Fecundity Estimates Research Articles

Investigating fecundity and egg loss using a non-invasive method during brooding in European lobster (Homarus gammarus)

AbstractThis article examines two important components of measurement of fecundity in the European lobster Homarus gammarus: (i) comparing the traditional gravimetric dry weight fecundity method against two non-invasive depth gauge methods initially developed for Homarus americanus and (ii) utilizing the depth gauge method to determine egg loss during the brooding period and its impacts on effective fecundity estimates. No significant difference was observed between fecundity estimates derived using either the traditional or depth gauge methods. Derived fecundity estimates from the two depth gauge methods differed by −0.31% (±2.7 s.e.) for cylinder and −1.1% (±2.4 s.e.) for ellipsoid fecundity estimates compared with the traditional method. This highlights the utility of the depth gauge method for providing fast, reliable and low-cost estimates without sacrificing lobsters or their egg masses. Egg loss is estimated to be as high as 44% from initial extrusion to hatching. The application of the non-invasive methods for estimating fecundity to other fisheries and stocks is discussed along with the importance of understanding egg loss in this commercially valuable fishery.

Population trends for two Malagasy fruit bats

Madagascar is home to three endemic species of Old World Fruit Bat, which are important pollinators and seed dispersers. We aimed to quantitatively assess population trajectories for the two largest of these species, the IUCN-listed ‘Vulnerable’ Eidolon dupreanum and Pteropus rufus. To this end, we conducted a longitudinal field study, in which we live-captured E. dupreanum and P. rufus, estimated species-specific fecundity rates, and generated age-frequency data via histological analysis of cementum annuli layering in tooth samples extracted from a subset of individuals. We fit exponential models to resulting data to estimate annual survival probabilities for adult bats (sA = .794 for E. dupreanum; sA = .511 for P. rufus), then applied Lefkovitch modeling techniques to infer the minimum required juvenile survival rate needed to permit longterm population persistence. Given estimated adult survival, population persistence was only possible for E. dupreanum when field-based fecundity estimates were replaced by higher values reported in the literature for related species. For P. rufus, tooth-derived estimates of adult survival were so low that even assumptions of perfect (100%) juvenile annual survival would not permit stable population trajectories. Age-based survival analyses were further supported by longitudinal exit counts carried out from 2013 to 2018 at three local P. rufus roost sites, which demonstrated a statistically significant, faintly negative time trend, indicative of subtle regional population declines. These results suggest that Malagasy fruit bat species face significant threats to population viability, with P. rufus particularly imperiled. Immediate conservation interventions, including habitat restoration and cessation of legally sanctioned bat hunting, are needed to protect Madagascar's fruit bats into the future.

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.

Reduced exploitation is associated with an altered sex ratio and larger length at maturity in southwest Pacific (east Australian) Pomatomus saltatrix

Pomatomus saltatrix is an important recreational fishing species with seven major populations worldwide. The reproductive biology of the southwest Pacific Ocean (east Australian) population is uncertain, with both an extended spawning and multiple spawning periods previously hypothesised. Here we demonstrate an altered sex ratio biased towards females and a larger length at 50% maturity (L50) compared to those recorded for the population 40 years ago, before comprehensive management strategies were implemented. We also report a second, previously undescribed, late-summer spawning event which was identified by analysing patterns in a gonadosomatic index across the whole population and an historical larval fish database. P. saltatrix are capable of spawning multiple times per season with estimates of batch fecundity ranging from 99,488 to 1,424,425 eggs per fish. When combined with the length frequency distribution of the population, the majority of eggs (64%) were shown to be produced by fish ≤40 cm fork length (FL). L50 was estimated at 30.2 and 31.5 cm FL for male and female P. saltatrix respectively, 4 cm larger than 40 years ago. The sex ratio of the population was found to have significantly shifted over the last 40 years from an equal sex ratio to a female dominated population (1.58 females:1 male). These dramatic alterations to the sex ratio and L50 highlights the value of monitoring the reproductive biology of exploited fish populations to ensure that management plans remain appropriate.

Digital Image Analysis as a Technique for Alewife Fecundity Estimation in a New Hampshire River

AbstractFecundity estimates are important in fisheries management to determine the reproductive potential and spawning stock biomass of a population. Traditional methods for determining these estimates, however, have been time consuming and tedious, often requiring long‐term sample storage in toxic preservatives. Recently, studies incorporated the use of scanners and image analysis software to produce equally reliable fish fecundity estimates. This study was undertaken to demonstrate the application of this technique with Alewife Alosa pseudoharengus, “a species of concern.” Ovaries were collected from fish ranging in size from 25 to 34 cm throughout their annual spawning migration (Newmarket, New Hampshire) and used to compare fecundity estimated gravimetrically following long‐term storage and by use of a flatbed scanner. Gonadosomatic indices were calculated throughout the collection period but were not found to differ over time. Comparisons within ovaries demonstrated that oocyte size and number did not differ among anterior, center, and posterior sections. Fecundity estimates did not differ between the two methods and increased with fish age and size ranging from 121,000 and 130,200 oocytes/female (25 cm) to 332,500 and 364,900 oocytes/females (34 cm), respectively. These results demonstrate that fecundity estimates using digital image analysis software were equally reliable as those produced by traditional methods but were generated more quickly and with less reliance on toxic preservatives.

Reproduction of invasive Loricariichthys platymetopon Isbrücker & Nijssen, 1979 (Actinopterygii, Loricariidae) on the upper Paraná River floodplain

Loricariichthys platymetopon ocorria originalmente nos rios Uruguai, Paraguai e baixo Paraná. Com a formação do reservatório de Itaipu em 1982, invadiu e colonizou o alto rio Paraná. Usando os dados obtidos trimestralmente em nove pontos de amostragem na planície de inundação do alto rio Paraná, foram caracterizadas as fases reprodutivas e células germinativas das fêmeas de L. platymetopon. Além disso, foram verificados: a variação no diâmetro dos oócitos, a fecundidade dos lotes, a fecundidade relativa dos lotes por comprimento padrão e peso total e os locais de reprodução na planície de inundação do alto rio Paraná. Foram registrados os estágios: oogônia única, cistos de oogônias e oócitos, oócitos de crescimento primário inicial, intermediário e final, oócitos de crescimento completo e oócitos maduros. As fases reprodutivas foram validadas pelos atributos das células germinativas e as fêmeas foram registradas nas seguintes fases: desenvolvimento, apto à desova, regressão e regeneração. O diâmetro dos oócitos variou de 100 a 4.100 µm. A fecundidade do lote variou de 372 a 1.392 oócitos.g-1 e a estimativa da fecundidade relativa do lote por comprimento padrão foi de 16 a 49 oócitos.cm-1 e, em peso foi de 3,6 a 6,4 oócitos.g-1. Os padrões reprodutivos de L. platymetopon na planície de inundação do alto rio Paraná mostraram os locais onde a atividade reprodutiva é mais intensa (lagoas do Guaraná, das Garças e Fechada e rio Baía) e locais onde é menos intensa (rios Ivinheima e Paraná). Assim, a resistência biótica do rio Ivinheima, devido à integridade desses ambientes nessa área, que faz parte da Área de Proteção Ambiental das Ilhas e Várzeas do Rio Paraná, tem impedido o sucesso reprodutivo desta invasora.

Fecundidad en gónadas maduras de Haliotis fulgens y Haliotis corrugata (Vetigastropoda)

