Isolation and no-entry marine reserves mitigate anthropogenic impacts on grey reef shark behavior

Juhel et al. (2019) Scientific Reports. DOI: 10.1038/s41598-018-37145-x

Reef sharks are vulnerable predators experiencing severe population declines mainly due to
overexploitation. However, beyond direct exploitation, human activities can produce indirect or sublethal
effects such as behavioral alterations. Such alterations are well known for terrestrial fauna but
poorly documented for marine species. Using an extensive sampling of 367 stereo baited underwater
videos systems, we show modifications in grey reef shark (Carcharhinus amblyrhynchos) occurrence
and feeding behavior along a marked gradient of isolation from humans across the New Caledonian
archipelago (South-Western Pacific). The probability of occurrence decreased by 68.9% between
wilderness areas (more than 25 hours travel time from the capital city) and impacted areas while
the few individuals occurring in impacted areas exhibited cautious behavior. We also show that only
large no-entry reserves (above 150 km²) can protect the behavior of grey reef sharks found in the
wilderness. Influencing the fitness, human linked behavioral alterations should be taken into account
for management strategies to ensure the persistence of populations.

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