Sodium fluoroacetate (1080) residues in longfin eels,Anguilla dieffenbachii,following exposure to contaminated water and food

Captive longfin eels (Anguilla dieffenbachii) were exposed to the vertebrate pesticide sodium fluoroacetate (1080) in the water column and through the ingestion of cereal pellet baits or possum muscle and gut tissue that contained 1080 residue. No mortality or unusual behaviour (in comparison with the controls) occurred in eels that were exposed to 1080. However, significantly greater weight loss occurred in eels exposed to 1080 compared with those eels that were not. No residue was detected in tissues of eels exposed to 1080 cereal baits through ingestion and direct (dermal and respiratory) absorption, or through direct absorption only. Low concentrations of 1080 were detected in muscle tissue of eels that consumed contaminated possum muscle (x = 0.0174 μg/g) or gut (x = 0.0306 μg/g) tissue. The primary factors affecting the concentration of 1080 detected in eel tissue included the dose of 1080 (mg/kg) that each eel" receiveddate="and number of days since the eel last fed on contaminated tissue. Based on the 1080 concentrations measured in eels in this study, the risk of acute poisoning to humans from eating contaminated eel flesh is considered extremely low. Even so, national and international perceptions and food safety standards have the potential to limit eel exports and/or close an eel fishery if 1080 residue was discovered in tissue.     

Effect of size grading on the growth performance of shortfin eel (Anguilla australis) during its yellow stage

It is generally believed that size grading in a fish farm improves the total biomass output, because it will minimise the stress imposed by larger individuals over small individuals, resulting in higher feed intake and growth rate. The objective of this study was to evaluate the effect of size grading on individual growth performance of yellow New Zealand shortfin eel (Anguilla australis). A 109 day trial was conducted in a recirculation aquaculture system (RAS) with 103 eels of similar initial weight (101 ± 12 g). All eels were individually marked by PIT (passive integrated transponder) tags. On day 42, eels were graded to establish the following groups: only small eels (S-graded ≤ 135 g), only large eels (L-graded > 135 g), and small and large eels together (S-ungraded and L-ungraded). The large eels showed better specific growth rate (SGR), feed intake (FI) and feed conversion ratio (FCR) than the small eels. Nevertheless, no significant differences were found either between L-graded and L-ungraded or between S-graded and S-ungraded. The age of eels was not significantly different between groups. These findings suggest that the individual growth rate performance of the eels is not primarily a consequence of social interaction among tank-mates.     

Distribution of helminths in the digestive tracts of New Zealand freshwater eels

The distributions of the nematode parasites Paraquimperia sp., Spirocamallanus sp., and Cucullanus sp. in the intestines and recta of Anguilla dieffenbachii and A. australis from Lake Ellesmere and the South Branch of the Waimakariri River were studied over two years. Peak occurrence of Paraquimperia was in the anterior intestine of A. australis and mid intestine of A. dieffenbachii. Male and female Spirocamallanus sp. established in the mid intestine, but as female worms grew they attached more anteriorly and thus maintained the mid body in the mid intestine, prevented the tail end entering the rectum, and maintained the vulvae close to male worms. Cucullanus sp. was most often found in the mid intestine, but occurred throughout the intestine, possibly because of migration with food. Paraquimperia and Spirocamallanus extended their range with crowding; Cucullanus increased in density in the mid intestine. Posteriad movement, with or without subsequent evacuation, was a general feature of all species in both hosts, held live or examined after death. Chilling and freezing slowed or arrested loss from dead hosts. Larger worms (Spirocamallanus sp.) moved and were lost more rapidly than small worms (Paraquimperia sp.); worm loss was more rapid from A. dieffenbachii than from A. australis.     

