Ivan Locci

Assemblages in a submarine canyon: influence of depth and time

In this work we have studied the assemblages from Quirra canyon (Sardinia). We analysed data from 25 trawl samples from the canyon, made at different times and depth. A total of 71 demersal species (38 teleosts, 5 cartilaginous fishes, 13 molluscs and 15 crustaceans) were examined. We found four groups using cluster analysis; each group is characterised by a certain depth or time. In particular we have shown that the time of the day appears to have a role in the movement of shrimps and other species. This phenomenon seems to be linked to trophic need and by the consequent different food availability into the Canyon.

Demersal assemblages in two trawl fishing lanes located on the Baronie Seamount (Central Western Mediterranean)

This work focuses on the species associations of the Baronie Seamount (north-eastern Sardinia, Italy), according to variations in depth and time of day. The aim was to highlight the potential vertical movements of the species and to compare these results to existing data from a submarine canyon. Twenty-two samples were taken at different depths and times along two trawl lines over the seamount. A total of 94 species were caught; among these, 4 8 bony fish, 9 cartilaginous fish, 13 molluscs and 24 crustaceans were selected for analysis. Cluster analysis showed 3 groups in which both depth and time of day play an important role in grouping. Nine species showed some daily and nocturnal movement, probably linked to trophic requirements. The daily movements according to size and sex of the shrimps Aristaeomorpha foliacea and Aristeus antennatus were also studied. For these two populations, the analysis showed an uneven distribution and the diel cycle appears to involve only the females. These species seem to adapt their life cycle to the geomorphology of the sea bottom. The diurnal movements from the base of the seamount to the edge of the continental shelf increase the range of the species distribution. In fact, the seamount, due to its geomorphological conformation, offers these species the opportunity to very quickly span a considerable range of depths. These movements are known to occur in the continental shelf and slope, but in the seamount they are broadened and can be studied more easily.

Body Temperature of the Atlantic Bluefin Tuna (Thunnus thynnus L.) in the Western Mediterranean

This study documents body temperature in the Atlantic bluefin tuna (Thunnus thynnus L.) in the Mediterranean Sea and temperature variability caused by the stress of capture. The investigation was carried out in the traditional trap (tonnara) of Isola Piana (Sardinia, W Mediterranean) where body temperature recordings were conducted on free-swimming bluefin confined in the system of nets known as “camere” or chambers. We tracked the body temperature of two bluefin tuna (214 and 191 cm CFL) using a commercial data logger (HOBO U12, Onset Computer Corporation), under two conditions: the pre-fishing phase, when specimens confined in the “camera di ponente” are undisturbed and the fishing phase when bluefin tuna are trapped in the “camera della morte” and undergo the stress of confinement and capture (mattanza). Body temperature increased by about 2°C during the “mattanza”, whereas no temperature variation was exhibited during the pre-fishing phase. The heat transfer coefficient (K), calculated for both bluefin tuna during the “mattanza”, revealed a rapid increase in heat transfer. Additional data on ambient temperature Ta, white muscle Tw (n = 65; 110–287 cm CFL) and red muscle temperature Tr, (n = 249; 107–287 cm CFL) were obtained from live fish during angling operations, and excess body temperature (Tx = Tr–Ta) was calculated. Mean red muscle temperature was 27.6 ± 1.48°C in an ambient temperature of 18.9 ± 0.84°C. The excess red muscle temperature Tx was 8.21–9.10°C, and the red muscle was 2.4 ± 1.78°C warmer than white muscle.