366 
Fishery Bulletin 95(2), 1997 
Table 3 
Mean and standard deviation (SD) caloric values, water content, and ash content of prey in the diet of striped marlin. 
Kcal/g Kcal/g Kcal/g 
Prey % Water SD % Ash SD wet wt SD dry wt SD ash-free dry wt SD 
Cephalopoda 
Dosidicus gigas 
70.02 
0.97 
2.95 
0.04 
Crustacea 
Pleuroncodes planipes 
72.66 
0.05 
4.67 
0.03 
Osteichthyes 
Etrumeus teres 
64.34 
1.10 
3.78 
0.04 
Sardinops caeruleus 
65.92 
0.38 
2.71 
0.01 
Merluccius productus 
68.92 
1.01 
5.60 
0.01 
Fistularia spp. 
64.44 
0.72 
13.05 
0.07 
Decapterus hypodus 
64.95 
0.34 
6.09 
0.03 
Selar crumenophthalmus 
68.64 
0.60 
7.00 
0.01 
Auxis spp. 
66.31 
0.83 
1.53 
0.03 
Scomber japonicus 
63.90 
0.10 
3.16 
0.03 
Batistes polylepis 
69.38 
0.54 
2.83 
0.15 
1.57 
0.08 
5.24 
1.20 
5.40 
0.13 
0.94 
0.01 
3.42 
0.11 
3.59 
0.01 
1.80 
0.05 
5.06 
0.03 
5.26 
0.01 
1.77 
0.02 
5.19 
0.09 
5.33 
0.01 
1.47 
0.06 
4.74 
0.57 
5.02 
0.06 
2.18 
0.04 
6.14 
0.11 
7.06 
0.01 
1.79 
0.01 
5.11 
0.12 
5.44 
0.01 
1.53 
0.03 
4.87 
0.02 
5.24 
0.00 
1.92 
0.05 
5.69 
0.28 
5.78 
0.03 
2.16 
0.01 
5.99 
0.01 
6.19 
0.00 
1.48 
0.02 
4.83 
0.14 
4.97 
0.01 
Mexico in the last two decades. Cabo San Lucas ap- 
pears to be an area with stable prey populations, 
probably the result of prevailing oceanographic con- 
ditions (Roden and Groves, 1959; Alvarez, 1983). 
In waters off Baja California, the thermocline is 
generally shallow and there is a correspondingly high 
standing crop of zooplankton (Brandhorst, 1958). 
Laevastu and Rosa (1963) suggested that the shal- 
low thermocline promotes a high standing crop of 
zooplankton and thus increases the production of 
small foraging organisms, which in turn may result 
in the aggregation of top predators. It is likely that 
the seasonal shifts in good fishing areas for striped 
marlin coincide with shallow thermocline areas. 
Feeding ecology, however, may play a major role in 
determining the distribution and abundance of 
striped marlin in some areas. 
Calorimetric analysis 
Of the eleven most important prey analyzed, P. 
planipes had a significantly low caloric content, com- 
mon in crustaceans (Golley, 1961; Slobodkin and 
Richman, 1961; Thayer et al., 1973). Paine (1964) 
concluded that the presence of calcium carbonate and 
calcium phosphate in cuticle and valves was the 
cause of their low caloric value. 
We found our results agree well with values from 
other studies. Thayer et al. (1973) found a caloric 
value of 5.74 kcal/g dry weight and 1.05 kcal/g wet 
weight for the squid Loligo brevis. For crustaceans, 
caloric values ranged between 2.12 and 6.03 kcal/g 
dry weight (average value: 5.74 kcal/g dry weight, 
range: 0.80-1.48 kcal/g wet weight). They also found 
fish contained 4.39 to 6.0 kcal/g dry weight and 0.67 
to 1.57 kcal/g wet weight. Cortes and Gruber (1990) 
estimated the energy content of prey of lemon shark, 
Negaprion brevirostris, and found caloric values of 
4.81 kcal/g dry weight and 0.68 kcal/g wet weight for 
cephalopods, Octopus spp. Crustaceans of the genus 
Callinectes yielded 3.2 kcal/g dry weight and 1.04 
kcal/g wet weight. For fish, Cortes and Gruber found 
values that ranged from 3.38 to 4.73 kcal/g dry weight 
and 0.96 to 1.86 kcal/g wet weight. 
Our results show that pelagic fishes and cephalo- 
pods yielded more than 80% of the caloric content in 
the diet of striped marlin. However, if we take into 
account that more than 70% of the stomachs were 
less than full and that the predatory capacity of 
striped marlin allows them to consume large quan- 
tities of prey in a short time, as is the case with yel- 
lowfin tuna, Thunnus albacares (Olson and Boggs, 
1986), a pelagic species with feeding habits similar 
to those of marlin in the eastern Pacific Ocean, we 
believe the estimated caloric values underestimated 
actual energy intake. 
In summary, we consider that striped marlin is a 
generalist as a predator and has a high predatory 
capacity, foraging mainly on schools of epipelagic 
organisms in neritic and oceanic zones. 
Acknowledgments 
We wish to thank Robert J. Olson of the Inter-Ameri- 
can Tropical Tuna Commission, David B. Holts of the 
