Stella McCartney has been talking about animal rights at fashion week for 30 years. She is usually a lone voice, but the issue is back in the headlines this season. Outcry over the physical restraining of a Peta protester at a catwalk show by Steven Kolb, the president of New York fashion week’s governing body, has put cruelty in wool production – previously considered niche compared to the hot button topic of fur – on the news agenda.

“There is no wool on the runway this season, and I’m proud of that,” McCartney said after her show. She has been working on wool alternatives, including Brewed Protein, a fermented alternative to cashmere and wool developed in collaboration with the Japanese biotech firm Spiber, which was first used in her collections a year ago.

The issue, she says, is “a tricky one. I’ve got alpacas at home, and I have to shear them. If you can shear a sheep in a kind, humane way, then I don’t, personally, think that’s the end of the world. When we do have wool in our collections it is responsibly sourced. But the way a lot of [wool production] is done today is deeply cruel.

“At the end of the day it’s about how kind you are, but monitoring that kindness requires real work. At Stella, we police everything from start to finish at my cost, at my time. If I use wool, I can show you exactly where it’s coming from, and I’m proud of that. But I’m alone in that, and I shouldn’t be.”

McCartney’s remarks on sustainability were interrupted by paparazzi clamouring for a portrait of the designer with the front row guest Jennifer Lopez, wearing a skirt suit with a faux-fur trim and matching stole with a dramatic black net face veil. Tension between fashion week razzmatazz and values-led gravitas is in the Stella McCartney DNA.

This season, McCartney’s spotlight is on sea life. “Sea life, not sea food. That’s the point I wanted to make,” she said, after posing with Lopez and dispatching Juliette Binoche with a promise to join her for a glass of champagne shortly. “I’ve never eaten fish, really, but my mum and dad used to point out that one minute people are watching a sea life documentary with David Attenborough and exclaiming about this magical world and the next, they are looking at a seafood menu. It is grotesque.”

The invitation to the show, held in the vast gardens of the British embassy in Paris, was delivered via a video message from 91-year-old Sylvia Earle, the legendary oceanographer who has spent more than 7,000 hours underwater. Fancy long-sleeved swimsuits walked the catwalk as evening looks; dolphins frolicked on T-shirts. The cursive hems of party dresses looked like Hokusai waves.

“We are at war with the oceans, at war with the creatures that live in there,” McCartney said. “For every fish you eat, countless are thrown back dead.”