Green’s Dictionary of Slang

North Sea rabbit n.

(N.Z.) a herring.

1918		Chron. NZEF 22 Nov. 206: Slim Jim leaned back and held up by the tail one of the ever popular ‘North Sea Rabbits’ [DNZE].
1938		Press (Canterbury) 2 Apr. 18: ‘[S]hell shock bread’ and ‘sandbag duff’ were not much liked; nor were ‘North Sea rabbits’ (herrings).
1941		Baker N.Z. Sl.
1988		(ref. to WWI) McGill Dict. of Kiwi Sl. 76/2: North Sea rabbit herrings to WWI soldiers.
2003		McGill Reed Dict. of N.Z. Sl. [as cit. 1988].