Differential Growth Among Cohorts of Age-0 Weakfish Cynoscion in Chesapeake Bay

Fishery Bulletin
745 – 752
Szedlmayer, Stephen;Weinstein, ;Musick,
Fish Biology, Management & Population Dynamics,Aquaculture-General
Pub ID:
Age-O weakfish Cyr/Qscion
regalis, were sampled from the
Chesapeake Bay-York River estuary
in 1983 and 1984 to test for the existence
of multiple cohorts and compare
growth rates. In both years
juveniles were first collected in the
estuary in late July, were significantly
more abundant from August to
mid-October, but were uncommon
by the end of October. Significantly
more weakfish were collected in
1983 than in 1984. Daily ages were
determined based on scale circuli.
Cohorts were separated by local minima
in birthdate distributions: cohort
1 hatched before 16 July 1983, cohort
2 (16 July-15 August 1983), cohort
3 (15 August-9 September 1983),
cohort 4 (5 May-20 June 1984), and
cohort 5 (5 July-l September 1984).
Compared with other cohorts, groups
1 and 4 had significantly slower
growth rates (0.83 and 0.84 mm/day,
respectively), while cohort 5 had a
significantly faster growth rate (1.09
mm/day), and cohorts 2 and 3 were
intermediate (both at 0.96 mm/day).
Weakfish juveniles were transient
and migrated up the estuary as they
grew. as indicated by cohort and age
distributions over stations and dates.
Also, cohorts appeared to partition
the estuary; for example, cohort 1
was more common up the estuary
compared with other cohorts. The
existence of multiple cohorts with
significantly different gr.owth rates
and apparent differential habitat use
suggests that the juvenile stage of
weakfish may show high variability
in survival, and the presence of multiple
cohorts within a single yearclass
must be considered in the estimation
of juvenile recruitment to the
adult population.
PDF File:
1990 Szedlmayer, Weinstein, Musick Fishery Bulletin.pdf

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