Distribution and reproduction of the Patagonian toothfish Dissostichus eleginoides Smitt around the Falkland Islands

Population characteristics of the Patagonian toothfish Dissostichus eleginoides were investigated based on material collected from both trawl and longline fisheries in Falkland Islands' waters. The fish occurred between 56 and 2122 m and attained 225 cm total length ( L _T). Males matured earlier, L _T at 50% maturity was 86 cm for males v . 90 cm for females. Subadult fish foraged at depths of <600 m, whereas adult Patagonian toothfish lived at >600 m. Spawning occurred on slopes of the Burdwood Bank at c . 1000 m depth with a minor peak in May, and a major peak in July to August. Males arrived at the spawning grounds first. Between spawning peaks both sexes remained around the Burdwood Bank with males occurring at greater depths than females. The Patagonian toothfish in south‐east Patagonia and the Falkland Islands had a long juvenile and sub‐adult period in the relatively shallow and warm waters of the outer shelf and upper slope unlike that of juveniles in other Patagonian toothfish populations. The migratory life style of the south‐west Atlantic population is probably very different from that of other populations, which tend to be resident as they are inclined to inhabit the waters around oceanic islands and sea mounts with narrow shelf areas.     

Cytomorphology of female and male gonads in Antarctic toothfish <Emphasis Type="Italic">Dissosctichus mawsoni</Emphasis> (Nototheniidae) from the Ross Sea in the summer period

Results of histological analysis of gonads of female and male Antarctic toothfish Dissostichus mawsoni caught in the Ross Sea of the Pacific sector in the period of Antarctic summer (December–February) 2004–2005 are presented. Morphological indices and index of gonad maturity are described and ecological criteria of assessment of maturity stages of ovaries, cytological indices of oocytes, and the type of toothfish oogenesis are determined. It was established that in the period of fishing Antarctic toothfish, females and males with gonads at maturity stage III dominate. Ovaries contain two groups of oocytes of the period of trophoplasmatic growth and large oocytes of the nearest spawning season that comprise the smallest proportion of total sex cells. In the testes of two male toothfish, the primary fusion of renal and generative tissues was revealed. It is suggested that the termination of gonad maturity of toothfish takes place from March to April, and spawning takes place from June to August.     

Macroscopic and histological analyses of gonads during the spawning season of Chionodraco hamatus (Pisces,Channichthyidae) off Terra Nova Bay,Ross Sea,Southern Ocean

A macroscopic and histological analysis of gonads was carried out during the spawning season of the high-Antarctic channichthyid Chionodraco hamatus in the western Ross Sea. Samples were collected between December and February during several years in the coastal waters of Terra Nova Bay. Gonad maturity stages were described for males and females according to macroscopic and histological scales. Using multi-year data, the estimated length at first spawning of females was about 35 cm TL, very similar to that obtained indirectly for males. Similar to many other high-Antarctic fish, C. hamatus is a summer spawner. The greater part of the stock was indeed in spawning condition between December and February, although a large proportion of females large enough to spawn probably did not spawn in that season. The present data confirm that C. hamatus, as is typical for Antarctic fish, probably spawns a single batch of oocytes once a year. In addition, vitellogenesis is a slow process that extends over at least 1 year. Discrepancies between the macroscopic and histological appearance of gonads were found. These were associated mainly with spent and resting females (maturity stages 5 and 2, respectively). This study demonstrates the importance of histological analysis of gonads in order to confirm the results of the macroscopic analyses routinely carried out in studies of reproductive biology. This is of particular importance in determining size at maturity and spawning stock biomass, for assessment purposes.     

Preliminary stock assessment of the Patagonian toothfish longline fishery around the Falkland Islands

An experimental fishery for Patagonian toothfish Dissostichus eleginoides was opened in Falkland Island waters briefly in 1992 and then from April 1994. One to two longlines per vessel were usually deployed at night, mostly fishing for 12–30 h at depths between 600 and 2000 m. The characteristics of the vessel, gear, fishing activities and the data collection and analyses methods are described. An initial evaluation of the authors' current understanding of toothfish biology and population dynamics in Falkland Island waters is given. A first analysis of toothfish numbers caught in 1994 suggests that these are changing at rates faster than expected from simple demographic processes. Therefore, despite an intensive monitoring of catch and fishing effort of each vessel, it is still not possible to derive reliable estimates for the size of the toothfish population currently exploited around the Falkland Islands. Migration patterns in and out of the fishery need to be understood before a reliable assessment of the fishery can be made. These results, together with current and future lines of research, are discussed in the light of data available from other toothfish fisheries in austral waters.     

