Proportion Of Mature Individuals Research Articles

The East Asian species <i>Thermocyclops taihokuensis</i> (Harada 1931) (Crustacea, Copepoda, Cyclopoida) in the Taganrog Bay of Azov Sea

In August–September 2021–2023, the composition and abundance of pelagic Copepoda in the Don River delta and in the eastern part of the Taganrog Bay of Azov Sea were studied. The East Asian copepod, Thermocyclops taihokuensis (Harada 1931) was recorded for the first time from the eastern part of the bay at a water salinity of 3.5–5.8‰. The species must have entered the Taganrog Bay with water from the Don River. The largest population of the invader was registered in the Don River delta in August 2021 ( 7.000 ind./m3); in the bay in September 2023 it reached 4.000 ind./m3. The body size and fertility of the invader were close to those in the Tsimlyansk Reservoir and the Don River. In 2023, the reproduction of T. taihokuensis was noted in the bay with an extremely low (about 1%) proportion of mature individuals in the population. The species seems to have not yet been fully naturalized in the bay, its population still being supported by bioflow from the Don River delta. The potential consequences of the introduction of this alien copepod for the zooplankton of Taganrog Bay are discussed.

Size and age structure and population of the kaluga Huso dauricus and the Amur sturgeon Acipenser schrenckii (Acipenseridae) in the Amur river

Based on research findings from 1963–2021 the analysis of size-age indicators, qualitative structure of populations and changes in the number of kaluga Huso dauricus and Amur sturgeon Acipenser schrenckii in the river was carried out. Amur. It is established that in the period from the 60s. last century to 2008–2011 in the kaluga and the Amur sturgeon in the Amur River, there was a reduction in the size range and number of age groups, the proportion of mature individuals, the level of replenishment of populations with juveniles and abundance. The main reason for these changes is INN fishing (illegal, unreported and unregulated). According to the results of research in 2021, it was revealed that the modern number of kaluga exceeded the figures of the 60s. last century. In the Amur sturgeon, the process of population growth has not yet reached the historical values noted in the 1960s–1970s, but exceeded the indicators of the 1980s and subsequent years. Despite the noted positive points, at present, the population of kaluga in the river. Amur is characterized by the smallest average size and age over 60 years of study. The situation is better for the Amur sturgeon, which is due to the lower interest of fishermen in this species and the large volume of release of its juveniles from sturgeon hatcheries (ORZ). The reason for the positive dynamics is the artificial reproduction that has been developing on the Amur over the past decade, as well as the introduced set of restrictions on the Pacific salmon fishery. To further increase the number of Kaluga and Amur sturgeon in the river. Amur, it is proposed to maintain the current volumes of artificial reproduction of sturgeons and extend the restrictive measures in the salmon fishery for at least the next 10 years.

Length Based Assessments for European Pilchard Sardina pilchardus and European Anchovy Engraulis encrasicolus, in the İzmir Bay, Aegean Sea

In the Mediterranean Sea, European pilchard Sardina pilchardus and European anchovy Engraulis encrasicolus are the most important small pelagic fish regarding their ecological role, and revenue. Here, we perform a comprehensive assessment of length-based methods for those small pelagics from İzmir Bay, Aegean Sea. Therefore, the Length-based Bayesian Estimator and Length-based Spawning Potential Ratio were used to evaluate the stock structure and status of two important small pelagic fish. The length range for Sardina pilchardus was from 7.1 cm to 17.3 cm in TL. The ratios Lmean/Lopt and Lc/Lc_opt were over 1, suggesting truncated length structure and fishing of not too small individuals. The proportion of mature individuals in the catch was far less than half (36%) suggesting that in these fisheries catch consists mostly of immature individuals. The length range for Engraulis encrasicolus was from 5 cm to 15 cm in TL. The ratios Lmean/Lopt and Lc/Lc_opt were over 1 (1.2 and 1.3, respectively), suggesting truncated length structure and fishing of large individuals. The proportion of mature individuals in the catch was over half (52%) suggesting that in these fisheries catch consists of adults. The estimated sizes at median 50% selectivity (SL50) for S. pilchardus (11.1 cm) was ∼0.6 cm shorter than its lengths at 50% maturity (L50) of 11.7 cm, which indicates that a large proportion of the catch was immature. The median estimate of the spawning potential ratio was ∼0.19 for S. pilchardus and ∼0.48 for E. encrasicolus.

