1. FISH AND BIG INVERTEBRATES AVERAGE BIOMASS CAUGHT PER FISHING TRIP
Cephalopod International Advisory Council, CIAC 2015, Hakodate (Japón),9-14 November 2015
CEPHALOPOD DISCARD ESTIMATES FROM THE HYDRAULIC DREDGES FLEET OPERATING IN THE GULF OF CÁDIZ (SW SPAIN)
Luis Silva1, Ana Juárez1, Miguel Cojan1
1Spanish Institute of Oceanography, Oceanographic Center of Cádiz, Spain,
INTRODUCTION
MORROCCO
Cádiz
-7.4
-7.2 -7
-6.8
-6.6
-6.4
-6.2
Longitud
36.8 37
37.2 L a t i u d
Sanlucar
Bonanza
Urbanización Matalascañas
Mazagón
Palos de la Frontera
La Rábida
Huelva
Punta Umbria
El Rompido
Lepe
Isla Canela
Ayamonte
Isla Cristina
V. R.Santo Antonio
Torre Zalabar
Torre Carboneras
Palacio
Torre La Higuera
Antenas
Río Tinto
Río Odiel
Rio Piedras
Torre de San Jacinto
Doñana National Park
Guadalquivir river
10 m
20 m 5m
GULF OF CADIZ
Strait of Gibraltar
Fishing grounds
Study Area
Target species
The fishery of the striped venus (Chamelea gallina) in the Spanish waters of the Gulf of Cadiz is carried out by a hydraulic dredges fleet of around 100 vessels, with artisanal characteristics. Annual landings of this only target species are around 3500 tonnes, discarding the rest of caught species because is prohibited to land them.The fishing grounds are located at depths between 4 and 12 m on sandy-muddy shallow waters, along 100 km of coast, in the western of the gulf of Cadiz. Discard composition is analyze, showing the mollusc cephalopod species discarded and analyzing her importance at qualitative and quantitative level. The interaction with others commercial fisheries in the study area will be analysed.
Chamelea gallina, locally called “chirla”, it is a Mediterranean mollusc bivalve that habit in atlantics waters of the gulf of Cadiz
The fleet
The hydraulic dredge through water pressure on the bottom in order to remove the seafloor.
MATERIALS AND METHODS
Discard composition was analyzed through a monitoring that consisted on monthly samplings onboard hydraulic dredges carried out between April 2008 and May 2009, with a total of 72 samplings. The discard of fish and big invertebrate, like the cephalopod species, were obtained weighing and counting the total catch. The rest of invertebrates were estimated by analyzing a small sampling of the total catch obtained with the hydraulic dredges, and posterior weighting to the total caught.
DREDGE
RESULTS AND CONCLUSION
CAUGTH
BIOMASS
DISCARDED
FISH AND BIG INVERTEBRATES
SMALL INVETEBRATES
AVERAGE BIOMASS CAUGHT PER FISHING TRIP
71%
TARGET SPECIES
29%
REST OF SPECIES
STRIPED VENUS: TARGET SPECIES
The estimated discarded biomass reported 23% of total biomass caught by trip (266 kg/trip on average), the rest being biomass of the target species. A total of 92 discarded species were identified, weighed and quantified, corresponding 46 species to molluscs, 26 species to fish, 14 species to crustaceans and 6 species belonging to other invertebrate groups. The molluscs reported 66% in weight, where the three cephalopods species identified contributed with 1.2%, equivalent to 1.9 kg per trip, on average. Sepia officinalis was caught in all months, with 1.6 kg/fishing trip, followed by Octupus vulgaris and Eledone moschata, with 0.23 kg/ fishing trip and 0.07 kg/ fishing trip, respectively. S. officinalis was mainly discarded in spring an summer (2.1 and 1.8 kg/trip, on average), due to this species is more frequent in shallow waters during these seasons, related to the reproduction and recruitment. In both Autumn and Winter was lower with only 1.2 kg/trip . The distribution sizes for S. officinalis showed a wide range from 2 to 28 cm for all period, with average size estimated of 9,3 cm. This average size indicates that 72% of total cuttlefish caught were below size at first maturity established in 10,8 and 11,9 cm, for males and females (Ramos et al., 2002). The lowest sizes were caught in recruitment period. O. vulgaris was present from the end of summer to January, with highs values in September-October, agreeing with the recruitment period in shallow waters where the food, bivalves mainly, area more abundant. E. moschata only was caught in autumn, due to his distribution area is located in the limit of “chirla” fishing ground.
The total estimated discard by fleet and year (April March 2009) was 25.5 tonnes, which represented 13% of the total landed by the artisanal fleet in the Gulf of Cádiz. This artisanal fleet share fishing ground with the hydraulic dredge fleet. However, the estimate obtained in the bottom trawl fleet, operating in deeper waters, showed almost zero discard values in the same period, with total landing about 700 t (Santos et al., 2012). Therefore, this value should also be taken into account as biomass caught in the Gulf of Cádiz.
Monthly average biomass of cephalopods species (kg/fishing trip) caught by hydraulic dredges in the gulf of Cadiz
Annual length frequency distribution (April 2008-March 2009)
Monthly average size (cm). April 2008-March 2009.
REFERENCES
Santos et al., Estimated on cephalopod discard by Spanish NE Atlantic Trawl Fishing Fleets. WD in ICES Report of WGCEPH 2012.
Ramos et al., Life history of Sepia officinalis in the Gulf of Cadiz. CIAC 2000.
ACKNOWLEDGE
Consejeria of Agriculture and Fishing of the Regional Government of Andalucian (Spain). // European Fisheries funds.