Effectiveness of deepwater marine protected areas: Implication for Okinawan demersal fisheries management

Deepwater snappers (Lutjanidae) support important commercial demersal fisheries in Okinawa and throughout much of the Indo-Pacific region. However, recent evidence suggests that over-exploitation has substantially reduced stock biomass throughout these regions. Deepwater marine protected areas (MPAs) are often established as a conservation and management tool, but there are few published studies on their efficacy. This study examined the effectiveness of a deepwater MPA in the Kita-Taikyu Bank (KB), based on the changes in relative abundance and size-frequency distributions for target species collected over seven years between a five-year period of year-round closure and subsequent seasonal closures. Etelis coruscans was the most abundant lutjanid in the KB, comprising 45.0% of the total number of individual deepwater snappers. The relative abundance of E. coruscans in the deepwater MPA was influenced by whether protection was year-round or seasonal; their abundance decreased significantly when the ban was lifted. Some distinct size modes of E. coruscans gradually grew larger during the year-round closure, but modes were indistinct after the change to seasonal closures. In addition, our results showed that the relative abundance of mature size classes had not fully recovered during the study period. In our tagging experiment for 151 deepwater snappers comprised of six species, two tagged Pristipomoides filamentosus were recaptured. These cases supplied some biological data regarding deepwater snappers: the periodicity of the growth zone formation and the low rate of cross-border movement of Pr. filamentosus. Our study suggested that deepwater snappers are rapidly depleted by fishing and very slow to recover. It also provided evidence of the potential success of MPAs for deepwater snappers; longer-term year-round closure of deepwater MPAs may be the best solution for affording long-lived fishery species the protection necessary for them to achieve maturity.