Observations of the 1992 U.S. Pelagic Pair Trawl Fishery in the Northwest Atlantic

Observations of the 1992 U.S. Pelagic Pair Trawl Fishery in the Northwest Atlantic PATRICIA GERRIOR, AMY S. WILLIAMS, and DARRYL J. CHRISTENSEN Introduction In the Northwest Atlantic, pelagi~ pair catch data were recorded for each tow trawlers have targeted albacore and other retrieved and processed aboard the ob Pelagic pair trawling involves a large tunas and swordfish, Xiphias gladius, in served vessel. As time permitted, length mesh, mid-water net towed between two this mid-water fishery. and sex data were recorded for indi vessels usually of similar size and With the U.S.lCanada, or Hague vidual animals, and biological samples horsepower. Meshes are several meters Line, boundary decision of 1984, the (gonads, hardparts for ageing, stom large at the mouth of the net decreasing U.S. swordfish harpoon fishery effec achs, tissue samples, etc.) were col in size back to the codend where they tively disappeared owing to loss of fish lected. For tows retrieved and processed range from 13 to 30 cm. Large-mesh pe ing grounds. U.S. swordfishermen in by the nonobserved vessel of the pair, lagic pair trawls have been used in the vestigated alternative fisheries, and a only tow location, effort, environmen Northeast Atlantic primarily for albacore, small number began to target swordfish tal, and catch data for the retained spe Thunnus alalunga, (Prado, 1988; Anony with a new gear type, the pelagic pair cies were recorded. Hence, no discard mous, 1991) and offMozambique, Africa, trawl, in 1991. Three pairs of vessels data were collected for tows processed l for several species of tunas (Schwarz ). targeted swordfish during this first sea on the nonobserved vessel. son. In 1992, two additional pairs en Results 1 A. Schwarz. 1993. Rio Rivuma, Boston, Mass. tered the fishery. However, swordfish Personal commun. regulations in 1992 precluded contin The nine observed trips ranged from ued targeting of swordfish and man 4 to 11 days in duration with an aver Patricia Gerrior and Darryl J. Christensen are with the Northeast Fisheries Science Center, Na dated observer coverage. This paper age of 7 days. Vessels departed from tional Marine Fisheries Service, NOAA, 166 summarizes the catch, bycatch, and ports in southern New England and New Water St., Woods Hole, MA 02543. Amy S. Wil fishing methods from pelagic pair trawl York. Fishing occurred primarily in the liams, formerly with NMFS, is at the University of Maine, Orono. trips observed in October and Novem mid-Atlantic region near Hudson Can ber 1992 off the U.S. mid-Atlantic yon with a smaller amount of effort as ABSTRACT-Pelagic pair trawling for coast. far south as Norfolk Canyon (Fig. 1). tuna, Thunnus spp., and swordfish, Xiphias Bottom depths fished were predomi Materials and Methods gladius, was introduced in U.S. Northwest nantly from 433 to 814 m (237 to 445 Atlantic waters in 1991. During autumn Observers were placed on pelagic fathoms), but ranged from 137 to 2,597 (October-November) of 1992 under the authority ofthe Federal Atlantic Swordfish pair trawlers selected by NOAA's Na m (75-1,420 fathoms). Limited fishing Regulations, the National Marine Fisher tional Marine Fisheries Service (NMFS) effort south of Hudson Canyon occurred ies Service placed observers aboard pelagic during the period from 14 October to in November as tuna became more dis pair trawl vessels to document the catch, 19 November 1992. To maximize ob persed and the weather deterioriated. bycatch, discard, and gear used in this new fishery. The fishery is conducted primarily server coverage of this pair trawl fleet, Pelagic pair trawl fishing operations at night along shelf-edge waters from June observers were placed on one vessel of were conducted at night with an in to November. In late 1991, revised regula a pair, and coverage was waived for the tended target species of bigeye tuna, tions restricted swordfish to bycatch in this second vessel for that trip. Although this T. obesus. Bigeye tuna was preferred fishery resulting in pelagic pair trawl ves fishery is generally conducted from late since it was more highly valued than sels targeting tuna throughout 1992. Analy ses of 1992 data indicate that albacore, T. June to mid-November, observations other tuna species caught. Pelagic nets alalunga, was the predominant species and data reported in this paper cover were towed for an average period of 4.4 caught, although yellowfin tuna, only the latter part of the 1992 fishery. hours at speeds ranging from 3.2 to 4.8 T. albaeares, and bigeye tuna, T. obesus, Observers collected vessel, eco knots (4.0 knots average). The size of were the preferred target species. Bycatch also included swordfish, large sharks, pe nomic, gear, catch, bycatch, and discard the net, vessel, and horsepower, and the lagic rays and other pelagic fishes, other data on each trip. Additionally, location, swimming capabilities of the target spe tunas, and marine mammals. effort, environmental, and complete cies likely dictated the observed tow- 24 Marine Fisheries Review 76 75 74 73 72 71 70 41 \ \ ,/ l., '-, I ''\, ,\oo{t'\ '\. , ,) , 40 500 m 1,000 m /' I NJ -, ~ ~ , 00 l» 1-0. ~. I, III Q'"~o () I l» :J I • -c " 0 I 'YG, :J , ~ I 0" 39 I • q, '?to I 0" I I, 38 37 36 Figure I.