Tim Paine has done a more than credible job as Australian Test captain in extraordinarily difficult circumstances. But despite his efficiency there is much conjecture about his successor - due in part because of the absence of suitable candidates, former captain Steven Smith notwithstanding.

Smith's captaincy ban ends in April 2020 and by then Paine may well decide he has had enough of what is a demanding job. In the meantime it'll be interesting to see if any captaincy candidates emerge as viable alternatives.

How has Australia, once regarded as the best groomer of captains in the cricket world, reached such a state of destitution?

Like many problems in cricket, it stems partly from the unwieldy international schedule. International demands mean that the better young players are rarely available for club or Sheffield Shield cricket, both of which used to be a substantial component of Australia's captaincy education system.

Players with captaincy potential had ample opportunity to lead teams that contained senior cricketers, who would pass on tips or point out errors of judgement. The only way to improve as a captain is to do the job and learn from the inevitable mistakes. Not only did the Australian system traditionally present opportunities for a candidate to graduate with honours, it also provided selectors with evidence (or otherwise) of leadership potential.

Another avenue for grooming captains has been lost with the dramatic reduction in the number of matches played by Australian touring teams. In the past, vice-captains occasionally had the opportunity to display their captaincy credentials, and in the process the players could acclimatise to their leadership style for when they took the step up to captaining.

There's another problem looming for Australian cricket in this regard - mental health. Good young batsmen are crucial to Australian cricket, not least because they are a source of future captains. When players like Will Pucovski are forced to take time out from the game to sort out mental-health issues, it potentially decreases the leadership pool. It's going to take a brave selector to burden a player like Pucovski with leadership duties when the pervading thought is, "Will the extra responsibility lead to another breakdown?"

So far it seems to be only batsmen who have been afflicted, which suggests bowlers should be given greater consideration for leadership roles. I once made the mistake of saying in front of Richie Benaud that batsmen tend to make the best captains. "Ah yes," mused Benaud, with the bottom lip protruding, "but it's only batsmen who say that."

There haven't been many bowling captains but those few have generally been very good leaders. Benaud was in that category, and although an allrounder, he was a bowler first and foremost. Imran Khan was highly successful, and like Benaud his primary skill was bowling. England's Ray Illingworth was another bowling allrounder and I learned a lot about captaincy while opposing him in two Ashes series. The high success rate of these captains confirms Imran's opinion that captains must understand bowling. Perhaps CA are on to something, given they appointed Josh Hazlewood and then Pat Cummins as co-vice captains of the Test team.

Another problem area for CA in their leadership search is the failure of young batsmen like Travis Head to establish their playing credentials at the highest level. Head has experience as captain of his state but is yet to cement a spot in the Test batting order.

Paine, the incumbent, is not one who subscribes to the theory that being a keeper-captain is any more difficult than doing the job as a batsman. There's every chance that Paine will further enhance his leadership reputation by the end of summer with victory over both Pakistan and New Zealand. At that point he'll decide whether he wants to build on that reputation or call it quits while he's in front.

If it's the latter then CA had better hope that either a good candidate has surged to the head of the queue or Smith is in the right frame of mind to tackle the job a second time. If Paine's successor is Smith, it'll mean the Australian captaincy production line is in need of a serious recharge.