Changes in the trophic interactions and the community structure of Lake Taihu (China) ecosystem from the 1960s to 1990s

As the third largest freshwater lake in China, Lake Taihu has suffered from overfishing, eutrophication, and physical disturbance over the last several decades. Evaluating and quantifying changes in the ecosystem can help us better understand and develop hypotheses to explain the dynamics of the ecosystem. In this study, trophic interactions and community structure of commercial fisheries species of Lake Taihu ecosystem were analyzed and compared for three time periods (1961–1965, 1981–1987, and 1991–1995) using the Ecopath with Ecosim model with the aim of evaluating the changes in the population dynamics and ecosystem development mechanism spanning the period from the 1960s to 1990s. The results show that the biomass of large predators decreased over the three decades, while the biomass of small species increased. Increases in the P/B ratios and fishing mortality levels observed for species groups reveal rapidly intensifying fishery stress over the three decades. The fisheries operated at the highest trophic level during the 1980s, and there are some indications of “fishing down the food web” in this ecosystem between the 1980s and the 1990s. Drawing upon Odum’s theory of ecosystem maturity, the structured, web-like ecosystem of the 1960s developed into a highly mature system during the 1980s; yet, in the 1990s, this structure became less complex and the system’s maturity fell to its lowest observed level. During this period, the successional development of the system occurred in reverse.     

Presumptive mycobacteriosis in North-east Atlantic mackerel, Scomber scombrus L.

A total of 9470 mackerel aged from 0 to 20 years was examined for a disease condition whose causative agent has not been identified but which resembles mycobacteriosis. The study area extended from off Portugal to the northern North Sea. Most mackerel over 2 years old snowed evidence of gross infection. Mean intensity increased with age, indicating a chronic disease of low pathogenicity. There is statistical evidence of an adverse effect on growth, and it is suggested that this may delay first spawning of some young mackerel for at least 1 year. Western stock mackerel appear to be more heavily infected than North Sea stock, and the lowest levels of infection were found off Portugal. The general level of infection decreased in the most recent year classes examined–those of 1982, 1983 and 1984.     

Long-term changes in crustacean zooplankton and water quality in a shallow, eutrophic Chinese lake densely stocked with fish

From surveys made in 1962–1963, 1973–1974, 1979–1996 at two Stations in Lake Donghu, a shallow eutrophic water body near Wuhan, P. R. China, the authors, derive long-term changes in species composition, standing crop and body-size of planktonic crustaceans. The species number decreased from the 1960s to the 1990s. The cladocerans dropped from 46 (1960s) to 26 (1980s) to 13 (1990s); the copepods decreased from 14 (1960s) to 10 (1980s) to 7 (1990s). From the mid-1980s on, the dominant crustaceans also changed: Daphnia hyalina and D. carinata ssp. were replaced by Moina micrura and Diaphanosoma brachyurum at Stations 1 and 2, respectively; Cyclops vicinus replaced Mesocyclops leuckarti.Densities and biomass of Cladocera decreased markedly after 1987. Annual average densities and biomass of cladocerans were statistically differences between 1962–1986 and 1987–1996 (P > 0.01). Annual average densities of Daphnia (Station 1 + Station 2) were negatively correlated with fish yield .Since the 1980s, annual average body length of Cladocera and Calanoida decreased, while annual average body length of Cyclopoida increased. In the same years, average body length of copepods was lower during May–October than during January–April and November–December.A 12-yr data analysis showed annual average concentration of chlorophyll^-a (Chl^-a) to be negatively correlated with annual average density of Daphnia, whilst lake transparency was positively correlated with annual average densities of Daphnia. The results imply that, since Daphnia feeds efficiently on phytoplankton, it could decrease concentration of Chl^-a, and enhance water transparency.     

DENSITY DEPENDENT GROWTH IN NORTH PACIFIC SPERM WHALES

Data from the North Pacific sperm whale (Physeter catodon Linnaeus, 1758) fishery were examined for a possible density dependent change in growth during 40 yr harvesting after World War II. Early in this period males from the eastern stock were 16.8 m or less in length. By the early 1970s the largest males in the catch exceeded 16.8 m in length and reached 18.9 m in the late 1970s. The proportion of males measuring over 16.8 m, among sexually mature males (≥14.0 m), increased from 0 to >20% during the 1970s. Increases in the maximum size of males were possibly preceded by a change in the frequency distribution of body lengths in the middle 1960s when only 10% of the postwar catch had been taken. Testis weights suggested an increase in body length at sexual maturity. Two of the three putative North Pacific stocks showed similar growth changes. Adult males taken in the Bering Sea did not show such changes during the exploitation which ended in 1972 because of overfishing. Females showed no detectable change in body size. It is concluded that: (1) density dependent effects on male growth are greater before sexual maturity than after it, (2) males may show density dependent changes even at a population level above 90% of the carrying capacity, (3) polygynous males acquire more mates and realize higher reproductive success because of increased body size, and (4) females appear to maximize production by maturing earlier and shortening calving intervals in response to density change.     

