The petitioners are drawing attention to the fact that our region has been heavily affected by the groundfish moratorium imposed by Fisheries and Oceans Canada back in May 1994. Since then, the Atlantic Groundfish Strategy, or TAGS, has been the only means of survival for a large part of our population.
Since 1994 the Atlantic Groundfish Strategy, or TAGS, has been not been the only means of survival for a small part of the population.
it says in the context that " since 1994, the Atlantic Groundfish Strategy, or TAGS, has been the only means of survival for a large part of our population."    So that means for the small remaining part of the population, this was not the only means of survival.                                                                                                                       So the statement "   Since 1994 the Atlantic Ground fish Strategy, or TAGS, has been not been the only means of survival for a small part of the population. ", is definitely correct                                             
( z1 means :polarity - :domain ( z2 strategy :name ( z3 name :op "Atlantic" :op "Groundfish" :op "Strategy" ) ) :mod ( z4 only ) :instrument-of ( z5 survive :ARG0 ( z6 part :mod ( z7 small ) :part-of ( z8 population ) ) ) :time ( z9 since :op ( z10 date-entity :year 1994 ) ) )