Many women described incidents where men had groped them, pinched their buttocks as they walked past, touched their breasts or attempted to rub up against them.
Others complained about men making suggestive comments about their body, asking about relationship statuses and making outright sexual advances.
Men also copped harassment from female visitors, the study revealed.
One male tour guide said the ongoing harassment from intoxicated women had become so intolerable that he quit the job he loved.
"It happened quite often - every night when I do the night tour. One lady, she approached me and said: 'Man, look at your body. Do you have anything inside?'" as she looked towards his groin.
Kiwis are the biggest travellers to the Cook Islands.
Of the 161,362 visitors to the Pacific nation last year, 107,585 were from New Zealand, 25,913 from Australia, and just over 8300 from the US.
Sadaraka said the research did not look into where the customers had travelled from.
The incident involving the New Zealand man - the head of a company travelling as part of a work group - was relayed by a male hotel manager who said the staff member involved came straight to him to report it.
"I went straight to his room and said: 'One more act like this and I'm going to ask you to leave the hotel'.
"He was drunk and he said: 'I paid for this hotel, I can do whatever I want'."
Sadaraka said findings revealed it was as if by going on holiday, and therefore having a level of anonymity in a foreign place, their morals suddenly changed or were forgotten.
"I had one girl say it was as if some people left their morals at the airport."
The behaviour was fuelled by alcohol, and a misunderstanding or interpretation of Cook Islands cultural norms such as greeting each other with a kiss.
Traditional dance costumes and dance movements were found to inadvertently influence visitors' behaviour - where they may see them as being seductive or provocative.
Sadaraka said over the course of her research, she spoke to and worked alongside the heads of Cook Islands Tourism.
As a result, she was recently invited to present her findings at a tourism industry conference held in Rarotonga.
She has outlined a number of key recommendations for those at the top of the industry, with the help of those she interviewed.
Among them was the need for all workplaces to have policies and procedures in place if such behaviour arose, a commitment from managers to back their staff and ways to educate people visiting from other countries.
One manager said: "Cook Islands Tourism needs to put it on the front page of their brochures: 'The dos and don'ts of your holiday in Rarotonga'."
Sadaraka hopes the study would identify and start more conversations within the industry in other parts of the Pacific too.
Cook Islands Tourism CEO Halatoa Fua said they acknowledged the concerns raised from Sadaraka's research.
"It should be noted that this is an inquiry into the employees' experiences of sexual harassment by customers in the Cook Islands hospitality industry, which does not include the customers' perspective."
Fua said the issue of sexual harassment was not specific to the Cook Islands and was a global issue.
"We will work with the tourism industry and Government on some of the key recommendations to raise awareness on sexual harassment, as well as implementing policies if not in place."
