Report of the Study Group on Redfish Stocks (SGRS)

A trawl-acoustic survey on pelagic redfish (Sebastes mentella) in the Irminger Sea and adjacent waters was carried out by Iceland and Russia in June/July 2007. The usual participation of Germany had to be cancelled due to short-term technical problems of their vessel. The German participant, however, compensated the Russian participant by funding additional days in the field, in order to ensure the complete survey area coverage. Nearly 350 000 NM2
were covered, with only slightly increased distances between hydroacoustic tracks and trawl hauls, compared to previous surveys. As relative survey indices, a total
biomass of 372 000 t was estimated at depths shallower than the “deep scattering layer” (DSL) by hydroacoustic measurements, and about 854 000 t within and deeper than the DSL by an experimental “trawl method”. In the shallower layer, the highest concentrations of redfish
were found southeast of Cape Farewell and in the southwestern survey area. In the deeper layer, high concentrations were also found southeast of Greenland, but as well in the northeastern survey area. The estimated biomass and abundance of redfish within and deeper
than the DSL derived from the trawl data, however, is considered highly uncertain due to the large error involved in the estimation.
Although the estimates divided by depth layers are not strictly comparable between years due to changes in the depth range covered in the deeper layer in the 2005 and 2007 surveys, the total estimates of the shallower and deeper layer combined can be compared between years.
The total relative biomass value of 1.2 million t derived in 2005 and 2007, encompassing the shallower and the deeper layer, represents a value within the range of the 1999 and 2001 estimates. The 2003 survey results were considered inconsistent due to unknown seasonal
effects, as the survey was carried out about three weeks earlier than usual.
The SGRS recommends that the survey should be continued, that it should be carried out every second year, that as many vessels as possible should participate to improve the quality of the derived estimates, and that the timing of the survey should be kept in June/July. The
Group recommends to ACFM to consider the 2007 survey for the 2008 advice and to reconsider the 2005 advice, as the relative survey indices since 1999 showed stability and the biomass in the deeper layer has to be taken into account. Moreover, the Group recommends that further nations should participate in the next surveys and that chartering of additional vessels and cost share should be considered as alternative to direct participation.