Surveys of subtidal reefs in the Southwest National Park Marine Nature Reserve 2004-2017
Surveys of subtidal rocky reefs were conducted in the Port Davey region as part of a broader study into the effectiveness of marine protected areas (MPAs) in Australian temperate waters. Surveys were undertaken with an identical methodology to that applied in corresponding studies in eastern and northern Tasmania, Western Australia, South Australia, New South Wales and Victoria. Surveys assessed fish size, diversity and abundance, as well as macro-invertebrate abundance and algae cover.
Ecological reef surveys of Tasmania’s South West National Park Marine Nature Reserve were conducted in March/April 2004 (15 sites), April 2005 (20 sites), March 2006 (26 sites), April 2007 (22 sites), April 2008 (21 sites), April 2009 (21 sites), March 2011 (21 sites), March 2012 (17 sites), February 2013 (21 sites), and April 2017 (17 sites), plus additional surveys in western Bathurst Channel in most years. Zoning regulations were introduced in the marine park in February 2005.
Surveys at Port Davey revealed a relatively low diversity of fishes, dominated by Notolabrus fucicola (purple wrasse) and Notolabrus tetricus (blue-throat wrasse). Mobile invertebrate assemblages were dominated by Haliotis rubra (blacklip abalone) and Jasus edwardsii (southern rock lobster) with other mobile invertebrate species only found at low densities. A very diverse algal community was recorded with some species dominating the assemblages throughout the area (i.e. Durvillaea potatorum, Ecklonia radiata, Phyllospora comosa).
Populations of black lip abalone and southern rock lobster changed little in no-take zones during the first nine years of survey, but have increased rapidly over the most recent four year period to 2017. Abalone are now an order of magnitude more abundant in no-take zones than in restricted take or external take zones. Rock lobsters were initially more abundant at the external fished sites outside Port Davey, presumably due to exclusion of sites with relatively high-quality habitat when zones were gazetted. Nevertheless, following a large recent increase in abundance, legal-sized lobsters are now an order of magnitude more abundant in protected zones than external fished zones.
Amongst fish populations, numbers of bastard-trumpter Latridopsis forsteri have remained stable in no-take zones while declining significantly at external fished zones, perhaps a consequence of warming climate. Marblefish (Aplodactylus arctidens) increased in numbers in no-take zones while remaining stable in fished zones.
The survey methodology is designed to detect biological responses of reef communities in no-take and restricted take zones to protection, including interactions. Ideally surveys will extend this data time-series, documenting changes in the abundance and size distribution of species of interest, including species affected by changing population numbers of the highly-targeted species. This should allow clear trends through time in protected zones to be differentiated from broader regional trends, allowing for assessment of marine reserve performance. Monitoring outcomes additionally provide a benchmark when assessing impacts of fishing and associated changes in species composition in SW Tasmanian waters.