Chapman etal.: Reproductive condition of Acipenser transmontanus 



629 



cisco Bay estuary has the largest population of white 

 sturgeon in California. Adults spend most of their 

 life in the bay and migrate into the Sacramento River 

 in the late winter or early spring to spawn (Pycha, 

 1956; Stevens and Miller, 1970; Kohlhorst, 1976). 

 White sturgeon are believed to reach sexual matu- 

 rity at age 10 to 30 years, and iteroparous females 

 spawn at intervals of two or more years (Pycha, 1956; 

 Semakula and Larkin, 1968). 



We focused our initial studies on the collection of 

 wild broodstock for captive breeding in order to de- 

 velop artificially induced spawning techniques and 

 hatchery technology (Conte et al., 1988). Concomi- 

 tantly, we sampled white sturgeon in San Francisco 

 Bay in order to characterize the composition of the 

 population in relation to sex and gonadal maturity. 



Materials and methods 



White sturgeon were collected in the San Francisco 

 Bay estuary, California, from late October to Febru- 

 ary 1983-86. The fishing grounds included the area 

 between Golden Gate Bridge, Angel Island, and San 

 Francisco Bay Bridge. Miller (1972) observed that 

 sturgeon congregate in this area to feed and that fish 

 that were ripe migrated into the Sacramento River 

 later in the season to spawn. Sturgeon aggregated 

 while feeding on herring eggs and were seen fre- 

 quently jumping out of the water. These aggregations 

 of sturgeon were located with sonar. Fishing gear 

 consisted of a short ( 167-214 cm) stiff pole (rated for 

 28 kg) equipped with reel (4/0), heavy monofilament 

 line (18-28 kg strength), leader (45-55 kg strength), 

 treble hook (4/0 or 5/0), and heavy sinker (142-227 

 g). The line was weighted with a sinker at the end of 

 the leader, and the treble hook was attached approxi- 

 mately 30 cm above the sinker. 



Sturgeon were usually encountered at water 

 depths of 6 to 9 m and were snagged as they rubbed 

 the line or hooked when they took a bait of herring 

 fillet or eggs. Water temperatures and salinities dur- 

 ing collection periods were 9-15°C and 24-32 ppt, 

 respectively. Further details on fish-collection tech- 

 niques are described and illustrated by Cuanang ( 1984 ). 

 White sturgeon broodstock handling, sampling, and 

 care followed procedures of Conte et al. ( 1988). 



Sturgeon were examined for external structure and 

 size, including morphometric and meristic charac- 

 ters. Measurements included fork and total length 

 (±0.1 cm), head length (±0.1 cm), mouth width (in- 

 cluding the lips, ±0.1 cm), and body weight (±0.1 kg). 

 Meristic characters of the scutes in the dorsal, lat- 

 eral, and ventral rows were recorded according to 

 the methods of Vladykov and Greeley (1963). Pro- 



portional measurements (snout and head) were ex- 

 pressed as percentages of the head and fork length, 

 respectively. Sturgeon were alive when sampled, and 

 all fish, except for ripe broodstock, were released af- 

 ter capture. Samples of gonadal tissue and blood 

 plasma were collected for histological analysis, but 

 sections of fin rays were not collected for age deter- 

 minations in order to avoid excessive trauma. 



Sex and stages of sexual maturity in white stur- 

 geon were examined by using histological slides of 

 gonadal tissue and light microscopy (Chapman, 1989; 

 Doroshov et al., 1991). Gonadal samples were col- 

 lected from 300 females and 325 males. Ovarian 

 stages in females were assigned a numerical score 

 according to differentiation in the shape and size of 

 the ovarian follicle (according to oocyte cytoplasm 

 staining properties, nuclear and cytoplasmic inclu- 

 sions, presence or absence of yolk platelets, differen- 

 tiation of the vitelline envelope, and differentiation 

 in the granulosa cells and thecal follicular layers). A 

 numerical score was assigned to each male testis 

 according to the proportion of cysts with different 

 types of germ cells that were counted in several ran- 

 dom fields on the slide (spermatogonia, spermato- 

 cytes, spermatids, and spermatozoa). Based on his- 

 tological scores, the following classification was as- 

 signed for individual fish: (1) "immature," (2) "ma- 

 turing," or (3) "ripe." Group-1 fish included females 

 in the previtellogenic stage of ovarian development 

 (in chromatin nucleolar stage and primary oocyte 

 growth) and males in the gonial proliferation stage 

 of testicular development. Group-2 fish included fe- 

 males with ovaries in early or intermediate phases 

 of vitellogenesis (oocyte cytoplasm containing yolk 

 bodies) and males with testes in the meiotic phase 

 (spermatocytes and spermatids). Group-3 fish in- 

 cluded females with ovaries containing large and 

 darkly pigmented oocytes exhibiting yolk polariza- 

 tion and germinal vesicle migration and males in the 

 postmeiotic testicular phase (spermiogenesis and 

 differentiated spermatozoa). 



Data on egg production (approximate individual 

 relative fecundity ) were collected from gravid females 

 that had been captured in the Sacramento River from 

 February to March 1991-94 in order that they might 

 spawn in the hatchery. Estimation of egg production 

 was based on the number of eggs collected surgically 

 (a procedure routinely performed during artificial 

 spawning of sturgeon [see Conte et al., 1988]) and 

 represents 60-80% of actual individual fecundity 4 

 The number of eggs removed from each female was 



4 The percentage of eggs collected was determined by comparing 

 egg production at spawning of domestically raised sturgeon with 

 a total fecundity estimate of domestic sturgeon (of equivalent 

 size) processed for caviar production. 



