122,942 research outputs found

    Factors determining spawning success in Penaeus monodon Fabricius

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    Spawning success in relation to the size of spawner, clumping of eggs, percentage of spawning and frequency of spawning was studied in Penaeus monodon collected off Tamil Nadu, India. The results indicated positive correlation between the size of spawner and the fecundity and hatching percentage, but not the start of hatching. Hatching characteristics were influenced by clumping of eggs or abortive spawning; the greater the clumping, the longer the time taken for hatching, resulting in a lower hatching percentage. The start of hatching time increased when the frequency of spawning increased. Lower hatching rate was observed as the frequency of spawning increased

    Biomass estimates of Pacific herring, Clupea pallasi, in California from the 1989-90 spawning-ground surveys

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    The 1989-90 spawning biomass estimate of Pacific herring, Clupea pallasi, from spawning-ground surveys in San Francisco Bay was 71,000 tons, a 5,000 ton increase over the 1988-89 biomass estimate of 66,000 tons. The San Francisco Bay herring biomass has been on an upward cycle since 1984, and results from spawning-ground surveys indicated that the population was at its highest level in eight years. In Tomales Bay the 1989-90 herring spawning biomass estimate was 345 tons. This was the third consecutive poor season. Herring have nearly abandoned Tomales Bay, and reduced freshwater in flows due to the current drought condition in California were the probable cause for the change in spawning behavior. An additional 445 tons were found in Bodega Bay by hydroacoustic surveys. The total herring biomass estimate for Tomales-Bodega area was 790 tons. January was the month of peak spawning activity in San Francisco Bay, with 30,000 tons of herring spawning during the month. In Tomales there was only one spawning run; it occurred on January 31, 1990. In San Francisco Bay, 67% of all spawning occurred along the San Francisco waterfront, and only 6% of all spawning activity was in the northern part of the bay. No spawning was found near Tiburon, Belvedere, Richmond, Berkeley, Candlestick Point, Sierra Point, Oyster Point, or Coyote Point. A total of 3.5 million m2 of eelgrass, Zoster marina, was measured in Tomales Bay this season, a decline of about 10% over the past two seasons. Eelgrass density kg/m2 did not change significantly this season. (34pp.

    Spawning and early development of captive yellowfin tuna (Thunnus albacares)

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    In this study we describe the courtship and spawning behaviors of captive yellowfin tuna (Thunnus albacares), their spawning periodicity, the influence of physical and biological factors on spawning and hatching, and egg and early-larval development of this species at the Achotines Laboratory, Republic of Panama, during October 1996 through March 2000. Spawning occurred almost daily over extended periods and at water temperatures from 23.3° to 29.7°C. Water temperature appeared to be the main exogenous factor controlling the occurrence and timing of spawning. Courtship and spawning behaviors were ritualized and consistent among three groups of broodstock over 3.5 years. For any date, the time of day of spawning (range: 1330 to 2130 h) was predictable from mean daily water temperature, and 95% of hatching occurred the next day between 1500 and 1900 h. We estimated that females at first spawning averaged 1.6−2.0 years of age. Over short time periods (<1 month), spawning females increased their egg production from 30% to 234% in response to shortterm increases in daily food ration of 9% to 33%. Egg diameter, notochord length (NL) at hatching, NL at first feeding, and dry weights of these stages were estimated. Water temperature was significantly, inversely related to egg size, egg-stage duration, larval size at hatching, and yolksac larval duration

    Seasonal, diel, and lunar spawning periodicities and associated sound production of white seabass (Atractoscion nobilis)

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    Spawning periodicities of white seabass (Atractoscion nobilis) were evaluated by observing spawning behavior, by collecting eggs, and monitoring recognizable sounds produced during the release of gametes. A total of 297 spawning events were documented from 15 male and 47 female white seabass contained within the seminatural confines of a 526-m3 net pen located in Catalina Harbor, Santa Catalina Island, California. Consistent spawning occurred from March through July 2001−03, and peaked in May at a photoperiod of 14 hours. Most spawning occurred within the 2-hour period following sunset or from 19:00−20:00 hours Pacific Standard Time. White seabass spawned at every phase of the lunar cycle; but an increase in successive spawning events followed the new moon. Most spawning occurred in water temperatures from 15 to 18°C, and there was no apparent correlation with tidal cycles. Seasonal and diel spawning periods were directly correlated with increases in the rate, intensity, and variety of white seabass sounds; this correlation may indicate that sounds function to enhance reproductive success. These findings can be extended to further develop seasonal fishery regulations and to better comprehend the role of sound in the reproduction of sound-producing fishes

    Biomass estimates of Pacific herring, Clupea harengus pallasi, in California from the 1987-88 spawning-ground surveys

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    The 1987-88 spawning biomass estimate of Pacific herring, Clupea harengus pallasi, in San Francisco Bay is nearly 69,000 tons. This is the fourth consecutive year that the San Francisco Bay population has increased, after reaching a low point of 40,000 tons in 1984. In Tomales Bay the 1987-88 herring spawning biomass was estimated at 2,061 tons. During the past five seasons, the Tomales Bay spawning biomass has been low in even years and high in odd years, indicating that spawning herring are not returning to Tomales Bay consistently. In San Francisco Bay, over 42,000 tons of herring spawned in January. Similarly, 90% of Tomales Bay herring spawned in January. No spawns were found during March in either bay. For the first time, in San Francisco Bay, no herring spawned in the Belvedere, Tiburon, or Angel Island areas. In addition, herring spawning was found in the Oakland-Alameda area for the first time and over 95% of all spawning occurred in the southern part of San Francisco Bay. During the past six seasons in San Francisco Bay, over 70% of all spawning escapement has been in the southern part of the bay. For the nine seasons prior to that, 94% of all spawning escapement was in the northern part of the bay. (31pp.

