Abstract--Survey standardization conducts can reduce the variability in trawl catch efficiency thus producing more precise estimates of biomass.

Abstract--Survey standardization conducts can reduce the variability in trawl catch efficiency thus producing more precise estimates of biomass. the same such procedure, towing with equal amounts of trawl warp forward both sides of the clear was experimentally investigated for its importance in determining optimal trawl geometry and for evaluating the effectiveness of the new National Oceanic and Atmospheric Administration (NOAA) national protocol upon accurate measurement of trawl warps. This new standard for measuring warp longitudinal dimensions requires that the difference between warp details can be no more than 4% of the distance between the otter doors measured along the bridles and footrope Trawl performance data from repetitive towing with warp differentials of 0 3 5 7 9 11 and 20 m were analyzed for their meaning on three determinants of flatfish catch efficiency: footrope distance off-bottom, bridle extent in contact with the bottom, and area swept on the net. Our results indicated that the distortion of the trawl caused by way of asymmetry in trawl warp detail could have a negative influence upon flatfish catch efficiency. At a difference of 7 m in warp continuance the NOAA 4% threshold value for the 83112 Eastern overlook trawl used in our reflection we found no effect forward the acoustic-based measures of door spread, wing spread, and headrope height off-bottom. However, the sensitivity of the trawl to 7 m of warp slip could be seen as footrope distances off-bottom increased slightly (particularly in the center region of the pure where flatfish escapement is highest), and as the width of the bridle path responsible for flatfish herding, together with the effective trap width, was reduced. For this overlook trawl, a NOAA threshold value of 4% should be considered a maximum. A more conservative value (les than 4%) would likely model potential bias in estimates of relative abundance caused through large differences in warp amplification approaching 7 m.

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Standardization of trawl examine procedures can reduce the variability in abundance indices between samples, scrutinize vessels, and over time at reducing the variability in trawl catch efficiency. as it is standardization was the focus of the lately developed U.S. National Oceanic and Atmospheric Administration (NOAA) protocols for the operation of its groundfish bottom trawl take a view ofs (Stauffer, 2004). The first of these protocols interests the measurement of towing cables or warps. For utensils towing with two warps, the NOAA protocols specify that the difference in longitudinal dimensions between port and starboard warps may not exce 4% of the wire longitudinal dimensions between otter doors measured along the bridles and footrope The ne for adopting similar a critical value was considered essential because of the belief that unequal warp lengths--from inaccurate measurement or succeeding stretching--would lead to distortion of trawl geometry and a change in catch efficiency, particularly for operations that use trawl winches with the brakes locate or locked. The adopted value, however, was chosen somewhat arbitrarily because experimental data showing the subject territory of trawl geometry or fishing performance upon warp symmetry was lacking for any of the bottom trawl contemplates subject to the protocols.

In this meditation we examine the effect of unequal warp fulnesss on the geometry of the 83-112 Eastern trawl which is used through the Alaska Fisheries Science Center (AFSC) to guard the annual eastern Bering Sea shelf contemplate Although we monitor a abounding suite of trawl dimensions, like as door spread, wing spread, and headrope height that are typically measured forward trawl surveys, our attention was primarily focused onward the distance between the footrope and lower bridles with the sea floor. Prior studies with this trawl have demonstrated that escapement in subordination to the footrope (Somerton and Otto, 1999; Munro and Somerton, 2002; Weinberg et al., 2004) and herding according to the bridles (Somerton and Munro 2001) are the chiefly important determinants of catch efficiency for flatfishes and other benthic species. Although we understand that catch efficiency hangs on animal behavior as well as trawl geometry a goal of our research was to assess whether the 4% critical value is appropriate to preclude an appreciable degradation of catch efficiency owing to warp asymmetry, the conclusion of unequal trawl warp lengths

Materials and methods

Experimental design

The experiment was managemented during 14-17 September 2003 along the Alaska Peninsula in Bristol Bay approximately 85 km NE of Amak Island (55[degrees]58'N 162[degrees]55'W) onward smooth, relatively level bottom at a midst of 82 m. Trawling was performed with the chartered 38-m unrelenting trawler FV Vesteraalen. The Vesteraalen is powered on a single 1725-hp engine and is equipped with split Rapp Hydema (Rapp Hydema AS, forebode Norway) trawl winches carrying 25 cm (1") diameter, compacted, solid-core trawl warp.

The 83-112 Eastern is a low-rise, 2-seam, flatfish trawl designed for use forward smooth, soft bottom. The nylon without deductions is constructed of 10.1-cm extend mesh in the wing and visible form [i]or[/i] frame 8.9 cm in the intermediate, and double 89-cm interstice lined with a 3.1-cm snare in the codend. It is towed behind a pair of 18 x 27 m carburet of iron "V" doors, weighing approximately 816 kg apiece, which are attached to the toil by two 3-m-long door leg (consisting of 16-cm long-link chain); a 122-m-long door leg extension (consisting of 19-cm diameter stranded wire); and a pair of 55-m-long bridles (consisting of 16-cm diameter bare stranded wire) upon each side of the unadulterated (Fig. 1). The 25.5-m-long (83 ft) headrope has 41 evenly spaced, 203-cm diameter floats that provide 1164 kg of total lift. The 341-m-long (112 ft) 52-cm diameter footrope is instituteed of 1.6-cm diameter stranded-wire pull protected by a single wrap of one as well as the other 1.3-cm diameter polypropylene line and split rubber trousers The footrope is weighted with 518 m of chain (08-cm proof-coil) attached at each tenth link, forming 168 apertures to which the netting is hung An additional 06-m-long 13-cm long-link chain extension associates each lower bridle to the trawl wing tips to help hold the footrope close to the bottom. Because the wire amplification between otter doors measured along the bridles and footrope is 1756 m the critical value for differential warp extent for this trawl established by means of the NOAA 4% rule is 7 m