Habitats:     Coral Reefs

Benefits:         Fish production, coastal  protection, tourism

Application:    MPA design & valuation

Pilot site:        Pohnpei & Palau

Micronesia covers 6.7 million square kilometers of Pacific Ocean, an area nearly equal to the continental United States. The region contains four percent of the world’s coral reefs and 480 species of coral—60 percent of all known species. It is also home to 650,000 people whose livelihoods and economies are highly dependent on functional reef systems. Yet these reefs are under threat from both local and global stressors, and insufficient resources and management capacity jeopardize their long-term well-being.

Geographic area considered by the Micronesia Challenge. From Harborne et al. 2018.

In 2006, leaders from the region stepped forward with the Micronesia Challenge, committing countries and jurisdictions to conserve at least 30 percent of near-shore marine resources and 20 percent of terrestrial resources by 2020. The Challenge includes the Federated States of Micronesia, the Republic of the Marshall Islands, the Republic of Palau, the U.S. Territory of Guam and the U.S. Commonwealth of the Northern Mariana Islands.

Mapping Ocean Wealth is building on existing knowledge of the region’s ecosystem services, with a particular focus on factors that affect the productivity of Micronesia’s coral-reef fisheries.

Fish Production

A local spear-gun fisherman searches for reef fish, like parrot fish and trivali, in the lagoon waters of Ant Atoll, Pohnpei, Federated States of Micronesia. Kirino. Photo credit: Nick Hall

A local spear-gun fisherman searches for reef fish, like parrot fish and trivali, in the lagoon waters of Ant Atoll, Pohnpei, Federated States of Micronesia. Kirino. Photo credit: Nick Hall

The study, led by the University of Queensland, compiled fish survey data from over 1,100 locations across the extensive reefs and island chains of five jurisdictions in Micronesia in the Pacific Ocean. Almost any level of fishing leaves a clear signal: unfished reefs have a rich abundance of larger fish, such as parrotfishes, groupers, snappers and sharks. Such species remain where there is still some fishing, but the larger individuals are lost. As fishing pressure increases, the average fish size declines, and gradually some species disappear completely from the community.

Using these ecological data alongside a host of other information on natural, social or economic variables, we built two models. One modelled cumulative fishing pressure using the average size of parrotfishes from the survey data. We assumed that more fishing would reduce average size. Parrotfish average size was closely linked both to human population density and to the distance to the nearest port. The second model examined the biomass of fish (or standing stock) currently present on the forereef slopes of Micronesia. This is strongly influenced by fishing pressure, of course, but many other factors played a part, including sea-surface temperature, oceanic productivity, upstream larval supply, depth and coral cover.

From these models, we generated, for the first time, continuous high-resolution maps of fishing pressure and predicted standing stock for Micronesia. We can use the models to generate hypothetical scenarios to show what the reefs would look like if there was no fishing at all (potential standing stock). This map shows how, even in the absence of humans, standing stock varies considerably among reefs. We can also see how areas differ in their ability to cope with fishing pressure. For example, Guam has some of the highest fishing pressure, but also appears to naturally support fewer fish, making it highly vulnerable to overfishing. By contrast, some reefs around Palau also have high fishing pressure, but they still have high standing stock because they naturally have more fish and can withstand more fishing pressure.

Comparing the differences between current and potential standing stock, we can also show the likely benefit of improved management. For example, some of the first species to be taken from reefs are the top predators, such as larger groupers, snappers and jacks. Our model is sufficiently robust for us to model their recovery, and in the more heavily fished areas around Guam and Pohnpei, we predict increases of 100-350 percent in standing stock of these species in the absence of fishing.

The strength and utility of these maps is considerable and field practitioners are already asking for specific outputs to support planning for improved fisheries management and Protected Area Network design in Micronesia. These same maps could also make a critical contribution to government commitments to undertake the Micronesia Challenge—a promise by all five jurisdictions to effectively conserve 30 percent of their marine resources by 2020.  The results of this study were published in Diversity and Distributions in 2018. Click here to access the paper.  Maps can be viewed interactively here.

Fishing pressure: The model used ecological observations of parrotfish, a sensitive indicator of fishing, to show a tight link between fishing pressure, human population density and proximity to ports.

Current biomass (standing stock) of 19 focal fisheries species, which are representative of all fishery species.

Potential biomass of 19 focal fisheries species in the absence of fishing. Note that some areas, even without human impacts, would have naturally lower biomass than others.

Potential gain in standing stock of six key predator species in the absence of fishing.