Investigating density-dependent catchability in bottom-trawl surveys

Geostatistical Assessment of Sampling Designs for Portuguese Bottom Trawl Surveys

New sampling designs for the Autumn Portuguese bottom trawl survey (ptBTS) were investigated to explore alternative spatial configurations and possible increments on sample size. The currently used stratified random design and five proposals of systematic based designs were assessed by a simulation study, adopting a geostatistical approach based on likelihood methods of inference. The construct...

Hierarchical Bayesian models of length-specific catchability of research trawl surveys

To estimate absolute abundance from research trawl surveys, the catchability of the fish to the gear must be known or estimated. Using 47 data sets of length-specific catchability, we conducted a hierarchical Bayesian metaanalysis of length-specific catchability for a number of different species groups. It was found that the Bayesian estimates of catchability were seldom near or above 1 for any...

Behavior-dependent selectivity of yellowtail flounder (Limanda ferruginea) in the mouth of a commercial bottom trawl

Reliability of trawl surveys on cod in Norwegian fjords

According to ICES, the International Council for the Exploration of the Sea, populations of coastal cod (CC) in Norway north of 628N have been declining since 1994. The estimates are based on analytical assessment in which the most recent estimates are tuned with survey information. We evaluate the quality of bottom-trawl surveys conducted in four North Norwegian fjords during autumn of the yea...

Decision Support to Sustainable Management of Bottom Trawl Fleet

A decision support concept (DSC) for sustainable management of the bottom trawl fleet was created in line with ecosystem-based management. It is based on principles that integrate ecological, social and techno-economic aspects of trawl fisheries in a multicriteria analysis approach. For the sake of greater transparency and improved stakeholder participation, elements of the proposed multicriter...