Life History of Mediterranean Horse Mackerel Trachurus mediterraneus (Carangidae) from Crimea (Black Sea)

Journal of Ichthyology - The sex ratio, body length–age structure, growth rate, maturity dynamics, and mortality are studied in Mediterranean horse mackerel Trachurus mediterraneus from the...     

REPRODUCTIVE MATURITY AND SEASONALITY OF MALE SPOTTED DOLPHINS, STENELLA ATTENUATA, IN THE EASTERN TROPICAL PACIFIC

We estimated age at attainment of sexual maturity and examined reproductive seasonality for male spotted dolphins, Stenella attenuata , from the eastern tropical Pacific Ocean. Maturity was determined by histological examination of testes. Average age at sexual maturation was 14.7 yr (the mean of two readers' age estimates). Testis and epididymis weight and seminiferous tubule diameters were reliable indicators of maturity, whereas age, length and color phase were less reliable. Seasonality was determined by changes in testis and epididymis weight, relative quantity of spermatids and spermatozoa, and lumen diameter, as well as an index of testis development (weight of the right testis and epididymis divided by length of the right testis). Testis and epididymis weights and index values peaked in July and August, midway between two predicted mating seasons for the northern offshore stock, but spermatozoa levels were elevated during the predicted breeding seasons.     

Geographic variation in the maturity and growth schedules of English sole along the U.S. west coast

Logistic regression analyses showed that the maturity v. length relationship for female English sole Pleuronectes vetulus varied significantly among sampling locations from California to British Columbia in June–September. Stepwise analyses found that latitude, bottom gradient, bottom temperature and sediment type were all significant factors. Regression analyses of age at length from subsamples indicated that latitude, maturity and bottom sediment had significant effects on growth. Data from the aged subsamples showed significant differences among age classes in the length v. maturity relationship with older fish attaining maturity at smaller sizes than younger fish. On a coast wide basis the length and age at 50% maturity were c. 230 mm and 4·7 years respectively. Growth rate and length at 50% maturity have decreased substantially relative to observations from the 1950s, but age at 50% maturity has increased.     

Year-class fluctuations in vendace,Coregonus albula (Linnaeus): Who's got the upper hand in intraspecific competition?

The vendace Coregonus albula (L.) populations in the lakes Mjøsa and Osensjøen exhibited fluctuating year-class strength. In Mjøsa, a strong year-class emerged every third year, except for the four year period between the strong year-classes 1969 and 1973. The difference between the strong and weak year-classes decreased from the 1960s, through the 1970s to the 1980s. The Mjøsa vendace matured sexually at age 2 +, and more than ten sexually mature age-groups were present in the population. Growth ceased at maturation, and asymptotic length was 23.6 cm. In Osensjøen, one strong year-class (1969) dominated the population during the period 1976–1987. The Osensjøen vendace matured sexually at age 3, and more than 15 sexually mature age-groups were present in the population. Growth ceased at maturation, and asymptotic length was 28.4 cm. In both lakes, vendace fed on crustacean zooplankton in the epilimnion throughout summer and autumn. Our data indicate that regular year-class oscillations occur as a result of the juvenile survival being negatively correlated to the number of adults.     

Sexual maturation of cod (Gadus morhua L.) in the southern Baltic (1990–2006)

