摘要:

A heavy infestation of aquatic weeds(Egeria densaandEleocharis sphacelata)in a 1.92 ha lake (Parkinsons Lake, North Island, New Zealand) disappeared within 2 years of the introduction of Chinese grass carp (Ctenopharyngodon idellaVal). The elimination of aquatic plants did not result in any significant change in dissolved oxygen, water temperature, or annual fluctuations in lake levels over the successive 2 years. Dissolved inorganic phosphorus concentrations did not increase appreciably although there was a short term rise in particulate phosphorus levels. Oxidised nitrogen fluctuations were small in the lake over the experimental period. Some reduction in water transparency occurred although chlorophyllalevels showed no overall increase. There were increases in zooplankton numbers and biomass. A large increase of ammonium nitrogen in the lake accrued 12 months after all macrophytes had been eliminated, this possibly was a result of heavy use of inshore water by cattle.

ISSN:0028-8330    

DOI:10.1080/00288330.1984.9516034

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

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.

ISSN:0028-8330    

DOI:10.1080/00288330.1984.9516035

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Differences in feeding between age classes, males and females, and hatchery reared and wild rainbow trout(Salmo gairdnerii)in Lake Rotoma are described. Analysis of results, in conjunction with other published data on trout foods and feeding, showed that there was a summer increase in epibenthic feeding which, in Lake Rotoma, was most apparent in the species of forage fish predated. When trout feeding on forage fish was examined in a variety of lakes, 2 trends emerged. In large, clear, oligotrophic lakes trout fed predominantly on smelt(Retropinna retropinna)which are shoaling, epipelagic fish. Trout in small turbid lakes fed mainly on the solitary, benthic bully(Gobiomorphus cotidianus).These differences in feeding on forage fish were associated with the effects of water temperature and turbidity on trout distribution and foraging behaviour.

ISSN:0028-8330    

DOI:10.1080/00288330.1984.9516036

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Mature rainbow and brown trout fed mainly on drifting invertebrates—caddis larvae and terrestrial insects in summer, and mayflies and stoneflies in winter. Rainbow trout in the Tutaek‐uri system ate more caddis larvae and fewer mayfly and stonefly nymphs than those in the faster‐flowing and more turbulent Mohaka River. The diets of the 2 species in the Mohaka were very similar, although brown trout ate more Nematomorpha and caddis larvae of the speciesOlinga feredayiand fewer of the small‐cased caddisBeraeoptera roriathan did rainbow trout. The overlap in their diets was considerable in both summer and winter. Rainbow trout ate more small (≤ 6 mm) prey than did brown trout, but the modal size of the main foods of both species was virtually identical. The 2 species overlapped in their feeding areas and contested positions. Rainbow trout fed mainly in the head and middle parts of pools at a depth of more than 1 m. Brown trout used rapids and backwaters as well as pools, and fed mainly at a depth of less than 1 m. There was some evidence that brown trout, the larger species in the Mohaka, partially excluded rainbow trout from feeding positions in rapids and tails of pools.

ISSN:0028-8330    

DOI:10.1080/00288330.1984.9516037

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The smallest size at which at least 50% of femaleJasus verreauxibore eggs during the egg‐bearing season (= size at onset of breeding) was ≥ 160 mm carapace length (CL) (range 160–184 mm CL). This was usually at least 10 mm CL greater than the size at which setae first developed on the endopodites of the pleopods, and amounts to at least a 2‐year age difference. An increase in the minimum legal size to at least 160 mm CL is necessary if it is considered desirable that most females be allowed to breed before becoming available to the fishery.

ISSN:0028-8330    

DOI:10.1080/00288330.1984.9516038

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The oxygen transport characteristics of lugworm blood were studied over a range of temperature and pH values encompassing tidal and seasonally dependent measurements from worm burrows. The blood showed a small carbon dioxide Bohr effect (?log P50/?pH = ‐0.14 to ‐0.06), contrasting with the known pH sensitivity of blood in the European lugworm,Arenicola marina.The exothermic nature of oxygen binding was greater for the New Zealand species (?H ≈ ‐36 kJ mol‐1) but less than that shown for most other invertebrates. The CO2‐Bohr effect was indistinguishable from the fixed acid Bohr effect, suggesting a lack of specific CO2binding by the blood. Worms acclimated at 15 and 25°C did not show thermal compensation of in vitro blood oxygenation; these data are discussed in relation to the temperature induced Bohr effect inA. marina.

