A groundbreaking study from the University of St Andrews has unveiled critical insights into the foraging dynamics of the Critically Endangered African penguin (Spheniscus demersus) amidst increasing competition with local fisheries. This comprehensive research reveals that during periods of low fish abundance, these penguins disproportionately overlap with commercial fishing vessels, exacerbating pressures on an already imperiled species. Published in the Journal of Applied Ecology, the study pioneers a novel quantitative approach termed “overlap intensity,” transforming our understanding of predator-fishery spatial relationships beyond mere geographic co-location.
For decades, African penguins have experienced a catastrophic population decline of nearly 80%, driven by habitat loss, oil spills, and, notably, competition with fisheries targeting sardines and anchovies—primary prey items critical to penguin survival and reproductive success. Traditional methods focused mainly on spatial overlap—where penguins and fishing vessels occupy the same waters—failed to capture the full extent of competition. This study breaks new ground by measuring not only where overlap occurs, but precisely how many individual penguins are exposed to potential resource competition, elevating the ecological interpretation of coexistence between predators and fisheries.
Utilizing high-resolution tracking data collected from breeding African penguins on Robben and Dassen Islands, the research team, including experts from the University of Exeter, the South African Department of Forestry, Fisheries and the Environment, and BirdLife South Africa, detected a striking pattern: overlap intensity surged dramatically in years characterized by low fish biomass. For instance, in 2016—identified as a poor fish stock year—nearly 20% of tracked penguins foraged in zones shared with active purse-seine fishing vessels. This figure represented a fivefold increase compared to years when fish stocks were more robust, during which overlap intensity fell to roughly 4%.
The purse-seine fishery, a technique involving the deployment of expansive nets encircling schooling fish, is integral to the sardine and anchovy market but also directly competes with African penguins that rely on these species for nourishment. The intensification of spatial overlap during resource-scarce periods implies heightened direct competition for dwindling prey, placing additional strain on penguin foraging efficiency—especially critical during breeding seasons when adults must provision their chicks. These findings emphasize the nuanced ecological challenges faced by central place foragers who repeatedly return to specific breeding colonies, necessitating efficient and reliable access to prey within constrained ranges.
By defining “overlap intensity” as a metric that captures the number of individuals simultaneously exposed to spatial resource competition, this research offers a robust, population-level analytic tool. This advancement enables marine ecologists and fishery managers to quantify ecological risks with unprecedented precision, facilitating more informed ecosystem-based fishery management. The metric holds promise for guiding adaptive spatial management frameworks—including the design and implementation of dynamic marine protected areas capable of responding to temporal fluctuations in fish abundance and predator foraging behavior.
This study’s implications extend well beyond academic theory, intersecting with urgent conservation policy debates in South Africa. Earlier this year, a landmark legal case spotlighted inadequacies in biologically meaningful fishery closures adjacent to penguin breeding colonies. Following advocacy efforts and court rulings, the South African government reinstated expanded no-fishing zones around Robben Island, recognizing the necessity of protecting crucial foraging habitats from direct human extraction pressures. This study provides empirical support for these regulatory actions by highlighting areas with high overlap intensity as hotspots of penguin vulnerability.
Lead researcher Dr Jacqueline Glencross from the Scottish Oceans Institute at the University of St Andrews emphasized the study’s contribution to conservation science: “We sought a method not merely to map where penguins and fisheries converge spatially but to reveal how many penguins are actually forced to compete with fishing operations. This dimension is critical in understanding cumulative ecological stressors and shaping effective conservation strategies.”
The findings underscore the complex, context-dependent nature of predator-prey-fishery interactions in marine ecosystems where overlapping species exhibit central place foraging behavior. Unlike pelagic predators with extensive home ranges, African penguins repeatedly return to nesting sites, concentrating their foraging efforts within relatively fixed spatial boundaries. Consequently, localized fish depletion by intense fishing pressure during critical reproductive periods can significantly impair penguin population viability—a dimension quantitatively captured for the first time by overlap intensity.
Furthermore, the research illustrates the potential for data-driven, fine-scale spatial management that aligns conservation objectives with sustainable fisheries. By integrating real-time fish biomass assessments with penguin tracking data, fishery closures and marine protected areas can be dynamically adjusted to minimize overlap intensity and thereby reduce adverse impacts on penguin foraging success and reproductive output.
This innovation in quantifying predator-fishery interactions also paves the way for comparable assessments in other marine species confronting human-induced resource competition. Ultimately, the overlap intensity metric serves as a vital bridge linking spatial ecology, conservation biology, and fisheries science toward holistic ocean stewardship in an era of rapid environmental change.
As the African penguin faces an uncertain future amidst shrinking prey resources and escalating human impacts, this research delivers a powerful scientific foundation for targeted management interventions. Protective measures informed by nuanced spatial overlap analyses have the potential to mitigate competitive pressures and enhance population recovery efforts. The integration of cutting-edge telemetry, ecological theory, and conservation action embodied in this study exemplifies the collaborative approach necessary to safeguard vulnerable marine predators globally.
Subject of Research: Animals
Article Title: Spatial overlap alone downplays the level of interaction between a central place forager and the local fishery
News Publication Date: 17-Nov-2025
Web References: 10.1111/1365-2664
Image Credits: Jacqui Glencross
Keywords: Marine biology
