Potential Annual Fecundity Research Articles

Female age at maturity and fecundity in Atlantic Striped Bass

AbstractObjectiveFemale age at maturity and fecundity for the Atlantic stock of Striped Bass Morone saxatilis were estimated using histological methods and image analysis.MethodsOvaries were obtained from surveys encompassing the spring spawning season (March–July; n = 343), primarily from the Chesapeake Bay, and in the fall months (September–December; n = 85), primarily from the Atlantic coast. Histological examination of oocytes revealed some Striped Bass in intermediate stages of maturation during the spawning season. These individuals were identified as undergoing pubertal development, defined as the transition from the juvenile stage to first sexual maturity. Pubertal development was characterized by ovaries containing a population of enlarged, lipid‐filled oocytes but noticeably lacking vitellogenin‐derived yolk globules during the spawning season, and those ovaries were classified as immature. Toward the end of the spawning season, increasing proportions of Striped Bass with unspawned ovaries and oocytes undergoing total atresia were observed.ResultThe female age and length at 50% maturity in Atlantic Striped Bass based on spring samples were 5.5 years and 609 mm total length, respectively. Fecundity was determined gravimetrically via image analysis of ovarian tissue samples from spawning capable individuals (n = 67). Potential annual fecundity was found to exhibit hyperallometric scaling with respect to body size. Specifically, the scaling exponent for the length–fecundity relationship was 3.24, which was greater than the scaling exponent of 3.05 for the length–body mass relationship. This indicates that large females possess a disproportionately greater reproductive capacity with respect to body mass than the equivalent biomass of smaller females.ConclusionCompared with previous studies spanning over a half‐century, age at 50% maturity and fecundity were found to be relatively invariant, although variation found between contemporary studies may represent methodological and interpretive differences. Reproductive‐related life history traits of female Atlantic Striped Bass are apparently robust to long‐term decadal changes in fishing intensity, stock size, habitat alterations, and environmental conditions.

Reproductive traits exhibited by the paedomorphic gobies exploited in the Majorcan transparent goby fishery (western Mediterranean) and their management implications

An important small-scale fishery in Majorca targets three similar goby species: Aphia minuta, Pseudaphia ferreri and Crystallogobius linearis. Histological examination of the gonads of these species sampled from landings during the fishing season revealed characteristic reproductive traits that could be defined as abbreviate iteroparity. The transparent goby (Aphia minuta) and Ferrer’s goby (Pseudaphia ferreri) showed batch abbreviate iteroparity as a reproductive strategy, whereas the crystal goby (Crystallogobius linearis) showed total abbreviate iteroparity. Despite their short lifespans, all of them have a spawning season whose duration is longer than the legal fishing season. Additionally, all of them maintain a standing stock of primary growth oocytes in their gonads, indicating more than one spawning season in their lifespan. These reproductive features partially offset their special sensitivity to potential overexploitation and environmental changes but also suggest that the fishery needs special management to avoid breaking the balance between sustainability and fishing effort. The results of size at maturity and potential annual fecundity in the three species of the fishery are also reported and discussed.

Fecundity pattern and spawning dynamics of the common cuttlefish Sepia officinalis

ABSTRACT The fecundity pattern of common cuttlefish, Sepia officinalis, was assessed in Thermaikos Gulf, one of the species’ main fishing grounds in the eastern Mediterranean. Female samples, collected with coastal fishing gears during the population spawning season (January–July), were analysed using a combination of histology and whole mount analysis of ovarian tissue. The potential fecundity was shown to vary seasonally, showing the highest values at the beginning of spawning, gradually dropping thereafter. Previtellogenic oocytes (<0.5 mm) were the most prevalent group occurring throughout the spawning period in all maturity stages. Low or null levels of oocyte recruitment during the spawning period in combination with seasonal drop in fecundity and clutch-specific egg production suggest that the fecundity pattern of cuttlefish displays similarities with the so-called ‘determinate fecundity’ pattern of fishes. Spent females end up having small reserves of secondary growth oocytes (pre- and vitellogenic) that will never be spawned. Potential annual fecundity was thus estimated as the difference in total fecundity between pre-spawners and spent females and equalled 2569 oocytes/eggs. For a spawning period of four months, the ratio between potential fecundity and clutch size (100–200 eggs) indicated 13–25 different spawning events with a mean interval of 5–9 days.

