Did Portuguese fisherman frequent New England prior to 1492?
There is some evidence that first Basque, then Portuguese and finally English(Bristol) fishermen visited Newfoundland and/or Greenland before Columbus. As these fishermen were shut out of the lucrative Icelandic fisheries controlled by the Hanseatic League ( a merchant guild which dominated European Trade in the 13th to the 15th century, and also controlled the fisheries around Iceland ). Each sought to replace the lucrative Icelandic fisheries with new as yet unfound fishing grounds further to the west. There is some evidence they found what we know today as Greenland and or Newfoundland. Then once having made the discovery kept it secret to protect their commercial interests.
Given that Iceland which lies only 700 miles east of Greenland was well known to Europeans long before Columbus. In 1262-4 Icelanders recognized the King of Norway as their monarch. In 1380 Norway and Iceland entered into a union with the Danish crown. In 1402-04 the Black Death (Plague) hit Iceland at the same time it was ravaging Europe. see Iceland Timeline
John Cabot or Giovanni Caboto, was an Italian navigator and explorer. His 1497 discovery of the coast of North America under the commission of Henry VII of England is the earliest known European exploration of coastal North America since the Norse visits to Vinland in the eleventh century.
However; There is evidence of a competition among the merchants and fishermen of several countries including Portugal over secret fisheries which are believed by some scholars to have been Newfoundland.
According to Gaspar Frutuoso a Portuguese priest, historian and humanist, writing nearly 100 years after the fact, João Vaz Corte-Real a Portuguese sailor and explorer diary records his finding a land he called Terra Nova do Bacalhau (New Land of the Codfish), speculated to possibly have been part of North America, specifically Newfoundland in 1473.
João Vaz Corte-Real
Fragmentary evidence suggests the expedition in 1473 was a joint venture between the kings of Portugal and Denmark, and that Corte-Real accompanied the German sailors Didrik Pining and Hans Pothorst, as well as (the possibly mythical) John Scolvus.
The claim that he discovered Terra Nova do Bacalhau (literally, New Land of the Codfish) originated from Gaspar Frutuoso's book Saudades de terra from around 1570-80. There is speculation that this otherwise unidentified isle was Newfoundland.
Lending support to this claim is scholarship which documents competition over the codfish market between fisherman before John Cabot "discovering Newfoundland", 1497.
The Theory goes that Codfish was a lucrative commodity in the fifteenth century and that the Basques were the first to find new fishing grounds which are believed to have been Newfoundland. That the Portuguese followed them. That English expeditions out of Bristol sent several expeditions prior to Cabot. That discoveries of all of these efforts were closely held secrets before Cabot to preserve their lucrative fishing grounds.
Cod: A Biography of the Fish that Changed the World
The Hanseatics monopolized the Baltic herring trade and in the fifteenth century attempted to do the same with dried cod..... By then, dried cod had become an important product in Bristol. Bristol’s well-protected but difficult-to-navigate harbor had greatly expanded as a trade center because of its location between Iceland and the Mediterranean. It had become a leading port for dried cod from Iceland and wine, especially sherry, from Spain. But in 1475, the Hanseatic League cut off Bristol merchants from buying Icelandic cod.
Thomas Croft, a wealthy Bristol customs official, trying to find a new source of cod, went into partnership with John Jay, a Bristol merchant who had what was at the time a Bristol obsession: He believed that somewhere in the Atlantic was an island called Hy-Brasil. In 1480, Jay sent his first ship in search of this island, which he hoped would offer a new fishing base for cod. In 1481, Jay and Croft outfitted two more ships, the Trinity and the George. No record exists of the result of this enterprise. Croft and Jay were as silent as the Basques. They made no announcement of the discovery of Hy-Brasil, and history has written off the voyage as a failure. But they did find enough cod so that in 1490, when the Hanseatic League offered to negotiate to reopen the Iceland trade, Croft and Jay simply weren’t interested anymore.
Where was their cod coming from? It arrived in Bristol dried, and drying cannot be done on a ship deck. Since their ships sailed out of the Bristol Channel and traveled far west of Ireland and there was no land for drying fish west of Ireland—Jay had still not found Hy-Brasil—it was suppposed that Croft and Jay were buying the fish somewhere. Since it was illegal for a customs official to engage in foreign trade, Croft was prosecuted. Claiming that he had gotten the cod far out in the Atlantic, he was acquitted without any secrets being revealed.
To the glee of the British press, a letter has recently been discovered. The letter had been sent to Christopher Columbus, a decade after the Croft affair in Bristol, while Columbus was taking bows for his discovery of America. The letter, from Bristol merchants, alleged that he knew perfectly well that they had been to America already. It is not known if Columbus ever replied. He didn’t need to. Fishermen were keeping their secrets, while explorers were telling the world.
John Day's Letter This letter was written by the English merchant John Day to an unidentified Spanish 'Lord Grand Admiral' who is believed to have been Christopher Columbus. Courtesy of the Spanish National Archives. Valladolid, Spain.
English Voyages before Cabot
the letter written by John Day, an English merchant active in the Spanish trade, reporting on John Cabot's expedition of 1497; Day claimed that what Cabot discovered "is assumed and believed to be the mainland that the Bristol men found."
As for your other question whether Europeans had made it to New England prior to the Mayflower, that is pretty much an unchallenged fact. Three months after the Pilgrims arrived a Plymouth an Indian named Samoset walked into their camp calling out "Welcome, Welcome Englishmen". Samoset, an Abnaki Indian from Maine had travelled to the Massachusetts bay aboard an English Merchant ship months earlier and was preparing to travel north to rejoin his people. He had learned English from other English fishermen who frequented his home island. He was the first Indian who the Pilgrims had spoken too since landing.
SQUANTO VISITS THE COLONY
In broken English, he told the Pilgrims that he was Samoset, Sachem of a tribe in Mohegan Island, Maine, where he had learned to speak a little English from his contact with the fishermen and traders who visited his island each year. He had been visiting the Wampanoags for the past eight months, but he intended to return to his own people within a short time. [He had sailed with Capt. Dermer from Monhegan to Cape Cod some six months before the arrival of the Mayflower, and spending the winter with the Nauset Indians, reached the Plymouth settlement on that Spring day in 1621.