Biological State and Trend
Habitat and Biology
Bottom type: Hard rocky bottom; Coral reef; Seagrass. Depth zone: Coastal (0 m - 50 m); Shelf - Uppershelf (up to 100 m); Shelf - Deepshelf (100 m - 200 m). Horizontal distribution: Neritic. Vertical distribution: Demersal/Benthic.
Octopus Octopus vulgaris
biology has been the subject of several studies in the subregion. Recent breeding and tagging experiments in fish tanks have highlighted a very rapid growth and therefore a very short lifespan.
The biology of the main cephalopod species in the subregion has been studied intensively during the years. Much is known about numerous aspects of their life-cycle and the number of available biological parameters available in scientific literature is quite large. A summary of all this information was presented to the CECAF ad hoc
Working Group on cephalopod resources in Santa Cruz, Tenerife in 1997 (Lamboeuf, 1997). Supplementary works have recently been published covering a series of biological aspects and questions about the fisheries, in particular about octopus. An updated reference list will be presented to the next Working Group.
Jurisdictional distribution: National
Considered a single stock: Yes
Three different octopus stocks have been identified in the subregion since the first Working Group assessment in 1978:
- Dakhla stock (26 °N–21 °N)
- Cap Blanc stock (21 °N–16 °N): Octopus - Mauritania
- Senegal–The Gambia stock (16 °N–12 °N): Octopus - Senegal and Gambia
This stock separation was based on data relative to the fisheries which has recently been confirmed by more accurate information thanks to the system of satellite control of vessels (VMS) and genetic analyses.
Cephalopods are caught in northwest Africa (northern CECAF subregion) both as a target species by the specific fishery and as bycatch by the non-specific fishery. These fisheries are led by a heterogeneous fleet of vessels from the small canoes to the bottom trawlers using such fishing gears as pots, jiggers and bottom trawls. Depending on nationality and characteristic, the fishery is divided into three main components for statistical purposes: i) artisanal, ii) national industrial, iii) industrial from other countries operating under fishing agreements, the most important of which those between the European Union and nearly all the northwest African coastal countries.
The main target species in the cephalopod fisheries are the octopus (Octopus vulgaris
), the cuttlefish (Sepia
spp., Sepia hierredda
mainly and Sepia officinalis
of which the proportion decreases towards the south) and the squid (Loligo vulgaris
). Sepia bertheloti
is another quite important cuttlefish species in the subregion which is sold under the name “bobtail squid”. Generally octopus is the most abundant species and has the highest commercial value in the cephalopod fisheries, with 65 to 75 percent of total landings. Its importance decreases towards the south where it is replaced by growing proportions of Sepia hierredda
. Squid virtually disappears in landings in the south of Senegal.
Three main bottoms are found along the northwest African coast, more or less coinciding with the distribution zones of the three octopus stocks of the subregion. From north to south these are: i) the zone between Cap Bojador (26 ºN) and Cap Blanc (21 ºN); ii) the zone between Cap Blanc (21 ºN) and the mouth of the Senegal river (16 º N); and iii) the zone between the mouth of the Senegal river (16 ºN) and the border with Guinea-Bissau (12 ºN).
In Morocco the cephalopod fishery is characterized by large fluctuations in catch and effort. It can be divided into several distinct periods depending on where in the region the fleet comes from and the management measures that are in place for this fleet:
Exploitation by foreign fleets: The cephalopod fishery started at the beginning of the 60s in the Atlantic zone south of Morocco between Cap Bojador and Lagouira. At this time cephalopods (octopus, cuttlefish and squid) where only exploited by foreign fleets (Japanese, Spanish). This period saw at the beginning the best catches per unit of effort reaching between 2 and 3 tonnes per day per vessel. The economic attraction for this fishery of this species provoked an intensification in their exploitation.
Exploitation by mixed companies: The cephalopod fishery saw an intermediate phase when the Spanish fleet was joined by a Moroccan fleet in establishment. There was then a period of combined exploitation beginning in the 80s which continued until the departure of the EU fleet in 1999. The national cephalopod fishery only began to develop in 1973 with four freezer trawlers. Afterwards it saw considerable impetus and stabilized, after the freeze in investment since 1992, at around 290 active freezer trawlers. In reply to an increase in effort and to the realisation of overexploitation, a system of biological rest periods was started in 1989. These last one month, October, and correspond to the main recruitment period. Due to their distance, until 1990 the cephalopod stocks were only accessible to the Moroccan and Spanish freezer trawler operating under a series of Morocco–EU fishing agreements which ended in 1999. However, with the development of the infrastructure and the attraction of the value of the products landed since 1993, there has been a massive migration of canoes (artisanal boats) from the north towards southern zones to exploit octopus. Coastal trawlers have also joined this movement, attracted mainly by the consequences of the biological rest period.
Due to the overexploitation, the cephalopod fishery has undergone a series of management measures integrating the new fleets (artisanal and coastal), notably the regulation of trawl mesh size and the size of first catch, as well as the reduction in fishing activity in the coastal zone. Additionally since 1993 the biological rest period has increased by one month to protect the reproduction period (one month in autumn and one in spring). Since 1997, this has grown from 2 to 4 months, two months in spring and two in autumn.
Exclusively Moroccan exploitation: Since 2000 the cephalopod fishery is only composed of a very heterogeneous Moroccan fleet, subdivided into three sections (ocean-going, coastal and artisanal). The artisanal section has become an important component of the fishery. In order to offset the effects of the increase in effort, the biological rest periods have gone from 4 to 7 months. Following a large drop in production in 2001, a management plan for the octopus fishery based on an overall quota was created. 2004 is the year in which the longest biological rest period for octopus is seen, lasting 8 months.
