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Abstract
Climate change and fisheries are transforming the oceans, but we lack a complete understanding
of their ecological impact [1-3]. Environmental degradation can cause maladaptive
habitat selection, inducing ecological traps with profound consequences for biodiversity
[4-6]. However, whether ecological traps operate in marine systems is unclear [7].
Large marine vertebrates may be vulnerable to ecological traps [6], but their broad-scale
movements and complex life histories obscure the population-level consequences of
habitat selection [8, 9]. We satellite tracked postnatal dispersal in African penguins
(Spheniscus demersus) from eight sites across their breeding range to test whether
they have become ecologically trapped in the degraded Benguela ecosystem. Bayesian
state-space and habitat models show that penguins traversed thousands of square kilometers
to areas of low sea surface temperatures (14.5°C-17.5°C) and high chlorophyll-a (∼11 mg
m-3). These were once reliable cues for prey-rich waters, but climate change and industrial
fishing have depleted forage fish stocks in this system [10, 11]. Juvenile penguin
survival is low in populations selecting degraded areas, and Bayesian projection models
suggest that breeding numbers are ∼50% lower than if non-impacted habitats were used,
revealing the extent and effect of a marine ecological trap for the first time. These
cascading impacts of localized forage fish depletion-unobserved in studies on adults-were
only elucidated via broad-scale movement and demographic data on juveniles. Our results
support suspending fishing when prey biomass drops below critical thresholds [12,
13] and suggest that mitigation of marine ecological traps will require matching conservation
action to the scale of ecological processes [14].