Development of physical measurement methods for non-invasive in-situ detection of plankton and fish

Background and Objective

The objective of the project is to use hydroacoustic and optical methods to enable the continuous, automated, high-resolution and non-invasive recording of marine organisms in their natural environment. Hereby, optical and acoustic methods can be used individually or in combination, in order to complement traditional sampling with net catches, since both methods can be used non-invasively in a wide variety of environments and provide high spatial and temporal resolution. For the detection of fish and zooplankton, for example, the acoustic methods with lower frequencies (38-200 kHz) offer the advantage that they can be used at moderate distances (tens to hundreds of meters) and cover large volumes. On the other hand, optical methods can be used to distinctly identify animals such as fish and zooplankton organisms; provided the magnification is large enough and the water is clear. In this context, so-called in-situ-instruments are employed at the Thünen Institute on various stationary, but also mobile equipment carriers, and autonomous evaluation procedures are being further developed to make use of the advantages of both optical and acoustic methods.

Target Group

Policy makers, Marine and Fisheries scientists

Approach

At the Thünen Institute, a wide variety of camera and sonar systems are used individually or in combination for continuous, partially automated, high-resolution and non-invasive recording of marine organisms. For example, based on the combination of a moored Acoustic Doppler Current Profiler (ADCP) and a video plankton recorder, the distribution patterns of zooplankton communities were studied with a high spatial and temporal resolution. The video plankton recorder also offers the advantage of investigating fragile species, such as gelatinous plankton, in-situ and, in combination with the ADCPs, identifying any zooplankton species through this imaging technique. The ADCP allows not only for a 3D measurement of the flow field, but also for a measurement of the acoustic backscatter strength along all four sound beams. With these data, it is possible to investigate daily or also seasonal vertical migration patterns of individual zooplankton communities. In general, however, the accurate characterization of different marine ecosystems with hydroacoustic data is limited without the additional integration of biological information. At the same time, only limited quantitative information can be derived from the use of optical data. Accordingly, since the acoustic and optical monitoring systems both have their individual advantages, but also weaknesses, both measuring methods have been and will be used simultaneously in several studies to benefit from the chosen combinations and to enable an autonomous and non-invasive monitoring of different marine ecosystems and their resources in the medium term.

Our Research Questions

How can optical and hydroacoustic measurement devices and their evaluation methods be best combined and further developed, depending on the scientific question, to enable an automated, non-invasive, and temporally and spatially high-resolution monitoring of marine ecosystems? How can we improve hydroacoustic and optical measuring methods and the quality of the data provided?

Preliminary Results

Publications in international journals Presentations and publications in the framework of different ICES expert groups, e.g., Working Group on Operational Oceanographic Products for Fisheries and Environment (WGOOFE), Working Group on Fisheries Acoustics, Science and Technology (WGFAST), Working Group on International Pelagic Surveys (WGIPS) Presentations at international scientific conferences