Some comments to the problem of adjusting TACs to mesh size changes.

Mesh assessments are usually carried out by calculating "short term losses" and "long term gains" expected from a change in the minimum legal mesh size, assuming no change in total fishing effort or its distribution by area and season (Gulland, 1961) • At the time these methods were developed, minimum legal meshand/ or landing sizes were the only regulatory measures applied on most demersal trawl fisheries. After the introduction of TACs one is faced with the problem of what effect a change in mesh size should have on the recommended TAC. Often this has been dealt with by simply calculating the catches corresponding to a range of fishing mortalities for the alternative mesh sizes and recommend TAC's corresponding to a certain value of the fishing mortality on the fully exploited age groups, identical for all mesh sizes. By this approach the "short term loss" is automatically transferred into the TAC, making the TAC for an increased mesh size smaller than the TAC for the present mesh size by an amount approximately equal to "short term losses". After a brief discussion of the assessment of short and long term effects of mesh size changes, this paper will mainly deal with the appropriateness or in-appropriateness of the usual methods applied for selecting TAC's and discuss alternatives

Regulation of the fishery for capelin

The effect of different regulatory measures on the fishery for Barents Sea capelin was studied by calculating yield per recruit and spawning stock per recruit for several fishing strategies. It is concluded that the minimum legal size should be at least 14 cm in order to protect fish younger than three years old

Analyse av fangst pr. enhet innsats data for vågehval. Sluttrapport til NFFR.

Innledning: Fangst pr. enhet innsats (cpue) data fra den norske vågehvalfangsten har tidligere vært analysert ved Havforskningsinstituttet med henblikk på å få et bilde av utviklingen i den nordøstatlantiske bestanden i etterkrigsperioden. Resultatene har bl.a. blitt gitt i forskjellige rapporter til Den internasjonale hvalfangstkommisjon (IWC) . Det har imidlertid vært en rekke problemer knyttet til tolkningen av resultatene. Mens cpue-indeksene for Vestfjorden indikerte en jevn nedgang på ca. 3% pr. år fra 1946, viste de publiserte tidsserier for Barentshavet liten systematisk utvikling når en så på hele perioden. For kortere perioder antydet imidlertid dataene mer jevne opp- og nedgangsperioder. De forskjellige tolkningsproblemene ga opphav til omfattende diskusjoner i IWC's vitenskapskomite. På tross av den store innsatsen som tidligere var lagt ned i analyse av dataene, vurderte en det både som mulig og viktig å komme frem til mer entydige konklusjoner ved hjelp av nye analysemetoder og utnyttelse av informasjon/data som tidligere ikke var fullt utnyttet

A model for incorporating changes in distribution of fishing effort in assessment of the effects of changes in trawl mesh size

Factors invalidating traditional mesh assessments are discussed with special emphasis on changes in distribution of fishing effort between areas inhabited by small and large fish. A model for studying the effects of such changes is constructed. Both studies of equilibrium situations and simulation studies, taking into account variations in year class strength, show that traditional mesh assessments may significantly underestimate the long term effects of mesh size changes. The short term effects will depend on the age composition in the stock when the mesh change is introduced and on the incoming recruitment. Finally the more general applicability of the model is discussed