Mid 17th century. Apparently either from Dutch roerbak, or from row + -er + back (although this is also attested later). Compare rowed and quot. 1641 at row.
Definition of rower-back in US English:
rower-back
nounˈrəʊəbak
rare, historical
A trough in which herrings are stirred into salt.
Origin
Mid 17th century. Apparently either from Dutch roerbak, or from row + -er + back (although this is also attested later). Compare rowed and quot. 1641 at row.