The ecology of the deep-sea benthic and benthopelagic fish on the slopes of the Rockall Trough,Northeastern Atlantic

A total of over 28,000 benthic and benthopelagic fish belonging to 34 families and comprising at least 85 species were collected from the Hebridean Terrace in the Rockall Trough between soundings of 500 and 2000 m. Commercial type trawls (20.6 m Granton or 140 foot German bottom trawls) fished on paired warps at 33 stations accounted for 89% of all individual caught, the remainder being caught by a 16.4 m prawn trawl fished on a single warp (22 stations) and a 3 m Agassiz trawl (12 stations). The stations sampled, with a few exceptions, fell into discrete bathymetric zones separated by increments of approximately 250 m and different combinations of nets were used at each of these zones. The catch composition of the commercial trawls differed from those of the other nets. The most obvious difference was that squalid sharks, the alepocephalid Alepocephalus bairdii and the black scabbard fish Aphanopus carbo were important in the commercial type trawls but were absent or poorly represented in the other nets. Net size and towing speed were considered to be important factors influencing the catch composition. Net selectivity was most apparent on the upper and mid slopes but less apparent on the lower slopes.Relatively few families contribute to the total biomass at a given bathymetric zone and because the families Squalidae and Alepocephalidae contribute significantly to the biomass on the upper and mid slope it is therefore concluded that small nets must grossly underestimate the biomass at these depths. The greatest biomass occurred at mid slope depths (750–1000 m).     

New dredge samples from the continental margin bordering Rockall Trough

Rockall Trough may represent the oldest part of the Atlantic Ocean north of latitude 51°N. Stratigraphical evaluation of this hypothesis has been hindered by the lack of dateable samples of the Trough's sedimentary succession. A recent programme of dredging, aimed at sampling the sediment prism along the Trough's upper continental slope, yielded five hauls of in-situ carbonate rocks. Microfaunal analysis of these rocks suggests that the deposition of the marginal sediment prism spans the Late Cretaceous—Recent interval, tending to confirm that Rockall Trough was already in being in Late Cretaceous times.     

Wyville Thomson Ridge Overflow Water: Spatial and temporal distribution in the Rockall Trough

Wyville Thomson Ridge Overflow Water (WTOW), which is the only part of the outflow from the Norwegian Sea not to directly enter the Iceland Basin, is shown to be a significant water mass in the northern Rockall Trough. It is found primarily at intermediate depths (600–1200 m) beneath the northward flowing warm Atlantic waters, and above recirculating Mediterranean influenced waters and Labrador Sea Water (LSW). The bottom of the WTOW layer can be identified by a mid-depth inflexion point in potential temperature–salinity plots. An analysis of historical data reveals that WTOW has been present in all but eight of the last 31 years at 57.5°N in the Rockall Trough. A denser component of WTOW below 1500 m has also been present, although it appears to be less persistent (12 out of the 31 years) and limited to the west of the section. The signature of intermediate WTOW was absent in two periods, the mid-1980s and early 1990s, both of which coincided with a freshening, and probable increase in volume, of LSW in the trough. Potential temperature–salinity diagrams from historical observations indicate that WTOW persists at least as far south as 55°N (and as far west as 20°W in the Iceland Basin) although its signature is quickly lost on leaving the Rockall Trough. We suggest that a transport of WTOW down the western side of the trough exists, with WTOW at intermediate depths entering the eastern trough either via a cyclonic recirculation, or as a result of eddy activity. Further, WTOW is seen on the Rockall–Hatton Plateau and in the deep channels connecting with the Iceland Basin, suggesting additional possible WTOW transport pathways. These suggested transport routes remain to be confirmed by further observational or modelling studies.     

鱼类自残行为研究进展

鱼类自残现象是鱼类之间相互残杀(食)的行为,除了遗传因素、鱼体的规格差异可引起自残现象外,大量的环境因素同样影响着自残行为发生的时间、频率和强度。本文综述了集约化养殖条件下,影响鱼类自残行为的主要环境因子,包括营养状态、光照(强度、周期)和养殖密度等,并简单介绍了遗传背景对鱼类自残行为的影响。结合鱼类自残行为发生机理的研究,进一步探讨了减少鱼类自残行为发生的措施。     

Water mass interaction at intermediate depths in the southern Rockall Trough,northeastern North Atlantic

