Access

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

If you need an accessible version of this item please contact JSTOR User Support

Population Densities of Juvenile Trout (Salmo trutta) in Five Upland Streams and Their Effects Upon Growth, Survival and Dispersal

D. T. Crisp
Journal of Applied Ecology
Vol. 30, No. 4 (1993), pp. 759-771
DOI: 10.2307/2404254
Stable URL: http://www.jstor.org/stable/2404254
Page Count: 13
  • Read Online (Free)
  • Download ($18.00)
  • Subscribe ($19.50)
  • Cite this Item
If you need an accessible version of this item please contact JSTOR User Support
Population Densities of Juvenile Trout (Salmo trutta) in Five Upland Streams and Their Effects Upon Growth, Survival and Dispersal
Preview not available

Abstract

1. Survival, growth and downstream dispersal of trout (especially 0 group) and the relationships of these variables to initial stocking density were studied in north Pennine streams. 2. Two methods were used. First, electrofishing censuses were made in a marked reach of each of four streams over a period of about 20 years. Second, downstream moving trout were trapped in two streams over a 10-year period. Each stream upstream of the trap was experimentally stocked with `swim-up' trout fry, using a different population density each year. 3. Before 1970 the four census reaches showed very large year-upon-year variations in August trout parr densities, with local failures of recruitment in some years. Population densities after completion of Cow Green Reservoir (1970) were generally higher but still showed wide fluctuations. 4. Survival (including the effects of losses by dispersal) from swim-up to early August, for starting population densities of 0-10 fry m-2, was about 10% regardless of initial density. Estimates of survival from August to early October were 30-50% for the census reaches and 55-65% for the areas upstream of the traps. However, for August 0 group densities of 0-0.9 m-2, estimated instantaneous loss rate from August of the first year of life up to age 40-65 months showed a positive curvilinear relationship to population density in the first year of life. Loss rate was, therefore, density-dependent during this period. 5. Estimated instantaneous growth rate day-1 of 0 group fish from swim-up to August and from swim-up to October was inversely related to the natural logarithm of August population density and this was most apparent for August densities of <0.15 fish m-2. 6. Although survival from swim-up to August was proportional (about 10%, at starting densities of 10 m-2 or less), the percentages of the total loss attributable to mortality and to downstream dispersal varied considerably with starting density. At starting densities around 4-5 fish m-2 dispersal was negligible. As initial density rose above 4-5 fish m-2 and towards 10 fish m-2 the percentage of loss attributable to dispersal rose towards 30%. As initial densities decreased from 4 to 1.4 fish m-2, the percentage rose to around 20%. Below a starting density of 1.4 fish m-2 the percentage decreased.

Page Thumbnails

  • Thumbnail: Page 
759
    759
  • Thumbnail: Page 
760
    760
  • Thumbnail: Page 
761
    761
  • Thumbnail: Page 
762
    762
  • Thumbnail: Page 
763
    763
  • Thumbnail: Page 
764
    764
  • Thumbnail: Page 
765
    765
  • Thumbnail: Page 
766
    766
  • Thumbnail: Page 
767
    767
  • Thumbnail: Page 
768
    768
  • Thumbnail: Page 
769
    769
  • Thumbnail: Page 
770
    770
  • Thumbnail: Page 
771
    771