Spawning Cohorts Research Articles

Spawning cohort trade‐offs of reproductive time and output in cyprinid fish along an elevation gradient

AbstractUnderstanding environmental requirements for fish reproduction in natural habitats is crucial for population conservation and restoration. However, such information is extremely scarce for the highly threatened schizothoracine fishes that cover large elevation ranges on the Tibetan Plateau. This research investigated the spawning time, output and environmental conditions of wild Schizopygopsis thermalis along an elevational gradient (i.e., from 1766 to 4372 m) in the upper Nu‐Salween River. It found that the spawning grounds of S. thermalis were mainly located at elevations between 3600 and 4372 m, and spawning habitats mostly consist of still marginal areas (still water <10 cm deep) with gravel substrates. Otolith microstructure analysis revealed, for the first time, that S. thermalis spawns in two seasons (i.e., winter: from December to next February, and spring: from April to May), with the winter spawning period generally longer than the spring spawning period. Winter spawning started earlier and ended earlier at higher elevations, while spring spawning occurred earlier at lower elevations but ended simultaneously at higher elevations. As elevation increases, reproductive output also increases, and spawning cohorts shift from winter‐dominant to spring‐dominant. Winter spawning cohorts were associated with lower water temperatures but higher discharges than the spring spawning cohort, and both cohorts showed elevation‐related environmental preferences. Our results suggest that schizothoracine fish can adapt spawning strategies to elevation‐related environmental conditions, which fill the gaps in the reproductive characteristics of schizothoracine fishes, and highlight the importance of conserving schizothoracine habitats at high elevations in the Qinghai‐Tibetan rivers.

Effectiveness of SNPs for Sibship Assignment in Farmed Banana Shrimp (Penaeus merguiensis)

Pedigrees are essential components in selective breeding programs to manage genetic diversity and obtain accurate genetic parameter estimates to ensure long-term response to selection in captive populations. High throughput and cost-effective sequencing technologies has offered opportunities of using single nucleotide polymorphisms (SNPs) to resolve penaeid shrimp pedigrees from mass spawning cohorts and communal rearing. Effects of SNPs for sibship assignment were investigated on 546 shrimp using two software programs, Colony and Sequoia. Assignment rates and accuracies using SNP subsets with six different minor allele frequencies (MAFs), four sets of SNPs, and five genotyping error rates were compared to the microsatellite-based pedigree established in a previous study. High MAFs and numbers of SNPs contributed to significant increases in assignment rates and accuracies, whereas genotyping error rates showed negligible impacts on assignment results. Sibship assignments achieved rates and accuracies of 98% and 83%, respectively, with a minimum number of 91 SNPs (average MAF ≥ 0.14), and the two different programs exhibited similar resulting patterns for different SNP subsets. High consistencies between SNP-based and microsatellite-based pedigrees showed that accurate pedigrees could be achieved by using SNPs and thus contribute to the long-term response to selection in farmed banana shrimp.

Trophic ecology of the squid Doryteuthis gahi in the Southwest Atlantic inferred from stable isotope analysis

The Patagonian longfin squid Doryteuthis gahi has an annual life cycle with two seasonal cohorts (autumn and spring spawners). Previous studies estimated the trophic level of adult squid by stable isotope analysis of their muscle or gladius tissues, but few studies compared different sizes and spawning cohorts. In this study, mixed models were used to compare carbon (δ13C) and nitrogen (δ15N) stable isotope signatures of muscle and gladius tissues of the autumn and spring spawning cohorts and squid of different sizes. A published isoscape model provided δ15N baselines to calculate the trophic level of D. gahi. Sampled herbivorous prey such as Euphausiacea, planktonic juveniles Munida gregaria and salps Ihlea supported the trophic level estimates. The autumn spawning cohort had higher δ13C values than the spring spawning cohort. δ15N values increased with increasing dorsal mantle length, suggesting an ontogenetic change towards larger prey. Muscle tissue was enriched in 15N but slightly depleted in 13C compared to gladius tissue. Adult squid had an estimated trophic level of ∼3.2, with no significant differences between spawning cohorts. Stable isotope values followed a seasonal trend, with lower δ15N values and lower δ13C value between July and September. Large individuals of the spring spawning cohort were found to have the least niche overlap with other groups of D. gahi. Our study of the trophic levels and ecology of D. gahi can provide important information on its role in the food chain and can build the basis of studies on interaction with other species, and the impact of environmental changes on their populations. This information can inform the development of management strategies aimed at preserving the balance of the ecosystem and ensuring its sustainable use.

