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1.
Eggs of rainbow trout (Salmo gairdneri Richardson) from five different lakes in North Island, New Zealand, were reared to discover whether they showed significant differences in survival which could be linked with DDT levels in the tissue. The muscle and gonads of pre‐breeding season fish and the parent females were assayed for DDT, as were the whole fry at the end of rearing. The highest DDT levels were found in fish from Lake Rerewhakaaitu, and eggs from these fish showed the least viability. Mortality was relatively low among eggs from fish out of the other lakes. Thus, DDT may possibly contribute to the high mortality found in eggs from Lake Rerewhakaaitu fish.  相似文献   

2.
Landlocked sockeye salmon (Oncorhynchus nerka), ranging in fork length (FL) from 105 to 313 mm, were captured in fine‐mesh gill nets set in the limnetic zone of the Waitaki hydro lakes (44° 30′ S, 170° 10’ E) in the South Island, New Zealand. A total of 443 stomachs was examined and the frequency of occurrence, volume and weight of prey items calculated. In the Ahuriri Arm of Lake Benmore the principal food (54% by weight) was zooplankton (Boeckella dilatata) whereas in the Haldon Arm of Lake Benmore it was larval and juvenile common bullies (Gobiomorphus cotidi‐anus) (73% by volume). In Lake Waitaki in winter, salmon had eaten insects (43% by volume) with smaller amounts of snails (Potamopyrgus antipo‐darum, 23%) and bullies (24%). In Lake Ohau adult insects may be an important food. There were also variations in diet with season and fish size. The stomachs of 147 brown trout (Salmo trutta) and 181 rainbow trout (S. gairdnerii) caught in the same gill nets were also examined. In contrast to sockeye salmon stomachs they contained negligible amounts of zooplankton (< 1% by weight) and large amounts of aquatic insects (50–58% by weight in the Ahuriri Arm of Lake Benmore). Comparisons with juvenile sockeye salmon and kokanee in North American lakes are made. The impact of introductions of sockeye salmon into other New Zealand lakes is discussed.  相似文献   

3.
An unusually high mortality of eggs and fry of rainbow trout (Salmo gairdneri Richardson) from Lake Taupo in 1966 was possibly caused by excessive exposure to DDT and its metabolites. The egg and fry mortality (44.6%), and DDT level in the fry (4.63 ppm), was compared with other similar cases of possible DDT poisoning in young salmonids, both in New Zealand and North America. Other possible adverse effects on young salmonids exposed to DDT were discussed.  相似文献   

4.
In order to characterize our study area and to provide reference values to be used in the future to measure the changes produced by an increase in contamination, the concentrations of chlorinated hydrocarbons have been investigated in fifty-one samples of seawater, taken at four different depths: air-sea interface, surface, one metre and bottom waters, and in twenty-three samples of surface sediments from Blanca Bay, Argentina. Of eleven organochlorine compounds we were looking for (α BHC, lindane, heptachlor, δ BHC. aldrin, heptachlor epoxide, dieldrin, o-p′DDD, p-p′DDD, o-p′DDT and p-p′DDT), seven could be detected in seawater and three in surface sediments with the following mean concentrations: α-BHC=48·2 ng l?1; lindane=54·2 ng l?1; heptachlor=45·0 ng l?1; δ BHC=12·5 ng l?1; aldrin=61·8 ng l?1 and ΣDDT=67·0 ng l?1; and δ BHC=3·2 ng g?1; lindane=4·2 ng g?1 and heptachlor=1·0 ng g?1 for seawater, regarding the surface waters, and sediment samples, respectively.Concentration factors among the different water layers were also studied to see if there was any correlation between chlorinated hydrocarbon contents and the water depths from which the samples were taken. As a mean value, the air-sea interface water contains 18 times more of these compounds than that of the water near the bottom. A comparison of the values corresponding to seawater and surface sediments from our study area with those levels measured in samples from other geographic locations is also presented.With the purpose to detect a relationship between chlorinated hydrocarbon concentrations and the contents of particulate matter (PM) on the one hand, and particulate organic material (POM) on the other hand, four groups of samples containing different amounts of PM and POM, respectively were formed. From a comparison of the results obtained, lindane, heptachlor and δ BHC showed a tendency to lower concentrations in those samples containing little PM whereas α BHC and aldrin remained without important changes. No significant correlation was found between organochlorine levels and contents of POM.  相似文献   

