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Young J.W.,CSIRO | Lansdell M.J.,CSIRO | Campbell R.A.,CSIRO | Cooper S.P.,CSIRO | And 2 more authors.
Marine Biology | Year: 2010

We examined the feeding ecology and niche segregation of the ten most abundant fish species caught by longline operations off eastern Australia between 1992 and 2006. Diets of 3,562 individuals were examined. Hook timer data were collected from a further 328 fish to examine feeding behaviour in relation to depth and time of day. Prey biomass was significantly related to predator species, predator length and year and latitude of capture. Although the fish examined fed on a mix of fish, squid and crustacea, fish dominated the diet of all species except small albacore (Thunnus alalunga) which fed mainly on crustacea and large swordfish (Xiphias gladius) and albacore which fed mainly on squid. Cannibalism was observed in lancetfish (Alepisaurus spp.). Multidimensional scaling identified three species groups based on their diet composition. One group consisted of yellowfin tuna (T. albacares), striped marlin (Tetrapturus audax) and dolphinfish (Coryphaena hippurus); a second group consisted of bigeye tuna (T. obesus), swordfish and albacore; and a third consisted of southern bluefin tuna (T. maccoyii) and blue shark (Prionace glauca). Of note was the separation of mako shark (Isurus oxyrhynchus) and lancetfish from all other predators. Prey length generally increased with increasing predator length although even large predators fed on a wide range of prey lengths including very small prey. Overall, differences in prey type and size, feeding times and depths were noted across the range of species examined to the extent that predators with overlapping prey, either in type or size, fed at different times of the diel period or at different depths. Taken together these data provide evidence for feeding niche segregation across the range of oceanic top predators examined. © 2010 Springer-Verlag. Source

Swadling K.M.,Tasmanian Aquaculture and Fisheries Institute | Kawaguchi S.,Australian Antarctic Division | Hosie G.W.,Australian Antarctic Division
Deep-Sea Research Part II: Topical Studies in Oceanography | Year: 2010

The distribution of mesozooplankton, based on the catch by a RMT1 net, in the upper 200 m of the South Western Indian Ocean sector (30°E-80°E) of the Southern Ocean was examined during the large-scale BROKE-West survey in summer 2006. Multivariate analyses revealed four groups of zooplankton that could be broadly linked to oceanographic features. The first group, occurring south of the southern boundary of the Antarctic Circumpolar Current (sbACC) and west of 40°E, was associated with waters from the eastern limb of the Weddell Gyre. The group was typified by moderate abundance (mean: 11,251 ind. 1000 m-3) and included foraminiferans, appendicularians and small copepods. Group 2 was composed of stations found in the deeper, warmer waters lying between the sbACC and the southern ACC front (sACCf), along with a few stations north of the sACCf. Sites in this group exhibited the highest mean zooplankton abundance (81,750 ind. 1000 m-3) and comprised large numbers of small copepods and appendicularians. Sites in group 3 fell south of the sbACC, were situated east of 50°E, and generally located near the Antarctic slope current (ASC), a strong and narrow jet of westward flowing water. Typical species for this group included Euphausia crystallorophias, Fritillaria spp. and Metridia gerlachei. Finally, group 4 represented neritic sites in the far southwestern corner of the survey region. Abundances were lowest (mean: 2588 ind. 1000 m-3) and the assemblage was dominated by E. crystallorophias, Neogloboquadrina pachyderma and Fritillaria spp. The four groups differed more by abundance than by composition. The suite of environmental variables that best correlated with patterns in the species data included chlorophyll a concentration, proximity to the ASC and length of time without an ice cover, all features which indicated that large scale oceanographic processes were underpinning the patterns in mesozooplankton distribution. © 2009 Elsevier Ltd. Source

Kawaguchi S.,Australian Antarctic Division | King R.,Australian Antarctic Division | Meijers R.,University of Tasmania | Osborn J.E.,University of Tasmania | And 3 more authors.
Deep-Sea Research Part II: Topical Studies in Oceanography | Year: 2010

