Ex situ target-strength measurements of ice krill (Euphausia crystallorophias)

Abstract

Ice krill (Euphausia crystallorophias) is key stone species for Antarctic neritic food web, replacing the most abundant Antarctic krill (Euphausia superba) in high latitdue coastal zones. To examine the relationship between target strength (TS: dB re 1 m2) and body length of ice krill, Ex situ TS measurements of ice krill were conducted using 38, 120, and 200 kHz split-beam echosounders. Mean TS were obtained from 21 individual ice krill with a broad range of body lengths (L: 13–36 mm). The length (mm) to wet weight (W; mg) relationship for ice krill was W = 0.001218 × 10-3L3.53 (r2 = 0.96). The mean TS-to-size relationship fits were TS38 kHz = -177.4 + 57 log10(L), (r2 = 0.86); TS120 kHz = -129.9 + 31.56 log10(L), (r2 = 0.87); and TS200 kHz = -117.6 + 24.66 log10(L), (r2 = 0.84). Empirical estimates of the relationship between the TS and body length of ice krill were established at 38, 120, and 200 kHz and compared with predictions obtained from both the linear regression model of Greene et al. (1991) and the Stochastic Distorted Wave Born Approximation (SDWBA) model. The measured TS values were lower than the predictions from both the Greene et al. model and the SDWBA model for Antarctic krill with g = 1.0357 and h = 1.0279, while the measured data fell within the SDWBA model predictions with g = 1.000–1.009 and h =1.025–1.039 for ice krill.gth (TS: dB re 1 m2) and body length of ice krill, Ex situ TS measurements of ice krill were conducted using 38, 120, and 200 kHz split-beam echosounders. Mean TS were obtained from 21 individual ice krill with a broad range of body lengths (L: 13–36 mm). The length (mm) to wet weight (W; mg) relationship for ice krill was W = 0.001218 × 10-3L3.53 (r2 = 0.96). The mean TS-to-size relationship fits were TS38 kHz = -177.4 + 57 log10(L), (r2 = 0.86); TS120 kHz = -129.9 + 31.56 log10(L), (r2 = 0.87); and TS200 kHz = -117.6 + 24.66 log10(L), (r2 = 0.84). Empirical e