| Summary: | Here we endeavoured to quantify the filtration mechanics of rorquals and the material properties of baleen “gums” (termed zwischensubstanz) by examining and testing the baleen of a fin whale (Balaenoptera physalus). It was hypothesized that fin whales use cross-flow filtration to filter krill from engulfed seawater such that krill and other debris do not become entangled in the baleen fringes. Cross-flow filtration was proposed as an alternate mechanism to dead-end sieving since it would create a highly concentrated suspension of krill inside the mouth (potentially at the oesophageal opening) and would also not require krill to contact the baleen, eliminating clogging and filtering efficiency losses. We tested filtration mechanisms by placing a sixty-two centimetre section of baleen from a fin whale in a circular water tank and imitating the whale’s environment through various flow scenarios and setups. It was not conclusively determined whether cross-flow filtration is the mechanism used by fin whales, but a new mechanism was proposed called centripetal filtration in which two slugs of water spiral anteriorly on the left and right side of the whale’s oral cavity. Further examination of this proposed mechanism is required. The material properties of the zwischensubstanz that holds baleen plates together and the development of baleen plates through this zwischensubstanz were also examined. Zwischensubstanz exhibits isotropic properties similar to soft rubber in compression with an average Young’s modulus of 2.56 ± 0.60 MPa and 44.4 ± 2.4% hysteresis when compressed at 0.5 Hz, as it appears to space the baleen plates and absorb stresses translated from the plates. Through this rubbery zwischensubstanz, the baleen plates develop from conical papillae to hard, keratinized plates. The zwischensubstanz forms a matrix around the papillae and is calcified and keratinized before exiting the zwischensubstanz as a fully developed plate. The discoveries made here with regard to centripetal filtration and the properties of zwischensubstanz are preliminary attempts at quantifying baleen whale filtration and its associated feeding structures. Such work has been rare in the literature and there are many questions left to be answered by eager scientists with regard to the greatest biomechanical event in the world.
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