Mackie et al.: Variability in reproductive development of Spanish mackerel (Scomberomorus commerson) 



345 



stock assessments, is unavailable or insufficiently 

 described in the literature for this species. The ob- 

 jective of our study was, therefore, to provide a com- 

 prehensive description of the reproductive biology of 

 S. commerson in Western Australian waters. 



Material and methods 



Collection and processing of samples 



Scorn beromorus commerson were collected onboard 

 vessels operating from a number of locations along 

 the WA coast between 1998 and 2002 (Fig. 1). These 

 locations were pooled into three regions to reflect 

 differences in fishing methods within the mackerel 

 fishery (Kimberley — east of 120°E, Pilbara — north 

 of 23 C S to the Kimberley border, and West Coast — 

 south of 23°S; Fig. 1). Scomberomorus commerson 

 are seasonally abundant in coastal waters although 

 low numbers are caught in the Pilbara region during 

 the "off-season." Samples were therefore collected 

 throughout the year from this region only. 



Fresh S. commerson collected from commercial 

 and recreational fishermen were measured (total 

 length |TL] and fork length |FL] in mm) and, where 

 possible, weighed to 0.1 kg (whole weight |WW] and 

 clean weight (viscera and gonads removed]). Heads 

 were removed and measured from tip of the mouth 

 to firm edge of the operculum (mm), and weighed 

 with gills intact (±0.1 gm). Gonads were removed 

 from the fish within hours of capture, macroscopi- 

 cally staged (see below), weighed where possible (±0.01 

 g), and preserved in 10% formalin and seawater solution. 

 Frozen head and viscera obtained from commercial and 

 recreational fishermen were also measured and weighed 

 as above. The thawed gonads were macroscopically staged 

 by using a simplified staging system (see below) that is 

 used in less detailed reproductive analyses. 



Preserved gonads were blotted dry with a paper towel 

 and weighed. A 4-mm slice from the mid-region was 

 processed by using standard histological techniques 

 and stained with Harris's haematoxylin and eosin for 

 microscopic examination. Full details of methods used 

 in the collection and analysis of S. commerson gonads 

 are provided in Mackie and Lewis. 2 



Biological analyses 



Gonads were staged macroscopically and microscopi- 

 cally. Macroscopic staging employed five developmental 

 steps that were compatible with the microscopic staging 

 system (Mackie and Lewis 2 ): 



Pilbara 



Kimberley 



>y 



'A Broome 



Port Hedland 



WESTERN 

 AUSTRALIA 



West 

 Coast 



•Geraldton 



NORTHERN 

 TERRITORY 



Figure 1 



Sampling locations used in the study of the narrow-barred Spanish 

 mackerel {Scomberomorus commerson) reproductive biology. 



undifferentiated. 



immature ("virgin 

 mature, resting; 

 reproductively developed; 

 spawning ("running, ripe 

 studies). 



in other studies); 



in other 



- Mackie, M. C, and P. D. Lewis. 2001. Assessment of gonad 

 staging systems and other methods used in the study of the 

 reproductive biology of narrow-barred Spanish mackerel, 

 Scomberomorus commerson, in Western Australia. Fisheries 

 Research Report 136, 25 p. Department of Fisheries, Perth, 

 Western Australia 6020, Australia, http://www.fish.wa.gov. 

 au/res/broc/frr/frrl36/index.html. [Accessed January 15 2002.] 



immature ("virgin" in other studies); 

 mature resting; 

 reproductively developed, ripe; 

 spawning ("running, ripe" in other 

 studies). 



The microscopic staging system had more stages and 

 allowed a more detailed description of spawning: 



Juvenile (J) undifferentiated. 

 Females 



stage 1 immature ("virgin" in other studies); 



stage la immature, developing; 



stage 2 mature, resting; 



stage 3 mature, developing; 



stage 4 reproductively developed; 



stage 5a prespawning; 



stage 5b spawning ("running, ripe" in other 

 studies); 



stage 5c postspawning; 



stage 6 spent. 