Distribution of helminths in the digestive tracts of New Zealand freshwater eels 1. Distribution of digeneans

The distributions of Stegodexamene anguillae and Telogaster opisthorchis in Anguilla dieffenbachii and A. australis studied over two years are described. Peak occurrence of S. anguillae was in the anterior intestine, declining posteriorly, except for mature flukes under crowded conditions in A. dieffenbachii which predominated in the mid intestine, declining anteriorly and posteriorly. Peak occurrence of T. opisthorchis was in the rectum of A. australis and posterior intestine of A. dieffenbachii; occurrence declined anteriorly. Distributions appeared to be maintained by selective site segregation. Flukes moved down the tract, with or without subsequent loss, in both host species held live or examined after death. T. opisthorchis were lost before S. anguillae, and the larger mature flukes of both parasite species were lost before the less mobile immature flukes. Fluke loss from electric‐fished A. dieffenbachii was more rapid than from netted A. australis. Chilling and freezing retarded movement in, and evacuation from, dead hosts.     

Prey selection and dietary overlap of shortfinned (Anguilla australis) and longfinned (A. dieffenbachii) eels during summer in the Horokiwi Stream,New Zealand

Benthic macroinvertebrates were collected and the diets of shortfinned eels (Anguilla australis) and longfinned eels (Anguilla dieffenbachii) inhabiting a small coastal New Zealand stream were examined to investigate intraspecific and interspecific trophic partitioning and prey selection. Our results showed intraspecific segregation of preferred prey among three size classes of juvenile shortfinned eels, but there was significant overlap between different size classes of longfinned eels. All size classes of both species of eel fed nocturnally on similar prey, and so there was no indication of temporal or trophic segregation. Therefore, habitat separation is assumed to be the main mechanism to reduce interspecific competition in these two co‐occurring species of eels.     

The growth of New Zealand freshwater eels in three Canterbury streams

The growth of both species of New Zealand freshwater eel, Anguilla australis and A. dieffenbachii, was studied by tagging in three streams using a stainless steel subcutaneous tag. Possible causes of the differences in growth rates are discussed.     

Reexamination of the spawning migration of Anguilla dieffenbachii in relation to water temperature and the lunar cycle

ABSTRACT

The oceanic spawning migration of female Anguilla dieffenbachii eels was previously studied using pop-up satellite transmitting tags (PSAT). The swimming depths and experienced-temperature data of 3 eels released in May 2006 were re-examined in relation to water temperature data, and also lunar cycle and regional hydrography as these latter aspects were not considered in the original study. Eel 2 and Eel 3 initially experienced lower water temperature above 600?m, suggesting they remained south of the subtropical-convergence front longer than Eel 1. Their experienced nighttime minimum depths showed linear relationships with the lunar cycle, because they swam shallower during new moon than during full moon. The eels experienced narrow deep-day temperature ranges at a wide range of depths compared to experiencing narrow shallow-night depth ranges where temperatures varied more widely, indicating that several different factors determine their day and night depth ranges.     

Tagging experiments on blue cod (Parapercis colias) in the Marlborough Sounds,New Zealand

From 1973 to 1976, 2430 blue cod (Parapercis colias) were tagged in the Marlborough Sounds. Tags from 84 fish (3.5%) were returned, after a mean 138 days at liberty. Of these, 71.6% had not moved significant distances. The remainder had travelled up to 41.7 km. Tag shedding rates, as indicated by multiple‐tagging experiments, were high. Results suggest that blue cod of the Marlborough Sounds and the adjacent islands belong to the same stock, and that, while some move significant distances, the majority stay in 1 place for extended periods.     

Microbial activity in natural and organically enriched intertidal sediments near Nelson,New Zealand

Two measures of microbial activity were used to characterise a variety of sediment habitats in three intertidal inlets in the Nelson region, South Island, New Zealand. Rates of microbial mineralisation potential and epibenthic microalgal production were compared with sediment textures, concentrations of photosynthetic pigments, ATP concentrations, and organic and inorganic nutrients. Baseline ranges for these parameters were established for relatively undisturbed estuarine sites for assessing future environmental deterioration and for comparison with sites affected by organic enrichment. Sediment mineralisation rates were increased more than 1000‐fold by enrichment from a fruit processing plant and microalgal production was enhanced by more than 50‐fold at a site exposed to slaughterhouse wastes. The remaining variables, although often strongly correlated with activity measurements, were not as sensitive as measures of enrichment. Sediment microbial activity measurements are proposed as a means of detecting changes in nutrient status of estuarine environments.     