Background: The term fecundity in abalone is defined according to an estimate of its absolute fecundity, which is the number of mature oocytes present in the gonad, or as potential fecundity, i.e., the total number of oocytes present in the gonad. In Mexico, few studies have estimated the fecundity of mollusks and these have been performed on gonads in different phases of gonadal development, obtaining values that are very different or overestimated, for example, values ranging from 80000 to 22 million oocytes in a gonad. Goals: Estimate the fecundity of Haliotis fulgens (blue abalone) and Haliotis corrugata (yellow abalone), using ma­ture gonads and a particle counter (Multisizer 3) to count only mature oocytes. Methods: Each month from October 2011 to February 2013, 30 adult organisms of each species were collected in two localities of Baja California Sur, Mexico (La Bocana and Bahia Tortugas). A histological analysis identified those that were mature females. To obtain the number of eggs per gram, triplicate oocyte counts were performed in a coulter counter Multisizer 3, in a solution of 4 g wet weight of mature oocytes diluted to 50 mL of filtered seawater (μm). Absolute fecundity was calculated by multiplying the total weight of the gonad by the number of mature oocytes present in one gram of oocytes. Results: The fecundity in La Bocana was found to be 2x106 eggs in H. corrugata and H. fulgens, while in Bahia Tortugas it was 4x106 eggs in H. fulgens. Conclusions: This study suggests that estimating absolute fecundity in species with partial spawning, such as H. fulgens and H. corrugata, should be per­formed on all females regardless of the degree of gonadal development. However, only mature oocytes should be considered as an indicator of absolute fecundity. Therefore, the use of an apparatus that counts and measures mature oocytes, such as a particle counter, facilitates and guarantees a good estimate of fecundity.

Evaluation of the use of portable ultrasonography to determine pregnancy status and fecundity in bonnethead shark Sphyrna tiburo.

This study examined the usefulness of portable ultrasonography in accurately predicting pregnancy and fecundity in the bonnethead shark Sphyrna tiburo by comparing ultrasound-obtained data with those obtained from animal dissection, the gold standard for elasmobranch reproduction studies. Mature female S. tiburo (n = 66) were collected throughout the period of reproduction and examined via portable ultrasonography using two different ultrasound transducers (8-5 MHz linear array transducer and a 5.0-2.5 MHz curvilinear array transducer) to determine pregnancy status and fecundity. Ultrasound-derived data were compared with validated assessments of pregnancy and litter size obtained using animal dissection to determine the level of agreement between the two approaches. Overall, there was strong agreement (90.9%) between pregnancy determinations obtained using ultrasonography and dissection. However, the effectiveness of portable ultrasonography in accurately determining specific stages of maturity and pregnancy differed slightly between transducer types (linear = 61.3%; curvilinear = 88.9%). Measurements of fecundity also agreed well between ultrasonography and dissection and there were no significant differences between mean fecundity estimates obtained using the two methods. In general, portable ultrasonography was found to be a good alternative to lethal sampling and animal dissection in obtaining reproductive data critical for the management and conservation of elasmobranchs. Special attention should be given to factors that can influence the reliability of ultrasound-derived data such as transducer type, embryo size and sound wave interference due to gut contents.

A model-based high throughput method for fecundity estimation in fruit fly studies

ABSTRACTThe ability to quantify fecundity is critically important to a wide range of experimental applications, particularly in widely-used model organisms such as Drosophila melanogaster. However, the standard method of manually counting eggs is time consuming and limits the feasibility of large-scale experiments. We develop a predictive model to automate the counting of eggs from images of eggs removed from the media surface and washed onto dark filter paper. Our method uses the simple relationship between the white area in an image and the number of eggs present to create a predictive model that performs well even at high egg densities where clumping can complicate the individual identification of eggs. A cross-validation approach demonstrates our method performs well, with a correlation between predicted and manually counted values of 0.88. We show how this method can be applied to a large data set where egg densities vary widely.

Life history traits of rare Antarctic dragonfishes from the Weddell Sea

AbstractThe life history traits of bathydraconids, deep-living fishes distributed all around the Antarctic continent, are poorly known. In particular, very few data are available on the relatively rare genera Akarotaxis and Bathydraco. With the aim to fill this gap, sagittal otoliths and gonads were analysed to assess individual age and reproductive features of Akarotaxis nudiceps (Waite, 1916), Bathydraco macrolepis Boulenger 1907 and Bathydraco marri Norman, 1938 collected in the Weddell Sea. Based on the annual growth increment patterns, age estimates ranged between 6–11, 5–11 and 8–11 years for A. nudiceps, B. macrolepis and B. marri, respectively. Most of the gametogenetic processes could be described based on gonad histology for both sexes. Females shared the reproductive features commonly reported in notothenioids, such as group-synchronous ovary development and prolonged gametogenesis. Total fecundity estimates were comparable between the two species of Bathydraco (1500–2500 eggs/female), whereas that of Akarotaxis was one order of magnitude smaller (200–250 eggs/female). Consistently, the mean size of late vitellogenic oocytes showed an opposite trend, being 1.6–1.8 mm in Bathydraco and 2.2 mm in Akarotaxis.

