摘要:

Abstract–Literature evidence suggests that lake‐dwelling longnose gar (Lepisosteus osseus) enter tributary streams to spawn, Until the present study, the dynamics of this breeding migration had never been investigated quantitatively. During the summers of 1991 and 1992, longnose gar were captured as they entered Weaubleau Creek, Missouri, a tributary of Harry S. Truman Reservoir. The in‐stream spawning migration began in early April and ended in late May, and was positively correlated with stream flow and water level, and negatively correlated with water temperature. In‐stream residence times ranged from 15 to 94 days, with males exhibiting longer residence times than females. Once in‐stream, longnose gar travelled as far as 10 km upstream and occupied certain pools at greater relative frequencies. Although the reason for this preferential utilization is not completely understood, it may relate to pool depth and riffle proximity. Longnose gar disperse from the spawning stream great distances, with gar captured in Weaubleau Creek being recaptured up to 48 km away. This information should provide fisheries biologists the means to consider the reproductive ecology of this species in their conservation and management

ISSN:0906-6691    

DOI:10.1111/j.1600-0633.1996.tb00041.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract–Growth, population composition and reproduction of bream were studied in Lake Volvi from 1989 to 1991. Females had a higher growth in length (L∞=507 mm, k=0.094) than males (L∞=452 mm, k=0.102). Growth can be characterized as medium, due to low food sources (zooplankton and chironimids). Large specimens are scarce because of high fishing mortality and low growth rate. All males greater than three years old, longer than 135 mm and all females greater than four years old and longer than 150 mm were sexually mature. These values of age and size of first maturity are the lowest that have been reported for this species. The size of the spawning egg is independent of the body

ISSN:0906-6691    

DOI:10.1111/j.1600-0633.1996.tb00042.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract–Data from the Swedish Electrofishing Register were used to study the effects of lakes on the growth of yearling (0+) brown trout in outlet streams. It was found that growth increased close to lakes. On average, the length of the longest yearlings was 10% greater 0‐100 m downstream from lakes as compared with more than 1 km downstream. Growth enhancement was most pronounced downstream from large lakes. This was exemplified with maximum yearling lengths in September in inlet streams (maximum yearlings 50‐100 mm) and outlet streams (65‐130 mm) of Lake Stora Le (area 200 km2), and inlet streams (50‐75 mm) and outlet streams (65‐95 mm) of Lake Anten (area 18 km2). It is suggested that this is a combined effect of both increased water temperature and outflow of lake seston. The growth pattern found was not correlated to population abundance or to the abundance of competitors o

ISSN:0906-6691    

DOI:10.1111/j.1600-0633.1996.tb00043.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract–I collected bluntface shiners,Cyprinella camura, once or twice monthly from February to November 1991 in Morganfork Creek, southwestern Mississippi. Examinations of mean largest oocyte diameter (LOD), female mean relative gonadal index (RGI), ovarian developmental condition, and male secondary sexual characteristics indicated thatC. camuraspawned from late March through mid‐August. There were significant positive correlations between mean LOD and mean daylength, mean maximum temperature, and mean minimum temperature (environmental variable means were calculated for the 28 day period prior to each sampling date). Mean day length and mean RGI were significantly positively correlated, but there was no significant relationship between mean maximum and minimum temperatures and mean RGI. Clutch size, RGI, and mean mature oocyte diameter (MMOD) of mature females were significantly correlated with length (standard length). Mean length, clutch size, and RGI of mature females in individual collections decreased significantly over the reproductive season. The corresponding decrease in mean MMOD was not signific

ISSN:0906-6691    

DOI:10.1111/j.1600-0633.1996.tb00044.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract–Juveniles of the Gulf coast population of walleye,Stizostedion vitreum, 22.4–89.9 mm SL (n=111) shrank significantly in SL and throat diameter over 12 months after being fixed in 10% formalin for 1 week and preserved in 50% isopropyl alcohol thereafter. Significant changes in body depth and total length (TL) were also determined for select larval fish prey that juvenile walleye might encounter in nature. The relationship between fresh SL and throat diameter in juveniles of the Gulf coast population of walleye (22.4–172.4 mm SL) is: throat diameter (mm) =−0.8783 + 0.0786 SL (mm) (r2= 0.988,P<0.0001,n= 135). In laboratory experiments on prey size choice, walleye selected available prey near or less than their mean throat diameter, although several larger prey (7.4% of total) were also consumed. To determine the actual spectrum of prey sizes available to juvenile piscivores, we must adjust the realized size of the predator and prey for changes caused by preservation. Preservation‐induced alterations in morphology translated into errors in the perceived pattern of prey size choice in walleye. The preservation‐induced changes documented in this study, which are also supported by a number of other empirical data sets, must be included when modeling the relationships between feeding ecology, morphology, growth, and ecologically relevant indices (condition factors, relative wei

ISSN:0906-6691    

DOI:10.1111/j.1600-0633.1996.tb00045.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract–Two almost eel‐free lakes (339 and 299 ha respectively) in southeastern Sweden were stocked with French elvers in the autumn of 1980. The introduced eel stocks were monitored from the time of stocking and onwards using outlet traps equipped with fine‐meshed screens and subsequently by test‐fishing with long‐lines and fyke‐nets. Up to and including the spring run of 1994, more than 5,900 eels or about 2,600 kg were recaptured from one of the lakes, mostly as migrating silver eels. This means a recapture rate of about 11%. In the other lake most recaptures came from fyke‐netting of the yellow eel stock. In this lake only 1.7% have been recaptured up to this point. These differences in yield and recapture rates from the two lakes are discussed in the context of lake productivity, growth rates, sex ratios, sizes of stocked elvers and size at silvering. In cconomic terms, the results from the higher‐yielding lake indicate an excellent rate of profit. After approximately 10 years, the investment (cost of the introduced elvers) was paid back at a lending inter

ISSN:0906-6691    

DOI:10.1111/j.1600-0633.1996.tb00046.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract–A total of 8,903 eels were collected in 503 fyke‐net samples during the months March to December from 1981 to 1994 in a small bay in Lough Derg, a mesotrophic lake. Variations in catch between months and between years are described. In addition to expected decreases in catch in the colder months, a regular reduction was observed in June. Low catches were observed from 1985 to 1987, coinciding with low water temperatures. A very low catch in August 1994 may have been a chance variation but could have been a first indication of the effects of poor recruitment or of increased commercial fishing effort. The results support the initial hypothesis that a long‐term study is required to determine the extent of variation in an eel popul

ISSN:0906-6691    

DOI:10.1111/j.1600-0633.1996.tb00047.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY