Demersal fish assemblages off the Seine and Sedlo seamounts (northeast Atlantic)

Seamounts are thought to support special biological communities, and often maintain high standing stocks of demersal and benthopelagic fishes. Seamount fish fauna have been described in several studies but few works have included species taken below 600 m. The demersal fish assemblages of the Seine and Sedlo seamounts (northeast Atlantic) from the summits to 2000 m depth were investigated based on longline survey catch data, conducted as part of the OASIS project. A total of 41 fish species from 24 families were caught at Seine near Madeira, and 30 species from 19 families were caught at Sedlo north of the Azores. Both fish faunas have high affinities with the neighbouring areas of the Azores, Madeira and with the eastern North Atlantic and the Mediterranean Sea. Overall abundances and mean body weights were slightly higher at Sedlo seamount, appearing in conformity with the latitudinal effect of increasing species abundance and productivity from south to north. The differential influence of the Mediterranean Water at each seamount may contribute to explain (a) the differences found in vertical distribution of common species, which tend to distribute deeper at Seine, and (b) the observed changes in the species composition and dominance in deeper waters. Multivariate analysis revealed a vertical structure that is approximately coincident with the expected zonation of water masses at each seamount. Physiological tolerance to the prevailing vertical hydrological conditions may explain the species distribution and the large-scale vertical assemblage structure found. However, further ecological factors like productivity patterns affecting the amount and quality of the available food appear to shape the abundance, diversity or dominance patterns of functional groups within those main assemblages. At Seine, the species Trachurus picturatus dominated the catches, mainly at the shallower edge of the plateau, appearing consistent with the sound-scattering layer interception hypothesis [Isaacs, J.D., Schwartzlose, R.A., 1965. Migrant sound scatterers: interaction with the sea floor. Science 150, 1810–1813]. At both seamounts mesopelagic feeders (e.g., Beryx splendens) dominate the upper-slope assemblages (<800 m), while the mid-slope assemblages (800–1200/1300 m) and the lower-slope assemblages (>1300 m) were dominated by squaliform species (e.g., Centrophorus squamosus, Centroscymnus coelolepis, Etmopterus princeps) along with Mora moro or the Antimora rostrata. The lower abundance of C. squamosus observed at Seine may be a result of the fishing activities in the area, since the species is an important by-catch of the black-scabbard fish fishery in the Madeira archipelago. The slightly higher predominance of scavenger species at Seine in deeper assemblages may be the result of an ecological response favouring this functional group in lower productivity regimes. Especially relevant was the record of large reproductive aggregations of B. splendens and Epigonus telescopus found at the edge of the Sedlo plateau.     

Demersal assemblages and depth distribution of elasmobrachs from the continental shelf and slope off the Balearic Islands (western Mediterranean)

When this article was originally published the author's     

The structure of demersal assemblages off Namibia in relation to abiotic factors

Groundfish surveys carried out between October 1992 and October 1996 were used to describe the demersal assemblages of the northern Benguela along the Namibian coast. Multivariate analyses indicated a clear separation between shelf and slope habitats, which were divided into three and two assemblages respectively. These divisions were distinct, with clear distributional boundaries separating them. Species determining the structure of these divisions and subdivisions and their relative abundances were identified. Depth, bottom temperature, bottom salinity and dissolved oxygen were all significantly correlated with the spatial distribution of the assemblages. Minor changes or shifts in the distribution of assemblages were observed over the study period, although patterns of species associations remained relatively constant.     

Distribution of Delphinidae (Cetacea) in relation to sea surface temperatures off Eastern and Southern New Zealand

Records of four species of Delphinidae, Delphinus delphis, Lissodelphis peroni, Lagenorhynchus obscurus, and Lagenorhynchus cruciger in waters to the east and south‐east of New Zealand are discussed in relation to surface temperatures.

In this region D. delphis appears to be largely confined north of the Subtropical Convergence and a minimum surface temperature of about 14°c, and near New Zealand from Hawke Bay southward in the warm water of the East Cape Current; L. peroni to the Subtropical Convergence and the subantarctic water to the south of it, between surface temperatures of 9°c and 16°c; L. obscurus to the immediate vicinity of the Subtropical Convergence and surface temperatures in summer of about 14° to 15°c, and L. cruciger across the Antarctic Convergence region, in a surface temperature range of 2° to 9°c.     

Feeding habits of two fish species in relation to invertebrate drift in a New Zealand river

The relationship between the composition of the invertebrate drift fauna and the feeding habits of the common river galaxias Galaxias vulgaris and the upland bully Phily pnodon breviceps was examined in the Glentui River, Canterbury, New Zealand, between 1500 h on 12 November and 1500 h on 13 November 1971. The drift consisted of both night‐active and day‐active components. Galaxias vulgaris fed mainly at night, with peaks of feeding at dusk and dawn. Philypnodon breviceps had two peaks of feeding, at midday and midnight, between the peak feeding times of G. vulgaris. Feeding of G. vulgaris on its major food items coincided with the presence of the food items in the drift, whereas feeding of P. breviceps did not coincide with the occurrence of the food items in the drift. It is concluded that G. vulgaris is primarily an open‐water feeder and that P. breviceps searches for food on the river bed.     

