Spawning seasons of Rasbora tawarensis (Pisces: Cyprinidae) in Lake Laut Tawar, Aceh Province, Indonesia

Rasbora tawarensis is an endemic freshwater fish in Lake Laut Tawar, Aceh Province, Indonesia. Unfortunately, its status is regarded a critical endangered with populations decreasing in recent years. To date no information on the spawning activities of the fish are available. Therefore, this study provides a contribution to the. knowledge on reproductive biology of R. tawarensis especially on spawning seasons as well as basic information for conservation of the species. Monthly sampling was conducted from April 2008 to March 2009 by using selective gillnets. The gonadosomatic index, size composition and sex ratio were assessed. The gonadal development was evaluated based on macroscopic and microscopic examinations of the gonads. The gonadosomatic index (GSI) varied between 6.65 to 18.16 in female and 4.94 to 8.56 for male. GSI of the female R. tawarensis was higher in March, September and December indicating the onset of reproductive seasons, the GSI and oocyte size being directly correlated with gonadal development stages. Although, a greater proportion of mature male than female was detected during the study, the sex ratio showed that the overall number of female was higher than male. The ovaries had multiple oocyte size classes at every stage of gonadal development, thus R. tawarensis can be classified as a group synchronous spawner or a fractional multiple spawner. The spawning seasons of R. tawarensis were three times a year and September being the peak of the reproductive season and the female was the predominant sex. This species is classified as a group synchronous spawner. (PDF contains 8 pages)

Studies of the sexual development and spawning of yellowfin tuna, Neothunnus macropterus, and skipjack, Katsuwonus pelamis, in three areas of the Eastern Pacific Ocean, by examination of gonads.

ENGLISH: Knowledge of the size and age at maturity, spawning seasons, and spawning areas of the tropical tunas supporting the fishery in the Eastern Pacific is an important part of the basic information required for understanding their life history, population structure, and fishery dynamics. Until a few years ago nothing was known of these matters. In 1947 the senior author and one of his colleagues (Schaefer and Marr 1948, Schaefer 1948) were able to demonstrate that both yellowfin tuna and skipjack spawn offshore from Central America at least during the late winter and spring months. During January to April many yellowfin tuna over about 70 cm. total length in commercial catches from that region were found to have gonads in advanced stages of maturity, and specimens caught during late June were found to be spent. Maturing skipjack were collected in late February, and spawned-out fish were observed in late March. Numerous very young juveniles of the yellowfin, down to 10 mm. in length, and two very young juvenile skipjack, were captured in this area between January and May. SPANISH: El conocimiento del tamaño y la edad que corresponden a la primera madurez sexual, así como de las estaciones y áreas de desove de los atunes tropicales que mantienen las pesquerías del Pacífico Oriental, constituyen parte importante de la información que es menester para comprender la historia natural, la estructura de la población y la dinámica de la pesquería. Hasta hace pocos años nada se sabía sobre el particular. En 1947 el autor principal y uno de sus colegas (Schaefer y Marr, 1948; Schaefer, 1948) pudieron demostrar que tanto el atún aleta amarilla como el barrilete desovan en el mar abierto, frente a América Central, por lo menos durante la última parte del invierno y en la primavera. De enero a abril encontraron que muchos de los atunes aleta amarilla de más de 70 cm. de longitud total, procedentes de las pescas comerciales de dicha región; tenían gónadas en avanzados estados de madurez, mientras que ejemplares pescados hacia fines de junio ya habían desovado. Se recolectaron barriletes en vías de maduración a fines de febrero, al paso que en los últimos días de marzo se encontraron especímenes que ya habían desovado. Numerosos ejemplares muy juveniles del atún aleta amarilla, tan pequeños como 10 mm., y dos barriletes también muy juveniles, fueron pescados en esta región entre enero y mayo. (PDF contains 65 pages.)

