Egg Retention Research Articles

Buoyancy and vertical distribution of Norwegian coastal cod (Gadus morhua) eggs from different areas along the coast

Abstract Stenevik, E. K., Sundby, S., and Agnalt, A. L. 2008. Buoyancy and vertical distribution of Norwegian coastal cod (Gadus morhua) eggs from different areas along the coast. – ICES Journal of Marine Science, 65: 1198–1202. There are significant genetic differences in coastal cod (Gadus morhua) along the Norwegian coast, and in order to maintain these differences, there must be mechanisms that ensure local retention of eggs and larvae in the spawning areas. The buoyancy of eggs from four different areas along the Norwegian coast was measured using a density gradient column, and the results from modelling experiments showed that in three of the groups (Tysfjord, Helgeland, and Øygarden), the buoyancy in combination with local hydrography would place the eggs in subsurface waters where retention is greater than in surface waters.

Does the fall phytoplankton bloom control recruitment of Georges Bank haddock, Melanogrammus aeglefinus, through parental condition?

In 2003, the Georges Bank stock of haddock ( Melanogrammus aeglefinus ) experienced the largest recruitment event recorded during its assessed history. Several hypotheses have been advanced to explain recruitment variability in this much-scrutinized stock, including variability in the retention of eggs and larvae on Georges Bank, the timing of haddock spawning, and variability in the spring bloom, which influences larval growth and survival. Although these processes may contribute to the formation of successful year classes, none of the factors associated with these previous hypotheses provides an adequate explanation of the 2003 recruitment event. We analyzed data on the dynamics of the fall phytoplankton bloom the year prior to spawning and show it to be highly correlated with subsequent recruitment. We suggest that the fall bloom affects recruitment through enhanced condition of adults and by increasing the quantity and quality of their reproductive output, which in turn leads to a higher probability of survival of their offspring. Although synoptic data on the fall bloom are limited and our analyses are correlative, our purpose is to stimulate a rigorous test of this promising “parental condition hypothesis”.

Influence of the time to egg stripping on eyeing and hatching rates in rainbow trout Oncorhynchus mykiss under cold temperatures

The effects of egg retention time in the abdominal cavity after ovulation on eyeing and hatching rates were studied in rainbow trout, Oncorhynchus mykiss, at cold temperatures of 2 and 8 °C. Two types of experiments were performed: 1) eggs with different retention times were grouped by 3-day intervals until 30 days post-ovulation (DPO) and fertilized with mixed milt from the same sources, and 2) partial volumes of eggs were obtained from individually identified females and stripped and fertilized with mixed milt at 7-day intervals for 35 days. The first experiment showed that the eyeing and hatching rates remained greater than 70 and 60%, respectively, throughout the 30-day experimental period except in the shortest DPO group which exhibited rates of 37.6% and 31.5%. The second experiment clarified that deterioration in egg quality did not occur before 30 DPO at 2 °C and 14 DPO at 8 °C. The eyeing rate also did not show any marked reduction during the experimental period (83%) at 2 °C during the period 28–35 DPO in marked contrast with the sharp drop to 3.6% at 8 °C during the same period. The present study demonstrated that the best stripping time was estimated in the range from 30 to 40 degree-days, and over-ripening of the eggs occurred from 224 degree-days after ovulation at least under cold temperature than in studies reported so far.

Reproductive modes in lizards: measuring fitness consequences of the duration of uterine retention of eggs

