Short answers, pulled from the story.
The haddock is distinguished by a dark oval black spot known as the Devil's thumbprint located between the lateral line and the pectoral fin. This unique signal on the fish's flank is the defining feature that separates the haddock from its cousin the Atlantic cod. The genus name Melanogrammus derives from Greek words for black and letter referencing this specific mark.
Haddock populations stretch across the North Atlantic Ocean with the largest stocks residing in the North Sea off the Faroe Islands around Iceland and along the coast of Norway. These demersal fish live near the bottom of the sea typically at depths between 50 and 200 meters though they can be found as deep as 500 meters. They prefer substrates made of rock sand gravel or shells and maintain a preference for water temperatures between 4 and 10 degrees Celsius.
The lifespan of the haddock is approximately 14 years with the longest recorded individual reaching 70 centimeters in length and weighing 4.5 kilograms. A haddock reaches sexual maturity at 4 years old in males and 5 years old in females though the population in the North Sea matures much faster with males reaching maturity at 2 years and females at 3 years.
The history of haddock populations is marked by periods of extraordinary productivity known as the gadoid outburst which occurred from the 1960s up to the early 1980s. Notable peaks in productivity occurred in 1962 and 1967 with lesser increases in 1974 and 1999. These revivals did not have a lasting effect on the population due to high fishing mortality which prevented the stocks from recovering to historical levels.
The smoking of haddock reached a level of refinement in the English town of Grimsby where traditional smokehouses have been family-run businesses for generations. One of the most popular forms is Finnan haddie named after the fishing village of Finnan or Findon in Scotland where the fish was originally cold-smoked over smouldering peat. Another smoked version the Arbroath smokie is produced in the town of Arbroath on the east coast of Scotland and is a hot-smoked haddock that requires no further cooking before eating.
Haddock is fished year-round using gear such as Danish seine nets trawlers long lines and gill nets often caught in mixed species fisheries with other groundfish like cod and whiting. The main fishing grounds in the eastern Atlantic are in the Barents Sea around Iceland around the Faeroe Islands in the North Sea the Celtic Sea and the English Channel. Landings in the eastern Atlantic have fluctuated around 200 to 350 thousand tonnes in the period from 1980 to 2017.