    Diurnal periodicity of activity in the spawning perch P. fluviatilis L. [Translation from: Kalamies 1972(7) 3, 1972]

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    Diurnal periodicity of spawning in the perch so far are rather meagre and found to be partly contrary to experiences of perch anglers. Therefore a study was made on the spawning during a 5-day period in the spring of 1971 in the Kuusamo area. Observations were made during the main spawning season, between 4- 9 June 1971. The perch were often measured, weighed and then released back into the water. The differences between spawning and non-spawning perch were studied as well as the time of roe discharge in a 24 hour period. Activity and environmental factors such as light intensity were also taken into consideration

    Biomass estimates of Pacific herring, Clupea pallasi, in California from the 1990-91 spawning-ground surveys

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    The spawning biomass of Pacific herring, Clupea pallasi, estimated from spawning-ground surveys in San Francisco Bay declined to 45,850 tons this season, following a peak of 71,000 tons in the 1989-90 season. This is the first major decline since the 1983-84 El Nino. In Tomales Bay the 1990-91 spawning biomass more than doubled to 779 tons. The spawning biomass has increased the past two seasons, while the fishery has been closed. There was no biomass estimate for Bodega Bay, but an additional 95 tons of herring were caught in Bodega Bay this season. The total herring biomass for the Tomales- Bodega area is a minimum of 874 tons. Humboldt Bay was surveyed by the Department for the first time this season, and spawning biomass was estimated to be 400 tons. January was the month of peak spawning activity in all spawning areas surveyed. In San Francisco Bay, 62% of all spawning occurred alonq the San Francisco waterfront; for the first time there was no significant spawninq in the northern part of the bay. Nearly 70% of the spawning activity in San Francisco Bay occurred on January 3-6, 1991. A total of 3.5 million m2 of eelgrass, Zostera marina, was measured in Tomales Bay this season. The change in eelgrass density this season varied from bed to bed, however the overall density of eelgrass in Tomales Bay declined. (44pp.

    The effect of temperature on the duration of spawning markers—migratory-nucleus and hydrated oocytes and postovulatory follicles—in the multiple-batch spawner Japanese flounder (Paralichthys olivaceus)

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    The duration of spawning markers (e.g. signs of previous or imminent spawnings) is essential information for estimating spawning frequency of fish. In this study, the effect of temperature on the duration of spawning markers (i.e., oocytes at early migratory nucleus, late migratory nucleus, and hydrated stages, as well as new postovulatory follicles) of an indeterminate multiple-batch spawner, Japanese f lounder (Paralichthys olivaceus), was evaluated. Cannulation was performed to remove samples of oocytes, eggs, and postovulatory follicles in individual females at 2–4 hour intervals over 27–48 hours. The duration of spawning markers was successfully evaluated in 14 trials ranging between 9.2° and 22.6°C for six females (total length 484–730 mm). The durations of spawning markers decreased exponentially with temperature and were seen to decrease by a factor of 0.16, 0.36, 0.30, and 0.31 as temperature increased by 10°C for oocytes at early migratory nucleus, late migratory nucleus, and hydrated stages, and new postovulatory follicles, respectively. Thus, temperature should be considered when estimating spawning frequency from these spawning markers, especially for those fish that do not spawn synchronously in the population

    Baltic cod reproduction in the Gotland Basin: annual variability and possible causes

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    Baltic cod spawning takes place in the deep basins and reproduction success is mainly related to environmental conditions (salinity and oxygen regimes, i.e. the 'reproduction volume'). Due to the Baltic Sea heterogeneity, cod reproduction success in the Southem and Centrat Baltic spawning grounds can differ significantly. Recent oceanographic changes i.e. decrease of water exchange and stagnation, as weil as a strong reduction of spawning stock caused the diminishing of the reproduction potential of the Gotland spawning grounds. The Gotland spawning grounds belong to four main cod spawning sites in the Baltic and historical analyses revealed that abundant generations of Baltic cod were produced when successful cod reproduction took place also in the Gotland Basin. Analyses of revised reproduction volume estimates for the Gotland Basin taking into account the spatial structure of hydrology in the basin during stagnation and aeration periods reveals high seasonal and inter-annual variability. To describe changes of abundance and distribution of the spawning stock and the recruits in relation to hydrographic conditions, results from trawl surveys carried out in 1975-1998 in the Gotland Deep are analyzed. In this analysis, the reproduction volume is used as a proxy for the environmental conditions

    Status of Pacific Mackerel spawning population, 1973

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    This is the first annual report of the status of the spawning population of the Pacific mackerel as required by Section 8388.3 of the Fish and Game Code. During 1972 and early 1973, several methods of determining population size were investigated as mechanisms for estimating the spawning population size of Pacific mackerel stocks north of Punta Eugenia, Baja California, and a method using tagging procedures proved to be the most acceptable. The estimate of the Pacific mackerel spawning population obtained by tagging procedures was 5,480 tons. This estimate agrees generally with those obtained from alternate methods in which previously computed spawning biomass estimates were correlated with partyboat catches in three different areas and the 1973 spawning biomass estimated from the resulting regression line. The estimates derived by these alternate methods are 6,970 tons, 4,730 tons, and 6,210 tons. All estimates are below the 10,000 ton spawning population minimum and thus there is no excess by which a harvest under Section 8388.5 of the Fish and Game Code could be allowed. (17pp.
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