5.
Temporary removal of aquatic plants in Lake Parkinson, a small, eutrophic dune lake, resulted in a number of changes to the population of stocked rainbow trout (Salmo gairdnerii). During each summer the lake stratified and low oxygen levels limited the distribution of trout to shallow (0–4 m) surface waters. In the first summer following weed removal the numbers of black shags (Phallacrocorax carbo) counted at the lake increased, and their predation resulted in a decline in trout density. However, the growth rate and condition of the trout population then exceeded that of trout present before weed removal. During the second summer after weed removal a cladoceran bloom was followed by low phytoplankton levels and high ammonia concentrations. A prolonged calm compounded this situation with the result that oxygen levels in bottom and surface waters dropped below 2 ppm. These low oxygen levels eliminated the trout population, but other fish species present survived. Elimination of aquatic plants affected the population dynamics of other fish species in the lake with potential implications for the trout. The experiment demonstrated the importance of weed beds in maintaining a stable fish community in lakes such as Lake Parkinson.  相似文献   

6.
The diet of brown trout (Salmo trutta) and rainbow trout (S. gairdnerii) was studied in specimens from Lake Benmore, a deep, oligo‐trophic lake in South Island, New Zealand. Between November and July, both species fed mainly on small molluscs (Potamopyrgus antipodarum, Physa sp., and Gyraulus corinna) gleaned from the littoral weed beds. Energy values for the three species of mollusc were determined: P. antipodarum, 6000 J g‐1; G. corinna, 5500 J g‐1; Physa sp., 9800 J g‐1. Potamopyrgus antipodarum yielded little energy to the fish, unless its shell broke during passage through the gut. Physa sp. was the most profitable mollusc, irrespective of shell breakage and Potamopyrgus antipodanim the least profitable. The mean energy value per snail for G. corinna and Physa sp. eaten by rainbow trout was 25–30% less than for snails eaten by brown trout, possibly because rainbow trout ingested empty shells from the sediment surface. Rainbow trout extracted about 20% more energy than brown trout from unbroken shells. In July, 84% of the brown trout switched to predation of common bullies, Gobio‐morphus cotidianus, probably as a result of bully reproductive behaviour. Rainbow trout did not show the same change, apparently because they were feeding in deeper water where few bullies were available. The low‐energy diet and its possible connection with growth rate are discussed.  相似文献   

7.
The presence of suitable gravel size alone can stimulate female rainbow trout (Salmo gairdneri) to excavate nests for spawning on the shores of Lake Rotoma. Emergent fry result from lake‐shore spawning, and could contribute significantly to the trout fishery in Lake Rotoma. Lake‐shore spawning could be enhanced by the use of stable artificial spawning beds that have adequate depth and appropriate sizes of gravel.  相似文献   

8.
Five lakes, varying from 10 to 100 hectares in area and each containing an existing population of Salmo gairdneri, were gill‐netted and stocked with tagged fish each year from 1960 to 1965 to determine the effect of regular stocking on the size and numbers of fish present. There was little natural spawning of trout in most of the lakes. Growth in length and weight of tagged fish was computed and an annual estimate of population calculated from the netting returns. Appendices give details of the statistical analyses of the data.

Fish production has been correlated with the trophic status of the lakes as indicated by their temperature and oxygen content. There was no clear relationship between lake size and trout production but trout production decreased as the environment became more eutrophic. Results also showed a close inverse relationship between numbers supported and average weight achieved by the trout. It is concluded that the angling potential of local lakes can be maintained despite the eutrophication resulting from intensive agricultural development of the catchments. These lakes will produce large‐sized fish if the trout population is kept relatively small.