Two spawning stocks of icefish Neosalanx taihuensis revealed from annual reproductive cycle analyses

Neosalanx taihuensis were sampled from the Tian-e-zhou Oxbow from March 2006 through November 2007. Two separate spawning seasons were identified based on the annual reproductive cycles of the females, designated as the autumn-spawning season and the spring-spawning season. Lifespan of the offspring of the spring-spawning fish was 1 year, with them dying after the subsequent spring spawning. Autumn-spawned females seem to be the offspring of the spring-spawning fish, based on monthly changes in the length-frequency distributions. Spring-mature females had higher absolute fecundity, gonadosomatic index, and relative condition factor in 2007 than in 2006. Relative condition factor of the immature female offspring of spring-spawning fish was higher in 2007 than in 2006, portending a further increase in reproductive investment during the spring spawning of 2008. The increasing reproductive investment suggests that the population of N. taihuensis in the Tian-e-zhou Oxbow may be recovering from its recent decline.

Spawning season and temperature relationships for sardine (Sardina pilchardus) in the eastern North Atlantic

Spawning temperature preferences for sardine (Sardina pilchardus) in the eastern North Atlantic were determined from field data. These were compared with climatological temperature cycles (1986-2002) derived from satellite data by geographical region, to predict spawning seasons. Optimum spawning temperatures were determined as 14.0-15.0oC from the English Channel to Portugal and 16.0–18.0oC for all north-west African regions. Spawning seasons were closely related to the general latitudinal trend of the annual temperature cycle, with modification by upwelling in the western Iberian and north-west African regions. Some differences between temperature-based spawning season predictions and field observations were related to variations in seasonal plankton production. Correlations in the annual time-series of favourable spawning temperatures suggested relatively strong linkages between the southern areas from Portugal to Senegal. There was no consistent relationship between annual variations in duration of temperature-predicted spawning seasons and observed field abundance of eggs.

Importance of reservoir tributaries to spawning of migratory fish in the upper parana river

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

A new data source for fisheries resource assessment: genetic estimates of the effective number of spawners. Final Report to the Fisheries Research and Development Corporation.

The development of innovative methods of stock assessment is a priority for State and Commonwealth fisheries agencies. It is driven by the need to facilitate sustainable exploitation of naturally occurring fisheries resources for the current and future economic, social and environmental well being of Australia. This project was initiated in this context and took advantage of considerable recent achievements in genomics that are shaping our comprehension of the DNA of humans and animals. The basic idea behind this project was that genetic estimates of effective population size, which can be made from empirical measurements of genetic drift, were equivalent to estimates of the successful number of spawners that is an important parameter in process of fisheries stock assessment. The broad objectives of this study were to 1. Critically evaluate a variety of mathematical methods of calculating effective spawner numbers (Ne) by a. conducting comprehensive computer simulations, and by b. analysis of empirical data collected from the Moreton Bay population of tiger prawns (P. esculentus). 2. Lay the groundwork for the application of the technology in the northern prawn fishery (NPF). 3. Produce software for the calculation of Ne, and to make it widely available. The project pulled together a range of mathematical models for estimating current effective population size from diverse sources. Some of them had been recently implemented with the latest statistical methods (eg. Bayesian framework Berthier, Beaumont et al. 2002), while others had lower profiles (eg. Pudovkin, Zaykin et al. 1996; Rousset and Raymond 1995). Computer code and later software with a user-friendly interface (NeEstimator) was produced to implement the methods. This was used as a basis for simulation experiments to evaluate the performance of the methods with an individual-based model of a prawn population. Following the guidelines suggested by computer simulations, the tiger prawn population in Moreton Bay (south-east Queensland) was sampled for genetic analysis with eight microsatellite loci in three successive spring spawning seasons in 2001, 2002 and 2003. As predicted by the simulations, the estimates had non-infinite upper confidence limits, which is a major achievement for the application of the method to a naturally-occurring, short generation, highly fecund invertebrate species. The genetic estimate of the number of successful spawners was around 1000 individuals in two consecutive years. This contrasts with about 500,000 prawns participating in spawning. It is not possible to distinguish successful from non-successful spawners so we suggest a high level of protection for the entire spawning population. We interpret the difference in numbers between successful and non-successful spawners as a large variation in the number of offspring per family that survive – a large number of families have no surviving offspring, while a few have a large number. We explored various ways in which Ne can be useful in fisheries management. It can be a surrogate for spawning population size, assuming the ratio between Ne and spawning population size has been previously calculated for that species. Alternatively, it can be a surrogate for recruitment, again assuming that the ratio between Ne and recruitment has been previously determined. The number of species that can be analysed in this way, however, is likely to be small because of species-specific life history requirements that need to be satisfied for accuracy. The most universal approach would be to integrate Ne with spawning stock-recruitment models, so that these models are more accurate when applied to fisheries populations. A pathway to achieve this was established in this project, which we predict will significantly improve fisheries sustainability in the future. Regardless of the success of integrating Ne into spawning stock-recruitment models, Ne could be used as a fisheries monitoring tool. Declines in spawning stock size or increases in natural or harvest mortality would be reflected by a decline in Ne. This would be good for data-poor fisheries and provides fishery independent information, however, we suggest a species-by-species approach. Some species may be too numerous or experiencing too much migration for the method to work. During the project two important theoretical studies of the simultaneous estimation of effective population size and migration were published (Vitalis and Couvet 2001b; Wang and Whitlock 2003). These methods, combined with collection of preliminary genetic data from the tiger prawn population in southern Gulf of Carpentaria population and a computer simulation study that evaluated the effect of differing reproductive strategies on genetic estimates, suggest that this technology could make an important contribution to the stock assessment process in the northern prawn fishery (NPF). Advances in the genomics world are rapid and already a cheaper, more reliable substitute for microsatellite loci in this technology is available. Digital data from single nucleotide polymorphisms (SNPs) are likely to super cede ‘analogue’ microsatellite data, making it cheaper and easier to apply the method to species with large population sizes.

