48 
Fishery Bulletin 95(1 ), 1997 
Point and the Kei River. On the basis of grow rate, 
fish-length and otolith-dimension relationships, and 
the appearance of growth zones, he concluded that 
silver kob within this area comprise at least three 
separate stocks. 
The objective of the present study was to provide 
information on the life history of A. inodorus occur- 
ring between Cape Point and the Kei River, includ- 
ing reproductive seasonality, spawning grounds, size 
at maturity, juvenile and adult distribution, and 
migration. Because the identification of discrete 
stocks or “management units” is essential for effec- 
tive management (Pawson and Jennings, 1996), the 
multiple stock concept is further developed with in- 
formation on distribution and abundance, life his- 
tory parameters, and mark-recapture data. 
Materials and methods 
The study area (from Cape Point to Kei River) was 
divided into three regions for sampling purposes 
(Fig. 1). These regions were identical to those used 
by Griffiths (in press, a); they were not divided ac- 
cording to political boundaries but rather generated 
to increase analytical resolution. Biological (March 
1990-January 1992) and length-frequency (January 
1990-December 1994) data were collected in each 
region from fish caught 1) by the line fishery, 2) by 
the inshore trawl fishery, 3) by trawlers during South 
Coast Biomass Surveys conducted by the Sea Fish- 
eries Research Institute, and 4) by research 
linefishing operations. Biological data were also ob- 
tained from silver kob caught by beach seines in False 
Bay (Oct 1991). Trawled fish were generally caught 
over sand or mud substrata, and line-caught fish over 
reef. Owing to the high relief rocky nature of the in- 
shore habitat west of Cape Agulhas, this species is 
not trawled in the southwestern Cape. 
Fish sampled for biological purposes were mea- 
sured (to the nearest 1 mm [total length]), weighed 
(to the nearest gram [fish <500 g], the nearest 20 g 
[fish 500 g-5 kg], or the nearest 100 g [fish 5 kg-25 
kg]), cut open, and sexed. Gonads were removed, as- 
signed a visual index of maturity (see Table 1), and 
weighed to the nearest 0.1 g. Males were assigned 
an index of drumming muscle development ( l=none, 
2=partially developed, 3=fully developed). Owing to 
logistical constraints, monthly biological data were 
obtained only for the southeastern Cape; in the other 
two regions biological sampling was limited to the 
spawning season. 
Areas of silver kob abundance were delineated by 
using returns from the commercial line fishery and 
data from South Coast Biomass Surveys (SCBS’s). 
Line catches consisted predominantly of adult fish, 
whereas trawl catches from SCBS’s comprised mostly 
juveniles and young adults (see below). Annual catch- 
per-unit-of-effort data (catch per outing) were plot- 
ted on a subregional basis for the commercial line 
fishery (an outing did not exceed one day), and the 
data from 14 SCBS’s (Table 2) were used to calculate 
Figure 1 
Map of the three coastal regions where silver kob were sampled, and localities mentioned in the text. 
