Lions coach Jim Schwartz will be back in 2013, but some of the coaches who surrounded him this year won't. (US Presswire)

Lions’ coach Jim Schwartz and GM Martin Mayhew chose to retain the team’s entire coaching staff following Detroit’s 10-6 2011 season because they believed that continuity in the locker room would help the team return to the playoffs in 2012.

Instead, that continuity produced a 4-12 record, leading Schwartz to promise that organizational changes would be made to help return the team to playoff contention.

The first of those changes came Monday with the news that WR coach Shawn Jefferson, OL coach George Yarno, and RB coach Sam Gash would not return in 2013.

News of Gash and, Yarno, and Jefferson’s departures was first reported by Mlive.com, and it’s unclear whether they were fired or if their contracts had expired and were not renewed.

Schwartz did not discuss the contract situations of specific Lions’ assistants when he met with the media for a season-ending press conference Monday. Schwartz did say that retaining all of Detroit’s coaches would be difficult and said he would be open to coaches leaving if they wanted to seek opportunities elsewhere.

“I recognize that some people would like to advance and there are going to be opportunities for some [current Lions’ coaches],” he said. “I’ve always taken the approach that if they have an opportunity -- particularly coordinator jobs or quality control guys that can get position jobs -- if we can’t fill that career advancement here, I certainly want our guys to advance.”

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Both Gash and Jefferson predate Schwartz in the Lions’ organization, and both men are coming off seasons that will put them in contention for jobs with other NFL teams. Gash spent six years in Detroit and has had to deal with near-constant roster change at the RB position during that span. Jahvid Best’s concussion issues meant that Gash faced depth problems from the beginning of training camp, and he responded by molding Joique Bell from a career practice squad player into a serviceable No. 2 rusher.

While Gash was able to handle the injury issues, his departure could have something to do with a lack of what Schwartz terms as “explosive” 20-plus yard runs this season. OC Scott Linehan’s gameplans often rely on big plays to soften defenses, and Gash’s backs didn’t begin to produce those types of plays until the second half of the year.

Yarno arrived in Detroit with Schwartz in 2009 after spending 2008 as the Buccaneers’ assistant O-line coach. Over his four years with the Lions, he turned the O-line into one of the NFC’s best pass-protection units. The line allowed just 29 sacks this season in an NFL-record 727 pass attempts.

Yarno’s pass-protection tutelage was mitigated somewhat by the O-line’s run blocking difficulties beyond the line of scrimmage -- something that must improve next season for Detroit to run a more balanced offense.

Jefferson spent eight years with the Lions, working with three different head coaches during that span. His departure means that Calvin Johnson will have a new position coach next season for the first time in his NFL career.

Johnson unknowingly gave Jefferson, who was rumored to be considering seeking a promotion after this year, a glowing reference recently when he credited his position coach with molding him into the player that has re-written the NFL record books.

“[Jefferson] brought me up in this game as far as mentally, getting my mindset right week in week out,” Johnson said.”[He] taught me a lot of tools of the trade to play receiver. When I came in [to Detroit], I was raw. First year, just came in here just off of talent. I won off of talent in college, but when you come here, you’ve got to redefine your skill set, and he's done a great job with me as far as that goes.”

Johnson also credited Jefferson with teaching him the leadership skills needed to be an elite NFL receiver.

“[Jefferson] holds me accountable for the [WR corps],” he said. “One, it teaches you leadership skills and it teaches you to come to work every day ready to work. Once you cross these white lines, it's time to work. He brought me up the right way.”

Schwartz said the team’s postseason evaluations are an ongoing process, leaving the door open for further staff changes in the next few days.

Follow Lions reporter John Kreger on Twitter at @CBSLions and @JohnKreger.