摘要:

The feeding ecology of the common smelt,Retropinna retropinna, was determined at several locations on the Waikato River system. The mean size of the dominant prey was found to increase as smelt mouth gape increased. Smelt smaller than 40 mm total length fed mostly on zooplankton. Chironomid larvae, pupae, and adults were the dominant foods of larger fish from most sites, although mysids and amphipods were the major prey in Lake Waahi and the Waikato River estuary. Algae were the dominant food in many smelt but ingestion was probably incidental. Seasonal and annual differences in dominant foods were minor. Common smelt are generalists, capable of feeding on the majority of smaller organisms present in their different environments; however, they may grow faster and achieve a larger adult size when food of optimal size and nutritive value is present.

ISSN:0028-8330    

DOI:10.1080/00288330.1997.9516753

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A method is described for modelling the distribution of velocity across a river cross‐section in a straight reach in uniform, steady flow. The method uses a finite element model based on a simplified Navier‐Stokes equation and a mixing length hypothesis. The model is applied to a representative river reach and a comparison is made with velocity gaugings in the reach. Good agreement is shown where flow conditions match the assumptions on which the model is based.

ISSN:0028-8330    

DOI:10.1080/00288330.1997.9516754

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We critically evaluate the prevailing view that the species composition of zooplankton communities in New Zealand lakes, and the abundance and size distribution of the zooplankton, are more commonly controlled by food and temperature than by predation. We conclude that predation may play a far more important role than was hitherto thought. This conclusion is based first on the seasonal zooplankton dynamics of several New Zealand lakes being similar to those in Danish lakes, in which fish predation has been shown to have major effects. Second, the indigenous planktivorous fish fauna in New Zealand lakes is dominated by larvae of benthic fish with a long breeding season (bullies) and other small potent zooplanktivores such as smelt and larvae of galaxiids. Patterns of diurnal vertical migration of zooplankton in several New Zealand lakes during summer are also consistent with it being a mechanism to escape from predation. Third, the dominant piscivorous fish (brown trout and rainbow trout) are only facultative piscivores and are therefore probably weaker predators on the planktivores than the more obligate piscivores in many north‐temperate lakes. Although various other explanations have been offered for the low ratio of zooplankton‐to‐phytoplankton biomass observed in New Zealand lakes, this phenomenon is equally consistent with high rates of predation. Re‐analyses of data from earlier investigations in Tomahawk Lagoon No. 2, provide evidence for a periodically high predation pressure on zooplankton during summer, which was further supported experimentally. We call for further investigation of top‐down control of zooplankton in New Zealand lakes. It is important not only for scientific understanding, but potentially also for lake management.

ISSN:0028-8330    

DOI:10.1080/00288330.1997.9516755

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The natural incidence of deformities in the larval head capsulesof Chironomus zealandicuswas investigated at four lake sites in the central North Island, New Zealand, in summer (December 1994) and winter (June 1995). Significant differences were observed between sites and seasons. Individuals from the peat lakes Ngaroto and Hamilton (Rotoroa) had the highest incidence of deformities during summer (78 and 48%, respectively) and these declined significantly in winter (40 and 26%). No seasonal differences were observed in larvae from the two sites chosen in Lake Rotorua. Individuals close to the Hamurana Stream in Lake Rotorua showed the lowest number of malformed head capsules during summer (32%). In order to assess the influence of substrate type, larvae from two different locations were cultured through their entire life cycle in three different substrates. Results overall indicated no clear pattern of substrate effect although some structures may be more sensitive indicators of substrate physico‐chemistry than others. The incidence of deformity tended to decline with successive laboratory culture.

ISSN:0028-8330    

DOI:10.1080/00288330.1997.9516756

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The acute toxicity of un‐ionised ammonia to seven New Zealand indigenous fish and one indigenous crustacean species was established. Shrimp (Paratya curvirostris) was the most sensitive species, followed by banded kokopu (Galaxias fasciatus), common bully (Gobiomorphus cotidianus), common smelt (Retropinna retropinna), redfin bully (G. huttoni), inanga (Galaxias maculatus), and longfin and shortfin eels (Anguilla dieffenbachiiandA. australis). The 96 h LC50at 15°C and pH 7.5 and pH 8.1 ranged from 0.75 to 2.35 mg NH3I−1for these species. Unusually, New Zealand fish were more tolerant to ammonia than some native invertebrate species tested by a similar method. Within the limits of the life stages and species tested here, adequate protection is provided for native fish by adopting US Environmental Protection Agency ammonia criteria.

ISSN:0028-8330    

DOI:10.1080/00288330.1997.9516757

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Seiche currents were observed in Wellington Harbour, New Zealand, with an Acoustic Doppler Current Profiler (ADCP). A 600 kHz Broad‐Band ADCP was deployed on the sea bed in Evans Bay in an upwards looking configuration for 20 days. The measured seiche periods were 159, 26, 17.3, and 8.3 min and there was evidence for seiching at periods of 15.8 and 14.7 min. These observations are in close agreement with the previous predictions of a finite‐difference numerical model. The seiching occurred during periods of wind with speeds in excess of 10 m s−1The seiches were found to be barotropic.

