A ban designed to end the "wasteful" practice of throwing dead fish back into the sea is set to cover key stocks such as haddock.

The discard ban has already been in place for 12 months for pelagic species like mackerel and herring.

But at the start of the new year on Friday, the ban will apply to some other stocks such as haddock, langoustines and prawns.

It means fishermen will have to land their whole catch of those stocks, rather than throwing any unmarketable fish overboard.

Environmental campaign group WWF's fisheries governance manager Helen McLachlan said: "The discards ban was introduced to end the wasteful practice of discarding healthy fish. January sees the start of a phasing period for some demersal species such as haddock and langoustine caught by trawlers.

"It is important that fishermen are supported to adapt to this new regime. This will mean new patterns of how and where to fish allowing more selectivity and avoidance of unwanted catches."

The Scottish Government said it has been working with the fishing industry to raise awareness of the new species covered by the ban and to provide information.

The change comes just weeks after late night talks in Brussels resulted in larger catch limits for 16 out of 23 Scottish fish stocks, including a 15% rise in the quota for North Sea cod and 47% for North Sea haddock.

Scottish Fisheries Secretary Richard Lochhead said: "No-one wants to see perfectly edible fish being thrown back into the sea dead, least of all our fishermen. The discard ban is an important step towards ending this wasteful situation.

"The ban covering species such as haddock and prawns from the beginning of 2016 will be a big challenge for the industry, but the significant increase in haddock quota for next year will help them to manage the impact.

"These changes will also benefit the industry by helping fish stocks to grow, which should in turn lead to further increases in quota. With the good news from the recent EU Fisheries Council the industry are well placed to cope with these changes and, I hope and expect, for a successful 2016."

The latest ban extension also covers other popular species such as sole and plaice.

A complete ban on the discarding of all quota species is set to be in place by 2019.

UK Fisheries Minister George Eustice said: "It is essential that we put an end to discarding, and the start of the demersal ban marks a significant milestone in achieving this.

"We fought hard to achieve the discard ban through our reforms to the Common Fisheries Policy - it is one of the most important changes to fisheries management since the creation of the Common Fisheries Policy and is crucial to making our fishing more sustainable.

"Together with careful quota management the discard ban will help us to achieve our shared ambitions of a profitable fishing industry by protecting our fish stocks for the future and safeguarding a healthy marine environment."