Wood et al.: A comparison between warm-water fish assemblages of Narragansett Bay and Long Island Sound waters 
99 
which is slightly less than the suggested lowest lethal 
temperature of about 8°C for northern puffer ( Hoff and 
Westman, 1966), 7.4° to 9°C for crevalle jack (Hoff, 
1971), and 10°C for spotfin butterflyfish (McBride and 
Able, 1998). The rapidly decreasing temperatures in 
the fall cooling cycle determine the length of time the 
warm-water fish are able to survive in temperate waters 
before colder temperatures overtake them. 
Trends in water temperature indicated that seasonal 
warming and cooling were the same between the two 
locations and that the warmer years were correlated 
with greater abundance of warm-water fishes. This has 
been observed in other estuarine waters as well, where 
major influxes of tropical and subtropical fish in New 
Zealand are linked to warm summers, although there 
have been several warm periods not accompanied by 
influxes (Francis et ah, 1999). The incidence of warm- 
water fish is generally increasing with time, indicating 
that this pattern of increased warm-water fish abun- 
dance is likely to continue to rise as temperate coastal 
waters continually warm on a global scale. However, 
this increase in warm-water fish abundance may not 
be exclusively related to temperature. The majority of 
warm-water fishes are caught between 17° and 21°C, 
and very few fish are caught at temperatures greater 
than 21°C. It is possible that very few fish are caught at 
21°C because temperatures are rarely recorded higher 
than 21°C in Narragansett Bay or Long Island Sound. 
In addition, not all warm years on record are accom- 
panied by heightened warm-water fish catch, and this 
result highlights the possibility that nontemperature-re- 
lated factors are contributing to the observed temporal 
trend. There are likely other processes that influence 
the abundance of these fishes, such as shifts in the 
transport mechanisms responsible for supplying warm- 
water fishes to more northern habitats. 
It is hypothesized that the major mode of northward 
transport for warm-water fishes is the Gulf Stream 
Current. Because many warm-water fishes arrive as 
larvae or juveniles, larval transport mechanisms are 
important to their arrival to summer habitats (Fli- 
erl and Wroblewski, 1985; Hare et al., 2002). Western 
boundary currents such as the Gulf Stream and the Ku- 
roshio Current, and their associated warm-core rings, 
meanders, and streamers provide physical mechanisms 
responsible for the pole-ward transport of many warm- 
water species (Craddock et al., 1992; Watanabe and 
Kawaguchi, 2003). The Gulf Stream and its associated 
currents consist of warmer Sargasso Sea water and 
introduce warm-water fish species into the continental 
shelf and slope waters near southern New England 
(Markle et al., 1980; Cowen et al., 1993). Hare et al. 
(2002) hypothesized four phases exist for northward 
larval transport and these are associated with warm- 
core rings. They hypothesized that larval fish were 1) 
entrained into the Gulf Stream, 2) transported to the 
northeastern shelf along the edge of the Gulf Stream, 
3) carried in warm-core ring streamers from the Gulf 
Stream and across the Slope Sea (the region between 
the Gulf Stream and the shelf edge of Cape Hatteras), 
and 4) ejected from warm-core ring streamers at the 
shelf edge where larval fishes enter the shelf-slope 
frontal zone. This mode of transport is the most likely 
explanation for how warm-water fishes end up in Nar- 
ragansett Bay and Long Island Sound, where they are 
observed in their early life stages. 
The observations presented here have not been pre- 
viously documented and provide valuable information 
regarding the community structure in these locations. 
Besides adding to our knowledge of the occurrence of 
warm-water fishes in northern estuaries, the changes 
in faunal assemblages noted in this study will become 
increasingly pertinent for future studies on climate 
change. If waters continue to warm on a global scale, 
it is thought that major western boundary current sys- 
tems, such as that of the Gulf Stream Current, may 
weaken (Frank et al., 1990) and therefore would trans- 
port fewer juvenile warm-water fishes northward to 
temperate areas. It is also thought that the general 
fish assemblages of temperate estuaries may shift from 
more vertebrate species (fish) to more invertebrate spe- 
cies (crabs) with increasing water temperatures (Col- 
lie et al., 2008). These ideas are contradictory to the 
thought that warming temperate waters would sup- 
port more warm-water fishes in temperate areas in the 
future. The information presented in this study may 
provide insight into future changes in species composi- 
tion and abundance that may occur if warming trends 
continue in the coastal regions of the northwest Atlantic 
Ocean. 
Acknowledgments 
We are grateful to P. Howell (Connecticut Department of 
Environmental Protection), K. Gottschall (Connecticut 
Department of Environmental Protection), D. Danila 
(Dominion Resources Services), C. Powell (Rhode Island 
Department of Environmental Management), and T. 
Lynch (Rhode Island Department of Environmental 
Management) for extracting and sharing fish survey 
data for this study. The Graduate School of Oceanog- 
raphy Fish Trawl is funded by the University of Rhode 
Island. We greatly appreciate comments from A. D. 
Wood, C. Recksiek, and K. Castro on previous drafts of 
this paper, as well as earlier reviews by J. Manderson, D. 
Mountain, K. McKown, and two anonymous reviewers. 
Literature cited 
Able, K. W„ and M. P. Fahay. 
1998. The first year in the life of estuarine fishes in 
the Middle Atlantic Bight, 342 p. Rutgers Univ. Press, 
New Brunswick, NJ. 
Allen, G. R. 
1985. Butterfly and angelfishes of the world, vol. 2, 352 
p. Aquarium Systems, Mentor, OH. 
Bigelow, H. B., and W. C. Schroeder. 
1953. Fishes of the Gulf of Maine. Fish. Bull., Fish. 
Wildl. Serv. 53: i— 577. 
