Stock Assessment Form Demersal species. Reference year: 1998-2013. Reporting year: 2014. Eurpean hake of the Gulf of Lions (07)
|Author(s)||Rouyer Tristan1, Jadaud Angelique1, Guijarro Beatriz2, Massuti Enric1|
|Affiliation(s)||1 : IFREMER, 1 rue Jean Monnet, BP 171, 34203 Sète, France
2 : IEO, Centre Oceanogràfic de les Balears; Moll de Ponent s/n; 07015 Palma de Mallorca, Spain
|Sponsor||CGPM/GFCM - Commission Générale des Pêches pour la Méditerranée/General Fisheries Commission for the Mediterranean.|
|Abstract||Fishery: Hake is one of the most important demersal target species for the commercial fisheries in the Gulf of Lions (GSA 7). In this area, hake is exploited by French trawlers, French gillnetters, Spanish trawlers and Spanish longliners. Since 1998, an average of 243 boats are involved in this fishery and, according to official statistics, the total annual landings for the period 1998-2013 have oscillated around an average value of 2008 tons (1736 tons in 2013). In 2009, because of the large decline of small pelagic fish species in the area, the trawlers fishing small pelagic have diverted their effort on demersal species. Between 1998 and 2013, the number of French trawlers operating in the GSA 07 has decreased by 39%, while it decreased by more than 30% between 2010 and 2013. This follows management measures to reduce the number of boats.The French trawler fleet is the largest both for the number of boats and the catch realized (41% and 72%, respectively). The length of hake in the trawler catches ranges between 3 and 92 cm total length (TL), with an average size of 21 cm TL. The second largest fleet is the French gillnetters (41 and 14% respectively, range 13-86 cm TL and average size 39 cm TL), followed by the Spanish trawlers (11 and 8%, respectively, range 5-88 cm TL, and average size 24 cm TL), and the Spanish longliners (6 and 6%, respectively, range 22-96 cm TL and average size 52 cm TL).
The hake trawlers exploit a highly diversified species assemblage: Striped red mullet (Mullus surmuletus), red mullet (Mullus barbatus), angler fish (Lophius piscatorius), black-bellied angler fish (Lophius budegassa), European conger (Conger conger), poor-cod (Trisopterus minutus capelanus), fourspotted megrim (Lepidorhombus boscii), soles (Solea spp.), horned octopus (Eledone cirrhosa), squids (Illex coindetii), gilthead seabream (Sparus aurata), European seabass (Dicentrarchus labrax), seabreams (Pagellus spp.), blue whiting (Micromesistius poutassou) and tub gurnard (Chelidonichtys lucerna).Data and parameters: The information used for the assessment of the stock consisted in annual size composition of catches (estimated from monthly or quarterly sampling in the main landing ports), official landings and biological parameters estimated from data collected in the GSA 7 (1998-2013) by IFREMER and for the DCF from 2002 to 2013). These parameters are length-weight relationship, sex-ratio and maturity ogive. They were computed using inbio (R scripts developed by IEO). From 1998 to 2012, the length-weight relationship was used to compute the mean weight at age. For 2013 we used the weight estimates produced by COST tools. The mean weights at age were computed as the average of males and females abundance weighted by the catch numbers and the weights were adjusted by sop correction. The growth parameters come from tagging experiments developed by IFREMER in the area (Mellon-Duval et al, 2010). The vector of natural mortality by age was calculated from Caddy´s formula, using the PROBIOM Excel spreadsheet (Abella et al., 1997).Assessment method: The stock assessment was performed over the period 1998-2013 using the a4a model (developed by the Joint Research Center) and the MEDITS index, over age classes ranging from 0 to 5+, as tuning fleet, instead of XSA for assessing the stock. A4a is a statistical catch at age model, which flexibility allows fitting a wide range of models to the data. Compared to XSA, a4a runs forward and allows to reach a better stability for last years estimates. As it is the first year this method was used, the results were compared to an XSA run, following the classically approach used for this model, involving sensitivity analyses on parameters to select the best run. The comparison of the a4a results with those from the XSA run displayed a good consistency as the trends for the various variables were found to be the same. The only notable differences were observed for the two last years of the fishing mortality time series, but that is likely to be linked to the well-known instability of the last years XSA estimates and to the better estimation of fishing mortality with a4a (no back-calculation in contrary to XSA). Consequently, the WG validated the use of the a4a for this assessment. The reference point F0.1 was estimated, because of the use of a new model. These methods were applied using the FLR libraries in the statistical software R.Model performance: XSA retrospective analysis did not show any trend.Results:Fcurrent (mean last 3 years, ages 0-3) 1.671
Biomass current (2011-2013) (tons) 2836
Biomass (33th) 3369
Biomass (66th) 4382
Current Recruitment (Thousands) 2011-2013 30224
Fcurrent/F0.1 9.6Diagnosis of stock status: The stock is in an overexploitation status with a relative low abundance with periodically higher recruitments (1998, 2001-2002 and 2007) which ensured the sustainability of the stock at the lower level of abundance of the series. Since 2007, the recruitment has reached the lowest level of the historical series 1998-2013. After reaching very high values in 2010 and 2011, the fishing mortality seems to have initiated a decreasing trend. However, the spawning stock biomass and the recruitment are still at low levels, with little signs of improvement. The current exploitation level is well above the level estimated to be sustainable. The important decrease in number of French trawler fleet since 1998, reducing the number of boats by 39%, is likely to start to have a positive effect on the stock. Advices and recommendation: Reduce fishing mortality
-Improve the fishing pattern of the trawlers so that the minimum length of catches is consistent with the minimum legal landing size
-Freezing of the effort in the Fishery Restricted Area It is important to notice that some management measures have been taken since 2011 (reduction from 2010 to 2013 by more than 30% of the number of trawlers). This measure was over at the end of 2013.