A review on roughhead grenadier (Macrourus berglax) biology and population structure on Flemish Cap (NAFO Division 3M) 1991-2007 based upon EU Flemish Cap bottom survey data

Abstract

The European Union has conducted since 1988 an annual bottom trawl survey in Flemish Cap (NAFO Div. 3M) in the 200-720 m depth range. The information on roughhead grenadier population structure recorded during the last 17 EU surveys (1991-2007) in Flemish Cap is presented. Depth and length/age distribution of captures, sexratios, catch curves, and abundance/biomass estimated by the swept area method are presented. In general, the biomass index increased from low levels to a peak of about 3000 tons in 1993, then decreased steady till 1997, since then remained around 1500 and 2000 tons till 2002. It increased again in 2003 to reach highest levels of the time series in 2004 and 2006 with 3575 and 3993 tons respectively. The biomass index in 2007 dropped sharply to 1367 tons. Age and length composition of the catches showed clear differences between the two sexes. The importance of males in the capture declines in larger fish, disappearing from the capture in largest length classes. Results show that roughhead grenadier has a prolonged life cycle and multiaged population structure with differences in growth and mortality between males and females.