Environment Canada. Environnement Canada. Mingelbier et al. - AFS 2014

Transcription

1 Towards Rebuilding the Yellow Perch Stocks in the Fluvial Lake Saint-Pierre (St. Lawrence River, Canada) By Mitigating the Impacts of Agricultural Practices ABSTRACT. Following two decades of dramatic decline of yellow perch landings in Lake Saint-Pierre (St.Lawrence River, Canada), fisheries were recently closed. While the fishing pressure was a determining factor in adult mortality, year class strength index pointed out important recruitment failures since the 1990 s. Lake Saint-Pierre is a large and shallow fluvial lake, (400km2; average depth is 3 m) listed as a biosphere reserve by the UNESCO in Despite its acknowledged socio-economic value (fishing, hunting, ecotourism, etc.), corn and soy crops were grown over large expanses in the floodplain. Using a spatially explicit modeling approach combined with land use analyses, we highlighted that current agricultural practices resulted in a net loss of the best potential spawning habitats for yellow perch. This is especially true for the shallowest portion of the spawning habitat in the floodplain, located just under the two-years flooding recurrence. Our 2D model was validated using 7-years of extensive larval sampling ( ) conducted early in spring just after hatching. We concluded that it is mandatory to restore the best spawning habitats in order to regain a higher level of recruitment. In order to assist the restoration efforts, we identified the most valuable areas for spawning around Lake Saint-Pierre. Marc Mingelbier Forêts, Faune et Parcs Québec Philippe Brodeur Forêts, Faune et Parcs Québec Frédéric Lecomte Université du Québec à Chicoutimi Jean Morin Environnement Canada Pierre Magnan Université du Québec à Trois-Rivières

2 Towards Rebuilding the Yellow Perch Stocks in the Fluvial Lake Saint-Pierre (St. Lawrence River, Canada) By Mitigating the Impacts of Agricultural Practices Marc Mingelbier Forêts, Faune et Parcs Québec Philippe Brodeur Forêts, Faune et Parcs Québec Frédéric Lecomte Université du Québec à Chicoutimi Jean Morin Environnement Canada Pierre Magnan Université du Québec à Trois-Rivières Environnement Canada Environment Canada

3 Context and study area Pop 1 Lake St.Francis Healthy population Water regulation Shore degradation (C.fishing >1970) (Agriculture) 4 genetically distinct YP populations Leclerc et al Pop 2 Pop 3 Lake St.Louis Pop 4 Lake St.Pierre Healthy population Urbanization Shore degradation (C fishing >1970) (Agriculture) Collapsed population Agriculture (Fishing >2012) (Urbanization) (Shore degradation) St. Lawrence River = the outflow of the 5 Great lakes Connecting Atlantic Ocean 3 fluvial lakes, 4 archipelagos, 3 estuaries 4 genetically distinct Yellow Perch populations State of fishery differs LSF & LSL healthy LSP collapsed Human pressures differ LSF & LSL: urban & no C. fishing >1970 and S. fishing in spring >1999 LSP: agriculture and no C.S. fish > /52

4 Two decades of decline in YP commercial landings Landings (tons) Commercial Recreational 5 years moratorium New management rules Buy back of commercial licenses (# active licenses) :

5 Recruitement failure in the LSP age 3 age 2+ age 1+ Gillnets CPUE Moratorium

6 Decreasing submerged aquatic vegetation SAV Abundance Absence Sparce Partial coverage of the bottom Total coverage of the bottom - Abundance of submerged aquatic vegetation ( 3X) - Invertebrates abundance and availability ( 15X) - Growth rate of YOY yellow perch ( 26 %) - Winter survival ( 5X) Hudon et al. (2012) Replacement by benthic cyanobacteria (Lyngbia wollei) Ministerial strategy aims restoring: -the habitat in the LSP floodplain and -the water quality (2013) de la Chenelière et al. (2014)

7 Potential habitat (ha) Extensive agriculture in the spawning habitat under the 2 years flooding recurrency! Despite the aknowledged socio-economical value of the LSP (fishing, hunting, ecotourism, listed as Biosphere reserve by UNESCO in 2000), corn and soy crops were grown over large expanses in the floodplain Y. perch N. pike Pristine situation Habitat loss ~ 75% Including agriculture Water flow at Sorel (m3s-1) Mingelbier et al. (2005)

8 Objectives 1. Model potential spawning habitat in a pristine state floodplain 2. Map land-use 3. Spatial analysis: pristine VS real situation yrs flooding recurrencies

9 2D modelling to quantify fish habitat Literature + Field sampling Yellow Perch spawning habitat ( ) Habitat suitability index Current velocity <10 cm/s Depth m Dense vegetation - NO inorganic substratum or scarce vegetation! Grid of square pixels 80 x 80 m Best habitats: HSI = 2 & 3 9 /52

10 Field sampling 0+ just after hatching

11 Land-use: aerial photographs 1950, 1965 and /52

12 Land-use: interpretation 28 hab. classes + numerisation <all other values> Culture annuelle Culture pérenne Dénudé Eau peu profonde (étg) Emprise Autoroute Exploitation (s,g,c) Ferme Feuillus Jeune friche Lac Marais submergé Marais émergé Marécage arborescent Marécage arbustif Mixte à dominance feuillus Mixte à dominance résineuse Perturbation forestière Plantation d'arbres Prairie humide Pâturage Pépinière Rivière Résidence isolée Résineux Terre agricole inondée Verger, vignoble Vielle friche ville, village, industrie 12 /52

13 Spatial analysis: Pristine VS real + flooding yrs Habitat loss ha Natural environment Suitable for spawning ( ) Unsuitable for spawning ( ) Open water (1997) Recurrence 2 years Habitat loss Roads, houses, etc. Agriculture: annual, perennial and pastures (1997)

14 Spawning habitat (ha) Spawning habitat to be restored in the floodplain 9000 Agriculture intensification ha To be restored Spawning Habitats After restoration

15 Conclusions Contrary to LSF and LSL, the YP fisheries in LSP have dramatically declined during the last two decades. The situation had become so critical that: Sport & Comm Fisheries were closed in 2012; Minister announced a strategy for restoring floodplain habitat and water quality (2013). Although fisheries contributed to the decline of YP in LSP, agriculture is too intense in this area, causing important deteriorations in both habitat and water quality. 2D explicit modelling coupled with land-use analysis revealed that: ha were lost in the floodplain, mostly under the 2 years flooding recurrency; This loss corresponds to the best spawning habitat (HSI 2 & 3) The present findings suggest that the situation will only improve when this species is provided with a healthy environment in which to spawn and develop. The restoration of these essential habitats is a great challenge that will require important cooperative efforts of governmental and non-governmental stakeholders.

16 Thank You!