1. One of the primary axes of life-history variation involves the proportion of embryonic development for which the offspring is retained within its parent's body; understanding trade-offs associated with prolonging that period thus is a critical challenge for evolutionary ecology. 2. Prior to oviposition, most oviparous squamate reptiles retain developing eggs in utero for about one-third of embryogenesis; the strong conservatism in this trait is a major puzzle in reptilian reproduction. To clarify fitness consequences of this prolonged uterine retention, we need to experimentally modify the trait and examine the effects of our manipulation. 3. We used transdermal application of corticosterone to induce gravid scincid lizards (Bassiana duperreyi) to lay their eggs 'prematurely', with relatively undeveloped embryos. Corticosterone application induced females to oviposit sooner (mean of 5.41 ± 0.51 days post-treatment) at earlier embryonic developmental stage (27 ± 0.21) than did controls (13.2 ± 1.22 days; embryonic stage 30.4 ± 0.16). 4. Corticosterone levels in the egg yolk were unaffected by maternal treatment, so effects of earlier oviposition should not be confounded by endocrine disruption of embryogenesis. Nonetheless, early oviposition reduced hatchling fitness. Hatching success was lower, incubation periods post-laying were increased, and neonates from eggs laid at earlier embryonic stages were smaller and slower. 5. These results suggest that retention of developing eggs in utero by oviparous squamates enhances maternal fitness, and does so via modifications to offspring phenotypes rather than (for example) due to accelerated developmental rates of eggs in utero compared to in the nest. 6. More generally, our data support optimality models that interpret interspecific variation in the duration of maternal–offspring contact in terms of the selective forces that result from earlier vs. later termination of that maternal investment.

Ovarian Torsion in a Green, Iguana iguana, and a Rhinoceros, Cyclura cornuta, Iguana

ABSTRACT Unilateral ovarian torsion was diagnosed in two unrelated iguanas based on gross and microscopic findings. Case No. 1 was an adult female green iguana, Iguana iguana, that died with severe egg retention and systemic bacterial infection with unilateral granulomatous oophoritis and a 360° clockwise torsion of the left ovary. Case No. 2 was a two year-old female rhinoceros iguana, Cyclura cornuta, that died after a seven day history of marked weakness, lethargy, anorexia and tremors, and had a 270° counterclockwise torsion in the right ovary with oophoritis and a coelomic serosanguineous effusion. This is believed to be the first report of ovarian torsion in iguanas, although follicular torsion has been recently documented in a green iguana.

Egg retention as risk-spreading in Trichogramma

Egg retention as risk-spreading in Trichogramma

The selective basis for increased egg retention: early incubation temperature determines hatchling phenotype in wall lizards (Podarcis muralis)

The thermal environment during development influences many aspects of the phenotype of hatchling reptiles. We hypothesized that temperature should differentially affect early incubation stages, in which differentiation dominates over growth, and late incubation stages, characterized by high growth rates. To test this idea, we incubated eggs of wall lizard (Podarcis muralis) under three regimes with the same mean temperature (29 °C), one constant and two variable with opposite sequences: first cold (25 °C) and then hot (32 °C), and vice versa. Hatchlings incubated at high temperature during the initial period had shorter hindlimbs and tails than those incubated under the other two temperature regimes and shorter heads than those incubated initially at low temperature. Thus, temperature experienced by embryos during the early external incubation period produced similar phenotypic responses compared to those reported in previous studies for the same constant temperature applied over the whole incubation period. Because female wall lizards select lower body temperatures during pregnancy, an increase of intrauterine retention would extend the time of exposure of developing embryos to suitable temperatures. Diminution of body temperature during pregnancy is contrary to the expected pattern under the hypothesis that egg retention has evolved to accelerate development, as proposed by the cold-climate model for evolution of viviparity in squamates, and the results of the present study support the alternative hypothesis of developmental optimization as a special case of the broader maternal manipulation view. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 92, 441–447.

Effect of photoperiod on parasitization by Trichogramma principium (Hymenoptera: Trichogrammatidae)

The effect of photoperiod on parasitization of the eggs of the Angoumois grain moth, Sitotroga cerealella (Olivier, 1789) by Trichogramma principium Sugonyaev & Sorokina, 1976 was investigated under several photoperiodic regimes of L : D = 3 : 21, 6 : 18, 9 : 15, 12 : 12, 15 : 9, 18 : 6 and 21 : 3. In all regimes, certain wasps delayed ovipositing in this non-preferred host. Potential fecundity of T. principium females (the number of mature ovarial eggs at emergence) and subsequent oogenesis (estimated by the number of mature ovarial eggs in non-ovipositing females) was independent of photoperiod. However, the percentage of females that oviposited was higher for females that developed and were kept under 6-12 h long photophase than for those that developed and were kept under ultra short (3L : 21D) and under long (18L : 6D and 21L : 3D) photophases. The average duration of the pre-oviposition (egg retention) period showed the opposite pattern to the photoperiodic response. A possible explanation of this reaction is that the delay in oviposition is adaptive if the probability of finding a better host is high. In autumn, when the last Trichogramma females are still active but their lepidopteran hosts are already much less abundant, then parasitization of any suitable host is the best strategy.