Spatio‐temporal dynamics in maturation and spawning of Patagonian toothfish Dissostichus eleginoides on the sub‐Antarctic Kerguelen Plateau

This study investigated maturation and spawning of Patagonian toothfish Dissostichus eleginoides in the Heard Island and McDonald Islands (HIMI) fishery on the Kerguelen Plateau in the Indian Sector of the Southern Ocean based on gonads and otoliths collected between 2004 and 2015 and using histological analyses and calibration of macroscopic staging criteria. Dissostichus eleginoides at HIMI spawn throughout the austral late autumn and winter months of May–August and spawning activity is concentrated on slopes along the west and south of the plateau around HIMI at depths of 1500–1900 m. Comparison between histological analyses and macroscopic gonad staging indicated that many fish that had spawned, as indicated by the presence of post‐ovulatory follicles, returned to a resting stage which was macroscopically indistinguishable from maturing fish. Furthermore, the occurrence of females of all size classes with low gonado‐somatic index and low macroscopic gonad stage during the spawning season suggested that a proportion of mature females did not spawn every year. Age‐at‐maturity estimates, based on the assumption that fish of macroscopic stages ≥2 were mature, decreased between the 2004–2009 and 2010–2015 periods for both sexes. The magnitude of this temporal variation in age at maturity, however, varied between gear types and fishing depths and variable sampling regimes probably influenced these variations. This study highlights the importance of correct interpretation of macroscopic gonad stages and understanding the influence of fishery operations on estimations of life‐history parameters.     

Satellite tracking of male rockhopper penguins Eudyptes chrysocome during the incubation period at the Falkland Islands

The foraging patterns of ten male rockhopper penguins Eudyptes chrysocome from the Falkland Islands were recorded during the incubation period by using satellite telemetry. Irrespective of study site and year, two different foraging areas could be identified. Three foraging trips were directed towards the slope of the Patagonian Shelf c. 140 km to the northeast of the breeding colony and these trips had a duration of 11–15 days. The seven other rockhopper penguins travelled c. 400 km towards the edge of the Falkland Islands' waters; all these foraging trips followed an anti-clockwise direction and lasted 16–27 days. The calculated mean daily travelling speed, based on the time spent underwater and the distance covered between two positions, was significantly higher in birds travelling to the edge of the Falkland Islands' waters compared with those foraging at the shelf slope (4.4±1.6 km/h vs. 3.4±2.0 km/h, respectively). The consistent foraging patterns exhibited during the long trips may be linked to the Falklands current, allowing the penguins to reach remote areas while reducing their energy expenditure. Potential interactions between commercial fisheries and hydrocarbon exploration are discussed.     

Spawning season and size at sexual maturity of <Emphasis Type="Italic">Kyphosus bigibbus</Emphasis> (Kyphosidae) from northwest Kyushu,Japan

The reproductive characteristics of Kyphosus bigibbus were examined using individuals collected between June 2004 and February 2009 off Nagasaki Peninsula in northwest Kyushu, Japan. The spawning season and size at sexual maturity of this species were characterized based on a gonad index and histological examination of the gonads. The spawning season extends from June to October. This species is assumed to be an indeterminate, multiple-batch spawner. Females reached sexual maturity at larger size than males (fork length at 50% sexual maturity: males 284 mm, females 360 mm).     

