Hampson, S. C., Marsden, I. D., Roberts, C. (2019, January). Recreational Survey and Evaluation of Cockle (Tuaki) Resources in the Avon-Heathcote Estuary/Ihutai: Summer 2017-2018. University of Canterbury.

Supported by the Avon-Heathcote Estuary Ihutai Trust as a 2017-2018 summer student project, this study was conducted in response to public concerns regarding whether cockle (Austrovenus stutchburyii) populations could sustain current and increased levels of harvesting in low tide mudflats near Redcliffs. To address this concern, cockle (tuaki) abundances were evaluated alongside recreational activities, estuary values, and current management practices.

Ten sites were selected between the Heathcote bridge, along the McCormacks Bay causeway to Monks Bay. Overall, tuaki abundances were highest at Monks Bay and lowest in the causeway channel where abundances had been reducing since 2012. All sites had individuals of a wide size range, indicating regular recruitment, and all sites had cockles of harvestable size, except for Monks Bay. Both wet and dry weight biomass was highest on the city site of the causeway, although values were considerably reduced compared to previous studies. Condition index was also generally low for most sites.

Of 101 estuary users surveyed, most were from local suburbs and over 40% visited the area frequently. Over 80% rated the estuary fair to good in terms of health, pointing to ‘good’ indicators such as wildlife presence and water quality. Generally, people were unaware of management practices in the estuary. Considering current and potential increases in recreational harvesters, it was estimated that 26% of harvestable size tuaki could be removed from the mudflats along the causeway annually, creating uncertainty regarding the sustainability of the population. Consequently, the report recommended future scientific investigations, education, signage and assessments of recreational shellfish catch in the estuary.