Phytoplankton biornass in relation to the surface hydrography of southern New Zealand and possible effects on the food chain

Abstract

The surface distribution of salinity, temperature, nitrate‐nitrogen (N0₃‐N), and chlorophyll a in the southern New Zealand, Foveaux Strait region in February 1977, 1978, 1979, and 1980 was highly variable. The source of new nitrogen appears to be incursions of high‐salinity water west and east of Stewart Island. Although it seems likely that the source of this high‐nutrient, high‐salinity water is vertical, a horizontal advective source cannot be ruled out The chlorophyll a content of surface waters was not related directly to the NO3‐N concentrations. This lower food chain variability may be linked to variability in economically important species. Oysters grew twice as fast in the summer of 1978/79 as they did in 1979/80. But the mean chlorophyll a values were very similar for February of both years (2.5 and 2.2 μg 1^?1, respectively). The elevated NO₃‐N levels in 1979 may have resulted in much higher phytoplankton levels later that summer and resulted in the higher oyster growth rate that year. The mechanisms driving this variability have yet to be determined.     

Hooker's sea lions in southern New Zealand

The discovery at Stewart Island of a hauling‐out ground regularly used by Hooker's sea lions (Phocarctos hooked) is described, and recent sightings of sea lions in southern New Zealand are reported. An attempted copulation between a male Hooker's sea lion and a dead female fur seal (Arctocephalus forsteri) is also described.     

On the dynamics of demersal fish assemblages off Namibia in the 1990s

Demersal fish surveys carried out off Namibia from 1990 to 2000 were used to study the dynamics of demersal fish assemblages on the shelf and upper slope. The study was performed on each major assemblage, i.e. over the shelf (100–300 m deep) and the slope (300–600 m). Changes in size spectrum, diversity, species composition and trends in abundance of the dominating species were analysed. The most evident changes were those related to overall abundance and diversity of the slope assemblage.     

Larval fish assemblages in nearshore coastal waters off central Chile: temporal and spatial patterns

In this study we identified spatial and temporal patterns in the distribution and abundance of larval stages of several fish species in nearshore waters off central Chile. Larvae were sampled monthly at two close (20 km apart) but contrasting localities, El Quisco and Las Cruces. Surveys corresponded to standard plankton tows stratified according to bathymetry and distance from shore. Our results indicate that at both localities: (1) there is a seasonal reproductive pattern for most of the species studied; (2) there is a seasonal-related change in larval species composition and abundance, with austral Winter–Spring being the time of greatest diversity; (3) larval stages of several species that, as adults occupy intertidal, estuarine–riverine, subtidal, benthic-demersal, epipelagic or mesopelagic habitats, are found within these coastal environments; (4) there is a distinctive cross-shelf pattern of larval distribution, which seems to correspond, at least for the intertidal species, with the shallower (<30 m depth) portion of area surveyed; and (5) there is a coupling between the patterns of distribution and abundance of the entire ichthyoplankton assemblage with short-term physical features such as wind forcing, Ekman transport, and local currents. Our findings suggest that both the specific composition as well as the abundance of larval fish species varies spatially and temporally and that this variability may result from the interaction of physical and biological factors at different scales.     

Variability in the structure of epiphytic assemblages of the Mediterranean seagrass Posidonia oceanica in relation to depth

The aim of the present study was to evaluate whether the variability in the structure of the epiphytic assemblages of leaves and rhizomes of the Mediterranean seagrass Posidonia oceanica differed between depths at a large spatial scale. A hierarchical sampling design was used to compare epiphytic assemblages at two different depths (10 and 20 m) in terms of both species composition and abundance and patterns of spatial variability in the Tuscan Archipelago (North Western Mediterranean Sea, Italy). Results showed significant differences in the structure of assemblages on rhizomes and leaves at different depths. These differences were related to species composition and abundance; differences were not significant for total biomass, total percentage cover and percentage cover of animals and algae. Whereas the higher variability was observed among shoots in all the studied systems, patterns of spatial variability at the other spatial scales investigated differed between the two studied depths. Moreover, in the present study, analogous patterns between depths resulted for both the assemblages of leaves and rhizomes, suggesting that factors that change with depth can be responsible for the spatial variability of both the assemblages (leaves and rhizomes), and operate regardless of the microclimatic conditions and the structure of assemblages.     

Mesoscale distribution of fish larvae in relation to an upwelling filament off Northwest Africa

Fish eggs and larvae were studied in relation to an upwelling filament off Northwest Africa, near the Canary Islands, during August 1993. The filament was entrained around a quasi-permanent cyclonic eddy of diameter 100 km. The sampled ichthyoplanktonic community was dominated by neritic larvae, 94.2% of which were captured in the oceanic area. Horizontal distributions of neritic and oceanic larvae were strongly influenced by the oceanographic features characteristic of the coastal margin. Neritic larvae were associated with upwelling and filament structures, while oceanic larvae were strongly excluded from these features. The results suggest that coastal upwelling and filaments are mechanisms of transport for neritic ichthyoplankton into oceanic waters, that sardine larvae are good tracers of offshore movements of upwelled waters, and that the cyclonic eddy functions as a larval nursery ground for neritic fish species.     

