S_L, Looking at my Chrismar map and the portage you have an arrow to isn't shown.

There is another way from Nym to Pickerel, the "Racer Portages". I've never used them, but they go from Nym's Black Bay, to Gillnet lake, to Pickerel.

Canoe Canada maintains a couple of portages from Nym to Batchewaung along the western shore through a small lake, not Jump Lake though.

The park also has a short portage from Batchewaung to Little Batchewaung Bay.

All depends on the wind conditions which way to go.