FINUCANE ET AL.: REPRODUCTIVE BIOLOGY OF KING MACKEREL 



Fecundity estimates were based on the number 

 of yolked eggs ^0.20 mm in diameter in the most 

 mature ovaries. Similar methods were discussed by 

 Hunter and Goldberg (1980) and used by Morse 

 (1980). A diameter of 0.20 mm was used to separate 

 immature and mature eggs, because it was at this 

 size that yolk first appeared. A gravimetric method 

 was used for fecundity and followed the procedures 

 of Finucane and Collins (1984). Ages of fish were 

 determined from otoliths (Johnson et al. 1983). 

 Analysis of covariance was used to test for differ- 

 ences in fecundity by year and area. Regression and 

 correlation were used to examine the linear and 

 curvilinear relationships between fecundity and fork 

 length, total weight, and age. 



RESULTS 



Gonads from 1,165 female and 593 male king 

 mackerel were examined. Fish ranged in FL from 

 351 to 1,554 mm, in TW from 658 to 31,780 g, and 

 in age from 1 to 13 yr. Temporal coverage varied 

 from 3 mo in area I to 12 mo in area II. Number 

 and percentage composition of fish by area were 

 area I, 85 and 4.8%; area II, 646 and 36.7%; 

 area III, 768 and 43.7%; and area IV, 259 and 

 14.7%. 



Analysis of the egg size distribution indicated that 

 there were significant differences (a = 0.05) in ED 

 between the inner, middle, and outer zones within 

 ovarian sections; there were no differences between 

 sections. Therefore, we took a wedge-shaped sam- 

 ple (representing the three cross-sectional zones) 

 from the middle of the right or left ovary as repre- 

 sentative of the entire ovary for ED analysis. King 

 mackerel ovaries were grouped into five reproduc- 

 tive stages based on ED. Stage I (immature ovaries) 

 contained eggs <0.06 mm. Eggs in stage II (resting 

 ovaries) ranged from 0.07 to 0.20 mm. Stage III 

 (maturing) and stage IV (mature) ovaries contained 

 eggs 0.21-0.50 mm and 0.51-0.71 mm, respective- 

 ly. Stage V eggs measured 0.71-1.20 mm and in- 

 dicated ripe ovaries. 



The seasonal progression of mean GSIs and EDs 

 indicated that king mackerel have a prolonged 

 spawning season that varied between areas (Figs. 

 2-5). Peak spawning months occurred from May 

 through September as observed in 14 ripe females 

 from areas I, II, and IV. A few fish were in spawn- 

 ing condition as early as April and as late as Octo- 

 ber. In area I, GSIs and EDs peaked in July and 

 August for both sexes. Area II fish had the highest 

 GSIs and EDs for both sexes during May. In area 

 III, GSIs for both sexes were greatest during June 



O 1 



O 2 



fir t 



VI 



-im- 



MALES 



NO. FISH 



2 23 36 



IX 



0.50 



0.40 



0.30 



0.20 



0.10 

 



FEMALES 



NO. FISH 3 11 12 



J J A 

 MONTHS 



Figure 2.— Seasonal maturation cycle of male and female king 

 mackerel from area I (Texas) shown by monthly gonadosomatic 

 index (GSI) and mean egg diameters (EDs) in mm. 



while EDs peaked in August. Area IV fish had the 

 highest female GSIs and EDs during July. 



Serial spawning was suggested by several lines 

 of evidence. Distribution of EDs was multimodal 

 during spawning months. The highest coefficient of 

 variation for GSIs occurred during the spawning 

 months, suggesting that eggs were maturing and 

 released serially throughout the spawning season 

 (Table 1). 



The size at maturation of king mackerel also 

 varied between areas. Maturity was based on the 

 number and percentage of fish with stage Ill-stage 

 V ova for each 50 mm FL interval. Length inter- 

 vals in which at least 50% of the females were 

 mature for areas I-IV, respectively, were 450-499 

 mm, 600-649 mm, 600-649 mm, and 650-699 mm 



843 



