A.T. Robertson Commentary Mark 1:19

"And going on a little further, he saw James the [son] of Zebedee, and John his brother, who also were in the boat mending the nets." — Mark 1:19 (ASV)

A little further (ολιγον). A Marcan detail.

Mending their nets (καταρτιζοντας τα δικτυα). See on Mt 4:21. Getting ready that they might succeed better at the next haul.