Designing marine fishery reserves using passive acoustic telemetry

Marine Fishery Reserves (MFRs) are being adopted, in part, as a strategy to replenish depleted fish stocks and serve as a source for recruits to adjacent fisheries. By necessity, their design must consider the biological parameters of the species under consideration to ensure that the spawning stock is conserved while simultaneously providing propagules for dispersal. We describe how acoustic telemetry can be employed to design effective MFRs by elucidating important life-history parameters of the species under consideration, including home range, and ecological preferences, including habitat utilization. We then designed a reserve based on these parameters using data from two acoustic telemetry studies that examined two closely-linked subpopulations of queen conch (Strombus gigas) at Conch Reef in the Florida Keys. The union of the home ranges of the individual conch (aggregation home range: AgHR) within each subpopulation was used to construct a shape delineating the area within which a conch would be located with a high probability. Together with habitat utilization information acquired during both the spawning and non-spawning seasons, as well as landscape features (i.e., corridors), we designed a 66.5 ha MFR to conserve the conch population. Consideration was also given for further expansion of the population into suitable habitats.

Life history aspects of 19 rockfish species (Scorpaenidae: Sebastes) from the Southern California Bight

The authors investigated various life history aspects of 19 rockfish species (Sebastes chlorostictus, S. constellatus, S. dalli, S. elongatus, S. ensifer, S. entomelas, S. flavidus, S. goodei, S. hopkinsi, S. levis, S. melanostomus, S. miniatus, S. ovalis, S. paucispinis, S. rosaceus, S. rosenblatti, S. rufus, s. saxicola, S. semicinctus) from the southern California Bight. These aspects included depth distribution, age-length relationships (of 7 species), length-weight relationships, size at first maturity, spawning season, and fecundity. Growth rates of female S. elongatus, S. hopkinsi, S. ova/is, S. saxicola, and S. semicinctus were higher than male conspecifics. Multiple spawning per season was found in 12 species. Generally, most species spawned between late winter and early summer, though there was some spawning within the genus throughout the year. Spawning season duration ranged from 2 (S. flavidus) to 10 months (S. paucispinis). Spawning seasons tended to start earlier in the year and be of longer duration in the southern California Bight, compared to published data on central California conspecifics. Males matured at a smaller length in 7 of the 17 species studied. Maximum fecundities ranged from 18,000 (S. dalll) to about 2,680,000 (S. levis). (PDF file contains 44 pages.)

