A review on roughhead grenadier (Macrourus berglax) biology and population structure on Flemish Cap (NAFO Division 3M) 1991-2006 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 16 EU surveys (1991-2005) in Flemish Cap is presented. Depth distribution of captures, length/age distribution of captures, growth rates, sex-ratios, 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 in 1994 and remained around 1500 and 2000 tons till 2002. It increased again in 2003 to reach high levels of 3575 tons in 2004 and decreased to 2387 tons in 2005. The biomass index in 2006 was 3933 tons, the highest in the time series. 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.