This video from Ireland says about itself:
12 February 2012
A short film showing a male Lumpsucker in Galway Bay over a 7 day period. Breeding time for Lumpsuckers is from February to May where they lay their eggs in coastal waters and males take care of them during a 6 to 7 week period until they hatch.
That is unusual. Usually, these young fish, hatched in the Oosterschelde in spring, should have migrated to the North Sea earlier in the year.
Maybe the cause is a recent invasive species: the warty comb jelly. Recently, this originally American species reached the Oosterschelde. Young lumpsuckers feed on it; maybe making it less necessary to go to the North Sea.