Using ring-recovery and within-season recapture data to estimate fecundity and population growth.

Tag‐recovery data from organisms captured and marked post breeding are commonly used to estimate juvenile and adult survival. If annual fecundity could also be estimated, tagging studies such as European and North American bird‐ringing schemes could provide all parameters needed to estimate population growth. I modified existing tag‐recovery models to allow estimation of annual fecundity using age composition and recapture probabilities obtained during routine banding operations of northern pintails (Anas acuta) and dark‐eyed juncos (Junco hyemalis), and I conducted simulations to assess estimator performance in relation to sample size. For pintails, population growth rate from band‐recovery data (λ = 0.93, SD: 0.06) was similar but less precise than count‐based estimates from the Waterfowl Breeding Pair and Habitat Survey (λ: 0.945, SE: 0.001). Models with temporal variation in vital rates indicated that annual population growth in pintails was driven primarily by variation in fecundity. Juncos had lower survival but greater fecundity, and their estimated population growth rate (λ: 1.01, SD: 0.19) was consistent with count‐based surveys (λ: 0.986). Simulations indicated that reliable (CV < 0.10) estimates of fecundity could be obtained with >1,000 within‐season live encounters. Although precision of survival estimates depended primarily on numbers of adult recoveries, estimates of fecundity and population growth were most sensitive to total number of live encounters. Synthesis and applications: Large‐scale ring‐recovery programs could be used to estimate annual fecundity in many species of birds, but the approach requires better data curation, including accurate assessment of age, better reporting of banding totals, and greater emphasis on obtaining and reporting within‐season live encounters.

Spatiotemporal variability in the reproductive dynamics of Skipjack Tuna (Katsuwonus pelamis) in the eastern Pacific Ocean

The reproductive dynamics of skipjack tuna (Katsuwonus pelamis) were investigated by sampling 8136 fish caught by purse-seine vessels in the eastern Pacific Ocean from January 1996 to January 1998. The overall sex ratio deviated significantly from the expected 1:1 ratio, with a greater number of males. Histological evaluations of ovaries from 3732 females provided the foundation for the estimates of length-specific reproductive characteristics. Spawning was widespread from about 19 °N to 12 °S and from 79 °W to 136 °W, and continuous throughout the year between about 15 °N and 10 °S. Spawning was observed for fish captured in unassociated sets, floating-object sets, and dolphin sets. Although spawning occurred from 24 °C to 30 °C, 76.9% took place between 26 °C and 29 °C. Results of fitting a general additive model to the maturity-at-length data indicated significant spatial variation in maturity, with estimated lengths at 50% maturity of 56 cm north of 15 °N, 53 cm between 15 °N and 5 °S, and 47 cm south of 5 °S. The significant spatial variation in estimates of relative fecundity (oocytes per gram of body weight) is attributed to the differences between relative fecundities north of 15 °N and between 15 °N and 5 °S. The estimated average batch fecundity, based on counts of late-stage migratory-nucleus or hydrated stages of oocytes from 129 fish, was 296,475 oocytes, and the estimated mean relative fecundity was 54.9 oocytes per gram of body weight. The estimated fraction of mature females in the population spawning per day was 0.21, equivalent to a spawning frequency of 4.76 d, whereas for actively spawning females, the fraction spawning per day was 0.85, equivalent to a mean spawning interval of 1.18 d.

