摘要:

The spawning migrations of landlocked sockeye salmon (Oncorhynchus nerka) within the Waitaki catchment from 1975 to 1992 are described. In late February and early March an overlapping succession of spawning runs, consisting of fish of different origins and ages, spawned in cool (8–12°C) spring‐fed tributaries of lakes Ohau and Benmore. The size, age, and sex compositions of the runs were highly variable. Mature fish ranged in age from 2 to 5 years and in length from 138 to 462 mm. Redds were constructed in gravel (15–30 mm diam.) in water 0.15–0.50 m deep, flowing at 0.20–0.50 m s‐1. Runs increased during the 1970s, reaching a peak number of over 18 000 in 1979. Dam construction that was completed in late 1979 blocked spawning migrations from Lake Benmore to Lake Ohau; spawning runs are now fewer than 100 fish per annum and may be insufficient to maintain the wild stock. Attempts to increase the spawning runs by liberating hatchery‐reared juveniles and by the transfer of mature fish into warm (14–19°C) rain‐fed streams have failed, possibly because of the premature emergence of fry in mid winter.

ISSN:0028-8330    

DOI:10.1080/00288330.1995.9516659

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Fish larvae were collected in stream benthic invertebrate drift nets from the Otira River, near Arthur's Pass, New Zealand during a study of benthic drift. They are identified as probably those of koaro (Galaxias brevipinnisGunther) on the basis of estimates of myomere counts (indicating Galaxiidae or Retropinnidae); by a process of elimination of likely species on the basis of distance up stream, elevation, and habitat characteristics; and by determining fish species in the Otira River tributaries upstream of the sampling location. This comprises the first likely record of emigrating larvae of koaro, a species known to be diadromous by the return migrations from the sea of whitebait juveniles during spring. A newly hatched larva of koaro is described and figured.

ISSN:0028-8330    

DOI:10.1080/00288330.1995.9516660

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The Whangamaire Stream (North Island, New Zealand) has high concentrations of nitrate nitrogen (NO−3‐N), biochemical oxygen demand (BOD5), and Kjeldahl nitrogen (TKN) as a result of catchment land use practices. The lower reaches of the stream drain intensively farmed land and have dissolved oxygen (DO) levels of 10–50% saturation. The dominant riparian vegetation,Apium nodiflorum, provides a large organic loading by intercepting nutrients in run‐off and then decaying in the stream channel. Water quality and reaeration aspects of the stream were studied in order to explain the observed low DO levels. Measurements of the reaeration coefficient at 20°C, K220, using methyl chloride (CH3Cl) as a gas tracer, yielded values of 1.1–3.0 d−1for the upper part of the study reach and 15.5–16.2 d−1for the lower reach (overall average 12.5 ± 2.5 d−1). These were in agreement with values inferred from single‐station diurnal curve analysis, which also showed that respiration was dominant in the lower reach where photo‐synthetic activity was inhibited by shade. The relatively large reaeration coefficients ensure that parts of the stream do not become anoxic at night time. Better riparian management and reduced nutrient inputs are likely to improve stream water quality.

ISSN:0028-8330    

DOI:10.1080/00288330.1995.9516661

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The influence of temperature on the acute toxicity of a technical formulation (86%) and pure formulation (99%) of pentachlorophenol (PCP) to less than 24‐h‐oldSimocephalus vetulusneonates was determined with 48‐h static toxicity tests. The technical grade PCP was significantly more toxic toS. vetulusthan the pure PCP (P <0.05). Sensitivity ofS. vetulusto technical PCP also significantly increased with temperature (P <0.05), but a significant temperature effect was not found with the pure PCP. The mean 48‐h LC50values for neonates exposed to technical PCP were 140 and 199 μg l−1at 22°C and 16°C, respectively, and for those exposed to pure PCP were 262 and 304 μg l−1, respectively.

ISSN:0028-8330    

DOI:10.1080/00288330.1995.9516662

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0028-8330    

DOI:10.1080/00288330.1995.9516663

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor