COCKLE SURVEY

 

THE 2022 COCKLE SURVEY 

The 2022 triennial Cockle Survey is taking place this weekend.

Date:   Sunday 6 November 

Start time:   1:30pm

(We don't think the rainy-day alternative will be needed - Sunday 20 November)

 

Anyone keen to participate can register interest at pauainlet@gmail.com. 

 

Location of the survey is based at the Pāuatahanui Wildlife Reserve, with the entrance beside the Lighthouse Cinema in Pāuatahanui village. 

Volunteers are asked to arrive at the specified time and gather at the Stout Cottage in the Reserve itself (about 100m from the entrance).

Full instructions, equipment and recording materials will be handed out to the groups of 2-4 people selected for one of the 30 transects to be measure. A health and safety talk will be part of this introduction.

We need around 100 volunteers, including team leaders. Those who have experience of past cockle surveys can put forward their names to be team leaders if they wish. Many volunteers have already been selected but a few extra may be useful.

 

NOTE: Team leaders are required to be at the Reserve before 1pm

 

Families and friends are welcome to join in as it can be a fun day for all. However, children under the age of ten may not find the activity exciting enough to maintain their interest throughout the 2-3 hours it is expected to take.

 

This is one of the most important activities that GOPI undertakes as part of its aims to monitor the health of the Inlet and the results are always anticipated with a great deal of nail biting. We naturally hope it indicates that the Inlet is still in a relatively healthy condition, despite the threats that it faces every day.

 

We look forward to seeing you at the Reserve on Sunday.

 

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People interested in the 2019 cockle survey can go to this link to view the FULL REPORT or read a summary of the results below.

  

Key findings of the 2019 Pāuatahanui Inlet cockle survey

  • The total number of cockles measured during the survey was more than 40% higher in 2019 than in 2016. The total cockle population of the Inlet is estimated to have increased by 32% since 2016. It is now at the highest level since 1976.
  • Most of the individual transects were found to have a higher, or markedly higher, number of cockles than in 2016. The highest number of cockles recorded in a single quadrat (0.1 square metres) was 279, much higher than in any previous survey.
  • The average density of cockles over the intertidal survey area was 38 per quadrat, slightly higher than in 2013, significantly higher than in 2016 and higher than for any previous GOPI survey since 1992.
  • The percentage of juvenile cockles in the population increased markedly between 1992 and 2004, from 1% to 16 %, and has since remained between 15.6 %  and 17.4%.

The following chart shows the time-series of population estimates from the year 1976 when it was originally carried out during an extensive survey of Pāuatahanui Inlet by DSIR.

Estimates of total cockle population size and 99% confidence intervals (CI) for Pāuatahanui Inlet, 1976-2019. The initial survey in 1976 (Richardson et al. 1979) used a different survey design. Surveys since 1992, carried out by the Guardians of Pāuatahanui Inlet, have used the same survey design and methods. Estimates using previous method (Method 1) shown in sky blue and estimates using weighting factors for transect length (Method 2) are shown in salmon. Trends in population size are shown as dashed lines. Data for surveys 1976, 1992 and 1995 are not available to recalculate mean population size and 99% CI using Method 1.

 

In summary, the increase in the population of cockles in the inter-tidal zone of Pāuatahanui Inlet in 2019, and the recovery of the population from the decline between 2013 and 2016, show the cockle population is in an improving state. The consistently high percentages of juvenile cockles since 2004 suggests successful settlement of larvae and good survival of spat (larvae that have settled), with possibly some migration of juvenile cockles from subtidal areas.

 

Looking at the individual sizes of cockles, the 2013, 2016, and 2019 populations suggest that all sizes of cockles were affected by the 2016 flood. Juvenile cockles are expected to be more vulnerable to changing environmental conditions such as increasing mud. However, the percentage of juvenile cockles was highest in 2016 (the year of the flood) and may have been driven by an extraordinarily large cockle spat settlement event. More than 50% of the cockles in 2019 were above spawning size (larger than 18 mm in length) and that should maintain future larval production in the Pāuatahanui Inlet.

 

It appears from the results that changes in the environmental conditions in Pāuatahanui Inlet, particularly the increase in terrestrial sediments considered deleterious to cockles, do not appear to have affected the inter-tidal cockle population in recent years. 

 

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Read previous NIWA reports: 1992    1995    1998    2001    2004    2007    2010     2013    2016

 

 

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

 
Last Updated: 04/11/2022 8:34pm