Bowers: Reproductive cycle of oocytes and embryos of Sebastes flavidus 



241 



clutch of yolked oocytes during embryonic gestation, 

 distinguishes single from multiple spawners. 



There were approximately 30-40 days between the 

 appearance of fertilized ova and well-developed larvae 

 or recently-spawned females. Therefore, gestation ap- 

 pears to be 30-40 days in S. flavidus. Moser (1967b) 

 estimated 1-2 months gestation for the multiple- 

 spawner S. paucispinus, and Boehlert and Yoklavich 

 (1984) noted 37 days for S. melanops, a single-season 

 spawner. Similarly, Mizue (1959) compared a multiple- 

 spawner, S. marmoratus to a single-season spawner, 

 S. inermis. His data suggest approximately 30-45 days 

 for embryonic gestation in both species. 



While the basic reproductive pattern among the 

 various Sebastes species is similar, variations exist in 

 reproductive strategy and life history (Boehlert and 

 Yoklavich 1984). Temporal variations in reproductive 

 seasonality of rockfishes are perhaps the most obvious 

 and, therefore, well documented. Releasing larvae over 

 an extended period of time increases the probability 

 that a portion of the reproductive population would en- 

 counter favorable environmental conditions for the sur- 

 vival of the progeny. Wyllie Echeverria (1987) listed 

 the peak parturition months for 34 species of Sebastes 

 and reported that larval extrusion occurs for up to 9 

 months in some species. In her study, from samples 

 collected over a 7-year period, the principal month of 

 parturition for yellowtail rockfish was February. In the 

 present study, and in more recent work (unpubl. data), 

 March was the peak month of parturition; however, the 

 samples were from a smaller geographical area. PhOlips 

 (1964), who sampled northern, central, and southern 

 California rockfish populations, determined S. flavidus 

 to be a "winter" spawner (November-March). Wyllie 

 Echeverria (1987) reported parturition for yellowtail 

 rockfish from north-central California to occur from 

 January to July. In the present study, a shorter par- 

 turition time was observed for the Cordell Bank 

 yellowtail population (January-March). This temporal 

 variance may reflect a clinal reproductive variation in 

 yellowtail rockfish populations. Care must be taken, 

 however, when interpreting and comparing results 

 where macroscopic characteristics are used. While field 

 assessments by microscopic staging of whole oocytes 

 or macroscopic examinations are less time-consuming, 

 validation by histological methods is required for 

 precise and detailed information (West 1990). Further- 

 more, studies on the impact of atresia and postovu- 

 latory follicles are relevant to understanding functional 

 relationships between yellowtail rockfish reproduction 

 and their environment. West (1990) suggests histology 

 as the appropriate method of use for these types of 

 studies. 



A prolonged reproductive season is characteristic of 

 the genus Sebastes, but the factors regulating such a 



mechanism are not clear. While temperature and 

 photoperiod appear to effect later spawning in higher- 

 latitude populations (Wooton 1984), inherent factors 

 may also play a key role in the prolonged seasonality 

 displayed by rockfishes. There is some evidence that 

 age, at least in yellowtail rockfish, may account for 

 some variation in parturition time within a season (M.J. 

 Bowers, unpubl. data; Eldridge et al. 1991). In addi- 

 tion, Boehlert and Yoklavich (1984) estimated 5 days 

 between hatching and birth in S. melanops, while par- 

 turition has been reported to occur immediately after 

 hatching in the ovary in the subgenus Sebasticus (Tsu- 

 kahara 1962). In this study, it could not be determined 

 if hatched larvae remained in the ovaries of yellowtail 

 rockfish. Further investigations are necessary to deter- 

 mine the occurrence, significance, and regulatory 

 mechansims of larval retention. 



Rockfish are an important economic resource to the 

 Washington, Oregon, and California fisheries. Esti- 

 mates of total commercial rockfish landings in 1985 

 were 37,806 mt (PFMC 1990). In the same year, recrea- 

 tional anglers landed approximately 4000 mt of rock- 

 fish in California alone. Yellowtail, blue, and black 

 rockfishes represented 30% of the recreational landings 

 (Lenarz 1986). Fluctuations in year-class strength 

 cause the fishery to be somewhat unpredictable (Lenarz 

 1986), leaving it difficult for optimal management 

 strategies to protect stock depletion and establish 

 harvest guidelines. The earlier one can predict recruit- 

 ment success, the more precise management decisions 

 are likely to be. Leaman (1988) discussed the value of 

 directing management models toward biological prin- 

 ciples. Responses of yellowtail rockfish ovaries to 

 environmental fluctuations are early indicators of 

 reproductive performance. This study documents the 

 process of oocyte development in yellowtail rockfish 

 and provides a basis for interannual comparisons. 



Acknowledgments 



To Richard Powers, owner and operator of the New 

 Sea Angler, my sincerest appreciation for his skill and 

 assistance collecting samples. My greatest debt in con- 

 nection with this work is to Dr. Bruce MacFarlane 

 whose tireless enthusiasm, assistance, and patience are 

 beyond mortal explanation. 



Citations 



Boehlert, G.W., and M. Yoklavich 



1984 Reproduction, embryonic energetics, and the maternal- 

 fetal relationships in the viviparous genus Sebastes (Pisces: Scor- 

 paenidae). Biol, Bull. (Woods Hole) 167:354-370. 



