Recent declines of black abalone Haliotis cracherodii on the mainland coast of central California

Abstract

The black dbalone Hal~otls cracherodil was once abundant in many lntert~dal habitats in southern Callforn~a USA Beginning In 1985 however, black abalone In southern California suffered mass moltal~ties attributed to a condltton telmed lvlthenng syndrome The mass mortalities and w~therlng hyndrome were confined to southern Califoinla except for Dlablo Cove, 70 kin no1 th of Polnt Conception, where mortalities were limlted to the immediate vlcinity of a watm-water dtscharge Beylnnlng In 1992 we monltoied 5 locations along the mainland coast ot central California to detelmine whether mass mortal~ties of black abalone would occur there Abalone numbers decreased at the 3 southern sltes but not at the 2 northern sltes The decline was greatest at the southernmost site Government P o ~n t (near Point Concept~on), where there was a 97% reduction in numbers between 1992 and 1995 The 2 sltes ~mmedlately upcoast of Government Polnt, Boathouse and Polnt Arguello, expenenced a 39 to 4Got, decllne ivh~le the 2 northernmost s ~t e s (Stalrs and P u n s ~m a ) expenenced a s l ~g h t increase In abalone All abalone size classes d e c l ~n e d at Government Polnt, Boathouse and Point Arguello lndicatlng the decllne was not caused by overharvesting Symptoms of w~therlng syndrome assessed by p u l l ~n g on indlv~duals were noted at Boathouse and Polnt Arguello Witheling syndrome was also detected in the flnal survey at Stairs, as lvas a sllght dechne In abalone abundance, suggestlng that mass mortal~ties may be beginning there Our observations demonstrate that w ~d e s p r e a d mass mortal~ty assoc~ated w ~t h w ~t h e l ~n g syndlome has reached central Cal~fornia and is progressing northward from Point Conceptlon