According to w:User:Pietro Shakarian:

It fell into the public domain because it was not renewed after its 25-year copyright term. Films and other copyrighted materials in the United States are supposed to be renewed 25 years after their release. I know this because I've researched in Walter E. Hurst's "Film Superlist" - a guide to every single American film copyrighted and renewed. Pretty much all the films released in 1930 that I looked up were renewed in 1955. If a film or material is failed to be renewed, then it falls into the public domain. Such was the case with "Oceantics".

This work is in the public domain because it was published in the United States between 1931 and 1963, and although there may or may not have been a copyright notice, the copyright was not renewed. For further explanation, see Commons:Hirtle chart and the copyright renewal logs. Note that it may still be copyrighted in jurisdictions that do not apply the rule of the shorter term for US works (depending on the date of the author's death), such as Canada (70 years p.m.a.), Mainland China (50 years p.m.a., not Hong Kong or Macao), Germany (70 years p.m.a.), Mexico (100 years p.m.a.), Switzerland (70 years p.m.a.), and other countries with individual treaties. العربية ∙ Deutsch ∙ English ∙ español ∙ français ∙ galego ∙ italiano ∙ 日本語 ∙ 한국어 ∙ македонски ∙ português ∙ português do Brasil ∙ русский ∙ sicilianu ∙ slovenščina ∙ українська ∙ 简体中文 ∙ 繁體中文 ∙ +/−