C. Yau

Distribution of deep-water benthic and bentho–pelagic cephalopods from the north-east Atlantic

The distribution of deep-water (150-4850 m) benthic and bentho-pelagic cephalopods in the northeast Atlantic is described, based on 592 specimens collected from commercial and research trawling. Thirty-six different species of cephalopod belonging to 14 families were identified, though problems remain with the taxonomy of some of the octopod genera. At the shallower depths (150-500 m) sepiolids were the most abundant group with five species identified. Sepiola atlantica, Sepietta oweniana and Rondeletiola minor were restricted to the shallow depths (<300 m), but Neorossia caroli (400-1535 m) and Rossia macrosoma (205-515 m) extended into deeper water. The squids Todaropsis eblanae and Loligo forbesi were also common in shallow areas (<250 m). Among the incirrate octopods, Eledone cirrhosa was found at depths of 208-490 m. Three putative species of Benthoctopus and two of Bathypolypus were identified occupying depths of 250-2700 m. Graneledone verrucosa was caught at depths of 1785-2095 m. Cirrate octopods dominated the cephalopod catch from the deeper areas, with Opisthoteuthis massyae occurring from 877 to 1398 m, O. grimaldii from 2165 to 2287 m, Stauroteuthis syrtensis from 1425 to 3100 m, Cirroteuthis muelleri from 700 to 4854 m, Cirrothauma murrayi from 2430 to 4850 m and Grimpoteuthis (five putative species) from 1775 to 4877 m. Abundance estimates of the more frequently caught species were calculated from swept areas of trawls and sledges in the Porcupine Seabight and on the Porcupine Abyssal Plain.

Behavioural observations on the scavenging fauna of the Patagonian slope

The scavenging fauna of the Patagonian slope (900–1750 m), east of the Falkland Islands was investigated using the Aberdeen University Deep Ocean Submersible (AUDOS), an autonomous baited camera vehicle designed to photograph scavenging fish and invertebrates. The AUDOS was deployed on ten occasions in Falkland waters. Nine experiments were of 10–14 h duration and baited with 800 g of squid and one experiment lasted six days, baited with a 10 kg toothfish ( Dissostichus eleginoides ). Analysis of photographs revealed considerable patchiness in the composition of the scavenging fauna. Hagfish ( Myxine cf. fernholmi ) dominated three of the shallower experiments including the 6-d experiment, arriving quickly from down-current, holding station at the bait and consuming the soft tissues first, with consumption rates of up to 200 g h −1 . In the other experiments, stone crabs (Lithodidae), the blue-hake ( Antimora rostrata ) and amphipods were the primary consumers, but the rate of bait consumption was lower. Patagonian toothfish ( D. eleginoides ) were attracted to the bait at each experiment, but did not attempt to consume the bait. The patchiness in the fauna may be a result of depth, substratum and topography, but in general the rapid response of the scavenging fauna indicates that carrion is rapidly dispersed, with little impact on the local sediment community.

Timing of spawning and recruitment in Loligo forbesi (Cephalopoda: Loliginidae) in Scottish waters

The timing of spawning and recruitment in the squid Loligo forbesi in Scottish waters is described on the basis of data from three sources: monthly samples of squid caught by commercial trawls (1986–1988), egg masses found by fishermen (1987–1991), and statistical data on animals caught by research trawls (1978–1987). Spawning females were present in samples from December to June, with peak spawning occurring in March. Most records of egg masses were from these months, but eggs were also found in August and September. These results suggest that there is an extended spawning season. Small squid (≤100 mm dorsal mantle length) were rarely present in commercial samples, but were recorded in research samples almost all year round. Thus there appears to be more or less continuous recruitment into the catchable population. The results of the present study are consistent with published data from other parts of the geographic range in that there is a regular seasonal peak in spawning, and spawning adults disappear from the population in summer. Further interpretation of the life-cycle of this species is not justified on the basis of current knowledge, and more information is needed on migrations, geographical variation, and lifespan in Loligo forbesi .

Estimating the abundance of Patagonian toothfish Dissostichus eleginoides using baited cameras: a preliminary study

The Patagonian toothfish Dissostichus eleginoides has been the object of a rapidly expanding longline fishery in the Southern Ocean. Little is known about the biology of D. eleginoides and traditional methods of estimating stock size using trawling techniques have proved ineffective because the adult fish are found in deep waters on the continental slope at depths of 700–2500 m. During September 1997, a preliminary study was undertaken using arrival times at an autonomous baited camera vehicle, the Aberdeen University Deep Ocean Submersible (AUDOS), to estimate the abundance and size of toothfish in waters around South Georgia (SG) and the Falkland Islands (FI). These are the first attempts at estimating the abundance of toothfish that are independent of catch data from the commercial fishery.

