An Assessment for Roughhead Grenadier (Macrourus berglax) in NAFO Subareas 2 and 3

It has been recognised that the recent catches of grenadiers by EU-Portugal and EU-Spain in Subarea 3, previously reported to NAFO as roundnose grenadiers, correspond to roughhead grenadier. Roughhead grenadier is taken as by-catch in the Greenland halibut fishery in the Regulatory Area mainly in Divisions 3LMN. Catches increased gradually and the largest proportion by country correspond to Spain and Portugal, with 6050 t. and 1089 t. respectively in 1998. A review of the biomass estimates from the available research surveys in Subareas 2 and 3 is presented. According to the Canadian fall surveys, it seems that the main part of the stock shifted from the northern Divisions (2GJand 3K) to the southern ones (3LN), and to greater depths (beyond 1000 m.) since early 90s. A review of the biological information available for this stock is also presented. Mean lengths (preanal fin lengths) of the catches show no decreasing trend since 1995. The age o fully recruitment to the fishery is 8, and the total mortality estimate (1997-1998) is Z = 0.43. Female age at maturity is 15, corresponding to a PFL of 26.5 cm. The Canadian fall survey series seems to be the best input for the assessment of this stock. At present the higher part of biomass is found in Div. 3L and 3N and at depths between 1000-1200 m. A yield per recruit has been performed using the input data presented in table 13. The partial recruitment vector comes from Cárdenas et al. (1995), The maturity curve at age from Murua and Motos (1997) and the mean weight at age from the 1998 agelength key. M is assumed as constant through the ages with a value of 0.2. The results of the yield per recruit analysis appears in Fig. 6. The estimated Fmax is 0.27 and F0.1 is 0.13. However it must be noted that this output is sensitive to possible changes in M, as if for instance M would be different between sexes, as suggest the results from Murua et al. (1999) and as it has been shown in the Greenland halibut (Anon. 1998). Any decreasing trend in the mean lengths, that would be an index of an excessive fishing pressure, is observed in the mean lengths of the catches since 1995 up to now. The available time series of catches at age is too short to analyse trends in the SSB, however it can be noted that only a 18 % and 10 % percent of the 1997 and 1998 catches respectively were above the female age at maturity (15 years). We have scarce information at the moment to assess an appropriate exploitation level, though survey series shows that at the current exploitation rate the biomass is increasing since 1994.