Chemical signatures in the otoliths of teleost fishes represent natural tags that may reflect differences in the chemical and physical characteristics of an individuals' environment. Otolith chemistry of Atlantic bluefin tuna (Thunnus thynnus) was quantified to assess the feasibility of using these natural tags to discriminate juveniles (age 0 and age 1) from putative nurseries. A suite of six elements (Li, Mg, Ca, Mn, Sr and Ba) was measured in whole otoliths using solution‐based inductively coupled plasma mass spectrometry. Otolith chemistry of age‐1 T. thynnus collected from the two primary nurseries in the Mediterranean Sea and western Atlantic Ocean differed significantly, with a cross‐validated classification accuracy of 85%. Spatial and temporal variation in otolith chemistry was evaluated for age‐0 T. thynnus collected from three nurseries within the Mediterranean Sea: Alboran Sea (Spain), Ligurian Sea (northern Italy), and Tyrrhenian Sea (southern Italy). Distinct differences in otolith chemistry were detected among Mediterranean nurseries and classification accuracies ranged from 62 to 80%. Interannual trends in otolith chemistry were observed between year classes of age‐0 T. thynnus in the Alboran Sea; however, no differences were detected between year classes in the Tyrrhenian Sea. Age‐0 and age‐1 T. thynnus collected from the same region (Ligurian Sea) were also compared and distinct differences in otolith chemistry were observed, indicating ontogenetic shifts in habitat or elemental discrimination. Findings suggest that otolith chemistry of juvenile T. thynnus from different nurseries are distinct and chemical signatures show some degree of temporal persistence, indicating the technique has considerable potential for use in future assessments of population connectivity and stock structure of T. thynnus.

SUMMARY: The application of statistical models on a time series of data arising from the MEDITS International Trawl Survey, an experimental demersal resources survey carried out during six years (1994)(1995)(1996)(1997)(1998)(1999) in the same season of the year (late spring -early summer) using the same fishing gear in a large part of the Mediterranean, has allowed for a study to compare, for the first time, the space-time distribution, abundance, and size structure of the two Aristeids Aristaeomorpha foliacea and Aristeus antennatus throughout most of the Mediterranean Sea. This research has shown a large variability among the six reference areas, that were arbitrarily defined within the basin. In particular the two shrimps do not seem to present any correlation or yield continuity in the years. The same lack of homogeneity was also observed in the time trend of the abundances and frequencies of each of the two species. These data seem to confirm the intrinsic variability of the species, the cause of which is still unknown and undocumented. Nevertheless, a longitudinal gradient of catches has been observed where A. antennatus is more abundant in the west and A. foliacea in the east of the basin.

On the basis of trawl survey data collected during the MEDITS project (1994-1999), the distribution of Mediterranean hake populations was described in coastal areas corresponding to about three quarters of both the latitudinal and longitudinal extensions of the Mediterranean Sea, and in the 0-800 m range. Abundance and biomass indices (in terms of number and kg per km2) are presented in 15 geographical sectors and 40 subareas from the Alborán Sea to the Aegean Sea. A statistical analysis by generalized linear modelling performed on such indices per main national blocks (Greece, France, Italy and Spain), and considering the effects of the six years of sampling and the depth, showed that biomass increased from west to east, while for all areas the most significant depth effect appeared between 100 and 200 m, corresponding to the depth range that hosts most of the summer nursery areas. The overall size-frequency distributions in shelf and slope waters, average sizes and total mortality coefficient Z per sector showed that the bulk of the MEDITS samples consisted of young individuals and, with only a few exceptions (western Sardinia, central Aegean), a generalized condition of growth overfishing was apparent. However, no negative trend was found, either in biomass or in average size of fishes, during the six years of the present study. Recruitment patterns were studied by distinguishing the youngest fish as Gaussian groups (modal length from 6 to 9 cm total length) in length-frequency distributions of each subarea and main stratum (shelf and slope). Considering the timing of MEDITS surveys (May-July), this approach emphasised the nurseries in the northern part of the western Mediterranean (Gulf of Lions, Ligurian Sea, northern Tyrrhenian Sea) and in the northern central Mediterranean, where recruitment occurs mainly during spring. On the other hand, few recruits were found in part of the central and particularly in the eastern Mediterranean, where recruitment occurs mainly in summer. MEDITS recruitment patterns therefore gave support to distinctions among Mediterranean hake populations, previously suggested on the basis of vertebral counts and other morpho-physiological, albeit fragmentary, data. In particular the central Mediterranean hake populations do not seem to be homogeneous, with an Adriatic unit very close to the northwestern one. The MEDITS experience therefore suggests that future management measures could take into account both general and regional patterns, the latter concerning mainly the younger fraction of the populations.

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Two specimens of the Azorean rockling Gaidropsarus granti (Regan 1903) were caught in the period August 1989–January 1990 on a seamount located about 29 nautical miles south of Genoa, Ligurian Sea. The records remained unpublished because of errors in the literature concerning the two Macaronesian species Gaidropsarus granti and Gaidropsarus guttatus. Old and recent records of G. granti are now used to characterize morphological and ecological traits of this species. In particular, G. granti is unmistakably adapted to a sedentary life on hard substrata, and all records occurred in offshore slope waters, frequently on banks and seamounts. Ecological characteristics and biogeographical considerations are introduced in the discussion about the origin of the Mediterranean records of G. granti, specifically whether this fish should be considered an introduced or a native species.