The total issuance worldwide of contingent capital securities fell sharply in 2015- dropping to US$101 from its 2014 calendar year total of US$175 billion, said Moody's Investors Service in its latest "Quarterly CoCo Monitor".Moody's said the primary reason for the fall was lower issuance by Chinese banks, due to "persistently weak market conditions and a slower pace of balance-sheet growth that may have reduced their short-term capital requirements."Some 76 per cent of global CoCos issuance was Additional Tier 1 capital, mainly subject to principal write-down with discretionary triggers, while the remaining 24 per cent was Tier 2.Over 2015, Asian banks accounted for 48 per cent of issuance and European banks 40 per cent, a result Moody's said was "largely reflecting the progress regulators in these two regions have made in implementing Basel III regulatory capital requirements."For Asian banks, CoCo issuance was intended to meet rapid balance sheet growth, while for European banks the attraction was the relatively low costs associated with funding through issuance of CoCos, compared to common equity. The European banks also used these instruments to shore up their capital ahead of regulatory stress tests in 2014.CoCo issuance continues to be concentrated among a group of large banks, with the top ten issuers - five European, four Chinese banks and one Australian bank -  accounting for 37 per cent of all issuance since 2009.Although the base of CoCo issuers has widened in recent months, Moody's expects the concentration among the top ten issuers to persist as the largest globally active institutions have to meet much higher capital requirements and buffers under Basel III and to comply with national regulations.