유기태 셀레늄과 비타민 E의 복합 급여가 산란계의 생산성, 셀레늄 축적 및 난질에 미치는 영향

비타민 E 100 IU, selenium yeast로 셀레늄을 0.9 ppm과 비타민 E를 50, 100 및 150 IU로 복합 첨가하였을 때 산란계의 산란율, 난중, 1일 산란량, 사료 섭취량, 사료 요구율, 난질, 계란의 저장성 및 계란 내 셀레늄 축적에 미치는 영향을 조사한 결과를 요약하면 다음과 같다. 시험 전 기간의 산란율과 1일 산란량은 비타민 E 100 IU 첨가구와 유기태 셀레늄 0.9 ppm과 비타민 E 50 IU 복합 첨가구가 대조구에 비하여 높았으며(P<0.05), 사료 섭취량과 사료 요구율은 대조구를 포함한 모든 처리구에서 차이가 없었다. Haugh unit는 5주에 비타민 E 100 IU 첨가구와 유기태 셀레늄 0.9 ppm과 비타민 E 50 IU 복합 첨가구가 대조구를 포함한 다른 처리구에 비하여 높았으며(P<0.05), 난황색은 1주에 유기태 셀레늄 0.9 ppm에 비타민 E 50 IU와 100 IU를 복합 첨가한 구가 대조구를 포함한 다른 처리구에 비하여 높았다(P<0.05). 계란의 셀레늄 함량은 유기태 셀레늄 0.9 ppm에 비타민 E 50, 100 및 150 IU를 복합 첨가한 모든 처리구가 대조구와 비타민 E 100 IU 첨가구에 비하여 높게 나타났다(P<0.05). 계란 난황 내 ACL은 유기태 셀레늄 0.9 ppm와 비타민 E 150 IU 복합 첨가구가 대조구를 포함한 다른 처리구에 비하여 높게 나타났다(P<0.05). 계란의 저장 기간별 Haugh unit는 대조구를 포함한 모든 처리구에서 저장기간이 경과할수록 감소하였으나, 셀레늄 0.9 ppm과 비타민 E 150 IU를 복합 첨가한 경우에는 저장 1일차에서 5일차까지의 Haugh unit에 유의적인 차이가 없었다. 이상의 결과를 종합하면 산란계 사료에 유기태 셀레늄 0.9 ppm 첨가하면서 비타민 E를 50, 100 및 150 IU를 복합 첨가시 산란율은 유기태 셀레늄 0.9 ppm 첨가하면서 비타민 E를 50 IU 복합 첨가하면 개선되었으며, 난황내 지용성 항산화물과 계란의 저장성은 유기태 셀레늄 0.9 ppm 첨가하면서 비타민 E를 150 IU 복합 첨가하면 향상되었다. To examine the effects of dietary organic selenium and vitamin E supplementation on egg production, egg weight, daily egg mass, feed intake, feed conversion, egg quality, lipid-soluble antioxidative capacity (ACL) in egg yolk, and selenium retention of egg in laying hens, Hy-Line laying hens of 77 wk old were replaced in the individual cage for 12 week. A corn-soybean meal based diet was supplemented with 0 (control), vitamin E 100 IU/kg and the combination of 0.9 ppm Se from selenium yeast (SY) and vitamin E 50, 100 and 150 IU/kg. Egg production and daily egg mass were significantly increased (P<0.05) in supplemental vitamin E 100 IU, and 0.9 ppm SY + vitamin E 50 IU than control for the whole experimental period. However, feed intake and feed conversion were not affected by supplemental vitamin E and SY. Haugh unit was significantly (P<0.05) higher in supplemental vitamin E 100 IU and 0.9 ppm SY + vitamin E 50 IU than control, 0.9 ppm SY + vitamin E 100 and 0.9 ppm SY + 150 IU in week 5. Haugh unit of the eggs during storage decreased significantly(P<0.05) from day 1 to day 11. However, Haugh units of the eggs from 0.9 ppm SY + vitamin E 150 IU treated groups did not decreased significantly until day 5. Yolk color was significantly (P<0.05) higher in 0.9 ppm SY + vitamin E 50 and 0.9 ppm SY + 100 IU than other treatment groups in week 1. Selenium concentrations of egg were significantly increased (P<0.05) in 0.9 ppm SY + vitamin E than control and vitamin E 100 IU groups. Lipid-soluble antioxidative capacity (ACL) in egg yolk was significantly (P<0.05) higher in supplemental combination of 0.9 ppm SY + vitamin E 150 IU when compared to those of other treatment groups.

