No abstract

No abstract

No abstract

In recent years a northward expansion of Sardinella aurita has been reported in the western Mediterranean. Considering the coexistence of its larvae with those of the dominant species Engraulis encrasicolus, the present study was conducted to compare their vertical distributions in 2 areas off the Catalan coast with different vertical environmental conditions. During summer, the water column was stratified with a deep chlorophyll maximum (DCM) beneath the pycnocline. However, the southern area, under the influence of the Ebro River, was characterized by a secondary surface chlorophyll maximum. Vertical distribution of larval food, nauplii and copepodites showed good agreement with the high chlorophyll layers. In the earliest stages of development, larvae of both species remained in the upper levels. From 6 mm standard length on they developed a day/night migratory behaviour to search for food during the day (feeding period). Therefore, in the south, where the abundance of potential food in the upper layers was relatively high, larvae of both species remained in the upper levels during the day. However, in the north, where food was restricted to the DCM, only E. encrasicolus larvae were able to reach these deep levels. The low temperatures (~15°C) detected at the DCM may restrict the vertical migration of S. aurita in accordance with their thermophilic character. This limitation might represent a restriction for the northward expansion of this species in the western Mediterranean.

Compared with their shelf-living relatives, the biology and ecology of most pelagic and deep-sea cephalopods are presently relatively little known because of the difficulty in catching them. To compensate for the lack of information regarding these cephalopods, scientists have had to make use of the limited and fragmentary data gathered from different sources, such as sporadic captures, strandings or stomach contents of their predators. In this study, we provide some biological and ecological information on eleven uncommon pelagic and deep-sea cephalopods collected over more than fifteen years of fishery surveys in the western Mediterranean Sea. The cephalopods investigated include two epipelagic octopuses (Ocythoe tuberculata and Tremoctopus violaceus), one deep-sea cirrate octopus (Opisthoteuthis calypso), the sepiolid Stoloteuthis leucoptera and seven teuthoid species inhabiting, preferentially, the mesopelagic and bathypelagic waters (Abraliopsis morisii, Ancistrocheirus lesueurii, Brachioteuthis riisei, Chiroteuthis veranyi, Chtenopteryx sicula, Onychoteuthis banksii and Taonius pavo). Although all of these species are either cosmopolitan or present a wide distribution in other oceans, they are nevertheless relatively rare in catches, and therefore, remain lesser known. The finding of T. pavo represents the first record of this cephalopod in the Mediterranean waters.