Chatfeild-Roberts, who is also chief investment officer at Jupiter and manager of its highly rated Merlin multi-manager range, says his growing list of responsibilities influenced his decision to step down.
"With my role having expanded since I became chief investment officer last year, I feel the time is right to hand over full-time responsibility for this portfolio to Simon," he said.
"He has delivered exceptional performance for investors since launching the Japan Income fund and has been taking on increasing responsibility for Jupiter Global Managed in the past year."
Under the guidance of Chatfeild-Roberts, the Jupiter Global Managed fund is a top-quartile performer over a 10-year period, with returns of 112.89 per cent – more than twice as much as the average IMA Global fund.
Performance of fund vs sector over 10-yrs
Source: FE Analytics
Somerville, who has worked as deputy manager on the fund since September 2010, will take over from 14 November 2011.
Chatfeild-Roberts will become deputy manager of the fund and will continue to provide input to the fund’s asset allocation strategy.
Although Somerville is a former head of global equities at Cazenove and has co-managed the Jupiter Global Managed fund since September 2008, he is best known for his expertise in the Japanese market. He manages Jupiter JGF Japan Select and Jupiter Japan Income, the latter of which is a top-quartile performer over a five-year period.
Performance of manager vs peer group over 5-yrs
Source: FE Analytics
According to FE Analytics, Somerville has returned 0.48 per cent in the last five years, compared with losses of 11.26 per cent from his peer group composite.
Chatfeild-Roberts has returned 24.51 per cent during this time.
Kerry Nelson, managing director of Nexus IFA, thinks Chatfeild-Roberts' decision to quit as lead manager could be a sign of things to come.
"I'd say there is a big chance he could take less and less of a role as lead manager [of the Merlin multi-manager portfolios]," she said. "Whenever a manager takes on responsibility elsewhere there's always the inevitability that he sacrifices his powers elsewhere."
"It is important to remember, however, that the Merlin funds are run by a team of three, who have been together for many years now. Given the character of Chatfeild-Roberts, he will still remain very involved in the running of the funds as deputy manager, so I don't think investors should feel too perturbed," she added.