The 28-year-old defenseman and and forward Francis Perron were acquired by the Sharks from the Senators for forwards Chris Tierney, Rudolfs Balcers and Joshua Norris, defenseman Dylan DeMelo, a first-round pick in the 2019 NHL Draft or 2020 Draft, a second-round pick in the 2019 draft and two conditional draft picks on Sept. 13.
Karlsson, the Senators captain from 2014-18, won the Norris Trophy twice and had 518 points (126 goals, 392 assists) in 627 games with Ottawa. He led the Senators in points or tied for the lead in each of his final five seasons with them.
The Sharks have been outscored 14-5 in a season-long three-game losing streak and have allowed at least four goals in seven of their past 11 games.
Ottawa looks to win its third straight game following a four-game losing streak.