Martini et a!.: A population profile for Myxine glutinosa 
523 
510 mm elsewhere in the WNA, and 450 mm in the 
ENA) or the minimum size at sexual maturity (400 
mm for the IGM vs. 200 mm for the ENA). Shrink- 
age may have affected some of the proportional com- 
parisons between the IGM and ENA samples, but 
the effect is not straightforward. The IGM hagfish 
(fresh measurement) have proportionately shorter 
prebranchial segments and tails than the ENA speci- 
mens (preserved measurement), and the IGM speci- 
mens are more slender (both in width and depth). 
The morphological measurements 
were made by different groups 
We do not believe that the differences observed 
among these populations reflect variation in proto- 
col between the research groups because differences 
in slime pore counts and cusp counts among the 
sampled populations remain if the IGM data are set 
aside, and a single team (Wisner and McMillan) col- 
lected the NWA, OGM, ENA, and MAC data sets. 
Conclusions 
Our analyses of the available data do not support a 
clean division between eastern and western North 
Atlantic populations of M. glutinosa. We therefore 
support retention of the species name M. glutinosa 
for both eastern and western populations pending 
the results of mtBNA analysis or other molecular 
comparisons. 
Specific arguments against species or subspecies 
division include the following: 1) Considerable vari- 
ability exists in the total slime pore count among the 
WNA groups examined; 2) Although there were sig- 
nificant regional differences in slime pore count be- 
tween the IGM and ENA samples, when compared 
as absolute values or as percentages of the total slime 
pore count, this was not the case for the other WNA 
groups; 3) Total cusp counts were also variable, with 
significant differences noted between NWA-IGM, 
NWA- MAC, IGM-ENA, and MAC-ENA; and 4) The 
degree of differentiation versus the ENA group, in 
increasing order, would be NWA (trunk slime pore 
percentage) — » OGM (total slime pore count) — > MAC 
(trunk slime pore count and cusp count) — » IGM (to- 
tal, trunk, and tail slime pore counts and cusp count). 
This pattern suggests, but does not prove, the ex- 
istence of clinal variations that may reflect the de- 
gree of relative isolation of the populations. Although 
on a map the Gulf of Maine appears continuous with 
the western North Atlantic, in fact it is almost com- 
pletely isolated from the offshore waters by exten- 
sive banks and shoals (Fig. 1A). There is only one 
deepwater connection (260-270 m) between the Gulf 
of Maine and the North Atlantic. This narrow con- 
nection, the Northeast Channel, extends between 
Brown’s Bank (BB), where the majority of the OGM 
samples were collected, and a shallow ridge that ex- 
tends northeast from George’s Bank (GB). Oceano- 
graphically the Gulf of Maine resembles a landlocked 
sea, like the Mediterranean, rather than a contigu- 
ous portion of the North Atlantic. For example, the 
salinity, temperature, tides, and current dynamics 
of the Gulf of Maine are distinct from those of the 
North Atlantic. This combination of factors could iso- 
late hagfish populations within the Gulf of Maine 
from those elsewhere in the western North Atlantic. 
The distinct characteristics of the Gulf of Maine en- 
vironment may also be linked to physiological differ- 
ences between M. glutinosa in the Gulf of Maine ver- 
sus the eastern North Atlantic. For example, M. 
glutinosa in the eastern North Atlantic have been 
maintained at water temperatures as high as 15°C 
(Palmgren, 1927; Gustafson, 1935), whereas speci- 
mens at the Shoals Marine Laboratory (Gulf of 
Maine) quickly become moribund as temperatures 
approach 10°C (Martini, personal obs.). 
The size difference between the IGM and other 
sampled populations could be a function of age, with 
members of the IGM population having longer 
lifespans. However, this is impossible to evaluate 
without growth rate or longevity data — which does 
not presently exist for this or any other species of 
hagfish. Alternatively, the large total size and large 
size at maturity for hagfish within the Gulf of Maine 
may reflect the relative availability of food. It is in- 
teresting to note that Kendall described winter floun- 
der (Pleuronectes americanus [formerly Pseudo- 
pleuronectes americanus ] ) of the George’s Bank re- 
gion as a separate species from those found elsewhere 
in the western North Atlantic, on the basis of its 
unusually large size; this proposal was ultimately 
rejected because there were no other morphological 
differences. It is not clear, however, that the ecosys- 
tem in the inner Gulf of Maine is significantly more 
productive than that of the Skaggerack in the east- 
ern North Atlantic; both areas support substantial 
commercial fisheries. 
Wisner and McMillan (1995) proposed species sepa- 
ration based on maximum size, size at maturity, and 
differences in the color of preserved specimens. As 
indicated above, the large maximum size and large 
size at maturity appear to be characteristic of the 
IGM population only, rather than a general charac- 
teristic of WNA populations of Myxine. We remain 
unable to evaluate the significance of the color dif- 
ferences in preserved specimens noted by Wisner and 
McMillan (1995) for eastern versus western North 
