BELAS BRUVs survey | belasproject

The BELAS BRUVs survey

In this page we explained what is a BRUV and how it works.

Now keep reading to learn about our sampling design and deployment strategy.

Sampling Design: Understanding the Ría de Vigo Ecosystem

To optimize our data collection, the Ría de Vigo is divided into three distinct zones, each with unique environmental characteristics:

INNER RIA:
- Characteristics: Strongly influenced by variations in salinity due to high winter rainfall.
- Challenges: Fluctuating environmental conditions and limited visibility.
MIDDLE RIA:
- Characteristics: Highly affected by human activities, with numerous marinas and heavy boat traffic.
- Challenges: Anthropogenic impact and complex underwater structures.
OUTER RIA:
- Characteristics: Connected to the continental shelf and open ocean, with greater depths and less human interference, strong upwelling events.
- Challenges: Increased depth and open ocean dynamics.

Note that each of these zones is further split into North and South sections. This subdivision helps balance the sampling design and ensures comprehensive coverage of the distinct environmental conditions present in each part of the Ría.

outer south

outer north

middle south

middle north

inner south

inner north

Depth Range Considerations: Light Penetration and Habitat

We categorized the depth into two ranges to capture the diversity of habitats and species:

0–15 meters:
- Habitat: Shallow waters, significant light penetration, presence of kelp forests.
- Visibility: Generally higher but can be affected by water turbidity.
15–30 meters:
- Habitat: Deeper waters with less light, often beyond the reach of kelp.
- Visibility: Limited visibility due to the rich, nutrient-loaded waters of the Ría.

Due to poor visibility below 30 meters, we opted to avoid deeper sampling to prevent recording unusable footage.

0-15 m

15-30 m

Our Deployment Strategy: Covering the Ría Efficiently

To ensure comprehensive coverage and independent sampling, we deployed the BRUV system across nine stations, with the following layout:

Three areas: Inner, Middle, and Outer Ría.
North/South delimitation
Two depth ranges per area: 0–15 meters and 15–30 meters.
Three stations per area: Stations are 800 meters apart to maintain independence.
Four BRUV deployments per station: Each deployment is separated by 250 meters to minimize overlap and maximize data quality.

This structured approach should provide us with detailed data on the species inhabiting the Ría de Vigo's diverse environments.

Challenges and Custom Solutions

Deploying the BRUV system in a dynamic and busy environment like the Ría de Vigo presented several challenges, including:

High human activity: Fishing, boating, and industrial operations.
Complex underwater topography: Navigating mussel rafts, marinas, and other structures.
Poor visibility: Rich, nutrient-laden waters reduce light penetration.

Our Solutions:

Custom-made frames and deployment techniques tailored to each specific environment.
Strategic planning and collaboration with local stakeholders to ensure safe and effective deployment.

This study aims to contribute to the growing body of research using BRUVs and provide new insights into the behavior and distribution of elasmobranchs in the Ría de Vigo.