Is the brown shrimp Crangon crangon (L.) population of the Vaccarès lagoon (Camargue, France, Rhône delta) an annual population?

Is the brown shrimp Crangon crangon (L.) population of the Vaccarès lagoon (Camargue,France, Rhône delta) an annual population?

To study the population dynamics of Crangon crangon in the Vaccarès lagoon in the Camargue (Rhône delta), the age of brown shrimp was determined using the method of Tiews (1954). This method consists in counting the number of segments of the outer branch of the first antenna. This number is correlated with the number of moults already accomplished by the shrimp. The duration of the intermoult depends on water temperature. Adapting this model to our environmental data, we determined the age of the brown shrimp. Hatching of larvae occurs in the sea in May, and juveniles enter the lagoon from June to September. Our results showed that Crangon crangon in the Vaccarès lagoon reached sexual maturity between 6 and 11 months, and individuals are 1 year old when they leave the lagoon. A few adults from the previous year (1⁺) migrate back to the lagoon the following year, but these older individuals represent only a very small part of the population, and have only been observed occasionally. The Vaccarès brown shrimp population can therefore be considered as annual, in contrast to northern European populations.