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Initial U.S. Exploration of Nine Gulf of Alaska Seamounts and Their

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resource has mounted due to constantly decreasing catch rates which, in 1976, were 16 t/hour. Reports of the highly valued cen­ Initial U.S. Exploration of Nine tral North Pacific seamount fisheries of Japan and the U.S.S.R. prompted Gulf of Alaska Seamounts and Their the first U.S. investigation of nine Associated Fish and Shellfish Resources major seamounts, and their associated fishery resources, in the Gul f of Alaska during a 40-day period in June and STEVEN E. HUGHES July 1979. This report is a summary of the topography, partial water tem­ perature profile, and general fishery resource information of the seamounts Introduction development of large Japanese and investigated. Soviet fisheries over several seamounts Based on the location of the "200­ Undersea mountains known as sea­ in the central North Pacific, north­ mile line" established by the Fish­ mounts are prominent features of the west of Midway Island. Takahashi and ery Conservation and Management ocean floor and are far more numerous Sasaki (1977) and Sasaki (1978) re­ Act of 1976, Dickens, Welker, Quinn, in the Pacific than in the Atlantic and ported Japanese catches of pelagic Giacomini, and Patten seamounts are Indian Oceans. Larina (1975) reported armorhead, Pentaceros richardsoni, located within the U.S. controlled the occurrence of 7,100 seamounts and alfonsin, Beryx splendens, have fishery conservation zone and Durgin, rising more than 0.5 km above the averaged 20,000-30,000 metric tons (t) Pratt, Applequist, and Surveyor sea­ Pacific Ocean seabed. Pacific sea­ annually since 1972. mounts are located outside that zone mounts are primarily of volcanic origin Catches have principally been ob­ in international waters (Fig. I). concentrated in the central and western tained by trawlers operating on four Methods Pacific, but clusters of spectacular seamounts west of Midway Island at undersea mountains also occur along long. 171 o_179°E, lat. 30o-36°N. They Operations were conducted from the the northeastern North Pacific and Gulf also reported that Soviet trawl catches chartered 35 m (108 foot) trawler-crab­ of Alaska. of armorhead and alfonsin in that area ber Sunset Bay. A variety of survey and In addition to the often striking geo­ may have reached 130,000 t in 1969, fishing gear was operated in an explor­ logical features of seamounts, which and while Soviet operations have con­ atory mode designed to determine sea­ may rise abruptly from ocean basin tinued, more recent catches are un­ mount topographic and temperature depths of4,000 m to within 20 m of the known. Also indicative of the initial profiles and determine the distribution ocean surface, some seamounts are high armorhead and alfonsin densities and composition of the pelagic and known to be inhabited by surprisingly over these seamounts, 1,500-4,000-ton demersal fisheries community. large quantities of marine life for their Japanese trawlers averaged catch rates Large scale Loran-C work charts relatively small surface areas. This has of 60.2 t/hour in 1972. Since that year, spanning the location of each seamount been convincingly shown by the recent however, concern for stability of the were prepared prior to the cruise and provided a means to map transected acoustic depth soundings, temperatures resulting from expendable bathyther­ mograph (XBT) casts, location of trawl hauls, location of fixed gear, and com­ ABSTRACT-The first U.S. exploration Welker, Durgin, Pratt, Applequist, Survey­ ments on seabed hardness as interpreted of fish and shellfish resources associated or, Quinn, Giacomini, and Patten) topog­ from the acoustic soundings. After with nine Gulf of Alaska seamounts was raphy and seabed conditions, as determined conducted during 40 days in June and July from acoustic mapping, are presented along each seamount was mapped, fishing 1979 from the 35-m crabber-trawler Sunset with fishery resource information for all gear was deployed as dictated by seabed Bay. The reconnaisance survey included but Applequist seamount. Species of com­ conditions. Bottom trawling to depths detailed acoustic soundings to map seabed mercial importance occurred primarily in of 385 fathoms (fm) was completed topography; determine the suitability of the demersal community and included two with a high opening 32 m (105 foot) substrate for deploying a variety of fishing species of king crab, Lithodes couesi gears; and exploratory fishing with sable­ and L. aequispina; snow (Tanner) crab, fish traps, king crab pots, bottom trawls, Chionoecetes tanneri; and sablefish, Ano­ midwater trawls, and photographic gear to plopoma fimbria. The pelagic community determine fish and shellfish species com­ consisted primarily of low densities of Steven E. Hughes is with the Northwest and position, their distribution, and relative highly diversified bathypelagic fishes and Alaska Fisheries Center, National Marine Fish­ abundance on and over the seamounts. squids including several rare species of eries Service, NOAA, 2725 Montlake Blvd. E., Descriptions of each seamount (Dickens, scientific interest. Seattle, WA 98112. 