No-fishing zones on the Great Barrier Reef (GBR) increase fish for fishers

New research shows that keeping fishers away from some reefs increases their catch of Coral Groupers (aka Coral Trout) on other reefs.

In contrast to National Parks on land, Marine Protected Areas (MPAs) typically include areas which not only prohibit taking native fauna for food but also are designed to supplement the ability of the public to “get a feed” elsewhere. However, the extent to which this is effective and makes up for the area lost to fishing is very difficult to measure.

Most juvenile and adult coral-reef fishes don’t move very far from their resident reef: they are site-attached. Nearly all marine bony fish families have a larval stage, which looks different from, and lives in habitat different from, the adult fish. Most reproduction is by external fertilization with little or no parental care. The tiny (about 1 mm) eggs float away to hatch in a day or two. After that, the larvae are entirely on their own and disperse in open water away from reefs for several days to several weeks, depending on species, before they need to find appropriate nursery habitat and leave open water habitat. This may be relatively close to where they were spawned, or many tens to even hundreds of kilometres away from their natal reef. All this means that the spatial scale of reef fish life history and management is set by the movement not of adults, but of larvae. This spatial scale, not only for biodiversity, but also for fisheries, is variable and often large.

MPAs contain a variety of zones with differing restrictions: for example, some may be open for fishing, whereas others are no-take (no fishing allowed). Fishers are often opposed to creating the latter as they assume that there will be fewer fish for them to catch because there are fewer reefs where fishing is allowed. In contrast, conservationists and many MPA managers argue that dispersal of larvae from the no-take reefs to the fished areas (called spillover) should theoretically more than make up for the loss of fishing at the no-take reefs, which on the GBR constitute 30% of Coral Grouper habitat. However, there has been little firm evidence that significant spillover actually takes place.

A team of marine ecologists (Bode et al. 2025) from Queensland University of Technology, James Cook University, The Great Barrier Reef Marine Park Authority and The Australian Institute of Marine Science, plus AMRI Senior Fellow, Jeff Leis, worked out a way to test the theory of ‘spillover’ of Coral Grouper larvae from no-take reefs of the GBR. The team used information on adult Coral Grouper distribution, size and abundance throughout the GBR collected over a many years, along with data on the number of eggs spawned by females of different sizes and importantly, a computer model that takes into account currents and the swimming behaviour of the larvae at different stages in their dispersal phase. This was combined to show that just over 50% of larvae supplied to the 70% of reefs open for fishing were spawned by fish on the 30% of reefs that are no-take.

Summary:

The team has been able to show that one of every two Coral Groupers caught by GBR commercial fishers comes from the no-take reefs. This offers very strong support for the Larval Spillover Theory, which is good news for fishers and managers. It is also good news for sustainability because over 60% of the Coral Grouper larvae supplied to the no-take reefs came from other no-take reefs. In short, no-take reefs support Coral Grouper populations on both fished reefs and no-take reefs. No-take reefs clearly punch above their weight: they are effective at biodiversity conservation and also at fishery supplementation.

Jeff Leis, PhD, Senior Fellow, Ichthyology, AMRI.

More information:

• Bode, M., Choukroun S., Emslie M. J., Harrison H., Leis J. M., Mason L. B., Srinivasan M., Williamson D. H., and Jones G. P. 2025. Marine reserves contribute half of the larval supply to a coral reef fishery. Science Advances 11(6):1-5. https://doi.org/10.1126/sciadv.adt0216

Further references:

• Steneck, R., and Jackson J. B. C.2025. Supply-side relief for the world’s largest coral reef. Science Advances 11(6):1-2. https://doi.org/10.1126/sciadv.adv5639
• Leis, J. M., Mason L. B., and Choukroun S. 2015. GBR-Larvo: A biophysical larval-fish dispersal model for the Great Barrier Reef based on empirical larval and adult behaviour data. International Council for the Exploration for the Sea, Copenhagen, Annual Science Conference, Expanded Abstracts, p. 2 pp.
• Bode, M., Leis J. M., Mason L. B., Williamson D. H., Harrison H. B., Choukroun S., and Jones G. P. 2019. Successful validation of a larval dispersal model using genetic parentage data. PLoS Biol. 17:e3000380. https://doi.org/10.1371/journal.pbio.3000380

Acknowledgements

Funding for this study was received from an ARC Discovery Grant (DP190103056) and an ARC Future Fellowship (FT170100274). The Larval Dispersal Model was developed with support from the Australian Department of Environment and Energy, through the Marine and Tropical Science Research Facility, National Environmental Research Program, and National Environmental Science Program.