Baltic cod, like other species, is susceptible to inter‐annual fluctuations in sexual maturation, depending on the length, age, sex, extent of the habitat area, and stock abundance of the cod population. Maturity is one of the biological indicators used to detect changes in a stock that can be caused by fishing. To address these issues specifically for the eastern Baltic cod stock, long‐term data (1990–2006) from Polish research vessels in the southern Baltic were examined. To date, the ICES has used the same maturity ogives over extended periods and assumed invariant sex ratios for the assessment of eastern Baltic cod. The combined maturity ogives calculated in the present study were markedly lower, particularly for age groups 2–4 (5), in all periods, than those used in the ICES assessment. Moreover, the proportion of females increased with length and age, suggesting that annual verification of the sex ratio is needed. The present study also revealed that the total length (L_50%) and the age (mean age‐at‐maturity; MAM_50%) at which 50% achieved first sexual maturity were higher for females than for males in the study period. The long‐term mean L_50% and MAM_50% for females were 43.9 cm and 4.3 years, respectively, and for males 34.8 cm and 3.4 years. There was also a spatial difference between calculated maturity ogives, with slightly lower L_50% (range: 1.4–8.6 cm) in the Gdańsk Basin than in the Bornholm Basin. The increasing trend in fishing mortality observed in 1993–2004 (ICES data) did not translate into a temporal trend in calculated maturity ogives. However, changes in L_50% and MAM_50% reflected recruitment variations (ICES data). The significance of these findings is discussed in the context of the environment and recruits abundance.     

The reproductive traits of Scomber japonicus (Houttuyn, 1782) in the Eastern Adriatic Sea

The aim of the present study was to investigate the fisheries biology of Scomber japonicus (Houttuyn, 1782) in the Adriatic Sea, to enable implementation of appropriate regulatory measures for fisheries. Reproductive biology and sexual patterns of S. japonicus (chub mackerel) were examined from monthly random samples of commercial catches from purse seine nets (10 mm stretched mesh size) in the eastern Adriatic Sea. The annual mean chub mackerel fork length (FL) was examined from 1998 to 2007. Average fork lengths were approximately 25 cm between 1998 and 2002, decreasing to 22 cm between 2003 and 2007. In addition, sex ratios fluctuated as a function of size and month: females were more abundant in the smaller length classes, as well as before and after spawning; males were more abundant in the larger length classes and during spawning. The overall sex ratio was 0.68; females were significantly predominant. 50% of the chub mackerel population was sexually mature at a FL of 18.3 cm, and both males and females reached sexual maturity at FLs of 20.4 cm and 16.8 cm, respectively. Based on gonad maturity stages, gonad weight and gonadosomatic index, chub mackerel spawned from May to August, with peak spawning in June for both sexes. The mean absolute fecundity was 181 277 ± 62 090 oocytes per ovary. A positive exponential correlation was found between fecundity and fork length, gonad weight, and total chub mackerel weight (r² = 0.640; r² = 0.686 and r² = 0.607, respectively).     

A MspI polymorphism in the bovine ornithine decarboxylase gene and its possible association with selection for milk production in Holstein bulls

A polymerase chain reaction (PCR)-based method for detection of a MspI-restriction fragment length polymorphism (RFLP) in the bovine ornithine decarboxylase gene was developed, and the allele frequencies of the polymorphism in two groups of Holstein bulls representing progeny-tested bulls during the 1950s-1960s and 1980s, respectively, were estimated. The frequencies of the MspI(-) allele were 0.229 and 0.077 and that of MspI(+) were 0.771 and 0–923 in the progeny-tested bulls of the 1950s-1960s and 1980s, respectively. The difference in allele frequencies between the two groups was statistically significant (P< 0.005). Genetic drift could be responsible for the changes in allele frequencies; however, it could also be possible that selection for milk production was associated with the changes of the allele frequencies in the two bull populations.     

Testes development and maturity classification of albacore (Thunnus alalunga ( Bonaterre, 1788)) from the Eastern Mediterranean Sea

The criteria of testicular maturity during the spawning season and for maturity rates are described according to age for 140 male albacore (Thunnus alalunga, Bonnaterre, 1788) sampled between April and August, 2002–2008 in the Eastern Mediterranean Sea. Histology of gonad samples was used to determine maturity status. Spermatogenesis and its relation to reproductive biology are reported. Fish ranged in fork length (FL) from 63 to 90 cm. The reproductive classes were based upon changes in the testicular morphology and stages of the germinative cells, i.e. immature, developing, maturing, spawning, and spent. Mature stages of testes including the smallest sample of a 63 cm male were observed from May to August of each year during the study. The reported evidence indicates that the size and age of first sexual maturity values of males of the Eastern Mediterranean population are nearly the same as in the Western Mediterranean population, but lower than in the Atlantic stock. The results of this histological investigation, conducted for the first time on this species in the Mediterranean Sea, will enable more precise future estimations for sustainability of the male albacore stock in the Eastern Mediterranean.     

