Using trend indices for endangered species

Initial appraisals of the status of endangered large-mammal populations may have to depend on indices of population trend. Such indices may possibly b e improved by using auxiliary variables. Various models were studied for po pulations of the Florida manatee (Trichechus manatus latirostris), Yellowst one grizzly bear (Ursus arctos horribilis), and Hawaiian monk seal (Monachu s schauinslandi). Several criteria for checking validity of the fitted mode ls were considered, and the simple R-2 criterion appears to provide useful comparisons. Multiple regression models overestimated the rate of change of the East Coast manatee population as determined from three other sources ( a covariance model, a non-linear model, and the rate estimated from reprodu ctive and survival data). A multiple regression model for grizzly bears usi ng three auxiliary variables exhibited a fairly high R-2 (0.84)and appeared to provide a better fit than did a non-linear model. A beach count index f or Hawaiian monk seals seemed to be unreliable for year-to-year comparisons in contrast to total population counts and estimates from a capture-recapt ure method. The use of auxiliary variables for checking and improving trend index data appears feasible and well worthwhile.