Size-related, seasonal and interdecadal changes in the diet of the Patagonian longfin squid Doryteuthis gahi in the South-western Atlantic

AbstractThe Patagonian longfin squid Doryteuthis gahi has an annual life cycle with two seasonal cohorts (autumn and spring spawners). Earlier studies on the Patagonian shelf found a predominance of Euphausiacea in the D. gahi diet, but no studies to date have investigated differences between feeding spectra of the two cohorts or decadal diet shifts. The present study investigated differences in diet of D. gahi on the Patagonian shelf sampled two decades apart, and differences between seasonal cohorts. Classical stomach content analysis and generalized additive models were used to investigate and model the influence of mantle length, sampling period and spawning cohort on the diet. Results revealed an ontogenetic diet change from ~70% Frequency of Occurrence of Euphausiacea in small squid to more than 60% FO of fish and Cephalopoda at larger sizes. Cannibalism was also frequently observed. Euphausiacea were ingested more frequently and in higher amounts during the austral summer and therefore were consumed more by the autumn spawning cohort, whereas fish was more frequently fed upon during austral winter and also by the spring spawning cohort. Cannibalism was also recorded more in austral winter months but, contrary to feeding on fish, was more prevalent in the autumn spawning cohort. Increased predation of Munida gregaria was observed in 2020 compared with 2001. This study is an important step towards improving the knowledge of D. gahi's two seasonal cohorts, providing data that can be used for future ecosystem modelling.

'Superbull' males: what role do they play and what drives their appearance within the Doryteuthis gahi Patagonian Shelf population?

Cephalopod populations exhibit high variability in life history characteristics, such as longevity and size-at-age. The aim of this study was to understand how characteristics of a newly described ‘superbull’ male morph in Doryteuthis gahi populations (Patagonian Shelf) arise and whether there is a selective advantage. At the population level, it is speculated that superbulls provide temporal and spatial connectivity, but individual benefit is less obvious. Age structure and reproductive potential of males was investigated to determine whether superbulls could provide connectivity. Environmental variables affecting size-at-age were explored to ascertain whether morphological differences were primarily phenotypically driven. Superbulls from the autumn spawning cohort were significantly older than the residual population, with added longevity potentially leading to spawning with the following cohort. A reduction in relative testis weight was apparent in superbulls, but spermatophore production remained high. Generalised additive mixed models indicated temperature, location and hatch year had significant effects on size-at-age. Weak correlations between warm El Niño–Southern Oscillation phases and superbull abundance were found. The results suggest that superbulls provide temporal connectivity and arise through phenotypic plasticity, likely providing connectivity as a side effect of body shape and size rather than a genetically selected advantage.

The response of North Atlantic diadromous fish to multiple stressors, including land use change: a multidecadal study

Reduction of freshwater habitat quality due to land use change can have major impacts on diadromous fish. Partitioning this impact from other potential drivers, such as changing marine conditions and climate, is hampered by a lack of long-term data sets. Here, four decades of data were used to assess the impact of land use change on Salmo salar and anadromous Salmo trutta in the Burrishoole catchment, Ireland, one of the few index sites for diadromous fish in the North Atlantic. Land use change was found to have no significant impact on the freshwater survival of either salmon or trout. However, climate impacted significantly on the survival of salmon and trout in fresh water, with poor survival in years with wetter, warmer winters, coinciding with positive North Atlantic Oscillation values. Additionally, cold springs were associated with higher survival in trout. The addition of hatchery fish into the salmon spawning cohort coincided with low freshwater survival. Our results highlight the necessity for a broad ecosystem approach in any conservation effort of these species.

