None.
I have thus far been unable to validate claims that this facility received four walruses in 1932. It is possible that these individuals included three animals exported from the Moscow Zoo by the L. Ruhe Animal Trading Company, whose owner was then the director of Zoo Hannover. One of these animals died en route to Tiergarten Nürnberg at Dutzendteich; two, young bull Schorsch and an unknown female, briefly stayed in Nürnberg before ultimately passing away at Tierpark Hellabrunn.
Siegfried and his female companion came under the ownership of animal trader Zeehandelaar on July 22nd of 1961, but evidently remained on-site at Zoo Hannover until their transfer to Saint Louis.
This facility no longer maintains a walrus exhibit, and to my knowledge there are no current plans to house them in the future.
Initially opened as Zoo Hannover, this facility became Adventure-Zoo Hannover at some point between 1997 to 2001.