Mooring time series, CTD data, and Argo float data were analysed to investigate some aspects of the circulation at the southern entrance to the Rockall Trough during 2003–2004. The in situ data are used to describe the distribution at intermediate levels of Sub-Arctic Intermediate Water (SAIW) and Mediterranean Water (MW), as well as the temporal variability in the presence of these two water masses. Salty, MW-influenced water was found in the southeastern part of the study area, near the continental slope as far north as Porcupine Bank, consistent with earlier reports. Apart from the main tongue, the distribution of MW is patchy, and MW parcels were found not only adjacent to the slope but also offshore. Further north and west, water at intermediate depths was influenced by the fresher SAIW. Unlike in some earlier studies, SAIW did not extend as far east as the continental shelf. The year-long hydrographic and current time series from a mooring on the western slope of the entrance, at the southern end of Feni Ridge, showed pulses of SAIW influenced water throughout winter and spring. In late spring, the fresh pulses almost completely ceased; throughout summer only a few weak and shortlived fresh anomalies appeared. The weakening of the SAIW signal did not seem to be caused by winter convection, which did not extend to sufficient depth that winter. The relatively weak SAIW presence during most of the study period may be linked to the near neutral state of the NAO index. The warm and saline conditions observed at the southern entrance to Rockall Trough were in agreement with the rising temperatures and salinities found over large parts of the subpolar North Atlantic in the late 1990s and early 2000s.     

Glacial and post-glacial sedimentary processes in the Irish Rockall Trough from an integrated acoustic analysis of near-seabed sediments

Near-seabed (<50 m) sediments were studied throughout the Irish sector of the Rockall Trough (ca. 123,000 km²) based on a combined analysis of shallow seismic (3.5 kHz) and multibeam swath data acquired by the Irish National Seabed Survey and reprocessed here at higher resolution. The detailed identification of seven acoustic facies served to classify the Rockall Trough into six main sedimentary provinces, incorporating the well-known Feni Drift, Donegal-Barra Fan and Rockall Bank mass flow. In the northern part of the study area, extensive mass transport deposits from both flanks of the trough are the dominant depositional features. Debris flow deposits formed by ice streaming of the British-Irish ice sheet characterise most of the Donegal-Barra Fan, whereas turbidite deposition occurs towards the toe of the fan. On the western margin of the trough, the post-glacial Rockall Bank mass flow deposit displays a rough topography with no acoustic penetration. Several failure scarps are visible on the flank of the bank where the mass flow originated, and pass downslope into large sediment lobes and smaller debris flow deposits. Smaller-scale mass transport deposits were also discovered close to some canyons indenting the eastern slope. High seismic penetration characterises the Feni contourite drift deposit, and precise mapping of its geographical extent shows that it is considerably wider than previously reported. The sediment waves that drape this drift are interpreted as predominantly relict features, and their varied geometry suggests a complex oceanographic regime. In the deeper part of the trough, the data reveal novel evidence of the widespread occurrence (about 12,000 km²) of distinct seismic and backscatter signatures indicating the possible presence of fluid escape structures within fine-grained sediments of mixed contouritic, hemipelagic and turbiditic origin. Sediment overloading and increased pore pressure resulting from extensive mass wasting to the north of the area is a likely cause of dewatering-rooted fluid migration towards the seabed, but further investigations are required to confirm the nature and origin of such fluids in the Rockall Trough.     

Near-bed particle deposition and resuspension in a cold-water coral mound area at the Southwest Rockall Trough margin,NE Atlantic

Cold-water coral reefs and mounds are observed mainly on slopes and topographic highs, in areas with high current speeds. Previous investigations of the near-bed hydrodynamic regime around cold-water coral mounds at the Southwest Rockall Trough margin have revealed the presence of internal waves with a diurnal tidal frequency. Hitherto only short-term measurements existed on the particle supply to the corals and data are lacking on the seasonal variability. Bottom landers equipped with sensors recording near-bottom current dynamics were deployed at two sites in a mound area on the Southwest Rockall Trough margin, one with a dense coral cover and one without coral cover. At both sites a similar seasonal variation in internal-wave activity was recorded with high activity during winter and summer months and less dynamic conditions in spring and autumn. Increased intensity of internal-wave activity, reflected in higher average near-bottom current speed and amplitude of daily temperature fluctuations, results in higher mass fluxes as recorded in the sediment traps. On the site without coral cover, mass fluxes are two times higher, compared to the site with dense coral cover. During periods of high mass fluxes a predominance of resuspended material was observed at both sites, as indicated by reduced ²¹⁰Pb activity and low organic matter concentrations. The flux of resuspended material largely masked the primary pelagic signal. However, low δ¹⁵N values in early spring and summer marked the arrival of fresh particles on both sites. A dense coral framework, baffling a large amount of particles settling between the coral branches, results in differences in particle flux, chemical composition and freshness of the trapped material. On the long term the presence of a coral framework plays a crucial role in the build-up of cold-water coral mounds.     

