Allen and Franklin: Settlement patterns of Atractosaon nobihs in the Southern California Bight 



635 



balanced design, three-way ANOVA was used to test 

 the effects on catch-per-unit-effort (CPUE) of combina- 

 tions of independent variables (station, month, and 

 depth). In 1989, a similar three-way ANOVA design 

 was used to test the effects of distance block (distance 

 from the mainland), month, and depth on CPUE. 

 CPUE was used in all parametric analyses in order to 

 minimize any negative impact that the large number 

 of zero-catch tows would have on the analysis. Since 

 replicates had to be combined, the three-way-inter- 

 action mean square was utilized as a conservative 

 estimate of sampling error for the 1988 ANOVA test. 

 In 1989, the ANOVA design was unbalanced due to two 

 missing stations in May at Santa Rosa Island. In this 

 case, cell means estimation was utilized to overcome 

 the imbalance. Since the three-way-interaction term 

 was originally found to be significant in the 1989 

 analysis, its mean square was pooled with the within- 

 sample error in order to partition out the effect of the 

 interaction on the main effects of distance block, 

 month, and depth individually. Correlations and canon- 

 ical correlation analysis were utilized to examine the 

 possible association of various environmental factors 

 with settlement of YOY white seabass. 



Results 



Length-frequencies 



The YOY white seabass captured during the 1988 sur- 

 vey ranged from 4.2 to 78mmSL (.r9.8mmSL). In 

 1989, the range was 4.5-51. 7mmSL (x 12.1mmSL). 

 Most YOY, however, ranged from 5 to 20mmSL (Fig. 

 2). Newly settled fish (<10mmSL) were caught from 



June through September. Individuals >20mmSL were 

 more common from July through October. 



Newly settled fish (< lOmmSL) made up 75% of all 

 YOY seabass in 1988 and 1989. Fish <20mmSL com- 

 prised 93% of the total catch. The paucity of larger 

 YOY in the samples (Fig. 2) from July to September 

 indicates that our beam-trawl catch may be biased 

 toward smaller, less-mobile fish. 



Studies utilizing the daily growth rings on white 

 seabass otoliths (Franklin and Allen, unpubl. data) in- 

 dicate that fish of 5-20 mm SL are ~37-104 days old. 

 Since settlement occurred consistently at ~5mmSL, 

 white seabass in this range settled at 0-68 days before 

 capture. The majority of those < 10 mm SL had settled 

 14-21 days before capture. 



Abundance and distribution 



Summer 1 988 Sampling along the mainland yielded 

 270 YOY white seabass. Most (58%) were captured at 

 five of the 16 stations: Stn. 2 (Refugio Beach, n 38), 

 Stn. 6 (Ventura, n 28), Stn. 10 (Malibu, n 30), Stn. 13 

 (Belmont Shore, n 31), and Stn 15 (Laguna Beach, 

 n 31) (Fig. 3). Mean catches (CPUE) were highest at 

 these five stations; furthermore, the variance of these 

 five means was also very high. This was especially true 

 at Stn. 2 (Refugio Beach) where 36 of the 38 YOY cap- 

 tured were taken during a single month (July). 



The CPUE for all stations was low in June 1988 (0.15 

 individuals/tow), peaked in July (1.10/tow), and de- 

 clined to 0.08/tow in October (Fig. 4). Catches in July 

 accounted for 52% (141 individuals) of YOY white 

 seabass taken in 1988. In June, catch was low (19 in- 

 dividuals) and white seabass were collected only from 

 southern stations (12, 13, and 15) (Fig. 5). By July, 



150 

 125 

 100 



S 75 



P 



bteiiiijfe^ 



".'^ , — "^ 



10 20 30 40 50 60 70 



LENGTH (2mmSL increments) 



80 



Figure 2 



Length-frequencies of YOY white seabass /I. nobilis from all 

 samples combined, 1988-89. Length increments are 2 mm 

 (n 3.54). 



2.0 



1.8 



1.6 



5^1.4 



+ 1.2 



^ 1.0 



zO.8 



I 0.6 



0.4 



0.2 



0.0 





3 4 5 6 7 H y 1 u 11 U' I :_! 1 4 1 5 1 

 STATION 



Figure 3 



CPLIE of YOY' white seabass A. nobilis by station, summer 

 1988. Bars represent 2SE of the mean. 



