Fishery Resources Monitoring System

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Horse mackerel - Northwest Africa, 2011
Marine Resource  Fact Sheet
Status of stocks and resources 2012
Horse mackerel - Northwest Africa, 2011
Fact Sheet Citation  
Chinchards dans la region Nord Ouest Africaine
Owned byFood and Agriculture Organization (FAO) – More
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Species:
FAO Names: en - Atlantic horse mackerel, fr - Chinchard d'Europe, es - Jurel, ru - Ставрида обыкновенная
Geographic extent of Horse mackerel - Northwest Africa
Main Descriptors
Considered a single stock: No        Spatial Scale: Regional
 
 
Habitat and Biology
Climatic zone: Temperate.   Bottom type: Unspecified.   Depth zone: Shelf (50 m - 200 m); Slope (200 m - 1000 m); Abyssal ( >1000m).   Horizontal distribution: Neritic; Oceanic.   Vertical distribution: Pelagic.  

Geographical Distribution
Jurisdictional distribution: Unspecified

Water Area Overview
Spatial Scale: Regional

Geo References
Resource Structure
Considered a single stock: No


The exploitation is directed towards three species: the Atlantic horse mackerel (Trachurus trachurus), the Cunene horse mackerel (Trachurus trecae) and the false scad (Caranx rhonchus). Because the false scad is caught only as bycatch, results reported for this species will be limited to catch data and abundance indices obtained from the acoustic surveys.

This subject has been described during earlier meetings of the Working Group (FAO, 2001 and 2002). The Working Group considers that one stock exists for each of the species. Additional studies, however, are necessary
Exploitation
 

In Northwest Africa, the horse mackerel is exploited by vessels of very different lengths, ranging from the canoe to the large pelagic trawler of 120 m length. The exploitation of these species is thus carried out both by the industrial fleets, almost exclusively of foreign origin, and the national coastal and artisanal fisheries.

Considering that the fishery statistics provided by the different fleets do not separate the three species of horse mackerel, the Working Group agreed to apply the separation key based on the data provided by observers from the Mauritanian Institute of Oceanographic Research and Fisheries (IMROP), sampling data from the Spanish Institute of Oceanography (IEO) in Las Palmas and data from Russian observers in Zone C. The key adopted for the data collected in 2011 is as follows:

- Zone C: north of Cap Blanc

  • 64 percent Trachurus trecae, 34.5 percent Trachurus trachurus and around 0.5 percent Caranx rhonchus.


- Zone C: south of Cap Blanc

  • Vessels sailing under Russian and Ukrainian flags: 14 percent T. trachurus, 78 percent T. trecae and 8 percent Caranx rhonxhus.
  • Other fleets: 22 percent T. trachurus, 58 percent T. trecae and 20 percent Caranx rhonchus.


In 2010 and 2011, the two species of Trachurus (Trachurus trachurus and Trachurus trecae) contributed about 88 percent and 96 percent, respectively, of the total catch of horse mackerel compared with false scad (Caranx rhonchus).

It is in the Mauritanian zone that the catches of horse mackerel are the most important. In 2011, horse mackerel catches in the subregion decreased by 39 percent compared with 2010. The species Trachurus trachurus is mainly caught in Mauritania (83 percent) and in Morocco (17 percent of the total catch of this species). The species Trachurus trecae is fished mainly in Mauritania (81 percent) and in Senegal (14 percent) and to a lesser extent in the south of Morocco (5 percent) (Figure 4.2.1).

In 2011, the fleet of Belize contributed most to the catch of small pelagics (33 percent of the total catch), with 50 percent of the horse mackerel caught in Mauritania.

The monitoring of the fishery has become more difficult because of the shift from charter licences to free licences. More than 82 percent of the catches obtained in 2011 are fished by vessels operating within the free licence system

Total catches

The catch of the species considered here has increased each year since 2003. In 2006, it dropped by 5 percent, and in 2007 it increased again by 4.2 percent. In 2008, it increased by a further 29 percent, from 432 700 tonnes to 556 699 tonnes. In 2009, catches declined slightly by about 9 percent. In 2011 there was a sharp decrease in catches (39 percent). Catch data for the three species of horse mackerel in the period 1990–2011 are presented by country and for the total subregion in Tables 4.2.1a, b and c.

The annual trends in catches of the three species of horse mackerel are shown in Figure 4.2.1.

In 2011, the decline in catches concerned the three species: Trachurus trachurus, Trachurus trecae and Caranx rhonchus with respectively lower catches of 59 percent, 23 percent and 66 percent. This sharp decline in catches over the entire series can be explained by the departure of some Russian vessels targetting these species in the Senegalese zone during the cold season (January–May).

In the Mauritanian zone where more than 81 percent of all horse mackerels were taken, the decrease in 2011 concerned the three species. The false scad declined sharply by 85 percent distantly followed by the Atlantic horse mackerel (Trachurus trachurus) with 52 percent in 2011 compared with 2010.

The false scad is fished mainly in Mauritania and Senegal and to a lesser extent in The Gambia.