Sexuality, sex change and maturation patterns in the yellowfin seabream, Acanthopagrus latus (Teleostei: Sparidae) (Houttuyn, 1782)

Macroscopic and histological studies were carried out to describe the reproductive styles and sex reversal and to follow gonadal changes in captive yellowfin seabream during the second year of life. Four reproductive styles are found in Acanthopagrus latus (Houttuyn, 1782): (i) males and females (gonochorism), (ii) functional males, (iii) transitionals and (iv) functional females. The species is a protandric hermaphrodite and begins life as a functional male with testicular zone undergoing active spermatogenesis, while the ovarian zone is arrested at the primary growth (perinucleolar) phase. Males and females were encountered in virtually all size‐classes. Functional males outnumbered the functional females in all size‐classes in which they were encountered. Sex reversal begins in the transitionals from July to August, after spawning in the functional males, at 14.9–20.2 cm standard length (SL) and, by November, maturation of the ovarian tissue begins. A. latus in cages in Kuwait waters spawns from January to April with a peak in February for males, and a peak in March for females and transitionals. Spawning begins in the 18.3–20.2 cm size‐range fish, peaking in the 20.3–22.2 cm size‐range in both males and females and also in the transitionals, although a few of the latter spawn from 14.9 cm SL. In relation to age, spawning begins at 20 months in males and peaks at 21 months. Females begin to spawn at 21 months with a peak at 22 months, while transitionals generally begin to spawn at 20 months, although a few 14–15‐month‐old sex‐changing individuals were encountered. Temperature, either alone or in combination with other unknown factors, triggers spawning in A. latus.     

Reproduction of the Arctic copepodCalanus hyperboreus in the Greenland Sea-field and laboratory observations

The seasonal vertical migration of adultCalanus hyperboreus Krøyer and their female reproductive biology have been studied in the central Greenland Sea, based on 7-month coverage during one annual cycle. Females dwelled in surface waters only between April and July. Gonad maturation began after the summer descent into deeper waters between September and October in the absence of food. Breeding was assessed from gonad development and egg production experiments. It started around the beginning of November and was mostly completed by March/April, before the spring ascent. The overwintering depth of females ranged from close to the surface to 3000 m, and mature females had a preference for shallower depths. Males were mostly found during the breeding period, where they inhabited the 500- to 1000-m layer. Female dry weight was highest in August and November and lowest in February. Field observations were supplemented by observations on gonad development and egg production of females, which were collected in June and August and kept in the laboratory for up to 6 months. Clutch size, spawning interval and fecundity were determined at 0°C. Females collected in June were mature earlier. Due to their low dry weight, they developed only small gonads and very few of them spawned. Females from August were much fatter and produced up to 1000 eggs in several clutches deposited at regular intervals.     

Interannual variability in reproductive traits of the Patagonian toothfish Dissostichus eleginoides around the sub‐Antarctic island of South Georgia

Commercial fisheries data, collected as part of an observer programme and covering the period 1997–2014, were utilized in order to define key reproductive traits and spawning dynamics of the Patagonian toothfish Dissostichus eleginoides at South Georgia. Multi‐year spawning site fidelity of D. eleginoides was revealed through the identification of previously unknown spawning hotspots. Timing of female spawning was shown to have shifted later, leading to a shorter spawning duration. A decrease in length and mass of female and male spawning fish and a reduced number of large spawning fish was found, evidence of a change in size structure of spawning D. eleginoides. During the study period fewer later maturity stage females (including spawning stage) were observed in conjunction with increased proportions of early stage female D. eleginoides. The findings are discussed in the context of reproductive success, with consideration of the possible effects such spawning characteristics and behaviours may have on egg and larval survival. This work presents the first long‐term assessment of D. eleginoides spawning dynamics at South Georgia and provides valuable knowledge for both the ecology of the species and for future fisheries management of this commercially important species.     

Oogenesis and gonad maturation in the copepodCalanus finmarchicus and the prediction of egg production from preserved samples