Simulated Transport and Retention of Pelagic Fish Eggs during an Irrigation Release in the Pecos River, New Mexico

ABSTRACT The Pecos River between Sumner Dam and Brantley Reservoir (320 km), New Mexico, contains populations of several pelagic-spawning cyprinid fish species, including the federally threatened Pecos bluntnose shiner (Notropis simus pecosensis). Females of this reproductive guild release semi-buoyant eggs that are fertilized and drift, incubate, and hatch on increased flows associated with spring runoff, summer rainstorms, or irrigation releases from Sumner Reservoir. We used artificial eggs (beads) to estimate transport and retention of natural eggs during an irrigation release in five reaches of the Pecos River occupied by bluntnose shiner. Bead retention was highest (1.7–4.5%/km) in the broad complex reaches of upper critical habitat and the quality section (upper 200 km), and bead retention was lowest (0.6%/km) in the narrow, deep, channelized reach of lower critical habitat (60 km). Only 10% of beads were transported more than 50 km from their release location in the reach with highest retention. Modeled spawning events in all five reaches showed highest egg retention of 35% in the reach that also had the highest density of adult Pecos bluntnose shiner (37 km from Cortez Gasline to Acme). The model predicted that during an irrigation release, about 90% of bluntnose shiner eggs produced during a natural spawning event are retained in the upper 250 km of occupied habitat, with only 10% passing downstream into unsuitable habitat or into Brantley Reservoir. We conclude that retention of drifting eggs is greatest during high flows when flood wave attenuation and channel storage are greatest and in broad complex channel reaches, which coincide with existing population centers.

Spawning, daily egg production, and spawning stock biomass estimation for common sardine ( Strangomera bentincki) and anchovy ( Engraulis ringens) off central southern Chile in 2002

In this paper, the first daily egg production method (DEPM) parameters were estimated for anchovy and common sardine stocks distributed in the central-south area off Chile (33–40°S). The study area was stratified according to the topography, shape and orientation of the coastal line, and the survey was carried out on the continental shelf during the main spawning peak (August–September, 2002). The bulk of the spawning of both species was successfully covered, which was characterized by a coastal distribution within the first 20 nautical miles, and following the inner zone associated with the 100 m bottom depth. The coastal distribution of the spawning can be related to the oceanographic conditions occurring during the transition from winter to spring (southern Hemisphere), which are characterized by the alternation between northerly and southerly winds. Probably, these factors are interacting to produce enrichment, concentration and retention of egg in coastal zones in the study area. The daily egg production rate ( P 0) was estimated for two geographic strata, and was different in each region. Also, the length frequency and adult reproductive parameters were different between geographic strata, specially the daily spawning fraction. For anchovy, the P 0 was lower in comparison with available estimates for the same species in Peru and in the north area off Chile. Also, the relative fecundity of anchovy was lower, probably because anchovy in the study area have bigger eggs as compared with the anchovy in Northern Chile. The DEPM parameters estimated for common sardine in the investigated area were similar to the range of existing values for the Engraulis genus in other upwelling areas. The stratified spawning stock biomass estimate was 133,031 t (CV = 44%) for anchovy and 706,792 t (CV = 68%) for common sardine. Probably, daily egg production and adult reproductive parameters of both species are highly variables and further research is suggested for improvements future DEPM application for the species.

