# Cockle Population Dynamics in a Complex Ecological Aquatic System

## TL;DR

This study examines cockle populations in Portugal's Ria de Aveiro, finding that environmental factors and overfishing threaten their sustainability.

## Contribution

The study provides new insights into cockle population dynamics and proposes management strategies for sustainable harvesting.

## Key findings

- Cockle density varied greatly across Ria de Aveiro, with peaks over 5900 individuals per square meter in summer and autumn.
- Environmental factors like salinity, temperature, and sediment strongly influence cockle distribution and growth.
- Average cockle size nears legal minimum, indicating potential overfishing and population risk.

## Abstract

The European cockle is a key shellfish in Portugal’s Ria de Aveiro, supporting both nature and local livelihoods. This study looked at where and when cockles are most common, how they grow, and where young cockles settle. We found differences across the lagoon: in some areas cockles were absent, while in others they were extremely abundant, especially in summer and autumn. Their numbers and growth were strongly shaped by water salinity, temperature, currents, and sediment. Alarmingly, the average size of cockles was close to the legal minimum for harvest, raising concerns about overfishing. These results show that both environmental conditions and harvesting pressure put the cockle population at risk. To secure this resource for the future, better management is needed, including strict compliance with minimum catch size, seasonal harvest bans, and habitat protection.

Cerastoderma edule, the European edible cockle, is a key species in the coastal ecosystems of Portugal, particularly in Ria de Aveiro, a biodiversity hotspot and a critical area for cockle harvesting. This study aimed to assess the population dynamics of C. edule in Ria de Aveiro, focusing on spatial and seasonal patterns in density, growth, cohort composition, and recruitment areas, to provide baseline data for sustainable management. Our results revealed marked spatial and seasonal variability in cockle density, ranging from complete absence at some upstream sites to peaks of over 5900 ind. m−2, with recruitment concentrated in summer and early autumn. Environmental gradients, particularly decreasing salinity inland, seasonal temperature shifts, and current velocity, strongly shaped the distribution of recruits and adults, while cohort lifespan and growth performance varied with sediment conditions and lagoon position. Concerningly, the maximum mean shell length observed is close to the legal minimum catch size, raising questions about population sustainability under current harvesting pressures. This interplay of environmental drivers and harvesting pressures poses risks to population viability. Effective management strategies, including adjusted catch sizes, seasonal harvesting bans, and habitat conservation, are essential to ensure the sustainable exploitation of cockles in Ria de Aveiro. Enhanced research and monitoring efforts are recommended to support informed management decisions and protect this valuable resource.