McBride et al.: Expansion of spawning and nursery grounds of Centropristis striata into a wanning Gulf of Maine 
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Days after marking Mean age (days) 
Figure 3 
Accuracy and precision of daily otolith microincrement readings in black sea bass ( Centro¬ 
pristis striata) collected in southeastern Massachusetts during 2006-2007. (A) Accuracy: 
estimated age minus days after marking with oxytetracycline in relation to the days after 
marking of captive fish held in an aquarium. Bubble size corresponds to number of marks 
on otoliths from 17 fish (1 fish of which had 2 marks). (B) Precision: estimated age differ¬ 
ence between 2 independent readings by the same reader in relation to the mean age of both 
readings for wild-caught fish. Each bubble represents one fish. In both panels, the dashed 
line indicates the mean of all differences, and the gray box depicts +2 standard deviations. 
For later examination in relation to age-0 fish dis¬ 
tributions, local sea-surface temperature data were 
measured from NOAA Buoy Station 44013, 30 km 
(or 16 nautical miles) east of Boston, Massachusetts 
(42°21'N, 70°39'W, National Data Buoy Center, web¬ 
site), 1984-2016. 
Results 
Microincrement analyses 
Otolith microincrements were validated as daily in 
marked fish held captive for up to 30 d (Fig. 3A). The 
mean bias, 0.22 d, was not significant (test of symme¬ 
try: x 2 =2.0, df=2, P= 0.37) and there was agreement be¬ 
tween known-age and estimated ring count along the 
distal edge of the OTC mark (Chang’s CV=1.8). Micro¬ 
increment counts made from wild-caught individuals 
were also repeatable (Fig. 3B). The mean bias, -1.6, 
was not significant (test of symmetry: % 2 =11.0, df=10, 
P=0.36) and there was high precision between the first 
and second paired readings (Chang’s CV=3.3). Wild- 
caught age-0 fish ranged in size from 32 to 88 mm TL 
(mean: 53 mm TL [SD 11]), and in age from 50 to 129 
days old (84 d [SD 16]) (n [no. of fish sampled]=381). 
Results based on daily age counts showed that 
black sea bass spawn from early May to mid-July off 
southern New England. Individual hatching dates for 
all aged black sea bass ranged from May 2 to July 21 
(mean: June 6 [SD 14 d], 77=381) (Fig. 4). Mean hatch¬ 
ing dates, pooled by year, were at least a week later in 
2006 (June 11 [SD 13 d], n=200) than in 2007 (June 1 
[SD 13 d], 71=181). They were only 1 d apart between 
Buzzards Bay and Nantucket Sound (June 6 [SD 14 d], 
n =273 and June 7 [SD 14 d], 77=108, respectively), and 
they were 2 weeks earlier in fish collected in estuaries 
(June 1 [SD 11 d], n=2bl) than at inshore sites (June 
16 [SD 12 d], re=124). 
Age-0 black sea bass had variable growth rates 
ranging from 0.32 to 1.22 (mean: 0.65 mm/d [SD 0.15]) 
(Fig. 5). Mean growth rates, pooled by year, were faster 
in 2006 (0.70 [SD 0.14]) than in 2007 (0.58 [SD 0.12]); 
pooled by locations, they were less variable between 
Buzzards Bay and Nantucket Sound regions (0.66 [SD 
0.15] and 0.61 [SD 0.12], respectively), than between 
estuaries (0.68 [SD 0.14]) and inshore sites (0.57 [SD 
0.13]). 
Trawl survey analyses 
Black sea bass have been spawning farther north for 
the last 40 years (Fig. 6). Before 2000, spawning was 
focused in Buzzards Bay and Nantucket Sound, and 
there were no indications of spawning in the Gulf of 
Maine. In the 2000s, developing females appeared in 
Cape Cod Bay. Since 2010, developing females have 
been caught as far north as Cape Ann off northeast¬ 
ern Massachusetts (42°39 , N, 70°36'W). Few spawning 
females were observed in the Gulf of Maine—a finding 
