The decomposed body was discovered last week by DoC marine ranger Jim Fyfe, who was able to identify it as the sea lion with the suspected wound by the tags found with its body. He returned the next day to sieve through the remains and found a .22 bullet.
"I'm pretty annoyed, a lot of work goes into looking after sea lions ..."
Its death would have a significant impact on the local population, he said. New Zealand sea lions are listed as a nationally critical threatened species - the same level as the kiwi or kakapo.
"Those who shoot marine mammals may be ignorant of how endangered their target is, but the law is simple - it is an offence to kill or harm any marine mammal."
Under the Marine Mammals Act, penalties of up to six months' jail and fines up to $250,000 can be imposed.
New Zealand Sea Lion Trust spokesman Shaun McConkey, of Dunedin, said BK was likely to be a second or third-generation Otago sea lion. With the death of an Otago female a few weeks ago and a dog attack, the shooting was all part of a worrying trend, he said.
"We need concerned locals to take ownership of this species and watch out for them - be their guardians. They are simply too spread out for DoC or the trust to keep them safe."
Sea lions had been shot, clubbed and rammed by cars in the past, he said.
"We were starting to hope this sort of behaviour might be in the past," said Mr McConkey, who has been studying the local sea lions for 17 years. With the main population at the Auckland Islands in rapid decline, it was hoped the sea lions in Otago would increase in number.
There is hope that coverage of the shooting will encourage people to dob in the culprit.
DoC spokesman David Agnew says there's a lot of local support for sea lion conservation.
He hopes the publicity will prompt people to come forward with information that will lead to someone being tied to the incident.
NZ sea lion
Formerly known as the Hooker's sea lion.
Status: Nationally critical.
Colour: Mature males brown to black, females lighter, predominantly creamy grey. Pups chocolate brown with paler areas around head.
Size: Adult male 250kg-400kg and 2.4m-3.5m long.
Breeding: Major colony on the Auckland Islands. Since 1993 small numbers have been breeding on Otago Peninsula. Breeding occurs over the summer months. Females give birth to a single pup every one to two years.
Pups are dependent on their mothers for milk and protection for the first year of their lives.