SANTA CLARA -- The 49ers capped a busy first day of free agency by acquiring Jonathan Martin in a trade with the Miami Dolphins on Tuesday night.
Martin, who left the Dolphins in late October amid a bullying scandal that rocked the NFL, played for 49ers coach Jim Harbaugh at Stanford and is expected to compete for the backup spot at both tackles. If Martin makes the opening day roster, the 49ers owe Miami a seventh-round pick in 2015, ESPN reported.
"Big news," Martin wrote on his Twitter account shortly before the deal was announced. "Beyond blessed."
In another tweet, he wrote: "Opportunities are few in the NFL ... Can't wait to get to work #9erEmpire."
The 49ers' first move of the day had been to sign safety Antoine Bethea, a two-time Pro Bowler from the Indianapolis Colts, after Donte Whitner left to join his hometown Cleveland Browns. Then they re-signed kicker Phil Dawson (two years) and cornerback Eric Wright (one year). That was followed by the acquisition of quarterback Blaine Gabbert in a trade with Jacksonville for another low-round draft choice, possibly two -- which qualified as a surprise until the Martin deal came along.
Martin, a second-round draft pick in 2012, hasn't played since abruptly leaving the Dolphins, citing constant harassment that was confirmed upon a league investigation.
Harbaugh supported Martin throughout the Dolphins scandal, saying he considered Martin a personal friend and describing him as someone who "epitomized the student-athlete model" at Stanford.
"Coach Harbaugh emphasized that he never doubted Martin's physical or mental toughness, and he believes that Martin can continue to have a successful career in the NFL," investigator Ted Wells wrote in his report. "Coach Harbaugh also said that the atmosphere in the Stanford locker room, in his view, was not materially different from that of the San Francisco 49ers' locker room."
Martin started all 23 games he played for the Dolphins -- 13 at right tackle and 10 at left tackle -- but he will be competing for a backup spot with the 49ers, who have Joe Staley and Anthony Davis entrenched as starters. Competition for the "swing tackle" spot will include Alex Boone and Adam Snyder,
"He's coming into a great group of guys, specifically the offensive line," Snyder told TMZ.com. "If he can help us win a Super Bowl, I'm all for it."
"Welcome to the Team Bro," tight end Vernon Davis wrote on Twitter. "We are all about winning over here. #49ers."
To that end, the overhaul of the defensive backfield is likely to have a bigger impact than Martin.
With the departures of Whitner and Carlos Rogers -- the latter was released Tuesday for salary-cap reasons -- the entire 2012 Super Bowl secondary will be gone if free agent Tarrell Brown chooses to sign elsewhere. Dashon Goldson started the exodus a year ago, signing with Tampa Bay, and Whitner followed suit Tuesday by taking a four-year, $28 million deal with the Browns.
"My time in San Fran will always be cherished," Whitner posted on Twitter. "I love everything about the place. I left my heart and soul out there each and every week."
The 49ers signed Bethea to a four-year deal worth $16-20 million, substantially less than what Whitner cost. Bethea, 29, was a sixth-round pick in 2006 from Howard University. Unlike Whitner, Bethea rarely draws penalties and went all of last season without being flagged. Whitner was flagged five times for unnecessary roughness last season, including once in the NFC Championship game loss to Seattle.
For Gabbert, the 49ers gave Jacksonville a sixth-round pick and the possibility of more compensation depending on Gabbert's role with the 49ers in 2014. That is not expected to be much, at least in the view of Bill Polian, the former Indianapolis Colts executive who now serves as an analyst for ESPN.
"I would not count on him to contribute to the squad," Polian said of Gabbert.
The 49ers passed on Gabbert in the 2011 draft to select his Missouri teammate, Aldon Smith, No. 7 overall. The Jaguars took Gabbert at No. 10, he went 5-22 as a starter, and he lost his job last season to Chad Henne amid injuries and poor production (one touchdown, seven interceptions).
"We thought highly of Blaine as an early entry into the 2011 NFL draft," 49ers general manager Trent Baalke said in a statement. "He is a high-character individual that will be given every opportunity to develop within our system."
The only other quarterback on the 49ers' roster is McLeod Bethel-Thompson, who finished last season on the practice squad.
Dawson, 39, will return after kicking the second-most field goals in 49ers history (32), including a franchise-record 27 in a row at one point. His first order of business will be to learn the nuances of kicking at Levi's Stadium, where the wind patterns already have caught Dawson's eye.
"I watched the video on 49ers.com the other day, and as everyone was marveling at the first set of automatic goal posts, I was just staring at the flags that fluctuated," Dawson said on a conference call. "Then I went to weather.com and saw it was only a 10 mph day. That's kind of the life I live."
SS Antoine Bethea (two-time Pro Bowler), QB Blaine Gabbert (2011 first-round pick who is 5-22 as a starter),
SS Donte Whitner (four-year, $28 million deal with Browns), CB Carlos Rogers (released).
K Phil Dawson (reportedly a two-year deal), DL Demarcus Dobbs ($1.4 million tender), LB Michael Wilhoite (tendered one-year contract), CB Eric Wright (one-year deal).
The following are free agents: CB Tarell Brown, CB Perrish Cox, C Jonathan Goodwin, RB Anthony Dixon, WR Kassim Osgood, WR Mario Manningham.