GUNDKRSON POPULATION BIOLOGY OV SKUAS I IS Ml II S 



in the WVI stock and age 7 in Queen Charlotte 

 Sound. 



FECUNDITY 



Methods Used in Fecundity Determination 

 Collection of Ovaries 



Previous fecundity work on Sebastes has indi- 

 cated that the time of ovary collection must be 

 carefully controlled. Lisovenko (1965) determined 

 fecundity for two groups of Pacific ocean perch in 

 the Gulf of Alaska, the first consisting of 61 fish 

 collected prior to fertilization and the second of 29 

 fish with fertilized ova. He found that the esti- 

 mated fecundity of the first group was 1.5-2.0 

 times higher than that of the second, considering 

 females of comparable size. Lisovenko attributed 

 this difference to eggs bursting when females were 

 hauled to the surface, but accidental extrusion of 

 the fertilized eggs could also have beem impli- 

 cated. Pacific ocean perch containing fertilized 

 eggs can be made to extrude these eggs by slight 

 pressure on the body cavity and make poor speci- 

 mens for determination of fecundity. 



If ovary samples are collected too far in advance 

 of fertilization, however, maturing oocytes that 

 will be fertilized in the fall are too small to be 

 differentiated from immature oocytes. The opti- 

 mal time to collect material for fecundity observa- 

 tions is therefore August-November, when imma- 

 ture and maturing oocytes can be differentiated, 

 but fertilization of ova has not yet occurred. 



Collection dates and times for fecundity samples 

 used in this study are shown below: 



Date Number 



(1973) Location collected 



22 Aug. Destruction Island, Wash. 14 



26 Aug. Tillamook Head, Oreg. 27 



19 Sept. S.E. Corner, Goose Island 40 



All fish from Queen Charlotte Sound were taken 

 from the landings of a commercial trawler, while 

 those from the southern region were collected 

 aboard the U.S.S.R. research trawler Seskar. The 

 cruise objectives of the Seskar were such that only 

 limited quantities of Pacific ocean perch were 

 caught off Washington, and collections made off 

 the Oregon coast were used to supplement those 

 from the WVI stock. 



Since between-area fecundity comparisons were 

 to be made, the attempt was made to collect 

 ovaries from Queen Charlotte Sound when the fish 

 were in the same stage of the reproductive cycle as 

 those off Washington and Oregon. Despite this, 

 gross examination of male gonads and data on 

 oocyte diameters (Gunderson 1976) indicated that 

 fish in the Queen Charlotte Sound collection were 

 not quite as advanced as those collected 1 mo ear- 

 lier off Washington and Oregon. 



All ovaries collected were placed in modified 

 Gilson's solution (Bagenal and Braum 1968) to 

 harden the eggs and separate them from sur- 

 rounding ovarian tissue. After about 1 mo, ovar- 

 ian tissue was removed from the eggs and the fluid 

 was changed. After the samples had been 

 in Gilson's solution for a total of 3 mo, they 

 were removed and stored permanently in 10 r r 

 ethyl alcohol. 



Differentiation of Mature and Immature Oocytes 



A series of ovaries was collected over the whole 

 range of the reproductive cycle so that the growth 

 progression of maturing oocytes could be followed. 

 All specimens were collected in the Washington- 

 Oregon region and their ovaries were placed in 

 Gilson's solution until- the oocytes separated from 

 ovarian tissue. Subsampling of the eggs in an 

 ovary was accomplished by the same technique 

 used to estimate fecundity (described below). 



The size frequency for the eggs in a specimen 

 was obtained by systematically measuring 

 (nearest 0.01 mm) those eggs lying on transect 

 lines drawn on a Petri dish, until a desired sample 

 size had been attained. Many of the eggs were 

 elliptical or irregularly shaped and, in these cases, 

 the longest axis parallel to the counting scale was 

 selected for measurement. One specimen was in 

 the "embryo or eyed larvae" stage of maturity and, 

 in this particular instance, all eggs with embryos 

 were measured along the longitudinal axis of the 

 embryo. 



The results (Figure 21 ) showed that there was a 

 significant overlap in the size of immature and 

 maturing oocytes during the period when fecun- 

 dity samples were collected. By October, the size of 

 maturing oocytes had increased substantially and 

 differentiation of maturing oocytes was 

 straightforward. Following fertilization of the 

 first brood, however, it appears that other groups 

 of oocytes begin to mature, so that several sizes of 

 eggs and embryos are present in ovaries that have 



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