The sea urchin Paracentrotus lividus is an important exploited resource on the Mediterranean coast and has been the subject of much research. In the Bay of Biscay, the situation is different, as some studies have been conducted on the Spanish Basque coast but few on the French part of that coast. However, the Basque coast offers favourable conditions for the development of this species, and its exploitation could be a source of potential diversification for fishermen, especially in the context of difficulties with some other resources. At the request of the managers of this coastal resource, a study was undertaken on sea urchins to improve knowledge of this stock, particularly about its biological characteristics. In this work, assessment consisted of determining the spawning process of the stock throughout the year by collecting data on sea urchin size and wet weights of the test, dry gonads and viscera. From September 2013 to September 2014, sea urchins were collected monthly at this site, from intertidal and subtidal areas, and then analysed in the laboratory. This study takes into account the tidal level in the sample design, which allows a novel highlighting of significant differences in biological characteristics between intertidal and subtidal individuals. Spawning occurs mainly during May and June, which is important knowledge for defining relevant management measures for fisheries.