Escapement of gadoid fish beneath a commercial bottom trawl: Relevance to the overall trawl selectivity

Selective haddock (Melanogrammus aeglefinus) trawling: Avoiding cod (Gadus morhua) bycatch

“…An alternative explanation for these differing results could be that the vertical distribution of species differs among areas (Engås et al, 1998). The escapement of fish beneath a ground gear of a survey trawl (Walsh, 1991) and a commercial fish trawl (Ingolfsson and Jørgensen, 2006) exhibited contrasting length dependencies to the separator trawl experiment reported by Engås et al (1998) as primary small fish escaped the trawl beneath the ground gear. The length dependency by which small fish enter the trawl closer to the seabed compared to larger fish also has been found for American plaice (Hippoglossoides platessoides) and yellowtail flounder (limanda ferruginea) (Walsh, 1992).…”

“…The fishing line was raised to the equivalent of 75 cm by a large danleno bobbin. Three collecting bags were made following the design described in Ingolfsson and Jørgensen (2006) to quantify the escapement beneath the raised fishing line. The headline height of the trawl was equal to 8 m and the spread of the upper wings to 22 m and of the lower wings to 20 m; towing speed was equal to three knots.…”

Fish behaviour in response to a midwater trawl footrope in temperate reservoirs

“…However, both marine and freshwater trawling considerably underestimates abundance of small fish at night because they obviously escape through the netting of the side panels (Říha et al, 2012;Williams et al, 2013). Therefore, experiments with side pocket-nets that catch fish escaping through the side panels would be a useful tool (Ingólfsson and Jørgensen, 2006;Suuronen et al, 1997;Williams et al, 2011). Important factor influencing avoidance behaviour was the fish size.…”

Estimation of gillnet efficiency and selectivity across multiple sampling units: A hierarchical Bayesian analysis using mark-recapture data

“…At the other extreme, gear efficiency in each sampled unit is assumed to be completely independent from the other sampled units, and individual efficiency estimates are required (e.g. Ingólfsson and Jørgensen, 2006). Yet by assuming sampling units are completely unrelated the data may become sparse in some individual units and lead to highly imprecise estimates.…”

“…An alternative approach to model selection of hierarchical models is cross-validation with a subset of the data (Stone, 1974;Gelman et al, 2004). Efficiency and selectivity of fishing gears is a well studied subject in the fisheries literature (Millar and Fryer, 1999;Bromaghin, 2005;Rosenberger and Dunham, 2005;Booth and Potts, 2006;Ingólfsson and Jørgensen, 2006). However, a drawback to results from such studies is their limited applicability to future research.…”