It was the soundtrack of summer as hundreds of thousands of Sharks fans across the country celebrated a maiden premiership that was 50 years in the making.But as the celebrations have continued the threat of a monster premiership hangover has loomed large with the loss of talismanic hooker Michael Ennis and then the exit of troubled fullback Ben Barba.Fullback-elect Valentine Holmes suffered a minor hamstring strain in their opening trial which could see him miss the season opener against the Broncos while youngster Jayden Brailey and Nu Brown were taken to England as the hooking options for the 22-6 World Club Challenge loss to Wigan.The roster may still be largely the same but they are two big outs for a team that has to summon the energy and desperation in order to do it all over again.Gains and lossesGains: Manaia Cherrington (Wests Tigers), Tony Williams (Bulldogs), Jeremy Latimore (Panthers), Daniel Mortimer (Titans)Losses: David Fifita (released), Mitch Brown (Leigh), Josh Cleeland (Bulldogs), Michael Ennis (retirement), Connor Tracey (Rabbitohs), Jesse Sene-Lefao (Castleford Tigers), Ben Barba (released), Jacob Gagan (Knights), Matt McIlwrick (Wests Tigers), Junior Roqica (London)What we knowPremierships are hard to defend. Although the Roosters were minor premiers the year after winning in 2013 and the Cowboys made the Preliminary Final last season, no champion team has qualified for the grand final the year after their success since Melbourne in 2008, who were thumped 40-0 by Manly. Coaches and players will tell you that there is the same hunger in the squad and a willingness to improve on how they performed in their title-winning campaign but the intangibles such as desperation and commitment rarely function at the same high level. A new No.9 will necessitate an adjustment in playing style and with three of the oldest players in the NRL on their books the sense of destiny that defined their 2016 season will be noticeably absent. Last year the Sharks won eight games by five points or less; they could very well turn into losses 12 months on.Rookie watchGiven his elevation into the squad for the World Club Challenge and the need to replace Ennis at hooker reigning Holden Cup Player of the Year Jayden Brailey looks set to play a significant role in the Sharks’ title defence. Also keep an eye out for towering prop forward Malakai Houma, who earned an NRL contract after impressive performances for Newtown in the Intrust Super Premiership last year. If he earns a debut he’ll be hard to miss; he’s the 189-centimetre, 112-kilogram monster charging onto the ball at a million miles an hour in the middle of the ruck.DepthSeventeen of the 24 players the Sharks used last year played at least 20 games, providing the stability that premiership charges demand. The additions of experienced first-graders in Jeremy Latimore and Tony Williams provides welcome depth in the forward pack and the likes of Jack Bird, Gerard Beale and Daniel Mortimer can cover a number of different positions if injuries hit hard in key positions. There are a raft of exciting young outside backs ready to step up if the three-quarter line suffers a couple of injury blows led by Jesse Ramien and James Tuitahu.Fantasy bankersHe doesn’t come cheap but with an average of 63 points per game (second highest in 2016) there’s good reason to pony up the money to purchase Andrew Fifita at his $601,000 asking price. Paul Gallen’s retirement from rep footy opens up the possibility of more regular high-scoring games through the Origin period while Valentine Holmes could prove an astute pick-up at $301,000 if he becomes Cronulla’s first-choice fullback.Crystal ballSharks aren’t accustomed to being the hunted but that’s the reality Cronulla players will have to come to terms with on a weekly basis in 2017. Hosting a strong Broncos team in the opening game of the season will give us some indication of their headspace and with trips to Canberra and Melbourne in the opening six weeks Cronulla are looking at a challenging start to their defence. The loss of Ennis cannot be underestimated and with the mental letdown that comes with a drought-breaking premiership a top four finish looks unlikely.