Making Up:
Join row ends of body/head together and turn right side out. 
With right sides out, oversew the row ends of the fins and sew in place on the body. 
Fold the tail naturally in half with the right side out and sew the row ends together, join the tail to the body as illustrated.

Teeth:
I worked my teeth in crochet with a size 3 hook. 
Work a slip stitch into the bottom seam of the mouth with white wool,
1 chain, 2 double crochet, 1 chain and one slip stitch into the same hole to create a tooth.
Slip stitch into the edge of the mouth.
1 slip stitch, 1 chain, 2 double crochet, 1 chain, 1 slip stitch into the same hole to create the next tooth.
Continue to create teeth evenly around the mouth, finishing with a slip stitch into the first stitch.  Try and work a tooth every 3 stitches – but don’t worry too much – my shark all had a variable number of teeth – roughly 9!

Alternatively, if you want to knit your teeth – cast on 65 in white and cast off. 
Sew the teeth into zig zags to create the teeth.  
I haven’t tried this, but this is how Catherine completed her original shark.

Add googly eyes to finish off your shark.