ISSN:0028-8330    

DOI:10.1080/00288330.1997.9516758

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Size‐fractionated phytoplankton standing stocks and potential primary production (PPP) off the west and east coasts of South Island, New Zealand, were evaluated in austral winter and spring 1993. These are the first size‐fractionated primary production data to be reported from the southern Subtropical Convergence (STC) and in oceanic New Zealand waters. Picophytoplankton (< 2 μm) formed > 30% of integrated chlorophyllaand daily PPP in most water types and seasons, except when the 20–200 μm size class dominated in west coast waters in spring and in the STC in winter and spring. In subtropical and STC waters, PPP was 30% higher than at similar latitudes in the North Atlantic Ocean. Interpretation of whether or not there was accumulation of chlorophyllain the various water types and seasons depends on microzooplankton grazing, because mesozooplankton grazing and the proportion of chlorophyllous particulate matter sinking out of the upper water column was low. In the STC in spring, phytoplankton growth was slowing down (potential doubling times were at most 1.01 per day at 10 m and PPP per unit biomass was lower than in water masses to the north and south), probably because of decreasing concentrations of dissolved reactive silica. A sedimentation event of diatoms is postulated to have occurred in the STC soon after our spring sampling dates. The balance between algal growth and loss factors in the south‐west Pacific depends on the unique combination of physical and chemical environmental conditions experienced there. The implications of the distribution of phytoplankton biomass and primary production by size‐fraction for carbon export is discussed.

ISSN:0028-8330    

DOI:10.1080/00288330.1997.9516759

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The introduced, mytilid bivalveMusculista senhousia(Asian date mussel) occurs on the east coast of New Zealand in the Auckland region. Eighteen sites were searched within the Tamaki Estuary: six had extensive mats of mussels and three contained small, isolated clumps. Core samples were taken monthly during 1994/95 from two of the mat‐forming populations. Densities reached 16 000 m−2at Bucklands Beach and 5000 m−2at Farm Cove. Both populations were dominated by a single cohort of mussels. Mussels grew to about 20 mm in 12 months, after which growth virtually ceased. Recruitment was sporadic into existing mats, but occurred adjacent to the monitored mat at Bucklands Beach in April 1995. The area occupied by the initial mussel bed at this site decreased by 60% over 1 year. Further core sampling revealed significantly fewer macrofaunal invertebrates under mussel mats compared to control samples taken from areas of beach without mussels. Infaunal bivalves were most adversely affected byM. senhousia, showing an 8‐fold decrease in abundance within mats compared to cores in the control area. Our results reveal thatM. senhousiain the Auckland area has similar life history features to those reported from populations outside New Zealand. We suggest that any adverse environmental effects caused byM. senhousiaare likely to be local and short‐lived.

ISSN:0028-8330    

DOI:10.1080/00288330.1997.9516760

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Phytoplankton biomass and growth rates were measured in Beatrix Bay, Marlborough Sounds, during 1994–95. In spring and summer, nitrate and chlorophyllaconcentrations in the mixed layer were low (typically < 1 mg N m3and < 1 to 3 mg Chi.am−3, respectively), and phytoplankton growth rates were moderate (average 0.3 d−1). Growth rates increased several‐fold in response to the experimental addition of inorganic N (but not to inorganic phosphorus). Higher nitrate concentrations were found below the pycnocline. During autumn and winter, nitrate concentrations in the mixed layer were high (up to 60 mg m3), but phytoplankton growth rates were lower than in summer (average 0.2 d−1), and did not respond to added nutrients. Chlorophyllaconcentrations, however, were highest during the winter (typically 3–6 mg m−3). Even so, low light levels meant integral photosynthesis per unit chlorophyllawas low in winter. Phytoplankton growth appears to be controlled by the availability of nitrogen in summer and by light in winter.

ISSN:0028-8330    

DOI:10.1080/00288330.1997.9516761

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Commercial gill‐nets of three mesh sizes (3.5”, 4.5”, 5.5” diagonal measure) were joined into a single net 300 m long and 5 m high, and set at three localities (New Plymouth, Palliser Bay, Bay of Plenty) in the lower North Island, New Zealand. The nets were bottom‐set in shallow (9–26 m depth) and deep (35–100 m depth) water, mostly for 16 h, to test the effects of mesh size on the species composition and sizes of fish caught. In 17 sets, 3284 fish of 55 species were caught. Across all species, larger fish were caught in deep water and at the two largest mesh sizes. The species caught and proportional composition of the catches varied both between locations and mesh sizes. Overall, there were important differences between mesh sizes, depths, and locations in the species composition and size distribution of gill‐net catches, as well as a wide range of species and sizes caught within single sets. Indications are that effective targeting of individual species at the nearshore‐pelagic interface may be confounded by bycatch.

ISSN:0028-8330    

DOI:10.1080/00288330.1997.9516762

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor