P. Sartor

Composition and spatial distribution of cephalopods in two north-western Mediterranean areas

The faunistic composition and the spatial distribution of the cephalopod fauna were studied and compared in two areas of the north-western Mediterranean: the Catalan Sea (Spanish coast) and the northern Tyrrhenian Sea (Italian coast). In all, 46 species were collected in the Catalan Sea and 36 in the northern Tyrrhenian Sea. The bathymetric distribution of common species does not differ notably between the two areas. In both, cephalopod abundance is greatest between 50 and 200 m deep. To compare the seasonal changes in bathymetric distribution, four representative species were selected. O. vulgaris is more abundant in both areas between 0 and 50 m in autumn; E. cirrhosa and I. coindetii between 50 and 200 m. Both the last species and S. elegans are more abundant in spring in the Catalan Sea and in autumn in the northern Tyrrhenian Sea. The results of cluster analysis show the presence, in both areas, of three clear associations: one group consists of shallow hauls, another of hauls made over the continental shelf and the third of deeper hauls.

The importance of cephalopods to trawl fisheries in the western Mediterranean

The aim of the study was to define the commercial importance of cephalopods caught by trawlers from five Italian and Spanish Mediterranean ports. From summer 1995 to spring 1996, samples of the catches of trawlers were taken on board. The type of fishing activity was recorded and data were collected from at least three commercial hauls for each port, season and bathymetric stratum ( 350 m). The species composition and yield of the retained and discarded portions of the catch were noted for each port. From these data the commercial importance of each species was evaluated. Cephalopods were commercially important particularly in the shallower bathymetric stratum (<150 m), where they constituted 8.2–30.0% of the total commercially retained catch. Discarding of cephalopods was minimal by mass in all bathymetric strata, only 0.06–1.69% of the total catch or 0.10–5.23% of the total discarded catch. However, in terms of number of species, the discarded component was notable.

Toothed whales in the northwestern Mediterranean: Insight into their feeding ecology using chemical tracers

Rissos dolphins, pilot whales and sperm whales rarely strand in the northwestern Mediterranean. Thus, their feeding ecology, through the analysis of stomach contents, is poorly known. The aim of this study was to gain further insight into the segregation/superposition of the diet and habitat of Rissos dolphins, pilot whales and sperm whales using chemical tracers, namely, stable isotopes (δ(13)C, δ(15)N) and organochlorines. Significantly different δ(15)N values were obtained in Rissos dolphins (11.7±0.7‰), sperm whales (10.8±0.3‰) and pilot whales (9.8±0.3‰), revealing different trophic levels. These differences are presumably due to various proportions of Histioteuthidae cephalopods in each toothed whales diet. Similar δ(13)C contents between species indicated long-term habitat superposition or corroborated important seasonal migrations. Lower congener 180 concentrations (8.20 vs. 21.73 μg.g(-1) lw) and higher tDDT/tPCB ratios (0.93 vs. 0.42) were observed in sperm whales compared with Rissos dolphins and may indicate wider migrations for the former. Therefore, competition between these species seems to depend on different trophic levels and migration patterns.

Biological aspects of Medorippe lanata (Linnaeus, 1767) (Brachyura: Dorippidae) from the eastern Ligurian Sea (western Mediterranean)

The aim of the present study is to investigate the demographic structure and to identify some aspects of the biology of an exploited population of Medorippe lanata (Brachyura: Dorippidae) in the eastern Ligurian Sea, western Mediterranean. 1364 specimens (639 males and 725 females) of M. lanata were collected on a monthly basis from January to December 2001, in a wide area of the eastern Ligurian Sea usually exploited by the Viareggio ‘rapido’ trawl fleet. M. lanata represented an important fraction of the discard, both in weight and in number of individuals. Maximum abundance of this species occurred in late summer-early autumn (up to 3369 ind. km−2 and 50.6 kg km− in August). The overall females: males sex-ratio was 1.13:1, while the monthly sex-ratio did not differ statistically from 1:1 in all months, except in September and October, when females significantly outnumbered males. The sampled population was composed of two cohorts from November to April. Sizes ranged from 10 to 29 mm carapace length (CL) for females and from 9 to 29 mm CL for males. The von Bertalanffy growth curve, computed for both sexes, gave a higher growth rate in males than in females. Recently moulted males and females were observed throughout the year, except in summer, when the highest number of ovigerous females was present. Females with external eggs were collected from March to November, with peaks in August and September. The monthly evolution of the ovarian maturity stages showed no clear temporal trend. At 21 mm CL, 50% of females were ovigerous or showed macroscopically mature ovaries. According to the dimorphism in chelae size, the presence of adult males (post-puberty stage) was observed all year round, from 18 to 29 mm CL, without evident temporal trends.