26 Marine Fisheries Review 155' 150' 145' 140' 135' 130' W GO'N 55' 200 m --... -------- 1000 m ------ 2000m --- 3000m ---- 4000m .. .50' Figure 1. -Location of the nine seamounts surveyed in the Gulf of Alaska, 31 May-4 July 1979. footrope Nor'easterl trawl equipped trawl net was of the east coast Canadian were of both the Korean style 1.5 m with rubber bobbins and a 32 mm "Diamond" series (54 m, 177 foot (5 foot) diameter conical and U.S. style (I \4 inch) mesh liner in the codend. footrope), equipped with a 32 mm 2.4 m (8 foot) long rectangular design. Trawl doors used to spread the bottom (I \4 inch) mesh codend liner and was Near the end of the survey, four 1.8 m trawl were 1.8 x 2.7 m (6 x 9 spread with 1.8 x 2.7 m (6 x 9 foot) (6 foot) square king crab pots were foot) steel V-type, each weighing about Suberkrub-type doors weighing 540 kg added to the trap strings to better 1,045 kg (2,300 pounds). The midwater (1,200 pounds) each. sample crab populations which were Seventeen sablefish traps fished in encountered in surprisingly high quan­ strings on the seabed (Hipkins, 1974) tities during the earlier survey period. 'Mention of trade names or commercial firms does not imply endorsement by the National were also used to sample the demersal Deep sea still photography was con­ Marine Fisheries Service, NOAA. fish and shellfish community. The traps ducted on Patton, Giacomini, and January 1981 27 2 Quinn Seamounts (Raymore ). The WSW of Cape Ommaney (Baranof of one large, steep peak composed of underwater camera and light source Island) offsoutheastern Alaska, Welker hard substrate. While a minimum depth were mounted to a triangular shaped Seamount's center is positioned at lat. of 388 fm was determined, a maximum metal frame suspended 2.5 m above a 55°06' 42" N, long. 140°20' 36" W. area of 1 nmi 2 occurs at depths less than baited ballast weight which was low­ Welker Seamount rises from abyssal 500 fm. ered to the seabed. Using this system, plain depths of 1,900 fm to within 385 Pratt Seamount time-lapse 35 mm photographs were fm of the ocean surface at the east edge. obtained during 4V2-6 hour periods at The top is rectangular and measures Located 46 nmi true north of Apple­ depths of 237-435 fm. 4 x 7 nmi (28 nmi 2) with the long axis quist Seamount and approximately 229 oriented north-south. Depths on top of nmi WSW of Cape Edgecumbe(Kruzof Results Welker ranged from 385 to 500 fm with Island) off southeast Alaska, Pratt Sea­ Seamount Descriptions most of the surface area at 420-450 fm. mount's center is positioned at lat. Rock pinnacles rising 5-20 fm high are 56° 14'22" N, long. 142°32' 00" W. Descriptions of the major topograph­ very common over the entire surface of Pratt rises from abyssal plain depths of ical features of all nine seamounts (Fig. the seamount. Areas of soft substrate about 2,000 fm to within 385 fm of the 1) were successfully completed and are common between pinnacles. ocean surface. The top is rather sym­ may be summarized as follows in order Temperature conditions derived from metrically shaped, measures 4 x 5 of their east to west trans-Gulf location. the XBT over and adjacent to Welker nmi, with most of the 20 nmi 2 of the Seamount were very similar and typi­ top surface area being at depths of400­ Dickens Seamount 0 cally displayed 8.0 -8.4°C surface 450 fm. The seabed over the central and Located 145 nautical miles (nmi) true readings, a thermocline at 11-38 fm, north central area is primarily soft west of Cape Muzon (Dall Island) and 3.r-4.2°C bottom temperatures. substrate while the east, west, and off southeastern Alaska, Dickens Sea­ southern edge areas consist of hard and Durgin Seamount mount's center is positioned at lat. soft patches ofsubstrate with occasional 54°3I'18"N, long. 136°56'OO"W. Located 60 nmi WNW of Welker rock pinnacles. This seamount rises from abyssal plain Seamount and approximately 215 nmi Surveyor Seamount depths of 1,600 fm to with in 228 fm of WSW of Cape Edgecumbe (Kruzof the ocean surface at the central posi­ Island) offsoutheastern Alaska, Durgin Located 58 nmi WSW of Pratt Sea­ tion. The top is rectangular in shape and Seamount's center is positioned at lat. mount and approximately 235 nmi true measures approximately 2 x 5 nmi 55°50'00"N, long. l41 0 51'30"W. south of Cape St. El ias (Kayak Island) 2 (10 nmi ) with the long axis oriented in Durgin Seamount rises from abyssal Alaska, Surveyor Seamount's center is a northeast-southwest direction.
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