Age, Growth, and Reproduction of Vermilion Snapper in the North‐Central Gulf of Mexico

AbstractVermilion Snapper Rhomboplites aurorubens is a commonly harvested species of reef fish in the northern Gulf of Mexico (GOM) and supports large commercial and recreational fisheries. Vermilion Snapper (139–535 mm TL) were collected from May 2015 through October 2016 from artificial and natural reefs in the north‐central GOM. Ages ranged from 0.8 to 13 years, and there was no significant difference in growth between males and females. Nonlinear curve fitting was used to estimate growth parameters and Akaike information criterion (AIC) was used to determine relative model fit. The two‐parameter von Bertalanffy growth function provided the best model fit and lowest ΔAIC score. Histological examination indicated that Vermilion Snapper are batch spawners with asynchronous oocyte development. Additionally, 17% of female Vermilion Snapper in the actively spawning subphase had 24‐h postovulatory follicles (POF) suggesting daily spawning is occurring. No immature fish of either sex were collected during this study. Both histologically determined phases and gonadosomatic index patterns defined a spawning season occurring from April through September. The spawning interval for Vermilion Snapper, 1.3 and 2.1 d, was estimated using the hydrated oocyte and POF methods, respectively. Batch fecundity estimates from 5,497 to 284,468 eggs per batch were determined using fish macroscopically classified as actively spawning (n = 25), and total annual fecundity was estimated to range from 450,754 to 32,549,776 eggs per spawning season. Mean relative batch fecundity was 70.7 eggs/g of gonad‐free body weight. Estimates from this study can be directly incorporated into population assessments and provide a region‐specific overview of the life history for the Vermilion Snapper from the north‐central GOM.

A state-dependent model for assessing the population consequences of disturbance on income-breeding mammals

Human activities continue to expand in marine and terrestrial environments, leading to increased interactions with wildlife that can have negative impacts on population dynamics. Approaches for quantifying how these interactions translate to population-level effects are therefore crucial for effective management practices and balancing human-wildlife tradeoffs. We developed a method using state-dependent behavioral theory implemented via Stochastic Dynamic Programming (SDP) for predicting the population consequences of disturbance on the physiology and reproductive behavior of an income-breeding mammal, using California sea lions (Zalophus californianus) as a motivating species. Emergent properties of the model included reproductive characteristics associated with long-lived species, such as variation in the age at first reproduction, early termination of pregnancy, and skipped breeding. In undisturbed model simulations, reproductive rates and the average wean date were consistent with empirically-derived estimates from sea lions and other marine mammals, highlighting the utility of this model for quantifying fecundity estimates of data-deficient species and addressing fundamental ecological processes. In disturbed model simulations, exposure to prolonged, repetitive disturbances negatively impacted population growth; in addition, short, infrequent disturbances had the potential for adverse effects depending on the behavioral response of sea lions and the probability of being disturbed. The adverse effect of disturbance on population dynamics was due to a combination of reduced pup recruitment (survival to age one) resulting from a lower wean mass and increased abortion rates that led to skipped reproductive years, both of which have been documented for marine mammal populations experiencing natural fluctuations in prey availability. The derivation of state- and time-dependent reproductive decisions using an SDP model is an effective approach that links behavioral and energetic effects at the individual level to changes at the population level, and one that serves a dual purpose in the ability to quantify basic biological parameters and address ecological questions irrespective of disturbance.

Egg masses of some stream‐dwelling caddisflies (Trichoptera: Hydrobiosidae) from Victoria, Australia

AbstractEggs are a largely neglected life stage in most ecological studies of aquatic insects, despite the importance of oviposition behaviour and fecundity estimates for many research questions. Incorporating egg stages into ecological research requires that ecologists can identify and quantify eggs, but descriptions of eggs and egg masses are scarce for many groups and particularly for Australian taxa. This paper focusses on stream‐dwelling caddisflies in the family Hydrobiosidae and provides species‐level identifications, morphological descriptions and images of egg masses of some species that commonly occur in south‐eastern Australia. All the species we identified laid plaque‐shaped egg masses attached to the underside of river rocks that protrude above the water surface. These egg masses can be identified in the field with the naked eye or the aid of a low‐magnification hand lens. Interspecific variations in egg mass morphology were primarily thickness and firmness of the spumaline layer, egg mass size and arrangement of eggs within the mass. We also provide some ecological information on clutch sizes and the physical characteristics of oviposition sites, and we discuss various ways in which these taxa could be exploited as model systems for ecological research.

