Cockle Survey

There have been six surveys of cockle numbers and sizes in the Pauatahanui Inlet. The first was conducted by DSIR in 1976 as part of the Pauatahanui Environmental Programme. The following five have been done by the Guardians at 3-year intervals since 1992, with the most recent being in November 2004. The 1992 survey found that the cockle population had declined to about 40% of the 1976 size. The subsequent surveys show some fluctuation but the differences from 1992 are not statistically significant and we thus can say that the population has stabilised at this new level.

Trend in total cockle population within Pauatahanui Inlet, 1976-2004.

We will never have an exact knowledge of the timing of the decline between 1976 and 1992 but it appears that the factors causing the decline no longer operate, at least at that highly destructive level. However, the fact that recovery towards the 1976 level has not occurred indicates that there has been a permanent deleterious change in the environment for cockles. The most likely major cause is the serious increase in the rate of sedimentation due to increased flow of sediment into the streams of the catchment from erosion and poor control of earth movements during suburban and rural development. Other factors such as increased heavy metal and hydrocarbon residue pollutants from road runoff may play a part. These factors are currently being investigated by the Greater Wellington Regional Council.

	1992	1995	1998	2001	2004
Juveniles as a percentage of total cockle population, 1992-2004.

On the brighter side, 2004 was a massive recruitment year, with the proportion of juveniles in the population being more than twice that in 1998 and 2001 (it is probable that juveniles were underestimated in 1992 and 1995). We can only hope that this will convert to a growth in the adult population over the next few years.   Additional reports and information During Sea Week 2001 we invited NIWA scientist Mike Hine to give an illustrated talk "Health of cockles in the Porirua Harbour and Pauatahanui Inlet". Read the press release. An archaeological dig on the south side of the Inlet in 2000 yielded some significant evidence about Maori resource use and the huge size of cockles found then. Read the abstract. Check out the Cockle Story (August 2007). Find out about the Transmission Gully proposal and its potential effects on the Inlet. Read about a pollution study undertaken on cockle flesh. For more information contact John Wells on 234 1788 or at wellsjm@xtra.co.nz.

Last updated: Thursday, March 13, 2008