272 
Fishery Bulletin 99(2) 
1000-1425 m 
%W 
POL 
OTH 
Figur e 4 
Percentage by weight (%W) and by number (%N) of prey species in the diet of individuals 
at 1000-1425 m depth. CoC = Copepoda Calanoida; BoA = Boreomysis arctica\ Bor = Boreo- 
mysis sp.; Mys = Mysidacea unidentified.; MYS = total Mysidacea; Amp = Amphipoda Gam- 
maridea unidentified.; AMG =- total Amphipoda Gammaridea; Rha = Rhachotropis sp.; Dec = 
Decapoda unidentified.; POL = Polychaeta; OTH = Others. 
danha ( 1988) reported that Bathypterois chibius consumes 
some amphipods and mysids in addition to calanoid cope- 
pods, a finding similar to our data for Bathypterois medi- 
terraneus. In the western North Atlantic (Crabtree et ah, 
1991) and eastern North Atlantic (Marshall and Merret, 
1977; Merret, 1987) Bathypterois longipes primarily feed 
on copepods, amphipods, and decapods, but the difference 
is the greater importance of the benthic prey for Bathyp- 
terois mediterraneus, especially at depths between 1800 
and 2250 m. 
In the Atlantic, Bathypterois dubius is restricted to 
depths of less than 2000 m (Sulak, 1984a); Bathypterois 
longipes inhabits depths below 2000 m. Sulak (1977) con- 
sidered the bathymetric and geographic distribution of 
these species to be a consequence of competitive interspe- 
cific exclusion, and this is supported by the results of Mar- 
shall and Merrett (1977). Bathypterois mediterraneus is 
the only abundant Mediterranean species of Bathypter- 
ois, with a lower bathymetric limit of 2800 m (Bauchot, 
1987). In the Catalan Sea, it ranges down to the maxi- 
mum depth of 2250 m and exclusively exploits a trophic 
niche unoccupied by any other species. This strategy en- 
ables Bathyptei'ois mediterraneus to be the dominant spe- 
cies below 1425 m, where resources are more limited. 
The relatively higher metabolism as a result of small 
size in Bathypterois mediterraneus , like other Bathypter- 
ois (Heezen and Hollister, 1971; Saldanha, 1977), is com- 
pensated by reduced mobility and coupled with a micro- 
phagous filtering diet based on organisms distributed 
more uniformly in space, such as calanoid copepods. This 
trophic strategy makes Bathypterois mediterraneus espe- 
cially fit for a nutrient-limited environment, such as the 
Mediterranean, particularly at greater depths (Carpine, 
1970; Tluel, 1983; Peres, 1985). 
Bathypterois species are dominant on the middle and 
lower slope and in the abyssal depths ofoligotrophic regions 
or similar less productive water masses. Sulak (1984b) 
and Merrett (1987) have noted the major importance of 
Chlorophthalmidae in marine fauna of oligotrophic envi- 
ronments. In more productive water masses, species with 
energetically expensive life history patterns dominate the 
ichthyofauna. In the Mediterranean, changes in biomass 
are evident so that the larger and middle-size dominant 
species between 1000 and 1200 m ( Mora moro, Phycis blen- 
noides, Trachyrhynchus trachyrhynchus, and Alepoeepha- 
lus rostratus ) are progressively replaced at greater depth 
by other smaller species such as Bathypterois mediterra- 
neus, Coryphaenoides guentheri, and Chalinura mediterra- 
nea (Stefanescu et al., 1993). The relative importance of 
Bathypterois mediterraneus increases as depth increases 
(Stefanescu et al., 1993), parallel to an increasing scarcity 
of trophic resources (Cartes, 1991; Cartes and Sorbe, 1993). 
This species is the most abundant fish of the lower slope 
assemblage (Morales-Nin et al., 1996) and exemplifies a 
species adapted to a food scarce environment by energeti- 
cally conservative feeding strategies. 
Acknowledgments 
We thank all the members of the BATIMAR research pro- 
gram for their collaboration, especially J. Rucabado and D. 
Lloris. We are grateful to J. E. Cartes for his collaboration 
in identifying several species and for his comments. The 
BATIMAR project was financed by CSIC and CAICYT ( PAC 
86-008/ID 821). We also thanks the anonymous reviewers 
for their valuable comments on the manuscript. 
Literature cited 
Bauchot, M.-L. 
1962. Description d'un nouveau Bathypterois mediter- 
raneen (Poisson Clupeiforme Bathypteroidae). Affinites et 
