Interesting study on the rate of baleen regrowth...
*Werth, A.J., Sformo, T.L., Lysiak, N., Rita, D., George, J.C. Baleen
turnover and gut transit in mysticete whales and its environmental
implications. Polar Biol *(2020). https://doi.org/10.1007/s00300-020-02673-8
https://link.springer.com/article/10.1007/s00300-020-02673-8#citeas
Abstract:
Baleen, a unique oral ?-keratin, has flat cortical layers enclosing hollow
horn tubules. Baleen grows continuously to replace erosive loss from
feeding-related wear. This is essential for maintaining efficient
filtration over a whale's long life history. Baleen fragments are seen in
stomach contents and feces. We focused on fin (Balaenoptera physalus) and
bowhead whales (Balaena mysticetus) but examined eleven mysticete species.
Histological features including variably-sized tubules plus differential
growth along plate axes (growing faster along the medial fringed edge) and
between plates of a rack (central plates growing faster than others) relate
to baleen strength and flexibility. Sheet-like cortical layers provide
strength and probably hinder erosive shedding, whereas medullary
(tubular/intertubular) keratin provides flexibility and likely promotes
shedding. To calculate amounts of grown/lost baleen we considered both
erosive wear and basal growth, recognizing that each !
plate represents several years of growth. We estimate average annual loss
of 70-100,000 cm2 (20-40,000 cm3) of baleen in balaenids and 25-50,000 cm2
(7-14,000 cm3) in balaenopterids. Baleen growth rates depend on age, size,
and other life history parameters; the most reliable calculations come from
morphometric data with plate dimensions measured along full racks. We argue
that baleen turnover has been underrated and baleen growth rates
underestimated in published literature. Baleen turnover maintains filter
integrity/porosity while gut passage possibly clears gastrointestinal
tracts of endoparasites. Large volumes of shed keratin hold potential
ecological consequences by providing food for microbial decomposers and
detritivores throughout ocean ecosystems, especially in polar regions where
most mysticete feeding occurs.
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Shauna Fry Bingham
NOAA Channel Islands National Marine Sanctuary
<https://channelislands.noaa.gov/>
