Africa’s only penguin species is being pushed into direct competition with commercial fishing vessels during years of low fish abundance – adding yet another threat to a seabird already teetering on the edge of collapse, a new study from the University of St Andrews has revealed.

Published today in the Journal of Applied Ecology, the research introduces a novel population-level metric dubbed “overlap intensity.” Unlike traditional spatial overlap assessments, this metric captures how many penguins are actually affected when purse-seine fishing vessels operate within their foraging grounds.

African penguins (Spheniscus demersus) have suffered an almost 80% population crash over the past 30 years. Competition with fisheries targeting sardines and anchovies – cornerstone prey for the species – has been widely cited as a key driver of the decline. Purse-seine vessels, which encircle schooling fish with large nets, operate throughout the penguins’ coastal range.

“We wanted a better way to assess how many penguins are potentially impacted when fisheries operate nearby – not just where the overlap occurs,” said lead author Dr. Jacqueline Glencross of the Scottish Oceans Institute at the University of St Andrews.

Drawing on fine-scale tracking data from breeding colonies on Robben and Dassen islands, the team – working with partners from the University of Exeter, South Africa’s Department of Forestry, Fisheries and the Environment, and BirdLife South Africa – found stark differences between years of plenty and years of scarcity.

In 2016, a poor year for fish biomass, roughly 20% of tracked penguins foraged in the same waters as active fishing vessels. In healthier years, that figure dropped to around 4%.

The results point to a dangerous escalation of competition when prey is limited—particularly during chick-rearing, when adult penguins must make efficient foraging trips or risk losing their young.

By quantifying overlap intensity at the population level, the study provides a new tool for assessing ecological risk and supporting ecosystem-based approaches to fishery management. The metric could also guide the creation of dynamic marine protected areas designed to shift with real-time predator-prey conditions.

The findings land at a pivotal moment for penguin conservation in South Africa. The species recently stood at the center of a landmark court case challenging inadequate fishery closures near breeding colonies. Earlier this year, conservation groups and the fishing industry reached a high-court settlement affirming the need for biologically meaningful no-fishing zones. The South African government has since reinstated enhanced closures around Robben Island—one of the key sites in the new study.

“This research highlights why those closures are necessary,” Dr. Glencross said. “Previously unprotected areas with high overlap intensity are where the penguins were most at risk.”

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