With respect to biological changes, it is perhaps more 
important to note changes in percentages of certain tem- 
perature class intervals rather than variations in tem- 
perature means or extremes since the TCI’s can be con- 
sidered areal estimates of suitable habitat for any given 
species. The reader should again be cautioned that the 
TCI analysis is intended primarily for comparing habitat 
conditions at the time of sampling and should not be con- 
sidered changes between stable annual conditions. Since 
cruises of some years differed by over a month, and the 
TCI percentages represent relatively transient 
phenomena, the value of this analysis is in interpreting 
how a species may be affected by the observed TCI per- 
centages. For example, during the autumn cruises of 
1964-68, relatively large amounts of 4°-6°C water were 
present in the Gulf of Maine (Fig. 15). These cold con- 
ditions were probably quite favorable for northern 
shrimp, Pandalus borealis, in the southern limits of their 
normal distribution in the western North Atlantic. Both 
commercial and research cruise indices of shrimp abun- 
dance have declined abruptly since 1969 coincident with 
the rapid decrease and disappearance of 4°-6°C water. 
Providing that temperature tolerances or preferences 
are known for various species, such as that of haddock, 
Melanogrammus aeglefinus, embryos surviving best at 
about 6°C (Laurence and Rogers 1976), some relation- 
ships can be examined. It appears from Clark’s’ data 
that the year-class strength of 2-yr-old haddock may be 
related to spawning season temperatures. Since 1968 ex- 
tremely small year classes have been produced in 2 of the 
3 yr that spawning temperatures averaged less than 
4.8°C; the two largest year classes were progeny of 5°- 
6°C temperatures, and temperatures of 6.2°-6.4°C 
produced intermediate-sized year classes. Unfor- 
tunately, these comparisons are available only during a 
period when the haddock stock and recruitment has been 
relatively small due to overfishing. 
It is unlikely that a simple linear relationship between 
temperature and spawning success exists, but tempera- 
ture trends of the magnitude encountered during the 
past decade undoubtedly influenced certain biological 
phenomena including changes in spawning time, growth 
rates, and distributional characteristics of several 
species. Some notable changes that occurred in this 
latest warming trend include increased populations of 
green crabs, Carcinides maenas, along the Maine coast 
(University of Rhode Island‘); northerly extended 
seasonal distribution of Atlantic mackerel, Scomber 
scombrus, (Anderson*); increased growth rates in the 
1970’s of Atlantic herring, Clupea harengus, (Anthony"’); 
7Clark,S. 1976. Georges Bank (Subdiv. 5Ze) haddock status report. 
Int. Comm. Northwest Atl. Fish. Res. Doc. 76/35, 8 p. 
‘University of Rhode Island. 1975. NEMRIP monthly newsletter, 
August 1975. Narragansett Bay Campus, Narragansett, R.I. 
*Anderson, E. D. 1975. The effects of a combined assessment for 
mackerel in ICNAF Subareas 3, 4, and 5, and Statistical Area 6. Int. 
Comm. Northwest. Atl. Fish. Res. Doc. 75/14, 14 p. 
‘Anthony, V.C. Growth rates of Atlantic herring (Clupea harengus) 
in the Gulf of Maine and Georges Bank. Northeast Fisheries Center, 
Woods Hole, Mass. Unpubl. manuscr. 
16 
and a general shift of juvenile silver hake, Merluccius 
bilinearis, since 1971 from Cape Cod and westward to 
Georges Bank and the Gulf of Maine (Davis''). 
Taylor et al. (1957) and Colton (1972) concluded that 
there were no general changes in the faunal composition 
of the Gulf of Maine during the warming trend of the ear- 
ly 1950’s nor the cooling period ending in 1966, but that 
distributional and spawning habits of several species, in- 
cluding haddock, were significantly altered. Although a 
more complete understanding of the net effects of tem- 
perature is required, other gross effects such as those 
stated might be evident if available biological data for 
the last decade are closely scrutinized. Certainly, there 
could be significant value in such correlation analyses of 
time-series data, especially after we have better 
measures of the dynamics involved with temperature 
variations in the Gulf of Maine and on Georges Bank. 
Because of the high variability of bottom-water tem- 
peratures between the two major areas and within their 
respective subareas during the seasons under study, it is 
important that references to temperature trends be iden- 
tified to specific localities and seasons. Contrary to such 
references, annual indices of mean bottom-water tem- 
peratures for Georges Bank and the Gulf of Maine from 
1968 to 1975 are shown in Figure 22. Since only spring 
and autumn data were available, the annual index must 
be considered a gross estimate of average conditions ob- 
served during these years, but the generalized warming 
trend shown is nevertheless of value in revealing the 
changes that have taken place. 
Subsequent to the preparation of most of this manu- 
script, bottom-water temperature data for 1976 became 
available. Preliminary analysis of the data indicates 
record high adjusted mean temperatures during the 
autumn for both Georges Bank (13.4°C) and the Gulf of 
Maine (9.3°C) and also during the spring in the Gulf of 
Maine (7.2°C). A relatively large inflow of 8°-10°C water 
‘Davis, C. W. Demersal distribution of juvenile silver hake (Merluc- 
cius bilinearis) from Cape Hatteras to western Nova Scotia, 1963-1975, 
Unpubl. manuscr. 
10+ 
o 
= 19))- 
Ww 
res 
« Georges Bank 
Ww 
<p 8 
Ei b 
= 
re) 
= 
eal E 
ioe) 
= 
os 
= i, Gulf of Maine 
1 1 1 1 
1968 1969 1970 1971 1972. 1973 1974 1975 
Figure 22.—Annual mean bottom-water temperatures in the Gulf of 
Maine and on Georges Bank, 1968-75. 
