NOTES 



COMPARISON OF VISCERAL FAT AND 



GONADAL FAT VOLUMES OF YELLOWTAIL 



ROCKFISH, SEBASTES FLAVIDUS, DURING 



A NORMAL YEAR AND A YEAR OF 



EL NINO CONDITIONS 



One of the severest El Nino events of the century 

 occurred off California during late 1982 and most 

 of 1983 (Rasmusson 1984). Associated with the 

 warm water and lack of upwelling were impressions 

 by many fishermen and biologists that macroplank- 

 tonic organisms were at low densities and that fish 

 were thinner than normal. A semiquantitative sam- 

 pling program off of San Francisco indicated that 

 euphausiids, a major component of the macroplank- 

 ton, were considerably less common in 1983 than 

 in either 1982 or 1984 (Smith 1 ). 



Yellowtail rockfish are abundant off northern 

 California and are an important component of 

 recreational and commercial catches in some areas. 

 The species feeds mostly on macroplanktonic 

 organisms such as euphausiids, salps, and small fish 

 (Phillips 1964; Pereyra et al. 1969; Lorz et al. 1983). 

 Annual cycles of visceral fat volume and gonad 

 volume are documented in Guillemot (1982) and 

 Guillemot et al. (1985). The studies showed that 

 visceral fat volume in both sexes of yellowtail rock- 

 fish is at a maximum during fall. The viviparous 

 species (Boehlert and Yoklavich 1984) mates in early 

 fall (September) and releases larvae during winter 

 (January-March) (Wyllie Echeverria 2 ). Guillemot 

 (1982) and Guillemot et al. (1985) showed that male 

 gonad volumes peak in fall and female gonad 

 volumes peak in winter. 



The purpose of this study is to determine possi- 

 ble effects of El Nino conditions by comparing 

 visceral fat and gonad volumes during 1983, a year 

 of El Nino conditions, with data collected during 

 1980, a normal year (Guillemot 1982). 



Methods and Materials 



Guillemot (1982) and Guillemot et al. (1985) util- 



ized data collected throughout the year. The 1983 

 data were collected only on 21 September, the ap- 

 proximate sexual activity peak for males, and 20 

 December, which slightly precedes the peak time of 

 larval release for females. Only 1980 data collected 

 within 20 d of the two 1983 collection dates and 

 samples collected from central California, between 

 Bodega Bay and Half Moon Bay, were used in this 

 study. In 1983 all specimens were collected from 

 landings made at Bodega Bay. 



Specimens were sexed, measured to the nearest 

 millimeter for total length, and viscera were re- 

 moved and preserved in 10% buffered Formalin 3 in 

 the field following the procedures of Guillemot et 

 al. (1985). After about 90 d of storage, visceral fat 

 and gonad volumes were measured to the nearest 

 milliliter by water displacement. Visceral fat of some 

 fish had dissolved to form a floating liquid. The 

 volume of this liquid was measured and added to the 

 total fat volume. Data from males larger than 379 

 mm, when 90% are mature, and from females larger 

 than 380 mm, when 85% are mature, were used 

 (Wyllie Echeverria fn. 2). 



As in Guillemot (1982) and Guillemot et al. (1985) 

 we used the following power equation to describe 

 the relationship between fat or gonad volume and 

 length: 



Y = aXP 



where Y = fat or gonad volume, and 

 X = total length. 



The parameters were estimated by first trans- 

 forming the variables to natural logarithms and then 

 using standard least squares linear regression 

 techniques. Analysis of covariance was used to 

 determine if separate lines for the two years 

 significantly reduced the variance from a common 

 line (Kleinbaum and Kupper 1978). This is a fairly 

 robust test in that if there is not a significant linear 

 relationship between the two variables for one or 

 both time periods, the test is nearly as powerful for 

 comparing the two means as an analysis of variance. 



'Smith, S. Unpublished data. Tiburon Laboratory, Southwest 

 Fisheries Center, National Marine Fisheries Service, NOAA, 3150 

 Paradise Drive, Tiburon, CA 94920. 



2 Wyllie Echeverria, T. 1983. Reproductive seasonality and 

 maturity of the rockfishes (Scorpaenidae; Sebastes) off central 

 California. Unpubl. manuscr., 66 p. Southwest Fisheries Center, 



Tiburon Laboratory, National Marine Fisheries Service, NOAA, 

 Tiburon, CA 94920. 



3 Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



FISHERY BULLETIN: VOL. 84, NO. 3, 1986. 



743 



