Sampling Plan for an Acoustic Survey of Kükenthal Peak (NAFO Division 6G) to Quantify Alfonsino (Beryx splendens) Biomass, Abundance and Size Composition

Abstract

NAFO Commission requested that the Scientific Council review the protocols for survey methodology, to inform the alfonsino assessment. Thus, this document presents an possible acoustic survey plan of the alfonsino population inhabiting Kükenthal Peak, located in the Corner Rise Seamount Chain, following the Commission’s request. The main objective of this survey plan will be to estimate the distribution, abundance, biomass and size composition of alfonsino (Beryx splendens) on Kükenthal Peak (NAFO Div. 6G) by conducting a hydroacoustic survey during February. Specific objectives will be: estimate the abundance (in number) and biomass (in weight) of alfonsino in Kükenthal Peak. Estimate the alfonsino size composition, length-weight relationship, sex ratio and sexual maturity characterization by sex. Collection of alfonsino gonad and otolith samples for future studies of maturity and age. And characterize the biological environment and the physical environment (Tº, S ‰,) of the pelagic habitat of this species to produce a map of these variables within the survey area in association with alfonsino abundance estimates. It is advisable for economic reasons to conduct the subject acoustic survey with a commercial vessel. Two strata with different levels of sampling effort are proposed due to the patchy distribution of alfonsino as revealed by the echograms provided by the skipper, and also the major occurrence of the species around the slope of the mountains, with little extension towards deeper water (i.e., no extension towards open waters). The survey design will consist on a systematic parallel transects with random starting point, with two different levels of sampling intensity, allocating the maximum effort in the area that historically contained the bulk of the acoustic and trawl commercial records. Transects will be placed to ensure they are perpendicular to the bathymetry of the survey area. There is some evidence that relates vertical migrations of alfonsino concentrations to the illumination of the sea (by the Sun and the Moon). The acoustic survey will carry during moon rising season in February and only collect acoustic data during the daylight hours (0800-2000 hours). Trawl hauls will be conducted only for fish identification and the collection of alfonsino length distribution and biological data. Therefore, trawl station locations will be selected according to the acoustic records.