Loss in weight in brown and rainbow trout as a result of spawning activities in local lakes and streams was found to be similar. Both male and female fish lost between 22 and 40 percent of their weight over a spawning period. This probably accounted for the observed low‐condition factor among older fish in the lake populations.  相似文献   

9.
New cold‐water coral (CWC) sites were recorded along the Apulian margin (Central Mediterranean). The species composition and depth distribution of CWCs were updated. A distribution of the CWC sites coincident with the course of the dense‐water masses that flow between the Southern Adriatic and Northern Ionian was confirmed. The faunal assemblages of five of these CWC sites were investigated and compared using experimental longlines during the spring–summer and autumn–winter seasons, between 2010 and 2014. Differences in ecological variables amongst the sites in each season were evaluated by means of a set of univariate and multivariate methods (analysis of variance, permutational multivariate analysis of variance, non‐metric multidimensional scaling). Although some differences were detected in relation to the different depths examined during spring–summer, the CWC sites showed similar features in terms of species richness and diversity as well as in the abundance of the same fish species (Galeus melastomus, Conger conger, Helicolenus dactylopterus, Merluccius merluccius, Phycis blennoides and Pagellus bogaraveo) most probably because of the distribution of adult specimens in structurally complex and heterogeneous habitats, which act as a potential ‘refuge network’ with respect to commercial fishing. The presence of maturing and mature individuals as well as post‐reproductive females indicates that these CWC sites also act as spawning areas, representing a potential ‘renewal network’ for the fish populations. The term ‘network’ used here refers to several similar subsystems (CWC sites) that play the same ecological role in a wider system (Apulian margin). These CWC communities need coherent conservation measures and management strategies according to the Ecosystem Approach to Fisheries.  相似文献   

10.
Underwater census and single‐pass electrofishing were compared for estimating relative abundance of juvenile brown trout in the Kakanui River, South Island, NZ. Mean sampling efficiency was lower, and the variability of sampling efficiency was much greater, for underwater census (0+ trout: x = 0.38, s = 0.368; 1+ trout: x = 0.62, s = 0.822) than for single‐pass electrofishing (0+ trout: x = 0.61, s = 0.143; 1+ trout: x = 0.74, s = 0.171). Sampling efficiency of both methods was dependent on temperature. Electrofishing became less efficient at higher temperatures whereas underwater census became less efficient at colder temperatures. The low, and highly variable, sampling efficiency for underwater census of 0+ brown trout was related to substrate hiding behaviour which is dependent on temperature. A ratio method for comparing relative abundance estimates is presented. Minimum significance values for the ratio (R) were derived for 0+ trout using temperature adjusted sampling efficiencies. To be statistically significant, relative abundance estimates made by underwater census had to differ by a factor of 6–7 times, whereas those made by single‐pass electrofishing had to differ only by about 2 times, depending on the number of fish counted. By confining comparisons of relative abundance estimates made by underwater census to the summer period, differences of about 3.5–4 times could be detected statistically. It was concluded that single‐pass electrofishing is superior to underwater census for estimating the relative abundance of juvenile brown trout in shallow (< 1 m) river habitat, especially when temperature varies widely as with season and time of day.  相似文献   

11.
The movements of 92 adult rainbow trout (Oncorhynchus mykiss) from Lake Taupo into the Tongariro River, New Zealand, were monitored using radio‐telemetry every 3 days during the main spawning period between May and November 2003. This study repeated one previously conducted in 1995. Differences in spawning site preference and resting locations between 1995 and 2003 probably reflect differences in the nature of the river as a result of major natural floods that occurred in 1998. Average migration times were slower than in 1995 and the correlation between flow and mean daily movement was less distinct owing to the dry and settled weather during July and August, although fish did respond to freshets when they occurred. Peak movement occurred between 1600 and 2000 h NZ Standard Time with no movement occurring between midnight and 0400. Fish adjusted their movement in response to changing photoperiod. Nineteen fish were observed above the mouths of natal tributary streams for several weeks in the main river stem before entering these tributaries.  相似文献   

12.
We reviewed lakes in New Zealand reported to have undergone regime shifts between macrophyte‐dominated clear water states and de‐vegetated, turbid states. Regime‐shifting lakes (RSLs) occurred along a wide latitudinal gradient. We obtained catchment land‐use data as well as data on the occurrences of introduced (non‐indigenous) macrophytes and herbivorous and benthivorous fish for the 37 RSLs and for 58 lakes with similar maximum depths and climates, but which had not been reported to have undergone regime shifts. All RSLs had a maximum depth <20 m and mean annual surface air temperature between 9 and 16°G Regime shifts were positively related to the percentage of the catchment in pasture and negatively related to the percentage of the catchment in forest. The occurrences of the introduced macrophyte Egeria densa and the introduced fish, Ameiurus nebulosus (catfish), Carassius auratus (goldfish), Scardinius erythrophthalmus (rudd), Cyprinus carpio (koi carp), and Tinca tinca (tench), were significantly correlated to regime shifts in lakes. Although the presence of other introduced aquatic macrophytes was not significantly correlated with RSLs, the number of exotic fish taxa present in lakes was strongly positively correlated with increasing prevalence of regime shifts. The strength of the correlations between land use and introduced species versus regime shifts illustrates a number of factors which could be managed to reduce the susceptibility of lakes to regime shifts and to restore lakes that have become de‐vegetated. Our findings also suggests that regime shifts in lakes were unlikely to have been common in New Zealand lakes before anthropogenic deforestation and introductions of introduced aquatic taxa.  相似文献   