Die Reproduktion von Dorschen (Gadus morhua L. und Gadus morhua callarias L. ) in der Ostsee unter besonderer Berücksichtigung der Arkonasee. Teil I: Allgemeiner Verlauf des jährlichen Reifeprozesses und der Laichaktivitäten in den verschiedenen Gebieten

From 1993 to 2003 special surveys were conducted to analyse temporal and spatial aspects of the spawning activities of cod in the Baltic Sea. The ICES advice for cod in the Baltic Sea is based on yearly stock assessments of two separate stocks the western (SD 22 – 24) and the eastern stock (SD 25 – 32). Both stocks are characterized by different spawning seasons. The general progression of the maturity suggests that two types of development can be distinguished. In the western Baltic Sea (SD 22) the maturity development is temporal stable, with a relative short, main spawning period from March to April - spring spawner. In the Arkona Sea and Bornholm Basin the main spawning season starts in June and probably finishes in September - summer spawner. The proportion of spawners in summer is significantly higher than in spring in the Arkona Sea and Bornholm Basin. This again underlines the importance of the Arkona Sea for the reproduction success of the eastern Baltic cod stock. The analysis furthermore show, that the proportion of male spawners was significantly higher than the proportion of female spawners in all areas and the investigated months. This observation suggests that the reproductive success is only limited by the number of female cod which participates in the spawning process.

Erste Ergebnisse zum Verlauf der Laichsaison von Dorschen in der westlichen Ostsee 1997

Investigations concerning the intensity and duration of spawning seasons of cod stocks are parts of the work of the reproductions ecology of commercial fish stocks in the Baltic Sea. The Institute of Baltic Fisheries Rostock has sampled and analysed data for this goal since 1992. The first data analyses for the spawning season 1997, sampled in the areas Kiel Bay, Mecklenburg Bay and Arkona Sea showed that the process of the spawning season is different compared to the years before. The spawning process starts earlier than the other years in Kiel Bay and Mecklenburg Bay. The results show that a high proportion of the spawning stock was part of the spawning process in this area. The Arkona Sea cod are regarded by ICES definition as belonging to the western cod stock. In this ICES sub-division only a low number of spawned cod was observed in March, the main spawning time of the western cod stock. Opposite to the theory of the stock units intensive spawning activities were observed in June as in the years before in the Arkona Sea.

Reproductive dynamics of female spotted seatrout (Cynoscion nebulosus) in South Carolina

We describe reproductive dynamics of female spotted seatrout (Cynoscion nebulosus) in South Carolina (SC). Batch fecundity (BF), spawning frequency (SF), relative fecundity (RF), and annual fecundity (AF) for age classes 1−3 were estimated during the spawning seasons of 1998, 1999, and 2000. Based on histological evidence, spawning of spotted seatrout in SC was determined to take place from late April through early September. Size at first maturity was 248 mm total length (TL); 50% and 100% maturity occurred at 268 mm and 301 mm TL, respectively. Batch fecundity estimates from counts of oocytes in final maturation varied significantly among year classes. One-year-old spotted seatrout spawned an average of 145,452 oocytes per batch, whereas fish aged 2 and 3 had a mean BF of 291,123 and 529,976 oocytes, respectively. We determined monthly SF from the inverse of the proportion of ovaries with postovulatory follicles (POF) less than 24 hours old among mature and developing females. Overall, spotted seatrout spawned every 4.4 days, an average of 28 times during the season. A chronology of POF atresia for water temperature >25°C is presented. Length, weight (ovary-free), and age explained 67%, 65%, and 58% of the variability in BF, respectively. Neither RF (number of oocytes/g ovary-free weight) nor oocyte diameter varied significantly with age. However, RF was significantly greater and oocyte diameter was smaller at the end of the spawning season. Annual fecundity estimates were approximately 3.2, 9.5, and 17.6 million oocytes for each age class, respectively. Spotted seatrout ages 1−3 contributed an average of 29%, 39%, and 21% to the overall reproductive effort according to the relative abundance of each age class. Ages 4 and 5 contributed 7% and 4%, respectively, according to predicted AF values.