Banding age ratios reveal prairie waterfowl fecundity is affected by climate, density dependence and predator–prey dynamics

Abstract Fecundity estimates for demographic modelling are difficult to acquire at the regional spatial scales that correspond to climate shifts, land use impacts or habitat management programmes. Yet they are important for evaluating such effects. While waterfowl managers have historically used harvest‐based age ratios to assess fecundity at continental scales, widely available age ratios from late summer banding (ringing) data present an underutilized opportunity to examine a regional fecundity index with broad temporal replication. We used age ratios from banding data and hierarchical mixed‐effect models to examine how fecundity of five North American dabbling duck species was affected by temporal variation in hydrological cycles, intra‐ and interspecific density dependence and alternate prey availability, and whether those relationships were consistent across a broad geographic area. Model‐estimated fecundity was within the range of traditional harvest‐based fecundity estimates for each species. Ecological covariates explained between 16% and 53% of the temporal variation in fecundity, dependent on species. Increasing wetland inundation and an indicator of vole population irruptions were consistent predictors of increasing fecundity across all species. Species exhibited mixed positive and negative responses to interspecific and intraspecific breeding pair densities hypothesized to affect nest and brood survival respectively, highlighting the importance of integrating brood survival into fecundity metrics for precocial species. Declines in fecundity over time and across space at more northern latitudes may reflect stronger policies for grassland and wetland protection in the U.S. versus Canadian portions of the prairies over the time period of our study. Maintaining the capacity of less permanent basins to rehydrate in wetter periods through easement protection benefits fecundity, particularly for late‐nesting species that acquire a greater proportion of their reproductive energy on the breeding grounds. Synthesis and applications. Age ratios derived from postbreeding banding operations allowed us to attribute variation in waterfowl fecundity to temporal ecological variables. Effects of habitat management for waterfowl may be masked unless analysts account for this temporal variation. Postbreeding‐pulse age ratios at capture could be useful as fecundity metrics in integrated population models and for evaluating population dynamics of extensively banded nongame species, especially if adjusted for capture vulnerability using within‐season recapture data.

Fecundity of Morocco Dentex Dentex maroccanus Valenciennes, 1830 Distributed in Izmir Bay (Central Aegean Sea of Turkey)

In this study, the reproductive properties of the Dentex maroccanus species distributed in the Aegean Sea were determined. A total of 439 fish were collected during the period from December 2012 to March 2014 from the commercial fishers who seasonally hunt in the Foça-Mordoğan region (İzmir, Turkey) were examined. After the measurement of the total lengths and body and gonad weights of the fish samples in the laboratory, their sexes were identified, which revealed that 140 of the samples were male, 206 of the samples were female and 93 of the sample were undeterminated. The female:male ratio was 1.5:1. The 5-point maturity phase discrimination method developed by Holden and Raitt for maturity stages in 1974 was macroscopically examined for female and male fish specimens. A total of 16 ovaries, which were determined to be at the 3rd and 4th stages of maturity according to the method, were used to determine fecundity. The gonadosomatic index values that were calculated based on the seasons revealed that the reproductive period of the species was summer (2.87) and autumn (2.10). The first maturation length for the species was 13.4 cm. Estimates of total fecundity varied between 74252 and 201187 eggs (mean: 123263±44586). There was an exponential relationship between fecundity and total length as F = 10.643L3.111. The diameter of the mature eggs ranged from 0.49 mm to 0.67 mm (mean: 0.59±0.06 mm).

