Publications

Marine protected areas (MPAs) are increasingly being used globally to conserve marine resources. However, whether many MPAs are being effectively and equitably managed, and how MPA management influences substantive outcomes remain unknown. We developed a global database of management and fish population data (433 and 218 MPAs, respectively) to assess: MPA management processes; the effects of MPAs on fish populations; and relationships between management processes and ecological effects. Here we report that many MPAs failed to meet thresholds for effective and equitable management processes, with widespread shortfalls in staff and financial resources. Although 71% of MPAs positively influenced fish populations, these conservation impacts were highly variable. Staff and budget capacity were the strongest predictors of conservation impact: MPAs with adequate staff capacity had ecological effects 2.9 times greater than MPAs with inadequate capacity. Thus, continued global expansion of MPAs without adequate investment in human and financial capacity is likely to lead to sub-optimal conservation outcomes.

Marine ecosystems provide a range of valuable services, some of which come with market prices to quantify value and others for which markets have not set prices. Lacking perfect information, policy makers are at risk of undercounting non-priced values and services, leading to biases in policy decisions in favor of services valued through markets. Furthermore, understanding users’ valuation of specific site attributes, such as marine biodiversity, can contribute to effective policy decisions. This paper presents a non-market valuation of private recreational boaters (PRBs) in the Channel Islands National Marine Sanctuary located in California, USA, using data from an intercept survey conducted in 2006 and 2007. A Random Utility Model is used to estimate PRBs’ daily trip values and the importance of specific site attributes. The average consumer surplus was estimated at $48.62 per trip, with a total non-market value of non-consumptive private recreational boating of $86,325 annually. PRBs show a preference for visiting locations with lower exposure to prevailing winds and greater species richness and abundance, which to the authors’ knowledge is the first time that PRBs have been found to value biological diversity in site choices. Furthermore, this suggests that improved biodiversity and productivity of marine ecosystems contribute to better recreational experiences. The results from this study reveal the importance of including non-market services and stakeholder's preferences into policy decisions.

Despite rapid growth in the marine tourism sector, the impacts of recreation on the marine environment are generally not well understood. Most existing studies of marine recreation ecology have focused on behavioural changes resulting from direct interactions between humans and wildlife including provisioning. However, non-consumptive, non-provisioning human impacts may also result in persistent behavioural impacts to shark populations. In this study, we examined differences in residency, abundance, and behaviour of reef sharks at Palmyra Atoll in response to long-term SCUBA diving activity, using a combination of survey techniques including baited remote underwater video systems and multi-year passive acoustic monitoring. In most locations with recreational diving operations, some level of human impact is pervasive, but on Palmyra, extractive fishing is prohibited, and scientific diving activities are concentrated on just a few sites that house long-term monitoring projects. These sites experience relatively intensive diving, while the majority of the island is entirely undived. Evidence from elsewhere has shown that sharks behaviourally respond to people in the water over short time scales, but our results indicate that this response may not persist. We did not detect differences in reef shark abundance or behaviour between heavily dived and undived locations, nor were there differences in shark residency patterns at dived and undived sites in a year with substantial diving activity and a year without any diving. Our results suggest that humans can interact with reef sharks without persistent behavioural impacts, and that well-regulated shark diving tourism can be accomplished without undermining conservation goals.

This paper develops a method for forecasting the marginal abatement cost (MAC) of climate policy using three features of the failed Waxman-Markey bill. First, the MAC is revealed by the price of traded permits. Second, the permit price is estimated using a regression discontinuity design (RDD) comparing stock returns of firms on either side of the policy's free permit cutoff rule. Third, because Waxman-Markey was never implemented, I extend the RDD approach to incorporate prediction market prices which normalize estimates by policy realization probabilities. A final bounding analysis recovers a MAC range of $5 to $19 per ton CO₂e.

What did coral reef ecosystems look like before human impacts became pervasive? Early efforts to reconstruct baselines resulted in the controversial suggestion that pristine coral reefs have inverted trophic pyramids, with disproportionally large top predator biomass. The validity of the coral reef inverted trophic pyramid has been questioned, but until now, was not resolved empirically. We use data from an eight-year tag-recapture program with spatially explicit, capture-recapture models to re-examine the population size and density of a key top predator at Palmyra atoll, the same location that inspired the idea of inverted trophic biomass pyramids in coral reef ecosystems. Given that animal movement is suspected to have significantly biased early biomass estimates of highly mobile top predators, we focused our reassessment on the most mobile and most abundant predator at Palmyra, the grey reef shark (Carcharhinus amblyrhynchos). We estimated a density of 21.3 (95% CI 17.8, 24.7) grey reef sharks/km², which is an order of magnitude lower than the estimates that suggested an inverted trophic pyramid. Our results indicate that the trophic structure of an unexploited reef fish community is not inverted, and that even healthy top predator populations may be considerably smaller, and more precarious, than previously thought.

