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Fishery Bulletin 96(4), 1998 
beromorus munroi ) — from tagging, catch data, and 
ageing and reproductive patterns (Begg et al., 1997; 
Begg and Sellin, 1998; Begg, in press). 
School and spotted mackerel co-occur in coastal 
waters of northern Australia and southern Papua 
New Guinea (Collette and Russo, 1984). Within Aus- 
tralian waters they are a major part of set gillnet 
and ring-net commercial fisheries and support popu- 
lar recreational fisheries, especially in the region 
from Moreton Bay to Townsville (Fig. 1). Between 
1992 and 1995 the Queensland commercial catch 
averaged 160 metric tons, and the recreational land- 
ings were estimated to be at least half as large as 
their commercial counterparts (Cameron and Begg 1 ). 
Tag-recapture data indicate that school mackerel 
move small distances, in contrast to spotted mack- 
erel that migrate annually along the Australian east 
coast (Begg et al., 1997). Both species reach 100 cm 
in fork length (LCF, tip of snout to fork of tail) and 8 
1 Cameron, D. S., and G. A. Begg. 1998. Fisheries biology and 
interaction in the northern Australian small mackerel fishery. 
Fisheries Research and Development Corporation 92/144. Un- 
published manuscript. 
Figure 1 
Sampling locations for school and spotted mackerel. 
kg in weight (Collette and Russo, 1984), and first 
maturity occurs within 2 years of age, between 35 
and 50 cm LCF (Begg, in press). Along the Queensland 
east coast, school mackerel spawn between October and 
January, whereas spotted mackerel spawn from Au- 
gust to October in northern Queensland waters (Begg, 
in press). A number of separate school mackerel stocks 
are thought to exist along the Queensland east coast, 
whereas spotted mackerel may form a single stock 
(Beggetai, 1997; Begg and Sellin, 1998; Begg, in press). 
The lack of a direct and widely applicable tech- 
nique to trace larval dispersal has encouraged de- 
velopment of a wide range of methods to deduce stock 
structure (Thresher et al., 1994) including analysis 
of the elemental composition of otoliths (Mulligan et 
al., 1987; Campana et al., 1994; Thresher et al., 1994; 
Edmonds et al., 1995; Proctor et al., 1995; Kalish et 
al., 1996). Inference about stock structure from these 
studies presumes that geographically distinct stocks 
possess a characteristic elemental composition that 
reflects the chemical constituents of the environment 
in which the fish reside. 
The elemental composition of otoliths has been 
measured by analysis of dissolved whole otoliths and 
by scanning otolith cores or sections with a variety 
of different electron beam and laser probes (Gunn et 
al., 1992; Campana et al., 1994). Solution-based or 
“bulk” chemical analyses of otoliths have the ben- 
efits of greater replication in sample sizes through 
reduced time and cost for preparation, calibration, 
and measurement (Campana and Gagne, 1995; 
Campana et al., 1995). However, bulk analysis of 
whole otoliths incorporate an integrated chemical 
signal that represents the entire ontogenetic history 
and home range of individual fish in a nonlinear form 
that is governed by the growth of the otolith matrix 
in terms of both rate of deposition and volumetric 
considerations. Consequently, the mean composition 
of an otolith in a bulk analysis could be dispropor- 
tionately dominated by the deposition of material 
prior to capture, preventing fine-scale resolution of 
individual affinities with spawning grounds and lar- 
val habitats (Campana et al., 1995). 
The present study was conducted to determine the 
utility of elemental analysis of whole otoliths in 
studying the prevailing hypotheses of a multistock 
complex for school mackerel and a single stock for 
spotted mackerel in coastal waters of eastern Aus- 
tralia. Analyses were specifically structured to ac- 
count for and distinguish the influence of fish age on 
elemental composition of otoliths. Interpretation of 
stock structure in this study relates to Ihssen et al.’s 
(1981) definition of a stock as “a group of randomly 
mating, reproductively isolated individuals of a single 
species with temporal or spatial integrity.” 