Fecundity of the blotched picarel, Spicara maena (Linnaeus, 1758) from Oran Bay (Western Mediterranean Sea)

The fecundity of the blotched picarel Spicara maena from the western Mediterranean (Oran Bay) was assessed by the volumetric method. Total length (TL) of studied females varied between 91 and 140 mm (mean ± SD: 111.9 ± 10.6 mm). Estimates of total potential annual fecundity varied from 16750 to 28125 oocytes per individual (mean ± SD: 21404.7 ± 2698.8). Relationships between total potential fecundity (F) and TL, total weight, gonad weight were established using the multiplicative regression model and a high significant correlation was found in all the cases.

Spatial and annual variation in fecundity and oocyte atresia of yellowtail flounder, Limanda ferruginea, in U.S. waters

Potential annual fecundity (PAF) was estimated over three years (2010–2012) for yellowtail flounder with individuals from the three stocks off the northeast U.S. coast. Down-regulation of PAF, the resorption of oocytes during development, was evident as the vitellogenic cohort advanced, so we directly measured atresia of vitellogenic oocytes using stereological techniques. PAF models including relative fish condition, stock area, year, and oocyte diameter of the leading cohort explained more variation than models with just size alone based on Akaike information criteria. In a given year, Gulf of Maine females had lower PAF at size than southern New England females. Interannual differences were evident: PAF of both stocks was higher in 2010 and lower in 2012, with 2011 showing less synchronization between these stocks. Differences in size at age and relative condition suggested that energy available for somatic and reproductive growth was lower in some years in the Gulf of Maine and Georges Bank, especially in 2011. Georges Bank PAF and condition were intermediate to the other stocks or more similar to the Gulf of Maine, varying annually. A latitudinal gradient in PAF is evident based on our results and relative to earlier studies that included Canadian stocks. The magnitude of down-regulation was variable across stocks and typically 3–25% of PAF. This can be accounted for in fecundity estimates, by the seasonal schedule of sampling and use of an oocyte diameter term in the fecundity model. Theoretical models of atresia patterns suggested variable rates over the later portion of clutch development. The timing of down-regulation varied among years, and its intensity was influenced by female relative condition. Fecundity was related to fish size, but was also affected by fish condition and oocyte diameter (a proxy for time until spawning), and spatial and temporal effects. A longer time series of PAF may identify environmental drivers that modulate annual stock reproductive potential.

Spawning Dynamics and Size Related Trends in Reproductive Parameters of Southern Bluefin Tuna, Thunnus maccoyii.

Knowledge of spawning behaviour and fecundity of fish is important for estimating the reproductive potential of a stock and for constructing appropriate statistical models for assessing sustainable catch levels. Estimates of length-based reproductive parameters are particularly important for determining potential annual fecundity as a function of fish size, but they are often difficult to estimate reliably. Here we provide new information on the reproductive dynamics of southern bluefin tuna (SBT) Thunnus maccoyii through the analysis of fish size and ovary histology collected on the spawning ground in 1993–1995 and 1999–2002. These are used to refine previous parameter estimates of spawning dynamics and investigate size related trends in these parameters. Our results suggest that the small SBT tend to arrive on the spawning ground slightly later and depart earlier in the spawning season relative to large fish. All females were mature and the majority were classed as spawning capable (actively spawning or non-spawning) with a very small proportion classed as regressing. The fraction of females spawning per day decreased with fish size, but once females start a spawning episode, they spawned daily irrespective of size. Mean batch fecundity was estimated directly at 6.5 million oocytes. Analysis of ovary histology and ovary weight data indicated that relative batch fecundity, and the duration of spawning and non-spawning episodes, increased with fish size. These reproductive parameter estimates could be used with estimates of residency time on the spawning ground as a function of fish size (if known) and demographic data for the spawning population to provide a time series of relative annual fecundity for SBT.

Estimating fecundity in the zygoparous species Helicolenus dactylopterus (Actinopterygii, Scorpaeniformes): adaptation of the gravimetric method

Bluemouth, Helicolenus dactylopterus is zygoparous species with internal fertilization spawning multiple batches of early-celled embryos in gelatinous masses. Its unusual reproductive strategy required methodological adjustments to estimate potential annual fecundity. The present study applied an adaptation of the gravimetric method, estimated batch fecundity based on different spawning fraction criteria (gestation, early-celled, and blastula females), and compared these estimates with the number of developing oocytes (NDOR) in the beginning of spawning to clarify the oocyte development pattern. Spawning fraction estimation based on the gestation criterion was considered the most reliable given its low variance and the subjectivity of staging early-celled embryos. On average, 87 batches were spawned with a mean spawning interval estimated at 1.73 days, and a mean relative annual total fecundity of 1,773 embryos g−1 carcass. The inexistence of a clear decreasing trend in the NDOR throughout the spawning season, and the lower NDOR estimates in females in the beginning of spawning comparing with relative annual fecundity (gestation criterion) suggests vitellogenic oocyte recruitment supporting previous results of indeterminate fecundity in Portuguese coast. The method proposed can be considered in fecundity studies of other commercial important species which extrudes gelatinous egg masses.

Reproductive tactics of the freshwater fish Brycon guatemalensis (Teleostei: characidae) in the lake Nicaragua

The Machaca Brycon guatemalensis is a trop- ical freshwater fish widely distributed in Central America continental water, and recognized to have potentiality for further fisheries development and recreational fishing opportunities in the Lake Nicaragua. The species presents a protracted spawning season that last 8 months. Both small and large females start spawning activity in July, but this is females size-dependent. The female length at 50 % maturity based on histological procedures was 27.3 cm, which differs from the ones previously reported based on the gonad macroscopic observations (34.9 cm). The present study indicates that B. guatemalensis has determinate fecundity and group-synchronous type ovar- ian organization. The studies of the potential annual fecundity of the species show that this allometrically increases above three with female size, indicating that larger females produce more eggs than predicted by weight. These results can be incorporated in the current fishery management to promote sustainability.

Determinate Versus Indeterminate Fecundity in American Shad, an Anadromous Clupeid

AbstractHistorical fecundity estimates of American Shad Alosa sapidissima used a determinate method that estimated annual fecundity as the standing stock of oocytes at a single point of time prior to spawning. Such fecundity estimates have been (1) reported for populations from the Canadian Maritimes to Florida, (2) applied to hypothesis tests of life history evolution, and (3) used in demographic models to advise management policy. However, American Shad have asynchronous development of yolked oocyte clutches, which suggests that new oocytes could arise after spawning commences, biasing the results of a determinate fecundity method downward. If so, annual fecundity should be a product of batch size and the number of batches—an indeterminate fecundity method. We investigated oocyte recruitment, atresia, and spawning intervals using gonad histology of females from the Mattaponi River, Virginia. Batch size (i.e., the number of hydrated oocytes prior to a spawning event) was estimated using a gravimetric method. Spawning duration was obtained from an independent acoustic tagging study. A size hiatus between primary and secondary oocytes was only evident in some individuals during spawning, so we conclude that an indeterminate fecundity method is necessary for this population of American Shad. Atresia was evident during spawning but was low at the end of the 2002 spawning season. Females spawned every 2.2–2.9 d, releasing 11–17 batches per season. Batch fecundity (range: 12,700–81,400) was 23% higher for repeat versus virgin spawners. A bootstrapped estimate of potential annual fecundity for a virgin female—as calculated with an indeterminate fecundity method—was 478,000–544,000 eggs (95% confidence interval), about double the previous (determinate) estimates from this river system (260,000 and 288,000). Until more comparisons are done with other populations, we urge caution in using the many published determinate fecundity estimates of American Shad and other Alosa species.

Batch fecundity and spawning frequency of invasive Hemiculter leucisculus (Basilewsky, 1855) in Erhai Lake, China

Hemiculter leucisculus are multiple spawners with indeterminate fecundity, although previous fecundity estimates have assumed a determinate spawning pattern. Batch fecundity and spawning frequency of H. leucisculus were studied in Erhai Lake, China, in which the fish, as an exotic species, has become a successful colonizer. Spawning frequency was 16.05 %, as determined from the percent of females with postovulatory follicles 12 to 36 h old during the peak reproductive period (from May 27 to August 8). The average interval between spawning was 6.2 days and there were more than 16 total spawning batches during the peak reproductive period. The average batch fecundity (mean ± SD) was 11,934 ± 5,921 hydrated oocytes in 40 females (standard length or SL: 9.1–14.4 cm), while relative batch fecundity was 560 ± 137 eggs g−1 wet weight. The total potential annual fecundity was approximately 190,944 oocytes over the whole spawning season and was much higher than the estimated standing stock (31,585 oocytes) of yolked oocytes (36 females, SL: 9.5–16.2 cm) at the beginning of the spawning season in April 2010. This high annual fecundity is likely to have contributed to successful invasion of Erhai Lake by H. leucisculus.

