Cockle survey


The 2016 triennial cockle survey was our most significant and, as it turned out, most demanding exercise of 2016. There is always a lot of planning that goes into this task, partly because it involves such a large number of volunteers who need to know the right procedure and also require close coordination on the day. However, because of November's storm, and the resultant conditions in the Inlet, the population count was, for the first time ever, postponed and moved to its fall-back date of 11 December. It was hoped that Inlet conditions would recover in the intervening period to allow the chance of valid data to be gained for a successful statistical analysis. If, because of the storm, the cockles suffered from the influx of sediment or high volumes of fresh water, it would be important to know this as a measure of the effect of a natural phenomenon. All we could do was hope for reasonable weather on the day.

Considering all the drama that the storm and resultant delay created, the exercise was in the end fairly successful. The main problems encountered were due to the reduced number of volunteers who turned up to help, many perhaps lost to alternative, seasonally focused plans. Not all stations could, therefore, be measured on the Sunday and some volunteer work was needed to fill in the gaps.

As usual the stats were collated and passed to NIWA for a full analysis and this report is now in and available here to be downloaded.

The 2016 NIWA report is available here as a PDF.


This is the full report on the analysis by NIWA, but a brief summary of the results is as follows.


Before December, and the storm and floods that had just occurred, the cockle population size in Pāuatahanui Inlet was expected to continue a long-term upward trend. However, the 2016 survey showed the first decline in population size since 2001 (See Figure below). For example, total population size increased 87% between 1995 (180 million cockles) and 2013 (336 million cockles). However, the population size of cockles declined by 14% between 2013 and 2016 to 288 million. Cockle counts were lower than in 2013 but there were signs that the population may have continued to increase if it wasn’t for the floods. The highest count (a 176-cockle quadrat) was higher than for any of the previous surveys.

Factors relating to the earthquake and floods prior to the December 2016 survey probably had a significant effect on the cockle population in the Inlet. The high levels of sediment deposition observed in the intertidal areas, and the high turbidity of the seawater, are likely to have caused mortalities that have reduced cockle density and, therefore, population size. These factors will also likely cause ongoing physiological effects. The high sediment deposition also affected sampling and data comparability to previous surveys. Two transects could not be sampled because of the high levels of sediment deposition observed in the intertidal areas. 

The negative trend in the cockle population size in 2016 probably reflects changes in the environmental conditions in Pāuatahanui Inlet, and the large flood events produced conditions that are less favourable for cockles. Rebuilding of the cockle population will depend on how long these conditions persist, along with the other climatic and biological factors that determine the recruitment and survival of cockles. The next survey will show how the population has responded. (Keith Michael, Fisheries Scientist NIWA).

Cockle Surveys



Read previous NIWA reports: 1992    1995    1998    2001    2004    2007    2010     2013

Read about cockles and cockle population trends in Cockles of the Inlet.





Last Updated: 13/08/2017 6:33pm