Chinese Conservation Education Trust

This was the seventh survey in the series of monitoring the changes to shellfish populations at Cockle Bay and in spite of the terrible weather most of the stations were sampled and good quality information collected. This is remarkable because sieving wet muddy sand and sorting through the shell debris to find, measure and record the number and sizes of all the live shellfish while rain is pouring down, is not at all easy. Indeed it is a rather miserable way to spend a Sunday morning!

All the CCET members who turned up and worked so hard are to be congratulated for their gallant efforts. Thanks also to Ken Tse and Cen Wen for their organisational work and we were pleased to receive support from the local Ministry of Fisheries Ranger, Barry Wood and the former DoC coordinator of community programmes, Linda Bercusson.

The state of the shellfish populations at Cockle Bay has been in the spotlight recently because it appears that the Bay has been coming under increasing harvesting pressure from the public. Apparently hundreds of cockle gatherers have been coming from near and far whenever the tide was low because they had heard that there were still plenty of cockles to be gathered at Cockle Bay. With all the collectors taking their daily allowance of 50 (and some suspected of taking more than they are allowed) the locals have become worried that the cockle beds might soon be stripped bare.

They approached Ministry of Fisheries about declaring special emergency regulations for controlling harvesting and the Ministry has imposed a temporary collecting ban over the summer period in order to give the cockle beds a chance to recover. This ban would not have been possible at short notice without hard data showing that cockle abundance was indeed in serious decline.

Thank you XiaoWen, for your participating all the events and always with the new friends;

Thanks to the regularity of the monitoring programme conducted by CCET under the direction of the Department of Conservation, it was possible for hard evidence to be assembled and presented so that Ministry of Fisheries could support and action the closure. Without CCET’s well organised efforts this would not have been possible; so all CCET members who have participated in these surveys are to be thanked for giving up their time during their week end breaks, and should be proud of the contributions that they have made.

The closure was based on information from the first six surveys and this most recent, seventh survey shows that the situation on the beach has become substantially worse over the last six months.

This suggests that closure of the beach for shellfish harvesting for just the up-coming summer and autumn period will be completely inadequate. Closure for such a short time implies that the life-cycle correction period for the cockle is within a single year: i.e. if the beach is closed for just six months, in that time enough very small cockles will have grown into large cockles in such numbers that it will be satisfactory for the public to start harvesting again.

It is well known that this is not the case. Small cockles take several years – perhaps up to five or more years - to grow into large cockles, and, moreover, our regular sampling has not shown good recruitment of juveniles across the beach.

The data for the CCET surveys is shown in the accompanying spreadsheets which show the numbers of bivalves for each survey and also the calculated running average on which population changes are best determined.

Of the four transects that we now survey (A = Headland, B = Boat ramp, C = Toilet block, D = North Pohutukawa) transects B and C are most informative because they have been sampled for the longest. Along those transects the greatest changes have been at the 300 m and 400 m stations low down on the shore, which is where harvesters go to gather cockles! Towards the top of the shore where few people bother to collect shellfish, changes to the abundance have been less marked or are statistically negligible especially at the 100m stations.

To emphasise the changes low on the shore, the sequence of cockle abundance (numbers / m²) for the 7 surveys at the 300m & 400m stations of transects B & C are shown below.

B.300 Actual : 455, 150, 635, 406, 360, 275, 230 / m²
B.300 Average : 455, 303, 413, 412, 401, 380, 359 / m²

B.400 Actual : 415, 378, 263, 305, 175, NS, 120 / m²
B.400 Average : 415, 397, 352, 340, 307, 307, 276 / m²

C.300 Actual : 340, 340, 244, 238, 120, 173, 45 / m²
C.300 Average : 340, 340, 308, 290, 256, 243, 214 / m²

C.400 Actual : 570, NS, 305, 483, 220, 110, 200 / m²
C.400 Average : 570, 570, 438, 453, 395, 338, 315 / m²

The running averages clearly show the steady declines in cockle abundance low on the shore.