Reproductive Dynamics and Potential Annual Fecundity of South Pacific Albacore Tuna (Thunnus alalunga)

The reproductive biology of albacore tuna, Thunnus alalunga, in the South Pacific Ocean was investigated with samples collected during broad-scale sampling between 2006 and 2011. Histology was done in a single laboratory according to standard protocols and the data analysed using generalized linear mixed-effects models. The sex ratio of albacore was female biased for fish smaller than approximately 60 cm FL and between 85 and 95 cm, and progressively more male biased above 95 cm FL. Spawning activity was synchronised across the region between 10°S and 25°S during the austral spring and summer where sea surface temperatures were ≥24 °C. The average gonad index varied among regions, with fish in easterly longitudes having heavier gonads for their size than fish in westerly longitudes. Albacore, while capable of spawning daily, on average spawn every 1.3 days during the peak spawning months of October to December. Spawning occurs around midnight and the early hours of the morning. Regional variation in spawning frequency and batch fecundity were not significant. The proportion of active females and the spawning fraction increased with length and age, and mature small and young fish were less active at either end of the spawning season than larger, older fish. Batch fecundity estimates ranged from 0.26 to 2.83 million oocytes with a mean relative batch fecundity of 64.4 oocytes per gram of body weight. Predicted batch fecundity and potential annual fecundity increased with both length and age. This extensive set of reproductive parameter estimates provides many of the first quantitative estimates for this population and will substantially improve the quality of biological inputs to the stock assessment for South Pacific albacore.

Differences in female individual reproductive potential among three stocks of winter flounder, Pseudopleuronectes americanus

Potential annual fecundity (PAF) and skipped spawning of winter flounder, Pseudopleuronectes americanus, were compared among the three stocks in United States waters and between two spawning seasons. Winter flounder have group-synchronous oocyte development and determinate fecundity. These characteristics enable estimation of PAF just prior to spawning by enumeration of the late-vitellogenic cohort of oocytes, in this case employing the autodiametric method. There was a low level of down-regulation, which was limited to fish in the earlier stages of vitellogenesis. Estimates of PAF increased substantially with female size and age, ranging from <0.5million to >5million eggs per female. Fecundity at size decreased with increasing latitude. On average, fish from the Southern New England (SNE) stock had the highest individual fecundities at length and Gulf of Maine (GOM) the lowest, but differences varied among the years. Fecundity at length of fish from Georges Bank (GB) was intermediate to these two stocks and displayed less variability at size; however, GB fish grow faster so they had the highest relative fecundity at age. Skipped spawning also exhibited geographic differences; it was infrequent (<2%) overall, but observed in the two coastal stocks (GOM more than SNE) in both years and was not observed in the GB stock. Fecundity at size between the two years was more similar for SNE fish, but all three stocks were synchronized with higher PAF in 2011 than 2010. Comparisons to previously published estimates suggest fecundity is highly variable in this species. Overall, different rates of reproductive productivity exist among individuals of the three stocks.

Developments in understanding of fecundity of fish stocks in relation to egg production methods for estimating spawning stock biomass

The use of egg production methods to estimate the spawning stock biomass (SSB) of fish depends critically on establishing the biological basis underpinning the methods. In this paper we review recent developments in knowledge of several key aspects of reproductive biology relevant to the estimation of annual egg production and daily specific fecundity at the individual and population level, as required in particular for application of the Annual and Daily Egg Production Methods respectively. The parameters to be estimated include spawning frequency, potential annual fecundity or batch fecundity, and rates of atresia prior to and during the spawning season. The initial development of egg production survey methods led to a significant growth in understanding of the reproductive biology of the target fish species. Drivers for further developments have come from the extension of the surveys to more species and areas, an increasing interest in evaluating time-series of reproductive potential in stocks, and the needs for research and development in support of marine aquaculture. A growing number of studies on field-caught and captive fish since the 1990s have led to important advances in our understanding of the triggering of maturation and gametogenesis, the subsequent processes of oocyte (follicle) growth and vitellogenesis, regulation of fecundity through atresia, batch spawning dynamics, and the influence of extrinsic factors such as day length, temperature and feeding. We conclude that the biological basis for egg production survey methods is now extremely well established for the main species being surveyed. However, the extension of the methods to a wider range of species has highlighted the practical difficulties in obtaining sufficiently precise and unbiased estimates of key parameters such as spawning fraction or sex ratio that are influenced by spatial distribution or catchability of several population components (e.g. mature, immature active spawning or spent). The definition and validation of spawning markers also remains a challenge, particularly for new species being surveyed. Given the often high cost of egg production surveys, particularly the annual method, there is a need for simulation studies to determine the relative performance of simpler and less expensive approaches to tracking SSB from egg surveys for use in stock assessment. Developments that expand the quantity and utility of the information yielded by the surveys, including integration of the surveys into broader ecosystem studies, could also be considered a way to improve cost-effectiveness.

