The Emperor Seamount Chain and Northern Hawaiian Ridge stretch from the Aleutian Trench to the northwestern Hawaiian Islands across the North Pacific basin (Figure 1). A series of seamounts outside the US EEZ (Figures 2 and 3) comprise an area meeting EBSA criteria.

Many of the seamounts in the area have been fully utilized by the commercial fishery since 1967. However, bottom fisheries in the area are currently managed by interim conservation measures of the North Pacific Fisheries Commission (NPFC) and voluntary measures of participants of the NPFC, including capacity limits, effort control, time-area closure, and deployment of vessel monitoring systems and onboard scientific observers.

Scientific surveys of commercial fish species, and benthic habitat and fauna have been conducted by some NPFC participants. Results of the scientific activities have been submitted to the Scientific Working Group of the NPFC. Former assessment reports are available from the NPFC website (http://nwpbfo.nomaki.jp/Assessment.html). Scientific information collected by these activities indicated that the area has moderate uniqueness, special importance for life-history stages of some species, vulnerability, biological productivity, and biological diversity relative to the surrounding deep sea floor.

Emperor Seamount Chain and Northern Hawaiian Ridge stretch for ca. 3000 km from the Aleutian Trench to the northwestern Hawaiian Islands in the western North Pacific Ocean (53-30°N, 164-177°E).

Physical characteristics: The Emperor Seamounts and Northern Hawaiian Ridge were formed as volcanic hotspot tracks as the Pacific tectonic plate moved over a mantle magma source (Wilson 1963, Sharp and Clague 2006, Stock 2006). The seamounts get progressively younger from north to south (85-30 million years old). Most of the seamounts in this region are classified as guyots (Smoot 1991). Topography of a guyot is characterized by flat plateau, upper slope and flanking slope near the base. Hard substrate on exposed top, ledges and slopes, and ledges and soft sediments on depressions provide habitats for some benthic organisms. The minimum depths of the seamounts range approximately 300 m to 2000 m, and southern seamounts are generally shallower than northern seamounts (Smoot 1985, 1986, 1991, Table 1). The chain of seamounts creates an oceanographical boundary and mesoscale eddies in the upper water column, and attract some pelagic species (Yasui 1986, Boehlert 1988).

Utilization by fishery: Most of the seamounts in the area have been utilized by commercial fisheries since 1967, and biological information on fish and benthos has been collected through scientific surveys, exploratory fisheries, and scientific observers onboard commercial vessels. North Pacific armorhead (Pseudopentaceros wheeleri) and Splendid alfonsin (Beryx splendens) are major target species in demersal fisheries in the Emperor Seamounts/Northern Hawaiian Ridge area (Fisheries Agency of Japan 2008 Appendices D and E). The North Pacific armorhead utilizes southern seamounts in this area as adult habitat and spawning ground, whereas larvae and juvenile are widely distributed in the epipelagic zone of the North Pacific Ocean (Fisheries Agency of Japan 2008 Appendix E). Splendid alfonsin is supposed to have a meta-population structure in the whole North Pacific Ocean, since there is no genetic differentiation within the ocean, and larvae can be transported from the Japanese archipelago to the Emperor Seamounts/Northern Hawaiian Ridge via the Kuroshio and Kuroshio Extension Currents. Both species mature in three to four years and are moderately fecund and productive (Fisheries Agency of Japan 2008 Appendix D). Productivity of these two species is relativiely higher than those of typical deepwater fish species, such as orange roughy (Hoplostethus atlanticus) and sablefish (Anoplopoma fimbria), which have extremely slow growth rates, late maturity, long life spans, and low natural mortality.

Biological characteristics: Forty-six fish species were recorded from the exploratory fishing operations (Fisheries Agency of Japan 2008 Appendix A), but none of these species are endemic to the Emperor Seamounts nor listed as vulnerable or endangered on the IUCN Red List. Hart and Pearson (2011) analyzed fish species recorded from the Emperor Seamounts and found that 41 out of 49 fish species were also recorded elsewhere in the Pacific Ocean.

Some precious corals were harvested from the 1960s to the 1980s; however, the initial abundance of precious corals is unknown. The interim measures to protect the cold-water corals were introduced in 2006 in the Emperor Seamount/Northern Hawaiian Ridge area.

Gorgonaceans (8 families, 24 genera), Alcyonaceans (6 families, 7 genera), Antipatharians (4 families, 5 genera) and Scleractinians (6 families, 16 genera) have been observed in Japanese scientific surveys in the Emperor Seamounts/Northern Hawaiian Ridge area. No endemic coral species have been identified. Although the prediction of habitat suitability models for some cold-water corals indicated higher probability of occurrence compared to the surrounding deep sea floor (e.g., Davies and Guinotte 2011), results of the actual sea floor observation with underwater cameras revealed that distribution of cold-water corals was sporadic and sparse both inside and outside the traditional fishing grounds (Yanagimoto et al. 2008), indicating relatively low density and diversity of corals in the area compared to adjacent Aleutinan Islands or other Pacific seamounts (Etnoyer and Morgan 2005, Heifetz et al. 2005, Stone and Shotwell 2007). Besides cold-water corals, some literature information is available for benthic crustaceans (Sakai 1978) and foraminiferans (Ohkushi and Natori 2001).

No marine teleost species, deep-water shark species or cold-water coral species found on these seamounts in this area so far are listed as the vulnerable or endangered species on the IUCN Red List. The relatively low diversity and endemism of fish and coral fauna observed in this area is in line with the recent views that seamounts are generally not isolated habitats with a highly endemic diverse fauna (Samadi et al. 2006, O’Hara 2007, Clark et al. 2012).

Source of scientific data: Underwater camera survey and dredge sampling have been conducted to collect scientific information on species composition, distribution and abundance of benthic organisms on some seamounts in the area. Scientific observers onboard commercial fishing vessels collect data on fish species and incidental catch of benthic organisms. These scientific data, together with commercial catch and effort statistics, are reported to the Scientific Working Group of the NPFC for rigorous scientific review.

Current fishery management: Many of the seamounts in the Emperor Seamounts/Northern Hawaiian Ridge area have been utilized by commercial bottom fisheries since 1967. Currently, bottom fisheries in the area are managed by interim conservation measures of the NPFC, which require fishing participants of the NPFC (i) to limit fishing effort to the existing level, (ii) not to allow bottom fisheries to expand into new areas (in particular, north of 45°N), (iii) to assess the impact of bottom fisheries on marine species or any vulnerable marine ecosystem (VME), and (iv) to cease bottom-fishing operations and move 5 miles away from the location where a fishing vessel encounters cold-water corals.

Japan and Republic of Korea have introduced additional voluntary measures as below:

Japan
  Limit the number and capacity of bottom-fishing vessels at current level
  Limit fishing effort at 80% of the 1996-2006 level
  No fishing operation north of 45°N
  No fishing operation on sea floor deeper than 1500m
  Equipment of each fishing vessel with vessel monitoring system
  Deployment of onboard scientific observers on each fishing vessel
  Temporary closure of fishing season in November and December
  Temporary closure of the C-H Seamount
  Temporary closure of southeastern part of the Koko Seamount

Republic of Korea
  Limit the number of bottom-fishing vessels at current level
  Equip each fishing vessel with a vessel monitoring system
  Deployment of onboard scientific observers on each fishing vessel

Scientific surveys of fish species, and benthic habitat and fauna have been conducted by some participants of the NPFC. Results of these activities are reported to the Scientific Working Group of the NPFC.