 Oogenesis and gonad development of Calanus finmarchicus during the winter spring transition in a fjord in Northern Norway were studied. A combination of observations on whole animals (macroscopic), taking advantage of their transparency, and histological sections was used to establish a system of gonad maturation stages, to describe the spawning cycle and to estimate egg production rates from preserved samples. During their development, oocytes change their shape and size, the morphology of the nucleus, and the appearance of the ooplasm. Four oocyte development stages were identified and related to a macroscopic system of four gonad developmental stages (GS) that can be applied to whole stained animals. During gonad development, the macroscopic morphological modifications of the gonads are mainly manifested in an increase in number and size of the oocytes and their distribution in diverticula and oviducts. The maturation processes during the spawning cycle (the period between egg depositions) were described from histological sections of females preserved at regular intervals after egg deposition. The macroscopic GS did not vary during the spawning cycle. This GS was a highly significant indicator for females, which spawned within 24 h after collection at 5°C. Another histological indicator for the last third of the spawning cycle is the appearance of distinct chromosomes, which, however, are only seen in histological sections. For the prediction of egg production rate of a Calanus population, in addition to the number of females spawning, knowledge of clutch size and the interval of clutch deposition is required. Clutch size was determined by counting the number of the oocyte stages to be released during the next spawning event in serial sections of the gonads. There was no significant difference in clutches laid by the females during 5 days before preservation. From the observations it seems that GS 4 predicts females that are ready to spawn within the minimum spawning interval characterisitic for a given temperature. If this holds true, it should be possible to predict in situ egg production rates solely from preserved samples. Received: 18 August 1995/Accepted: 6 January 1996     

Falkland Islands biogeography: converging trajectories in the South Atlantic Ocean

Aim This paper describes the biogeographical setting of the Falkland Islands, in the context of the relationships of the islands’ biota to other sub‐Antarctic/cold temperate lands. Location The analysis focuses primarily on the Falklands biota, and explores its relationships to those of Patagonian South America and South Africa, other southern lands and the islands of the sub‐Antarctic Pacific, Indian and Atlantic Oceans. Methods The study derives largely from literature sources on the biota and geological history of the Falkland Islands. Results The animals and plants known from the Falkland Islands exhibit strong affinities with those of Patagonian South America, and especially Tierra del Fuego; additional affinities are with various remote islands of the sub‐Antarctic, as well as New Zealand and to a lesser extent Australia; often these are shared with Patagonia. While the biotic affinities might be interpreted, by some, as indicating a former Gondwanan/South American geological connection of the Falklands, geological evidence points to the Falklands formerly having a land connection to south‐eastern South Africa. Only faint hints of a South African biotic connection remain. The historical biotic and geological connections of the Falklands thus conflict. Moreover, the Falklands biota is so strongly Patagonian that derivation of that biota is best seen as resulting from dispersal, much of it probably recent. This dispersal biota appears to have replaced, and perhaps displaced, the South African biota present on the islands as they detached from South Africa and drifted across the south Atlantic Ocean, as it opened up as South America and Africa drifted apart.     

Gonadal morphology and difference in reproductive development of two isolated populations of Astyanax rivularis (Teleostei,Characidae)

Individuals of the same species may present different reproductive tactics depending on the environment in which they develop and mature. The present study aimed to define the gonadal development phases of males and females of Astyanax rivularis and to carry out a comparative analysis of the reproductive development of specimens captured in two isolated environments of the São Francisco River basin in Serra da Canastra, Brazil (Point 1: low vegetation and river showing calm and crystalline waters with small well formations; Point 2: current waters, and well-established areas of arboreal vegetation). Thus, the gonads of A. rivularis specimens were collected, fixed and processed with techniques for light microscopy. Five maturation phases of the females' reproductive cycle were established: immature, developing, spawning capable, regressing and regenerating. Three maturation phases of the males' reproductive cycle were observed: spawning capable, regressing, and regenerating. There are differences in the phases of gonadal development of A. rivularis between the two sampling points so that, possibly, animals upstream of the waterfall demonstrate a delay in the reproductive cycle in relation to animals downstream.     

