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

ABSTRACT: 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.

SUBMITTER: Sherley RB

PROVIDER: S-EPMC5805942 | biostudies-literature | 2018 Jan

REPOSITORIES: biostudies-literature

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

Sherley Richard B RB Barham Barbara J BJ Barham Peter J PJ Campbell Kate J KJ Crawford Robert J M RJM Grigg Jennifer J Horswill Cat C McInnes Alistair A Morris Taryn L TL Pichegru Lorien L Steinfurth Antje A Weller Florian F Winker Henning H Votier Stephen C SC

Proceedings. Biological sciences 20180101 1871

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 <i>Spheniscus demersus</i> in response t ...[more]

PMID: 29343602

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Project description:OverviewEight years of octopus fishery records from southwest Madagascar reveal significant positive impacts from 36 periodic closures on: (a) fishery catches and (b) village fishery income, such that (c) economic benefits from increased landings outweigh costs of foregone catch. Closures covered ~20% of a village's fished area and lasted 2-7 months.Fishery catches from each closed siteOctopus landings and catch per unit effort (CPUE) significantly increased in the 30 days following a closure's reopening, relative to the 30 days before a closure (landings: +718%, p<0.0001; CPUE: +87%, p<0.0001; n = 36). Open-access control sites showed no before/after change when they occurred independently of other management ("no ban", n = 17/36). On the other hand, open-access control sites showed modest catch increases when they extended a 6-week seasonal fishery shutdown ("ban", n = 19/36). The seasonal fishery shutdown affects the entire region, so confound all potential control sites.Fishery income in implementing villagesIn villages implementing a closure, octopus fishery income doubled in the 30 days after a closure, relative to 30 days before (+132%, p<0.001, n = 28). Control villages not implementing a closure showed no increase in income after "no ban" closures and modest increases after "ban" closures. Villages did not show a significant decline in income during closure events.Net economic benefits from each closed siteLandings in closure sites generated more revenue than simulated landings assuming continued open-access fishing at that site (27/36 show positive net earnings; mean +$305/closure; mean +57.7% monthly). Benefits accrued faster than local fishers' time preferences during 17-27 of the 36 closures. High reported rates of illegal fishing during closures correlated with poor economic performance.Broader co-managementWe discuss the implications of our findings for broader co-management arrangements, particularly for catalyzing more comprehensive management.

Dataset Information

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

Publications

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

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