A preliminary analysis of trace-elemental signatures in statoliths of different spawning cohorts for Dosidicus gigas off EEZ waters of Chile

We applied solution-based ICP-MS method to quantify the trace-elemental signatures in statoliths of jumbo flying squid, Dosidius gigas, which were collected from the waters off northern and central Chile during the scientific surveys carried out by Chinese squid jigging vessels in 2007 and 2008. The age and spawning date of the squid were back-calculated based on daily increments in statoliths. Eight elemental ratios (Sr/Ca, Ba/Ca, Mg/Ca, Mn/Ca, Na/Ca, Fe/Ca, Cu/Ca and Zn/Ca) were analyzed. It was found that Sr is the second most abundant element next to Ca, followed by Na, Fe, Mg, Zn, Cu, Ba and Mn. There was no significant relationship between element/Ca and sea surface temperature (SST) and sea surface salinity (SSS), although weak negative or positive tendency was found. MANOVA analysis showed that multivariate elemental signatures did not differ among the cohorts spawned in spring, autumn and winter, and no significant difference was found between the northern and central sampling locations. Classification results showed that all individuals of each spawned cohorts were correctly classified. This study demonstrates that the elemental signatures in D. gigas statoliths are potentially a useful tool to improve our understanding of its population structure and habitat environment.

Growth and Mortality in Coastal Populations of Winter Flounder: Implications for Recovery of a Depleted Population

AbstractWe studied growth, mortality, and settlement distributions of juvenile Winter FlounderPseudopleuronectes americanusin two bays of Long Island, New York, to better understand localized population dynamics of a species experiencing a protracted population decline. Juvenile mortality in Long Island bays ranged between 0.02 and 0.04 per day and was as high as or higher than values reported for other systems. Settlement distributions had multiple peaks (cohorts) occurring between March and late July in 2007 and between February and May in 2008. The presence of multiple cohorts limited the usefulness of field‐derived, length‐based estimates of growth, resulting in unrealistic values compared with otolith‐based measures (field based: −0.05 to 0.25 cm/d; otolith based: 0.05–0.06 cm/d). Thus, we recommend the use of otolith methods or the repeated measurement of individuals to estimate growth of juvenile Winter Flounder. Otolith‐based growth rate was significantly higher for Port Jefferson Harbor during 2007 than for all other year × location combinations. Together with previous research showing genetic differentiation and migratory diversity, our finding of multiple spawning cohorts in Long Island Winter Flounder suggests a degree of isolation, and local management will be needed to support healthy populations. Future research to determine adult spawning, migratory behavior, stock structure, duration of the larval period, and settlement timing is required to unravel the complex behavior of Winter Flounder.Received July 10, 2014; accepted April 10, 2015