Maturity Ogives for South Pacific Albacore Tuna (Thunnus alalunga) That Account for Spatial and Seasonal Variation in the Distributions of Mature and Immature Fish

Length and age at maturity are important life history parameters for estimating spawning stock biomass and reproductive potential of fish stocks. Bias in estimates of size and age at maturity can arise when disparate distributions of mature and immature fish within a population are not accounted for in the analysis. Here we investigate the spatial and temporal variability in observed size and age at maturity of female albacore tuna, Thunnus alalunga, using samples collected across the South Pacific. Maturity status was identified using consistent histological criteria that were precise enough to allow for mature but regenerating females to be distinguished from immature females during the non-spawning season, permitting year-round sampling for maturity estimation in albacore. Using generalised linear mixed models, we found that the proportion of mature females at length varied significantly with latitude and time of year. Specifically, females at northern latitudes (∼10–20°S, where spawning occurs) were mature at significantly smaller lengths and ages than females at southern latitudes (∼20–40°S), particularly during the spawning season (October–March). This variation was due to different geographic distributions of mature and immature fish during the year. We present a method for estimating an unbiased maturity ogive that takes into account the latitudinal variation in proportion mature at length during a given season (spawning or non-spawning). Applying this method to albacore samples from the western region of the South Pacific gave a predicted length at 50% mature of ∼87 cm fork length (4.5 years).     

Changes in diet and morphology of Finnish goshawks from 1960s to 1990s

We studied the morphology of the goshawk in northern Finland by measuring skin and skeletal characters of 258 museum specimens dated between 1961 and 1997. We predicted a decrease in the size of male goshawks from the 1960s because availability of their main prey, grouse, has decreased since then and grouse have been replaced in the diet by smaller prey during the breeding season. Based on the assumption that winter is the most critical period for females, we predicted that female size should have increased because their winter diet consisted of more and more mountain hare, which is a prey generally larger than grouse. Analyses revealed that male size has indeed decreased since the 1960s, while adult females have increased in size. Our data suggest that these morphological shifts were the result of selective pressures due to changes in diet. We also found changes in the (size-independent) shape of the hawks. Relative wing and tail lengths of adult hawks became longer between 1980 and 1990 compared with the 1960–1970 period, while relative juvenile wing and tail lengths tended to decrease. As a result of these morphological changes size dimorphism between the sexes increased from the 1960s to the 1990s. Received: 18 January 1999 / Accepted: 14 July 1999     

Growth and production of the dominant pelagic fish, Acanthobrama terraesanctae, in subtropical Lake Kinneret, Israel

Acanthobrama terraesanctae (local name lavnun), an endemic planktivorous cyprinid, dominates total fish numbers (>80%) in Lake Kinneret, and may have a significant top-down impact on the lake ecosystem. The length of young-of-the-year fish calculated from the von Bertalanffy equation agreed with field observations of juvenile growth. An unusual bi-modal length-frequency distribution observed in May 1993 provided additional help in age identification. Males grew more slowly than females and reached a lower maximum length. Total mortality coefficients (exponents) of males and females >12 cm (minimal legal size of fish in the catch) were similar ( c. 1·52). An average cohort reaches maximum biomass during its second year. Maximum production is created at the end of the second year. The production: biomass ratio of the population was 1·16, and 36% of total lavnun standing stock was taken by fishing. From the late 1980s to early 1990s, when standing stock and population structure were stable, the average harvest of 1000 t was consistent with a total lavnun biomass of 2800 t, which constitutes 50–70% of the total fish stock measured acoustically in the lake. Such a biomass could be sustained by the known production of zooplankton. Absence of verified growth data for lavnun contributed to the collapse of the fishery in 1993, because it hampered timely revision of fishery policy in response to the drastic changes in the lavnun stock in 1992.     

我国陆地棉基础种质表型性状的遗传多样性分析

选用43份陆地棉基础种质为研究材料,随机区组排列种植,并进行果枝数、铃数、株高等田间性状调查和衣分、铃重、纤维品质等测定.按照不同时期、不同来源、不同生态区对这些基础种质分别进行表型性状的遗传多样性分析.结果表明:基础种质间在产量、品质、农艺性状等表型性状上差异显著或极显著,遗传多样性指数为0.88;3期基础种质大部分性状差异不显著,但第2、3期基础种质比第1期的纤维长、整齐度高、细度好、衣分增加、早熟性提高、抗病和耐旱性增强,第2期基础种质遗传多样性和遗传丰富度最高;来自不同棉区的基础种质表型性状差异较大,黄河流域棉区基础种质综合性状较好,长江流域棉区产量性状较高,北部特早熟棉区早熟性好,美国引进种质抗黄萎病性较强;国内基础种质比国外品种在纤维长、强、细上的变异系数均有不同程度降低,但国内基础种质表型多样性比引进品种高.以上研究说明引进品种经过长期的环境适应、自然选择和人工选育后,产生了表型变异较为丰富的基础种质类型.     

