Posted in | Ecology | Ecosystems

Study Identifies Best Policies for Achieving Sustainable Fisheries in the Western Indian Ocean

A group of scientists from the Wildlife Conservation Society (WCS), Macquarie University, James Cook University, and the University of Queensland have completed a major study that will enable countries and communities of the Western Indian Ocean to evaluate and restore fish populations while simultaneously recognizing the most appropriate policies that will help to obtain global sustainable and conservation targets.

Lead author Dr. Tim McClanahan surveys high fish biomass on reefs off Vamizi Island in northern Mozambique. CREDIT: Emily Darling / WCS.

The team used data that was collected over a period of over 25 years. This data was based on fish research and surveys focusing on the success of fishing closures to develop predictive models of recovery that will be useful for marine managers, while analyzing the condition of reef systems and their fish populations in the Western Indian Ocean. The results utilized earlier studies to forecast the recovery time taken up by the depleted reefs to levels where fishing is considered to be sustainable, or conservation goals are achieved.

The study titled "Modeling Reef Fish Biomass, Recovery Potential, and Management Priorities in the Western Indian Ocean" was published in the online journal, PLOS ONE. The authors are: Tim McClanahan of the Wildlife Conservation Society; Joseph M. Maina of the Wildlife Conservation Society, the University of Queensland, and Macquarie University; Nicholas A.J. Graham of James Cook University and the University of Queensland; and Kendall R. Jones of the University of Queensland.

This study covers 45 years of fish recovery in 18 of the region's best protected areas--an area of 7,000 square miles--to produce these unusually extensive findings. The study will help guide conservation actions for the entire Western Indian Ocean, a region filled with coastal communities that rely on fishing for their livelihoods. Fish biomass is key for maintaining the ecosystem services that keep reef systems functional; fishing and other human activities can disrupt these sensitive ecosystems. Fortunately, we can leverage previous research to identify predictors that will help guide governments at many levels in ways that can safeguard coral reefs, fish populations, and the communities that rely on them.

Dr. Tim McClanahan, Senior Conservationist, WCS

McClanahan and his team, used the data gathered between 1987 and 2014 to develop and examine predictive models that will help to identify the factors associated with the fish biomass levels in the region's coral reefs, a few of which described up to 66% of the variability that existed in the surveyed reef systems.

The various types of fisheries management or restrictions played a vital role in predicting fish biomass. A tremendous increase in fish biomass was consistently obtained due to the fishing closures that had a high degree of enforcement and compliance, just like strict gear restrictions. Fish biomass considerably reduced because of the fished reef systems that did not have gear restrictions.

The distance that existed between coral reefs and the nearby fish market had a significant impact. A shorter distance was usually linked to lower fish biomass levels. Factors with the least significance included a few potential predictors like habitat and water temperatures. Current speeds and water quality were not modeled, because these data was not found in most of the sites.

The study developed a map of coral reef biomass in the Western Indian Ocean together with a recovery time estimation of 8.1 years for every single reef system to reach 1,150 kg of fish biomass per hectare, the important level to conserve coral reef ecosystems. The average time taken up by depleted reefs to support sustainable yields and maximum species diversity was between 1.74 and 2.9 years in duration. The recover times differed based on the country and were reliant on the condition of their resources. The recovery time could go on for a period of 20 years in most resource-depleted countries.

A prioritization analysis was performed by the authors in order to select areas that require increased management efforts. Traditionally, prioritization exercises used conservation targets based on global treaties for example, Aichi biodiversity targets.

This study utilized fish biomass recovery targets that were both empirical and ecologically informed, thus improving the probability for management effectiveness in selectively important areas. Prioritization minimized the fish biomass recovery time to obtain a nation’s conservation and sustainable goals.

One study detected the area suitable for protecting reefs to obtain 20% protection of coral reefs for no-fishing or conservation zones and comprising 50% of reef systems enclosed in fishing zones that are sustainable. As a result of this, nations are allowed to choose reefs for these management objectives that will result in fast recovery.

The study finally analyzed three significant management scenarios for obtaining the conservation goal of protecting 20% of the reef found in the region. This goal could be rapidly achieved by allowing countries to work together on a regional conservation plan and simultaneously protect areas comprising the highest fish biomass. National conservation plans would almost be extremely effective and would not even need the efforts of obtaining regional collaboration. The last option was to consider a plan in which fishing communities first protected the most resource-depleted reefs. The authors pointed out the success that can be obtained from the same combination of the three approaches by depending on the scales of governance instead of just relying on one.

Implementing management measures to restore fish biomass is the number one action coastal communities, nations and regions can take themselves to help coral reefs face the coming threats of global climate change. The study provides three complementary pathways to achieving sustainable fisheries in the Western Indian Ocean region within a decade--articulating empirically sound actions that critical for the long-term viability of some of the world's most biodiverse and important coral reef systems.

Dr. Caleb McClennen, Vice President, WCS

This study was funded by the John D. and Catherine T. MacArthur Foundation and the Western Indian Ocean Marine Science Association Marine Science for Management Program.

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