An analytical assessment of NAFO roughhead grenadier Subareas 2 and 3 stock.

Catch and research survey data from 1992-2005 on the roughhead grenadier stock in NAFO Subareas 2 and 3 are fitted to the eXtended Survivors Analysis (XSA) model. The model results indicated that the stock biomass has been increasing from 1996 to 2005. The biomass estimated for the beginning of 2005 was around 70.000 tonnes, the highest in the time series. Fishing mortality has declined since 1999 and showed the lowest value in the time series in 2005. Over the last few years, there have been two years with very good recruitment at age 3, which may increase the exploitable biomass in the future. The assessment results showed that the current roughhead grenadier Subarea 2 and 3 stock status is healthy. While the analysis indicated that there was a clear retrospective pattern in the model estimates (i.e., fishing mortality being underestimated and total biomass overestimated), the sensitivity analysis showed that the results were robust to the model set up. Although the short time series available, in addition to the wide age composition of this species, the low fishing mortality level estimate by XSA and the lack of convergence in the retrospective analyses, the results showed that the XSA model adequately fitted the data and that the XSA estimated trends are similar to those observed by research surveys. Therefore, it could be concluded that this assessment model may be an appropriate tool to be used in the quantitative assessment of the roughhead grenadier stock in NAFO Subareas 2 and 3

A Review on Roughhead Grenadier (Macrourus berglax) Biology and Population Structure on Flemish Cap (NAFO Division 3M) 1991-2005 Based Upon EU Flemish Cap Bottom Survey Data

The European Union has conducted since 1988 an annual bottom trawl survey in Flemish Cap (NAFO Division 3M) in the 200-720 m depth range. The information on roughhead grenadier population structure recorded during the last 14 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 present ed. In general, the biomass index increased from low levels to a peak of about 3 000 tons in 1993, then decreased in 1994 and remained around 1 500 and 2 000 tons till 2002. It increased again in 2003 to reach the peak of 3 575 tons in 2004. The biomass index in 2005 was 2 387 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 li fe cycle and multiaged population structure with differences in growth and mortality between males and females

Assessment of Roughhead Grenadier, Macrourus berglax, in NAFO Subareas 2 and 3

According the autumn Canadian survey (2J+3K) and the Spanish 3NO survey, the roughhead grenadier total biomass indices would indicate a general increasing trend from 1995 onwards. The catch / biomass (C/B) indexes obtained using the Canadian autumn survey and the Spanish 3NO biomass index in the period 1995-2004 show a clear decrease trend from 1995 to 2004, due to an increasing trend in the survey biomass and a decreased of catches. The Z estimate from the catch curve based upon commercial catch at age data (1992-2004) was 0.355 for ages 8 to 20, the value estimate from the catch curve of the UE Flemish Cap survey (1994-2004) was 0.511 for the same ages and 0.394 for the catch curve of the Spanish 3NO survey data (1997-2004). The Separable VPA (Pope and Shepherd, 1982) stock assessment model was fitted to the stock data, years 1993 to 2004 and ages 3 to 20, for the roughhead grenadier Subarea 2 and 3. The model seems to fit adequately the data. The results of the Separable VPA were used to start a traditional VPA. The mean fishing mortality for ages 8 to 20 in the period 1993-2004 was 0.259 and is similar than those calculated by the catch curves with the catch matrix data (0.255) and with the Spanish 3NO survey data (0.294) for the same ages. Moreover the trend of F bar (8-14) of the VPA is similar to the catch/survey biomass ratio for the Canadian Autumn survey (2J3K) and the Spanish 3NO survey. However the VPA biomass trend is total different from the biomass trend of the Canadian Autumn (2J3K) and Spanish 3NO surveys, in the last years the biomass of the surveys show a great increase and the VPA biomass is stable at the lowest levels of the series. Recruits at age 3 have the same problem, survey show in 2004 the biggest recruitment of the series while VPA show for 2004 a normal recruitment

Roughhead Grenadier NAFO Subareas 2 and 3 Age Disaggregate Data (1992-2003)

The aim of this document is to compile all available information for the stock of roughhead grenadier in NAFO Subareas 2 and 3 which in turn will allow carry out an age disaggregate assessment in the future. This document present the catch at age matrix as well as mean weights and lengths by age of roughhead grenadier in NAFO Subareas 2 and 3 between 1992 and 2003, resulting of applying the Spanish ALK available to the national catches length distributions. We have also transformed the Spanish 3NO survey length distributions in age distributions applying a mix ALK (3M survey and catches ALK)

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

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

Monitoring Update of the Roughhead Grenadier Stock Assessment in NAFO Subareas 2 and 3

The revised catch history after 1987 is presented, total SA 2+3 roughhead grenadier catch in 2000 was 4767 tons. The trends in biomass estimates from four survey series are examined: Canadian fall, Canadian spring, Spanish spring 3NO and EU summer 3M. Only the Canadian fall surveys are considered to cover adequately the species distribution range. The biomass index from this survey in 2000 was 29139 t , 36 % of it in Div. 3L. Commercial catch include mainly ages between 5 and 10, with a peak at age 6. An age structured production model has been performed as a trial. The result of it indicate a moderate decrease in the total biomass but a sharp decrease in SSB. The F reference obtained is 0.41. The C/ B index using data from the Canadian fall survey is 0.16 (C/B1999 = 0.27)

Standardized CPUE Indices for Greenland Halibut in NAFO Divisions 3LMNO Based on Spanish Commercial Catch Rates

Standardized CPUE series using a Generalized Linear Model for Greenland halibut in Div. 3LMNO, based on catch and effort data from the Spanish trawl fleet since 1991 are presented. Fixed factors considered in the model were: year, month, vessel, Division and depth and the interactions analysed were: Division – depth and month – Division. All the factors and interactions analyzed are significant. The total proportion of variance explained by this model was 40%. The results indicate a decrease trend in the catch rate index in recent years from highest values in 2000

A Review of the Fishery and the Investigations of Roughhead Grenadier (Macrourus berglax) in Flemish Cap and Flemish Pass

We review the fishery and biological investigations carried out in the Flemish Cap and Flemish Pass area during the 25 years of NAFO history. In particular, we examine the information available on the biology and population structure of roughhead grenadier recorded in the following 7 research surveys carried out in the Flemish Cap and Flemish Pass area (NAFO Div. 3LMN): Russian bottom trawl research survey (1974–86), Russian longline research survey (1982), Canadian deepwater bottom trawl research survey (1991, 1994 and 1995), European Union longline research survey (1996), European Union Flemish Cap bottom trawl research survey (1988–2004), Canadian autumn bottom trawl research survey (1978–2004) and Spanish 3NO bottom trawl research survey (1995–2004). In addition, biological data collected aboard Spanish commercial fishery vessels were analysed from 1997 to 2004. Indices of biomass from various surveys suggest stability during recent years. Most surveys indicated catch rates as well as average fish size increased with depth. Growth studies by sex demonstrated both sexes grew similarly up to 9–10 years, but the male growth was slower thereafter. Estimates of size and age at 50% maturity and fecundity were very similar for the different data sets studied, showing a late maturity and low fecundity. All the studies examined found that the roughhead grenadier show a very wide feeding spectrum

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

Spanish Research Report for 1998

11 páginas, 9 tablasPeer reviewe