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Population structure, reproductive strategies and demography of redfish (genus Sebastes) in the Irminger Sea and adjacent waters (ICES V, XII and XIV; NAFO 1)

Contract nr: QLK5-CT-1999-01222
Project type: RS (Research and Technological Development Project)
Starting date: 01-01-2000
Duration: 48 months
Total cost: 5,799,840 EUR
EC Contribution: 2,864,992 EUR
Scientific Officer: Dominique LEVIEIL
Research topic: 5.1.2. Sustainable fisheries and aquaculture

The present proposal has been internationally developed to increase the fragmentary and preliminary biological knowledge about commercially exploited golden and deep-sea redfish stocks (Sebastes marinus L. and S. mentella Travin) in the Irminger Sea and adjacent waters, within the frame of an agreed four-year research programme. The multidisciplinary intentions are designed to jointly investigate unsolved problems in the field of stock delimitation, reproductive strategies and demography as three separate tasks, respectively. A total of 16 scientists and six technicians from the Federal Research Centre for Fisheries (EU-Germany, coordination), Institute of Marine Research (EU-Spain), Marine Research Institute (Iceland), Institute for Marine Research (Norway) and the University of Bergen (Norway) will collaborate and contribute to the various analyses.

Two commercially exploited redfish species occur in the Irminger Sea and adjacent waters, golden redfish (Sebates marinus, Linnaeus 1758) and deep sea redfish (Sebastes mentella, Travin 1951) which are presently treated as three management units straddling European, Faeroes, Icelandic and Greenlandic EEZs as well as international waters. They are defined as golden redfish and deep-sea redfish on the continental slopes and oceanic redfish distributed over the pelagic Irminger Sea waters. The pelagic occurrences of redfish below 500 m and the “giants” of the Reykjanes Ridge remained unidentified. This project is divided into three workpackages:

1. Population structure,
2. Reproductive strategies,
3. Abundance and demography.

Workpackage 1 focuses on the species and population structure and the identification of possible distinct gene pools of the redfish occurrences in the Irminger Sea and adjacent waters. The identification and delimitation of the self-sustaining stock units is the prerequisite and basis for any management actions in accordance with the FAO “Code of Conduct for Responsible Fisheries” (Food and Agriculture Organisation) and the UN Agreement on “Straddling and Highly Migratory Fish Stocks”. Recently, the annual exploitation rates exceeded 200,000 tonnes although knowledge is lacking about the recruitment processes or migration patterns of different life stages. At present, there is only preliminary information available about the species and population structure for Sebastes marinus and deep-sea S. mentella inhabiting the shelves and continental slopes off Greenland, Iceland, Faeroe Islands and even the pelagic water column above 2000 m depth. For larvae and juveniles, even the discrimination of species is doubtful. Preliminary information suggests the existence of various distinct gene pools but is based on a limited material in terms of temporal coverage as well as the size groups investigated. It is therefore very important to intensify the genetic investigations before any firm conclusions can be drawn.

A variety of methods is proposed to enlighten the redfish population structure. Sub-workpackage 1.1 deals with the classical morphometric and meristic stock identification approach, while sub-workpackage 1.2 is designed to identify morphometric differences from the otolith shapes and to track the recruitment by comparative analyses of the elemental contents in the central otolith region (nucleus). Sub-workpackage 1.3 uses a variety of molecular genetic markers such as isozymes and other proteins, DNA based methods such as microsatellites, amplified fragment length polymorphisms (AFLP), nuclear DNA and mitochondrial DNA genes, to study the population structure and the species identification.

Reproductive strategies of the ovoviviparous S. marinus and S. mentella in the Irminger Sea and adjacent waters by species and stock will be investigated within workpackage 2. The task will also consider ecological consequences due to the longevity of redfish and the maternal care for their embryos. Sub-workpackage 2.1 aims at a description of the variation in sexual maturation in time and space. By means of histological techniques, the length at first maturation (maturity ogive) and reproductive cycles will be identified. The expected variation in reproductive processes between areas and seasons will be compared with the environmental effects and findings of the population structure analyses (workpackage 1). Sub-workpackage 2.2 deals with the estimation of female fecundity during four different stages of the ovary development. Size and age effects on the female fecundity as well as egg and larvae condition will be investigated. We expect precise information on the amount of larvae released by the females and ecological background comparing the results with oviparous and short-lived species.

Changes in abundance, structure and productivity of the three commercially exploited redfish management units will be monitored within workpackage 3. Sub-workpackage 3.1 is a conglomeration and co-operation of the various groundfish and hydro-acoustic surveys carried out by the partners involved. Despite the fact that some of the survey methods applied differ between partners, joint and detailed analyses on a stock-by-stock basis instead of national reports are considered very useful. Within the frame of the proposed project, the survey methodology will be improved to achieve a more precise monitoring of the stocks independent from the information based on commercial fisheries. Sub-workpackage 3.2 represents the first attempt to construct an international database including fishery information on all redfish catches in ICES Div. V, XII and XIVb. This international database will allow an appropriate annual analysis of the trend in catch rates, standardised and corrected for national, vessel, area and seasonal effects. The results will contribute significantly to the estimation of the quantitative reaction of the redfish stocks to the removed biomass by the recently increased exploitation.

Information about changes in the age, composition and growth is obligatory for an assessment of the productivity of the redfish stocks. However, the difficulties related to age determination in redfish are well documented in the 1995 report of the ICES “Workshop on Age Determination of Redfish (ICES 1995)”. The use of otoliths instead of scales was recommended and the comparative age readings from thin otolith sections resulted in the best agreement between readers. Sub-workpackage 3.3 takes up this result and establishes an otolith exchange programme between three partners to further improve the precision of information about the demography of the stocks. The age reading will be validated by the measurement of the ratio between two radioisotopes in the otolith cores. This ratio will be used as a index of the elapsed time since incorporation of the radioisotopes and will, therefore, provide an alternative to the subjective ‘annuli count’ age readings.


Hans-Joachim RÄTZ
Federal Research Centre for Fisheries
Tel.: +49 49 38905169
Fax: +49 40 38905263

Consejo Superior de Investigaciones Cientificas
Tel.: +34 986231930
Fax: +34 986292762
  Thorsteinn SIGURDSSON
The Marine Research Institute of Iceland
Tel.: +354 5520240
Fax: +354 5623790
  John DALEN
Institute of Marine Research
Tel.: +47 55238457
Fax: +47 55238584
  Gunnar NAEVDAL
University of Bergen
Tel.: +47 55584980
Fax: +47 55584980