Distribution patterns and population structure of Illex coindetii (Cephalopoda: Ommastrephidae) in the Southern Tyrrhenian Sea: Historical series of 14 years trawl survey

The occurrence and bathymetric distribution of the squid Illex coindetii (Cephalopoda: Ommastrephidae) in the southern Tyrrhenian Sea (Central Mediterranean) was assessed using trawl survey data collected from 1994 to 2007 as part of the MEDITS Project. The study area covered approximately 7256 km2, with depths of 10–800 m. The highest mean values for density and biomass indices for I. coindetti were obtained in the 101–200 m stratum. At this depth range, the highest density and biomass values occurred in 1998 (1121 N/km2) and in 2003 (42.52 kg/km2), respectively. A cartographic presentation of the mean biomass and density values showed that the species had a wide bathymetric distribution (35–600 m), although the bulk of the catch occurred in the 70–180 m depth range. I. coindetii were characterised by a very wide size range, with the dorsal mantle length (DML) varying between 25 and 300 mm. The length classes of the specimens ranged from 25 to 120 mm for immature and from 60 to 210 mm and from 65 to 300 mm for males and females, respectively. Recruits were collected in all surveys and were distributed at depths of more than 50 m, although the highest values were recorded in the 101–200 m stratum. The logistic fits of the proportions of both the mature specimens and all specimens together resulted in an overall Lm50% of 150 and 105 mm for females and males, respectively. The spatial distribution of I. coindetii indicated that the species was more abundant along the Calabrian coasts, while the recruits were concentrated in the eastern part of the study area (Cape Vaticano, Calabria). The results of this study highlight the need for a more comprehensive study of both environmental processes affecting the abundance and distribution of I. coindetii and the life history of the species in the southern Tyrrhenian Sea in order to improve our understanding of the species’ dynamics in relation to environmental variability.

► Historical series of 14 years trawl survey in the Southern Tyrrhenian Sea.
► In the study area Illex coindetii occurs mainly between 100 and 200 m.
► Both adults and recruits appear mainly localized along the Calabrian coasts.
► LFD shows that females reach larger size than males.