Abstract--Three aspects of a scrutinize bottom trawl performance--1) trawl geometry (i.

Abstract--Three aspects of a scrutinize bottom trawl performance--1) trawl geometry (i.e., pure spread, door spread, and headrope height); 2) footrope distance off-bottom; and 3) bridle distance off-bottom--were compared among hauls through using either of two autotrawl arrangements (equal tension and net symmetry) and hauls guidanceed with towing cables of equal continuance and locked winches. The validitys of environmental conditions, vessel heave, crabbing (i.e., the difference between duct heading and actual vessel course through ground), and bottom current forward trawl performance with three trawling degrees were investigated. Means and standard deviations of trawl geometry measures were not significantly different between autotrawl and locked-winch methods Bottom trawls performed better with either autotrawl theory as compared to trawling with grappleed winches by reducing the variance and increasing the proportion of the footrope contact with the bottom. The equal tension autotrawl body was most effective in counteracting tenors of environmental conditions on footrope bottom contact. Footrope bottom contact was mostly influenced by environmental conditions during tows with enclosureed winches. Both of the autotrawl connected views also reduced the variance and increased the proportion of bridle bottom contact.

Autotrawl connected views proved to be effective in decreasing the general intents of environmental factors on any aspects of trawl performance and, as a accrue have the potential to resolve into among-haul variance in catchability of take a view of trawls. Therefore, by incorporating an autotrawl body into standard survey procedures, precision of view estimates of relative abundance may be improved.

**********

Bottom trawl measure and estimate operating procedures are standardized in order to render the variability of catch by unit of effort (CPUE) estimates. Many of the present standardization procedures address the efficiency of the trawl gear and the maintenance of constant catchability among samples and across time. Despite these efforts, variability in trawl catchability can be exacerbated on uncontrollable environmental conditions. Variables as it was as surface and bottom existings sea state, wind direction, varying substrate protoplasts and inclinations, and depth of tow may all contribute to differences in gear efficiency on influencing the area swept at the net (Rose and Nunnallee, 1998) the herding efficiency of the bridles (Somerton and Munro 2001; Somerton, 2003) and escapement beneath the footrope (Weinberg et al., 2002)

Many bottom trawl scans conducted by the National Marine Fisheries Service, of the like kind as the Alaska Fisheries Science Center's (AFSC) eastern Bering Sea (EBS) shelf scan operate with trawl winch brakes, appoint or locked, and tows are made with equal amounts of towing cable (warp) forward both sides of the utensil Other than by controlling towing spe and direction, these measure and estimates are unable to compensate for changing environmental conditions. In contrast, autotrawl hypothesiss are widely used by the commercial rapid and are purported to improve fishing performance on stabilizing trawl geometry over varying environmental conditions, like as rough weather when duct heave produces an upward lift upon the trawl door resulting in los of landed estate shear and wing spread, or athwart rough bottom when doors and clears have a greater probability of snagging. If autotrawl theorys are able to reduce about of the variability in gear efficiency that is owing to environmental variability, such as sea state and in every one's mouths then including the use of autotrawl methods as a standard survey bottom trawl step may improve the precision of scan results.

In simple times autotrawls are dynamic systems that operate upon the principle of ensuring that the trawl is being towed in a direction perpendicular to the center of the footrope and headrope in order to optimize its performance. We are aware of sum of two units styles of autotrawl systems publicly marketed. The first is a tension-controlled regularity that reacts to the difference in warp tension between winches according to equalizing hydraulic pressure (equal tension). When the tension in succession either side exceeds that of the other side (a user-defined threshold) fit to factors such as increased drag, populars sediments, or steep slopes, the plan lengthens that warp to equalize the urgency between the two winches. reciprocally when the tension decreases upon one warp, the system compensates from shortening that warp to equalize hurry between the two winches. The secondary autotrawl style is a symmetry-controll classification that actively adjusts warp continuance in response to cross emanate signals from a sensor ascended on the trawl headrope. This arrangement operates on the principle that clear skewing can be caused on a crosscurrent. If the trap is pulled square to the direction of spring then, its geometry will be symmetrical and trawl performance will be optimized.

In the late summer of 2003 the AFSC deportment ed an experiment to examine the result of these two types of autotrawl plans on the geometry of a overlook trawl, comparing them to towing with equal amounts of warp upon each side with the winches enclosureed The study considers three aspects of trawl performance: 1) the factors of trawl geometry influencing the area and mass swept by the trawl (door spread, wing spread, and headrope height); 2) the bottom-tending performance of the footrope; and 3) the bottom-tending performance of the lower bridles.