In 2004, the fall in production necessitated a revision of the management plan, which was based partly on the reduction of the overall quota adjusted seasonally and partly on the reduction in effort of the coastal and artisanal sectors following their uncontrolled development over the last decade. The artisanal sector saw the number of vessels reduced to 2 800. For the coastal fleet (190 trawlers), only 100 trawlers are authorized to fish in the zone to the south of Cap Bojador per trip. As for the ocean-going sector, a system of individual transferable quotas has been created. The revision of the cephalopod fishery management plan also covered zoning with a demarcation of fisheries sub-units and zones where trawling is forbidden. In November 2002, the zone between 24° N and 25° N which is normally the main nursery for the Dakhla stock, where the greatest concentrations of juveniles are usually found in autumn, was declared a protected zone and therefore fishing was forbidden. This remained in place until 2005. The revision of the management plan also covered other technical aspects, notably passing from a minimum size of T8 to T7 with a tolerance threshold of 5–10 percent for T8 depending on the season and the increase in minimum mesh size to 70 mm instead of 60 mm.
Several fleets share the exploitation of cephalopod resource along the Moroccan continental shelf. They differ in their technical characteristics and above all in the level of investment and employment generated. Their strategies are tied to the dynamic of the resources and the markets.
Freezer trawler fleet: This is composed of 290 vessels which practise trawl fishing (Spanish and Korean types). They go to sea for an average of fifty days. With the setting up of the seasonal quota, the trips cover a period of between 100 and 120 days on average. The length of these vessels is between 30 and 40 metres. Their tonnage varies between 200 and 600 GRT with an engine power of 600 to 2 000 HP. During the last trips, the number of active vessels has been around 230.
EU fleet: This fleet operated under the Morocco–European Union fishing agreement from 1995 to 1999. It was mainly composed of around one hundred Spanish cephalopod trawlers. These vessels practised the Spanish technique of backwards or sideways trawl fishing using three types of conservation. The GRTs varied between 100 and 400 GRT, with an engine power of 600 to 1 000 HP. The European trawlers ceased operations on 30th November, 1999.
Coastal fresh fish fleet: This fleet is made up of around 100 vessels. The average power and tonnage of this fleet are 400 HP and 60 GRT respectively. The type of trawl used is the atomic trawl (60 mm) and a trip lasts between 6 and 10 days during which time the fish are preserved in boxes under ice. Since 2003 the presence of around one hundred longliners fishing squid and cuttlefish can also be seen, with 235 HP and an average estimated age of four years.
Small trade artisanal fishery fleet: This comprises wooden boats of less than 2 GRT and equipped with outboard motors of between 15 and 25 HP. This fishery uses passive gears: pot and jig.
The number of artisanal fishery vessels saw a notable increase between 1993 and 2002. After this time, the number of boats has not stopped decreasing following the censuses and the regulations which came into force covering this sector. Currently there are 3 000 boats. The fishery is usually practised along the coast, but the range can go beyond 20 nautical miles.
The data series in tonnes for the 26° N to 20°50’ N zone of the three sectors of the national fleet and the Spanish industrial fleet was used in the model. As an abundance index the Working Group used two different abundance indices series, the CPUEs from the ocean-going Moroccan cephalopod fishery and those of the trawl surveys between Cap Bojador and Lagouira.
As the data series did not provide a good fit to the model because of an irregularity in the yield series due to changes in the way the octopus stock is exploited, several attempts were made using annual and monthly catches. It was however decided to only consider the data series from 2001 onwards as this was estimated to be relatively homogeneous. It also coincided with the application of the management plan in this fishery. The trawl survey indices were kept as they cover the whole distribution zone.
Schaefer dynamic production model
The Schaefer dynamic production model implemented in an Excel spreadsheet was used to assess the state of the stock and the fisheries of Octopus vulgaris
. The model is described in Appendix 2.
The model provides a satisfactory fit to the data. Current biomass is half the target biomass B0.1 (Table 1) and effort in the last year is above that producing the B0.1 biomass.
Table 1: Indicators on the state of the stock and the fishery of Octopus vulgaris
|Stock/abundance index|| F cur /F SYcur|| B cur /B 0.1|| F cur /F 0.1|| B cur /B MSY|| F cur /F MSY|
Fcur/FSYcur: Ratio between the observed fishing mortality coefficient during the last year of the series and the coefficient that would give a sustainable yield at current biomass levels.
Bcur/B0.1: Ratio between the estimated biomass for the last year and the biomass corresponding to F0.1.
Fcur/F0.1: Ratio between the observed fishing mortality coefficient during the last year of the series and F0.
Bcur/BMSY: Ratio between the estimated biomass for the last year and the biomass coefficient corresponding to FMSY.
Fcur/FMSY: Ratio between the observed fishing mortality coefficient during the last year of the series and the coefficient giving maximum long term sustainable yield.
The results show that the Dakhla octopus stock is overexploited. This situation is confirmed by the last survey results carried out by the research vessel in which the relative biomass fell due to the way the stock is exploited which does not allow it to build up again.
Scientific Advicefor Management considerations
The assessment indicates that the octopus stock in the subregion is overexploited. Consequently the Working Group recommends that fishing effort be reduced in all fleets targeting the octopus stock in the region.
It is also recommended that control of the management measures be reinforced.
Source of information
FAO Fishery Committee for the Eastern Central Atlantic/Comité des pêches pour l’Atlantique Centre-Est. “Report of the Working group on the assessment of demersal resources, Sub-Group North” Banjul, The Gambia, from 6 to 14 November 2007. “Rapport du Groupe de travail FAO/COPACE sur l’évaluation des ressources démersales dans la zone Nord” Banjul, Gambie, du 6 au novembre 2007. Rome, FAO . 2010. .
The bibliographic references are available in the report included in "Source of Information".