The flowmeter readings for each tow were converted to 
m:® of water filtered. These values for a given cruise were 
then plotted against maximum tow depth. Obvious dis- 
crepancies in volume values caused by windmilling, etc., 
were corrected on the basis of average tow depth-volume 
filtered values. Numbers of larvae per unit volume and 
numbers under a unit surface area were then deter- 
mined for each tow. 
ICHTHYOPLANKTON SUMMARIES 
The families, genera, and species of larval fishes iden- 
tified on each cruise are summarized in Table 1. The 
families are arranged in phylogenetic order (based on 
Greenwood et al. 1966) and the genera listed in al- 
phabetical order. Often the specific identity of larvae 
could not be ascertained and separation was made only 
to the generic or family level. This was most often the 
case for oceanic specimens collected in slope water along 
the edge of the continental shelf. Because of seasonal and 
annual differences in the species composition and abun- 
dance of larvae, the same taxa were not enumerated for 
each cruise. We have summarized the abundance, length 
frequencies, and distribution of larvae on an individual 
cruise basis and have included only the dominant taxa 
(Table 2) and species of commercial interest which oc- 
curred in at least 5% of the total stations occupied. Lar- 
vae of 12 species of fishes are included in this summary, 
as well as 2 familial groupings: 
CLUPEIDAE (herrings) 
Clupea harengus harengus - Atlantic herring 
GADIDAE (codfishes and hakes) 
Gadus morhua - Atlantic cod 
Melanogrammus aeglefinus - Haddock 
Merluccius bilinearis - Silver hake 
Pollachius virens - Pollock 
Rhinonemus cimbrius - Fourbeard rockling 
Urophycis chuss - Red hake 
AMMODYTIDAE (sand lances) 
Ammodytes dubius - Northern sand lance 
STROMATEIDAE (butterfishes) 
Peprilus triacanthus - Butterfish 
BOTHIDAE (lefteye flounders) 
Citharichthys arctifrons - Gulf Stream flounder 
Scophthalmus aquosus - Windowpane 
PLEURONECTIDAE (righteye flounders) 
Glyptocephalus cynoglossus - Witch flounder 
MYCTOPHIDAE (lanternfishes) 
PARALEPIDIDAE (barracudinas) 
Statistics for individual taxa were calculated for each 
cruise using the dominance-frequency method of Fager 
and McGowan (1963). These statistics are summarized 
in Table 2. The abundance (no./100 m‘) of species and 
families for individual cruises and stations are listed in 
Tables 3-10. The species length frequencies for in- 
dividual cruises are given in Tables 11-14. The dis- 
tributions (no./10 m?) of species and families are shown 
in Figures 1-8. The no./100 m° values listed in Tables 3-10 
can be converted to no./10 m® by multiplying these 
values by d/10, where d is the sample depth. 
DISCUSSION 
A conspicuous and significant aspect of the larval fish 
distribution is the almost total segregation of coastal 
(boreal) and oceanic (tropical and subtropical) species 
north and south of the 100-m isobath during the Decem- 
ber surveys. This divergence coincided with the location 
of the coastal/slope water boundary (thermal front) 
which is manifest in the surface layer (upper 100 m) 
along the edge of the continental shelf during Novem- 
ber-January (Colton and Stoddard 1972). In late winter 
and spring, the surface thermal front is located further 
(approximately 20 km) offshore (Wright 1976), and 
oceanic, vertebrate and invertebrate indicator species do 
not occur along the edge of the shelf (Colton 1961; Col- 
ton et al. 1962). In late summer and early fall when shelf 
water temperatures are maximum, the surface thermal 
front is no longer present (Colton and Stoddard 1972), 
and oceanic indicator species are frequently found over 
Georges Bank and contiguous areas (Figure 1; Colton 
1961; Colton et al. 1962). 
To illustrate the relationship of temperature to the dis- 
tribution of coastal and oceanic larval fish species during 
December, we determined integrated temperatures to a 
maximum depth of 100 m, or to the bottom in shoaler 
areas, using Albatross IV Cruise 74-13 expendable bathy- 
thermograph values at standard depths of 0, 10, 20, 30, 
50, 75, and 100 m. The distribution of these integrated 
temperatures and a plot of the abundance of larval At- 
lantic herring, Myctophidae, and Paralepididae versus 
integrated temperature values are shown in Figure 9. All 
larval barracudinas and lanternfishes were collected in 
areas where the integrated temperature was above 11° 
and 13°C respectively. Ninety-one percent of the positive 
larval herring tows were made in areas where the in- 
tegrated temperature was below 13°C and 80% of the 
positive tows were below 11°C. 
We do not imply that the observed distribution pat- 
terns of larval fishes are controlled directly by tem- 
perature. Laboratory experiments have shown the upper 
lethal temperature (and salinity) for early stage larval 
herring to be appreciably higher than the temperature- 
salinity values characteristic of slope water (Blaxter 
1960; Holliday and Blaxter 1960). There are marked dif- 
ferences in abundance, species composition and species 
diversity of zooplankton between coastal and slope 
water. The mean standing crop is greater in coastal water 
and the number of species greater in slope water (Clarke 
1940; Grice and Hart 1962). It is possible, therefore, that 
the distribution of coastal fish species, such as herring, is 
more contingent on biological factors (availability of 
suitable zooplankton forage organisms) than on the phy- 
sical characteristics of their environment. Hopefully, 
when additional data from these cruises have been 
processed, we will be able to elucidate the biotic and 
