Stock Assessment Form Demersal species. Reference year: 2004-2013. Reporting year: 2014. Red mullet of the Gulf of Lions (GSA 07)
|Author(s)||Jadaud Angelique1, Rouyer Tristan1, Guijarro Beatriz2, Massuti Enric2|
|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: In the Gulf of Lions (GSA 7), red mullet is exploited by both French and Spanish trawlers. Information on French gillnetters is only available for 2011 and 2013, but although it is suspected that they have been fishing red mullet in the past, no data is available to quantify their catches. Between 2004 and 2013, around 100 boats have been involved in the fishery. According to official statistics, during this period the total annual landings have oscillated around an average value of 200 tons and the French trawlers have been dominating the fishery, as they represent 73% of the catches (165 tons) on the period. After 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, this can explain the high catches of 2010.
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. From a maximum number of 123 trawlers in 2004, the French fleet catching red mullet is nowadays composed by 61 units. This follows management measures to reduce the number of boats. The mean modal lengths in the catches of the French and Spanish trawlers were 13.9 and 14.9 cm, respectively and the length at first capture is about 6 cm. Catch is mainly composed by individuals of age 0, 1 and 2 (Figure 3.1.2.), while the oldest age class (4+ group) is poorly represented. In GSA 07, the trawl fishery is a multi-specific fishery. In addition to M. barbatus, the following species can be considered important by-catches: Merluccius merluccius, Lophius sp., Pagellus sp., Trachurus sp., Mullus surmuletus, Octopus vulgaris, Eledone sp., Scyliorhinus canicula, G. melastomus, Trachinus sp., Triglidae, Scorpaena sp.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 (2004-2013) by IFREMER for the DCF. These parameters are length-weight relationship, sex-ratio and maturity ogive. They were computed using inbio (R scripts developed by IEO). From 2004 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. Size compositions were converted from number at length to number at age by knife edge slicing (deriving the growth from DCF data) from 2004 to 2012, whereas in 2012 and 2013 age-length key from otolith readings were used. Natural mortality was estimated using PROBIOM (Abella et al., 1997).Assessment method: The assessment was carried out by means of Extended Survivor Analysis (XSA) over the period 2004-2013, and calibrated with indices from the scientific survey MEDITS, and yield-per-recruit (Y/R) for the period 2011-2013. These methods were applied using the FLR libraries in the statistical software R.Model performance: No concern was raised about that issue. Results:
Fcurrent (average last 3 years, ages 0-3) 0.45
F0.1 (estimated in 2012) 0.14
Biomass current (tons) 2011-2013 1022
Biomass (33th) 597
Biomass (66th) 690
Current Recruitment (Thousands) 2011-2013 35077
Diagnosis of stock status:
The stock is in an overexploitation status with a relative high abundance and punctually higher recruitments (2005, 2006 and 2013). This diagnostic is based upon analytical results based on fishing mortality. The exploitation level is currently above the level estimated to be sustainable since the referent point F0.1 is equal to 0.14 and current fishing mortality (Fcurrent 2011-2013) is equal to 0.45. The current fishing mortality is the lowest of the series and the spawning stock biomass currently follows an upward trend. The exploitation is mainly concentrated on young individuals (age 0-2), moreover 60% of the recruitment (age 0) is mature. The current biomass (2011-2013) is above the 66th percentile.
However computed over a relatively short time-period (2004-2013), the increase in spawning stock biomass and the decrease in fishing mortality have to be noticed. The important decrease in numbers 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.