Coral reefs are a food source for millions of people in the tropics, but many do not deliver the expected catch any more. What influences fish abundance in these environments? An international team of 39 researchers explored this question on 2,500 reefs in 46 countries and collected a tremendous amount of data. The headed by lead author Prof. Josh Cinner from James Cook University in Australia could now form the basis for new approaches to conservation. The study has been published recently in the renowned journal “Nature” – coinciding with the start of the world’s largest international coral reef conference . Dr. Sebastian Ferse from the Leibniz Center for Tropical Marine Ecology in Bremen is one of the co-authors of the study.
Inefficient fisheries management and good access to the nearest markets – these are some of the main factors for overfishing in reefs. The “Nature” study shows that some reefs still have unexpectedly high fish abundance despite these conditions.
The scientists conducted more than 6000 transect surveys on coral reefs around the equator. “Certain parts of the reefs are marked using a line and the number and species of fish are then being documented in this marked area,” explains Dr. Sebastian Ferse. He studied reefs in North Sulawesi in Indonesia, which are among the most species-rich on the planet. The observations focused on species directly dependent on the reefs, among them economically valuable fishes such as wrasses, groupers or parrotfish.
In addition the researchers collected a wide range of data on environmental conditions, fisheries management and socio-economic conditions at the studied coastal sites. The statistical analysis showed that the fish biomass on most reefs could be explained as a result of the considered factors: Size and accessibility of the nearest fish market, transport infrastructure, compliance with management rules and the local reef habitat had a strong influence on the biomass of reef fish.
“Roughly six per cent of the reefs were outliers and had a significantly higher or lower fish biomass than expected. Some reefs in almost pristine areas performed worse than others with high population density and fisheries. These were exciting findings, and we began to look into the reasons for these deviations,” reports Dr. Ferse.
“We were particularly interested in these bright spots with more fish than expected based on their exposure to pressures like human population, poverty, and unfavourable environmental conditions, “ says Prof. Josh Cinner from James Cook University in Australian and lead author of the study. “To be clear, bright spots are not necessarily pristine reefs, but rather reefs that have more fish than they should have, given the pressures they face.” The bright spots were predominantly located in the Pacific, and included sites in the Solomon Islands, Papua New Guinea and Kiribati.
The locations with more fish biomass than expected were characterized for example by an involvement of the coastal population in fisheries management, or still had centuries-old fishery traditions with rules and restrictions in place.
Locations that positively stood out also were places where people are highly dependent on marine resources and are lacking alternative sources of income. In those areas there is a great necessity for a sustainable use of reef resources.
Dr. Ferse says: “These exceptional cases provide a good basis for us to study how coastal communities have managed to keep their reef fisheries in an unexpectedly good shape, thus going against the global trend.”
In contrast, the locations with significantly lower fish biomass than expected were characterized by environmental pressures such as storms or coral bleaching, and in particular by technological improvements in fisheries, transport or refrigeration.
“The classical technical measures of fisheries management therefore run the risk of being traps leading to overexploitation of resources. Alternative approaches of fisheries management that include local populations should be considered instead”, says Dr. Ferse. “Tropical coral reefs are highly complex systems which react very sensitively to changes in their environments. Any type of protection or management must be based on an exact analysis of the local conditions.”
“We believe that our results can show and offer solutions for the conservation of coral reef fisheries,” explains Prof. Josh Cinner. “Specifically, investments that foster local involvement and provide people with ownership rights can allow people to develop creative solutions that help defy expectations of reef fisheries depletion.”
The study has been published in internationally renowned journal “Nature” on June 15, 2016.