Coral Trout thriving in Great Barrier Reef protected zones

A long-term study published this week in Current Biology has revealed that coral trout in protected ‘No-Take Marine Reserves’ (NTMRs) are bigger and more abundant than those in fished ‘blue zones’ of the Great Barrier Reef Marine Park.

Coral trout (Plectropomus spp) are a reef dwelling fish belonging to the Serranidae family and are a popular ‘food fish’ around the world. Due to this, coral trout are a favourite target species for all sectors of the fishing industry and have high market prices both locally and overseas. Overfishing of such species instigates an array of problems, for example studies on the Great Barrier Reef have shown that both recreational and commercial fishing for coral trout can alter the ratio of males to females in a population 1. As fisherman tend to target the largest individuals, in the case of coral trout this means males are more likely to be removed from the population than females, which could potentially be affecting the reproduction and health of coral trout populations.

Coral Trout (Plectropomus spp) individuals

Coral Trout (Plectropomus spp) individuals

The study, conducted by the Australian Institute of Marine Science and the ARC Centre of Excellence for Coral Reef Studies at James Cook University, combined a vast amount of information from underwater surveys carried out between 1983-2012, on reefs spread across approximately 150,000 km2 (more than 40 per cent) of the Great Barrier Reef Marine Park.

In 2004, the marine park was ‘rezoned’ leading to the expansion of NTMRs where fishing is prohibited (also called ‘green zones’). These zones were expanded to cover about one-third of the total park area, having previously made up less than five percent of the park. The team’s long term data analysis suggested that the original marine park zoning plan that was put in place in the 1980s began to improve fish stocks, but that the expanded protection in 2004 greatly improved on this.

The study revealed that coral trout biomass has more than doubled since the 1980s in NTMRs, with most of the growth occurring since the 2004 rezoning – with the density, mean length, and biomass of coral trout being consistently greater in NTMRs  than on fished reefs over both the short and medium term. The team also found no clear or consistent differences in non-target fish density, fish species richness, the percentage cover of benthic organisms or coral cover between NTMRs and fished reefs suggesting that it is target species such as coral trout that are benefitting most from the fishing ban.

“It’s heartening to know the green zones are working as we had expected,” said lead author Michael Emslie from AIMS. “Among the world’s coral reefs, fishing on the Great Barrier Reef is relatively light but it has still reduced the number and average size of the few fish species that are taken by fishers. Data since the 1980s show that green zones have been effective in restoring numbers of coral trout to their former levels.

Although the benefits of NTMRs for exploited species were expected, an unanticipated result in the study was that the reduction in the reef area where fishing is allowed after the 2004 rezoning did not reduce densities of coral trout in these ‘blue zones’. After an initial decline from 1980s levels, populations of coral trout on fished reefs remained stable or increased slightly from 1996 until 2012, suggesting that the catch rates of the Great Barrier Reef Line Fishery have been sustainable since the creation of the Great Barrier Reef Marine Park.

Hugh Sweatman of AIMS and co-author of the paper, said “Australia’s Great Barrier Reef Marine Park is looked upon as a benchmark for large-scale reserve networks around the world. Unlike many places where coral reefs are found, Australia is a developed country where fishing is fairly light and well regulated. Yet even here we see clear effects of fishing — the benefits of no-take reserves would be much more obvious where large coastal populations depend on reefs for their daily food, so fishing is more intense and everything is taken.”

Such studies present compelling evidence that effective protection within green zone networks can play a critical role in conserving marine biodiversity and enhancing the sustainability of targeted fish populations.

Coral Trout on the GBR – Courtesy of AIMS

– JK

Photo Header Credit: Getty Images

Article Source: 

Michael J. Emslie et al. Expectations and Outcomes of Reserve Network Performance following Re-zoning of the Great Barrier Reef Marine Park.Current Biology, March 2015 DOI: 10.1016/j.cub.2015.01.073

Additional References: 

1. Newman, S. J., van Henwerden L., and Choat H. 2009. ‘Coral Trout Study Points the
Way’ in Western Fisheries magazine, September 2009.

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