Physical characteristics such as water temperature, turbidity, and salinity (via conductivity measurements), along with metocean data (including wave and underwater currents), help to inform whether a site is suitable for aquaculture. Further biological and chemical parameters such as pH, Chlorophyll-a, dissolved oxygen (DO), and CO2 can help indicate how a particular site is performing and whether any intervening works are required to improve the immediate conditions. In addition, these parameters can provide more comprehensive understanding of the impact and frequency of marine heatwaves and harmful algal blooms (HAB), both of which are increasing common around the world and directly linked to fish mortality rates.
Advanced Measurements
In recent decades, the need for aquaculture professionals to measure these parameters in real time has been supported by rapid technological advancements. Turbidity measurements were once collected using a Secchi disk—a simple device deployed off the side of a vessel to give an indication of water clarity—but today, real-time measurements of turbidity can be measured using optical in-situ techniques. These methods use a transmitted light detector to measure how much of the light is scattered by particles within the water. Such technology is split between nephelometers, which use a 90° detector angle, and optical backscatter (OBS), which uses a larger detector angle, with further scatter methods available depending on the application.
The Valeport Hyperion delivers high-performance measurements in a compact and robust package. (Image credit: Valeport)
Measurements of Chlorophyll-a, the most abundant form of Chlorophyll within photosynthetic organisms, previously involved the collection of water samples for laboratory analysis, using high-performance liquid chromatography (HPLC) to determine the concentration of Chlorophyll-a present. A useful feature of Chlorophyll-a is its ability to fluoresce when excited with light of a particular wavelength. This characteristic allows for in-situ, real-time measurements of the pigment with a suitable fluorometer, dramatically decreasing both the time and cost required to obtain Chlorophyll-a measurements.
Access to real-time monitoring data is revolutionizing the way in which the fisheries and aquaculture industries operate, improving efficiencies and reacting faster to potential hazards, such as HABs or eutrophication events (excessive richness of nutrients in a water body). Whilst this data is clearly of high importance to aquaculture, measurements of parameters including turbidity and Chlorophyll-a provide insight into the health of the wider ocean and, by extension, traditional fisheries.
Sustaining Global Fish Stocks
Most of the world’s fisheries rely on specific habitats, including seagrass meadows, mangroves, and reefs, which act as nurseries for juvenile fish. Multiple cod, pollock, and herring species, in particular use seagrass meadows for this purpose. These habitats, however, are under great strain due to human-induced habitat degradation. On a global scale, the role of seagrass meadows within the climate system cannot be understated—they occupy ~0.2% of the seabed but can sequester 35 times more carbon than tropical rainforests.
HydroSurv, a Devon-based uncrewed surface vessel (USV) manufacturer and operator, has achieved significant advancements in acoustic mapping techniques for seagrass assessment, initially leveraging the Valeport VA500 altimeter and an advanced machine learning toolchain to ascertain critical parameters such as seagrass coverage, density, and canopy height to derive the submerged aquatic biomass and therefore the carbon sequestration potential.
Harnessing Optical Fluorometry
Responding to requests from public body commissioners, HydroSurv has since extended the yield of data from the survey system by integrating Valeport Hyperion Chlorophyll-a and Turbidity sensors into the payload. This enhancement allows simultaneous collection of environmental data alongside hydroacoustic measurements providing a more comprehensive understanding of seagrass ecosystems and, by extension, their ability to sustain juvenile fish and species critical to global fish stocks.
The Valeport Hyperion range of fluorometers provides accurate measurements of environmental parameters for a variety of applications via the method of optical fluorometry. This process utilizes the natural ability of certain substances to fluoresce by exciting a water sample at a certain wavelength (determined by the parameter of interest) and detecting an emission at an alternative, higher wavelength. This allows for highly precise measurement of the environmental parameters at very low concentrations—some Hyperion fluorometers can detect the equivalent of 1.5 drops in an Olympic-sized swimming pool!
Valeport’s Hyperion sensors are ideal as a stand-alone sensor or part of a multi-sensor array. (Image credit: Valeport)
The resulting processed data is effortlessly hosted and visualized with HydroSurv’s EasySurv cloud-based GIS application, which not only facilitates visualization but also empowers users with temporal difference modeling tools to monitor the rate of change between individual surveys. Additionally, EasySurv offers the flexibility to incorporate further metadata into datasets, enabling spatial analysis of other parameters.
As HydroSurv enters its third phase of development, supported by co- funding from DEFRA (Department for Environment Food and Rural Affairs) and Innovate UK, it is now scaling its demonstration surveys. Pilot initiatives are underway at worksites in Falmouth, Plymouth, and Salcombe to showcase the efficacy and versatility of HydroSurv’s cutting- edge approach using Valeport products.
To find out more about Valeport’s oceanographic instruments, visit: www.valeport.co.uk
This feature appeared in Environment, Coastal & Offshore (ECO) Magazine’s 2024 Summer edition Fisheries & Aquaculture, to read more access the magazine here.
