Broadband and tilt-angle-dependent target strength of northern shrimp (Pandalus borealis): Measurements and comparison with scattering models

There is a need to improve the efficiency and reduce the environmental footprint of northern shrimp ( Pandalus borealis ) fisheries. Northern shrimp are mainly harvested using demersal trawls, which are fuel-intensive and can impact the seabed. Although shrimp primarily occur near the seabed, they are known to migrate vertically at night, suggesting that pelagic trawling may be a viable alternative if shrimp can be acoustically detected in the water column at commercially relevant densities. To develop acoustic methods for shrimp detection and identification, reliable knowledge of target strength (TS), which describes the acoustic backscatter from an individual target, is needed. However, available TS data for shrimp are limited. In this study, we measured the frequency- (34–380 kHz) and tilt-angle-dependent TS of tethered shrimp. The measured TS generally increased with frequency and was highest at broadside incidence. The measurements were compared with predictions from DWBA and FEM–BEM scattering models using the same prescribed shrimp geometry and assumed homogeneous material properties. TS generally decreased away from broadside incidence, while frequency-dependent variability became more pronounced. Overall, there was good agreement between modelled and measured TS at broadside incidence, but poorer agreement away from broadside incidence. At off-broadside incidence, refining the spatial discretisation of the DWBA model substantially improved its agreement with FEM–BEM predictions. However, both models predicted a stronger reduction in TS away from broadside than observed in the measurements. Improved TS measurements and scattering modelling are therefore needed to support acoustic detection of shrimp and the development of more efficient, lower-impact harvesting methods.