摘要:

The effects of decreasing discharge on the behaviour and distribution of O+ brown trout (Salmo truttaL), were studied in the Silverstream, a tributary of the Taieri River, Otago. The preferred habitat is runs, where the behaviour is territorial, but with decreasing discharge most of the population moved into pools and adopted shoaling behaviour. Analysis of the physical changes indicated that current velocity was the significant factor, with a threshold value of 0.30 m s‐1for poolward movement. The discharge giving a mean run velocity of 0.30 m s‐1was compared with empirical criteria for minimum satisfactory flows for fish, and very close agreement was found.

ISSN:0028-8330    

DOI:10.1080/00288330.1984.9516023

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The diet of the grey mullet (Mugil cephalusL.) was studied in Lake Waahi, and the Waikato River at Huntly —2 highly productive freshwater habitats in New Zealand. Grey mullet fed all year despite temperatures ranging from 7–26°C. Their diet was found to include a wide range of algal species, some macrophyte detritus, inorganic particles, and occasionally the snailPotamopyrgus antipodarum.The food items selected reflected their availability in the 2 habitats. The source of these food items is discussed and the environmental effects of mullet feeding activities are considered briefly.

ISSN:0028-8330    

DOI:10.1080/00288330.1984.9516024

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Condition changes of female rig,Mustelus lenticulatus,were related to migration and reproduction in Golden Bay, north‐western Nelson, New Zealand. Female reproductive state (size of embryos in uteri) was compared with condition (weight of liver as a percentage of body weight calculated from a length‐weight regression equation). It was found that females gained condition before moving into the shallows but lost condition during the occupation of inshore areas of Golden Bay in spring and summer. Liver lipids appeared to be depleted before parturition and as a consequence females may experience nutritional stress during late pregnancy.

ISSN:0028-8330    

DOI:10.1080/00288330.1984.9516025

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The feeding of rig(Mustelus lenticulatus)from Golden Bay, north‐western Nelson was investigated in relation to condition, reproduction, and migration patterns. Prey importance was assessed by an index of relative importance (IRI). Prey composition was further examined by cluster analysis. Feeding intensity was assessed by weight of stomach contents as a percentage of body weight, and by mean number of prey consumed. Rig fed predominantly on benthic invertebrates (pagurid and brachyuran crustaceans, and echiurans). Inshore migration of females in summer did not appear to be related to feeding in order to gain condition for reproduction. It is suggested that males move inshore to mate. Golden Bay could act as a nursery ground for juvenile rig, providing food and protection from predation.

ISSN:0028-8330    

DOI:10.1080/00288330.1984.9516026

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Food utilisation by benthic insect larvae at 6 sites along a West Coast, South Island river system (Devils Creek and the Inangahua River) was studied by gut content and stable carbon isotope analyses. At forested and open sites the dominant materials ingested by all species of Ephemeroptera, Plecoptera, and Trichoptera examined were fine detrital particles in the 0.45–75 urn size range. Diatoms and filamentous algae were eaten in varying amounts by some species. Larvae ofDeleatidium(Ephemeroptera) and Chironomidae were the numerically dominant prey of the stonefly,Stenoperla prasinaat all sites. Stable carbon analyses indicated that most species were dependent largely on carbon of terrestrial origin at forested sites, whereas autochthonous material was used increasingly further down Devils Creek. However, in the large, open Inangahuajliver13C/12C ratios of insects were similar to those found in the forested tributaries and indicated a return to allochthonous dependence by the fauna. Although algae appeared to be ingested sparingly by stone‐surface browsers at forested sites, some such asDeleatidiumhad13C/12C ratios indicating the incorporation of substantial autochthonous carbon. To explain this it is suggested that heterotrophic organisms within stone‐surface organic layers use algal exudates as a major source of energy, and that they and their products (e.g., slimes) are subsequently ingested and assimilated by organic layer feeders.

ISSN:0028-8330    

DOI:10.1080/00288330.1984.9516027

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Baquacil was tested against axenic and monoxenically grown pathogenic free‐living amoeba cultures fed with bacteria. When the initial concentration of Baquacil and/or the exposure time were increased, survival rates were reduced. Monoxenically cultured amoebae created a greater Baquacil demand than amoebae grown axenically.

ISSN:0028-8330    

DOI:10.1080/00288330.1984.9516028

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Neothrix armatais recorded for the first time from Lakes Rotorua and Rotokakahi, andStreblocerus serricaudatusfrom Lake Tikitapu.

ISSN:0028-8330    

DOI:10.1080/00288330.1984.9516029

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

To minimise the error in biomass estimates from stratified random trawl surveys, the allocation of trawl stations amongst strata should be made according to prior information on fish distribution. Often such information is slight. A 2‐phase survey strategy is proposed in which allocation of trawl stations in Phase 2 is based on catches obtained in Phase 1. Computer simulations based on 2 sets of real survey data indicate that this strategy reduces the skew in the biomass estimate (thus reducing the probability of gross over‐estimation) as well as reducing the expected error. The efficiency of the 2‐phase design compared to the conventional design was 127% and 180% on the 2 survey areas. In additon, the adaptive nature of the design strategy allows for greater flexibility at sea.

ISSN:0028-8330    

DOI:10.1080/00288330.1984.9516030

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Lake stability (S) calculations quantify the resistance a column of water has to vertical mixing. Data from a selection of New Zeland lakes have been used to show a predictive relationship between the seasonal maximum stability (Smax) and mean depth (z, volumersurface area). Because of their proportionality, Smaxcan be substituted for the total annual stability (Stot) for the purposes of lake comparisons, although Stotwould be a better ecological parameter if enough data were available. Stability calculations in the euphotic zones of lakes enable useful comparisons to be made regarding growth conditions for different types of phytoplankton, in particular buoyant cyanophytes, and especially in relation to light penetration. An example is given where the degree of thermal stratification (stability) could be related to wind stress energy.

ISSN:0028-8330    

DOI:10.1080/00288330.1984.9516031

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The oceanic circulation around New Zealand is strongly controlled by the bottom topography. One consequence of this control is the influence of the circulation on the depth of the mixed layer, which results from the isopycnals tilting upwards over shallowing bottom topography. The influence is strongest on the winter depth of the mixed layer, which marks the top of the main thermocline. In some regions where the depth of the mixed layer exhibits considerable relief both alongshore and offshore, and the transit time of the water is short compared to that for the horizontal current shear to be cancelled by the vorticity input from the vertical current shear, conservation of vorticity arguments may be applied to the flow of the mixed layer. Where these criteria are met, both near East Cape and on the west coast continental shelf near the head of the Hokitika Canyon, vorticity arguments indicate that the mean current would be expected to increase shorewards.

ISSN:0028-8330    

DOI:10.1080/00288330.1984.9516032

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor