摘要:

Spatial and temporal variation in relative density of 0+ and 1+ brown trout was examined over three summers in the Kakanui River, North Otago, New Zealand. Both 0+ and 1+ trout were distributed throughout the river. Spatial variation in relative density was much higher than annual variation. Within years, relative density of 0+ brown trout varied by 5 to 92 times between sites (mean coefficient of variation, CV = 1.08) and of 1+ trout by 18 to 84 times between sites (CV = 1.13). Mean relative density of 0+ brown trout varied by 1.5 to 2.0 times between years (CV = 0.35) and of 1+ trout by 3.6 to 23.2 times between years (CV = 0.96). The pattern of 0+ trout spatial distribution was not closely related to the distribution of redds (which also were distributed throughout the river) and not related to the distribution of benthic invertebrate food. By their second summer, most trout occupied the middle and lower reaches of the river. Mean length of both 0+ and 1+ trout increased with distance downstream. Floods greater than 290 m3s−1, and with a return period of 4 years, during the late incubation and early fry stages (August‐November) were associated with impaired recruitment, yet a large flood (816 m3s−1) in March 1994 had no apparent effect on the survival of 0+ trout 80–100 mm in length.

ISSN:0028-8330    

DOI:10.1080/00288330.1995.9516674

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Otolith daily growth increment patterns were used to discriminate between early life‐history patterns of 0+ rainbow trout and to determine the contribution of each to adult recruitment. Inlet stream residents had narrow increments (2.13–3.18 μm) and Outlet Creek residents generally had wide increments (3.63–4.26 μm) across the entire otolith radius. The dominant otolith growth pattern in lake juveniles comprised narrow increments before emergence (3.23–3.66 μm) with wide increments (4.34 μm) soon after emergence. This “early lake migrant” pattern was consistent with incubation in cool inlet streams followed by emigration to the warmer lake upon emergence. Discriminant function analysis (DFA) using mean increment widths at 50, 150, and 200 |im from the primordia discriminated between these patterns (78% overall classification success; 96.5% for inlet stream residents, 60.0% for Outlet Creek residents, 77.0% for early lake migrants). Estimated proportions (from DFA) of the early life‐history types in the adult population were 28% inlet stream residents, 17% Outlet Creek residents, and 55% early lake migrants. Assuming daily formation of growth increments, mean fork length and mean number of days after emergence that early lake migrants entered the lake was 25.8 (± 1.1) mm and 1.4 (+ 6.4) days, respectively. Inlet stream residents appeared to emerge earlier in the spring and have higher survival than early lake migrants.

ISSN:0028-8330    

DOI:10.1080/00288330.1995.9516675

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Vertical distributions of adult rainbow trout (> 25 cm fork length, FL) were determined with a SIMRAD ES470 split‐beam echosounder in two 80–90 m deep lakes differing in water quality. Between November 1993 and February 1994, most trout (> 80%) were between 10 and 40 m, within or close to the thermocline. However, a small group of fish occupied colder waters, deeper than 50 m. In February, surface water temperatures > 21.0°C and hypolimnetic oxygen levels < 2.5 g m−3compressed the habitable depth range for trout in Lake Rotoiti to 12–35 m compared with 12–80 m in Lake Rotoma. Deeper‐dwelling trout inhabiting waters over 50 m in Lake Rotoiti would have been forced into shallower waters at this time. However, the vertical distribution of the remaining trout in Lake Rotoiti was not compressed. In March 1994, adult trout were still present in waters 10–40 m deep in both lakes, but many of the smaller fish had moved into shallower waters (< 10 m deep), probably because of declining water temperatures in the epilimnion and increased densities of their preferred prey. At this time, the lower depth range for trout in Lake Rotoiti was limited to 28 m by the 2.5 g m−3oxygen level and trout occupied warmer waters than they did in Lake Rotoma. When oxygen was not limiting, water temperature was the main variable determining the depth of the trout, and monthly changes in the mean depth of trout between both lakes and months were explained by a thermo‐regulatory model for trout movement.

ISSN:0028-8330    

DOI:10.1080/00288330.1995.9516676

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0028-8330    

DOI:10.1080/00288330.1995.9516677

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor