85 
Effect of environmental conditions 
on the distribution of Pacific mackerel 
(Scomber japonicus) larvae 
in the California Current system 
Email address for contact author: ed.weber@noaa.gov 
Fisheries Resources Division 
Southwest Fisheries Science Center 
National Marine Fisheries Service 
National Oceanic and Atmospheric Administration 
8604 La Jolla Shores Drive 
La Jolla, California 92107 
Abstract — We modeled the prob- 
ability of capturing Pacific mack- 
erel (Scomber japonicus) larvae as a 
function of environmental variables 
for the Southern California Bight 
(SCB) most years from 1951 through 
2008 and Mexican waters offshore of 
Baja California from 1951 through 
1984. The model exhibited acceptable 
fit, as indicated by the area under 
a receiver-operating-characteristic 
curve of 0.80 but was inconsistent 
with the zero catches that occurred 
frequently in the 2000s. Two types 
of spawners overlapped spatially 
within the survey area: those that 
exhibited peak spawning during 
April in the SCB at about 15.5°C 
and a smaller group that exhibited 
peak spawning in August near Punta 
Eugenia, Mexico, at 20°C or greater. 
The SCB generally had greater zoo- 
plankton than Mexican waters but 
less appropriate (lower) geostrophic 
flows. Mexican waters generally 
exhibited greater predicted habitat 
quality than the SCB in cold years. 
Predicted quality of the habitat in the 
SCB was greater from the 1980s to 
2008 than in the earlier years of the 
survey primarily because tempera- 
tures and geostrophic flows were more 
appropriate for larvae. However, stock 
size the previous year had a larger 
effect on predictions than any envi- 
ronmental variable, indicating that 
larval Pacific mackerel did not fully 
occupy the suitable habitat during 
most years. 
Manuscript submitted 2 June 2011. 
Manuscript accepted 13 October 2011. 
Fish. Bull. 110:85-97 (2012). 
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. 
Edward D. Weber (contact author) 
Sam McCIatchie 
The Pacific mackerel (Scomber japoni- 
cus) is a coastal pelagic species that 
ranges from southeastern Alaska to 
Banderas Bay, Mexico (Fig. 1) in the 
northeastern Pacific (MBC Applied 
Environmental Sciences 1 ). It is man- 
aged by the Pacific Fishery Manage- 
ment Council in U.S. waters and fished 
commercially in the U.S. and Mexico 
primarily by purse-seine vessels that 
also harvest anchovy ( Engraulis 
mordax ), jack mackerel ( Trachurus 
symmetricus), market squid ( Loligo 
opalescens), and sardine ( Sardinops 
sagax). There is also a charter-boat 
sport fishery based primarily in south- 
ern California (Crone et ah, 2009). 
Like most coastal pelagic spe- 
cies, the Pacific mackerel fluctuates 
greatly in abundance through time 
(Soutar and Isaacs, 1974). These 
fluctuations are partly correlated 
with environmental conditions, such 
as temperature and upwelling rates 
(e.g., Parrish and MacCall, 1978). 
When Pacific mackerel populations 
are large, they form an important tro- 
phic link between small prey items 
(zooplankton and smaller fish) and 
larger avian, mammalian, and pi- 
scine predators (Castro Hernandez 
and Santana Ortega, 2000). There- 
1 MBC Applied Environmental Sci- 
ences. 1987. Ecology of important 
fisheries species offshore California. OCS 
Report MMS 86-0093, 290 p. U.S. Dept. 
Int. Min. Manage. Serv., Pacific Region, 
Los Angeles, CA. 
fore, understanding environmental 
variables that affect Pacific mackerel 
distribution and abundance may help 
managers to better evaluate both the 
fishery and ecosystem conditions in 
the California Current system. 
Three distinct stocks are believed 
to exist in the northeast Pacific 
Ocean: one in the Gulf of California, 
one near Cabo San Lucas at the tip 
of Baja California (22.9°N; Fig. 1), 
and one that ranges from Alaska to 
Cabo San Lucas. The northernmost 
stock is most common from Monterey 
Bay, California (36.9°N), to Punta 
Abreojos, Baja California (26.7°N; 
Roedel, 1952). These stocks were de- 
lineated on the basis of differences 
in vertebral meristics and physical 
features however, great heterogene- 
ity in migratory behavior and physi- 
cal features also exists within pur- 
ported stocks (Roedel, 1952). Pacific 
mackerel are very mobile. Marked 
Pacific mackerel that were initially 
captured in the southern California 
Bight (SCB) have been recaptured as 
far north as Tillamook Head, Oregon 
(45.9°N), and as far south as Mag- 
dalena Bay, Baja California (24.6°N; 
Fry and Roedel, 1949). They gener- 
ally migrate from south to north in 
summer and reverse the migration in 
winter. Pacific mackerel tend to move 
from inshore during the spawning 
season, March to May, to offshore as 
far as 400 km during the remainder 
of the year (MBC Applied Environ- 
mental Sciences 1 ). 
