The efficient perception of the underwater flow field is of great significance to the development of underwater intelligent equipment. Driven by unique whisker receptors of the harbor seals, this study proposes and demonstrates a bioinspired whisker sensor based on orthometric fiber Bragg grating (BIWS-OFBG). Four FBGs are deployed around an artificial whisker as basic sensing units. The hydrodynamic information is encoded as the wavelength evolution of the FBGs. In the underwater experiment, BIWS-OFBG obtains the vortex street distribution in the bionic fishtail wake. It realizes frequency locking with a root-mean-square error (RMSE) of 0.0208 Hz and rotation direction recognition of the vortex with a maximum detection distance of 300 mm. Oscillatory stimulus are also detectable. Based on the theoretical model, we further give the calibrated function to express the relationship between wavelength shift and steady flow velocity. A maximum sensitivity of 0.86 nm/(m/s) is achieved. The suggested device provides a new framework for the design of bionic whisker sensors. Replacing integrated circuits with optical fiber sensing units will greatly enhance the adaptability of sensors in extreme application scenarios.