北太平洋柔鱼微卫星标记的筛选及遗传多样性分析

PDF HTML阅读 XML下载 导出引用 引用提醒 北太平洋柔鱼微卫星标记的筛选及遗传多样性 DOI: 10.5846/stxb201303030334 作者: 作者单位: 上海海洋大学海洋科学学院,上海海洋大学海洋科学学院,上海海洋大学海洋科学学院,上海海洋大学海洋科学学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金(41276156);国家863计划(2012AA092303);国家发改委产业化专项(2159999);上海市科技创新行动计划(12231203900) Isolation and genetic diversity of microsatellite DNA of Ommastrephes bartramii in the North Pcific Ocean Author: Affiliation: SHOU,shou,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:采用(AC)12、(AG)12两种生物素探针,通过磁珠富集法构建了柔鱼部分基因组微卫星富集文库。68个阳性克隆中有60个含有微卫星序列,重复次数在10次以上的占86.84%,最高重复次数为33次。其中,完美型微卫星占60.53%,非完美型微卫星占36.84%,混合型微卫星占2.63%。除探针使用的AC/TG、AG/TC重复外,还得到ACAG、AGAC重复序列。利用筛选出的8个微卫星位点对北太平洋柔鱼6个群体的遗传多样性及遗传结构进行分析。结果表明,8个微卫星位点均为高度多态性位点(PIC=0.787-0.987),位点Bo103与位点Bo105极显著偏离Hardy-Weinberg平衡(P < 0.01)。6个地理位置的柔鱼群体显示出较高的遗传多样性水平(Ho=0.672-0.761,He=0.808-0.851)。两两群体间的Fst值以及AMOVA分析结果均表明,群体间遗传分化不显著(Fst=0.00559,P > 0.05),遗传差异主要来自于个体间。基于Nei's遗传距离的UPGMA聚类树显示,北太平洋东北部2个柔鱼群体(NE1、NE3)聚为一类,西北部3个群体(NW1、NW2、NW3)与东北部1个群体(NE2)另聚为一类,且群体NW1与群体NE2亲缘关系最近,遗传距离与地理距离线性相关分析没有呈现出正相关性(R=0.175,P > 0.05)。遗传结构分析结果推断北太平洋柔鱼存在1个理论群。柔鱼个体具有较强的游泳能力,在海流的作用下,群体之间存在较强的基因交流。建议今后在柔鱼资源开发利用过程中将北太平洋柔鱼看作1个管理单元。 Abstract:The neon flying squid Ommastrephes bartramii is found circumglobally in subtropical and temperate waters in the world and supports important fisheries in the North Pacific Ocean. The population of the North Pacific O. bartramii comprises a fall spawning cohort and a winter-spring spawning cohort. Most of the fall cohort occurs east of 170°E, whereas the winter-spring cohort is widely distributed across the North Pacific Ocean. Two spawning cohorts can be further subdivided into four stocks: a central and an eastern stock of the fall cohort separated near 160°W, and a western and a central-eastern stock of the winter-spring cohort separated near 170°E in which the fall cohort was the target of a driftnet fishery before 1993 while the west stock of winter-spring cohort became main fishing target of an international jigging fishery. Being a short-lived ecological opportunist, neon flying squid exhibits large fluctuations in stock abundance and distribution on the feeding grounds and large fluctuating recruitment on the spawning grounds in response to environmental variability. In order to improve our understanding of population structure, the genetic diversity of O. bartramii populations in the North Pacific Ocean was examined using microsatellite markers. Two types of biotin-labeled oligos were employed and part of microsatellite-enhanced genomic library of O. bartramii was constructed by the method of streptavidin magnetic beads. Sixty of 68 positive clones comprised microsatellite sequences and repeat number of more than 10 accounted for 86.84% with the largest one of 33. Of these were 60.53% perfect, 36.84% were imperfect, and the rest were compound type (2.63%). Repeats including (ACAG)n and (AGAC)n were also detected except that of AC/TG and AG/TC. Microsatellite markers were isolated and screened, and 8 of them were then used for the analysis of genetic diversity and genetic structure of six populations of O. bartramii in the North Pcific Ocean. Results showed that all the 8 loci were highly polymorphic (PIC=0.787-0.987), and locus Bo103 and locus Bo105 were extremely significant deviated from Hardy-Weinberg equilibrium (P < 0.01). All of the 6 different geographic populations showed high genetic diversities (Ho=0.672-0.761, He=0.808-0.851). Pairwise F test and AMOVA analysis detected no significant genetic differentiations among populations, and genetic differences mainly came from individuals. UPGMA clustering tree based on Nei's genetic distance demonstrated that two stocks (NE1 and NE3) in the northeast of the North Pcific Ocean clustered together, while the three stocks (NW1, NW2 and NW3) in the western part as well as one stock (NE2) in the eastern part clustered together, and the genetic distance between NW1 and NE2 was closer. Relations between genetic distance and geographic distance did not show positive correlation (R=0.175, P > 0.05), indicating that different populations of O. Bartramii could mingle together. Genetic structure simulation analyses suggested that there was only one logic population of all individuals, and extensive gene exchange might occur among the populations, which could be attributed to the influence of ocean currents and swimming ability of O. bartramii individuals. The North Pacific O. bartramii should be considered as a single stock in their assessment and management. 参考文献 相似文献 引证文献

