I find that pilchards thawed more than once go soft really fast. Basically refreezing them once they have been thawed makes them burley..

Same goes with Skipjack. Once its been thawed its buggered. The flesh goes brown and nothing will eat it.

With the Pilchards just take as many as you think you are going to need and leave the rest in the freezer. With skipjack saw it in half if you think you wont be using it all.