Let’s first try and narrow this down and clarify / define some items. On a side note: this is a fantastic question which touches on the exciting areas of transnational history, identity, and globalisation. Before anything I am going to talk solely within the Anglo world- this itself will be shown to be far less limiting that maybe expected. First, the term sea shanty is referring to a very specific period, about 4-5 decades between c.1840-1880. This is not to say that "sea songs" are only that old. These were specifically composed shanties for work or expression of the “mood” of the crew. Essential all the shanties we have today and you can find recordings of are from a number of compilers who carried out their task prior to the first world war. As our study of shanties rely on these collectors a very brief overview of some issues should be raised and hopefully you and others will find interesting. The collecting occurred during a period of changes and movements of identity within England and wider notions of what may be an idea of Britishness. The collectors were seeking out what they believed to be authentic shanties based on their own perceptions of the countries seafaring culture, history, personal identity, and assumptions of the maritime character of the English.(1) This shaped what songs they saw ‘“fit” to be recorded. As such, songs found in print, by some, were deemed to have been ‘contaminated.’ (2) Thus, what should be concluded from this is that beyond the complications of collecting oral tradition as it’s dying out from a population which is highly mobile and spread across the globe, is that what we do have, carries a potent bias to any study.
Now, this is where it gets fun,and hopefully to the core of your question. I want to give a moment of background information. First, Sailors, and Merchant ships, throughout the age of sail and into the 19th century were markedly global communities. Anglo-Sphere ships were crewed by West-Indians, Africans, African-Americans, Continental European, and South-American. Ships had a high turnover rate with only small parts of a crew staying on for more than one voyage.(3) Second, Shantites changed and morphed quickly due to these changes, mostly likely faster than those found on land. Finally, musicscape, and folk music studies, along with those working with oral traditions, have shown the influence songs have upon local communities for identity. These local identities, which are markedly different from modern political-nation-state identities have strong geographical markers to them.
Shanties
Shanties themselves, as stated, are for specific tasks aboard a ship that required hard labour. Regional various did exist to a certain extent, and small changes within songs did occur as will be outlined below. However, what is important is that the core of the shanty was to remain understandable to every member of the crew- this under the ever changing cultural and personal make up of the crews. They were sung by two groups: the Shantyman and the Crew. The Shantyman knew the song, and “led” the crew in the shanty. The Shantyman could pick and change the lyrics as needed, and were pulled from a personal repertoire. Their choice of words were chosen based on the knowledge of the crew, where verses could be adapted to ‘mak[e] up little rhymes which would fit’ with the current crew. (4) Other small changes as well could occur. Specific verses were said to be changed out to target individual officers, or actions of officers thus, changing the lyrics of some verses but maintaining the core point of the song as a form of release and form of expression by the crew to officers. (5) Now to try and address your specific point of region variations. This would have appeared but again, these would be slight changes to the songs lyrics. I’ll give two examples
https://www.youtube.com/watch?v=t8s_Z13jEeo (Norwegian)
https://www.youtube.com/watch?v=mDjOAsxeokw (South Australia)
What is shown above are the slight changes that occur in a shanty to match the crew make up, or the port of all. The song itself keeps the core of a return to port,however changes are found in name (miss Nancy Blair) as well as rounding Cape Horn.
This is a very small change, and others were seen in the popular song “The Liverpool Judies” which could interchange different ports (Liverpool for Newyork or San Francisco) but the core of the song about being shanghaied would be kept even if markers of the outgoing port changed. However greater changes could occur giving better representation to the oceans and ports where the ship was sailing. The last example of change, and sadly not regional, is of “re-purposing” a shanty. Songs about sweethearts who were off fighting Napoleon saw lyrics which marked places, events, etc, change in order to adapt to sailing around Cape Horn to California. (6) What I want to try and capture in this, while giving examples which touch of change and variation as per your question, is that there was no real established canon of lyrics. Thus, with the turn over of crews, and the immense cultural diversity of crews, Shanties saw great change and variation within just the Anglo seafaring world. Shanties were noted by original collectors and current scholarship for the influences specifically from African/west-Indian, and African-American music but also from Continental European. This matches the crew makeup and demonstrates that shantites were highly mutable.
I want to make two conclusions here. First, Sea shanties did have regional variations, but more exemplar of the shanty would be to say that the regional variation was one based on the changes, always in movement, and mutability of the oceans and the effects of this space upon those who plied a trade upon it. Studying the human interface with the ocean, how we have been shaped by our interactions and how these interactions of turned around to shape out perception of the ocean. For Shanties, the regional variations were thus based on ports of call, the composition of, for all intents and purposes the geographical, political, cultural, land which was the ship, that the present crew lived within. Second, and off topic a bit from your question but tied directly to it is the question of identity. During this very same period English travelers who wrote about maritime communities commented about the similarities they saw among those across the British isles, France, Netherlands, and Scandinavia. While land based folksongs, had far less, and slower change, Shanties were always in motion. Contemporaries would not have understood a specific canon of “folk music” as sailors, but of a series of core songs and rhymes which could be found on every ship and song by crew members from around the globe. While the words varied, the locations rooted to the songs change (this being markedly different from land), there was a shared knowledge and identity through the meanings of the songs based on a shared and globe experience of life at sea. James Carpenter in 1931, commenting about the strangest and the cosmopolitanism found what he was looking for “British” shanties said: ‘But the chanteys arose, not from an integral race with common ideals a background, shut in by accommodatingly stationary mountains and seas, but from the sons of Cain, bounded by the ever-shifting walls of the forecastle.’(7)
Other
-Arthur Knevett, ‘Cultural and Political Origins of the Folk-Song Society and the Irish Dimension’, Folk Music Journal 10,5 (2015)
-Stan Hugill, Shanties From the Seven Seas (London, 1961(
* -Kelby Rose, ‘Nostalgia and Imagination in Nineteenth-Century Sea Shanties’ Mariner’s Mirror, 98 (2013)
-Frank T Bullen, Songs of Sea Labour (London, 1914)
-W.B Whall, Ships, Sea Songs and Shanties (Glasgow, 1910)
-Graeme Milne, 'Collecting the Sea Shanty: British Maritime Identity and Atlantic Musical Cultures in the Early Twentieth Century' IJMH 29,2 2017