Age, Growth, and Reproduction of Greater Amberjack off the Southeastern U.S. Atlantic Coast

AbstractThe greater amberjack Seriola dumerili is a pelagic, epibenthic species that is widely distributed in the Atlantic, Pacific, and Indian oceans. Life history samples from a total of 2,729 greater amberjacks were collected between 2000 and 2004 by personnel of the Marine Resource Monitoring Assessment and Prediction program and National Marine Fisheries Service port agents from recreational fisherman and in commercial fish houses from Cape Lookout, North Carolina, to Key West, Florida. Ages were estimated using thin transverse otolith sections from 1,996 specimens; sex and reproductive state were assigned to 2,517 fish based on histological preparations of gonadal tissues. Ages of greater amberjacks sampled ranged from 1 to 13 years; these data were described with a von Bertalanffy growth equation fitted to all aged specimens: Lt = 1,241.5 × [1 − e−0.28(t+1.56)]. Sexual dimorphism was evident; females were larger at age than males. Size at 50% maturity was 644 mm fork length (FL) for males and 733 mm FL for females. Age at 50% maturity for females was 1.3 years. Estimates of potential annual fecundity ranged from 18,271,400 to 59,032,800 oocytes for 930‐1,296‐mm specimens and from 25,472,100 to 47,194,300 oocytes for ages 3‐7. Peak spawning occurred primarily off south Florida and the Florida Keys during April and May. Even though the extremely fast growth, early maturation, very high fecundity, and wide distribution of greater amberjacks suggest that the population would be difficult to overexploit, a recent stock assessment of the Gulf of Mexico population shows that the species is vulnerable to overexploitation and should managed more conservatively than the life history characteristics imply.

Reproductive Biology and Protandrous Hermaphroditism in Acanthopagrus latus

Detailed macroscopic and histological studies of the gonads of a full size and age range of Acanthopagrus latus from each season in Shark Bay, Western Australia, demonstrate that this species is a protandrous hermaphrodite in this large subtropical embayment. Although our scheme for the changes that occur in the ovotestes of A. latus during life is not consistent with some of the conclusions drawn for this species elsewhere, it is similar to that of Pollock (1985 J. Fish. Biol. 26: 301–311) for the congeneric Acanthopagrus australis. The ovotestes of males develop from gonads which contain substantial amounts of both testicular and ovarian tissue. The testicular component of the ovotestes of all males regresses markedly after spawning. During the next spawning season, the ovotestes either become gonads in which the testicular zone again predominates and contains spermatids and spermatozoa (functional males), or gonads in which the ovarian zone now predominates and contains mature oocytes (functional females). Once a fish has become a functional female, it remains a female throughout the rest of its life. In Shark Bay, A. latustypically spawns on a limited number of occasions during a short period in late winter and early spring and has determinate fecundity. The mean potential annual fecundity was ca. 2 000 000. The total length of 245 mm, at which, during the spawning period, 50% of A. latus become identifiable as males, is very similar to the current minimum legal length (MLL) of 250 mm, which corresponds to an age of ca. 2.5 years less than that at which 50% of males become females. Thus, although the spawning potential ratio suggests that the present fishing pressure is sustainable, the current MLL should be reviewed if recreational fishing pressure continues to increase.

Gross and histological observations of ovarian development in twaite shad, &lt;i&gt;Alosa fallax fallax&lt;/i&gt;, from Rivers Mira and Guadiana (Portugal)

SUMMARY: In order to describe the stages of oogenesis of twaite shad, Alosa fallax fallax, 265 females were collected between March and June 1997, February and June 1998 and January and April 1999 in the Rivers Mira and Guadiana. From the histological study of ovaries a total of eight developmental stages were delineated. Gross examination of paired ovary revealed that they could be placed into one of seven maturity stages according to their stage of development. Two stages of atresia, alfa and beta, were identified. Upon cessation of spawning, the ovaries still contained some oocytes at various stages of development but with a greater number of atretic oocytes. The simultaneous occurrence of oocytes at different stages of development in the ovary indicates asynchronous oocyte development. Oocyte size frequency distributions do not show a gap in size between cortical alveoli and vitellogenic oocytes during the spawning season. This may represent the ability of twaite shad to push oocytes through vitellogenesis from a previtellogenic condition during the spawning period. This has important implications for twaite shad fecundity, because fish with this type of oocyte development depend on estimates of batch fecundity and spawning frequency to determine potential annual fecundity.