Age validation, growth estimation and cohort dynamics of the bony flying fish Hirundichthys oxycephalus off eastern Taiwan

Flying fishes (Exocoetidae) are commonly found in the epipelagic zone and play an important role in Taiwan in maintaining the stability of the marine ecosystem, local culture and coastal fisheries. However, little is known about their biology and life history, even though several species are of important commercial value in western Pacific countries. Overexploitation of one of the dominant species, the bony flying fish Hirundichthys oxycephalus, is a critical issue in the fishery management and resource assessment of this species. In the present study, H. oxycephalus eggs were harvested off northeastern Taiwan, while adult fish were collected mainly off the southeastern coast of Taiwan. We validated the daily periodicities of the growth increments in 3 otolith pairs based on the successive otolith examination of fish reared in the laboratory from fertilized eggs. The asteriscus was determined to be the most suitable otolith for age determination of the fish. Age (in days) was calculated by counting the number of growth increments on the mounted otolith and adding 11. By using a growth coefficient of 0.0075 d−1, the asymptotic length of these fish was estimated to be 253.86 mm. Back-calculated hatching dates indicated that an occurrence of the summer spawning cohort coincided with the known egg-fishing season off the northeastern coast. On the other hand, the source of the adult fishery off the southeastern coast originated from a new winter spawning cohort. The cohort dynamics of this species were found to be more complicated than previously thought. Our findings could be added to the information already known about the reproductive ecology of H. oxycephalus and used to improve the fisheries management of these fish.

Comparison of growth histories of immature Japanese common squid Todarodes pacificus between the autumn and winter spawning cohorts based on statolith and gladius analyses

Growth of the autumn and winter spawning cohorts of the Japanese common squid Todarodes pacificus was examined based on daily growth increments in the statolith and gladius. The samples were taken from three groups of young (≤180 days old) squid: the autumn cohort collected in the Tsushima Current and the winter cohort collected in the Pacific near the coast and 1100 km offshore. The growth rate based on statolith analysis was highest in the winter cohort near the coast and similar in the two other groups. The daily growth based on gladius analysis during the month before capture was also highest in the winter cohort near the coast, and fluctuated more in the autumn cohort than in the winter cohort. The results suggest that gladius growth increments will be an important tool in future studies of growth in T. pacificus.

Establishment of new wintering areas in herring co-occurs with peaks in the ‘first time/repeat spawner’ ratio

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 409:189-198 (2010) - DOI: https://doi.org/10.3354/meps08620 Establishment of new wintering areas in herring co-occurs with peaks in the ‘first time/repeat spawner’ ratio Geir Huse1,*, Anders Fernö1,2, Jens Christian Holst1 1Institute of Marine Research, 5817 Bergen, Norway 2Department of Biology, University of Bergen, 5020 Bergen, Norway *Email: geir.huse@imr.no ABSTRACT: Norwegian spring spawning (NSS) herring migrate to wintering areas in late summer and remain there for about 5 mo in dense aggregations. First-time spawning cohorts typically adopt the wintering area of the spawning stock. However, over the last 50 yr the NSS herring stock has occupied 7 discrete wintering grounds, spanning from the high seas to narrow fjords, which shows that there is considerable plasticity in choice of wintering area. We show that 5 cases of establishment of new wintering areas take place when abundant first-time spawning cohorts take up the adult migration pattern. The ratio in abundance between age 4 and age 5+ herring is on average 14 in the years when new wintering areas are established compared to 0.3 in years without changes. The wintering areas vary greatly with regards to temperature and distance to the feeding and spawning grounds, features that heavily affect energy expenditure during wintering and migration. Rather than being strictly optimized, the establishment of new wintering areas seems to be governed by general school cohesion mechanisms when naïve first-time spawners flood the population and the social learning process is disrupted. KEY WORDS: Norwegian spring spawning herring · Wintering area · Demography · Schooling · Migration Full text in pdf format PreviousNextCite this article as: Huse G, Fernö A, Holst JC (2010) Establishment of new wintering areas in herring co-occurs with peaks in the ‘first time/repeat spawner’ ratio. Mar Ecol Prog Ser 409:189-198. https://doi.org/10.3354/meps08620 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 409. Online publication date: June 23, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

