Is the ocean really getting louder?

OCR mathematician Tom Reuterdahl and I have just finished a modeling exercise aimed at determining how loud the ocean was prior to industrial whaling. The premise of the investigation is that while some 50,000 cargo ships are now plying the sea at any given time with noisy propellers, engines, and power plants, back in the early 1800’s there were millions of whales that were making equally loud – albeit not similar noises.

Our objective was to determine through historic whaling records what the pre-whaling populations were for some of the louder whales, such as Blues (184 -189dB) Bowheads (177 dB), Humpbacks (160 dB), Fin (186 dB) and Sei (156 dB) (all re: 1μPa). Presumably getting these numbers, and factoring the net noise density of each whale, we would be able to determine what the ocean sounded like when all of the whales were still swimming around in it.

The investigation was a deep dunking in a field of uncertainties, mostly due to the systematic under-reporting of kills by whalers. Initially this under-reporting was done to avoid taxes levied on a per-animal basis by national governments. When it became apparent that the entire industry was going to crash, the International Whaling Commission (IWC) was founded to regulate the takes through “scientific population studies” and catch limits – setting up yet another reason to under-report!

Under the IWC the under-reporting continued often, by huge factors. For example: In the later years of IWC “regulation” the Soviets had reported taking 2,710 humpback whales in the waters of the Southern Hemisphere when the real total was more than 48,000! (A startling paper by Phil Clapham and Yulia Ivashchenko details this “Soviet Deception”).

All tolled there were millions of whales killed, most of them after the First World War with the application of exploding harpoons and gargantuan factory processing ships. These industrial techniques made the practice of hand-thrown harpoons from wind and human-powered vessels seem almost sustainable.

Researching and writing the paper was an interesting journey into a dark practice that ended up extracting stunning quantities of biomass (living animals) from the ocean – mostly to be used for lubrication, lighting, and margarine.

Even with the all of the loose approximations and numerical uncertainties we found that the ocean was pretty noisy 200 years or more ago.

But of course the noise was not the mechanistic grind of engines, or the explosive rumble of global seismic airgun surveys, rather it was more akin to dawn chorus of any biologically diverse and well populated habitat – wherein the riot of birdcalls and the buzzing of insects are the dominant features in the natural soundscape.

I’ll be delivering this paper at the 2nd International Conference on Aquatic Noise next week.