General Fisheries Commission for the Mediterranean - GFCM

How an invasive sea snail triggered cooperation in the Black Sea


BU | FR | TR | UK

From 200 m all the way down to its deepest point of 2 200 m, the Black Sea is nearly as lifeless as a foreign planet. At its surface, however, it hosts a rich and productive ecosystem providing the lifeblood of coastal communities for millennia. It is in this fertile environment that the invasive species, Rapana venosa (commonly known as rapa whelk), settled and rapidly reproduced, threatening local ecosystems through its prodigious appetite for other molluscs.

Rapa whelk was first observed in the Black Sea in 1947. Genetic studies have indicated that one single female and one single male (likely arriving with imported oyster spat) were responsible for the entire population that has since exploded in the Black Sea and spread from there to almost every corner of the globe.

Bulgaria, Georgia, Romania, Turkey and Ukraine have now joined forces in an unprecedented display of regional cooperation to complete a comprehensive and standardized mapping of the species in the Black Sea.

Rapa whelk in Turkey©Central Fisheries Research Institute (SUMAE)

Kept in check by natural predators in its native habitats of the western Pacific, rapa whelk has encountered very few obstacles in the Black Sea, finding itself at the top of the food chain with a buffet of native species to choose from. Needless to say, its arrival has led to considerable declines in several Black Sea commercial species.

Over time, however, rapa whelk has itself gradually become a significant revenue source for local fishers and processors. Small-scale fishers, who make up more than 85 percent of the Black Sea’s vessel fleet, particularly rely on its robust numbers. The sea snail is now massively exported to its native east Asia, where it’s commonly eaten.

With rapa whelk currently fished close to its sustainable limit in the Black Sea, efforts to curb, or even eradicate its population have now evolved into policies to maintain its stocks and provide for the multimillion-dollar market developing around it. Under the framework of the General Fisheries Commission of the Mediterranean (GFCM) of the Food and Agriculture Organization of the United Nations (FAO), the first large-scale effort to survey this sea snail’s population was completed this week.

Researchers and fishers from various countries have swept all across the sea to perform 450 hauls of Rapana venosa. “This survey-at-sea will have an important scientific impact as it will provide valuable information on rapa whelk biology and ecology in the Black Sea that will be an important asset for the sustainable management of the stock,” says Dr George Tiganov from the National Institute for Marine Research and Development in Romania.

The survey, part of the GFCM's BlackSea4Fish project funded exclusively by the European Union, will provide estimates of the Black Sea population’s distribution, abundance and age structure. “The scientific significance of the survey is great,” explains Dr Oleksandr Chashchyn from the Southern Research Institute of Marine Fisheries and Oceanography in Odessa. “It will allow us to give practical recommendations to fishers.”

These data are indeed essential for management at this critical stage of finding a balance between protecting native ecosystems from the invader and preserving the stock of an increasingly important commercial species. Following the conclusion of this first survey, the coordinators of the study are planning to repeat the process twice a year in order to stay up to date on key population dynamics.

This transition witnessed with the rapa whelk – from initial population bloom and devastation to a commercially important stock requiring its own management – is progressing to various degrees with a variety of invasive species in the Mediterranean and around the world.

Sorting Rapa whelk in Bulgaria ©Institute of Fish Resources

Measuring Rapa whelk in Turkey ©Istanbul University

“We are very proud that the 2018 Sofia Ministerial Declaration delivers on its objectives. The BlackSea4Fish project is the realization of an exemplary scientific cooperation among Black Sea countries that at the end of day will result in improving scientific advice,’’ says Ms Valérie Lainé, Head of the delegation of the European Union to the GFCM. "We are happy that the presence of the GFCM in the Black Sea continues to increase thanks to the support of all the member countries, the European Union and the BlackSea4Fish project,” says Mr Abdellah Srour, GFCM Executive Secretary. “It’s an amazing collaboration,” adds Dr Nazli Demirel, coordinator of the BlackSea4Fish project, who views the survey as a benchmark for future cooperative efforts to assess similar situations. “For the first time in the Black Sea, countries are performing a survey at the same time with the same methodology throughout the Black Sea and we are hoping to extend this synergy to other key commercial species.”

Sorting Rapa whelk in Georgia ©National Environmental Agency


Learn more about the regional research programme for rapa whelk fisheries in the Black Sea.