Catch comparison between rockhoppers and bobbins ground gear on the Norwegian bottom sampling trawl

In a study aimed at improving the reliability of the Norwegian bottom sampling trawl, comparative fishing between standard bobbins gear and rockhopper ground gear were carried out in the Barents Sea. The catch ratios bobbins/ rockhopper (B/R) for cod and haddock show a higher efficiency for rockhopper than for bobbins, especially for small fish. The catch ratio B/R for cod varied by time of day. Rockhopper seemed to have a higher efficiency compared to bobbins during daytime. The same trend was not found for haddock. These experiments confirm earlier experiments that rockhoppper is more effective than bobbins gear in catching fish close to the bottom. This is particulary true for small cod

Behaviour of Atlantic salmon (Salmo salar L.) recorded by data storage tags in the NE Atlantic – implications for interception by pelagic trawls

In a project carried out in the Nordic Seas (Northeast Atlantic) in 2002 - 2004, 413 Atlantic salmon (Salmo salar L.) were tagged with data storage tags (DST) either logging temperature and depth (StarOddi, Milli) or just temperature (Dallas semiconductor, iButton). The main aims were to study various marine life history traits of salmon, such as winter habitats, diurnal patterns of vertical migration, feeding activities. Another aim was to collect salmon behaviour data with relevance for issues related to by-catch of salmon in pelagic fisheries. In this paper we focus on possible implications of the diurnal depth distribution of salmon in relation to catchability of salmon in sampling trawls versus commercial fisheries. Five DSTs were returned from fishermen. Four of these were Milli-tags and are used in this presentation. Time from release to capture ranged from 48 - 128 days. The DSTs logged data at alternating intervals of 1, 5, 30, 60 and 120 min. almost 45000 recordings were retrieved. The data records were grouped in different phases: post-release; oceanic feeding & migration; coastal migration; estuarine migration; in-river phase. Salmon stay in the upper 5 m for 60% of the time during the oceanic phase, making deep dives (280 m) in between. The proportion of time the salmon stay at the surface (<2 m) decreases from 5.5 to 2.5% between 9 and 17 h

Space-time recapture dynamics of PIT-tagged Northeast Atlantic mackerel (Scomber scombrus) reveal size-dependent migratory behaviour

Based on GIS-mapping and semi-parametric modelling of recaptures from PIT-tag experiments in the North Sea nursery area (September 2011), the Celtic Seas spawning area (May-June 2014-2021) and the Icelandic Waters feeding area (August 2015-2019), we argue that the distribution of Northeast Atlantic (NEA) mackerel is influenced by a size-dependent migratory behaviour. The time-space recapture dynamics revealed that larger mackerel tended to migrate a longer distance between spawning and feeding areas, either through a western route from the Celtic Seas into the Icelandic Waters and the Greenland Sea or by following the main route northwards through the Faroe-Shetland Channel into the Norwegian Sea. This long-distance travel resulted in turn in delayed arrival in the North Sea wintering area. During the return spawning migration into the Celtic Seas, larger individuals remained in the front, likely heading to spawning grounds farther south than smaller conspecifics. Migration patterns also evolved with time at liberty as the mackerel grew older and larger, while possibly covering a progressively wider area over its annual migration cycle as suggested from the tagging data. However, the study also showed large inter-annual variability in the recapture patterns which likely reflect changes in environmental condition (prey availability and ocean current), NEA mackerel population demographics, and the spatial fishery dynamics.publishedVersio