The effect of travel time on oviposition behavior and spatial egg aggregation: experiments with Drosophila

AbstractA higher degree of spatial egg aggregation is often observed in environments where resource patches are more sparsely distributed. This suggests a higher probability of species coexistence when resource distribution is sparse. However, it is still unclear how the degree of spatial egg aggregation increases. I propose a model to explain this phenomenon, which assumes that (i) egg load (the number of mature eggs in ovaries) increases in the travel period between resource patches and (ii) the retention of eggs in the ovaries is harmful (egg load pressure). With these assumptions, a female would lay accumulated eggs on arrival at a new resource patch, resulting in a higher degree of spatial egg aggregation. Laboratory experiments with three drosophilid species, Drosophila simulans Surtevant, Drosophila auraria Peng, and Drosophila immigrans Sturtevant, support the model. This study provides evidence that host availability affects the spatial egg aggregation via egg load.

Testing the function of the domed nests of Saltmarsh Sharp-tailed Sparrows

Saltmarsh Sharp-tailed Sparrows (Ammodramus caudacutus) build ground nests, often with a closely-woven dome, in marshes that frequently flood during high tides. To test the hypothesis that domed nests help reduce the loss of eggs and chicks due to flooding or predation, we examined the characteristics and fate of 102 nests at sites along the coast of Connecticut. To test whether nest structure was tailored to suit microhabitat conditions, we also measured vegetation characteristics around nests. Finally, we conducted artificial nest-flooding experiments to determine whether removal of domes reduced egg retention during flooding. We found no significant effects of nest structure on breeding success or failure, and few significant correlations between nest structure and microhabitat. The height of nests above the ground, however, increased with vegetation height, supporting the hypothesis that nest construction is influenced by flooding, but not supporting the hypothesis that predation risk is important. Dome removal experiments showed that domes have a highly significant effect on the retention of eggs during flooding, suggesting that domes help eggs survive the regular tidal flooding of marshes. SINOPSIS. Poniendo a pruebas la funci´ on del domo de los nidos de Ammodramus caudac-

Effects of Telemetry Transmitter Placement on Egg Retention in Naturally Spawning, Captively Reared Steelhead

AbstractMaturing female anadromous salmonids receiving intraperitoneally implanted telemetry transmitters (tags) may experience difficulty depositing eggs during natural spawning. We allocated maturing adult female steelhead Oncorhynchus mykiss to three treatment groups: (1) fish whose tags were surgically implanted in the body cavity (internal), (2) fish whose tags were implanted between the skin and muscle tissue (subdermal), and (3) nontagged fish. The steelhead were then allowed to spawn in an experimental channel. Internally tagged females retained significantly more eggs than did the subdermally tagged and nontagged control groups; subdermally tagged and nontagged control fish did not differ significantly. Females in the internally tagged, subdermally tagged, and nontagged groups retained an average of 49, 11, and 2% of their eggs, respectively. The onset of sexual activity did not differ significantly among treatments. Postspawning mortality was 70% for internally and subdermally tagged females and 0% for nontagged females. Each research or monitoring program should weigh the costs associated with transmitter use (where they are known) against the value of information obtained and should carefully evaluate assumptions about transmitter effects. For these reasons, the use of electromyogram electrodes and other telemetry transmitters for monitoring imperiled fish populations should be employed with caution. We suggest that subdermal implantation techniques be considered in future studies during the reproductive period to reduce egg retention caused by internally implanted transmitters.

