Spatia-temporal . structure of the deep-water shrimp Aristeus antennatus ( Decapoda : AristeidaeJ population in the western Mediterranean

Instituto de Ciencias del Mar (CSIC). Paseo Nacional sin 08039 Barcelona. Spain Spatia-temporal . structure of the deep-water shrimp Aristeus antennatus (Decapoda: AristeidaeJ population in the western Mediterranean Abstract.-The spatio-temporal structure of a population of the deep-water shrimpAristeus antennatus on the fishing grounds off Barcelona, Spain, in the western Mediterranean Sea was studied, and the relationship between fluctuations in catch ofthis species and spatio-temporal changes in the size and sex composition of shoals is described. Fluctuations were monitored by using a sample design based on fixed seasonal sampling of three different habitats (upper submarine canyon, middle slope, and lower slope). The results explain changes in fishing fleet and fishing location. The stock appears to remain constant at approximately optimum levels ofexploitation because part of it is unexploited below 1,000 m. Factorial correspondence analy. sis indicated a generally strong influence of depth on the abundance of deep-water shrimp, explaining 63.14% of the variance. However, the influence of seasonality was stronger when only samples taken at depths shallower than 1,000 m (75.22%) were considered. Females contributed most to the catches on the upper and middle slope throughout the year, and catches of females were strongly related to seasonality (P<0.05). The combined interaction of depth and seasonality on the abundance of males was significant (P<0.05). Juveniles were present in the catches from autumn to spring, and the combined effect of depth and seasonality on the abundance of juveniles was also significant (P<0.05). The role ofthe regional submarine canyon as a zone of higher energy and biomass in the recruitment of this species is discussed, and the importance of spatio-temporal factors linked to the life cycle ofdeep-water shrimps is highlighted. The results demonstrate that comprehensive ecological studies ofexploited species are essential to proper fisheries management. As fishing activity has expanded into deeper waters, deep-water shrimps (Dendrobranchiata and Caridea) have become an important resource in different parts of the world, e.g. Australia (King, 1981; King and Butler, 1985) northern Europe (Anon., 1992), and the Pacific (Gooding, 1984) and Indian (Jones, 1969) oceans. In the Mediterranean Sea in particular, these shrimps are the target of a traditional fishery <Relini and Orsi Relini, 1987; Tobar and Sarda, 1987; Campillo et aI. , 1990; Demestre, 1990; Demestre and Lleonart, 1993), In addition, deep-water shrimps, particularly aristeid species (Dendrobranchiata, Penaeoidea: Aristeus antennatu8 Risso, 1816), play an important ecological role in Mediterranean deep-sea communities at depths below 400 m (Peres, 1985;Abello et aI., 1988; Abello and Valladares, 1988; Cartes and Sarda, 1993). Population structure, biological cycles, life history, and spawning strategies of deep-water shrimps differ from those oflittoral species (Garcia and Le Reste, 1987) and are poorly understood. The life history of deep-water penaeoidean species is not dependent upon lagoonal or littoral systems, and growth in such species tends to be slower than that in littoral penaeid species (Garcia and Le Reste, 1987; Demestre, 1990). The presence and abundance of such species are linked to the topography ofthe continental slope and submarine canyons. However, their behavioral patterns are complex and not well understood (Tobar and Sardli, 1987; Cartes et aI., 1993). Pandalus borealis (Anon., 1992) (Pandalidae, Caridea) is the most extensively studied shrimp species from a fisheries perspective. This species exhibits major differences with respect to species ofother genera inhabiting subtropical deep-sea regions, such as Aristeus, Aristaeomorpha, Parapandalus, and Plesionika; it is protandrously hermaphroditic and distributed in shallower waters. Migratory patterns, short and medium-term fluctuations in abundance, aggregating behavior, recruitment, and larval and postlarval dis-