Symposium Abstract: Effects of 135 years of Oyster (Ostrea chilensis) Fishing on the Benthic Habitat,Associated Macrofaunal Assemblages, and Sediments of Foveaux Strait, Southern New Zealand
H. J. Cranfield, K. P. Michael, G. Carbines, D. P. Gordon, B. Manighetti, A. Dunn, and A. A. Rowden
Management of the oyster fishery, and understanding of the impact of this longstanding fishery on the benthic environment, has been facilitated through periodic surveys. Fishers’ and institutional fishing records and the results of biological, acoustic, and sediment surveys have been analysed to show how historical changes to benthic habitat relate to fishing. The seafloor once consisted of bioherms, hundreds of metres wide and many kilometres long, aligned with the tide, separated by similarly wide swaths of relict pebble-gravel sediment. The macrofauna of bioherms was dominated by bryozoa, (over 200 species), and bivalve molluscs, (over 60 species). Oysters were localised on this habitat alone which was also important for blue cod, Parapercis colias. Much biohermal epifauna was removed as bycatch of the oyster fishery and oysters were subsequently depleted locally more rapidly. Bioherm habitat was important in the formation of biogenic sediments and the recruitment, growth, and survival of both oysters and blue cod. The expansion of relict pebble gravel seafloor with the erosion of biohermal sediments relates directly to areal expansion of fishing as oyster beds were serially depleted. Mytilid bivalves and styelid tunicates are identified as early colonisers of regenerating bioherms, and helical circulation patterns in the tidal flow are implicated in the formation of these linear structures within which fine sediments again begin to accumulate. Regeneration of habitat and rebuilding of oyster and blue cod populations in the absence of oyster dredging suggest that MPAs and rotational fishing could be effective in conserving both habitat and fisheries.