Spawning by Female Chinook Salmon Can Be Detected by Electromyogram Telemetry

AbstractNew methods to detect spawning of anadromous salmonids in their natural environment are needed to improve understanding of breeding behavior patterns, natural selection on reproductive traits (e.g., spawn timing), and interactions between artificially propagated and wild fish. We implanted maturing female Chinook salmon Oncorhynchus tshawytscha with coded electromyogram (CEMG) transmitters and continuously recorded spawning activity to develop an algorithm capable of accurately detecting spawning events from CEMG data. Marked increases in female digging frequencies immediately after spawning (cover digging) strongly correlated with CEMG values. The algorithm detected averages of 65% and 86% of the actual spawning events in 2003 and 2004, respectively. The algorithm accurately detected zero spawning events for the two female salmon that did not spawn. The presence of CEMG transmitters did not affect the digging frequency, number of nests constructed, or the reproductive life span of implanted fish. However, the CEMG tagging procedure or the presence of tags significantly increased egg retention. Pedigree analyses of DNA confirmed that females implanted with CEMG transmitters exhibited significantly lower individual reproductive success relative to that of nontagged females (73% and 66% reduction in two separate experiments). Subsequent research in adult steelhead O. mykiss has indicated that alternative implantation techniques hold promise for reducing the effects of the tags on reproductive success. We suggest that remote monitoring of salmonid spawning behavior is now possible with CEMG technology and should be tested in natural habitats.

Home range and elevated egg densities within an inshore spawning ground of coastal cod

Abstract Espeland, S. H., Gundersen, A. F., Olsen, E. M., Knutsen, H., Gjøsæter, J., and Stenseth, N. C. 2007. Home range and elevated egg densities within an inshore spawning ground of coastal cod. – ICES Journal of Marine Science, 64: 920–928. Atlantic cod (Gadus morhua) along the Norwegian Skagerrak coast are structured into genetically distinct local populations. Mechanisms contributing to this genetic structure may include spawning site fidelity of adult cod as well as retention of pelagic early life stages close to the spawning grounds. Spawning in sheltered inshore localities is likely to favour retention of eggs and larvae, the opposite situation to offshore spawning. A combined study was made of area utilization by adult cod and the distribution of cod eggs within an inshore locality of the Norwegian Skagerrak coast. The behaviour of adult cod was studied using acoustic telemetry and kernel modelling, and eggs were sampled throughout the spawning season. Generalized additive models were applied to test hypotheses about the spatial dynamics of the eggs, and the best model described a central spawning area that retained its integrity through time. Adult cod were confined to small parts of the study area and remained there throughout the spawning season. The average home range of the adult cod was 27 ha. Overall, the study demonstrated two mechanisms by which coastal (i.e. inshore) cod maintain their population structure: spawning site fidelity and the spatial dynamics of their eggs.

Nox regulation of smooth muscle contraction

The catalytic subunit gp91 phox (Nox2) of the NADPH oxidase of mammalian phagocytes is activated by microbes and immune mediators to produce large amounts of reactive oxygen species (ROS) which participate in microbial killing. Homologs of gp91 phox, the Nox and Duox enzymes, were recently described in a range of organisms, including plants, vertebrates, and invertebrates such as Drosophila melanogaster. While their enzymology and cell biology are being extensively studied in many laboratories, little is known about in vivo functions of Noxes. Here, we establish and use an inducible system for RNAi to discover functions of dNox, an ortholog of human Nox5 in Drosophila. We report here that depletion of dNox in musculature causes retention of mature eggs within ovaries, leading to female sterility. In dNox-depleted ovaries and ovaries treated with a Nox inhibitor, muscular contractions induced by the neuropeptide proctolin are markedly inhibited. This functional defect results from a requirement for dNox-for the proctolin-induced calcium flux in Drosophila ovaries. Thus, these studies demonstrate a novel biological role for Nox-generated ROS in mediating agonist-induced calcium flux and smooth muscle contraction.