Rapid species replacements between fishes of the North American plains: a case history from the Pecos River

A non-native population of plains minnow Hybognathus placitus in the Pecos River, New Mexico, USA, replaced the endemic, ecologically similar Rio Grande silvery minnow Hybognathus amarus in less than 10 years. Competitive exclusion is hypothesized as a mechanism of replacement. The following evidence was examined for potential support: (1) the historical population trend of H. amarus versus H. placitus; (2) relative suitability of the modified flow regime for H. amarus versus H. placitus; (3) potential for habitat overlap; and (4) spawning periodicity and body length in the non-native population of H. placitus. Historical data indicate H. amarus did not decline until H. placitus was present, after which it disappeared rapidly and H. placitus proliferated. The natural flow regime of the Pecos River was changed via base-flow reductions and capture of springsnowmelt runoff, making it similar to flow regimes associated with likely source populations of non-native H. placitus. Spring runoff is an important spawning cue for H. amarus, but not H. placitus and H. placitus appears to be naturally more tolerant of diminished streamflow. Extant H. placitus were associated with a relatively pristine river reach that was most likely the stronghold for the replaced H. amarus population. Given high ecological similarity, habitat overlap was likely high during the period of replacement. Hybognathus placitus in the Pecos River had a protracted spawning season (April through September), whereas extant H. amarus in the Rio Grande had a short spawning season (a few days in May or June during snowmelt runoff). Most H. amarus die after their first spawning season and few exceed 60 mm standard length (SL), whereas quite a few H. placitus survive at least until their second spawning season and exceed 60 mm SL. Co-occurrence of multiple spawning cohorts may stabilize annual reproductive output of H. placitus and larger individuals may be more fecund and produce larger eggs that survive better. Spawning flexibility, greater size, and higher environmental tolerance likely gave H. placitus a reproductive and survival advantage over H. amarus, consistent with a deterministic pattern of rapid species replacements in the plains, in which tolerant, competitive species from the Red River drainage or Gulf of Mexico coast rapidly replace more sensitive, endemic congeners in disturbed, remnant habitats.

Life history of the neon flying squid: effect of the oceanographic regime in the North Pacific Ocean

The North Pacific Ocean population of the neon flying squid Ommastrephes bartramii, which un- dertakes seasonal north-south migrations, consists of autumn and winter-spring spawning cohorts. We ex- amined life history differences between the 2 cohorts in relation to the oceanographic environment. The differ- ences could be explained by seasonal north-south movements of the following 2 oceanographic zones: (1) the optimum spawning zone defined by sea surface temperatures; and (2) the food-rich zone defined by the position of the transition zone chlorophyll front (TZCF). The 2 cohorts use the food-rich zone in different phases of their life cycles. The spawning grounds for the au- tumn cohort occur within the subtropical frontal zone (STFZ), characterized by enhanced productivity in win- ter due to its proximity to the TZCF, whereas the spawning grounds for the winter-spring cohort occur within the subtropical domain, which is less productive. As the TZCF shifts northward in spring, the autumn co- hort continues to occur in the productive area north of the TZCF, whereas the winter-spring cohort remains in the less productive area to the south until it migrates into productive waters north of the TZCF in the summer or autumn. Consequently, the autumn cohort grows faster than the winter-spring cohort during the first half of its life cycle, whereas the winter-spring cohort grows faster during the second half. This growth pat- tern may be responsible for differing migration pat- terns; males of the autumn cohort do not have to migrate given their early fast growth in the STFZ, whereas those of the winter-spring cohort must mi- grate to the food-rich subarctic frontal zone to compen- sate for their slow growth. These biological and eco- logical differences between the 2 cohorts suggest flexibility of their life history response to oceanographic environments. Hatchling of the neon flying squid Ommastrephes bartramii

Degeneration of postovulatory follicles of the Bay of Biscay anchovy (&lt;em&gt;Engraulis encrasicolus&lt;/em&gt; L.)