Changes in Greenland Halibut Growth, Condition and Fecundity in the Northwest Atlantic (Flemish Pass, Flemish Cap and Southern Grand Bank)

The Greenland halibut fishable stock has been declining substantially since late-1980s, according to both surveys and commercial fishery indices, particularly among the ages 10+, which corresponds to the females age at 50% maturity. In this paper the effect of this apparent reduction in the stock abundance on growth and reproductive parameters is examined. Among growth parameters, the analysis of the first year growth is undertaken both by cohort and by geographic areas, assuming that density dependence might be the most severe at younger age classes. This is made using records of the respective first annual ring otolith diameters. Other growth related index such as the condition factor is also analysed. Neither significant differences in the first year growth have been observed between areas analysed, nor between cohorts, during the period 1988 to 1996. Mean condition factor-at-age for ages 1 to 13 were stable during this same period. About the reproductive parameters, two aspects are considered: the interannual variations in length-at-maturity and in the potential fecundity. Female length at maturity varied between 64.5 and 69.5 cm. Female potential annual fecundity ranged between 15 000 and 158 000. It increases with female age, but the mean fecundity-at-age variations were not significant either between years of sampling or between cohorts. A common feature observed is the relative stability of those characteristic through the period analysed, which could support a certain resiliency of the life history traits in this species.

The effect of Kudoa paniformis infection on the reproductive effort of female Pacific hake

The effect of the myxosporidean Kudoa paniformis on the annual reproductive effort of the coastal stock of Pacific hake (Merluccius productus), on which it is a common parasite, is investigated. Female Pacific hake collected off the central Oregon coast in December 1988 were analyzed for prevalence and intensity of parasites. Reproductive effort was estimated by the number of yolked oocytes present in the ovaries immediately prior to spawning (potential annual fecundity), using the volumetric method. The effect of the parasite was evaluated through an analysis of covariance where fecundity was modeled as a function of fish length and parasite prevalence. An additional analysis of covariance evaluated the effect of the intensity of parasite infection on fecundity. Results show that the fecundity of Pacific hake is significantly reduced in the presence of K. paniformis infections and that the detrimental effect escalates with the intensity of infection. The potential effects on the population dynamics of the Pacific hake coastal stock are discussed.

On the fecundity of the Black Sea bream, Spondyliosoma cantharus (L. ), from the Adriatic Sea (Croatian coast)

The fecundity of the Black Sea bream from the eastern middle Adriatic (Croatian coast) was assessed by the volumetric method using 59 ovaries in pre-spawning stage from fish between 18.5 and 33.5 cm total length. Estimates of total potential annual fecundity varied between 31,670 and 554,070 eggs per female. Relationships between total potential fecundity and total length (TL), total weight (TW) and age (A) were established using the multiplicative regression model. Relative fecundity is constant, reaching a maximum of 850 eggs per g in the 30.5 cm to 31.0 cm length class.

Ovarian development and the potential annual fecundity of western stock hoki (Macruronus novaezelandiae)

Hoki (Macruronus novaezelandiae) form two of New Zealand's largest spawning fisheries, one centred off the west coast of the South Island (WCSI), the other in Cook Strait. Research data collected during surveys 1983–96 show that ovarian development begins on the feeding grounds between March and April, whereas spawning occurs mainly in July and August. Research has also shown that a significant proportion of adult hoki do not develop to spawn in a given year. Plans to estimate the absolute abundance of the western spawning stock off the WCSI using an egg production method require estimates of total annual fecundity and proportion spawning. Although determinate spawners, hoki are capable of multiple spawning in one season, and it is difficult to differentiate between fish about to spawn and fish that have already begun to spawn on the WCSI. In this study, we applied a modified stereological technique to samples of western stock hoki obtained from the feeding grounds south of New Zealand in May to determine the feasibility of estimating fecundity, at the same time as estimating the annual proportion developing to spawn. Mean fecundity estimates ranged from 0.4 million to 3.0 million oocytes and compare favourably with previous unpublished estimates of fecundity in early spawners on the west coast. We concluded that samples collected from the Southern Plateau during surveys of pre‐spawning hoki in May could provide useful estimates of fecundity.