ORLANDO – SeaWorld Entertainment's stock has soared since the Orlando-based company revealed plans to phase out its signature killer whales, but it still has challenges ahead.

An activist investor wants board members replaced. Some die-hard fans and employees feel let down, saying SeaWorld surrendered to its enemies. And while the Humane Society of the United States endorsed the parks' decision, other animal advocates are continuing to call for the whales' release and an end to keeping other sea creatures such as dolphins.

SeaWorld stopped breeding its orcas in March, meaning that in the next few decades it should no longer have any. Many theme-park experts and analysts considered the move inevitable, since SeaWorld had suffered such a financial blow from the 2013 anti-captivity documentary "Blackfish."

"I understand you may feel betrayed," Chief Executive Joel Manby told fans in an online forum last week. "But … the data showed, and trends showed, it was a SeaWorld without whales or it would probably be a world without SeaWorld."

The company's stock price had declined sharply in value after executives acknowledged that controversy over orcas was contributing to an attendance decline. Since announcing an end to orca breeding March 17, SeaWorld has seen more than a 20 percent increase in its stock. It closed at $20.87 on Monday.

SeaWorld would not make executives available for an interview.

Activist investor Greg Taxin, whose Luma Asset Management has about a 4 percent stake in SeaWorld, said the company made the right move by ending killer-whale breeding.

Still, Taxin said SeaWorld needs to replace board members. Taxin wouldn't say whether he had nominated replacements for any of the company's 10 directors in advance of the shareholder meeting later this summer.

"We believe the company took far too long to respond effectively to the challenge of 'Blackfish' … and that the board bears responsibility for the delayed response, ineffective response for several years that has cost shareholders significant value," he said. "We just think it would be useful to have new people on this board who have proven extremely able in this industry to help navigate these future issues that may arise."

SeaWorld can still expect opposition from groups such as People for the Ethical Treatment of Animals, despite the Humane Society's support. PETA staged a protest at SeaWorld three days after the company's announcement. PETA wants SeaWorld to release its whales to sea pens.

Other animal advocates applauded SeaWorld's move but will continue calling for more concessions. "This is a great first step but there are more steps to take," said Naomi Rose, a marine mammal scientist with the Animal Welfare Institute, who would like SeaWorld's orcas retired to ocean sanctuaries.

Humane Society Chief Executive Wayne Pacelle said release would be difficult.

"There are definite issues of expense, the health of the animals, that are unsettled," he said. "What we're committed to is having a discussion about it and being prudent and fact-driven on it, and we're not clamoring at this moment for movement of the animals."