The degeneration of postovulatory follicles (POFs) in time and at different temperatures was studied for the Bay of Biscay anchovy. For this purpose a key of 7 POF stages, solely defined on the basis of their histological degeneration characteristics, was applied. The novelty of this procedure is that it separates staging of POFs from their ageing process. The female gonads, taken from several captivity experiments and field samples, were classified in this way. Water temperature in captivity tanks corresponded to high values (17-21°C), except for one case in which different day and night temperatures were applied. In addition, 472 field samples (11948 anchovy females) from several cruises were examined; of these, 126 samples (3348 females) were identified as coming from areas of high sea surface temperature (weighted mean =17.76°C, s.d.=0.84) and 131 samples (3181 females) as coming from areas of low sea surface temperature (weighted mean =14.42°C, s.d.=0.75). There was close agreement in the succession of POF stages over time after spawning between the experiment and the field samples. The first four stages of POF degeneration occurred in less than 24 h, and by the end of the first day the POFs were mainly in Stage V. Stages VI and VII showed their highest occurrence during the first and second half of the second day after spawning, respectively. Full resorption of POFs was achieved in about 55-60 h. For the range of temperatures examined (13-19°C), little effect of temperature on the degeneration of POFs over time was noticed. The advanced degeneration stages were found all day round, showing some overlapping periods when successive spawning cohorts co-occurred. The application of these results for ageing POFs is discussed.

Modeling the influence of oceanic‐climatic changes on the dynamics of Pacific saury in the northwestern Pacific using a life cycle model

AbstractA life cycle model for Pacific saury (Cololabis saira) was developed to clarify the possible causes of interannual and decadal variability in its abundance. In the model, the population of saury is composed of two spawning cohorts: one spawned in the Kuroshio region during autumn–winter and the other spawned in the Kuroshio‐Oyashio Transition Zone during winter–spring. The life cycle of saury was divided into six stages: namely egg, larval, juvenile, young, immature and adult stages. The life cycle model combines growth, survival, fishing and reproductive processes, in which the effects of sea surface temperature (SST) in the Kuroshio region and El Niño‐Southern Oscillation (ENSO) events on the winter‐spawning cohorts, the effects of SST in the Oyashio region on the spring‐spawning cohorts, and the effects of fishing on the two spawning cohorts are taken into account. Results of basic modeling, in which environments are assumed stable and the stock is affected by fishing only, shows that the interannual fluctuations in the abundance are small and could hardly explain the observed large annual changes in abundance. On the contrary, results of modeling incorporating the effects of oceanic‐climatic changes corresponded well with actual interannual‐decadal variations in abundance. These results suggest the following environmental effects: (1) SST in the Kuroshio region affects decadal changes in abundance; (2) ENSO events influence the survival of the winter spawning cohort and result in large interannual variations in the abundance. It is concluded that large‐scale climatic and oceanic changes strongly affect the abundance of saury.

Spatial and temporal variation in elemental signatures of statoliths from the Patagonian longfin squid (Loligo gahi)

We quantified elemental signatures in statoliths of 718 Patagonian longfin squid (Loligo gahi) collected in the vicinity of the Falkland Islands (southwest Atlantic) and at sites on the Patagonian Shelf and coastal Peru. All squid were assigned to a spawning cohort by size, spawning condition, and back-calculated spawning date based on daily increments in statoliths. The remaining statolith was then analyzed for six elemental ratios (Mg/Ca, Mn/Ca, Sr/Ca, Cd/Ca, Ba/Ca, and Pb/Ca) using high-resolution inductively coupled plasma mass spectrometry (ICP-MS). Elemental concentrations in the statoliths were broadly similar to other biogenic aragonites. Differences in Sr/Ca ratios in statoliths among geographic locations were generally consistent with a negative correlation between Sr/Ca and temperature. Variations in statolith Cd/Ca and Ba/Ca values confirmed that during winter months, the squid were foraging deeper in the water column. Both Mg/Ca and Mn/Ca ratios in statoliths decreased with squid size, probably corresponding to a decrease in the contribution of the organic component of the statolith. Elemental signatures in the statoliths of L. gahi varied significantly geographically and between spring- and autumn-spawned cohorts, which must therefore have spent significant portions of their life histories in different environments.

