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Hamilton, New Zealand

Hawes I.,University of Canterbury | Safi K.,NIWA Ltd | Webster-Brown J.,University of Canterbury | Sorrell B.,University of Aarhus | Arscott D.,Stroud Water Research Center
Antarctic Science | Year: 2011

Abstract We observed ice formation and water column attributes in four shallow Antarctic ponds between January and 7 April 2008. During that time ponds went from ice-free to > 80 cm thick ice, near-freshwater to hypersaline, well-lit to near darkness and temperatures fell to below zero. Here we examine shifts in biological activity that accompanied these changes. During February, freeze-concentration and ongoing photosynthesis increased dissolved oxygen concentration to up to 100 mg l-1, with a near-equivalent decrease in dissolved inorganic carbon and a pH rise. Benthic photosynthesis was responsible for 99% of estimated biological oxygen production. Net oxygen accumulation ceased in late February, pH began to fall and inorganic carbon to increase, but the pool of dissolved oxygen was depleted only slowly. Anoxia had been attained in only one pond by April and there was little accumulation of indicators of anaerobic activity. The nitrogen and phosphorus balances of the ponds were dominated by organic forms, which, like DOC and CDOM, behaved conservatively. Conversely, inorganic nitrogen and phosphorus uptake was evident throughout the study period, at a molar ratio of 16N:1P in two of three ponds, consistent with uptake into biological material. We found no coupling between N and P uptake and photosynthesis. © Antarctic Science Ltd 2011. Source


Pinkerton M.H.,NIWA - National Institute of Water and Atmospheric Research | Bradford-Grieve J.M.,NIWA - National Institute of Water and Atmospheric Research | Hanchet S.M.,NIWA Ltd
CCAMLR Science | Year: 2010

A quantitative food web of the Ross Sea is presented here as a step towards investigating ecosystem effects of the fishery for Antarctic toothfish (Dissostichus mawsoni). The model consolidates quantitative information on trophic links across all the major biota of the Ross Sea and tests for data consistency. The model has 38 trophic groups and is balanced in terms of annual fows of organic carbon in an average recent year (1990-2000). The focus of the model is on the role of Antarctic toothfish in the food web which means that the model has greater taxonomic resolution towards the top of the food web than the base. A survey of the available literature and both published and unpublished data provided an initial set of parameters describing the annual average abundance, imports, exports, energetics (growth, reproduction, consumption) and trophic linkages (diets, key predators) for each model group. The relative level of uncertainty on these parameters was also estimated. This set of parameters was not self consistent, and a method is described to adjust the initial parameter set to give a balanced model, taking into account the estimates of parameter uncertainty and the large range of magnitude (>6 orders of magnitude) in trophic fows between groups. Parameters for biomass, production rate, growth efficiency, diet fractions and other transfers of biomass between groups were adjusted simultaneously. It was found that changes to the initial set of parameters needed to obtain balance were reasonably small for most groups and most parameters. The mean absolute change for all key parameters (biomass, production rate, growth efficiency) and all groups together was 1.7%, and for diet fractions was 0.6%. Large but not implausible changes in biomass, production/biomass and production/consumption parameters were needed to balance the microzooplankton (34-47%), ice bacteria (61-72%), and ice protozoa (24-54%), components of the model. Trophic levels are in close agreement with those derived from isotope and other ecosystems. In the balanced model, there is only enough large (>100 cm) toothfish production to satisfy 6.5% of the diet of Weddell seals, 5.6% of the diet of orca and 2.6% of the diet of sperm whales. The model does not support the hypothesis that depletion of Antarctic toothfish by fishing would change the diet of predators of toothfish (Weddell seals, orca, sperm whales) by large amounts throughout the Ross Sea, though the importance of toothfish as prey items to these predators is not tested and requires further investigation. The model shows that large toothfish consume 61% of the annual production of medium-sized demersal fishes and 14% of the annual production of small demersal fishes, implying a potential for the fishery to affect these prey through trophic cascades. There is a need to establish monitoring of medium and small demersal fishes in the Ross Sea, and to model potential changes to these groups due to the fishery. Source


Kingham S.,University of Canterbury | Longley I.,NIWA Ltd | Salmond J.,University of Auckland | Pattinson W.,University of Auckland | Shrestha K.,University of Auckland
Environmental Pollution | Year: 2013

This research assessed the comparative risk associated with exposure to traffic pollution when travelling via different transport modes in Christchurch, New Zealand. Concentrations of PM1, UFPs and CO were monitored on pre-defined routes during the morning and evening commute on people travelling concurrently by car, bus and bicycle. It was found that car drivers were consistently exposed to the highest levels of CO; on-road cyclists were exposed to higher levels of all pollutants than off-road cyclists; car and bus occupants were exposed to higher average levels of UFP than cyclists, and travellers were occasionally exposed to very high levels of pollution for short periods of time. PM10 and PM2.5 were found to be poor indicators of exposure to traffic pollution. Studying Christchurch adds to our understanding as it was a lower density city with limited traffic congestion compared most other cities previously studied. © 2013 Elsevier Ltd. All rights reserved. Source


Parkerk S.J.,NIWA - National Institute of Water and Atmospheric Research | Grimes P.J.,NIWA Ltd
CCAMLR Science | Year: 2010

This study uses histological assessments to determine age- and length-at-spawning for female and male Antarctic toothfish (Dissostichus mawsoni) from fish sampled in the Ross Sea spanning the 2000-2009 fishing seasons. A characterisation of the oocyte developmental cycle of D. mawsoni shows that once development begins, oocytes grow and accumulate at the cortical alveoli stage for at least one year. Individual oocytes are then recruited into the vitellogenic phase over at least a 6-12 month period, resulting in a developed group of oocytes accumulating at the final maturation stage by approximately May each year. The age at 50% spawning for females on the Ross Sea slope region is 16.6 years (95% CI 16.0-17.3) or 133.2 cm (95% CI 130.9-135.7) by length. On average, males spawn at a younger age with an A50% of 12.8 years (95% CI 11.9-14.0) or 120.4 cm (95% CI 114.8-126.7) by length. Evidence of skip-spawning was observed for females only and results in a fatter, right-shifted ogive, increasing the functional difference between male and female ogives. The degree to which the overall population ogive is biased right (older) by applying the slope-derived ogive to the northern Ross Sea region depends on the proportion of the total population occurring in the northern Ross Sea region, which is currently unknown. Source


Parkerk S.J.,NIWA - National Institute of Water and Atmospheric Research | Bowden D.A.,NIWA Ltd
CCAMLR Science | Year: 2010

Implementing measures to avoid significant adverse impacts to vulnerable marine ecosystems (VMEs) requires a specific list of the taxa that are considered vulnerable in the fishery being assessed. New Zealand identified an interim list of taxa to monitor in fishery by-catch in the Ross Sea as part of its benthic fisheries impact assessment. The rationale for including or excluding each taxonomic group is described relative to the group's fragility, longevity, organism size and spatial distribution. Additional considerations such as organism mobility, community diversity, endemism, taxonomic resolution and presence in fishery by-catch are also important. Thirteen coarse-resolution taxonomic groups are identified as vulnerable to bottom longline fishing activities in the Ross Sea region, including two indicator-only taxa. Source

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