Seasonal Sexual Segregation by Monomorphic Sooty Shearwaters Puffinus griseus Reflects Different Reproductive Roles during the Pre-Laying Period

Tracking technology has revolutionized knowledge of seabird movements; yet, few studies have examined sex differences in distribution and behavior of small to medium-sized, sexually-monomorphic seabirds. Application of bird-borne geolocation-immersion loggers revealed seasonal segregation in the sexually-monomorphic Sooty Shearwater Puffinus griseus, mainly in the pre-laying period, when there were clear differences in reproductive roles. Shearwaters first returned to the Falkland Islands on 27 Sept±8 d; males, on average, 8 d earlier than females. Prior to egg-laying, distribution at sea, colony attendance and behaviour depended on sex. Males foraged locally over the southern Patagonian Shelf and Burdwood Bank, spending mainly single days at sea and intervening nights in the burrow. Females, who flew for more of the day during this time, foraged in more distant areas of the northern Patagonian Shelf and Argentine Basin that were deeper, warmer and relatively more productive. Attendance of females at the colony was also more variable than that of males and, overall, males were present for significantly more of the pre-laying period (38 vs. 19% of time). Sex differences were reduced following egg-laying, with males and females using similar foraging areas and making trips of similar mean duration in incubation (7.6±2.7 d) and chick-rearing (1.4±1.3 d). Congruence continued into the non-breeding period, with both sexes showing similar patterns of activity and areas of occupancy in the NW Atlantic. Thus, seasonal changes in reproductive roles influenced patterns of sexual segregation; this occurred only early in the season, when male Sooty Shearwaters foraged locally, returning regularly to the colony to defend (or maintain) the burrow or the mate, while females concentrated on building resources for egg development in distant and relatively more productive waters.     

Reproductive biology and growth of bluestripe herring Herklotsichthys quadrimaculatus (Rüppell, 1837) in the northernmost waters

In order to examine the reproductive biology and growth of Herklotsichthys quadrimaculatus in the northernmost part of its reproductive range, the size frequency, gonadal development, and otolith daily increments of this species were collected from the coastal waters of Okinawa Island, southern Japan. Juveniles (<25 mm standard length, SL) were found from April to August. Their size increased to ca. 100 mm SL in November and subsequently remained unchanged. The gonadosomatic index of females was higher (>3.0) between March and August, which was the estimated spawning period. The modal hatching period back‐calculated from otolith daily increments was from April to May, which would be the peak of spawning. Because mature and spent ovaries also contained mature and immature oocytes, it was concluded that females spawn several times during the spawning season. Age determination from otolith increments showed logistic growth up to 97 mm (ca. 180 days post‐hatch), after which growth was almost stagnant. Maximum size and age were 121.6 mm SL and 384 days, respectively. The adult size decreased between August and September, indicating a change in the age cohort. Thus, the fish reached the end of their lifespans after spawning. Some of these ecological features were different from those of a previous study performed in southern areas; these differences suggest a flexible life history that could change to adapt to the surrounding environment.     

Differences in reproductive strategies between obscure puffer Takifugu obscurus and ocellated puffer Takifugu ocellatus during their spawning migration

Reproductive strategies were compared between obscure puffer Takifugu obscurus and ocellated puffer Takifugu ocellatus captured in waters near Yangzhong Island in the lower reaches of the Yangtze River during the spawning migration season from February to June in two consecutive years (1995 and 1996). Results showed that obscure puffer and ocellated puffer have adopted different reproductive strategies, including different spawning times, different size at maturity, and different number and size of oocytes, resulting in two different larval sizes. In detail, the timing of the spawning migration and status of gonad development of obscure puffer was about 1 month earlier than that of ocellated puffer; the obscure puffer was obviously longer and heavier than ocellated puffer in both mature male and female fish; mean GSI of obscure puffer females (15.8%) was significantly higher than that of ocellated puffer females (14.6%); the average diameter of ocellated puffer eggs (1.49 ± 0.12 mm) was significantly larger than that of the obscure puffer (1.22 ± 0.08 mm); and obscure puffer females (320.8 oocytes mg^?1 somatic wet weight) had significantly higher relative fecundity than ocellated puffer females (125.2 oocytes mg^?1 somatic wet weight). These differences in reproductive strategies between two closely related species of the Takifugu genus indicate that both obscure puffer and ocellated puffer fit the r/K dichotomy. Obscure puffer shows K‐selected characters with maturity at relatively large size and r‐selected characters with relatively many and small offspring, whereas ocellated puffer shows r‐selected characters with maturity at a relatively small size and K‐selected characters with relatively few and large offspring.     

