Three Rivers cockle fishery: stock survey results

We have used external contractors to undertake the biannual stock assessment of Three Rivers cockle fishery 2025 (Spring and Autumn). This is the summary of the findings provided by the contractor following the survey conducted in August.

The survey:

• provides an estimation of cockle weights and cockle densities within the Three Rivers
• provides the total cockle biomass for the whole cockle fishery, which is broken down into five defined beds
• provides the spatial analysis distribution of each year class
• provides their size-frequency distribution

We will use the data to:

• calculate the harvestable surplus and
• inform a Habitats Regulations Assessment (HRA) as part of the management plan

This is set out in The Cockle Fishing Management and Permitting (Specified Area) (Wales) Order 2024.

The survey uses a fixed grid of 192 sampling stations at 200m intervals. One sample from each station is taken using a 0.1m² quadrat. The samples are sieved using a 4mm mesh sieve and any live cockle retained are taken as a sample. 

For each station, they recorded:

• cockle counts and weights for four year classes (year 0, year 1, year 2 and year 3+)
• cockle weight of shell length 15mm and greater, and 21mm and greater
• length measurements to show the size distribution across the five defined beds

The total estuary count for summer 2025 was calculated as 4.20 billion (4.20 x10⁹) and the total weight 9,216 tonnes (Table 1). 

Harvestable surplus calculations are based on lower confidence interval cockle weight estimations at the minimum landing size, following the removal of a defined cockle biomass for bird food. This is a precautionary approach to the variability within the sample data.