Lac Léman: Effects of Exploitation, Eutrophication, and Introductions on the Salmonid Community

1972 ◽  
Vol 29 (6) ◽  
pp. 867-875 ◽  
Author(s):  
P. J. Laurent
Keyword(s):  
Salmo Trutta ◽  
Salvelinus Alpinus ◽  
Central Zone ◽  
Perca Fluviatilis ◽  
Rutilus Rutilus ◽  
Salmo Gairdneri ◽  
Algal Flora ◽  
Indigenous Species ◽  
Roach Rutilus Rutilus ◽  
Size Limits

Review of 14 years of data concerning the geographic and hydrographic characteristics of Léman show that this lake is in the process of eutrophication: nutrient levels are increasing, oxygen levels are decreasing in the deep waters, and the algal flora has changed. The effect of the current warming of the climate on its evolution is taken into consideration.Since 1900 the fishing regulations of the Swiss and French have been dissimilar. Excessively small size limits and at certain times the abusive use of nets have repeatedly led to a reduction of the most valued species.French catch data, covering more than 70 years, reveal fluctuations which reflect biological disturbances due primarily to overexploitation and also to eutrophication. Landings have increased but value has decreased.Numerous introductions have been made purposely or accidentally. Certain of these species have had deleterious effects (sticklebacks) and some beneficial (introductions of a new population of coregonines after the extinction of the indigenous species).Some aspects of the biology of the most valued salmonids (Salmo trutta, Salmo gairdneri, Salvelinus alpinus) have been shown as well as the results of attempts to repopulate them using pisciculture and marking. Plantings of rainbow trout along the shoreline during summer gave best results (percentage return and growth being most important), although their reproduction seems to be doubtful.Overexploitation of coregonines followed by that of perch (Perca fluviatilis) has left roach (Rutilus rutilus) to inhabit all the central zone of the lake. This valueless species is favored by eutrophication and is thus able to utilize plankton without undergoing competition from coregonines and young perch, or predation by larger perch. No fishing profits are derived from the invasion of the lake by roach.

Salmonid or nonsalmonid lakes: predicting the fate of northern boreal fish communities with hierarchical filters relating to a keystone piscivore

2008 ◽  
Vol 65 (9) ◽  
pp. 1945-1955 ◽  
Author(s):  
Johan Spens ◽  
John P. Ball
Keyword(s):  
Brook Trout ◽  
Salmo Trutta ◽  
Large Scale ◽  
Fish Assemblages ◽  
Salvelinus Alpinus ◽  
Fish Communities ◽  
Perca Fluviatilis ◽  
Boreal Lakes ◽  
Roach Rutilus Rutilus ◽  
High Connectivity

We determine if lacustrine salmonids show large-scale patterns of coexistence with the keystone predator northern pike ( Esox lucius ) and test an approach to predict fish communities using coexistence rules set in the context of three hierarchical filters that a species must pass to be present. The mutually exclusive species distribution patterns that we detected among 1029 lakes were repeatedly verified from results of whole-lake interventions with rotenone and introductions. Essentially, pike did not coexist with self-sustaining salmonid populations in lakes. High connectivity to pike (derived from maps) largely predicts the absence of lacustrine salmonids. Our analysis strongly suggests that pike prevented self-sustaining populations of brown trout ( Salmo trutta ), Arctic char ( Salvelinus alpinus ), and brook trout ( Salvelinus fontinalis ) in lakes. High connectivity to pike resulted in nonsalmonid lake fish communities, most often including both European perch ( Perca fluviatilis ) and roach ( Rutilus rutilus ). Our analysis suggests that if pike were not present in many boreal lakes where they now dwell, salmonid fish assemblages would prevail, a sharp contrast from the present pike-driven homogenized state with mainly nonsalmonid fish communities.

Relative Importance of Phosphorus Supply to Phytoplankton Production: Fish Excretion versus External Loading

1990 ◽  
Vol 47 (2) ◽  
pp. 364-372 ◽  
Author(s):  
Åge Brabrand ◽  
Bjørn Andreas Faafeng ◽  
Jens Petter Moritz Nilssen
Keyword(s):  
Algal Growth ◽  
Perca Fluviatilis ◽  
Rutilus Rutilus ◽  
Phosphorus Release ◽  
Selenastrum Capricornutum ◽  
Phosphorus Loading ◽  
External Loading ◽  
Phytoplankton Production ◽  
Roach Rutilus Rutilus ◽  
Order Of Magnitude

In laboratory tanks with bream (Abramis brama), perch (Perca fluviatilis), and roach (Rutilus rutilus) concentrations of phosphorus and nitrogen increased with time. Phosphorus was mainly released as soluble molybdate-reactive phosphorus (SRP); nitrogen almost exclusively as ammonium. The release increased with the species' tendency to forage on littoral sediments and with a smaller fish size. Bioassays with the test algae Selenastrum capricornutum showed that released phosphorus was readily available to algal growth. The total supply of phosphorus to the epilimnion of Lake Gjersjøen was calculated from the external supply from the tributaries and the estimated phosphorus release from total roach biomass. From May to October 1980 phosphorus release from the roach population contributed about the same order of magnitude as the total phosphorus loading from the watershed. During the period with the most serious phosphorus depletion to the phytoplankton (July, August, and September), the phosphorus supply from fish was about double that of the external phosphorus supply, confirming the important role of sediment-feeding fish populations in the eutrophication processes of lakes.

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