Factors influencing net width and sea floor contact of a survey bottom trawl

Improving area swept estimates from bottom trawl surveys

“…Considerable attention has been given in recent years to the standardization of survey gear and procedures to reduce variability in survey estimates (e.g., Stauffer, 2004;ICES, 2009) since it has been demonstrated that inconsistent trawl performance (i.e., non-standard trawl geometry) can result in variable catch efficiency and increased uncertainty in CPUE estimates (e.g. Koeller, 1991;Weinberg and Kotwicki, 2008). These efforts have helped reduce problems of non-stationary effort that were caused by non-uniformity of survey gear or trawling methods used on different vessels or by different vessel personnel.…”

Effect of tow duration on estimations of CPUE and abundance of the grenadier Coelorinchus jordani (Gadiformes, Macrouridae)

“…Wassenberg et al (1998) provides a possible explanation for the unexpected behavior of the bottom trawl, wherein CPUE and estimated biomass estimations declined with an increase in the tow duration. Studies on the behavior of the bottom trawl have shown that the net and footrope may bounce and skip over the ground because of snagging of the footrope behind obstacles (Weinberg and Kotwicki, 2008). Fulanda and Ohtomi (2011) observed similar jumps in the ground rope, registered as spikes in the depth profile of the trawl net during towing, and attributed the anomaly to variations in the sea bottom topography.…”

The accuracy of self-reported fisheries data: Oregon trawl logbook fishing locations and retained catches

“…When towing a bottom trawl the fishers must adjust the amount of cable deployed if the bottom depth changes because otherwise the trawl gear will not properly "tend the bottom". Too little cable can cause the trawl to come off the bottom; too much cable can result in greater spread of the trawl doors and distortion of the trawl mouth (Weinberg and Kotwicki, 2008). Trawl captains need to know the depth where their gear is fishing, but the specific location is probably less important except in terms of changes in depth that they may encounter during a tow.…”