The decision drew immediate criticism and outrage.
Protesters gathered outside the court building chanted: “It’s not abuse, it’s rape”, and shook their fists at the building.
The so-called “Wolf Pack” case had already sparked widespread anger around Spain following concern over increased reports of sex attacks at the annual festival and over the mistreatment of women in general.
It has also drawn international attention, coming at a time of heightened global concern over the sexual abuse of women in the wake of the Harvey Weinstein scandal.
After a five-month trial held behind closed doors to protect the victim’s identity, a judge read out the sentences in the court in the northern region of Navarra.
The state prosecutor had asked for prison sentences of more than 20 years for each of the men.
Instead they were given nine-year sentences.
Under Spanish law, the lesser charge of sexual abuse differs from rape in that it does not involve violence or intimidation.
The charge is used in cases of sexual activity between underage partners and those seen not capable of giving permission for sexual contact, such as those who are severely handicapped or under the influence of drugs or drink.
Feminist groups have scheduled protests in Spanish cities around the country, including outside the justice ministry in Madrid, in reaction to the sentence.
“If five people surrounding a girl is not aggression, the question has to be what is wrong with our criminal code?” former secretary of state for equality Soledad Murillo said in comments published in El Pais newspaper.
The National Police also showed their support for the victim, saying in a tweet: “No is no – we are with you.”
The regional government of Navarra, where the San Fermin festival takes place, will appeal the ruling, Spanish press quoted a regional government spokeswoman as saying.
No one at the regional government could immediately be reached for comment.
The five men, including a former police officer and a former soldier, and the victim were not present in court.
The men, dubbed by Spanish media “The Wolf Pack” after the name of their WhatsApp group, have been held in custody since July 2016.
The judge, who did not give the reasoning behind the sentence, also ordered the men to pay the victim €50,000 ($60,825) in compensation.
The ruling can be appealed in Spain’s Supreme Court.
The incident took place in the lobby of a building in the early hours of the morning at the San Fermin festival, which brings more than 1mn people to Pamplona for the nine-day-long festival in July.
The woman was found crying by two people who rang the police when she said she had been sexually assaulted.
She made a statement to the police, describing the five men who were later arrested.
Fragments of video from the men’s mobile phones taken at the scene were used as evidence in the trial, alongside witness accounts and biological examination results.
The defence team argued that the incident was a case of consensual group sex.
The running of the bulls involves hundreds of people dressed in white shirts and red neckerchiefs running down narrow streets in front of fighting bulls before ending in the city’s bull-ring, where bullfights take place in the afternoon.
The festival is just as famous for the drinking and revelry on the sidelines, with huge street parties, processions and firework displays.
The event draws thousands of tourists from all over the world.
Thousands of people took to the streets two years ago to protest against sexual assault at the festival and the Pamplona council has mounted a campaign against sexual harassment in recent years, increasing policing and encouraging women to report attacks.
