Impacts of Morphological Characteristics on Target Strength of Chub Mackerel (Scomber japonicus) in the Northwest Pacific Ocean

Abstract

Chub mackerel (Scomber japonicus) is an important commercial fish in the Northwest Pacific Ocean. Accurate target strength (TS) underpins acoustic stock assessment but the TS of S. japonicus is still poorly understood. In this study, the Kirchhoff-ray mode (KRM) model was used to estimate the TS of S. japonicus and its relationship with sound wave frequency and fish morphology. The results revealed that TS values varied with pitch angle shifts, with the impact on fish scattering strength being greater at higher frequency. This is less important because 38 kHz has been used for the biomass assessment of these fish resources. At frequencies of 38 kHz, 70 kHz, 120 kHz and 200 kHz, TS was greatest at a pitch angle range of -10° to 0°, which was related to the angle of the swim bladder tilt. There were almost no differences between TS estimated using the measured pitch angle distributions and using the universal distribution. When the measured pitch angle was N[-3°,4°], the average TS of S. japonicus with body length of 12.04–22.17 cm at four frequencies was -48.88 dB, -49.14 dB, -49.75 dB and -48.55 dB, respectively. The regression intercept (b20) in TS–body length equation was -73.27 dB, -73.56 dB, -74.18 dB and -73.46 dB, respectively. Variation in TS range at 0–300 m depth was about 10 dB. The simulated broadband target strength spectrum shows the scattering characteristics of individuals with different swim bladder length between 0–250 kHz. These results could be used for identification of S. japonicus in echograms and provide reference for acoustic stock assessment of S. japonicus in the Northwest Pacific Ocean.

Acoustic target strengths and swimbladder morphology of Chub mackerelScomber japonicusin the Northwest Pacific Ocean

“…Reported TS measurements at b 20 using the tethered method included −64.1 dB at 25 kHz and −65.5 dB at 100 kHz for lengths of 23.0–26.8 cm [19] and −67.2 dB, −69.9 dB, −66.9 dB, and −71.1 dB for lengths of 26.2–38.3 cm at 50, 75, 120, and 200 kHz, respectively [20]. A previously reported KRM model used for frequencies of 38, 70, 120, and 200 kHz for S. japonicus TS (FL=15.4–26.2 cm) b 20 yielded −66.02, −66.50, −66.00, and −67.35 dB, within 1 dB of the present study’s results [22], while another study reported values 5–6 dB lower, indicating significant outcome differences based on model parameters [7].…”

“…Chub mackerel swimbladders were previously reported as showing a long extension, bending below the vertebral column, with a volume-to-body ratio of 3.2%, length ratio of 25%, and posture angle of 11.9° [20]. The reported range of body length of 18 specimens was 12.98∼22.17 cm, with a mean of 16.08 ± 3.15 cm (mean ± SD); the SBL range was 1.45∼6.63 cm, with a mean of 3.64 ± 1.49 cm; and the swimbladder tilt angle was 1.7° to 14.0°, with a mean of 8.26° ± 3.62° [7]. Although both of these studies lack SBH/SBL results, the SBL/SL findings of our study also classify our specimens as having round swimbladders.…”

“…The copyright holder for this preprint this version posted May 6, 2024. ; https://doi.org/10.1101/2024.05.03.592349 doi: bioRxiv preprint abundance of the Pacific stock of chub mackerel declined in the 1990s and early 2000s. Since 2013, when a strong year class occurred, its abundance dramatically increased [6,7]. In Korea, chub mackerel has consistently recorded the second-highest catch volume after anchovy, with an average annual catch of 110,640 metric tons from 2018 to 2022 [8].…”

Acoustic Target Strength of Thornfish (Terapon jarbua) Based on the Kirchhoff-Ray Mode Model

“…Another significant factor affecting the TS of T. jarbua is the pitch angle, which is related to the individual size, swimming posture as well as living conditions [39]. In this study, two classic types of pitch angle distributions were adopted to calculate the average TS of T. jarbua [34].…”

“…The KRM model was adopted to quantify the TS variation of walleye pollock (Theragra chalcogramma) for elaborating the influence of its ontogeny, physiology, and behavior [38]. In addition, it was also used to evaluate the impacts of morphological characteristics on the TS of chub mackerel (Scomber japonicus) [39].…”