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Age, growth and hatch dates of ingressing larvae and surviving juveniles of Atlantic menhaden Brevoortia tyrannus.
Lozano, C; Houde, ED; Wingate, RL; Secor, DH
Ages, growth and hatch dates of ingressing Brevoortia tyrannus larvae were determined in a 3 year sampling survey at the mouth of the Chesapeake Bay, U.S.A. To determine if otolith-aged cohorts had variable relative survival, hatch dates of summer-caught young-of-the-year (YOY) juveniles collected throughout the Chesapeake Bay were compared with hatch dates of ingressing larvae. Modal total length of ingressing larvae was similar among years: 28 mm in 20052006 and 20072008, and 30 mm in 20062007. Ages of ingressing larvae ranged from 9 to 96 days post hatch (dph); mean ages were similar among years, but significantly older in 20062007 (50 dph) than in 20052006 (44 dph) and 20072008 (46 dph). Larval growth rates differed among years. Earliest growth, when larvae were offshore (020 dph), was faster in 20062007 (0.62 mm day-1), than in 20052006 and 20072008 (0.55 mm day-1 in these years). Subsequently, from 30 to 80 dph, growth was slowest in 20062007. Hatch dates of ingressing larvae occurred from September to March and 90% (20072008) to 98% (20062007) had hatched prior to 31 December. In contrast, most surviving YOY juvenile B. tyrannus had hatched in January to February, suggesting selective mortality of early-hatched individuals, apparently during the overwinter, larval to juvenile transition period.
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