13.
The diets of eight demersal fish species from the upper continental slope (c. 24CM‐50 m) were determined from samples taken during late January and early February 2004, off the Wairarapa coast, North Island, New Zealand. Diets were from a combination of benthopelagic and benthic sources, with most species exhibiting ontogenetic shifts in diet, in that larger‐bodied food (fish and/or natant decapod prawns) was more important in the diets of larger fish. Javelinfish (Lepidorhynchus denticulatus), silver roughy (Hoplostethus mediterraneus), and capro dory (Capromimus abbreviatus) had predominantly benthopelagic diets, whereas the diets of sea perch (Helicolenus percoides), Bollons’ rattail (Caelorinchus bollonsi), two‐banded rattail (C. biclinozonalis), and silverside (Argentina elongata) were predominantly benthic, with the crab Carcinoplax victoriensis an important food item. The diet of Oliver's rattail (C. oliverianus) was a mix of benthopelagic and benthic organisms. Generally, levels of dietary overlap between the eight species were low. Overall, the diets of these fish probably reflect regional and seasonal levels of food availability. Notes on food observed in the stomachs of a further 18 species, for which there were fewer than 10 stomach samples per species are also provided.  相似文献   

14.
The limnology of Lake Rerewhakaaitu (36°18'S, 176° 30'E) was studied at various intervals between 1971 and 1974; comparisons were made between the main lake (area 6.32 km2, mean depth 7 m, maximum depth 15 m), and the smaller (0.15 km2) and deeper (mean depth 15 m, maximum 31 m) crater which are connected by a narrow, 1 m deep channel. The main lake was usually homothermal, although temporary stratification periodically occurred, and the oxygen content of the deeper water could be as low as 2 g.m‐3. The crater showed strong thermal and chemical stratification persisting well into the winter. Its heat budget and other factors related to lake stability are compared with those of some other New Zealand lakes. The failure of the crater to become fully re‐oxygenated during its brief period of homothermy is believed to be related to its morphometry, since the amount of phytoplankton did not appear to be great enough to explain the low levels of dissolved oxygen in the hypolimnion. The hypolimnetic oxygen deficit in 1973–74 was 0.038 mg. cm‐2.day‐1. Qualitatively the phytoplankton, usually dominated by desmids, was characteristic of oligotrophic waters, but quantitatively the main lake could be rated as mesotrophic. Differences were also found in the abundance of zooplankton between the crater and the main lake: there were usually more Bosmina but considerably fewer Ceriodaphnia in the main lake which had greater numbers of Piona. Adult Calamoecia were generally more abundant in the crater.  相似文献   

15.
A small‐scale experiment was done to test the feasibility of thermally marking hatchery‐reared rainbow trout (Oncorhynchus mykiss Walbaum) fry that are released into rivers and impoundments in New South Wales (NSW), Australia. Fry of rainbow trout were exposed to two different 48‐h thermal cycles each of a cold and warm water period. One thermal regime consisted of a cold water period during which the temperature was reduced from 14 to 8°C for 18 h followed by a return to 14°C for 30 h. For the second thermal treatment, water temperature was reduced to 4°C for 10 h followed by a period of 38 h at 14°C. Thermal cycles were repeated 4 and 8 times for each thermal regime, respectively. Following a growth period after treatment, obvious marks were visible on all treated otoliths as distinct from control otoliths. The 10°C differential treatment created the most visible patterns and growth of these fish was not significantly different from control fish. This marking method could be applied to normal hatchery practices to evaluate the effectiveness of large‐scale rainbow trout stockings in NSW.  相似文献   

