"It looks like I knit the two halves from picked up stitches along two paralel rows on the top of the hat. I picked up & knit 18. Then, on every right side row I decreased one stitch along the edge closest to the head hole (mouth). On one side it was a K2tog & on the other side it was a SSK in order to make the stitches lean the right way. I knit the last 2 or 3 stitches together at the top of each half. Then I cut a piece of plastic from a milk jug or a plastic to-go cup to fit in the space. This helped the fin stand erect instead of flopping over. I also put a plastic piece in the tail."

Other Modifications she made:
1) Added a picot edge in white for teeth between the end of the knit “lips” and the short rows.
2) Decreased after the fin area with PSSO every other row for # rows & PSSO every row for # rows.
3) Made tail fin like this (beginning on WS row):
Row 1: P11
Row 2: KFB3, K5, KFB3 (17 sts)
Row 3: P17
Row 4: KFB4, K9, KFB4 (25 sts)
Row 5: P25
Row 6: KFB5, K15, KFB5 (35 sts)
Row 7: P35
Row 8: KFB4, K27, KFB4 (43 sts)
Row 9: P43
BO
4) After BO, the tail looks like that of a whale, not a shark. Block the tail AGRESSIVELY to maintain triangular shark look BEFORE sewing the two halves together.