Spatial and temporal variation of commercially important bivalve species in the Algarve coast, Portugal

Dissertação de mestrado, Biologia Marinha, Faculdade de Ciências e Tecnologia, Universidade do Algarve, 2015

Artisanal fisheries in the Algarve are a very important industry for local communities and for the local economy. The target species in this fishery are the white clam (Spisula solida), the striped venus (Chamelea gallina), the donax clam (Donax trunulus) and razor clam (Ensis siliqua). The Portuguese Institute of the Sea and Atmosphere (IPMA) is responsible for the management of these fisheries and the existing resources, to ensure its sustainable development. It is known that in addition to the fishing pressure exerted on these coastal bivalve populations, there are environmental factors that influence their growth and reproductive success. This study was based on the monitoring campaigns of these bivalve banks, held annually by the IPMA, from 1999 to 2011, as well as environmental data of rainfall, an indicator of food availability (chlorophyll a), wind index and Sea surface Temperature (SST) over these 13 years. The objectives of this study are to analyze the variation of the spatial and temporal distribution of these species in the Western and Eastern Algarve, as well as to evaluate how the studied environmental parameters condition the abundance of the species concerned, in the following year, for the period before spawning and for the period after spawning + one month. Thus, annual distribution maps were elaborated for each species and region (Western and Eastern) and 16 linear models were applied to all four studied species, the two regions (Barlavento and Sotavento) and the study period ( three months before spawning and spawning + one month The results of this study showed that the distribution and abundance of these species varies over the years, revealing different patterns of banks in terms of preference or absence for each species, and that all the analyzed environmental factors were significant in determining their abundance, the following year. The most significant environmental parameters affecting abundance were the rainfall and the chlorophyll a levels, especially in the Western area. In general, increasing chlorophyll levels were beneficial in contributing to the abundance of species either breeding adults or growing larvae, while the most abundant rainfall levels were positive for adult populations, and negative to the early life stages of these bivalves. This study also shows the need to develop a better understanding of the relationship between the environmental parameters studied and the specific characteristic of the Algarve coast, so there can be a better management of the stocks, and an anticipated prediction of the populations’ growth, which will enable a better monitoring of these important bivalve communities.

Artisanal fisheries in the Algarve are a very important industry for local communities and for the local economy. The target species in this fishery are the white clam (Spisula solida), the striped venus (Chamelea gallina), the donax clam (Donax trunulus) and razor clam (Ensis siliqua). The Portuguese Institute of the Sea and Atmosphere (IPMA) is responsible for the management of these fisheries and the existing resources, to ensure its sustainable development. It is known that in addition to the fishing pressure exerted on these coastal bivalve populations, there are environmental factors that influence their growth and reproductive success. This study was based on the monitoring campaigns of these bivalve banks, held annually by the IPMA, from 1999 to 2011, as well as environmental data of rainfall, an indicator of food availability (chlorophyll a), wind index and Sea surface Temperature (SST) over these 13 years. The objectives of this study are to analyze the variation of the spatial and temporal distribution of these species in the Western and Eastern Algarve, as well as to evaluate how the studied environmental parameters condition the abundance of the species concerned, in the following year, for the period before spawning and for the period after spawning + one month. Thus, annual distribution maps were elaborated for each species and region (Western and Eastern) and 16 linear models were applied to all four studied species, the two regions (Barlavento and Sotavento) and the study period ( three months before spawning and spawning + one month The results of this study showed that the distribution and abundance of these species varies over the years, revealing different patterns of banks in terms of preference or absence for each species, and that all the analyzed environmental factors were significant in determining their abundance, the following year. The most significant environmental parameters affecting abundance were the rainfall and the chlorophyll a levels, especially in the Western area. In general, increasing chlorophyll levels were beneficial in contributing to the abundance of species either breeding adults or growing larvae, while the most abundant rainfall levels were positive for adult populations, and negative to the early life stages of these bivalves. This study also shows the need to develop a better understanding of the relationship between the environmental parameters studied and the specific characteristic of the Algarve coast, so there can be a better management of the stocks, and an anticipated prediction of the populations’ growth, which will enable a better monitoring of these important bivalve communities.