Effects of exploitation evident in age-based demography of 2 deepwater snappers, the goldeneye jobfish (Pristipomoides flavipinnis) in the Samoa Archipelago and the goldflag jobfish (P. auricilla) in the Mariana Archipelago

Abstract

The paucity of species-specific biological information for most exploited Indo-Pacific deepwa¬ter snappers (Lutjanidae) limits stock assessment options and management strategies. To improve stock assessments, age-based demographics were esti¬mated for 2 deepwater snapper species, the goldeneye jobfish (Pristipomoides flavipinnis) in the Samoa Archipelago and the goldflag jobfish (P. auricilla) in the Mariana Archipelago. Each archi¬pelago has locations where fishing had not occurred for at least 30 years, pro¬viding a rare opportunity to examine the effects of exploitation on the age and size compositions, growth, and mortal¬ity of these species. Overall, age-based data reveal a greater effect of fishing pressure than those based on size. This difference highlights concerns with size-based analyses; when species have protracted asymptotic growth trajecto¬ries, the resulting fishing impacts may not be readily apparent in size-based analyses because size and age become decoupled. This decoupling also con¬founds comparisons of growth among areas with different exploitation levels. Mortality estimates derived from an age-based catch curve for the unfished areas (where total mortality equals natural mortality) were comparable to those produced by using a maximum-age-based natural mortality estimator. The comparison of these methods indi¬cates that the age-based natural mor¬tality estimator is suitable for use in deepwater snapper stock assessments when direct measures of natural mor¬tality are unavailable.