Introduction of multi‐frequency acoustics and mid‐water trawl sampling to the CALCOFI program.

Abstract

The CALCOFI program has evolved over time, continually expanding its interdisciplinary study of the southern California Current ecosystem. Historically, CALCOFI comprised studies of physical and chemical oceanography, phytoplankton, zooplankton, ichthyoplankton, marine mammals, and seabirds. However, there was little focus on the mid‐trophic level and the mesopelagic micronekton. In 2010, multi‐frequency acoustics, combined with mid‐water trawl sampling, was introduced. Data were collected with an EK‐60 equipped with five frequencies (18, 38, 70, 120, and 200 kHz) and a Matsuda–Oozeki–‐Hu Trawl (MOHT). Frequency spectrums were generated for all organisms caught in the net using target strength models and categorized into different acoustic groups. Inverse techniques and dB differencing were subsequently used to estimate their abundance and distribution across the CALCOFI grid. [Work supported by NOAA and The Moore Foundation.]