Role of intraspecific competition in intrinsic growth rate regulation in an Oikopleura dioica (Tunicata) population

Planktonic Oikopleura dioica respond almost instantly to opportunistic algal blooms, but it is unknown whether the population increase can change from an exponential to a logistic model to avoid a final sudden collapse. To test the hypothesis that intraspecific competition regulates the intrinsic rate of natural increase (r), density-dependent effects on growth and reproduction performance were investigated in O. dioica via laboratory incubations. Over a large food concentration range, batch maturation was observed above the per capita food supply (PFS) of 8.1 µgC/ind. in 4.5 d. Somatic growth was saturated beyond this PFS value, whereas gonad length increased continuously. Below this threshold, individuals reached small body and gonad lengths, and maturation was rarely observed during the incubation period. The gonad/body volume and maturation ratios also increased with the PFS. Instead of the food concentration, the r values were regulated by competition pressure via variability in maturation duration and the proportion of mature individuals in the cohorts. When the minimum food demand was satisfied in the designated generation time, the r value tended to be regulated by the spawning proportion in the population. Otherwise, prolonged development duration and decreased r values were expected.

Catch dynamics of set net fisheries in Israel

Artisanal fisheries are globally common, providing almost 50% of total world landings. However, due to overfishing, they are worldwide on the verge of collapse. Fisheries in the eastern Mediterranean Levantine Basin must additionally cope with extreme thermal conditions, meaning that fish are typically smaller relative to other regions. In Israel, mesh size restriction has been suggested as a means to rebuild stocks, but data on artisanal fishing landings across mesh size are extremely sparse. The aim of this study was to quantify set net catches across different mesh sizes in order to identify fishing methods that can benefit both fish populations and fishers. We hope to identify which mesh size provide the highest ratio of commercial to non-commercial fished biomass, the lowest variance in fisher’s revenues and benefits the reproductive potential of the resource by targeting mature individuals. We found that across the range of mesh sizes examined, smaller mesh sizes (i.e. 25, 28, 30) did not catch a larger proportion of individuals below reproductive size but, rather, smaller species. The 43 mm mesh, caught larger individuals with lower total biomass but of larger species, with similar proportions of individuals below reproductive size to smaller mesh sizes. Net mesh size was not associated with fisher revenue. Trammel nets were found to be the least selective in relation to non-commercial by-catch, although the proportion of mature individuals in the catch was larger than for the other nets examined. These findings suggest that mesh size restrictions, across the range of mesh sizes examined, will not result in a decrease in catch of individuals below reproductive size but rather shift the species composition of the catch towards large-bodied, often high trophic level, species. Thus, mesh size restrictions are unlikely to rebuild fish stocks of high-value commercial species nor increase fisher revenue. We suggest that artisanal fisheries management in the Levantine Basin should evaluate new management measures and consider reducing overall fishing pressure along with implementing ecosystem-based fisheries management, such as the closure of fish reproduction and recruitment areas and establishment of marine protected areas.

