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

Krag, Ludvig Ahm; Holst, René; Madsen, Niels; Hansen, Kurt; Frandsen, Rikke

doi:10.1016/j.fishres.2009.09.001

Cited by 34 publications

(15 citation statements)

References 16 publications

(28 reference statements)

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“…In addition to optical or acoustic observations, fish behaviour can be inferred from the catch composition (e.g., by using spatially divided gear designs). Examples of such designs are separator trawls [9] – [11] and similar experimental designs in which the trawl body is divided into vertically separated collecting bags [5] , [12] – [15] . However, installing separating panels or other separating devices inside the trawl body introduces new structures that can affect fish behaviour [5] .…”

Section: Introductionmentioning

confidence: 99%

Inferring Fish Escape Behaviour in Trawls Based on Catch Comparison Data: Model Development and Evaluation Based on Data from Skagerrak, Denmark

Krag¹,

Herrmann²,

Karlsen³

2014

PLoS ONE

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During the fishing process, fish react to a trawl with a series of behaviours that often are species and size specific. Thus, a thorough understanding of fish behaviour in relation to fishing gear and a scientific understanding of the ability of different gear designs to utilize or stimulate various behavioural patterns during the catching process are essential for developing more efficient, selective, and environmentally friendly trawls. Although many behavioural studies using optical and acoustic observation systems have been conducted, harsh observation conditions on the fishing grounds often hamper the ability to directly observe fish behaviour in relation to fishing gear. As an alternative to optical and acoustic methods, we developed and applied a new mathematical model to catch data to extract detailed and quantitative information about species- and size-dependent escape behaviour in towed fishing gear such as trawls. We used catch comparison data collected with a twin trawl setup; the only difference between the two trawls was that a 12 m long upper section was replaced with 800 mm diamond meshes in one of them. We investigated the length-based escape behaviour of cod (Gadus morhua), haddock (Melanogrammus aeglefinus), saithe (Pollachius virens), witch flounder (Glyptocephalus cynoglossus), and lemon sole (Microstomus kitt) and quantified the extent to which behavioural responses set limits for the large mesh panel’s selective efficiency. Around 85% of saithe, 80% of haddock, 44% of witch flounder, 55% of lemon sole, and 55% of cod (below 68 cm) contacted the large mesh panel and escaped. We also demonstrated the need to account for potential selectivity in the trawl body, as it can bias the assessment of length-based escape behaviour. Our indirect assessment of fish behaviour was in agreement with the direct observations made for the same species in a similar section of the trawl body reported in the literature.

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Section: Introductionmentioning

confidence: 99%

Inferring Fish Escape Behaviour in Trawls Based on Catch Comparison Data: Model Development and Evaluation Based on Data from Skagerrak, Denmark

Krag¹,

Herrmann²,

Karlsen³

2014

PLoS ONE

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“…Thorough effort was put into investigating the performance of the retainer bag to ensure that no secondary escape occurred. Previous studies have reported that fish escape is highly length dependent (Eng as and Godø 1989;Walsh 1989Walsh , 1992Dahm and Wienbeck 1992;Godø and Walsh 1992;Ing olfsson and Jørgensen 2006;Krag et al 2010;Brinkhof et al 2017). It is reasonable to assume that the overall escape rate would be considerably higher under circumstances with more abundant small fish than found in the current study.…”

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confidence: 43%

“…This value implies that groundgear catch efficiency could be closer to the least conservative estimate—an observation that is corroborated by other studies reporting the same behavior (Main and Sangster ; Walsh ; Krag et al. ). Nevertheless, Ingólfsson and Jørgensen () reported that some fish escaped under both side sections of the groundgear, indicating that the more conservative estimate for catch efficiency may be more appropriate ( hf = 0.0).…”

Section: Discussionmentioning

confidence: 99%

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Catch Efficiency of Groundgears in a Bottom Trawl Fishery: A Case Study of the Barents Sea Haddock

Larsen¹,

Herrmann²,

Brinkhof³

et al. 2018

Mar Coast Fish

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The catch efficiency of two types of groundgear—a conventional rockhopper and a new type of groundgear called the semicircular spreading gear (SCSG)—was investigated through experimental fishing for Haddock Melanogrammus aeglefinus conducted in the Barents Sea. A retainer bag was attached behind the footrope of the trawl, and the number of fish that were overrun by the trawl was compared with the catch in the trawl cod end. The catch efficiency increased slightly for larger Haddock for both groundgears. The SCSG was found to have a significantly higher catch efficiency than the conventional rockhopper groundgear. The estimated improvement in catch efficiency varied between 4.5% and 12.3%, with an equivalent reduction in escape rate underneath the groundgear of more than 70%. The rockhopper groundgear can have a catch efficiency as low as 76%, corresponding with values reported in previous studies. Average catch efficiency for the rockhopper gear was significantly lower during the night in comparison with the daytime. No such difference was found with the SCSG. The SCSG is more efficient for catching Haddock, and it is lighter than the rockhopper groundgear. Both are important factors in reducing seabed impact and fuel consumption. When compared to results of a similar study on Atlantic Cod Gadus morhua, we found that in general, both groundgears had a greater catch efficiency for Haddock, which accords with differences in behavior between the two species.

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“…Both fish behaviour and fish morphology affect the sorting efficiency and size selectivity of a specific selection device (Sistiaga et al, 2011), and both aspects have been widely investigated in relation to the selectivity of cod and haddock in trawls. Specially, haddock is one of the most studied species regarding escape behaviour in demersal trawls (Wardle, 1993;Krag et al, 2010;Winger et al, 2010). Several studies on this species include the effect and efficiency of inserting square mesh panels in the trawl.…”

Section: R a F Tmentioning

confidence: 99%

Size selectivity and length-dependent escape behaviour of haddock in a sorting device combining a grid and a square mesh panel

Herrmann

Sistiaga

Grimaldo

et al. 2019

Can. J. Fish. Aquat. Sci.

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Size selectivity of a new sorting section combining a sorting grid and a square mesh panel was tested for haddock (Melanogrammus aeglefinus) in the Barents Sea demersal trawl fishery. Sampling data for a wide size range enabled investigating the selection process for this species in detail, both for the grid and the square mesh panel. Contrary to earlier studies modelling size selectivity for grids and square mesh panels, which assume that the escape behaviour of all sizes of fish is equal, we applied a model that accounted for haddock of different sizes showing different escape behaviours. Our results demonstrated that this model could describe the experimental data collected better than existing models. Specifically, our results showed that the likelihood for smaller haddock to seek escape through the grid and the square mesh panel was higher than that for bigger haddock that still would manage to escape through the devices if they attempted. The new modelling approach presented in this study may be applicable to other species, selection devices, and fisheries.

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

Cited by 34 publications

References 16 publications

Inferring Fish Escape Behaviour in Trawls Based on Catch Comparison Data: Model Development and Evaluation Based on Data from Skagerrak, Denmark

Inferring Fish Escape Behaviour in Trawls Based on Catch Comparison Data: Model Development and Evaluation Based on Data from Skagerrak, Denmark

Catch Efficiency of Groundgears in a Bottom Trawl Fishery: A Case Study of the Barents Sea Haddock

Size selectivity and length-dependent escape behaviour of haddock in a sorting device combining a grid and a square mesh panel

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