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The science
Sound speed. The porpoise converts echo delay into range with R = c Δt / 2. The speed of sound in sea water follows the Mackenzie (1981) nine-term formula in temperature T, salinity S and depth D (about 1490 m/s at 10 C, 35 ppt). Warmer or saltier water is faster, so an animal that assumed a fixed 1500 m/s would misjudge range by (1500/c - 1) R (readout above).
Click interval. Porpoises wait for the echo of the previous click before sending the next: ICI ≈ 2R/c + lag (lag about 20 ms while tracking). As the prey gets closer the interval shrinks; inside a couple of metres the animal switches to a fast "buzz" with intervals of a few milliseconds. The model uses exactly this rule; the numbers are typical, not measured for one animal.
Sonar equation. Echo level EL = SL - 2 TL + TS. The one-way transmission loss is TL = 20 log10 R + α R (spherical spreading plus absorption). The echo is detected when EL ≥ NL + 10 log10 BW - DI + DT, with noise spectral level NL, bandwidth BW (16 kHz), receiving directivity index DI and detection threshold DT. Without absorption the maximum range is R = 10(SL + TS - floor)/40: every 40 dB of budget is a factor 10 in range, because the sound has to travel there and back.
Absorption. The Ainslie and McColm (1998) formula (boric acid, magnesium sulphate and viscous terms, pH 8) gives about 40 dB/km near 130 kHz at 10 C and 35 ppt; it grows roughly as f², which is why high-frequency clicks buy resolution (wavelength c/f is about 11 mm at 130 kHz) at the price of range.
Honest simplifications. Straight sound paths in uniform water (no refraction, surface or bottom reflections, no reverberation); the target is a point scatterer with constant target strength (real fish echoes fluctuate with aspect); the receiver is an ideal energy detector; the transmit beam and the head-movement scan are not modelled; the prey school and the hunting behaviour are a cartoon of real behaviour. Source level, directivity, bandwidth, noise, threshold and target-strength values are typical orders of magnitude, not data for a particular animal. The wavefronts are drawn slowed down by the factor you choose; the swimmers move at normal speed, so during one click cycle the animals move far more than they do in reality (the readout shows the real distance, a few centimetres).
Check the typical values against a bioacoustics source before quoting them.