After figures released this week showed professional authors' median annual incomes have collapsed to to £11,000, The Society of Authors' chief executive has claimed that traditional publishers' terms "are no longer fair or sustainable".

Earlier this week, the Authors' Licensing & Collecting Society released a survey of almost 2,500 writers which found that the median income of a professional author last year was £11,000, down 29% since 2005 – a period in which median earnings for UK employees have fallen by 8%. By this year, according to the survey, just 11.5% of professional authors said they earned their income from writing alone, compared with 40% in 2005.

The ALCS set its findings against Department of Culture, Media and Sport figures which show that in 2014, the creative industries were worth £71.4bn per year to the UK economy. "In contrast to the decline in earnings of professional authors, the wealth generated by the UK creative industries is on the increase," it said. "If unchecked, this rapid decline in the number of full-time writers could have serious implications for the breadth and quality of content that drives the economic success of our creative industries in the UK."

Nicola Solomon, who heads the 9,000-member strong Society of Authors, said that publishers, retailers and agents are all now taking a larger slice of the profit when a book is sold, and that while "authors' earnings are going down generally, those of publishers are increasing".

"Authors need fair remuneration if they are to keep writing and producing quality work," she said. "Publisher profits are holding up and, broadly, so are total book sales if you include ebooks but authors are receiving less per book and less overall due mainly to the fact that they are only paid a small percentage of publishers' net receipts on ebooks and because large advances have gone except for a handful of celebrity authors."

On top of that, said Solomon, "publishers are doing less for what they get. There are still important things they do – a traditional publisher can edit, copy edit, design, market, promote, make your book better, deal with foreign sales. With ebooks, though, publishers' costs are less, so authors should get a better share. They do not have to produce, distribute or warehouse physical copies. Even on traditional books, publishers' production costs have gone down but authors have not benefited from these costs savings. And, increasingly authors are being asked to do a lot of marketing and promotion themselves."

Earlier this week, the award-winning children's writer Mal Peet told the Guardian that his royalties for the last half of 2013 were £3,000. Evie Wyld, who has won prizes including Australia's Miles Franklin award, said that she earns around £8,000 per year from writing novels. "This is because although I got a generous (I think) advance for my last book, it takes me a long time to write the books," she said. "On top of that I write articles which are time-consuming, which I don't necessarily enjoy, and that I'm not terribly good at, and do events, as well as running a bookshop. Winning the awards has been vital for staying afloat this year. It's meant, most importantly, that I'm able to start a new book."

The ALCS survey of writers – which covered members of ALCS, the Society of Authors, the Writers' Guild of Great Britain and the National Union of Journalists – also found that writers are still making most money from printed books, but digital earnings are on the rise. Compared with a 2007 survey, when "only a small proportion of writers had received any money from digital publications", digital books were found to be the third largest sector in terms of financial importance to writers.

Self-publishing, meanwhile, is becoming an increasingly attractive option for writers, according to the survey, which found that just over 25% of writers had published something themselves. Writers were investing a mean of £2,470 in publishing their own work, with the median investment at £500, and typically recouping their investment plus 40%. Eighty-six per cent of those who had self-published said they would do so again.

Mark Edwards is an author who topped Amazon's charts with the self-published thrillers he co-wrote with Louise Voss before landing a deal with HarperCollins. Unhappy with his deal, he then returned to self-publishing, and released The Magpies, which he says sold 160,000 copies before Amazon Publishing acquired rights.

"I spent 15 years trying to get a deal before self-publishing. When I finally got a deal it was a disappointment so I returned to self-publishing, which rescued my writing career. Lots of writers are seeing other writers having success via self-publishing and deciding to try it themselves. I would encourage any mid-list author to try it. A lot of writers who've got back the rights to their novels are now self-publishing them and having a lot of fun in the process," he told the Guardian.

It offers, he said, "freedom and control", and higher royalties. "As the writer, you will always be the person who cares most about your work, and if you can channel that passion and energy and know what you're doing, this can be more effective than having a team of people who have 10 other books coming out that week." But it is not a simple route. "Some aspiring writers think it will be easy, but your chances of success are as slim as getting plucked from an agent's slush pile. Writers shouldn't see self-publishing as an easy way to find success. It's hard work and you need to be obsessive, smart and talented to make it work. But if you do, the rewards can be great."

The Society of Authors includes self-published writers among its members if they have sold 300 copies of a single title in print form, or 500 copies in ebook form, within a 12-month period. According to Solomon, most writers would "still prefer a traditional publishing deal but the terms publishers are demanding are no longer fair or sustainable".

"What a writer needs to do is to consider very clearly, at the very beginning, what they are getting into," she said. "It's a Dragon's Den. You could go out and do it yourself, or you could go with a traditional publisher. There is still an imprimatur of quality from going with a traditional publisher, and you may well sell more copies, particularly in physical, but you are giving a vast amount away for that: probably well over 90% of the list price of the physical or ebook. More importantly almost all publishers ask for those rights for the whole lifetime of copyright with very limited possibilities of getting your rights back, even if sales are woeful. Authors need to look very carefully at the terms publishers offer, take proper advice and consider: is it worth it, or are you better off doing it yourself?"