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past projects

seabirds, nutrients, and the human footprint

Seabirds can provide important nutrient to their nesting islands by depositing nutrient rich guano (i.e. seabird poop). However, some seabirds now include anthropogenic food sources in their diet (e.g., your french fries). These seabirds then deposit large amounts of their anthropogenically-subsidized guano onto their nesting islands. This work explores the role anthropogenic food subsidies may have in island nutrient budgets by studying seabirds on the Channel Islands in southern California. Anacapa Island and Santa Barbara Island form part of the Channel Islands National Park and seasonally support a large population of nesting Western gulls (Larus occidentalis). Although a marine bird, these gulls also frequently forage on anthropogenic food sources. This project sheds light on the nutrient input by Western Gulls to the islands, and the role humans may have in subsidizing the nutrient budget of these protected islands.

where did the gulls go?

an animation of the foraging patterns of some of our tagged gulls

are we fishing out schooling behavior?  

Schooling is a common behavior in fish that increases reproductive success and reduces the odds of being attacked by their natural predators. However, humans could influence the frequency of this behavior. However, collecting in large groups makes schooling fish especially vulnerable to exploitation by modern technologies designed specifically to capture entire fish schools such as large surround nets. While we know these technologies have depleted schooling fish numbers, it remains unclear how the historical benefits of schooling behavior are counterbalanced against increased risk of harvest mortality in an Anthropocene ocean.    


Illustration of the selection pressures on schooling fish. Individual fish are subject to both predation from natural predators (left) and modern fishing

(right). The parameter ρ controls the relative importance of these two selection pressures (ρ = 0 means only natural predators, ρ = 1 means only human predators,

while intermediate values of ρ indicate a mixture of natural and human predators). The curves provide a qualitative illustration of the selection on group size in the

different scenarios. Figure from Guerra, et. al 2020, Proc. Royal Soc. B.

Another way in which humans might influence the tendency for fish to form schools is by fishing out the naturally predators. For species that use schooling behavior primarily as a predator avoidance strategy, fishing out their natural predators might reduce the tendency for them to form schools.

On coral reefs, multiple generations of fisheries have severely depleted predator populations and low-trophic level fish are now experiencing relaxed predation pressure by natural predators. Various coral reef fish, in particular herbivorous parrotfish and surgeonfish, are known to form large schools, although the drivers and importance of this social behavior remain unresolved. 

This project focused on the behavior of three reef fish species on two Pacific Islands: Palmyra Atoll (USA), an uninhabited island protected form fishing and has stable reef predator populations; and Moorea (French Polynesia), an inhabited island that experiences higher fishing pressures and hosts predator populations 4-5x lower than those on Palmyra Atoll. Using this model system, we shed light on whether 1) we are directly or indirectly changing fish schooling behavior through fishing and other anthropogenic impacts and 2) if the behavioral ecology of a schooling fish differ from that of a solitary fish of the same species?

managing human-wildlife conflict in the ocean

Human-wildlife conflict has been receiving increased scientific and management attention, predominantly in terrestrial systems, as a side effect of successful predator conservation and recovery. These same conflicts exist in the ocean; however, they are mostly regarded in a region- or taxa-specific context despite evidence that human wildlife conflict is prevalent across the global oceans and likely to increase as a result of successful conservation

measures. Can the lessons learned from conflicts on land promote more sustainable success in the sea? Or, do ocean human-wildlife conflicts create unique challenges that require new solutions? This project synthesized evidence from human-wildlife conflicts in the ocean and provides initial suggestions for progressing with effective management in the ocean. Humans have extensive experience managing conflict with terrestrial predators and several of the strategies are transferable to marine predators, but several important differences between systems necessitate a marine-specific focus and evaluation of existing mitigation strategies. Further, in managing marine wildlife conflict, it is crucial to recognize that perceived conflicts can be just as important as actual conflict and that, in many cases, human-human conflict is at the root of human-wildlife conflict. As efforts to recover important predator populations continue, humans are faced with the exciting opportunity and a new necessity to constructively manage these recoveries to continue to meet goals for marine conservation while simultaneously promoting human safety and industry in the seas.

the worth of giants

Photo by: National Park Service

While the economic value of wildlife has been historically attributed to its consumptive use, the growth of ecotourism has added extra dimensions to the economic valuation of wildlife by including an accounting of the non-consumptive use of species. In California, the critically endangered giant sea bass  is paradoxically both a flagship species in the local recreational dive industry and regularly landed and sold in California’s commercial fisheries when incidentally caught. Correspondingly, giant sea bass are of economic value to a diverse set of local stakeholders.


We explored the differences in the economic value of giant sea bass to two key stakeholders - commercial fishers and recreational scuba divers. Using California commercial fishery landing receipt data, we determined the average annual landing value of giant sea bass to be $13.5k USD. By estimating the annual number of recreational charter boat divers and determining divers average willingness-to-pay for a giant sea bass sighting using surveys, we approximated the average value of giant sea bass to recreational divers to be $2.7M USD per year. The results highlight the value of giant sea bass beyond its worth to fisheries and underscore the importance of incorporating externalities such as benefits and value to recreational divers and the recreational dive industry when developing policies and management plans for the species.

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