Of the 51 million people engaged in fishing in the world, an estimated 50 million work in artisanal fishing, a sector that, according to the FAO, accounts for almost half of global fish production. However, most scientific studies have focused on the analysis of industrial fishing, leaving artisanal fishing aside. This means that most small-scale fisheries do not have the detailed information needed to apply the most commonly used stock assessment methods in fisheries science, often resulting in ineffective or non-existent management. Precisely to try to provide 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 CIMA-Consellería do Mar that study two fishery resources in the Vigo estuary: razor clams and sea cucumbers. In the final stretch of these studies, the research teams presented the results this Friday at an event aimed at agents involved in the management of razorfish and sea cucumber fisheries in Galicia, from razorfishers, technical assistance from the guilds and area biologists from the Ministry of the Sea to research staff interested in the subject. The event, in which around thirty people participated, was held via streaming via the Remote Campus.
The project on 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 researcher Ana Tubío. On the other hand, 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, provide simple management tools that can be used to know the state of the resource on a day-to-day basis”, as explained by Alba Hernández, researcher and technician at the CIM. In both cases, the studies were developed in close collaboration with Ecimat and with the technical assistance and the razor clam and sea cucumber harvesters involved in the exploitation plans for these resources in the estuary. The development of the project also had co-financing from the FEDER/ESF Galicia 2014-2020 Operational Program.
Sea cucumber, a highly coveted marine resource in the East and on the Mediterranean coasts
The sea cucumber (Holothuria forskali) is a highly sought-after marine resource in the East and on the Mediterranean coasts, to such an extent that cases of overexploitation have occurred. However, as 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 (sea cucumber, royal sea cucumber, sea cucumber, etc.) as a discard product species from the Gran Sol. Subsequently, the first plans for the management of sea cucumbers were developed for the brotherhoods 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 that the project for the study of the biology, population status and genetic diversity of the sea cucumber (Holothuria forskali) in the Vigo estuary was born, in collaboration with the Centro de Investigacións Mariñas-Cima Corón, Anfaco-Cecopesca and the San Xosé de Cangas fishermen’s brotherhood. The objective was to advance knowledge about reproduction, essential for the establishment of closures; growth, necessary to know the age at which individuals form part of the exploitable biomass; the size of first maturity, which allows the establishment of a minimum legal size that ensures the reproductive success of the population and the standardization of biometric measures that allow the monitoring of the population with the least possible error.
Among the main results of the project, as Tania Ballesteros explained to the sectors involved in the virtual event, “we were able to establish which measures are most appropriate 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 spawning period, which is essential for establishing closures (November-February). In addition, we already have sufficient knowledge to set a minimum legal size at least in the Cangas bank (150 g wet weight). Likewise, the data obtained at Ecimat on the cultivation of this species that was not described before the start of the project was presented, such as embryonic, larval and juvenile development. Despite having 70 g individuals born in our facilities, the initial objective was to determine the time to reach a commercial size, consequently this objective is halfway after running out 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.
An IT platform to improve the management of the razor sector
The study of the spatial variability of the reproductive cycle of razorfish (Ensis magnus) in the Vigo estuary was developed in collaboration with atlanTTic, with the aim of supporting the management of the razorfish fishery, studying, on the one hand, the spatial heterogeneity in the reproduction and distribution of the stock, and on the other hand, the different methods of studying and visualizing the state of the banks, with the aim of promoting an exploitation method based on biological information obtained continuously.
And although a significant effort has been made to study the biology of razor clams over the last two decades, “this species, like many sedentary invertebrates, is distributed heterogeneously, occupying dispersed banks connected to each other by the larval stages, and there may be spatial variations in its vital strategy, even between relatively close banks”, explains Alba Hernández, who observed in her doctoral thesis, developed in the Ecocost group, differences in the reproductive cycle between the banks of the Pontevedra estuary. Furthermore, the reproductive cycle can present variations from year to year due to its interaction with environmental variables, making it impossible to apply the same rotation schemes each year. As part of the thesis, a simple management tool was created that allowed the gonadal state of the resource to be adapted to its exploitation. Thanks to the use of this tool and the workshops held with the guilds, it was possible to reduce the closure to one month, which generated interest among the guilds and the Consellería do Mar, giving rise to this new project that was launched in 2017, shifting the focus to the Vigo estuary.
Thus, between January 2018 and July 2019, members of the Ecocost group studied the mesoscale differences 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 autumn, when the temperature is higher, the water is rich in nutrients, and E. magnus accumulates reserves. An onset of gametogenesis was also observed in autumn, when the 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 fishery management, adapting the rotational harvesting plan and the closure period to the variability found in the gametogenic stage of razor clams within the estuary.
On the other hand, in the 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 has been reinforced through the creation of an IT platform called Navalleando, developed by atlanTTIc, in collaboration with CIM-UVigo. In this platform, Ana Tubío points out, “data relating to razorfish biology and the physical parameters of the water are entered by the fishing sector (razorfishers and technical assistance) and data on the opening or closing of a school are entered by the fishing staff of the Xunta de Galicia”. This platform allows the reproductive state of the resource to be visualized, the degree of breakage of the razorfish, the main factor that regulates the cycle of this species, the temperature of the seabed and the state of exploitation in each of the schools. “The collaboration of all the actors involved in the management of this resource, the ease of data entry, its quick and simple consultation and its attractive presentation make this platform a very useful tool for the management of razor clams, which can serve as an example for the management of other bivalves,” the researchers emphasize.
Source: DUVI