Hydrodynamic controls on cold-water coral growth and carbonate-mound development at the SW and SE Rockall Trough Margin,NE Atlantic Ocean

Long-term (⩽1-year) records obtained by seabed observatories (BOBO) and repeated (24-h) CTD casts show the presence of a highly energetic environment in and around two cold-water carbonate-mound provinces, on the Southwest and Southeast Rockall Trough (SW and SE RT) margin. Carbonate mounds, covered with a thriving coral cover, are embedded mainly in the Eastern North Atlantic Water (ENAW) and are observed in a confined bathymetric zone between 600 and 1000 m water depth. Cold-water corals seem to be restricted in their growth by temperature and food availability. The presence of living corals on top of the carbonate mounds appears linked to the presence of internal waves and tidal currents in the water column, and consequently carbonate mound structures are shaped by the local hydrodynamic regime. Mound clusters have an elongated shape perpendicular to the regional contours and corresponding to the direction of the highest current speeds. On the SW RT margin temperature, salinity and current speed reflect a diurnal tidal pattern, causing maximum temperature variations at 900 m depth of more than 3 °C. Current speeds up to 45 cm s⁻¹ occur, and a residual current of 10 cm s⁻¹ is directed along the slope to the southwest. At the SE RT margin the temperature of the bottom water fluctuates more than 1 °C with a semi-diurnal tidal cyclicity. Amplitudes of average and peak current speeds here are comparable with those measured on the southwest margin, but the residual current in this area is directed to the northeast. Tidal currents and internal waves at both margins force the formation of intermediate and bottom nepheloid layers and bring fresh food particles with increased velocity to the mounds. The distribution of corals in both mound areas is considered directly related to the presence of enhanced turbidity. An increase in temperature can be directly related to an increase in the amount of particles in the water column. Current velocity increases when a transition occurs from cold to warm waters. High current velocities prevent local sedimentation but provide sufficient food particles to the corals, so that the corals thrive at the mound summits.     

Helen's Reef: a microgabbroic intrusion in the Rockall intrusive centre,Rockall Bank

Rockall Island is composed of 52 ± 9 Ma (m.y.) aegirine granite and forms part of a nearly planated intrusive complex. The nearby Helen's Reef lies within the complex but is composed of Cretaceous (81 ± 3 Ma) microgabbros. The petrography and chemistry of the microgabbros differ from Mid-Ocean Ridge tholeiites but are similar to the Tertiary gabbroic rocks of northwestern Scotland. The relationship of the Cretaceous igneous activity to the evolution of the North Atlantic Ocean is discussed briefly.     

温度对鱼类摄食及生长的影响

Temperature is the critical factor for feeding and growth of fish. Results of studies indicated that, under different temperature, some parameters, such as food consumption (C) , special growth rate (SGR) and ecological conversion efficiency (Eg) changed remarkably. Different fish species had different responsive model to temperature. This paper introduced that the relationship between temperature and growth and feeding of some fishes, including Atlantic cod (Gadus morhua), sea bass (Dicentrarchus labrax), Northern pike (Esox lucius), arctic charr (Salvelinus alpinus), cobia (Rachycentron canadum), turbot (Scophthalmus maximus), and so on, which were studied for a long time in abroad. 　　At the same time, at home , some researchers had found out some rules in their works. Many rules could be described as equations. These researchs have very important signification on assessment of fishery resources and aquaculture.     

Food and feeding of small fish in the Rakaia River,New Zealand

Benthic macroinvertebrates and fish species were collected at monthly intervals during a 12‐month period, from 3 areas of the lower Rakaia River. The composition and abundance of the benthos and stomach contents of the fish were analysed for seasonal trends, food niche breadth and overlap between pairs of fish species, and overlap between the benthos and the diet of each fish species. The diets of bluegilled bully (Gobiomorphus hubbsi), upland bully (G. breviceps), juvenile longfinned eel (Anguilla dieffenbachii), Galaxias brevipinnis, G. paucispondylus, and juvenile brown trout (Salmo trutta) were similar to the proportions of prey species in the benthos. Deleatidium and chironomid larvae dominated the benthos in all seasons and formed the majority of food items in the diet of these species. Food niche overlap between these species was high, indicating potential competition, but preferred habitat and feeding habit differences plus low fish population density and abundance of main prey items probably eliminate the occurrence of any serious competition. The diet of the other fish species differed from this pattern. The common bully (Gobiomorphus cotidianus) ate proportionally more chironomid larvae and fish eggs than occurred in the benthos; torrentfish (Cheimarrichthys fosteri) ate proportionally more chironomid larvae than occurred in the benthos; and quinnat salmon (Oncorhynchus tshawytscha) depended largely upon prey species of terrestial origin, such as adult Deleatidium and dipterans.     

