Porter is forced by the Superintendent to get rid of the manta due to a hysterical overreaction prompted by media reports of a scared couple. It's not a task he relishes. It required the boys to persuade Flipper to head back to shore and he ignores both Sandy and Bud's pleading - a rare occurrence. Porter gets a posse of guys together to net the manta (also fascinating footage) and it gets taken out to the open sea and Flipper isn't mad with Bud for breaking his word.
Some observations. This episode is the last but 3 of the entire Flipper series. It features the boys in their trade mark cut off blue jeans for the whole episode; a swan song especially for Sandy who made this an integral part of his character in the movies then the TV series. The Flipper TV series was filmed over the summer months so this would place the filming of this episode as likely August 1966 when Luke Halpin was 19 and Tommy Nordon was 14. After 3 years of being the little brother (actually 4 if you count the pilot filmed in 1963), by the end of the series Bud was now bigger as in thicker set than his fellow actor who was 4 1/2 years older as Halpin retained his lean swimmer's physique. Luke Halpin is showing signs of tiring in his Sandy Ricks role - by now he has been acting in the role for 5 years or the lion's share of his teen years. He was not to know then but it ended up being a career limiting role as he struggled to get meaningful adult movie or TV roles after the Flipper series finished. It was an ignominious wind down to a career that had seen him star in most of the major TV shows and productions during the golden age of television in the mid/late 50s.