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.
fish schools on coral reefs
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 focuses on the behavior of the convict tang (Acanthurus triostegus) 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 seek to shed light on the following questions:
Are we directly or indirectly changing fish schooling behavior through fishing and other anthropogenic impacts?
How does the behavioral ecology of a schooling fish differ from that of a solitary fish of the same species?