318 
Fishery Bulletin 116(3-4) 
+ + 
▲ 
A A + 
tt A A 
+ + - 
+ + 
+ + + 
▲ A 
+ 
+ ♦ 
B 
w O 
▼ 5 
o o ° 
▼ o 8 
cjf v o § ▼ ° T C 
o ▼ 
O o 
oo 
Figure S 
Nonmetric multidimensional scaling plots comparing distributions of 
(A) size classes II (A) and III ( + ) and (B) oceanic (▼) and coastal (O) 
fishing grounds for blue sharks (Prionace glauca) collected off northern 
Peru between February and December 2015. Size class II represents 
fish 150.0-229.9 cm in total length (TL), and size class III represents 
fish 230.0-309.9 cm TL. The coastal and oceanic fishing grounds were 
categorized by using the Peru-Chile Trench (with an average distance 
from shore of 130 km or 70 nautical miles) as the boundary. The stress 
level of this plot is 0.06. 
(IMARPE 4 ) and as a component of the diet of dol- 
phinfish (Coryphaena hippurus ) (Solano et al., 2015). 
However, recent investigations have begun to assess 
basic aspects of its ecology. Orosco-Montenegro (2016) 
reported that the abundance of larvae of Argonauta 
spp. is higher during the summer (318 individuals/m 2 ) 
than during the fall (9 individuals/m 2 ) along the Peru- 
4 IMARPE (Institute del Mar del Peru). 2015. Crucero 
1502-04 de “Evaluacion hidroacustica de los recursos pelagi- 
cos.” Inst. Mar Peru, Inf. Ejec., 42 p. [Available from web¬ 
site] 
vian coast, while Sajinez et al. (2016) 
mentioned that Argonauta spp. abun¬ 
dance is highly related to SST, with 
increased abundance during positive 
anomalies. During the sampling year, an 
SST positive anomaly of 1.7°C (SD 1.2) 
(DHM 5 ) was reported for the Nino 1+2 
region (in the eastern equatorial Pacific 
Ocean between 0-1 (rS and 90-80°W). 
Therefore, the elevated consumption of 
Argonauta spp. that we observed (16.1% 
PSIRI) may have been a response to 
higher abundances of this species during 
the SST positive anomaly if we consider 
the opportunistic foraging behavior of 
the blue shark upon abundant available 
prey (Stevens, 1973). The elevated con¬ 
sumption of Argonauta spp. is what most 
makes the blue shark a consumer with 
a high degree of specialization. However, 
further investigations are needed to fur¬ 
ther confirm this feeding pattern and to 
evaluate how this degree of specialization 
varies during La Nina periods. 
The consumption of flying fish eggs 
(in patches) recorded in this study may 
suggest, as Nakano and Seki (2003) pro¬ 
posed, the ingestion of prey (or objects) 
whose silhouettes are detected against 
light from the sea surface. However, the 
maximum number of individuals of cer¬ 
tain small-size species (e.g., Argonauta 
spp.=102, P. monodon- 34, Doryteuthis 
(Amerigo) gahi=25, Peruvian ancho- 
veta=24, Grimalditeuthis bonplandi=14) 
reported in different samples may also 
reflect a habit of foraging upon shoals of 
small-size species (Tricas, 1979). Further¬ 
more, Trieas (1979) indicated that blue 
sharks benefit from schools of spawning 
squid, such as those of the opalescent 
inshore squid ( Loligo opalescens). There¬ 
fore, Argonauta spp. could be prey of blue 
sharks within spawning areas of Argo¬ 
nauta spp. off northern Peru, as well, es¬ 
pecially considering that abundant fertil¬ 
ized and nonfertilized Argonautidae eggs 
were found in 21 stomachs. 
Scavenger behavior 
Blue sharks are considered active scavengers in the 
open ocean (Garibaldi and Orsi Relini, 2000). However, 
this behavior has only been discussed because of the 
discovery of cephalopod and marine mammal parts in 
stomachs of blue sharks (Markaida and Sosa-Nishiza- 
5 DHN (Direction deHidrografiayNavegaeiom). 2015. Anom- 
allas de la temperatura superficial del mar en el Pacific© ecu- 
atorial. Bol. Oceanogr., December 2015, 9 p. [Available from 
website] 