-Distribution of all tows from observed pelagic pair trawl trips, Oct.-Nov. 1992. ing speeds. One vessel of the pair typi Two different pelagic nets, Le Drezen2 (American manufacture) were used by cally retrieved the net and processed the (French manufacture) and Shuman the vessels. The vessels towed these fish. Pelagic pair trawl fishennen gen trawls about 183 m (l00 fathoms) apart erally alternated processing the catch 2 Mention of trade names or commercial firms does not imply endorsement by the National with net openings ranging from about between the two vessels each tow. Marine Fisheries Service. NOAA. 23 to 55 m (13-30 fathoms) depending 56(3). /994 25 on the net used (Anonymous, 1991; ing was not done in a paired configura Discarded bycatch (excluding marine Venturo, 1993). Most observed vessels tion. A total of 46 otter trawl tows were mammals) included swordfish, three utilized a transducer, or net sounder, made with 38 tows (83%) observed. tuna species, three species each of placed on either the headrope or Albacore, yellowfin tuna, T alba sharks and rays, Myctophidae, squid, footrope to determine the depth and cares; bigeye tuna, and swordfish were Loligo pealei; unspecified fish, louvar, opening of the net. While fishermen the primary species caught and landed Luvarus imperalis; jellyfish, and snipe believe that net depth recorded by the (Table 1) from pelagic pair trawl opera eels (Nemichthyidae) (Table 1). A total transducer is important to fishing suc tions. While most captains intended to of 12 marine mammals were caught on cess and marine mammal avoidance target bigeye tuna owing to its higher four observed trips (Table 2). (Venturo, 1993), only limited headrope, value, albacore was the predominant Owing to night fishing operations and or gear, depth data were collected in species caught (70%). Small amounts because marine mammals were not al 1992. With the transducer, fishermen of bonito, Sarda sarda; mako shark, ways brought on board, species identi are able to adjust headrope depth dur [surus sp.; and little tunny, Euthynnus fication and determination of condition ing a tow and from tow to tow. Headrope alletteratus, were also retained. Tuna were difficult. For example, one tow depths observed ranged from 9 to 55 m species were landed both dressed with three unidentified marine mam (5-30 fathoms) below the surface. (headed, gutted, and tailed) and round, mals was released in entirety in the Observers were placed aboard 9 of while all landed swordfish were dressed. water since one of the mammals was the 11 vessels operating in the fishery In accordance with 1992 swordfish believed to have been alive. Atlantic in 1992 and recorded vessel character regulations, each vessel was allowed to pilot whales, Globicephala melas, were istics for the five pairs involved. One retain and land two swordfish per trip. observed taken in the Bay of Biscay pair pair included three vessels, with one Fifty-three swordfish were caught on trawl fishery on one 15 day trip (Collet3). vessel alternating from trip to trip with the observed trips with 15 retained and No sea turtles or sea birds were ob the two other vessels. A majority of the 38 discarded. Of the discarded sword served in the 1992 catches. vessels were <10 years old and ranged fish, 18 were released alive, 15 of which Discussion in length from 23 to 27 m (74-87 feet). were tagged. The two-fish retention Vessel size appeared to be well matched regulation resulted in highgrading, or Since the nine pelagic pair trawl trips for most of the pairs; however, horse upgrading, of swordfish on two ob observed in 1992 covered only 20% power between vessels of a pair was served trips. Highgrading typically in (about I month) of the 5-month fishing more disparate, e.g. 850 hp versus 675 volves discarding processed/stored fish season, these observations provide a hp. Dissimilar vessel specifications may to replace them with larger fish or spe partial spatial and temporal character have been otherwise compensated for cies of a higher value later in the trip. ization of the pelagic pair trawl fishery. but not recorded by observers. Extrapolation of these data is not pos A total of 10 I pelagic pair trawl sets Table 1.-Retained and discarded catch from observed sible since the total number of 1992 was made during the 9 observed trips pelagic pair trawl tows, Oct.-Nov.

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