The company reported in a blog post on February 6 that Dart, 12, a Pacific white-sided dolphin, died at the park.
SeaWorld says the exact cause of death hasn't been determined, but veterinarians had been monitoring the dolphin for about a month. The aquatic mammal was under constant veterinary care and was with two companions — Betty and Hailey — and its caretakers when it died.
SeaWorld said Dart was "high-energy, extremely playful, enjoyed participating in shows and interacting with his trainers."
Dart was born at SeaWorld San Antonio in September 2003.
SeaWorld said that veterinarians are also treating Betty, 37, also a Pacific white-sided dolphin — the oldest at the park. Betty, who has been at SeaWorld San Antonio for more than 20 years, is under 24-hour veterinary care "for indications of inflammation or a possible infection."
SeaWorld, citing the National Marine Mammal Laboratory and the National Oceanic and Atmospheric Administration, says, while no one is completely sure, the average lifespan of a Pacific white-sided dolphin is believed to be between 36 and 40 years.
"It has been a difficult time for our San Antonio team, with several other recent deaths. While there are no apparent connections between these deaths, our veterinarians will be conducting a thorough review of all the cases as they work through the post-mortem examination process," the company said in its blog post.
In December, Unna, an 18-year-old orca, died "from a resistant strain of a fungus called Candida." In November, a two-year-old beluga whale named Stella died. Last July, a three-week-old beluga calf died at the park.