Page 2 - Ragonese_Bianchini_1996

126 S. Rawmese. M.L. Bianchini l Fisheries Research 26 ( 1996) 125-137

l. Introduction

The blue-and-red shrimp, Aristeus antennatus Risso 1816, represents an important tra-
ditional resource for the Mediterranean deep-water tra wl fisheries (Re lini and Orsi-Relini,
1987; Yahiaoui, 1990; Arculeo et al., 1992; Matarrese et al., 1992; Mura et al., 1992;
De mestre an d Lleonart, 1993; Demestre and Martin, 1993), especially for those operating
in the Western basi n ( Sardà, 1988). The spatial distribution of this shrimp is qui te complex
( Sardà et al., 1993), but normally the species shoals in deep waters of the upper an d middle
slope ( 400-800 m) and it is caught by trawling on muddy bottoms, near to submarine
trenches and canyons.
In the Strait of Sicily, Aristeus antennatus is generally less abundant than its companion
species, Aristaeomorphafoliacea Risso 1827 ( Ragonese and Bianchini, 1992; Ragonese et
al., 1994b); nevertheless, the blue-and-red shrimp represents a valuable resource even for
Sicilian fishcrmen (Arena, 1985). More than 1000 tons ofred shrimps (bothAristeus and
Aristaeomorpha), worth about 16 million US$, were landed during 1991 in Mazara (Anony-
mous, 1992), a harbour in southern Sicily which hosts the largest tra wl fteet in Italy.
Despite the large quantity of biologica! and dynamics information available for the
Western Mediterranean stocks of Aristeus antennatus (Demestre and Lleonart, 1993;
De mestre an d Martin, 1993), only scanty data exist on the biology an d dynamics of the
blue-and-red shrimp population in the Strait of Sicily (Azouz, 1972; Arena and Li Greci,
1973; Arena, 1985; Ragonese and Bianchini, 1992). Unfortunately, there are no series of
catchcs and effort records available, and attempts to assess this resource are based only on
length data gathered in multispecies trawl surveys (Levi, 1991).
In this paper, growth, mortality and yield-per-recruit ofthe female population of Aristeus
antennatus in the Strait of Sicily are investigated to indicate the exploitation leve l sustained
by this stock.

2. Materials and methods

Length-frequency distributions (LFD) w ere derived from four seasonal random stratified
experimental trawl surveys carried out in the Strait of Sicily by the Institute of Fisheries
( ITPP-CNR) of Mazara between spring 1986 an d winter 1987.
Hauls were limited to l h in daylight; an 'Italian' bottom trawl with 18 mm mesh side in
thc cod-end. towed at about 2.7 knots, was used; sampling periods lasted for 15-20 days
according t o the meteorologica! conditions (Levi, 1991, for a description of the generai
programme).
Middle dorsal oblique carapace lengths (CL, mm) were measured on board on fresh
specimens; the LFD offemales, by 2 mm class sizes, w ere compiled for each survey ( spring,
summer an d autumn 1986, an d winter 1987), but male shrimps were no t further considered
as they are poorly represented in the fishable population.
The LFD were investigated using the Compleat ELEFAN software (Pauly, 1987; Gay-
anilo et al., 1989) following the sequential population analysis approach ( Caddy, 1986).
The classica] von Bertalanffy growth function (VBGF) was chosen as the elective growth
mode! ( Ricker, 1975).