Various sources of information suggest that the main part of catches landed as ‘anchovy’ in Mauritania could in fact be juvenile horse mackerel that have been processed into fishmeal and hence are unidentifiable. An observation programme has been set up on board the pelagic fleet in order to split these species.

Fishing effort

The pelagic resources of Northwest Africa are being exploited by different fleets and particularly by foreign vessels that have changed continuously over recent years.

In 2011, the industrial trawler fleets that were active in the Mauritanian zone were composed of:

- Vessels registered in Belize (32 percent of the total industrial effort in fishing days).

- A Ukrainian fleet which represented 7 percent of the total fishing effort.

- Vessels operating under agreements with the European Union, including:

  • a Dutch fleet (targeting sardinella and catching horse mackerel as bycatch) (only 7 percent of total effort in fishing days);
  • a Lithuanian fleet (12 percent of the total industrial fishing effort) and a Latvian fleet (6 percent of the fishing effort);
  • Polish vessels (4 percent).


- A Russian fleet, which made up 8 percent of total effort in third place in terms of number of fishing days.

In the northern Moroccan zone (Cap Spartel–Cap Boujdor), the Atlantic horse mackerel (Trachurus trachurus) is exploited by a national fleet composed of purse seiners and coastal trawlers. The purse seiners target mainly the sardine, so horse mackerel is taken only as bycatch. The trawlers do not target horse mackerel.

In Senegal, horse mackerel is taken both by an increasing industrial fishery in 2011 and by the artisanal fishery that takes it as bycatch.

In 2011, fishing effort increased slightly in the Mauritanian zone (Figure 4.2 2).

Recent developments

In 2011, there was a slight increase in the number of vessels operating under charter agreements in the Mauritanian zone. However there was a marked decrease in CPUEs for the two species of Trachurus confirmed in the acoustic abundance indices estimated during the July survey carried out by R/V ATLANTIDA in 2012.

The number of observers on board different fishing vessels declined sharply in 2011 (13 boardings compared with 21 in 2010).

The spatial length and age distribution of two species of Trachurus shows some heterogeneity between the north and the south particularly between Zone C and the Mauritanian zone, which can reflect either the different fishery strategies of the fleets or be an indication of the different positioning of the recruitment and adult zones which require more thorough analysis. Moreover, the absence of age classes 0 and 1 in the catches occurring in Mauritanian waters is to be explored in relation to assumptions on possible confusion of juveniles of horse mackerel with anchovy in catch statistics.
Assessment
 
Data

The Working Group made an analysis for the two main species of horse mackerel Trachurus (Trachurus trachurus and Trachurus trecae).

Input data

The Working Group prepared the data needed for the application of the dynamic production model for the two species. Due to the lack of acoustic surveys in the Senegalese–Mauritanian zone, the assessment was based on CPUEs provided by Russian scientists: this index is standardized in relation to a reference vessel.

The possible effects of the environment are taken into account based on anomalies observed in certain years of the series.

The initial parameter values (intrinsic growth rate [r] and carrying capacity of the ecosystem [K]) used in fitting the model are presented in Table 4.6.4.
Assessment Model
Type:  Biomass-aggregated

The Schaefer dynamic production model (1954), implemented on an Excel spreadsheet, was used to assess the stocks of the two Trachurus sp. species in the subregion. This model was used to estimate the development of biomass and fishing mortality during the period 1991–2011. The Working Group then proceeded with a projection of abundance and catches over the following five years using different management scenarios and the same model implemented on a second spreadsheet (Appendix II).
Schaefer dynamic production model
Overall Assessment Results

Trachurus trachurus

The fit of the model using the Russian CPUE index is presented in Figure 4.6.3. The fit is satisfactory (R² = 63 percent).

The results indicate that the current biomass is equal to the biomass B0.1. Current fishing mortality is almost equal to the fishing mortality F0.1. These results show that the stock is fully exploited (Table 4.6.5).

Table 4.6.5: Summary of the current state of the stock and fishery of Trachurus trachurus
Stock/indices Bcur/B0.1 Fcur/FSYcur Fcur/FMSY Fcur/F0.1
Trachurus trachurus/Russian CPUE series 106% 110% 91% 101%

Bcur/B0.1: Ratio between the estimated biomass for the last year of the series and the biomass corresponding to F0.1.
Fcur/FSYcur: Ratio between the observed fishing mortality coefficient for the last year of the series and that which would produce a sustainable catch at the current biomass level.
Fcur/FMSY: Ratio between the observed fishing mortality coefficient for the last year of the series and that which would extract a maximum sustainable yield over the long term.
Fcur/F0.1: Ratio between the fishing mortality coefficient observed for the last year of the series and F0.1.

Trachurus trecae

The fit of the model based on the Russian CPUEs is presented in Figure 4.6.4b. The Pearson correlation coefficient was high (84 percent).

Current estimated biomass represents about half the B0.1 biomass (45 percent). The current level of fishing effort exceeds by 27 percent the level that maintains the stock at a durable level. The current effort is higher (92 percent) than the one producing maximum sustainable yield (FMSY) (Table 4.6.6). These results show that the stock is overexploited.

