Population structure and habitat preferences of red porgy (Pagrus pagrus) in the Azores, central north Atlantic

摘要

A 10-year bottom longline survey and a smaller scale hook-and-line survey were used to study how habitat and fishing might affect the population structure of red porgy (Pagrus pagrus) at various scales in the archipelago of the Azores, central north Atlantic. The size and sex of fish caught responded to local factors rather than fishing or larger scale (geographic) factors. Young-of-the-year red porgy recruit to shallow, sandy habitats located inshore, and apparently migrate toward deeper and progressively rockier bottoms. This pattern seems to explain why red porgy are only found around the islands' shores, being absent from shallow seamounts where suitable adult habitat exists but juvenile habitat is absent. The probability of sex-change was higher in sites whenever abundance was low. Significant large-scale differences among islands may well be attributable to exploitation, as the lowest abundances were consistently found off islands subject to higher fishing efforts. We also found some evidence of positive effects on porgy abundance and biomass from a 4-year ban on inshore longline fishing, but such benefits lack further (temporal) evidence. Recruitment to the fishery varied twice by an order of magnitude during the 10-year longline monitoring period, reflecting also high natural variability. These findings highlight the need to explicitly include the habitat essential for growth and, eventually, the presence of adequate ontogenic migration corridors when devising schemes of spatial management of red porgy populations, including marine reserves.