Initially considered a marine pest, rapa whelk are now exported around the world and underpin millions of dollars in revenues for Black Sea nations.
As rapa whelks are believed to be currently fished close to sustainable limits, Bulgaria, Georgia, Romania, Turkey and Ukraine have joined forces to launch a comprehensive survey of the species in the Black Sea.
Under the framework of the General Fisheries Commission of the Mediterranean (GFCM) and the BlackSea4Fish project, this survey will mark the first step towards the rational management of this important resource for the region. After completing over 300 hauls, the survey will provide an estimate of the distribution, abundance, size and age structure of the rapa whelk population in the Black Sea.
A species native to the western Pacific, rapa whelks (Rapana venosa), were first noticed in 1946 in Novorossiysk Bay in Russia, one of the Black Sea’s busiest commercial ports, where it is thought to have been transported via biofouling.
Over subsequent decades, while other benthic species suffered from a deterioration in ecological conditions in the region, the rapa whelk with its its high fecundity and broad tolerance to salinity, water pollution and oxygen deficiency continued to thrive.
Its predatory nature, a lack of competition from other predatory gastropods and an abundance of potential prey species has further contributed to its successful establishment in the Black Sea.
In parallel with the expansion of rapa whelk, sharp declines were noted in other commercial mollusc species on which rapa whelk feeds, such as oysters, scallops, clams and mussels. Since the early 1980s, a buoyant market for the species emerged in the Far East, with South Korea, Japan and, China paying high prices for frozen and processed rapa whelk meat.
In 2018, GFCM assessments revealed that rapa whelk is now being harvested close to maximum sustainable yield (MSY). This situation is a remarkable example illustrating the challenges in the management of non-indigenous species (NIS): should the biomass of the species be kept as low as possible to reduce the damage to the ecosystem, or should it be kept at a level that can achieve maximum sustainable yield from an economically important resource?
‘In order to gain more information on the species, a research programme was established through a Recommendation GFCM/42/2018/9,’ explained the co-ordinator of the BlackSea4Fish project, Nazli Demirel.
‘In response to this, for the first time in the Black Sea, countries have been collaborating closely to establish a common protocol to conduct a comprehensive scientific survey-at-sea that will allow a holistic management of rapa whelk in the region.’
The Central Fisheries Research Institute (SUMAE) of the Turkish Ministry of Agriculture and Forestry is the first institution of six to implement the survey, starting 31st August. It will be followed by the Institute of Fish Resources (IFR), National Institute for Marine Research and Development Grigore Antipa (NIMRD), National Environmental Agency (NEA) under the Ministry of Environmental Protection and Agriculture of Georgia, Ukraine and Istanbul University. These surveys will then be conducted twice a year in order to understand the variations of this resource over time (annual and seasonal) and space.