Schooling behaviour of Antarctic krill was induced repeatedly over a period of one year in the Australian Antarctic Division research aquarium. The details of the laboratory setup suitable for krill to school are described. Light intensity and food condition were found to affect krill swimming patterns and schooling behaviour. Krill swam in polarised groups and responded as a group to objects that produced sharp contrasts but not to less distinct objects. Schools broke up when they encountered dense phytoplankton patches, and aggregated more tightly when kept with a white featureless background. The diel nature of school formation was observed under simulated natural light conditions with stronger and tighter schools during daytime and no obvious schooling behaviour during night. These behavioural patterns are further discussed in terms of their costs and benefits of feeding and predation risk, in conjunction with the diel vertical migration behaviour of krill. Crown Copyright © 2009. Source

Young J.W.,CSIRO | Guest M.A.,Tasmanian Aquaculture and Fisheries Institute | Lansdell M.,CSIRO | Phleger C.F.,CSIRO | And 3 more authors.
Progress in Oceanography | Year: 2010

Signature lipid and fatty acid analysis were used to discriminate the diet of swordfish (Xiphias gladius, orbital fork length: 60-203 cm) from waters off eastern Australia. The fatty acid (FA) composition of a range of known prey (squid, myctophids, and other fishes) of swordfish, taken from stomach samples and from net tows, was compared with that of the white muscle tissue (WMT) of swordfish from the same region. Swordfish muscle was lipid rich (average 24-42% dry weight), as was the skeleton (28-41%). The robustness of the approach was also tested by comparison against a key squid prey species that was collected and stored using different protocols: (i) fresh frozen, (ii) fresh frozen, then thawed, and (iii) stomach content collection. The FA profiles were generally similar, with the ratio of docosahexaenoic acid (DHA) and palmitic acid (16:0) in particular showing no significant difference. Major fatty acids in swordfish WMT were 18:1ω9c, 16:0, 22:6ω3, and 18:0. Multidimensional scaling showed that the swordfish WMT grouped closely with small fish prey including myctophids, and not with squid. Squid contained markedly higher 22:6ω3 than swordfish. Individual prey species of the myctophidae could also be separated by the same technique. These results were supported by traditional stomach content analyses (SCA) that showed fish were the dominant prey for small swordfish sampled from southern waters whereas squid were the main prey in more northern waters, matching the FA patterns we found for the two regions. We propose that where general diet patterns are established, signature FA analysis has good potential to compliment or in some cases, replace temporal and spatial monitoring of trophic pathways for swordfish and other marine species. © 2010. Source

Oakes J.M.,Southern Cross University of Australia | Eyre B.D.,Southern Cross University of Australia | Ross D.J.,Tasmanian Aquaculture and Fisheries Institute | Turner S.D.,Southern Cross University of Australia
Environmental Science and Technology | Year: 2010

Stable isotope analysis of a novel combination of carbon and nitrogen pools traced inputs and processing of primary-treated (PE) and secondary-treated effluent (SE) from a paper and pulp mill (PPM) in a temperate Australian estuary. Distinct carbon stable isotope ratios of dissolved organic carbon (DOC) near the PPM outfall indicated large PE and reduced SE inputs of DOC. DOC was remineralized to dissolved inorganic carbon regardless of season, but rates were lower in winter. PE discharge in winter elevated DOC concentrations along much of the estuary. Distinct stable isotope ratios confirmed particulate organic matter (POM) input from PE and SE to the water column and into the sediment. This was relatively localized, indicating rapid POM settlement regardless of season. SE discharge increased nutrient inputs and enhanced algal productivity, particularly in summer when chlorophyll-a concentrations were elevated throughout the estuary. SE discharge reduced pCO2 from levels associated with PE discharge. However, the estuary remained heterotrophic as subsequent respiration or decomposition of algal material offset reductions in PPM organic matter input. The influence of the PPM was apparent throughout the estuary, demonstrating the ability of anthropogenic inputs, and changes to these, to affect ecosystem functioning. © 2010 American Chemical Society. Source

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