▁National ▁Se ash ore . ▁Since ▁then , ▁few ▁new ▁horses ▁have ▁been ▁introduced ▁to ▁the ▁island , ▁though ▁four ▁Arab ians ▁were ▁introduced ▁in ▁the ▁early ▁ 1 9 9 0 s ▁in ▁the ▁hopes ▁of ▁divers ifying ▁and ▁better ing ▁the ▁existing ▁population . ▁Since ▁ 1 9 8 1 , ▁the ▁N PS ▁has ▁been ▁monitoring ▁the ▁horses ▁and ▁tracking ▁their ▁impact ▁on ▁the ▁environment . ▁In ▁ 1 9 9 1 , ▁an ▁out break ▁of ▁eastern ▁equ ine ▁en ce phal itis ▁killed ▁about ▁ 4 0 ▁horses , ▁or ▁approximately ▁ 1 8 % ▁of ▁the ▁her d . ▁The ▁population ▁on ▁C umber land ▁Island ▁is ▁one ▁of ▁seven ▁fer al ▁horse ▁her ds ▁on ▁US ▁bar rier ▁islands . ▁ ▁Character istics ▁ ▁A ▁ 2 0 0 9 ▁resource ▁assess ment ▁of ▁the ▁C umber land ▁Island ▁National ▁Se ash ore ▁by ▁the ▁National ▁Park s ▁Conserv ation ▁Association ▁( NP CA ) ▁estimated ▁that ▁there ▁were ▁approximately ▁ 2 0 0 ▁fer al ▁horses ▁on ▁C umber land ▁Island . ▁As ▁of ▁ 2 0 1 0 , ▁ 1 2 1 ▁horses ▁were ▁counted ▁on ▁the ▁island ▁during ▁the ▁year ly ▁census . ▁C ens uses ▁conducted ▁between ▁ 2 0 0 0 ▁and ▁ 2 0 1 0 ▁have ▁counted ▁between ▁ 1 2 0 ▁and ▁ 1 5 4 ▁horses . ▁Not ▁all ▁horses ▁are ▁counted ▁during ▁the ▁census , ▁and ▁park ▁management ▁estimates ▁that ▁approximately ▁ 5 0 ▁horses