Hawke, L. (2008, February). Assessment of fish populations in the Avon-Heathcote Estuary: 2007. National Institute of Water and Atmospheric Research.

Comissioned by the Christchurch City Council (CCC), this report is the third of six planned annual surveys of the Avon-Heathcote Ihutai estuary designed to monitor changes in fish species diversity and abundance before and after the 2010 construction of an ocean outfall to remove wastewater discharge from Te Ihutai. Trawling for adult fish in the main channels was predominantly used to integrate long term changes and describe recreational fishing experiences, while beach seining for juvenile fish at high-tide margins was used to reflect recent events in the estuary.

Overall, the abundance of most fish species in 2007 was similar to 2005 and 2006 data, suggesting that the sampling intensity was sufficient to reliably assess changes over time. Yellowbelly flounder abundance was intermediate in 2007, comparatively high in 2005, and low in 2006, suggesting that annual variation in short lived species is not unusual. What was notable from this study and previous studies was that the relative abundance of two important flatfish species in the estuary appeared to have changed since the 1960s. Adult sand flounders were noticeably fewer since 1965, whereas adult yellowbelly flounders were larger and more abundant.

The report concluded that these changes in abundance may be related to several factors, including commercial fishing pressure and increasing sea temperatures, in addition to wastewater discharge into the estuary. They recommended future surveys continue to be conducted in November to prevent sea lettuce clogging sampling nets and maintain sampling consistency.