ISSN:0028-8330    

DOI:10.1080/00288330.1984.9516039

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Larval stages ofA. simplex(Rudolphi, 1809, det. Krabbe, 1878) andP. decipiens(Krabbe, 1878), infecting marine teleosts from New Zealand waters are described and compared morphometrically to pre‐adult and adult stages.A. simplexlarvae were positively identified using adults obtained from in vitro cultivation. Some morphometric variations compared to overseas descriptions are noted; the main differences being the small size ofA. simplexlarvae and the long intestinal caecum inP. decipienslarvae and adults from New Zealand waters.

ISSN:0028-8330    

DOI:10.1080/00288330.1984.9516040

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Possible invertebrate intermediate hosts ofAnisakis simplex(Rudolphi, 1809, det. Krabbe, 1878),Thynnascaris adunca(Rudolphi, 1802), andPseudoterranova(=Phocanema) decipiens(Krabbe, 1878) were determined from examination of stomach contents of teleosts which are regularly infected by these parasites. The euphausiid,Nyctiphanes australis,and the galatheid crab,Munida gregaria,are possible sources ofA. simplexlarvae.M. gregariais a definite source ofT. aduncalarvae (and adults). Smaller zooplankton (e.g., copepods and decapod larvae) could also be sources ofT. aduncalarvae. No potential hosts ofP. decipienslarvae were apparent. Naturally occurring invertebrate hosts of anisakids were found in plankton samples.A. simplexlarvae were found inN. australis. T. aduncalarvae occurred in chaetognaths(Sagittaspp.), a medusa, and a decapod larva. These anisakid larvae are all morphologically similar to Stage III larvae from teleosts. Experimental infection ofN. australisandM. gregariawith Stage II larvae ofA. simplexandT. aduncawas unsuccessful. Infection rates, host specificity, and larval morphology are discussed.

ISSN:0028-8330    

DOI:10.1080/00288330.1984.9516041

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The invertebrates and macroalgae in 42 permanent and temporary ponds and kettles in glacial moraine south of Lake Ohau, and 36 sites in moraine west of Lake Tekapo, South Island, New Zealand, were sampled in December 1980, and taxonomic lists were compiled. Most organisms belonged to taxa characteristically found in shallow waters elsewhere in New Zealand, but new distributions for the rare cladoceransNeothrix armata, Monospilus dispar,andEphemeroporus barroisiwere recorded, and the presence ofSimocephalus acutirostratusin New Zealand was confirmed. Darkly pigmentedDaphnia carinatawere recorded for the first time as also were co‐occurringBoeckella triarticulataandBoeckella dilatata.Cluster analysis of the data from both areas identified 3 groups of taxa with a high probability of co‐occurrence. Some species were absent from all the sites in 1 area but present at several sites in the other. This may reflect differences in adaptation to drought, or the limited sampling regime, but is also consistent with the areas being in different ecological districts. Ponds which still contained water in late autumn were sampled for pH (6.7–7.0), conductivity (K20, 17–79 μS cm‐1), sodium (0.35–4.60 mg L‐1, chloride (0.89–5.68 mg L‐1), and osmolality (21–37 mOsM).

ISSN:0028-8330    

DOI:10.1080/00288330.1984.9516042

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The macrophyte distribution of Lake Alexandrina (737 m a.s.l.), a small, homothermous, South Canterbury high‐country lake, is closely related to depth. Shallow water communities, mostly dominated byIsoetes alpinusKirk, extend to a depth of about 4 m, but do not grow above 0.7 m because of strong wave action. Mid‐depth communities consist of a tallElodea canadensisMichx./Myriophyllum triphyllumOrchard community between 2 and 4 m at the shallow northern end of the lake, large areas ofChara fibrosavar.acanthopitys(A.Br). Zanev. at the southern end, and aMyriophyllum triphyllum/Nitella hookeriA.Br. community at 2–6 m on the steeply descending eastern and western sides of the lake. Pure stands ofElodea canadensismay replace the last community, particularly on the eastern side. A deep water characean community ofChara globularisThuill. andChara corallinaKl. ex Willd. extends from 4 m to 10–11 m with 100% cover;C. corallinacontinuing sparsely to 16 m. Maximum above‐ground biomass recorded for the summer 1982–83 was 1350 g m‐2(dry weight) forC. globularisand 1100 g m‐2forE. canadensis.

ISSN:0028-8330    

DOI:10.1080/00288330.1984.9516043

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor