Fishermen / Seamen Records

Hallo,
Could someone inform me if there are any records for fishermen in Hannover?
I am trying to trace the origins of Hermann DETTMAN. His family were mostly
farmers, but he and his brother worked on the fishing boats. These two
brothers arrived in Hull, England in a fishing smack when Hermann Dettmann
was 16 years old in 1880. Their last port of call was in Denmark.
Would they have had to have a permit to work on the boats?

Danke,
Rena, England