First record of manta rays off New Zealand

Three manta rays were seen and photographed in the western Bay of Plenty, New Zealand, in March 1968. Although the species or genus could not be identified, this sighting represents the first substantiated record of the manta ray family (Mobulidae) in New Zealand and confirms the statements of fishermen that, in summer, mantas occasionally appear in offshore game‐fish waters in north‐eastern New Zealand.     

Macrobenthic polychaete assemblages of the continental shelf and upper slope off the west coast of the South Island,New Zealand

Polychaete assemblages are described from replicate box‐core samples collected in summer 1983 at 18 stations on the continental shelf and upper slope (28–943 m) off the west coast of the South Island, New Zealand, south‐eastern Tasman Sea (c. 41–43°S, 169–172°E). Three main station groupings were identified by multivariate analysis: (1) inner shelf sandy stations characterised by Prionospio australiensis, Aricidea (Acesta) sp., Magelona cf. dakini, Paraprionospio aff. pinnata, Aglaophamus sp., Heteromastus filiformis, and Magelona sp.; (2) middle to outer shelf muddy stations characterised by Levinsenia cf. gracilis, Prionospio australiensis, Paraprionospio coora, Aglaophamus verrilli, and Auchenoplax mesos; and (3) upper slope sandy mud or mud stations characterised by Prionospio ehlersi. A combination of water depth and sediment clay content provided the best correlation with the biotic pattern. Spionidae was the most abundant family (49% of polychaete individuals), which may reflect the scope for opportunistic species in a shelf environment characterised by a high input of terrigenous sediment and episodic upwelling.     

Continental shelf benthos off Otago Peninsula,New Zealand

Benthic macrofauna of the continental shelf off Otago Peninsula, south-eastern New Zealand (45°51′S, 170°52′E) was surveyed by dredge sampling during 1973–1975. Numerical classification (Canberra metric coefficient and flexible sorting) was used to produce site groups and species groups, and three major benthic communities were recognised: a shallow-water (14–25 m) fauna inhabiting well-sorted fine sand, a mid-shelf fauna (concentrated in the depth range 50–76 m) associated with sediments containing the greatest proportions of gravel and siltclay, and a predominantly sand-bottom fauna occurring mainly on the outer shelf (87–150 m). All station groups were dominated numerically by polychaetes (mean of 36·6–56% of individuals) with Mollusca (13·8–25%) or Crustacea (12·1–19·4%) the next most abundant group.The inshore sand fauna was the most distinct, characteristic elements being the trochid gastropod Antisolarium egenum, an amphipod of the genus Hippomedon and dense patches of the spionid polychaete Spiophanes bombyx. Diagnostic species of the mid-shelf mixed sediments were Lepidonotus jacksoni, Psammolyce antipoda, Lumbrineris brevicirra and Phyllamphicteis foliata (Polychaeta), Terenochiton otagoensis, Micrelenchus caelatus caelatus, Maoricolpus roseus roseus and Zegalerus tenuis (Mollusca), Ampelisca chiltoni (Amphipoda) and Amphipholis squamata (Ophiuroidea). Outer shelf sand stations were faunally less distinct, but among the more characteristic species were Euthalenessa fimbriata, Sigalion sp. and Euchone sp. (Polychaeta) and Gari stangeri (Bivalvia). Several abundant species were widely distributed among station groups, notably Nephtys macroura, Lumbrineris magalhaensis, Phyllochaetopterus socialis and Owenia fusiformis (Polychaeta) and Nucula nitidula and Tawera spissa (Bivalvia).Free-living lunulitiform Bryozoa of the genus Otionella were a characteristic component of inner and outer shelf sand faunas, and their inshore penetration probably marks the outer limit of a turbulent zone.Species diversity (Margalef's d) varied markedly across the shelf and appeared to be related primarily to the degree of sediment heterogeneity. Mixed sediments of the middle shelf were particularly rich in species.     

Records of pelagic copepods off Kaikoura,New Zealand

Additions to the pelagic copepod fauna of Kaikoura, New Zealand, include 20 species previously unrecorded and the males of 8 species for which females only had been recorded; further information concerning 2 other species is added.     

Demersal fish and megafaunal assemblages on the Cretan continental shelf and slope (NE Mediterranean): seasonal variation in species density, biomass and diversity

The demersal fish and megafaunal assemblages in the area of Heraklion Bay, Crete, were sampled during four research cruises from September 1994 to September 1995 within the framework of the CINCS project, using a stratified trawl survey at depths ranging from 50 to 1000 m. The sampling at 1000 m depth was the deepest ever made in Greek waters, using a bottom otter trawl. Species density and biomass were found to vary between depths and seasons, with higher values occurring at the shallow stations. Species distribution and communities are also reported. A total of 127 species of osteichthyes, chondrichthyes, crustaceans, and cephalopods were recorded, four of which were found for the first time in Greek waters. Percent similarity index (PSI) was used to assess the differences in the relative abundance of species pairs between depth zones and seasons. Principal component analysis (PCA) was applied to examine station variability statistically.