Abstract:
From 1996 through 1998 I collected mature female black rockfish off Oregon and
examined ovaries and otoliths to estimate weekly, age-specific larval production. In
all reproductive seasons, older black rockfish extruded larvae earlier in the season,
followed by progressively younger fish. Each year, beginning in May, I collected
young-of-the-year (YOY) benthic juveniles that settled out in nearshore waters and
determined their birthdates from counts of daily rings of lapillar otoliths. I compared
the birthdate distribution of juvenile survivors to the age-specific temporal distribution
of larval production to estimate the contribution of each adult female age group, ages
6-8, 9-11, 12-14, and 15+ to juvenile recruitment. The results from 1996 show a
disproportionately greater contribution to benthic YOY recruitment by older fish.
1997 results show a relatively even contribution among maternal age groups. In 1998
most of the YOY recruits came from younger fish extruding larvae late in the season.
I then examined larvae per recruit (LPR) models to evaluate the effects of fishing
mortality on spawning potential of black rockfish, incorporating my estimates of age-specific
maternal reproductive success. When it is evident that certain age groups are
more successful at reproducing, as observed in black rockfish, changes in that
population's age composition must be considered beyond simply reducing the estimate
of total larval production.
