The Onosatogawa River: Playing with Fiddler Crabs

Along Osaka Bay, there are many man-made factory islands and beaches, so few truly natural things are left. However, at the mouth of the Onosatogawa River in south Osaka is a natural mudflat where a protected species of fiddler crabs live.  It is really a treat to spend an afternoon observing all the different species that thrive in this mudflat


Onosatogawa River

The Onosatogawa River forms between Sennan and Hannan City in southern Osaka. It is only a 15-minute walk from the Sennan Aeon Shopping Center. The mudflat is on the Sennan City side, right next to the incineration center. 

the mouth of the Onosatogawa River
Around the river is a small neighborhood.
Kansai Airport is in the distance!

There are few pristine rivers in south Osaka. However, in recent years, volunteers have made a real effort to clean up the rivers and beaches. Thanks to them, the Onosatogawa River is now also a great place for bird watching. 

We came at low tide, so we could find many marine creatures, particularly crabs, in the dry sand. Given that it is Osaka, this is rather surprising because many people think Osaka is just full of factories. You may think they aren’t that special because they are crabs, but it is wonderful to see Osaka’s native wildlife enduring here!  

maybe sleeping?
Can you find a fish hiding?
Native crab in the Onosatogawa River
mame kobushigani(??)
native species of crab in the Onosatogawa River
kefusa isogani (Hemigrapsus peniicillatus)

The Onosatogawa River is notably famous for its fiddler crabs. In the Onosatogawa River, there is a small mudflat where literally hundreds of fiddle crabs live.

The males have one large claw that they use to wave to invite the female crabs to their burrow.  

The fiddler crabs are very shy, so they typically hide the moment they see people, but if you wait still, the carbs will come out of their burrow and wave their claws. 

The Japanese call fiddler crabs “shiomaneki” (lit. tide inviter) because it looks as if they wave their claws to bring the tide back. 

fiddler crabs in Onosatogawa River
White fiddler crabs. Their eyes are really cute too
I think this is Ashihara gani (Helice tridens)

We took a video of fiddler crabs waving their claws. It certainly looks really cool when they do that and we really hope he can get his mate soon enough.

Though Osaka is proud of its reputation as a bustling modern and industrial city, it is of the utmost importance that Osakans protect their natural wonders. Even the tiny crab. 


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