Reproductive Cycle of Donax punctatostriatus (Hanley, 1843) (Bivalvia: Donacidae) in a Sandy Beach of Sinaloa, Mexico

The reproductive cycle, stages of gonadal development, and minimum size of sexual maturity are described for a population of the clam Donax punctatostriatus Hanley, 1843 from a sandy beach in southern Sinaloa, Mexico. A total of 880 clams were collected from January 2009 to June 2010; 3.2% were sexually undifferentiated and 1.4% had the trematode parasite Postmonorchis sp, in the gonadal tissue. The total length of the clams ranged from 3.5–25.64 mm ( = 13.51, S.D. = ±4.47 mm). The sexual proportion did not differ significantly from ♀1:1♂ (p > 0.05). The minimum size at sexual maturity (L50) was L50 = 12.03 mm. The gametogenic cycle comprise six stages of gonadal development (0-V). The population is reproductively active throughout the year and spawning is continuous, with three major peaks in April, July and September 2009. In March, when the water temperature was between 21–23 °C, most individuals were in stage I. This period is characterized by a rapid maturation of gametes. At the end of October and during November, when water temperature was warmer (25–28 °C), 50% of the individuals were in stage V (spent). Recruitment was more intense from July to October of 2009, when the highest temperatures of the year were recorded (28–31 °C). Photoperiod and the proportion of mature individuals of both sexes were significantly correlated (Pearson's correlation value = 0.62; p < 0.05). Since this clam is a potential resource for human consumption, the information here presented may contribute to a better management and use of their populations in the Mexican Pacific.

Effects of a crustacean parasite and hyperparasite on the Japanese spiny oyster Saccostrea kegaki

Parasitism is one of the most common interspecific interactions, but little information exists on the detailed relationships among hosts, parasites, and hyperparasites (secondary parasites) in marine ecosystems. Pea crabs parasitize a wide variety of marine animals, and the crabs themselves are often parasitized by other animals. The present study investigated the relationships among the oyster Saccostrea kegaki, its parasite, the pea crab Pinnotheres boninensis, and a hyperparasite, the isopod Onychocepon resupinum. Field sampling was conducted during the oyster’s reproductive season (June–September 2014 and 2015) to evaluate effects of the pea crab on the body weight, maturation, and sex of the oyster in western Japan (Banshozaki, Shirahama Town, Wakayama Pref.; 33.41°N, 135.20°E). The relationship between the pea crab and the isopod and indirect effects of the isopod on the oyster were also investigated. The pea crab reduced the oyster’s body weight and affected its reproduction: the proportion of mature individuals was lower in infested oysters (39.1%) than in non-infested ones (86.2%). The isopod affected the crab’s sexual characteristics: infested female crabs had poorly developed ovaries, and infested males showed degrees of feminization and increased body size. The prevalence of the isopod was much higher in male (47.1%) than female (6.4%) crabs inside the oyster shells, suggesting that the parasitized male crabs became larger and were forced to remain inside the shells. Therefore, the isopod appears to have an indirect negative impact on the oyster by changing the male crab’s traits.

Reproductive biology of the planehead filefish Stephanolepis hispidus (Pisces: Monacanthidae), in the Canary Islands area

The reproductive biology of the planehead filefish, Stephanolepis hispidus, in the waters of the Canary Islands area was studied. The study was conducted with a sample of 906 specimens from 8.9 to 25.9 cm in total length (TL) that were caught in fish traps from February 1998 to August 1999. Females predominated in the catches, and the sex ratio of 1.0:1.4 significantly deviated from the theoretical 1:1 distribution. This ratio varied when calculated by the length classes and by the season. Based on the monthly evolution of the Gonadosomatic Index (GSI) and the proportion of mature individuals, the spawning season occurred between May and October, with a peak in July and August for both sexes. This species accumulates energy reserves in the liver to be spent during the maturation of the gonads and spawning. The mean size at sexual maturity (L50) was 13.9 cm TL in females and 14.9 cm TL in males. The fecundity of S. hispidus fluctuated between 14,071 and 91,323 (mean = 55,239 ± 19,079), and the relative fecundity oscillated between 460 and 1,238 oocytes/g of eviscerated weight (mean = 904 ± 206). The diameter of the oocytes was 0.47 mm (SD = 0.10). The described reproductive characteristics provide options to fishery managers including regulations for spatial and temporal fishing closures to protect the breeding fish during spawning and the selectivity of fishing gears. Thus, it is proposed that fishing be limited to water depths greater than 30 m and that the minimum legal length of fish be established at 18 cm TL.