Reproductive biology of Todaropsis eblanae (Cephalopoda: Ommastrephidae) in Scottish waters

During a study based on catches taken in the northern North Sea by selected Scottish fishing boats during 1985-1992, large numbers of the normally rare short-fin squid, Todaropsis eblanae (Cephalopoda: Ommastrephidae), were recorded in 1987 and 1990. Our findings, supported by data obtained from plankton/young fish surveys in 1988 and 1989, suggest that in northern waters Todaropsis eblanae generally mates and spawns during late summer and early autumn (June-November). Successful hatching events appear to occur during October-March, producing juvenile (stage I) squid in the early part of the year (January-June). Estimations of maximum male reproductive output and female fecundity were up to 130 spermatophores and -28,000 eggs per individual, respectively.

Scavenging by megabenthos and demersal fish on the South Georgia slope

The scavenging megafauna of the South Georgia and Shag Rocks slope in the south-west Atlantic (625–1519 m) were investigated using autonomous baited camera systems. Two surveys were conducted: the first in 1997 (13 deployments) used a conventional 35 mm stills camera with a 200 J flash, whilst the second in 2000 (15 deployments) used low-light digital video cameras. The scavenging community responded rapidly to the arrival of bait on the sea floor and was dominated by stone crabs (Lithodidae) and toothfish (Dissostichus eleginoides). Stone crabs took up residence around the bait until it was consumed, with a maximum number of 108 in the field of view after four hours. The most frequently observed crab species was Paralomis formosa. Paralomis spinosissima, Neolithodes diomedea and Lithodes sp., were also observed. Toothfish were the most frequently observed scavenging fish and were seen during all but one deployment, typically making brief visits (1–2 min) to the bait, but appeared startled by the flash in the 1997 survey. Labriform swimming (sculling with the pectoral fins) was the principal form of locomotion in toothfish (0.22 body lengths (BL) sec−1), but they were capable of more rapid sub-carangiform (using caudal trunk and fin) motion (3 BL sec−1) when startled. Other scavenging fish observed included the blue-hake Antimora rostrata, grenadiers (Macrourus spp.), skates, liparids and zoarcids.

Ecology of Sepiola Atlantica (Mollusca: Cephalopoda) in the Shallow Sublittoral Zone

The ecology of the sepiolid Sqyiola atlantica in Firemore Bay, Loch Ewe, on the west coast of Scotland was investigated by beam trawling surveys. Low densities of this species were present in the shallow sublittoral zone of the sandy bay. A size range of 4-21 mm dorsal mantle length (DML) was obtained, with no significant differences detected between the mean sizes of males and females. Males reached gonadal maturity slightly earlier and at a slightly smaller size than females. Sq^iola atlantica was present in the bay in each of the months in which sampling took place suggesting a resident population, the structure of which varied considerably. Juveniles were found over a prolonged period of the year but peak recruitment (animals of 4-10 mm DML) was in May and July. Animals <4 mm DML were not caught and no egg masses were found in the trawls. In aquarium conditions, S. atlantica fed on live crustaceans such as mysids, Crangon crangon and Palaemon serratus, although Corophium volutator, an estuarine crustacean not normally found in the marine sandy bay, was the most accepted food.

Implication of the visual system in the regulation of activity cycles in the absence of solar light: 2–[125I]iodomelatonin binding sites and melatonin receptor gene expression in the brains of demersal deep-sea gadiform fish

Relative eye size, gross brain morphology and central localization of 2–[125I]iodomelatonin binding sites and melatonin receptor gene expression were compared in six gadiform fish living at different depths in the north–east Atlantic Ocean: Phycis blennoides (capture depth range 265–1260 m), Nezumia aequalis (445–1512 m), Coryphaenoides rupestris (706–1932 m), Trachyrincus murrayi (1010–1884 m), Coryphaenoides guentheri (1030 m) and Coryphaenoides (Nematonurus) armatus (2172–4787 m). Amongst these, the eye size range was 0.15–0.35 of head length with a value of 0.19 for C. (N.) armatus, the deepest species. Brain morphology reflected behavioural differences with well–developed olfactory regions in P. blennoides, T. murrayi and C. (N.) armatus and evidence of olfactory deficit in N. aequalis, C. rupestris and C. guentheri. All species had a clearly defined optic tectum with 2–[125I]iodomelatonin binding and melatonin receptor gene expression localized to specific brain regions in a similar pattern to that found in shallow–water fish. Melatonin receptors were found throughout the visual structures of the brains of all species. Despite living beyond the depth of penetration of solar light these fish have retained central features associated with the coupling of cycles of growth, behaviour and reproduction to the diel light–dark cycle. How this functions in the deep sea remains enigmatic.