, showing the promise of considering multiple ecosystem services in developing approaches to adapt to sea-level rise, ocean acidification, and rising sea temperatures.

Ecosystem-based adaptation in fisheries and along coastlines and changes in aquaculture practices can improve resilience of species and habitats to future environmental challenges. Opportunities to use market incentives – such as compensation for services or nutrient trading schemes – are relatively untested in marine systems. Relocation of communities in response to rising sea levels illustrates the urgent need to manage human activities and investments in ecosystems to provide a sustainable flow of benefits in the face of future climate change.

We analyze a policy experiment in an Alaskan commercial fishery that assigned a portion of an overall catch quota to a voluntary co-op, with the remainder exploited competitively by those choosing to fish independently. Unlike the individual quota system advocated by many economists, the policy encouraged coordinated fishing and did not require a detailed assignment of rights. We model the decision to join and behavior under cooperative and independent fishing. The data confirm our key predictions: the co-op attracted the least skilled fishermen, consolidated and coordinated effort among its most efficient members, and provided shared infrastructure. We estimate that resulting gains in rent were at least 33 percent. Some independents were disadvantaged by the co-op’s formation, however, which prompted them to oppose it in court. We analyze the source of their disadvantage and provide guidance for designing fishery reform that leads to Pareto improvements, enabling reform without losers.

As with many marine species, the vast majority of coral-reef fishes have a bipartite life cycle consisting of a dispersive larval stage and a benthic adult stage. While the potentially far-reaching demographic and ecological consequences of marine dispersal are widely appreciated, little is known of the structure of the larval pool and of the dispersive process itself. Utilizing Palindrome Sequence Analysis of otolith micro-chemistry (PaSA;) we show that larvae of Neopomacentrus miryae (Pomacentridae) appear to remain in cohesive cohorts throughout their entire pelagic larval duration (PLD; ∼28 days). Genetically, we found cohort members to be maternally (mtDNA) unrelated. While physical forcing cannot be negated as contributing to initial cohort formation, the small scale of the observed spatial structure suggests that some behavioral modification may be involved from a very early age. This study contributes to our ongoing re-evaluation of the processes that structure marine populations and communities and the spatial scales at which they operate.

Although experiments have shown that habitat structure may influence the distribution of species and species interactions, these effects are still not commonly integrated into studies of community dynamics. Since habitat structure often varies within and among communities, this may limit our understanding of how various factors influence communities. Here, we examined how mussel bed complexity (the presence and thickness of mussel layers) influenced the persistence of whelks (Nucella emarginata) and interactions with a top predator (ochre sea stars, Pisaster ochraceus) and prey (mussels, Mytilus californianus). Results from a mark–recapture experiment indicate that whelk recapture rates are higher in more complex habitats, and laboratory experiments demonstrate that habitat complexity affects whelk feeding, growth, and nonconsumptive interactions with a keystone predator. Habitat complexity therefore has direct effects on species and also may lead to trade-offs among feeding, refuge, and other factors, potentially influencing the distribution of whelks and the effects of both whelks and sea stars on intertidal communities. These results demonstrate that habitat structure may play an important role in intertidal communities and other habitats and should be further considered in the experimental design of future studies of community dynamics.

Benefits of marine reserves for conservation and fisheries management are predicated upon reduced mortality for target organisms inside reserves. Interestingly however, very few studies describe how reserves influence mortality rates (but see Attwood 2003; Willis & Millar 2005; Götz et al. 2008; Taylor & McIlwain 2010). Empirical studies of marine reserves focus on differences in organism density, abundance and size inside versus outside reserves (reviews by Côté et al. 2001; Halpern 2003; Lester et al. 2009), which is sensible because a common objective of conservation is to increase these attributes for depleted populations. Understanding changes in mortality across space in relation to reserve protection is a critical component of evaluating not only the conservation benefit of reserves, but also the contribution of reserves to fisheries management objectives.

Concerns over fishing impacts on marine populations and ecosystems have intensified the need to improve ocean management. One increasingly popular market-based instrument for ecological stewardship is the use of certification and eco-labeling programs to highlight sustainable fisheries with low environmental impacts. The Marine Stewardship Council (MSC) is the most prominent of these programs. Despite widespread discussions about the rigor of the MSC standards, no comprehensive analysis of the performance of MSC-certified fish stocks has yet been conducted. We compared status and abundance trends of 45 certified stocks with those of 179 uncertified stocks, finding that 74% of certified fisheries were above biomass levels that would produce maximum sustainable yield, compared with only 44% of uncertified fisheries. On average, the biomass of certified stocks increased by 46% over the past 10 years, whereas uncertified fisheries increased by just 9%. As part of the MSC process, fisheries initially go through a confidential pre-assessment process. When certified fisheries are compared with those that decline to pursue full certification after pre-assessment, certified stocks had much lower mean exploitation rates (67% of the rate producing maximum sustainable yield vs. 92% for those declining to pursue certification), allowing for more sustainable harvesting and in many cases biomass rebuilding. From a consumer’s point of view this means that MSC-certified seafood is 3–5 times less likely to be subject to harmful fishing than uncertified seafood. Thus, MSC-certification accurately identifies healthy fish stocks and conveys reliable information on stock status to seafood consumers.