Extirpation for Conservation: Applying Predictors of Extinction Risk to Eradicate Introduced Trout Populations for Lake Restoration

The restoration of mountain lakes affected by non-native fishes requires the removal of the introduced species. While extensive research has illuminated the physical habitats and complex food webs of mountain lake ecosystems, little is known about the self-sustaining fish populations, particularly in our study area, Waterton Lakes National Park (WLNP), Canada. We used generalized linear models to examine four population characteristics associated with the vulnerability of populations to depletion by gillnetting: 1) catch per unit effort (CPUE), 2) proportion of females, 3) proportion of mature individuals and 4) length of mature trout, as a proxy for age at maturity. There were significant differences between populations in CPUE and length of mature trout, but not in the proportion of females or mature individuals. We thus incorporated the former characteristics to rank 11 trout populations by their susceptibility to eradication. Two lakes in the Lineham basin were the best candidates for trout eradication due to their low population density and large size at maturity. The application of demographic characteristics to select introduced populations for eradication is a simple yet meaningful step in restoration commonly constrained by a lack of biological knowledge.

Temporal trends in age and size at maturation of four North Sea gadid species: cod, haddock, whiting and Norway pout

Younger ages and smaller sizes at maturation have been observed in commercial fish stocks over the last century. We establish that age and length at 50% proportion mature (i.e. the proportion of mature individuals in a population or the probability that an individual is mature) decreased from the 1970s to the 2000s in North Sea cod Gadus morhua, haddock Melanogrammus aeglefinus and whiting Merlangius merlangus, but not in Norway pout Trisopterus esmarkii. The potential contributions of demography, phenotypic plasticity and evolution to these trends were assessed. First, maturation trends were extricated from demographic effects and growth-dependent plasticity by estimating probabilistic maturation reaction norms (PMRNs). PMRN midpoints have significantly shifted downwards at most ages for cod, haddock and whiting, but not for Norway pout. Second, increased temperature and food abundance, loosened trophic competition and relaxed social pressure may also trigger growth-independent plasticity in maturation. Principal component regression of PMRN midpoints on annual estimates of relevant environmental vari- ables exhibiting a temporal trend suggest that, despite some evidence of environmental effects, PMRN trends were mostly independent of growth-independent plasticity in haddock, whiting and male cod, but not in female cod. According to these findings, evolution of maturation, potentially in response to fishing, is plausible in haddock, whiting and male cod, but unlikely for Norway pout, and does not explain trends in female cod maturation. In agreement with life-history theory, the maturation response was larger in fast-growing, late- and large-maturing species exhibiting moderate reproductive effort.

Prospects for the use of strains of the genus Trichoderma to obtain vermicomposts with fungicides and growth-stimulating properties

The addition of the Trichoderma asperellum MG-97 strain and of a biological product Trichodermin-M based on it enables the reduction in terms of composting of organic wastes. As a result of composting, one observes an increase in the biomass of worms with a high proportion of mature individuals in comparison with the control. The obtained biopreparation has increased fungicide and plant growth-stimulating properties.

Reproductive Biology of Pacific Ocean Perch and Northern Rockfish in the Aleutian Islands