Reproductive biology of the blue jack mackerel,Trachurus picturatus (Bowdich, 1825), off the Canary Islands

The reproductive cycle of the blue jack mackerel, Trachurus picturatus, had not been described for the Canary Islands. Between March 2005 and March 2006 monthly samples of T. picturatus were collected randomly at the central fishery wharf from the commercial catches of purse‐seiners in Tenerife Island waters (Canary Islands). Some 2472 specimens were analysed, with total lengths from 10.4 to 31.9 cm. Although females outnumbered males in summer, males were more abundant in the sex ratio (1.36 : 1). Based on the monthly evolution of the gonado‐somatic index and the proportion of mature individuals, the spawning season occurred between January and April, peaking in February. Lengths at first maturity (LFM) were calculated from the maturity ogives by the Gompertz model for all specimens (22.79 cm), for males (21.20 cm) and for females (23.05 cm). In this area the minimum legal size for T. picturatus is actually smaller than the length at first maturity and should be revised to avoid depletion of the stock.     

The Dynamics of a Metapopulation: Changes in Life-History Traits in Resident Herring that Co-Occur with Oceanic Herring during Spawning

Different populations of Atlantic herring are regarded as forming a metapopulation, but we know little about the dynamics of the connectivity and degree of interbreeding between the populations. Based on data from three periods between 1962 and 2011, we identified the presence of two components of herring in a small semi-enclosed coastal marine ecosystem based on different somatic growth patterns and mean vertebrae sum (VS). The two components were interpreted as belonging to a resident herring population and the migratory, oceanic Norwegian spring spawning (NSS) herring population, and they co-occurred during spawning. In the 1960s, resident herring characterized by slow growth and low VS co-occurred with rapid growth, high VS oceanic NSS herring. Similar slow-growing resident and rapid-growing NSS herring were found in the 1970–80s, but both populations now had low VS suggesting similar origins. Finally, in the 2000s both populations showed rapid growth. The changes coincided with the NSS herring going from a state of high abundance and oceanic distribution to a collapse in the late 1960s that resulted in a coastal distribution closer to resident herring populations, before full recovery and resumption of the migratory, oceanic pattern in the 1990s. During all three periods, NSS herring were only present in the local system up to an age of about five years, but the synchronous spawning of the populations supports mixed spawning and interbreeding. During the investigation period both longevity, length at age (growth) and length-at-first maturity increased markedly for the resident herring, which then became more similar to the NSS herring. Genetic and/or cultural factors are believed to be the main causes of the observed changes in life history traits, although some effect of changes in environmental factors cannot be excluded. Our study suggests that relationships among populations in a metapopulation can be highly dynamic.     

Development of body weight in the Norwegian population

In Norwegian adult men, body mass index (BMI) increased from around 25 kg/m(2) in the late 1960s to around 26.5 kg/m(2) in the late 1990s, and the prevalence of obesity increased from about 5% to 15% in the same period. In women the prevalence of obesity actually decreased from around 13% in the late 1960s to 7% in the late 1980s. However, during the last years the prevalence has also increased reaching about 13% in the late 1990s. It is important to note that both mean and median BMI has increased with a shift in the distribution to the right. The proportion of normal weight individuals has thus decreased, whereas the proportion of obese has increased. The increase in BMI has occurred in different age groups. Although obesity is associated with low education and a sedentary lifestyle, the increase in BMI has also occurred in the more educated and physical active.     

Growth of female southern elephant seals Mirounga leonina at Macquarie Island

Body growth of 137 female southern elephant seals (Mirounga leonina) over 1 year of age was investigated at subantarctic Macquarie Island. An asymptotic straight line, snout–tail body length of 2.57±0.03 m was estimated to be attained at 9 years of age, using a three-parameter Gompertz equation. A significant increase of approximately 0.1 m (5%) in mean body length of females between 1 and 10 years of age was estimated to have occurred between the 1950–1960s and 1990s at Macquarie Island. This is consistent with a reduction in both the rate of population decline and the age of onset of sexual maturity. Age determination using dental cementum layers and the importance of standardised measurements in pinniped growth studies are discussed.