长江口环境条件对日本鳗鲡(Anguilla japonica)鳗苗溯河洄游的影响

长江口是日本鳗鲡鳗苗的手要产区,利用2007年1-5月在长江口的长兴岛、横沙和杭州湾小洋山4个取样点得到的日本鳗鲡鳗苗渔获量数据,初步研究了鳗苗的补充时间分布以及补充量与潮汐、月相等环境因素之间的关系.发现鳗苗在长江口的补.充时间从1月下旬开始到5月中旬结束,鳗苗日产量峰值出现日期从长江口外向内逐渐推迟,与其洄游路线致.长江口附近潮汐为半月潮,每月有两次涨落潮,鳗苗溯河量与潮汐周期呈现一定的节律性,每月有两次鳗苗峰值.河口区鳗苗溯河具有潮流选择性,长江口内鳗苗溯河量起汛潮多于落汛潮:长江口外鳗苗溯河量和潮汐振幅呈现正相关趋势.日本鳗鲡鳗苗的溯河量与月相变化也有一定的关系;朔月望月的平均单网捕捞量之和占总平均单网捕捞量的93.13%,而上下弦只占6.87%.经过方差检验,朔月鳗苗溯河量多于望月,且二者之间存在极显著差异(P<0.01).     

Records of subantarctic fur seals in New Zealand (Note)

Subantarctic fur seals (Arctocephalus tropicalis) appear as stragglers on New Zealand coasts. Four records are noted, the most recent at Antipodes Island in December 1989.     

The influence of habitat availability on juvenile fish abundance in a northeastern New Zealand estuary

Management of fish populations is often focused on the exploitation of adult fish. Maintaining the habitat requirements of all life stages may also be an important consideration. We investigated the value of structured habitat to juvenile fishes within a northeastern New Zealand harbour using artificial seagrass units (ASUs). Specifically, we deployed ASUs across treatments with high vs. low habitat manipulations. We hypothesised that if the abundance of recruiting juvenile fishes was greater on the high habitat availability treatments this would suggest that the availability of habitat was limiting juvenile fish abundance. Our analyses were focused on the four most abundant fishes that settled on our ASUs: snapper (Pagrus auratus); spotty (Notolabrus celidotus); trevally (Pseudocaranx dentex); and an assemblage of pipefish species. For snapper, spotty and pipefish, abundance was greater on the high habitat availability treatments. This result would be unlikely to occur if the availability of juvenile fishes was limiting, suggesting that juvenile fish abundance is more likely to be limited by habitat. In terms of spatial gradients, spotty abundance and size increased with distance into the harbour. The spatial gradient present for spotty indicates the importance of placing the habitat dependency of juvenile fish into a landscape context. Overall, these results demonstrate that maintaining structured habitats may be an important consideration for some valuable inshore fish populations in northeastern New Zealand.     

The application of multivariate statistical methods to phytoplankton counts from the Hauraki Gulf,New Zealand

The phytoplankton population from a station in the Jellicoe Channel area of the Hauraki Gulf, New Zealand, was fairly constant, in terms of total population and species composition, throughout the year. Correspondence analysis enabled us to identify 3 groups of species. The largest of these comprised the core species which were present most of the time and included some, such as the coccolithophores, with a strongly seasonal occurrence. The species in the second group were mainly large centric diatoms and appeared for short periods during the winter months, apparently brought in by incursions of oceanic water. The third group of species occurred between April 1970 and October 1971 when there was a period of unusually warm weather: the winds were lighter and more often blowing onshore and this perhaps led to warmer, less nutrient‐rich surface waters being brought into the Gulf.     

