McBride et al.: Expansion of spawning and nursery grounds of Centropristis striata into a warming Gulf of Maine 
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Sea temperature (°C) 
Figure 8 
(A) Increasing distribution (solid circles= maximum 
latitude) of age-0 black sea bass (Centropristis stri¬ 
ata) in trawl surveys conducted during autumn by 
the Massachusetts Division of Marine Fisheries and 
the Northeast Fisheries Science Center from 1978 to 
2016, plotted with increasing sea-surface temperatures 
(x=mean for September of each year) in the southern 
Gulf of Maine. Both regression slopes were signifi¬ 
cantly different than zero (autumn distribution, solid 
line: y=0.38+0.021x, P<0.001, coefficient of determina¬ 
tion [r 2 ]=0.29; September temperatures, dashed line: 
y=-130+0.073x, P<0.001, r 2 =0.46). (B) Year-to-year 
comparison of maximum latitude and mean September 
sea-surface temperature (dashed line, y=39.3 + 0.177x, 
P=Q.03, r 2 =0.18). Temperature data for 1984-2016 come 
from NOAA Buoy Station 44013, 30 km east of Boston, 
Massachusetts (see Fig. 7). 
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cooler, but such adjustments would not push spawning 
or hatching outside a May-July period. 
We note few differences in hatching dates among 
our sampling years or locations. There was no differ¬ 
ence between years, and although temperature may 
drive spawning seasonality, June temperatures at the 
buoy in offshore waters of Boston varied by less than 
0.5°C between 2006 and 2007 (14.2°C vs 14.5°C), leav¬ 
ing little contrast between our years of sampling. It 
may be that—with the longer-term pattern of warming 
temperatures—black sea bass spawning seasonality is 
undergoing a directional selection so that spawning 
begins earlier in the year (Pankhurst and Munday, 
2011), which would justify replicating our study design 
to test such a hypothesis in Massachusetts waters. We 
were curious whether there was a spatial difference 
in hatching dates between neighboring Buzzards Bay 
and Nantucket Sound but found no difference. Finally, 
earlier hatching dates for fish that settle in estuarine 
sites, as opposed to inshore sites, may arise from early 
warming in estuarine waters, if warmer water initi¬ 
ates earlier seasonal spawning. However, our sampling 
design was confounded in two specific ways. First, dif¬ 
ferent gears were used in estuarine and inshore sites, 
which may lead to gear selectivity, although this seems 
unlikely because the smallest mesh was a similar size 
in both gears. Second, sampling at estuarine sites be¬ 
gan earlier than at inshore sites: if all fish originated 
across the same hypothetical hatching date distribu¬ 
tion, then fish sampled earlier (versus later) would ex¬ 
perience less cumulative mortality, resulting in differ¬ 
ent back-calculated hatching dates between early and 
late samples. Or they may have experienced different 
dispersal patterns with respect to age and habitat. 
These may be interesting considerations to pursue in 
the future, but their resolutions are not likely to re¬ 
veal a radically different perception of spring-summer 
spawning by black sea bass in coastal waters off south¬ 
eastern Massachusetts. 
It is unlikely that spawning occurs later, such as in 
August, but our study design may not have captured 
late spawning. For example, larvae from a hypothetical 
August spawning may have been too small to be re¬ 
tained by traps or they may have had a high mortality 
rate. However, spawning after July by local fish is not 
consistent with the predominance of immature or spent 
individuals observed by Kolek (1990), Caruso (1995) 
and Wuenschel et al. 2 in late summer. Late summer 
spawning is occurring farther south. For example, a 
check of the NMFS-NEFSC data base from 35°N to 
41°N shows an average of 8.9% (range: 3-19% by 1° 
latitude) of mature females are in spawning condition 
(ripe or ripe and running) during autumn, whereas the 
percentage of spawning females drops to 0.3% north 
of 41°N. Thus, if black sea bass spawn into autumn in 
Massachusetts waters, it is rare. 
The dynamics and overlap between spawning and 
targeted fishing seasons is relevant for managing the 
reproductive potential of a fish population (Peer and 
Miller, 2014). For example, the (Massachusetts and 
