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We describe the feeding habits of 70 blue sharks (Prionace glauca) and 39 salmon sharks (Lamna ditropis) caught at 0-7 m depth at night by research drift gillnets in the transition region of the western North Pacific during AprilMay of 1999 and 2000. Blue sharks of 50-175 cm total length fed on a large variety of prey species, consisting of 24 species of cephalopods and 16 species of fishes. Salmon sharks of 69-157 cm total length fed on a few prey species, consisting of 10 species of cephalopods and one species of fish. Important prey for the blue sharks were large, non-active, gelatinous, meso-to bathypelagic cephalopods (e.g., Chiroteuthis calyx, Haliphron atlanticus, Histioteuthis dofleini and Belonella borealis) and small myctophid fishes. Important prey for the salmon sharks were midsized, active, muscular, epi-to mesopelagic squids (e.g. Gonatopsis borealis, Onychoteuthis borealijaponica and Berryteuthis anonychus). Our results suggest that blue sharks feed on cephalopods mainly during the daytime when they descend to deep water. Salmon sharks may feed opportunistically with no apparent diurnal feeding period. Blue sharks and salmon sharks have sympatric distribution in the transition region in spring; they have different feeding habits and strategies that reduce competition for food resources.

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ABSTRACT:We examined the feeding habits of the neon flying squid Ommastrephes bartramii from late spring to mid-summer in relation to its northward migration in the transitional waters of the central North Pacific. The winter-spring cohort (ca. 15 to 25 cm in May and 20 to 35 cm in July) and the autumn cohort (ca. 30 to 45 cm in May and 35 to 50 cm in July) were identified by their dorsal mantle lengths. In May and July, the winter-spring cohort was distributed only in the transition zone (TZ) south of the subarctic boundary. This cohort preyed primarily on crustaceans such as euphausiids and amphipods in May, but in July, their primary prey shifted to the sternoptychid fish Maurolicus imperatorius. In May, the larger-sized autumn cohort was also distributed only in the TZ, but in July, these individuals migrated to the transitional domain (TD) north of the subarctic boundary. The main prey of the autumn cohort were micronektonic animals that dominated the TZ in May: the transitionalwater myctophid Symbolophorus californiensis, and 2 subtropical myctophids, Ceratoscopelus warmingi and Electrona risso. Secondary important prey items included the transitional-water squid Onychoteuthis borealijaponica and subarctic gonatid squids such as Gonatus berryi and Berryteuthis anonychus. In July, the main prey species in the TD were S. californiensis and O. borealijaponica, both of which also migrated from the TZ into the TD, crossing the subarctic boundary in summer. We estimated the feeding impact of the autumn squid cohort on myctophids in the TD during summer.

Rua do Porto 18, 9939 430 Sao Joao, Lajes do Pico, Açores, PortugalDespite its charismatic appeal to both scientists and the general public, remarkably little is known about the giant squid Architeuthis, one of the largest of the invertebrates. Although specimens of Architeuthis are becoming more readily available owing to the advancement of deep-sea fishing techniques, considerable controversy exists with regard to topics as varied as their taxonomy, biology and even behaviour. In this study, we have characterized the mitochondrial genome (mitogenome) diversity of 43 Architeuthis samples collected from across the range of the species, in order to use genetic information to provide new and otherwise difficult to obtain insights into the life of this animal. The results show no detectable phylogenetic structure at the mitochondrial level and, furthermore, that the level of nucleotide diversity is exceptionally low. These observations are consistent with the hypotheses that there is only one global species of giant squid, Architeuthis dux (Steenstrup, 1857), and that it is highly vagile, possibly dispersing through both a drifting paralarval stage and migration of larger individuals. Demographic history analyses of the genetic data suggest that there has been a recent population expansion or selective sweep, which may explain the low level of genetic diversity.

Aquatic pollution resulting from extensive usage of organotin compounds has been of great concern due to their deleterious effects in organisms. However, organotin contamination in deep-sea ecosystems has not yet been studied. The present study was attempted to determine butyltin compounds (BTs), including mono-(MBT), di-(DBT), and tributyltin (TBT) in deep-sea organisms collected from Suruga Bay, Japan, in order to elucidate the contamination status and accumulation characteristics. The organisms were collected between 135 and 980 m in the aphotic bathyal zone and compared with those collected from shallow waters. Total butyltin (∑BT: MBT + DBT + TBT) concentrations in the tissues of deep-sea fish, crustaceans, cephalopods, echinoderms, and gastropods were up to 980, 460, 460, 130, and 21 ng/g wet wt, respectively. These levels were lower than those in shallowwater organisms from the same bay but comparable to those reported in industrialized areas like Tokyo Bay, suggesting the expansion of BT pollution in deep-sea ecosystems. Deep-sea organisms from Suruga Bay contained much higher levels of BTs than previously reported organochlorine concentrations. BT accumulation appeared to be less lipid dependent. Among BTs, TBT was the predominant compound except in cephalopods, suggesting a fresh input of TBT into the deep-sea environment. To our knowledge, this is the first report on the detection of organotin residues in deep-sea organisms.

Our newly developed underwater high definition video camera system took the first live images of adults of the mesopelagic large squid, Taningia danae, between 240 and 940 m deep off Ogasawara Islands, western North Pacific. The resulting footage includes attacking and bioluminescence behaviours, and reveals that T. danae is far from the sluggish neutrally buoyant deep-sea squid previously suspected. It can actively swim both forward and backward freely by flapping its large muscular triangular fins and changes direction quickly through bending its flexible body. It can attain speeds of 2-2.5 ms(-1) (7.2-9 km h(-1)) when attacking bait rigs. They emitted short bright light flashes from their large arm-tip photophores before final assault, which might act as a blinding flash for prey as well as a means of measuring target distance in a dark deep-sea environment. They also emitted long and short glows separated by intervals while wandering around the double torch lights attached to the bait rig, suggestive of potential courtship behaviours during mating.

The giant squid, Architeuthis, is renowned as the largest invertebrate in the world and has featured as an ominous sea monster in novels and movies. Considerable efforts to view this elusive creature in its deep-sea habitat have been singularly unsuccessful. Our digital camera and depth recorder system recently photographed an Architeuthis attacking bait at 900 m off Ogasawara Islands in the North Pacific. Here, we show the first wild images of a giant squid in its natural environment. Recovery of a severed tentacle confirmed both identification and scale of the squid (greater than 8 m). Architeuthis appears to be a much more active predator than previously suspected, using its elongate feeding tentacles to strike and tangle prey.