Table 4.6.6: Summary of the current state of the stock and fishery for Trachurus trecae
Stock/indices Bcur/B0.1 Fcur/FSYcur Fcur/FMSY Fcur/F0.1
Trachurus trecae /Russian indices 45% 127% 192% 212%

Bcur/B0.1: Ratio between the estimated biomass for the last year of the series and the biomass corresponding to F0.1.
Fcur/FSYcur: Ratio between the observed fishing mortality coefficient for the last year of the series and that which would produce a sustainable catch at the current biomass level.
Fcur/FMSY: Ratio between the observed fishing mortality coefficient for the last year of the series and that which would extract a maximum sustainable yield over long term.
Fcur/F0.1: Ratio between the fishing mortality coefficient observed for the last year of the series and F0.1.

Discussion

For Trachurus trachurus, the fit of the model using the Russian CPUE indices indicates that the current biomass is close to the biomass (B0.1) which reflects full exploitation of the stock and that the current fishing mortality is equal to that which maintains the stock at a sustainable level.

The data available to the Working Group (Russian scientific surveys and commercial surveys) did not allow conclusions to be reached concerning recruitment.

For Trachurus trecae, despite the decline in catches observed in 2011, the stock of Cunene horse mackerel still remains in a critical situation. It is noteworthy that this species is heavily targeted by a demersal and pelagic fleet operating in the Mauritanian zone.
Projection

In order to provide different options for management, the Working Group made projections based on two different catch levels in the same production model.

Scenario 1:Maintain fishing effort at its current level (Status quo).

Scenario 2:Decrease effort by 20 percent in order to obtain a better stock yield in the long term

The projections were carried out over the next five years (from 2011).

Trachurus trachurus

Scenario 1 (Status quo): The projection based on the Russian CPUE abundance indices for the period 2012–2016 shows that the catches and the abundance index remain at the same level observed in 2011 (Figure 4.7.1a).

Scenario 2 (reduction of 20 percent in fishing effort): The catches, which were at the 2011 level, decline slightly in 2012. Afterwards, catches remain at almost the same level until 2016. In this scenario, the abundance index increases slightly to arrive at a level only 20 percent above the target abundance in 2016 (Figure 4.7.1b).

Trachurus trecae

The projections are based on the assessment using the Russian CPUEs.

Scenario 1 (Status quo): When implementing this scenario, the catches show a continuous decline until 2016. The biomass, which was at 50 percent of the reference value (U0.1) drops sharply in 2012 and continues to decline until 2016 when the level is less than 40 percent of the reference value (Figure 4.7.2a).

Scenario 2 (reduction of 20 percent in fishing effort): With a reduction in effort of 20 percent, the catches decrease in 2012. They increase slightly over the next four years (2013–2016). The abundance, after having shown a slight decline in 2012, increases during the period 2012–2015 (Figure 4.7.2b).
Scientific Advice

Follow-up of recommendations made in 2011

With respect to the four research recommendations that were formulated by the Working Group in 2011, it was noted that only three of these have been implemented. These concern the preparation of a separation key established by the Russians, a study of the spatial distribution of the Cunene horse mackerel and resolution of the confusion between the juveniles of horse mackerel and anchovy in catch declarations made in fisheries logbooks. With regard to the separation of anchovy and juveniles of horse mackerel, a separation key will be proposed by IMROP in 2012 to correct the previous series.

Recommendations in 2012

The Working Group suggests the following research recommendations:

  • Conduct acoustic surveys throughout the subregion (see the same recommendation in the present Working Group).
  • Enhance available biological data on horse mackerel to improve the data quality for the analytical model.
  • Analyse the spatial-temporal distribution of cohorts in the subregion based on existing data (scientific surveys, logbooks, sampling, ichthyologic data, etc.).
  • Propose a separation key for juveniles of horse mackerel and anchovy.


for Management consideration

The fisheries concerned are multispecific, targeting the two Trachurus species. Given the situation of overexploitation of the two species of Trachurus (Cunene horse mackerel and Atlantic horse mackerel), the Working Group recommends reducing fishing effort by 20 percent in relation to 2011 for both species.

The Group reiterates the recommendation that the catches of both Trachurus species should not exceed the 2011 level.
Biological State and Trend
 
Trachurus trachurus
 Exploitation state: Fully exploitedExploitation rate: Fcur/F0.1: 101%
Abundance level: Bcur/B0.1: 106%
Trachurus trecae
 Exploitation state: OverexploitedExploitation rate: Fcur/F0.1: 212%
Abundance level: Bcur/B0.1:45%
Source of information
 
Report of the FAO Working Group on the Assessment of Small Pelagic Fish off Northwest Africa./Rapport du groupe de travail de la fao sur l’évaluation des petits pélagiques au large de l’afrique nord-occidentale. Dakar, Senegal, 21–25 May 2012. Click to openhttp://www.fao.org/docrep/019/i3346b/i3346b.pdf
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