CHICAGO, IL - NOVEMBER 10: of the Chicago Bears of the Detroit Lions at Soldier Field on November 10, 2013 in Chicago, Illinois. The Lions defeated the Bears 21-19. (Photo by Jonathan Daniel/Getty Images) Mel Tucker. (Jonathan Daniel/Getty Images)

By Adam Hoge-

(CBS) — The Bears made changes to their defensive coaching staff Sunday, but the changes did not include defensive coordinator Mel Tucker.

Head coach Marc Trestman announced that Tucker will return for the 2014 season, but defensive line coach Mike Phair and linebackers coach Tim Tibesar have been let go.

The remainder of the coaching staff will remain in place for next season.

“We thank Mike and Tim for their effort and dedication,” Trestman said in a statement. “They are men of high character and integrity. These are not easy decisions and we do not attribute our lack of success on defense to two individuals. We need to improve in all areas defensively and that will be a focal point for us this offseason. The process starts with me as the head coach. Our search for a defensive line and linebackers coach has begun and we will be looking for the best candidates whose experience can bring the most out of our veteran and young players in both areas.”

Phair was previously on former head coach Lovie Smith’s staff and spent three seasons as the Bears’ defensive line coach. Tibesar spent just one season with the Bears after serving as Purdue’s defensive coordinator in 2012. Before that, he was on Trestman’s coaching staff with the Montreal Alouettes for three seasons.

One candidate for the defensive line coach position could already be on the Bears’ staff. Assistant defensive line coach Mike Sinclair was well received in the Bears’ locker room in 2013 and was previously Trestman’s defensive line coach in Montreal for five seasons.

Changes on the coaching staff seemed inevitable after the Bears endured the worst defensive season in franchise history, statistically. The defense allowed a total of 6,497 yards from scrimmage in 2013, 521 more than any other season in franchise history.

There was some speculation that those changes would include firing defensive coordinator Mel Tucker and that speculation only grew after Trestman said “everything is on the table” in a press conference four days after the season ended. Trestman and general manager Phil Emery were in the process of evaluating the entire season at that point and were not ready to commit to Tucker, despite deflecting blame to a rash of injuries and speaking positively of the work the defensive coordinator did during the season. Those evaluations resulted in Tucker being brought back.

“We believe Mel is the right person to lead our defensive unit,” Trestman said in Sunday’s statement. “He fully understands where we need to improve, has the skill set and leadership to oversee the changes that need to be made and to execute our plan to get the results we know are necessary.”

At the conclusion of the season, Trestman said he liked what he saw early in the season from the defense, but admitted he wasn’t as pleased with how the unit finished in the final three weeks of the season. Much of that was due to injuries to players like Lance Briggs, Charles Tillman, Henry Melton, Nate Collins, and D.J. Williams.

“What we saw in the first three games was a Mel Tucker defense that looked very similar quite frankly to the tape that I looked at (of) 2012,” Trestman said Jan. 2. “That’s the facts. That’s what it looked like to me. So No. 1, the transition to the schematics was outstanding and the teaching was very clear, our gap controls, our fits, our ability to disrupt, all those things came into play.”

And, after additional evaluation, that was enough for Trestman to determine that Tucker deserves another year with what should be a healthier, younger group that will likely be playing a somewhat different scheme better suited to their talents.

Adam Hoge covers the Bears for CBSChicago.com and is a frequent contributor to 670 The Score. Follow him on Twitter at @AdamHoge.