Management of Sand Beaches for the Protection of Shellfish Resources.
Thesis DisciplineEnvironmental Sciences
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Exposed sand beaches are increasingly under pressure from human population growth and recreation. Activities, such as vehicle driving and horse riding, can pose a significant threat to specialist fauna living in the sediment. Few studies have evaluated how vehicles affect sand beach fauna and none have examined the impacts of horse users on burrowing bivalves. The research questions addressed were: do vehicles and/or horses on sand beaches impact on intertidal shellfish populations? Following on from this, can management policies mitigate any negative impacts from such activities on sand beaches? This research required an interdisciplinary approach utilising methodologies from coastal geomorphology, biological science and management. The intertidal distribution of the New Zealand surfclam Paphies donacina (southern tuatua) determined seasonally on six exposed surf beaches along Pegasus Bay. The impacts of vehicle and horse users on shellfish survival were experimentally investigated, and novel in situ methods were developed to examine the effects of horses on bivalve survival. Intertidal tuatua were small (< 30 mm) and shallowly buried. Found approximately 30 m below the last high tide line, they may be exposed to vehicle and horse users. There was a positive linear relationship between the number of vehicle passes and tuatua mortality (% tuatua mortality = 4.8 + 0.23 x number of vehicle passes). On average, horse riding resulted in 36.9% tuatua mortality within a single hoof print, but walking resulted in lower mortality than trotting or galloping. Extrapolative modelling predicted that the long-term presence of these users would be highly detrimental to shellfish. Reducing the temporal frequency and spatial extent of vehicle and horse users on sand beaches could decrease shellfish mortality. The thesis results were used to evaluate current management techniques and provide management options to minimise the potential impacts of beach users on shellfish resources.