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A distinction is drawn between three development phases for char lake ranching: - A ranching expansion phase (Phase 1: 1984-93): During this period, the level of releases of Arctic char autumn fry gradually went from zero to 150,000 autumn fry (34/ha). The percentage of autumn fry from seed fish caught in Lake Geneva fell regularly, going from 100% to 22% over the period of 1989-1993; - A ranching phase at a high level (Phase 2: 1993-2002) during which, apart from 1999 (100,000), the annual releases fluctuated from 150 to 200,000 autumn fry, with the level targeted being 150,000; - A medium-level ranching phase (Phase 3: 2003-2008) during which the annual releases fluctuated from 60 to 130,000, with an average level in the vicinity of 100,000. In the 2002-2005 period, there was a gradual decline in ranching, which went from a level of 150,000 to 60,000. Annual releases of autumn char fry from 1984 to 2008 • The effectiveness and yield of lake ranching As is the case for the whitefish, the effectiveness of ranching in relation to the char was estimated via marking campaigns. Firstly, these made it possible to assess the respective contributions of artificial and natural restocking in char fisheries during the initial (1985 cohort), middle (1990 cohort) and recent (2003 and 2004 cohorts) phases of reoligotrophication. The end objective aimed for was to make a judgement about the development of population supports depending on the marked fish rate and therefore the development of the contribution made by natural restocking. As a supplement, these markings made it possible to assess the restocking yield (kg of catches/1,000 autumn fry released). The Table below summarises the marking data compiled since 1985. Lake Bourget and the «Belledonne» massif YEAR 1985 TYPE OF MARKING Adipose fin ablation 1990 Fins ablation 2003 2004 Fluorescent marking Fluorescent marking NUMBER OF FRY RELEASED (% MARKED) 10,300 (100%) 92,500 (55%) 120,900 (100%) 90,000 (100%) RELEASE STAGE Autumn fry Autumn fry Autumn fry Autumn fry CONTRIBUTION TO CATCHES R 35 - 40 % S 25 - 35 % R 55 - 90 % S 50 - 90 % R 60 - 90 % S 75 - 85 % R 60 - 90 % S 90 % Assessment of the char fry marking campaigns R: Contribution to catches of seed fish S: Contribution to captures in the fishing season. In bold: Contribution to the dominant age category AMATEUR FISHING YIELD (KG/1,000 FRY) PRO FISHING YIELD (KG/1,000 YIELD) TOTAL YIELD (KG/1,000 YIELD) 26 30 56 14 12 26 8.7 9.1 17.8 6.2 6.2 12.4
In 1985, the monitoring highlighted the great effectiveness of the ranching carried out with fed fry (autumn fry). Indeed, the quantities released were very low, but even so, the contribution of fry released in 1985 attained a level of 35 % on average. In other terms, this release gave rise to a good yield, namely 55.6 kg per 1,000 char fry released. Moreover, the char produced by ranching stayed around for a long time (up to stage 6+) in terms of fishing, and as seed fish in spawning grounds. The study conducted during the recent period shows that the contribution made by restocking is still largely dominant within the context of char production in spite of the reoligotrophication of Lake Bourget. Thus, the stocks and the catches stemming from this are greatly dependent on the release of young fish carried out 3 years before (cf. the Figure above). However, in spite of its strong contribution, lake ranching seems less effective than it was in its early days if you refer to the yields calculated during the various periods. For the 1990 cohort, the ranching carried out on the one hand played an important role both in terms of the fishery and in the fishing of seed fish, with this applying to the 3 age categories (2, 3 and 4 years) constituting the bulk of the catches. For 3-year-old chars (the age category at which they are mature), ranching makes a major contribution that is close to 90 %. It can be stated that at the start of the lake ranching, its contribution to the fishery as well as to reproduction was an important one. More recently, the development of mass marking techniques (fluorescent marking) has enabled a new assessment of ranching during the reoligotrophication period. The last two marking operations carried out in 2003 and 2004 showed that ranching made a very strong contribution to catches of fish and seed fish, amounting to 90 %. In other terms, only 10 % came from natural restocking. The yields seem to be down compared to the start of lake ranching as they were 18 and 13 kg/1,000 fry released respectively in 2003 and 2004. These marking campaigns suggest that there was a downward trend in the ranching yield between its initial phase and the recent period. For example, for the same release level of 90,000, there was a lower yield in 2004 than in 1990. Number of fry released from 1987-2010 and the CPUE in terms of the number of chars per trip This drop in the yield is perhaps related to the change in the environment, trophic resources (reoligotrophication) and fish stocking (the increase in the stocks of whitefish, which is a trophic competitor of the char’s, and the increase in pike (which is a predator)). Recent catches by professional fishermen do therefore have the same magnitude as during the previous reference period (1920-1950), with the exception that they are largely based on the success of releases of young fish rather than on natural restocking. In spite of everything, even though it is low (around 10 %), there is still a portion of the char population that is the result of natural stocking. The spawning grounds which contribute to this residual functionality do however still have to be located, and their characteristics need to be ascertained. 31
Page 1: Sustainable management of leisure a
Page 5 and 6: Contents I. About SILMAS...........
Page 7 and 8: 1. The general framework: the Alpin
Page 9 and 10: 1. Objectives Within the SILMAS pro
Page 11 and 12: III. Presentation of interesting fe
Page 13 and 14: SPECIES BEFORE 1900 PRESENT DAY Whi
Page 15 and 16: For the Cyprinidae, mainly roaches
Page 17 and 18: 2. LAke ANNECY (f): Fishing managem
Page 19 and 20: selling to private individuals, and
Page 21 and 22: and quality monitoring of the lake
Page 23 and 24: Lastly, observation of the whitefis
Page 25 and 26: 3. LAKE BOURGET (f): Assessment of
Page 27 and 28: . Fishing yield (CPUE) The yields a
Page 29: C. DEVELOPMENT OF THE POPULATION OF
Page 33 and 34: vulnerable species and supporting t
Page 35 and 36: D. RESULTS: SUCCESSES AND DIFFICULT
Page 37 and 38: B. THE PROTECTION ZONE AND USAGE-RE
Page 39 and 40: C. DEVELOPMENT OF THE REGULATIONS I
Page 41 and 42: 1. LAKE ISEO (i): Restoration of fi
Page 43 and 44: C. THE SOLUTIONS IMPLEMENTED The 80
Page 45 and 46: (Photos: R. BENDOTTI) - Start of th
Page 47 and 48: 2. LAKE SERRE-PONÇON (f): Project
Page 49 and 50: The pike, which is a higher-level p
Page 51 and 52: water level and which cannot withst
Page 53 and 54: The development principle for the s
Page 55 and 56: This site is fed by water from a sm
Page 57 and 58: this surface area has been used for
Page 59 and 60: as a spawning zone and as a habitat
Page 61 and 62: E. PARALLEL RESEARCH EFFORTS CARRIE
Page 63 and 64: The various situations referred to
Page 65 and 66: purposes (Annecy, Bourget): the num
Page 67 and 68: VI. Summary sheets relating to each
Page 69 and 70: LAKE ANNECY France Characteristics
Page 71 and 72: LAke SERRE-PONÇON France Character
Page 73 and 74: LAke ossiach Austria Characteristic
Page 75 and 76: LAke idro Italia Characteristics LA
Page 77 and 78: LAke candia Italia Characteristics
Page 79 and 80: lake Caldonazzo Italia Characterist
Page 81 and 82:
lake garda Characteristics LAKE Ita
Page 83 and 84:
lake tergalo Italia Characteristics
Page 85 and 86:
Summary of the action 5.3 85
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