Workshop on the development of practical survey methods for measurements and monitoring in the mesopelagic zone (WKMESOMeth)

The Workshop on the development of practical survey methods for measurements and monitoring in the mesopelagic zone (WKMESOMeth) chaired by Ciaran O'Donnell (Ireland), and Gavin Macaulay (Norway), met in Galway, Ireland, 27-28 April 2019.

The workshop objectives were to catalogue current mesopelagic surveys, report on existing data and research findings, report on opportunities and limitations of mesopelagic surveys, evaluate and report on potential for mesopelagic surveys, and determine requirements for carrying out mesopelagic surveys.

Fifteen survey programs currently report acoustic density of fish in the mesopelagic zone, with nine more reporting the capacity to do so. In addition, five large-scale international mesopelagic research projects are underway.The main additional effort required to obtain mesopelagic information on existing surveys were identified to be dedicated trawling for mesopelagic organisms using a trawl designed to catch such organisms, the use of more than one acoustic frequency (preferably several), and careful survey design modification to ensure that the addition of mesopelagic activities does not adversely affect existing surveying objectives.

Limitations in using acoustic techniques to quantify mesopelagic species from existing acous-tic surveys include the lack of acoustic target strength knowledge, the lack of operational range for the higher acoustic frequencies when operated from a surface vessel and obtaining adequate ground-truth information on the species-composition of the observed backscatter. Absolute biomass estimates require more survey and sampling effort and tools than do rela-tive biomass estimates.

An important aim of the workshop was to identify methods that could be used on the Inter-national blue whiting spawning stock survey (IBWSS). The IBWSS survey program has the ca-pacity to do this without disrupting the core work program. However, additional time and re-sources are required. Suitable reporting structures, analysis tools and data repositories already exist within ICES Working Group on International Pelagic Surveys (WGIPS). Similar considera-tions apply to other existing survey programs.

The development of protocols for the classification of mesopelagic fish during the IBWSS survey, through WGIPS, are encouraged and could also be used for the re-analysis of other existing acoustic survey data. This would provide acoustic density and distribution of meso-pelagic fish where none currently exists.