16.
Brown trout Salmo trutta Linn, were marked with individual tags and recaptured throughout a year in two small Canterbury streams. The growth recorded showed a marked seasonal variation which differed in pattern in the two streams. There was a considerable difference in the growth rate between the two populations and fish transferred from the slow‐growth stream to the faster‐growth stream showed an immediate response to the change.  相似文献   

17.
Measurements of selenium in sediments and benthic infauna of Lake Macquarie, an estuary on the east coast of Australia, indicate that sediments are a significant source of selenium in the lake's food web. Analysis of surficial sediment samples indicated higher selenium concentrations near what are believed to be the main industrial sources of selenium to the lake: a smelter and a power station. Sediment cores taken from sediments in Mannering Bay, near a power station at Vales Point, contained an average of 12 times more selenium in surficial sections than sediment cores from Nord's Wharf, a part of the lake remote from direct inputs of selenium. The highest selenium concentration found in Mannering Bay sediments (17.2 μg/g) was 69 times the apparent background concentration at Nord's Wharf (0.25 μg/g). Pore water concentrations in Mannering Bay were also high, up to 5 μg/l compared to those at Nord's Wharf which were below detection limits (0.2 μg/l). Selenium concentrations in muscle tissues of three benthic-feeding fish species (Mugil cephalus, Platycephalus fuscus, Acanthopagrus australis) were significantly correlated (p<0.05) with surficial sediment selenium concentration. Selenium concentrations in polychaetes and molluscs of Mannering Bay were up to 58 times higher than those from Nord's Wharf. Two benthic organisms, the eunicid polychaete Marphysa sanguinea and the bivalve mollusc Spisula trigonella, were maintained at different densities in selenium-spiked sediments. Both animals accumulated selenium from the spiked sediment, confirming that bioaccumulation from contaminated sediments occurs. Collectively, these data suggest that benthic food webs are important sources of selenium to the fish of Lake Macquarie.  相似文献   

18.
高原湖泊鱼类生长特性与形态差异研究   总被引：1，自引：0，他引：1  
根据2009年8—11月洱海流域采集的2991尾鱼类样本,研究了其生长特性与形态差异。结果表明,洱海流域大部分鱼类表现为匀速生长或近匀速生长,但有两种鱼类(中华青、大理裂腹鱼)呈现强异速生长。肥满度以吃食性鱼类最高(鲫、鲤、团头鲂),滤食性鱼类次之(鲢、鳙)。对主要优势种——麦穗鱼、鲫的形态分析表明,洱海麦穗鱼、鲫种群与西湖、茈碧湖、海西海三个湖泊的麦穗鱼、鲫种群在形态上均无显著差异。西湖、茈碧湖、海西海三个湖泊的麦穗鱼种群之间以及鲫种群之间均存在种群间差异(C.D<1.28),其中茈碧湖、海西海两个湖泊的鲫种群在眼径/头长性状上的差异达到亚种水平(C.D=1.5)。  相似文献   

19.
The submerged vegetation of Lakes Sumner, Marion, Katrine, Taylor, and Sheppard was surveyed in May 1987. These high‐altitude lakes lie at c. 600 m a.s.l., within the largely unmodified upper Hurunui catchment. Submerged vegetation was diverse and included numerous short shallow‐water species, dense swards of Isoetes alpinus, low covers of taller native vascular plants, and charophyte meadows beyond the depth limit of vascular plants to a maximum of 15 m. A sparse deepwater bryophyte community was observed from 11 to 32 m depth in Lake Sumner. Displacement of native vegetation by dense growths of the adventive oxygen weed Elodea canadensis over mid‐depths of 3–6 m was noted in all lakes, except Lake Marion.  相似文献   

20.
Fourteen hundred trout, mainly Salmo gairdneri, supplied by the four Government and nine Acclimatisation Society hatcheries in New Zealand were examined for the presence of spores of Myxosoma cerebralis (Hofer, 1903) (Protozoa: Myxosporida) in their head cartilage. The only positive result obtained was of a 24% infection rate in fish from the Otago Acclimatisation hatchery at Waitati, near Dunedin, which has since been closed down. Sixty fish were examined from Acclimatisation Societies hatcheries and 200 from Government Hatcheries to give a 95% chance of detecting infections of 5% and 1.5%, respectively, of the fish in these hatcheries. A formula is given for estimating sample sizes on the bases of probable infection rates and the degree of certainty of detection that is required.  相似文献   

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