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- Berglund, Olof, et al.
(författare)
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Factors influencing organochlorine uptake in age-0 brown trout (Salmo trutta) in lotic environments
- 1997
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Ingår i: Canadian Journal of Fisheries and Aquatic Sciences. - 1205-7533. ; 54:12, s. 2767-2774
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Tidskriftsartikel (refereegranskat)abstract
- In 1994 and 1995, we investigated the relationship between stream morphology and water chemistry and levels of organochlorines (HCB, PCB, and DDT) in young-of-the-year brown trout (Salmo trutta) from 25 streams in southern Sweden. Contrary to earlier findings for lakes, we found a positive relationship between trophic status (total phosphorus) and uptake of persistent pollutants in stream biota (trout). This difference between benthic, stream environments and pelagic, lake environments may be related to processes affecting pollutant uptake, i.e., pollutant "spiralling" or the shift from heterotrophy to autotrophy in streams. Land use in the catchment area of the streams also affected pollutant levels in trout, with higher levels in agricultural landscapes and lower levels in forested areas. Size of catchment area, however, did not influence uptake of pollutants in trout. The results indicate that eutrophication of streams by agricultural activities and excessive nutrient loading may increase uptake of persistent pollutants in stream biota.
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| 4. |
- Eklöv, Anders
(författare)
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The distribution of brown trout (Salmo trutta L.) in streams in southern Sweden.
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis examines the effect of water quality, habitat and species interactions on the occurrence and abundance of stream fishes in southern Sweden. I found that improvements in water quality between the 1960s and 1990s have led to recolonization of streams by brown trout (Salmo trutta L.), stone loach (Barbatula barbatula L.) and eel (Anguilla anguilla L.). The response was greatest for brown trout and was best explained by increased dissolved oxygen concentrations. The occurrence of other species, specially the nine-spined stickleback (Pungitius pungitius L.), ide (Leuciscus idus L.) and brook lamprey (Lampetra planeri L.) decreased between the 1960s and 1990s. The decrease was greatest for nine-spined stickleback and was related to the increase in sites with trout, indicating that nine-spined stickleback may be sensitive to predation or competition. In-depth studies of brown trout showed that physical habitat influenced trout densities, especially for 0+ trout, where high densities were associated with narrow streams and with cover. Field manipulations of cover indicated that submerged macrophytes supported high 0+ trout densities in small and medium-sized streams, where other types of instream cover were scarce, and therefore may be especially important in canalized streams. Interspecific and intraspecific interactions also affected trout densities as well as trout behaviour and growth. In a field survey, trout density was inversely related to the abundance of piscivores. Moreover, experiments in artificial stream channels showed that the presence of piscivores could cause habitat shifts and decrease food intake by brown trout. Other experiments in these stream channels showed that intraspecific size-class competition in trout reduced food intake by smaller individuals. Intraspecific competition also seems to explain variation in length of 0+ trout in the field as body length was inversely correlated with trout density, indicating that density may affect trout growth.
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- Greenberg, Larry, 1955-, et al.
(författare)
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Effects of Predation and Intraspecific Interactions on Habitat Use and Foraging by Brown Trout in Artificial Streams
- 1997
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Ingår i: Ecology of Freshwater Fish. - : Wiley. - 0906-6691 .- 1600-0633. ; 6:1, s. 16-26
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Tidskriftsartikel (refereegranskat)abstract
- We studied habitat use, foraging rates and behavior of 10 cm and 12 cm long brown trout, Salmo trutta, at two densities, 1.5 and 3.0 fish. m−2, in artificial streams that contained either the amphipod, Gammarus pulex, alone or G. pulex together with the piscivore, northern pike, Esox lucius. Gammarus were stocked in and largely restricted to the pools at a density of 128 Gammurus. m−2. pool−1 Large trout (12 cm) used pools more and riffles less when small trout (10 cm) were present than when small trout were absent. Small trout consumed fewer Gammarus when together with large trout than when alone, but showed no difference in habitat use in the presence and abscnce of large trout. Habitat use and number of Gammarus consumed per trout were not affected by trout density for either size-class when alone. For both size-classes of trout, use of pools and foraging rates were higher in the absence than in the presence of pike, and pike primarily resided in the pools. The number of aggressive interactions by both size-classes of trout decreased when pike was present. Our results indicate that for habitats that differ in food resources and predation risk, size structure may affect habitat use and foraging by brown trout.
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- Larsson, Per, et al.
(författare)
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Persistent pollutants in a salmon population (Salmo salar) of the southern Baltic Sea
- 1996
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Ingår i: Canadian Journal of Fisheries and Aquatic Sciences. - 1205-7533. ; 53:1, s. 62-69
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Tidskriftsartikel (refereegranskat)abstract
- Persistent pollutants in an Atlantic salmon (Salmo salar) population spawning in a river of southern Sweden were investigated. The population was characterized by a high growth rate. Some males reached 20-30 kg after 3 to 4 years in the sea. The fat content of migrating salmon varied by one order of magnitude and was the most significant correlate of pollutant concentrations. No relationships were recorded between fat content and gender, age (weight, length), year at sea, or different measures of condition. The reasons for this may be the varied evolutionary strategies for maximizing reproductive output; male salmon may enter the spawning river as small grilse and spawn opportunely, or migrate at a larger size, when they can hold spawning territories in the river. Females have a greater and more uniform size, and spend more energy on gonadal products. The varying fat content of individual fish may also be attributed to foraging in different areas of the Baltic and thereby to migration distances as well as foraging strategies. When pollutant levels were normalized for fat content, other factors such as age (weight, length) were shown to be important for uptake; older fish had higher levels of pollutants than younger ones
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