Monitoring fish assemblages is needed to assess whether Marine Protected Areas (MPAs) are meeting their conservation and fisheries management goals, as it allows to track the progress of recovery of exploited species and associated communities.

This study proposes an improvement to traditional transect surveys (underwater visual census) to better account for differences in behaviour among and within species; as for example most high trophic level predators (HTLPs) are shy fish which rarely swim close to divers, and, consequently, their abundance may be under-estimated with commonly used transects.

The authors suggest that monitoring programs adopt transects of variable surface area to best census fish of different size and behaviour and state that the sampling and analysis framework adopted in this study could markedly improve surveys of fish assemblages. It is highlighted that the proposed approach will provide more accurate estimate of the abundance and biomass of large, shy fish and of cryptobenthic fish and juveniles, thus providing a more realistic description of fish assemblage composition and trophic pyramids.

Additionally, the study verified that MPAs offer significant protection for HTLPs. Inside MPAs, the contribution of HTLP reached >25% of total fish biomass, against <2% outside MPAs.

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0178511

Prato G, Thiriet P, Di Franco A, Francour P (2017) Enhancing fish Underwater Visual Census to move forward assessment of fish assemblages: An application in three Mediterranean Marine Protected Areas. Plos One 12: e0178511

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