For broadly distributed, often overexploited species such as elasmobranchs (sharks and rays), conservation management would benefit from understanding how life history traits change in response to local environmental and ecological factors. However, fishing obfuscates this objective by causing complex and often mixed effects on the life histories of target species. Disentangling the many drivers of life history variability requires knowledge of elasmobranch populations in the absence of fishing, which is rarely available. Here, we describe the growth, maximum size, sex ratios, size at maturity, and offer a direct estimate of survival of an unfished population of grey reef sharks (Carcharhinus amblyrhynchos) using data from an eight year tag-recapture study. We then synthesized published information on the life history of C. amblyrhynchos from across its geographic range, and for the first time, we attempted to disentangle the contribution of fishing from geographic variation in an elasmobranch species. For Palmyra’s unfished C. amblyrhynchos population, the von Bertalanffy growth function (VBGF) growth coefficient k was 0.05 and asymptotic length L_∞ was 163.3 cm total length (TL). Maximum size was 175.5 cm TL from a female shark, length at maturity was estimated at 116.7–123.2 cm TL for male sharks, maximum lifespan estimated from VBGF parameters was 18.1 years for both sexes combined, and annual survival was 0.74 year^-1. Consistent with findings from studies on other elasmobranch species, we found significant intraspecific variability in reported life history traits of C. amblyrhynchos. However, contrary to what others have reported, we did not find consistent patterns in life history variability as a function of biogeography or fishing. Ultimately, the substantial, but not yet predictable variability in life history traits observed for C. amblyrhynchos across its geographic range suggests that regional management may be necessary to set sustainable harvest targets and to recover this and other shark species globally.

Perhaps the most fundamental insight from fisheryscience is that ecosystems impose important and pre-dictable constraints on food production from the sea.The familiar hump-shaped growth curve implies thatthe growth rate and carrying capacity of a specieslimit its production: Once stocks are depleted, furtherincreasing fishing pressure will only lead to decreasesin catch. This logic underpins fishery science andeconomics, nearly all fishery management legislation,and, most importantly, recent calls to restore fishstocks around the world (1). In PNAS, Cao et al. (2)propose a series of concrete steps for ecosystem andfishery restoration in the world’s superpower of fish-ing, China. Their call is couched within the complex,and often misunderstood, norms of Chinese culture,and appropriately distances itself from the western view of ocean management that is often taken forgranted here.

A stylized representation of “western” fisheryobjectives is to optimize the catch of commerciallyimportant fish stocks while ensuring a more naturalecosystem and persistence of all species. Under thisapproach, the fishery economy is believed to be inti-mately intertwined with natural ecosystems; the for-mer cannot thrive without the latter. We are toldthat such ecosystem protection increases production,ensures resilience, and delivers a suite of other ser-vices (such as carbon sinks or storm protection).

Territorial use rights in fisheries (TURFs) paired with marine reserves (henceforth called "TURF-reserves") have been proposed as a viable management strategy to combat overfishing in many small-scale fisheries by combining the TURF benefits of exclusive access with the conservation, spillover, and resilience benefits of reserves. When appropriately designed and implemented, TURF- reserves can encourage stewardship and empower fishers to better manage their resources. While tools that assist spatial design in marine nearshore contexts exist, they are data intensive, require expertise in software operation, and often need Internet connection. We developed the TURF-Reserve Design Tool to assist spatial design in settings where these elements are not present by providing an easy-to-use decision support tool for small-scale fisheries contexts. This tool consists of a spatial bioeconomic model that allows managers to analyze the relative performance of TURF-reserve designs for a specific setting by assessing the relative ecological and economic outcomes of each design.

Unsustainable fishing in marine systems creates fisheries management and conservation challenges, with implications for ecosystem health, livelihoods, economies, and seafood supply. Thus there is a need for management approaches that can support productive fisheries and healthy ecosystems. Property rights, and particularly spatial rights or territorial use rights in fisheries (TURFs), are increasingly proposed as a solution. It has been suggested that TURFs may align fishers’ incentives with long-term stewardship, resulting in improved yields and positive conservation outcomes. Here we examined this idea by reviewing existing theoretical and empirical evidence for TURF performance in achieving both fisheries and conservation goals, and find equivocal evidence that TURFs can consistently deliver on this promise. We then explored the potential to improve outcomes by implementing no take marine reserves with TURFs (“TURF-reserves”). We evaluated theoretical and empirical evidence in the literature and develop a simulation model to examine tradeoffs for achieving conservation and fishery objectives. With our model, we examined different management regimes (e.g., open access vs TURFs), harvest controls within the TURF (e.g., selectivity and harvest rate restrictions), and varying reserve sizes. We found that combining reserves with TURFs does not eliminate the tradeoff between fisheries and conservation goals if the TURF already effectively controls fishing pressure. However, given the results from our literature review, many TURFs may not achieve effective fisheries management. Thus, TURF-reserves may be better able to balance fisheries and conservation goals relative to TURF-only systems, but outcomes will depend on target species mobility, TURF size, and fishing intensity outside the TURF-reserve.

Unsustainable fishing in marine systems creates fisheries management and conservation challenges, with implications for ecosystem health, livelihoods, economies, and seafood supply. Thus there is a need for management approaches that can support productive fisheries and healthy ecosystems. Property rights, and particularly spatial rights or territorial use rights in fisheries (TURFs), are increasingly proposed as a solution. It has been suggested that TURFs may align fishers’ incentives with long-term stewardship, resulting in improved yields and positive conservation outcomes. Here we examined this idea by reviewing existing theoretical and empirical evidence for TURF performance in achieving both fisheries and conservation goals, and find equivocal evidence that TURFs can consistently deliver on this promise. We then explored the potential to improve outcomes by implementing no take marine reserves with TURFs (“TURF-reserves”). We evaluated theoretical and empirical evidence in the literature and develop a simulation model to examine tradeoffs for achieving conservation and fishery objectives. With our model, we examined different management regimes (e.g., open access vs TURFs), harvest controls within the TURF (e.g., selectivity and harvest rate restrictions), and varying reserve sizes. We found that combining reserves with TURFs does not eliminate the tradeoff between fisheries and conservation goals if the TURF already effectively controls fishing pressure. However, given the results from our literature review, many TURFs may not achieve effective fisheries management. Thus, TURF-reserves may be better able to balance fisheries and conservation goals relative to TURF-only systems, but outcomes will depend on target species mobility, TURF size, and fishing intensity outside the TURF-reserve.