There are a variety of research efforts to improve methods in fisheries acoustics. Many of these aim to reduce the uncertainties associated with various aspects of the technique:
- The Species Identification Methods From Acoustic Multifrequency Information (SIMFAMI) Project
The goal of the SIMFAMI project is to enable the identification of fish species using acoustic methods. Not all echo traces can be ground-truthed. Echotraces are therefore often identified on the basis of their shape, position and density. In Figure 2, for example, the tall dark pillar-like objects are classic echotraces characteristic of schools of herring. However, the acoustic properties of fish can vary according to the particular type of sound that is transmitted from an echosounder. Using a multi-frequency echosounder, it is possible to measure the differing responses of fish to the different frequencies of sound.
- The Combining Acoustic and Trawl Data for Estimating Fish Abundance (CATEFA) Project
The CATEFA project aims to investigate how acoustics can be used during trawl surveys to improve the estimation of the abundance of demersal species.
Marine Scotland scientists also conduct research into statistical interpolation techniques to improve the estimation of abundance, but more specifically to determine the uncertainty of estimates due to statistical sampling (i.e. determine the confidence limits of the estimates). Geostatistics are being investigated, including kriging and conditional simulations.
- The Under Sea Ice Pelagic Surveys (USIPS) project
The USIPS Project looked at the use of an Autonomous Underwater Vehicle (AUV) platform on which to deploy an autonomous echosounder. One of the results of this project demonstrated that fish did not avoid the research vessel MRV Scotia. Scotia is very quiet: she was the first vessel to be built to a specification recommended by ICES intended to limit noise emission such that survey vessels should not disturb the natural distribution of fish.
What the USIPS Project Demonstrated
The results of the USIPS project justified the additional expense that noise reduction measures incurred in the construction of new research vessels (5-10% of build cost). In future, fisheries research vessels should be built to the same rigorous noise specification as Scotia in order to ensure that avoidance is not a source of bias.
AUVs may one day be used for acoustic surveys. In the meantime they can be used for specific behavioural studies and to sample environments which remain inaccessible to conventional research vessels such as the sea surface, the deep sea and under sea ice.