DNA markers indicate that distinct spawning cohorts and aggregations of Patagonian squid, Loligo gahi , do not represent genetically discrete subpopulations

The Patagonian squid, Loligo gahi D’Orbigny, has been described as having temporally and spatially identifiable spawning aggregations. Variation at six microsatellite loci was used to assess whether seasonal and geographical spawning groups around the Falkland Islands represent distinct sub-populations. Genetic variation at these loci is high in this species (mean expected heterozygosity=0.87; mean number of alleles=14.7). No evidence of significantly different allele frequencies was found, either between samples from putative spawning cohorts or geographical areas, indicating that L.gahi around the Falkland Islands comprise a single genetically homogeneous population. Age structure analysis of samples (from statolith growth increments) indicated substantial spread in hatching dates among individuals of similar size and maturity status, suggesting the potential for extensive interbreeding between seasonal cohorts. A sample of L.gahi from the SE Pacific (Peru) displayed distinctly different gene frequencies (and allele size distribution at one locus) from SW Atlantic samples, supporting the suggestion that SE Pacific and SW Atlantic populations may represent distinct subspecies.

Growth rate variability of Pacific saury, Cololabis saira, larvae in the Kuroshio waters

AbstractGrowth rate time series of Pacific saury, Cololabis saira, larvae in the Kuroshio waters were constructed using a previously reported relationship between early life stage growth rates and environmental factors in winter (January to March) 1971–2000, including sea surface temperature, chlorophyll a concentration and copepod density. Pacific saury has been commercially exploited and its stock size shows large fluctuations. It spawns from autumn to spring. Growth and survival in the early life stage have been considered the major factors controlling recruitment fluctuations. The winter spawning cohort showed a fast and stable growth rate during their early stage. Ages of 40 mm juveniles (t40) calculated from growth rate estimations were stable during the 30‐yr period and showed a significant positive correlation to the Pacific Decadal Oscillation index in winter. A negative correlation between the t40 and the catch record of medium size saury (24.0–28.9 cm) was detected but was not significant. Recruitment of the winter spawning cohort is thought to be regulated not only by the duration of the vulnerable larval period but also by other biological factors, i.e. mortality after the larval stage and the abundance of predators.

A Population Genetic Analysis of the Potential for a Crude Oil Spill to Induce Heritable Mutations and Impact Natural Populations

The primary environmental impact following an oil spill typically is acute toxicity to fish and wildlife. However, multigenerational effects through toxicant-induced heritable mutations might also occur. Some polycyclic aromatic hydrocarbon (PAH) components of crude oil are potentially mutagenic, although specific components and doses that induce mutations are poorly known. We applied population genetics concepts to assess the extent of mortality and the persistence of deleterious heritable mutations resulting from exposure to potential mutagens, such as crude oil. If lethal mutations are induced, the population will experience some mortality, but the mutations are quickly removed or reduced to low frequency by natural selection. This occurs within one or a few generations when mutations are dominant or partially recessive. Totally recessive alleles persist in low frequency for many generations, but result in relatively little impact on the population, depending on the number of mutated loci. We also applied population genetics concepts to assess the potential for heritable mutations induced by the Exxon Valdez oil spill in Prince William Sound, Alaska, to affect pink salmon populations. We stress that breeding units (e.g., streams with distinct spawning populations of salmon) must be considered individually to assess heritable genetic effects. For several streams impacted by the oil spill, there is inconsistency between observed egg mortality and that expected if lethal heritable mutations had been induced by exposure to crude oil. Observed mortality was either higher or lower than expected depending on the spawning population, year, and cohort considered. Any potential subtle effect of lethal mutations induced by the Exxon Valdez oil spill is overridden by natural environmental variation among spawning areas. We discuss the need to focus on population-level effects in toxicological assessments because fish and wildlife management focuses on populations, not individuals.