Demographic Parameters of Yellowfin Croaker, Umbrina roncador (Perciformes: Sciaenidae), from the Southern California Bight1
The yellowfin croaker, Umbrina roncador Jordan & Gilbert, 1882, is a common nearshore and surf-zone species in the southern California bight. Age was determined for individuals (n ¼ 1,209) using annual increments in otoliths, and size at age was modeled using the von Bertalanffy growth curve (L y ¼ 307:754 mm, k ¼ 0:278 yr À1 , t 0 ¼ À0:995 yr; maximum age ¼ 15 yr). Females (L y ¼ 313:173 mm, k ¼ 0:307 yr À1 , t 0 ¼ À0:771 yr) grew significantly faster and larger than males (L y ¼ 298:886, k ¼
... :269 yr À1 , t 0 ¼ À1:072 yr). Age and growth modeling based upon otolith length (OL) and width (OW ) measurements were assessed and were consistent with body measurements. Males and females were found in all size classes and in an overall 51 : 49 ratio that was not significantly different from a 50% sex ratio, suggesting that these fish are gonochores. Fish were reproductive during summer months, with gonadosomatic indices (females, 5.65%; males, 5.51%) consistent with group-spawning fishes. Data from two separate monitoring programs indicated that yellowfin croaker catch-per-unit-effort (CPUE) fluctuated appreciably from 1992 to 2006 on both spatial and temporal scales. CPUE also declined significantly in the latter years of these programs. Based on samples collected between 2003 and 2004, an estimate of overall annual total mortality was A ¼ 0:4492, and instantaneous coefficient of total mortality was estimated at Z ¼ 0:5964. Recruitment year classes were back calculated using annual survivorship. Year class strength was variable and declined significantly by the end of this study. Considering the high temporal and spatial variation in estimates of abundance and recruitment, coupled with the likelihood that these fish employ a probable group-spawning reproductive behavior, we recommend a cautious approach for the future management of this species.