Pollination and reproduction of an invasive plant inside and outside its ancestral range

Comparing traits of invasive species within and beyond their ancestral range may improve our understanding of processes that promote aggressive spread. Solanum elaeagnifolium (silverleaf nightshade) is a noxious weed in its ancestral range in North America and is invasive on other continents. We compared investment in flowers and ovules, pollination success, and fruit and seed set in populations from Arizona, USA (“AZ”) and Greece (“GR”). In both countries, the populations we sampled varied in size and types of present-day disturbance. Stature of plants increased with population size in AZ samples whereas GR plants were uniformly tall. Taller plants produced more flowers, and GR plants produced more flowers for a given stature and allocated more ovules per flower. Similar functional groups of native bees pollinated in AZ and GR populations, but visits to flowers decreased with population size and we observed no visits in the largest GR populations. As a result, plants in large GR populations were pollen-limited, and estimates of fecundity were lower on average in GR populations despite the larger allocation to flowers and ovules. These differences between plants in our AZ and GR populations suggest promising directions for further study. It would be useful to sample S. elaeagnifolium in Mediterranean climates within the ancestral range (e.g., in California, USA), to study asexual spread via rhizomes, and to use common gardens and genetic studies to explore the basis of variation in allocation patterns and of relationships between visitation and fruit set.

Atlantic mackerel daily spawning dynamics and implications for batch fecundity estimations

Abstract The present study contributes to a better understanding of the daily spawning dynamics of southern NEA mackerel (Scomber scombrus) with implications for the estimation of batch fecundity. It shows that there is a time window during the day, mainly in the afternoon, during which the advanced oocyte mode in imminent spawners separates from the remaining, smaller oocytes. This synchronicity in the separation of the spawning batch amongst imminent spawners corroborates evidence for the existence of daily spawning synchronicity in the population. This is particularly important for applications of the daily egg production method, DEPM, because such pattern facilitates both the ageing of eggs for the estimation of the daily egg production at sea and the ageing of postovulatory follicles for the estimation of spawning frequency. For NEA mackerel, batch fecundity could only be measured when a clear hiatus was established between the spawning batch and the smaller oocytes. Hydrated females that do not show such hiatus would not be valid for batch fecundity measurements suggesting that the “hydrated oocytes method” is not fully applicable for this stock. Knowing the time of day at which the batch is separated, will facilitate the sampling of valid females for the estimation of batch fecundity.

Reproductive biology of Klein’s sole, Synapturichthys kleinii (Actinopterygii: Pleuronectiformes: Soleidae), off Tunisian coast (central Mediterranean)

Background. Klein&rsquo;s sole, Synapturichthys kleinii (Risso, 1827), is a rare fish, included in the IUCN Red List as Data Deficient, and its biology is poorly known. Biological investigations of S. kleinii have been surprisingly rare in Tunisian waters. In the presently reported study, we investigated the reproductive period, size at first sexual maturity, and fecundity of S. kleinii along the Tunisian waters, with the aim of achieving the first complete and comprehensive description of the reproduction of this fish in the Mediterranean Sea. Materials and methods. A total of 294 specimens of S. kleinii were sampled over two years, off the Tunisian coasts. Sex ratio was estimated through the seasons of the year and the size classes. The stage of maturity was determined macroscopically only for females. Monthly gonadosomatic index (GSI), monthly hepatosomatic index (HSI), and condition factor (K) were calculated for males and females of S. kleinii. Size at first maturity was estimated only for females during the spawning season. Eighteen mature females at spawning stage were collected, weighed, and fixed in 4% formaldehyde solution for fecundity estimation. Results. Annual sex ratio showed significant differences between males and females. In specimens exceeding 27 cm in total length females outnumbered males significantly. The Klein&rsquo;s sole reproduction period started in October and ended in January. The gonadosomatic index reached highest values in November for females and males. Females attained sexual maturity at 20.53 cm total body length (TL). Total fecundity ranged from 3647 to 23 174 eggs. We found a low correlation coefficient between total fecundity and total length, but a high correlation coefficient between eviscerated weight and ovary weight. Conclusion. Our results constitute a preliminary baseline for monitoring changes in the biological indexes linked to the reproduction cycle and length at first sexual maturity of S. kleinii. The presently acquired data will enable biologists to assess the status of this fish and develop culture technology in natural waters and will be useful for the fishery biologists and conservation biologists, for successful development, management, production, and ultimate conservation of this favoured Tunisian food fish.