Vertebral abnormalities in free-living Chinook salmon (Oncorhynchus tshawytscha,Walbaum) in New Zealand

Spinal abnormalities are common in farmed Chinook Salmon in New Zealand. We report spinal abnormalities in adult Chinook salmon which were predominantly hatchery reared and released as smolts and which we term free-living. We compare these to rates seen in farmed New Zealand salmon. 101 free-living adult salmon were radiographically assessed for spinal curvatures (lordosis, kyphosis, scoliosis; LKS) and other vertebral abnormalities. Severity of abnormality was assessed on a three-point scale. Abnormal vertebral bodies were detected in 88.1% of free-living salmon. Spinal curvatures were the most common abnormality type with 83.2% of fish showing this abnormality but only one free-living Chinook had LKS of severity greater than 1. Farmed Chinook salmon are reported to have LKS rates of 29% with 18% of LKS abnormalities of severity greater than 1. These results suggest that free-living Chinook salmon frequently develop spinal abnormalities, but these abnormalities are less severe than those observed in farmed salmon.     

Neophrynichthys heterospilos,a new species of fathead sculpin (Scorpaeniformes: Psych rol utidae) from New Zealand

A second species of Neophrynichthys is described from 20 specimens collected from the Campbell Plateau, south of South Island, New Zealand. It differs from its sole congener, N. latus, in having 25–26 pectoral rays (versus 22–24), cirri on head more than twice as large, half as few (c. 50 versus >100), and generally absent from the mid‐region behind the eyes (versus being relatively dense), and in spotted colour pattern covering much less than 50% of the dorsal surface of the head (versus >50%). This new species is the sixth psychrolutid known from New Zealand. The genus Neophrynichthys is formally diagnosed by two synapomorphic characters unique among psychrolutids: having light spots on a dark ground colour and having an open fourth and fifth infraorbital, fifth and sixth cranial arch, medial extrascapular, and posterior tabular of the pterotic.     

Effects of sea urchin (Evechinus chloroticus) grazing in Dusky Sound,Fiordland, New Zealand

Evechinus chloroticus (Val.) is known to be an important grazer of subtidal barren habitats in northern New Zealand but its role in structuring rocky reef communities at colder southern localities is poorly understood. The present study was prompted by a proposal for the establishment of an E. chloroticus fishery in Dusky Sound, Fiordland, New Zealand. To determine the ecological importance of E. chloroticus in Dusky Sound, sea urchins were experimentally removed from shallow fucoid fringe (upper zone), mid‐depth barrens (middle zone), and deeper algal meadow (lower zone), at eight sites and compared with a paired set of eight control sites. Two years of continuous removal of E. chloroticus resulted in conspicuous changes to the algal community at all depth zones examined. The density of fucoid algae (Carpophyllum spp., Sargassum spp., Cystophora spp., and Landsburgia quercifolia) increased mostly in the upper and middle zones, although smaller increases were also observed in the lower zone. Changes in cover of herbaceous, turfing and crustose algae observed in the middle and lower zones were larger than in the upper zone. Density increases of the kelp Ecklonia radiata were observed mainly in the lower zone, although still important in the middle zone. These results show that E. chloroticus can have a strong influence on the structure of algal assemblages in Dusky Sound hence the development of an E. chloroticus fishery in this area should be treated with caution.     

Nyctiphanes australis (Euphausiacea) and an upwelling plume in western Cook Strait,New Zealand

Quantitative data are presented on the distribution of adult and larval stages of the euphausiid Nyctiphanes australis G. O. Sars, in western Cook Strait, New Zealand, an area influenced by an upwelling plume. The behaviour of N. australis in the Kahurangi Point region at different stages of its life history appears to ensure its maintenance, in general, over the continental shelf on an upwelling coast. Population structure at the source of the upwelling near Kahurangi Point differed from that in regions “down stream” from the plume. Nyctiphanes australis was most abundant at the “downstream” eastern end of the upwelling plume, and the evidence suggesting that the dense populations there may be resident is discussed. Possible reasons for low densities of furcilia II and III stages in the eastern plume region are considered.