I am not challenging you on this, but as beaver are not meat eaters, it would seem a waste to place crawfish or fish oil into a lure for them, and it would be repulsive.
Different oils are different types in carrot is bitter while apple is sweet. The carrot would spike awareness, but the apple would have more appeal. The tree oils again would if you have those trees or brush in your North Dakota waterways would appeal to a certain point. It is like would a sweet corn lure work surrounded by a 100 acres of sweet corn or if a raccoon only ate crawfish would they even trigger for a sweetcorn scent.
When breeding season is about here, the castor mixed with the oil sac is the primary lure as it triggers territory and breeding.
When you cut a concentrate of oil with a base oil or grease, odorless is best or it competes, but it still dilutes the scent and competing scents as in apple or poplar does not enhance often but retards the lure. For the ratios, this is from an online multi purpose type lure to provide an idea of the ratios.
It is far too loaded up for beaver and I would use the 4 oz castor, oil sac, mineral or propylene and then the 6 drops of Sweet Flag.
I hope that helps.
Leave it to Beaver (Beaver - Muskrat - Mink - Otter - Marten - Fisher - Fox)
4 oz. Beaver Castor
4 oz. Beaver Oil Sacs
1 capful Tonquin Musk
1/2 oz. Ambrette Musk Crystals
1capful Canton Musk
5 drops Lavender Oil
4 drops Oil of Fennel
1 capful Bergamot Oil
6 drops of Sweet Flag Oil
4 oz. Propylene Glycol