Sampling herring in the Norwegian Sea by pelagic trawl

When the stock of Norwegian spring-spawning herring is distributed in the Norwegian Sea in summertime, pelagic trawl sampling may be rather challenging because of substantial variation in vertical distribution (from surface and down to 400 m depth), and avoidance of vessel and trawl gear. In this paper the operation and performance of the «Åkratrål» during pelagic trawl sampling of herring by R/V «G.O. Sars» on cruises in the Norwegian Sea 1996 - 1997 are described. The sampling results with regard to capture success, catch size and geograpically segregated length distributions are presented. The implications of the sampling results on the reliability of the acoustic estimate of stock size are discussed

Swimming behaviour of schools related to fish capture and acoustic abundance estimation

Dr. Scient. Thesis. / Department of Fisheries and Marine Biology. University of Bergen. Norwa

Acoustic measurements of schooling herring. Estimation of school biomass and target strength

The connections between reflected echo energy and dimensions of fatty herring schools were studied by a combination of multibeam sonar and a calibrated echo integration unit. A relation between the area and the biomass of the schools was established. A target strength relation was derived by preseining echo integration and sonar measurments of schools. Method deficiencies and improvements for school biomass estimation using sonar and preseining target strength measurements are discussed

Survival of mackerel and saithe escaping through sorting grids in purse seines

Technology for efficient size-selection of mackerel and saithe in purse seines has been developed. A critical constraint for application of the technology is the survival of escaping fish. We have conducted a series of mesoscale experitnents where penned fish were forced through rigid grids and into new storing net pens to quantify the survival of mackerel and saithe. These experiments showed insignificant mortality of both mackerel and saithe. Full scale experiments during mackerel purse seining off western Norway and saithe purse seining in fjords in western and northern Norway have also been conducted. During these experiments control groups were established by transferring parts of the catch gently from the purse seine to attached net pens. Experiment groups were established by collecting fish escaping through the selection grids in attached net pens. The net pens were then towed up to 30 nautical miles for anchoring inshore. In the mackerel experiments, up to 95% of the fish in the control groups and up to 60% in the experiment groups were alive one month after the experiments. This indicates that the size selection process in mackerel purse seining induce too high mortality to be recommended in commercial fishing. On the other hand, the mortality in the saithe experiments was insignificant, and the use of size selection grids in saithe purse seines can therefore be recommended

Implementing the ecosystem approach: experiences from the North Sea, ICES, and the Institute of Marine Research, Norway

Journal homepage: http://www.int-res.com/journals/meps

Good ethics or political and cultural censoring in science?

Peer-reviewed journals are the cornerstones to communicating scientific results. They play a crucial role in quality assurance through the review process, but they also create opportunities for discussions in the scientific community on the implications of the results or validation of methods and data. This requires that journals adhere to commonly accepted scientific standards and are open about their editorial policy. Norwegian scientists experience problems in getting research on minke whales accepted for publication where the data have been collected in association with commercial whaling. The journal Biology Letters refuses to publish papers based on data from the Norwegian whale register while publically claiming a sole focus on scientific quality. Although there are good arguments for claiming that clearly unethical research should not be rewarded with scientific publications, one also has to realize that some fields of research are beset with unresolved ethical and cultural debates. In these cases, it is to the benefit of the progress of science, and indeed society, to be open about the issues and support arguments through scientific studies. Political or cultural censoring of scientific information will in any case jeopardize the role of journals in quality assurance of scientific research and undermine the credibility of science as a supplier of objective and reliable knowledge.publishedVersio