Variable population responses by large decapod crustaceans to the establishment of a temperate marine no-take zone

In 2003, an area adjacent to Lundy Island was designated as the United Kingdom's first no-take zone (NTZ) for nature conservation. The only significant fishery at Lundy was for lobster (Homarus gammarus L.) and various crabs. The Lundy NTZ provided an opportunity to test hypotheses about the recovery of crustacean populations from fishing. Using an experimental potting program, we simultaneously compared changes in the crustacean populations within the NTZ with those in proximal control (Near Control) locations and two distant control (Far Control) locations. Comparisons were repli- cated over 4 years, and the results analysed using asymmetrical analysis of variance. There was evidence of a rapid, large increase in the abundance and sizes of legal-sized lobsters within the NTZ, and evidence of spillover of sublegal lobsters from the NTZ to adjacent areas. The NTZ also appeared to cause a small, but significant increase in the size of brown crab (Cancer pagurus L.) and a decrease in the abundance of velvet crabs (Necora puber L.) (the latter potentially owing to predation and (or) competition from lobsters). Unlike many previous studies, these results are unambiguous, owing to a robust asymmetrical experimental design. We suggest that regulatory and conservation agencies use this approach, which we have demonstrated to be relatively straightforward, whenever the NTZ requiring evaluation cannot be replicated. Resume´ : En 2003, une region adjacente a l'oˆle de Lundy a etedesignee la premiere zone de peche interdite (NTZ, no- take zone) pour la conservation de la nature au Royaume-Uni. La seule peche commerciale d'importance aLundy etait celle de homards (Homarus gammarus) et de divers crabes. La NTZ de Lundy fournit l'occasion de tester des hypotheses concernant le retablissement des populations de crustaces apresl a peche. En utilisant un programme experimental de cap- tures au moyen de casiers, nous avons compareles changements dans les populations de crustaces dans la NTZ et en meme temps dans des sites temoins avoisinants et deux sites temoins eloignes; nous avons repetel'experience pendant quatre ans et avons analyseles changements au moyen d'une analyse de variance asymetrique. Il y avait des indications d'un accroissement rapide et important dans l'abondance et la taille des homards de taille legale dans la NTZ et d'un de ´- bordement vers les regions adjacentes de homards de taille inferieure a la taille legale. La NTZ semble aussi avoir produit un accroissement petit mais significatif de la taille des crabes dormeurs (Cancer pagurus )e t un declin de l'abondance des etrilles communes (Necora puber) — ce declin sans doute dua la predation et(ou) a la competition par les homards. Contrairement aux etudes anterieures, nos resultats sont sans ambiguo¨teacause d'un plan experimental asymetrique ro- buste. Nous suggerons aux agences de reglementation et de conservation d'utiliser cette meme methodologie que nous avons demontreeetre relativement simple lorsque les NTZ a evaluer ne peuvent etre etudiees par reiteration. (Traduit par la Redaction)