Bottom currents in Nankai Trough and Sagami Trough

Mean flows and velocity fluctuations are described from direct measurements of bottom currents made at three stations across Nankai Trough and two stations in Sagami Trough from May 1982 to May 1984. Aanderaa current meters were moored 7 m above the bottom. The observed mean flows indicate a counter-clockwise circulation in Nankai Trough with current speeds of 0.9–2.1 cm sec^–1. The mean flows were larger on the slopes than on the flat bottom of the trough. The mean flows observed in Sagami Trough show an inflow into Sagami Bay which is considered to be a part of the Oyashio undercurrent from the north that flows along the eastern coast of Honshu. Velocity fluctuations with periods greater than 100 hr were less energetic in the troughs than those at a station west of Hachijo-jima Island. A highly energetic fluctuation with a period of 66.7 hr was observed on the northern slope of Sagami Trough in the velocity component parallel to the trough axis. A maximum current speed of 49 cm sec^–1 was observed in Sagami Trough.This study was sponsored by the Ministry of Education, Science and Culture, Japan.     

冲绳海槽中南部柱状沉积物氧化还原敏感元素赋存机理与环境指示意义

沉积物中氧化还原敏感元素（Redox Sensitive Element,RSE）含量变化是上覆水体氧化还原环境良好的替代指标。本文通过冲绳海槽中南部两个柱状沉积物（深度：30 cm）粒度、总有机碳、总氮及其同位素含量和氧化还原敏感元素含量等指标,探究复杂环境背景下冲绳海槽柱状沉积物中RSE的赋存机理与环境指示意义。研究发现,柱状沉积物中除了Cr亏损,其他RSE均显示有不同程度的富集。“粒控效应”对冲绳海槽柱状沉积物的RSE含量影响较小;分析可知,海水表层生产力是影响沉积物氧化还原环境的主要因素,通过Mn（氢）氧化物的吸附或解吸附作用实现RSE的富集与亏损。δCe、V/Cr、Ni/Co和V/（V+Ni）等指标指示沉积物整体处于氧化−弱氧化环境。沉积物中Mn元素通过还原作用以Mn²⁺形式向上扩散,在25～30 cm处被含氧间隙水氧化富集形成锰峰,指示柱状沉积物0～25 cm处为氧化环境,25～30 cm处为弱氧化环境。     

Occurrence and recruitment of fish larvae in a northern New Zealand estuary

The occurrence of fish larvae and the effect of diel and tidal variation on catches was studied at about biweekly intervals for a year in Whangateau Harbour, a small well mixed northern New Zealand estuary. Larvae from 31 taxa were identified. The annual pattern of larval occurrence was typical for fish in temperate waters, with a major peak of abundance in early summer. For six taxa, larval densities were significantly greater in night-time than in daytime catches, and analysis of length-frequency distributions suggested that for two species this was due to daytime net avoidance.No significant differences were found between the densities of larvae caught on flood and ebb tides, but changes in length-frequency distributions were significant for two species. Recently hatched larvae of an unidentified goby were found leaving the harbour, where they were probably spawned, while older larvae of this species appeared to be recruiting back in. Larvae of the flounder Rhobosolea plebeia were also apparently recruiting into the harbour. In the absence of a two-layered circulation pattern larvae relied upon tidal transport for recruitment, and probaby ensured their retention by rapidly settling to the bottom.     

Social interactions can affect feeding behaviour of fish in tanks

Fish from the same clutch of eggs, so of the same age and family, can differ substantially in size after some time in a tank as result of social interactions. On the basis of computer simulation studies I here demonstrate that it is possible to mimic this empirical observation using the rules of the standard Dynamic Energy Budget (DEB) model, supplemented with a simple stochastic module for interaction between individuals that have identical parameters. The remarkable result is that length-at-age of two individuals in a tank where the number of food particles is kept constant closely follows von Bertalanffy growth curves with very different parameters, while in reality the individuals have identical parameters. The empirical observation demonstrates that fish are close to the supply end of the supply–demand spectrum and that age-based models for growth don't apply to supply systems. The significance of the result is discussed.