274 
NOAA 
National Marine 
Fisheries Service 
Abstract — We examined the stom- 
ach contents of 3 vertically migrat- 
ing myctophid fish species from the 
eastern tropical Pacific (ETP) Ocean 
and used a classification tree to ex- 
amine the influence of spatial, bio- 
logical, and oceanographic predictor 
variables on diet. Myctophum nitid- 
ulum (n=299), Symbolophorus rever- 
sus (n=199), and Gonichthys tenui- 
culus, (n=82) were collected with dip 
nets from surface waters, and prey 
taxa were quantified from bongo net 
tows from August through November 
2006. A classification tree produced 
splits with longitude and sea surface 
salinity (SSS), thereby separating 3 
geographically and oceanographi- 
cally distinct regions of the ETP 
(offshore, nearshore, and intermedi- 
ate), where diet was similar among 
the 3 species. Myctophids consumed, 
primarily, ostracods offshore (76.4% 
mean percentage by number [MAi,;]), 
euphausiids nearshore (45.0%), and 
copepods (66.6%) in the intermediate 
region. The offshore region was char- 
acterized by a greater abundance of 
ostracods in the zooplankton commu- 
nity (17.5% by number) and within 
a deep mixed-layer depth (MLD) 
(mean 52.6 m, max 93.0 m). SSS was 
low in the nearshore region (<32.9 
psu) and the MLD was shallow. The 
intermediate region represented a 
transition zone between the oceano- 
graphic condition of the offshore and 
nearshore regions. Our results indi- 
cate that these 3 myctophid species 
share a similar regional diet that is 
strongly influenced by longitude, os- 
tracod availability, SSS, and MLD. 
Manuscript submitted 13 May 2015. 
Manuscript accepted 6 April 2016. 
Fish. Bull. 114:274-287 (2016). 
Online publication date: 28 April 2016. 
doi: 10.7755/FB.114.3.2 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Fishery Builetin 
<%■ established 1881 
Spencer F. Baird 
First U.S. Commissioner 
of Fisheries and founder 
of Fishery Bulletin 
Oceanographic influences on the diet of 3 
surface^migrating myctophids in the eastern 
tropical Pacific Ocean 
Joel E. Van Noord (contact author)’''* 
Robert J. Olson^ 
Jessica V. Redfern^ 
Leanne M. Duffy^ 
Ronald S. Kaufmann’ 
Email address for contact author: ioel.vannoord@noaa.gov 
Present address: California Wetfish Producers Association 
P.O. Box 1951 
Buellton, California 93427 
' Marine Science and Environmental Studies Department 
University of San Diego 
5998 Alcala Park 
San Diego, California 92110 
^ Inter-American Tropical Tuna Commission 
8901 La Jolla Shores Drive 
La Jolla, California 92037 
3 Southwest Fisheries Science Center 
National Marine Fisheries Service, NOAA 
8901 La Jolla Shores Drive 
La Jolla, California 92037 
The Myctophidae (lanternfishes) 
comprise a family of fishes whose 
members are both extremely abun- 
dant and distributed throughout the 
world’s oceans (Gjosaeter and Kawa- 
guchi, 1980 ; Irigoien et al., 2014 ). 
Species making up this family of fish 
serve roles as both important preda- 
tors (Pakhomov et al., 1996) and prey 
(Naito et al., 2013); furthermore myc- 
tophids transfer energy from lower 
to higher trophic levels in food webs 
(Brodeur et al., 1999). Myctophids 
are also influential in the transfer of 
carbon to the deep sea because they 
feed in surface waters and return to 
the mesopelagic zone (Davison et al., 
2013). The family is speciose, with 
as many as 250 species in 33 gen- 
era (Catul et ah, 2011). In some in- 
stances, as many as 50 species can be 
found in close proximity, simultane- 
ously feeding on similar prey (Hop- 
kins and Gartner, 1992). 
Resource partitioning, broadly de- 
fined as differences in resource use 
among co-occurring species (Schoen- 
er, 1974), has been used to explain 
how diverse myctophid assemblages 
can co-occur without competitively 
excluding one another (Hopkins and 
Gartner, 1992). Myctophids have 
been shown to partition resources by 
size (myctophid size) (Shreeve et al., 
2009; Saunders et al., 2015), migra- 
tion depth, and prey type (Hopkins 
and Gartner, 1992; Pepin, 2013). 
Co-occurring myctophid species of 
similar size that are found in the 
same habitat either partition di- 
etary resources or feed opportunisti- 
cally on prey in the proportions that 
are available. For example, dietary 
resource partitioning has been de- 
