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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.

Little is known about the behavior and migration of deep-sea snappers, as observation of their deep-sea habitats is difficult. Manual acoustic tracking of deepwater longtail red snappers Etelis coruscans was conducted at the Ojika Se Bank, in the waters around the Satsunan Islands, Japan, to investigate their post-release horizontal and vertical behavior. Eight individuals were tagged with transmitters equipped with depth sensors for tracking. At least six of these eight fish survived after release. The fish gradually dispersed from the Ojika Se Bank, and only one-third remained there 33–34 days after release. The fish that remained at the Ojika Se Bank moved horizontally by 2.2 ± 2.0 km daily, but remained near the top of the bank. The fish were distributed in the 168.8- to 288.8-m depth range, and moved vertically by up to 50.0 m between consecutive days. To the best of our knowledge, this is the first report on the daily fine-scale horizontal and vertical movements of any species of deep-sea snapper.

Onaga Etelis coruscans is an important component of the commercial deep-water handline fishery in Hawaii and is one of the more valuable species because of its local popularity. This species is part of a management unit called the Deep 7, a data-poor fishery comprising six snapper and one grouper species for which information about age, growth, longevity and maturity is incomplete. Although some life history information is available for onaga, prior estimates of maximum age (~10–20 years) likely suffered from underestimation of age, whereas two recent studies provided estimates that were similar to the work presented here—a refined age reading protocol revealed age estimates up to 55 years. This maximum age estimate and the age reading protocol used on onaga otoliths were validated using bomb radiocarbon dating. Using an otolith reference image age reading protocol that relied on the validated otolith sections, almost all onaga otoliths covering nearly the full body size range were used to generate valid growth parameters that may be sexually dimorphic. An empirical estimate of age at the length at which 50% of individuals reach maturity (L50) is 11 years, and fish near the minimum retention size in Hawaii (1 lb (~0.45kg) or ~30-cm fork length) may be just 2–3 years old.