Elucidation of ecosystem attributes of an oligotrophic lake in Hokkaido,Japan, using Ecopath with Ecosim (EwE) |
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Authors: | Md Monir Hossain Takashi Matsuishi George Arhonditsis |
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Institution: | 1. Graduate School of Fisheries Sciences, Hokkaido University, 3-1-1 Minato-cho Hakodate, Hokkaido 041-8611 Japan;2. Department of Physical & Environmental Sciences, University of Toronto, Toronto, Ontario, Canada M1C 1A4;1. Institut de Recherche pour le Développement, UMR MARBEC & LMI ICEMASA, University of Cape Town, Private Bag X3, Rondebosch, Cape Town 7701, South Africa;2. Ecopath International Initiative Research Association, Barcelona, Spain;3. Institut de Ciències del Mar (ICM-CSIC), Barcelona, Spain;1. Fisheries Centre, University of British Columbia, 2202 Main Mall, V6T1Z4 Vancouver, BC, Canada;2. Université Européenne de Bretagne, Agrocampus Ouest, UMR985 Ecologie et Santé des Ecosystèmes, 65 rue de Saint-Brieuc, F-35042 Rennes, France;1. Ecopath International Initiative Research Association, Mestre Nicolau 8, Bellaterra, Barcelona 08193, Spain;2. Fisheries Centre, University of British Columbia, 2202 Main Mall, Vancouver, BC, Canada V6 T 1Z4;3. Istituto nazionale di Oceanografia e di Geofisica Sperimentale, Trieste, Italy;4. Alaska Fisheries Science Center, 7600 Sand Point Way N.E., Building 4, Seattle, WA 98115, USA;5. Commonwealth Scientific and Industrial Research Organisation, Ecosciences Precinct, 41 Boggo Rd, Dutton Park, Brisbane, QLD 4102, Australia;6. Université Européenne de Bretagne, Agrocampus Ouest, UMR985 Ecologie et santé des écosystèmes, Rennes Cedex, France;7. NOAA Fisheries, Northeast Fisheries Science Center, 166 Water Street, Woods Hole, MA 02536, USA;8. University of Washington, Joint Institute for the Study of the Atmosphere and Oceans (JISAO), Seattle, WA, USA;9. Centre for Fisheries, Environment and Aquaculture Science, Pakefield Road, Lowestoft, Suffolk NR33 0HT, UK;1. National Fisheries Resources Research Institute, Jinja, Uganda;2. University of Iceland, School of Engineering and Natural Science, Reykjavík, Iceland;3. University of South Florida, College of Marine Science, St. Petersburg, USA;4. United Nations University Fisheries Training Programme, Reykjavík, Iceland;5. Kenya Marine Fisheries Research Institute, Kisumu, Kenya;1. IRSTEA, UR EABX, Aquatic Ecosystems and Global Changes, 50 avenue de Verdun, 33612 Cestas cedex, France;2. CNRS, UMR 7208 BOREA, Université de Caen Basse-Normandie, Esplanade de la Paix, CS 14032, 14032 Caen cedex 5, France;3. Cooperative Institute for Marine and Atmospheric Studies, University of Miami Rosenstiel School of Marine and Atmospheric Science, NOAA Atlantic Oceanographic and Meteorological Laboratory, 4301 Rickenbacker Causeway, Miami, FL 33149, United States;4. Littoral Environnement et Sociétés, UMR 7266 CNRS-Université de La Rochelle, 2 rue Olympe de Gouges, 17042 La Rochelle cedex, France;5. UMR 6249 Laboratoire Chrono-Environnement, Pôle Universitaire du Pays de Montbéliard, 4 place Tharradin, BP 71427, 25211 Montbeliard cedex, France;6. Laboratoire de Cytologie Végétale et Phytoplanctonologie, Département des Sciences de la Vie, Faculté des Sciences de Bizerte, Université de Carthage, Zarzouna, Bizerte, Tunisia;1. National Fisheries Resources Research Institute, Jinja, Uganda;2. University of Iceland, School of Engineering and Natural Science, Reykjavik, Iceland;3. University of South Florida, College of Marine Science, St. Petersburg, USA;4. United Nations University Fisheries Training Programme, Reykjavk, Iceland;5. Kenya Marine Fisheries Research Institute, Kisumu, Kenya |
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Abstract: | The fishing practices in the oligotrophic Lake Toya, Hokkaido, Japan, have profound implications in the ecosystem sustainability. The status of the sockeye salmon (Oncorhynchus nerka) population has become a serious concern among the lake managers and policy makers during the last decades. While the decline of the sockeye salmon population has been well documented in Lake Toya, there is considerable uncertainty with regards to the impact on the broader system dynamics. In this study, our objective is to address this knowledge gap by undertaking a synthesis of the Lake Toya food web using the mass-balance modeling software Ecopath with Ecosim (EwE). Our primary research question is to examine the repercussions of the declining sockeye salmon population on the trophic dynamics of the lake. Namely, we assess if there are any competing species that might have benefited from the decrease of sockeye salmon standing biomass and to what extent do these changes propagate through the Lake Toya food web? Our analysis pinpoints the critical role of the Japanese smelt (Hypomesus transpacificus nipponensis) in the system, which demonstrates a wide range of effects on several functional groups at both higher and lower trophic levels in Lake Toya. In particular, being a substantial portion of the masu salmon (Oncorhynchus masou) and adult sockeye salmon diets, the Japanese smelt has a positive impact on the top predators of the system. Amphipods, insects, and shrimp strongly benefit from the autochthonous and allochthonous organic matter in the system, while the tight coupling between phytoplankton and zooplankton seems to be particularly critical for the integrity of the Lake Toya food web. Whereas the values of the different ecosystem attributes (e.g., primary production/biomass, biomass/total throughput, system omnivory index, amount of recycled throughput, Finn's cycling index) provide evidence that Lake Toya is an immature system, we note that the internal redundancy and the system overhead estimates suggest that the lake possesses substantial reserves to overcome external perturbations. We also examined the effects of a variety of fishing policies on the biomass of masu salmon and adult sockeye salmon, which verify the belief that the adult sockeye population is quite fragile with high likelihood to collapse. Our analysis also predicts that sockeye will not rebound unless the fishing pressure exerted is substantially reduced (>50% of the reference levels used). Masu salmon seems to benefit under all the scenarios examined indicating that the intensity of the current fishing activities is significantly lower than its biomass accumulation rate in the system. |
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