Able et al.: Larval abundance of Paralichthys dentatus as a measure of recruitment and stock status 
71 
Developmental stage 
Figure 2 
Frequency of developmental stages for summer flounder ( Para- 
lichthys dentatus) at ingress from Little Egg Inlet, New Jersey, 
and Beaufort Inlet, North Carolina. Stage notation refers to 
the scheme of Keefe and Able (1993) as depicted in the head 
views. The right and left eyes are bilateral and symmetrical 
in premetamorphs. At the first stage of metamorphosis, F-, 
the eyes are bilateral but asymmetrical and the right eye is 
just dorsal to the left eye. By stage F, the asymmetry due to 
the movement of the right eye is most evident. At stage G, the 
right eye has reached the dorsal midline and is visible from 
the left side of the fish. Stage H- differs from G in that the 
cornea of the eye is visible from the left side of the fish. At 
stage H, the right eye has migrated halfway and is midline 
at the dorsal edge of the head. By stage H+, the right eye 
has reached the left surface but has not yet reached its final 
resting place. At stage I, the eye is set in the socket and the 
dorsal canal has closed. 
chrony in magnitude of abundance of ingressing 
summer flounder larvae between Little Egg and 
Beaufort inlets (and their respective relationship 
with SSB and REC) using two methods: 1) aver- 
age cross-correlations of series values (r); and 2) 
measures based strictly on change (Buonaccorsi et 
al., 2001). For the latter method, the data consisted 
of n series, measured at T points in time, where x it 
is the larval concentration at a given inlet, SSB, 
or REC. The relative direction of change was cal- 
culated as A y , where A =( number of times series i 
and j move in same direction)/ (T-l). This expres- 
sion was then modified into a correlative measure 
by using r y =2A y -1 (Buonaccorsi et al., 2001). For 
both methods, a large, positive value of r or r sig- 
nals strong synchrony in magnitude of abundance 
between populations (reject H 0 ), a value near zero 
corresponds with weak synchrony in magnitude 
of abundance (accept H 0 ), whereas a value below 
zero is indicative of populations consistently out of 
phase (accept H 0 \ Jones et ah, 2003). In all cases, 
data were lagged to relate spawning stock biomass 
to subsequent larval abundance at ingress and 
recruitment. Spawning stock biomass in year y 
was related to larval abundance at ingress during 
the fall-winter of year y and the winter-spring 
of year y+1 and to recruitment in year y+1. All 
time series data on abundance were natural log 
transformed (In). 
Results 
Patterns of larval ingress 
At both Little Egg Inlet and Beaufort Inlet, the 
larvae captured at ingress were in similar stages of 
development, i.e., transitional stages (stages F— I, based 
on Keefe and Able, 1993) nearing the completion of eye 
migration (Fig. 2). These same individuals had overlap- 
ping sizes from 10 to 17 mm standard length (SL) and 
most (90%) were between 12 and 15 mm SL in both 
inlets, but with slightly larger individuals at Beaufort 
Inlet (Fig. 3). Summer flounder larvae were consistently 
more abundant at Beaufort Inlet than Little Egg Inlet 
(average for all positive months, 8.18/1000 m 3 compared 
to 4.95/1000 m 3 , respectively, Fig. 4). 
The timing of ingress differed within and between 
inlets (Figs. 4 and 5). In the year-round collections 
at Little Egg Inlet, larvae were found from October 
through June over the study period (1989-2006). Before 
1998, larvae were more abundant in the late winter and 
spring (January-March). The inconsistently late occur- 
rence of the peak in 1993 is an artifact due to missed 
collections during the peak period of ingress. From 
1998 onwards, larvae were typically more abundant in 
the fall and early winter (October-December; Fig. 5). 
From 1989 through 1998 fall and early winter larvae 
averaged 1.66/1000 m 3 , whereas from 1999 through 
2006 they averaged 9.08/1000 m 3 . At Beaufort Inlet, 
larvae occurred from December through the end of the 
sampling period in April or May, but individuals were 
most abundant from February through April. It is pos- 
sible that larvae continued ingress but were undetected 
because sampling typically ended at the end of April or 
May (Fig. 4). Abundance at Beaufort Inlet varied annu- 
ally, but seasonal patterns of ingress did not vary over 
the time series as strikingly as at Little Egg Inlet (Fig. 
5). From 1989 through 1998, the late winter and spring 
larval abundance average (6.62/1000 m 3 ) was similar 
for those from 1999 through 2006 (7.76/1000 m 3 ). 
Relationships between larval abundance at ingress, 
spawning stock biomass, and recruitment 
Estimated spawning stock biomass of summer flounder 
has increased since the late 1990s and reached the 
highest values during 2000-06 (Fig. 6A). Estimated 
recruitment has been variable over the same period (Fig 
6B). A Beverton-Holt model has been used to describe 
the stock-recruitment relationship, but this model essen- 
tially predicts constant recruitment over the range of 
observed spawning stock biomass (NEFSC 1 ). Trends 
in larval abundance at Little Egg Inlet are similar to 