The ocean plays a critical role in supporting human well-being, from providing food, livelihoods and recreational opportunities to regulating the global climate. Sustainable management aimed at maintaining the flow of a broad range of benefits from the ocean requires a comprehensive and quantitative method to measure and monitor the health of coupled human–ocean systems. We created an index comprising ten diverse public goals for a healthy coupled human–ocean system and calculated the index for every coastal country. Globally, the overall index score was 60 out of 100 (range 36–86), with developed countries generally performing better than developing countries, but with notable exceptions. Only 5% of countries scored higher than 70, whereas 32% scored lower than 50. The index provides a powerful tool to raise public awareness, direct resource management, improve policy and prioritize scientific research.

There is a growing focus around the world on marine spatial planning, including spatial fisheries management. Some spatial management approaches are quite blunt, as when marine protected areas (MPAs) are established to restrict fishing in specific locations. Other management tools, such as zoning or spatial user rights, will affect the distribution of fishing effort in a more nuanced manner. Considerable research has focused on the ability of MPAs to increase fishery returns, but the potential for the broader class of spatial management approaches to outperform MPAs has received far less attention. We use bioeconomic models of seven nearshore fisheries in Southern California to explore the value of optimized spatial management in which the distribution of fishing is chosen to maximize profits. We show that fully optimized spatial management can substantially increase fishery profits relative to optimal nonspatial management but that the magnitude of this increase depends on characteristics of the fishing fleet and target species. Strategically placed MPAs can also increase profits substantially compared with nonspatial management, particularly if fishing costs are low, although profit increases available through optimal MPA-based management are roughly half those from fully optimized spatial management. However, if the same total area is protected by randomly placing MPAs, starkly contrasting results emerge: most random MPA designs reduce expected profits. The high value of spatial management estimated here supports continued interest in spatially explicit fisheries regulations but emphasizes that predicted increases in profits can only be achieved if the fishery is well understood and the regulations are strategically designed.

In addition to fostering biodiversity goals, marine protected area (MPA) implementation has economic consequences for both commercial and recreational fisheries. During the implementation of the State of California (USA) Marine Life Protection Act (MLPA), which mandates the creation of an MPA network in California's state waters, the stakeholders and policymakers utilized a pair of economic analyses that addressed these considerations. One was a comparative, static assessment of short-term, “worst case” potential socioeconomic impacts to important fisheries based on surveys of local fishermen. This analysis made no assumptions about fishery management outside of MPAs, assumed no spillover of fish from MPAs into fished areas or reallocation of fishing effort, and estimated the maximum potential dollar-value economic impacts over a short time scale. The other was a dynamic, bioeconomic assessment of the changes in spatial distribution of biomass and catch, based on published biological parameter values, oceanographic models of larval connectivity, and a range of possible levels of fishing. This analysis explicitly accounted for fish population dynamics, spillover, fisher movement, and fishery management outside of the MPAs, but was limited to long-term, equilibrium-based results because of a lack of baseline abundance data. Both evaluation methods were novel in their spatial resolution and their use directly in an MPA design process, rather than after implementation. The two methods produced broadly similar (at a regional spatial scale) evaluations of the likely effects of proposed MPAs on fisheries, at least when the bioeconomic model assumed fishery management was conservative. Our experience with these analyses in the MLPA Initiative process led to several suggestions for future MPA design efforts: (i) since the change in fish biomass inside MPAs partly depends on fisheries management outside of them, it is useful to integrate or coordinate conventional fishery management and MPA planning efforts; (ii) integrate modeling assessments early into MPA design, as part of a post-implementation adaptive management approach; and (iii) integrate empirical fishery data into bioeconomic models in order to improve representations of human behavior and short-term forecasts of changes in fished populations.

