Neil K. Dawe1, W. Sean Boyd2, Terri Martin3, Shannon Anderson4, Margaret Wright5
1 Canadian Wildlife Service, retired; corresponding author; 5421 Robertson Road, Delta, B.C. V4K 3N2; e-mail: email@example.com
2 Environment Canada, Science and Technology, 5421 Robertson Road, Delta, B.C. V4K 3N2
3 City of Campbell River, 301 St. Ann’s Road, Campbell River, B.C. V9W 4C7
4 Fisheries and Oceans Canada, Ecosystem Management Branch – South Coast Area, 150-1260 Shoppers Row Campbell River V9W 2C8
5 Fisheries and Oceans Canada, Resource Restoration, 1965 Island Diesel Way, Nanaimo, B.C. V9S 5W8
Abstract: We document significant, negative changes in vegetation composition of intertidal marshes on constructed and natural islands in the Campbell River estuary between 1994 and 2012. We also provide compelling evidence that vegetation changes were caused primarily by resident Canada Geese. Of the 9 dominant plant species present in the estuary, all showed significant changes in frequency and/or mean cover values over time. Four species, Carex lyngbyei, Deschampsia cespitosa, Eleocharis palustris and Triglochin maritima, declined significantly in frequency or cover values. Five species, Juncus balticus, Potentilla egedii, Isolepis cernua, Lilaeopsis occidentalis, and Agrostis sp., showed significant increases in frequency or cover. In 1994, marshes on all islands, excluding higher elevations of Nunn’s Island, were dominated by C. lyngbyei. However, by 2012 all marshes were dominated by J. balticus. An estimated minimum of 12 tonnes of C. lyngbyei dry mass is being lost annually from island marshes as input to the estuarine food web, a result of the goose impacts to the marshes. Prior to the late 1980s, the Canada Goose was an uncommon bird in the Campbell River area. However, over the period 1991–2001 their winter numbers increased at a rate of 18% per year but now appear to have stabilized. The summer goose population on the Campbell River estuary now averages more than twice the Campbell River area winter numbers. That, coupled with banding data, suggests a moult migration may be occurring as geese move from southern regions of the island, and perhaps elsewhere, to the Campbell River estuary. If the island marshes on the estuary are to recover it will be necessary to reduce the number of Canada Geese to some small fraction of their current level or eliminate them altogether from the area.
Key Words: Agrostis sp., Branta canadensis, Campbell River estuary, Canada Goose, Carex lyngbyei, Deschampsia cespitosa, Eleocharis palustris, grazing, grubbing, impacts, Isolepis cernua, Juncus balticus, Lilaeopsis occidentalis, moult migration, Potentilla egedii, resident geese, Triglochin maritima, Vancouver Island.
Dawe, N. K. , W. S. Boyd, T. Martin, S. Anderson and M. Wright. 2015. Significant marsh primary production is being lost from the Campbell River estuary: another case of too many resident Canada Geese (Branta canadensis)? British Columbia Birds 25: 2–12. First published on-line April 2014.
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