Researchers from the CIM-UVigo analyze biological parameters and provide management tools for razor clams and sea cucumbers

Of the 51 million people who are dedicated to fishing in the world, it is estimated that 50 of them work in artisanal fishing, a sector that accounts for, according to FAO, almost half of world fish production. However, the majority of scientific studies focused on the analysis of industrial fishing, leaving artisanal fishing aside. This implies that most small-scale fisheries do not have the detailed information necessary to apply the most commonly used stock assessment methods in fisheries science, often resulting in ineffective or non-existent management. Precisely to try to bring tools adapted for use in artisanal fisheries, the Marine Research Center of the University of Vigo has been participating for three years in two research projects led by the CIMA-Consellería do Mar that study two fishing resources of the Vigo estuary: the razor and the sea cucumber. In the final stretch of these studies, the research teams presented the results this Friday at an event aimed at the agents involved in the fisheries management of razor clams and holothuria in Galicia, from harvesters, technical assistances of the Fishermen´s Cooperatives and area biologists from the Consellería do Mar to the research staff interested in the matter. The event, in which about thirty people participated, was held by streaming through the Remote Campus.

The project about the study of the spatial variability of the reproductive cycle of razor clams in the Vigo estuary and its application to fisheries management, is led by professor Elsa Vázquez and was developed by the researcher Ana Tubío. For its part, the study on the biology, population status and genetic diversity of Holothuria forskali in the Vigo estuary is led by Professor Jesús Souza Troncoso and carried out by Tania Ballesteros. Both projects, born within the Ecocost group (CIM-UVigo), seek to offer, “on the one hand, information on the most relevant biological parameters for the fisheries management of these species in the estuary and, on the other hand, to bring tools of simple management that can be used to know the state of the resource on a day-to-day basis ”, as Alba Hernández, a researcher at CIM, explains. In both cases, the studies were developed in close collaboration with technical assistants and razor and sea cucumber growers involved in the exploitation plans for these resources in the estuary.

The sea cucumber, a highly coveted marine resource in the East and on the Mediterranean coasts

The sea cucumber (Holothuria forskali) is a highly coveted marine resource in the East and on the Mediterranean coasts, to such an extent that it has become overexploited. However, as the researcher Tania Ballesteros explains, in Galicia the exploitation of local species is recent and it was not until 2013, when the Vigo Shipowners Cooperative began the exploitation of Parastichopus regalis (“carajo de mar, carallote real”, se cucumber, etc.) as a discarded species from the Great Sun. Later, the first plans were developed for the management of holothurians for the Cooperative of Cangas, Coruña-Barallobre, Grove, Aldán and Vigo. But despite the high catches and the granting of new exploitation plans in Galicia, many aspects of the biology of this species are still totally or partially unknown, and it is in this context where the project was born for the study of the biology, population status and genetic diversity of holothuria (Holothuria forskali) in the Vigo estuary, in collaboration with the Marine Research Center-Cima Corón, Anfaco-Cecopesca and the San Xosé de Cangas fishermen’s cooperative. The objective was to advance knowledge about reproduction, essential for the establishment of closures; growth, necessary to know the age at which individuals are part of the exploitable biomass; the size of first maturity, which allows establishing a legal minimum size that ensures the reproductive success of the population and the standardization of biometric measures that allow monitoring the population with the least possible error.

Among the main results of the project, as Tania Ballesteros explained to the sectors involved in the framework of the virtual event, “we were able to establish which measures are more suitable in each situation for monitoring the fishery, as well as aspects of the reproductive cycle to take into account in management, such as the maturation and fundamental laying period to establish closures (November-February). In addition, we already have enough knowledge to set a minimum legal size at least in the Cangas bank (150 g wet weight). Likewise, the data obtained in Ecimat on the cultivation of this species not described prior to the start of the project, such as embryonic, larval and juvenile development, were presented. Despite having individuals of 70 g born in our facilities, the initial objective was to determine the time to reach a commercial size, consequently this objective is halfway after we were left without a source of funding ”. The CIM researchers also offered simple tools so that those responsible for managing this resource can follow the evolution of the reproductive cycle in the coming years.

A computer platform to improve the management of the razor clam sector

The study of the spatial variability of the reproductive cycle of the razor clam (Ensis magnus) in the Vigo estuary was developed in collaboration with atlanTTic, with the aim of supporting the management of the razor clam fishery, studying, from one band, the spatial heterogeneity in the reproduction and distribution of the stock, and on the other hand, the different methods of study and visualization of the state of the banks, in order to promote a method of exploitation based on biological information obtained continuously.

And it is that despite the fact that during the last two decades an important effort was made to study the biology of the razor, “this species, like many sedentary invertebrates, is distributed in a heterogeneous way occupying dispersed banks connected to each other by the larval phases, and there may be spatial variations in their vital strategy, even between relatively close banks ”, Alba Hernández explains, who observed in her doctoral thesis, developed in the Ecocost group, differences in the reproductive cycle between the banks of the Pontevedra estuary . In addition, the reproductive cycle may vary from year to year due to its interaction with environmental variables, making it impossible to apply the same rotation schemes each year. Within the framework of the thesis, a simple management tool was created that made it possible to adapt the gonadal state of the resource to its exploitation. Thanks to the use of this tool and the workshops carried out with the fishermen´s cooperatives, it was possible to reduce the closure to one month, which generated interest among the cooperatives and the Consellería do Mar, giving rise to this new project that began in 2017, moving the focus to the Vigo estuary.

Thus, the members of the Ecocost group studied, between January 2018 and July 2019, the differences at the mesoscale level in the reproductive cycle of E. magnus in five exploited banks of the Vigo estuary using histological methods and estimated that the size at which the species reaches sexual maturity is 88.23 mm (L50) and 93.00 mm (L90). The results of the work also show a reproductive cycle characterized by a stage of sexual rest during the summer and early fall, when the temperature is higher, the water is rich in nutrients, and E. magnus accumulates reserves. An onset of gametogenesis in autumn was also observed, when temperature and nutrients decrease and gametogenesis begins at the expense of stored reserves, as well as a period of successive spawning interspersed with gonadal restorations during winter and spring. These results can be used in the management of the fishery, adapting the rotational harvesting plan and the closed period to the variability found in the gametogenic stage of the razor blade within the estuary.

On the other hand, in these last three years they have also tested the efficiency of the tool through the state of the reproductive cycle in the Vigo estuary and its use was reinforced through the creation of a computer platform named “Navalleando”, developed by atlanTTIc, in collaboration with the CIM-UVigo. In this platform, Ana Tubío points out “the data related to the biology of the razor and the physical parameters of the water are entered by the fishing sector (“navalleiros /as” and technical assistance) and the data on the opening or close of a bank are introduced by the fishing staff of the Xunta de Galicia ”. This platform allows to visualize the reproductive state of the resource, the degree of breakage of the razor, the main factor that regulates the cycle of this species, the temperature of the seabed and the state of exploitation in each of the banks. “The collaboration of all the persons involved in the management of this resource, the ease of entering the data, its quick and easy consultation and its attractive presentation make this platform a very useful tool for the management of the razor clams, which can serve as an example for the management of other bivalves ”, the researchers emphasize.

Source: DUVI