Age and size composition, growth rate, reproductive biology, and habitats of the West Australian dhufish (Glaucosoma hebraicum) and their relevance to the management of this species

Samples of the commercially and recreationally important West Australian dhufish (Glaucosoma hebraicum) were obtained from the lower west coast of Australia by a variety of methods. Fish <300 mm TL were caught over flat, hard substrata and low-lying limestone reefs, whereas larger fish were caught over larger limestone and coral reef formations. Maximum total lengths, weights, and ages were 981 mm, 15.3 kg, and 39 years, respectively, for females and 1120 mm, 23.2 kg, and 41 years, respectively, for males. The von Bertalanffy growth curves for females and males were significantly different. The values for L∞, k, and t0 in the von Bertalanffy growth equations were 929 mm, 0.111/year, and –0.141 years, respectively, for females, and 1025 mm, 0.111/year, and –0.052 years, respectively, for males. Preliminary estimates of total mortality indicated that G. hebraicum is now subjected to a level of fishing pressure that must be of concern to fishery managers. Glaucosoma hebraicum, which spawns between November and April and predominantly between December and March, breeds at a wide range of depths and is a multiple spawner. The L50’s for females and males at first maturity, i.e. 301 and 320 mm, respectively, were attained by about the end of the third year of life and are well below the minimum legal length (MLL) of 500 mm. Because females and males did not reach the MLL until the end of their seventh and sixth years of life, respectively, they would have had, on average, the opportunity of spawning during four and three spawning seasons, respectively, before they reached the MLL. However, because G. hebraicum caught in water depths >40 m typically die upon release, a MLL is of limited use for conserving this species. Alternative approaches, such as restricting fishing activity in highly fished areas, reducing daily bag limits for recreational fishermen, introducing quotas or revising specific details of certain commercial hand-line licences (or doing both) are more likely to provide effective conservation measures.

On the identification of the early developmental stages of clupeiform fishes from Indian waters

Among about 65 species of clupeiform fishes present in the seas around India, most are distributed along both the east and west coasts and have similar spawning seasons and spawning grounds. The most difficult problem experienced with regard to the identification of their early developmental stages is the overlapping sets of diagnostic features among many species within the same genus as well as among species belonging to two or more genera. From studies carried out recently, the present paper sites a few instances wherein certain subtle characters have been used for distinguishing the early developmental stages of a few allied species.

Biology of Bombay duck, Harpodon nehereus (Ham., 1822), from Mumbai waters, India

Morphometric and meristic study of Harpodon nehereus (Hamilton, 1822) from Mumbai waters indicated that the specimens belonged to a homogenous population. Based on the meristic study, the fin formula can be written as B sub(23-269), D sub(12-139), P sub(11-139), V sub(9), A sub(13-15), C sub(19), L sub(40). Length-weight study revealed an allometric relationship, presented as Log W= -3.1362 + 3.6059 Log L. The analysis of food and feeding habits revealed the species to be voracious, carnivorous and cannibalistic, feeding mainly on Acetes spp., juveniles of H. nehereus itself, prawns and Coilia dussumieri. The feeding intensity was found to be the maximum during September and November, and also in mature specimens which may be the preparation for the ensuing spawning activity. Reproductive biology indicated two peak spawning seasons in November and March. However, the species as a whole has prolonged breeding season and spawning occurs throughout the year. Average fecundity was estimated as 314 ova/g body weight of fish and the length at which 50% of female specimens mature (Lc sub (50)) was calculated as 255 mm.

Observations on the ingression and distribution of larval prawns in the Nethravati-Gurupur estuary, Mangalore

The spatial and temporal distributions of larval prawns of penaeids and non-penaeids in the estuarine waters of Mangalore were studied. Larvae appear to be passively brought in by the incoming flood tides to the estuary, enjoy a wider distribution throughout the estuarine complex with abundance towards the mouth. The distribution of larval prawns was more in Nethravati than in the Gurupur stretch. The influence of temperature, hydrogen-ion-concentration, salinity and dissolved oxygen on the distribution of larvae in the estuaries is discussed. Inference on spawning seasons of commercially important prawns in the neighbouring waters has been arrived at based on their larval abundance.