Egg distribution, bottom topography and small-scale cod population structure in a coastal marine system

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 333:249-255 (2007) - doi:10.3354/meps333249 Egg distribution, bottom topography and small-scale cod population structure in a coastal marine system Halvor Knutsen1,2,*, Esben Moland Olsen1,2, Lorenzo Ciannelli2,4, Sigurd Heiberg Espeland2, Jan Atle Knutsen1, Jan Henrik Simonsen1, Stig Skreslet3, Nils Chr. Stenseth1,2 1Institute of Marine Research, Flødevigen, 4817 His, Norway2Centre for Ecological and Evolutionary Synthesis (CEES), University of Oslo, PO Box 1066, Blindern, 0316 Oslo, Norway 3Bodø University College, Department of Fisheries and Natural Sciences, 8049 Bodø, Norway 4Present address: College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331, USA *Email: halvor.knutsen@imr.no ABSTRACT: Coastal marine species with pelagic egg and larval stages, such as the Atlantic cod Gadus morhua, can be structured into genetically distinct local populations on a surprisingly small geographic scale considering their dispersal potential. Mechanisms responsible for such small-scale genetic structure may involve homing of adults to their natal spawning grounds, but also local retention of pelagic eggs and larvae. For example, spawning within sheltered fjord habitats is expected to favour local retention of early life stages. Here, we studied the distribution of cod eggs along inshore– offshore transects in 20 Norwegian fjords. The general pattern exhibited across all fjords was a higher concentration of cod eggs inside the fjords than further offshore. In particular, fjords with shallow sills (model threshold 37 m) show an abrupt reduction in egg density over the sill. This study provides empirical support for an offspring retention hypothesis, which may help to explain the maintenance of local population structure in pelagic marine systems. KEY WORDS: Atlantic cod · Gadus morhua · Egg distribution · Population structure Full text in pdf format Supplementary appendices PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 333. Online publication date: March 12, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Density, climate, and the processes of prespawning mortality and egg retention in Pacific salmon (Oncorhynchusspp.)

In 2004 and 2005, exceptionally large runs of sockeye salmon (Oncorhynchus nerka) to the Alagnak River system in Bristol Bay, Alaska, coincided with weak runs to the nearby Kvichak River system. Restricted fishing to protect the Kvichak populations resulted in densities on the Alagnak River system's spawning grounds that were 11.5-fold (in 2004) and 9.0-fold (in 2005) above the long-term (1956–2003) average. Carcass sampling indicated that 23% (2004) and 44% (2005) of the potential egg deposition was lost to prespawning mortality or incomplete spawning in the Alagnak populations. Much lower levels of egg retentions were observed in spawning populations in the Kvichak River and Wood River systems, where the runs did not appreciably exceed the escapement goals, indicating that density-dependent spawning failure may have occurred. However, in 2005, significantly higher egg retention rates were observed in the Alagnak River system despite slightly lower densities than in 2004, indicating that environmental processes (probably low river levels and high temperatures) influenced prespawning mortality as well. More limited sampling in 2006 revealed only 3% egg retention in one of the Alagnak populations, but the combination of lower density and cooler conditions did not allow us to determine the relative contributions of these two factors to spawning failure.

Oxytocin Dosage in Turtles

Oxytocin dosage was determined experimentally for the red-eared slider (Trachemys scripta elegans). Five dosages including 20, 10, 5, 4, and 2 units/kg were experimentally compared in 253 female turtles in a series of experiments conducted in 1999 and 2000. The 3 highest doses were equally effective overall following a maximum of 2 injections. The 2 lower doses were equally effective overall following a maximum of 2 injections. Success rate (i.e., turtles laid all eggs or retained 2 or fewer eggs following a maximum of 2 injections) ranged from 100% (20 and 10 unit/kg doses) to an average of 88.9% for the lowest doses (4 and 2 units/kg). When reduction in oxytocin exposure is desired, the lower dosages are recommended; when turtles are being treated for egg retention, the higher dosages may be more desirable. No difference in oxytocin efficacy was found among 3 species of chelonians (red-eared slider; stinkpot, Sternotherus odoratus; and painted turtle, Chrysemys picta) when oxytocin was given at 4 units/kg. No difference in efficacy was found among 2669 red-eared sliders from 2 collecting areas in west-central Illinois induced with 4 units/kg between 2000 and 2005.