A central challenge for natural resource management is developing rigorous yet practical approaches for balancing the costs and benefits of diverse human uses of ecosystems. Economic theory has a long history of evaluating tradeoffs in returns from different assets to identify optimal investment strategies. There has been recent progress applying this framework to the delivery of ecosystem services in land use planning. However, despite growing national and international interest in marine spatial planning, there is a lack of parallel frameworks in the marine realm. This paper reviews an ecosystem service tradeoff analysis framework and provides a more comprehensive synthesis for how it can be applied to marine spatial planning and marine ecosystem-based management. A tradeoff analysis approach can reveal inferior management options, demonstrate the benefits of comprehensive planning for multiple, interacting services over managing single services, and identify ‘compatible’ services that provide win–win management options.

Managing fisheries by delegating authority to an association of users, often organized as a cooperative, is gaining increased attention as a strategy for implementing rights-based reform. Assigning rights to groups rather than individuals can facilitate coordination and collective action and enable efficiency gains similar to those achieved when a firm organizes inputs centrally. Evidence from developed country fisheries managed by cooperatives indicates that coordination gains can be substantial. Furthermore, these gains often take forms overlooked in the traditional fishery reform literature, including those from enhanced product recovery and quality, improved spatial and temporal deployment of effort, and reduced environmental damage. In developing countries, assigning management responsibility to user groups can facilitate user-based provision of public goods in situations where governments do not function well. Developing country fishery cooperatives commonly provide monitoring and enforcement of access limitations, limits on fishing effort, and actions to conserve shared stocks. This article reviews empirical evidence on the performance of fishery cooperatives in developed and developing countries. A key conclusion is that using a combination of rights-based instruments can achieve efficiencies that cannot be captured by any single instrument.

Cooperatives are increasingly proposed as solutions for sustainable fisheries management. While individual case studies and economic theory suggest that cooperatives may manage fisheries effectively under some conditions, there is little empirical evidence comparing the actions of cooperative fisheries across a diverse set of environments. This study applies a standardized survey method to collect data from a set of cooperatively managed fisheries from around the globe, documenting their social, economic, and ecological settings as well as the cooperative behaviors in which they engage and the role they play in conservation. The resulting database covers 67 cooperatives from the major oceanic regions of the world, providing a unique overview of the global diversity of fishery cooperatives. It enables empirical analysis of the links between the characteristics and contexts of fisheries, such as the development status of the host nation, fisheries management practices, and species characteristics, and the collective actions taken by fishery cooperatives. The evidence shows that cooperatives form in a variety of development and governance contexts, and in diverse kinds of fisheries. Fishery cooperatives often take actions directed toward coordinating harvest activities, adopting and enforcing restrictions on fishing methods and effort, and taking direct conservation actions such as establishment of private marine protected areas.

No-take marine reserves directly promote the recovery of predatory species, which can have negative indirect effects on prey populations in reserves. When harvesting also occurs on prey species there is potential conflict between the direct and indirect effects of protection, and reserves may not have conservation benefits for prey species. For example, sea urchins are fished in many regions, but may decline in reserves due to increased predation rates. To investigate this potential conflict, this paper compares density, size, biomass and reproductive potential of both a harvested and an unharvested urchin species between a long-term reserve and unprotected sites in California. Consistent with density-mediated indirect interactions, densities of the unharvested species were 3.4-times higher at unprotected sites compared to reserve sites. However, for the harvested species, densities were comparable between reserve and unprotected sites. Both species were consistently larger at reserve sites, and the biomass and reproductive potential of the harvested species was 4.8- and 7.0-times higher, respectively, than at unprotected sites. This is likely due to differences in size-selectivity between harvesting and predators, and potential compensatory effects of predators. While the generality of these effects needs to be tested, these results suggest mechanisms whereby reserves can benefit both predator and prey species.

Coordinating decisions and actions among interacting sectors is a critical component of ecosystem-based management, but uncertainty about coordinated management’s effects is compromising its perceived value and use. We constructed an analytical framework for explicitly calculating how coordination affects management decisions, ecosystem state and the provision of ecosystem services in relation to ecosystem dynamics and socio-economic objectives. The central insight is that the appropriate comparison strategy to optimal coordinated management is optimal uncoordinated management, which can be identified at the game theoretic Nash equilibrium. Using this insight we can calculate coordination’s effects in relation to uncoordinated management and other reference scenarios. To illustrate how this framework can help identify ecosystem and socio-economic conditions under which coordination is most influential and valuable, we applied it to a heuristic case study and a simulation model for the California Current Marine Ecosystem. Results indicate that coordinated management can more than double an ecosystem’s societal value, especially when sectors can effectively manipulate resources that interact strongly. However, societal gains from coordination will need to be reconciled with observations that it also leads to strategic simplification of the ecological food web, and generates both positive and negative impacts on individual sectors and non-target species.