2009-10: After being acquired in a trade from Shawinigan in 2008-09, Danick Gauthier skated in 66 games for the Saint John SeaDogs in his first full QMJHL season. He scored 13 goals with 9 assists and was plus-8 with 68 penalty minutes. The SeaDogs had the QMJHL's best record, losing just 12 games and finishing first in the Atlantic Division, but lost in the league finals to Atlantic Division runner-up Moncton. Gauthier scored 6 goals with 4 assists and was plus-five with 8 penalty minutes in 21 playoff games. He was ranked 147th amongst North American skaters in Central Scouting's final rankings prior to the 2010 NHL Draft but was not selected.
2010-11: Overshadowed by the higher profile scorers on a Saint John team that won 58 of 68 games during the season, captured the QMJHL playoff title, and won the Memorial Cup, Gauthier was a solid two-way forward for the Sea Dogs. He scored 11 goals with 19 assists and was plus-21 with 78 penalty minutes in 65 games. Gauthier had 3 goals with 1 assist and was plus-3 with 21 penalty minutes in 18 playoff games. The Sea Dogs defeated host Mississauga in the Memorial Cup final. Gauthier played in three games at the tournament and was plus-two with no points or penalties.
2011-12: Gauthier attended the Phoenix Coyotes rookie camp before returning to Saint John for an overage season. He was the leading scorer for the Sea Dogs with 47 goals and 39 assists in 66 games and was plus-46 with 67 penalty minutes. The Sea Dogs were the league's dominant team; winning the regular season and playoff titles. Gauthier scored 13 goals with 8 assists and was plus-12 with 28 penalty minutes in 17 playoff games. The SeaDogs suffered back-to-back overtime losses at the Memorial Cup after winning their first two games. Gauthier scored 1 goal with 1 assist and was plus-two with eight penalty minutes in four games. He was signed as a free agent to a three-year entry-level contract by Tampa Bay in March, 2012.