A histological investigation of the occurrence of non-reproductive female bluefin tuna Thunnus thynnus in the Mediterranean Sea

The presence of non-reproductive Atlantic bluefin tuna Thunnus thynnus females in the Mediterranean Sea was investigated through histological analysis of the gonads. Three hundred and twenty-six ovary samples were collected from adults captured at different locations in the Mediterranean Sea during the reproductive seasons between 1998 and 2008. Only three specimens were considered to be in a non-reproductive state: two of them were in a reabsorbing state showing ovaries with early vitellogenic oocytes and extensive α and β atresia of vitellogenic follicles; the third showed gonads with perinucleolar oocytes and was considered to be in a resting state. The low occurrence of non-reproductive individuals found in this study makes it unlikely that non-reproductive individuals aggregate with reproductive ones during their migration towards spawning grounds. Further research is suggested in order to investigate the potential presence of non-reproductive individuals on non-spawning grounds during the reproductive season.     

Variation in the diet of the Patagonian toothfish with size, depth and season around the Falkland Islands

The ontogenetic and seasonal variations in the feeding spectrum were studied in 756 specimens of the Patagonian toothfish Dissostichus eleginoides (16–159 cm total length, L_T) collected on the shelf, continental slope and bathyal waters (67–1960 m, depth range) around the Falkland Islands between April 1999 and August 2002. On the shelf, small toothfish (<40 cm L_T) were active predators taking mostly one relatively large prey item at a time (mainly near‐bottom Patagonotothen ramsayi and Loligo gahi). Medium‐size toothfish (40–60 cm L_T) fed on the same prey, but the number of prey items increased to 1–2 items per fish. Large toothfish (>60 cm L_T) switched their diet to other large pelagic fishes occurring near the bottom (Macruronus magellanicus and Micromesistius australis australis), again taking mostly one prey item at a time. The diet of medium‐size D. eleginoides on the shelf varied seasonally depending on the abundance and migrations of the major prey species. Patagonotothen ramsayi was abundant in the diet throughout the year, whereas L. gahi appeared only from February to October during its offshore seasonal migrations to the depth range of D. eleginoides. During November to January, L. gahi migrated inshore to spawn and disappeared from the toothfish diet, being substituted by M. australis australis which dispersed on the shelf after spawning. After its ontogenetic descent to the lower part of the continental slope (500–1000 m depths), toothfish took less active (than on the shelf) fishes such as Antimora rostrata whilst also feeding on active near‐bottom macrourids and skates. In their deepest habitat (>1000 m depths), toothfish became a typical opportunistic predator, feeding mainly on relatively small and inactive fishes, squids and prawn‐like crustaceans Acanthephyra pelagica and Thymops birsteini. Decrease in hunting activity with depth could be related to a specific adaptation to keep neutral buoyancy by increase of lipid content in white muscles of D. eleginoides with size.     

Spatial variation in reproduction, and occurrence of non-reproductive adults, in orange roughy, Hoplostethus atlanticus Collett (Trachichthyidae), from south-eastern Australia

This study was designed to determine whether orange roughy reproduce throughout their distribution in Australian waters, and if so, whether commencement of spawning and length at maturity vary within the region. We found that females from four widely separated sampling areas reproduced in 1988, but that the onset of spawning and length at maturity were not the same in all the areas. In New South Wales, ovulation was finished by mid-June, and 50% of females were mature at 28 cm standard length (S.L.). On the other hand, females from eastern and western Tasmania and South Australia did not spawn until mid-July, and 50% of females from Tasmania were not mature until 32 cm S.L. Females from all areas had oocytes with yolk granules at least 5 months before ovulation. However, in the few months before spawning, some adult females from all areas had not undergone vitellogenesis or were resorbing all yolky oocytes. The best estimates of the proportion of these non-reproductive females were made in March and April, when the single batch of eggs to be spawned was clearly distinguishable, and before spawning aggregations had formed. In 1990 in eastern Tasmania, at the site of a major spawning aggregation, the best estimate of the proportion of non-reproductive fish was 45%. We suggest that scarcity of food, coupled with the cost of joining a spawning aggregation, may result in intermittent spawning in this long-lived species.     

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.