Bayesian inference reveals positive but subtle effects of experimental fishery closures on marine predator demographics

• Published in: Proceedings of the Royal Society. B, Biological sciences Vol. 285; no. 1871; p. 20172443
• Main Authors: Sherley, Richard B., Barham, Barbara J., Barham, Peter J., Campbell, Kate J., Crawford, Robert J. M., Grigg, Jennifer, Horswill, Cat, McInnes, Alistair, Morris, Taryn L., Pichegru, Lorien, Steinfurth, Antje, Weller, Florian, Winker, Henning, Votier, Stephen C.
• Format: Journal Article
• Language: English
• Published: England The Royal Society 31.01.2018; The Royal Society Publishing
• Edition: Royal Society (Great Britain)
• Subjects: African Penguin; Animals; Bayes Theorem; Bayesian analysis; Benguela Ecosystem; Birds; Closures; Colonies; Conservation of Natural Resources; Demographics; Demography; Ecosystem assessment; Ecosystem management; Environmental changes; Fish; Fisheries; Fisheries management; Fishery management; Fishing; Fishing Closures; Food Chain; Forage; Forage Fish; Global Change And Conservation; Growth rate; Marine ecosystems; Marine Protected Areas; Models, Biological; Population Dynamics; Population growth; Predators; Predatory Behavior; Prey; Seabird–fisheries Interactions; South Africa; Spheniscidae - physiology; Statistical inference; Strategic management; Survival; South Africa; Benguela ecosystem; fishing closures; seabird–fisheries interactions; forage fish; marine protected areas; African penguin
• ISSN: 0962-8452; 1471-2954
• DOI: 10.1098/rspb.2017.2443

Global forage-fish landings are increasing, with potentially grave consequences for marine ecosystems. Predators of forage fish may be influenced by this harvest, but the nature of these effects is contentious. Experimental fishery manipulations offer the best solution to quantify population-level impacts, but are rare. We used Bayesian inference to examine changes in chick survival, body condition and population growth rate of endangered African penguins Spheniscus demersus in response to 8 years of alternating time–area closures around two pairs of colonies. Our results demonstrate that fishing closures improved chick survival and condition, after controlling for changing prey availability. However, this effect was inconsistent across sites and years, highlighting the difficultly of assessing management interventions in marine ecosystems. Nevertheless, modelled increases in population growth rates exceeded 1% at one colony; i.e. the threshold considered biologically meaningful by fisheries management in South Africa. Fishing closures evidently can improve the population trend of a forage-fish-dependent predator—we therefore recommend they continue in South Africa and support their application elsewhere. However, detecting demographic gains for mobile marine predators from small no-take zones requires experimental time frames and scales that will often exceed those desired by decision makers.