AbstractEstimates of maturity (i.e., the proportion of mature individuals at age) play an important role in assessing stock productivity; however, this information has not been published for rockfishes in the Aleutian Islands. Ovary and otolith samples were collected from Pacific Ocean Perch Sebastes alutus and Northern Rockfish S. polyspinis during both fishery‐independent and fishery‐dependent cruises in 2010 to investigate maturity and other aspects of reproductive biology. Histological examination of ovaries indicated that both species exhibited general parturition in April, while specimens caught in the summer and fall were maturing and generally exhibited progressive stages of vitellogenesis. Histological analysis was more reliable when characterizing ovary condition than were macroscopic or visual assessments during the developing period. Estimates of natural mortality, based on a relationship with the gonadosomatic index, were 0.040 for Pacific Ocean Perch and 0.042 for Northern Rockfish. Mean fecundity estimates calculated for Northern Rockfish (89,320 oocytes) were correlated more with length and weight than age. Estimates of age and length at 50% maturity were 9.1 years at 32.4 cm for Pacific Ocean Perch and 7.6 years at 27.7 cm for Northern Rockfish and indicate maturation at younger ages than do previous studies from the Gulf of Alaska. This information on reproductive biology will improve estimation of fishing mortality reference points and management of these commercially important species in the Aleutian Islands.Received June 22, 2012; accepted December 10, 2012

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

Summary 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.

Reproductive biology of alfonsino Beryx splendens

The main aim of this work is to provide a detailed analysis of the reproductive cycle of Beryx splendens in the Juan Fernández Archipelago. The gonadosomatic index (I(G)) and maturity ogives in both sexes were estimated using an extensive database collected by onboard scientific observers between January 2006 and October 2009. A histological analysis of maturation was also completed for females collected between May and December 2001. Variations in both I(G) and proportion of mature individuals were observed in fish with a fork length (L(F)) >37 cm for females and >33 cm for males. The main reproductive season was in the austral winter and spring (June to November). Fork length at 50% maturity (L(50)) was estimated as 39·67 cm for females (95% c.i. =39·34, 40·02 cm) and 36·88 cm for males (95% c.i. =36·45, 37·36 cm) using macroscopic analysis of gonads. Estimates for females using histological data varied slightly with an estimated L(50) of 43·67 cm (95% c.i. =42·82, 44·91 cm). Changes in I(G) and maturity were modelled as a function of month and L(F) within a generalized additive model framework. A high porportion of immature individuals were found throughout the year. The results of this study are compared with reproductive traits reported for B. splendens in other areas of its distribution and are discussed with reference to exploitation, vulnerability and conservation of the B. splendens stock in Juan Fernández Archipelago.

Seasonal trends of the reproductive cycle of Octopus vulgaris in two environmentally distinct coastal areas

Octopus vulgaris is an important fisheries resource, particularly in Iberian waters. Species life cycle is short with capacity to adapt to different environmental conditions and, considered a simultaneous terminal spawner. Data on maturation and other biological parameters collected from January 2007 to November 2010 are used to define spawning seasons for octopus landed by the small-scale trap fisheries in two oceanographically distinct Portuguese coastal areas: the northwest coast (western Iberia upwelling system) and the south coast (Gulf of Cadiz system). On a monthly basis, we followed the proportion of mature individuals, and the Gonad-Somatic and Hayashi Indices. Length–weight relationship, weight-at-maturity, body condition and energy allocation were other biological parameters studied. Spawning season was markedly different in both areas. The northwest population spawns from March to July, in synchrony with the northwest coast upwelling season, and the south coast population spawns mainly in summer, between August and September. A less intense spawning peak in early spring is present occasionally in the south coast. Weight-at-maturity is geographically indistinct, but in both areas males mature at smaller sizes than females. Body condition increases significantly during maturation and mass allocation for reproduction results indicate that males and females channel energy to reproduction from several sources.

Phenotypic plasticity of life history traits in relation to reproductive strategies in Boa constrictor occidentalis

The close connection between reproductive ecology and life history in snakes leads to trade-offs between reproductive and other life-history traits. Optimal energy allocation to growth and reproduction is a key factor to determine life history structure. Therefore, elucidating the relationship between body size variations and reproductive characters is essential for a better understanding of life-history plasticity. The aim of this work was to determine to what extent life-history differs among populations of Boa constrictor occidentalis and to identify possible life-history trade-offs between morphological and reproductive traits. We compared two populations from areas that are separated latitudinally, with different climatic conditions and vegetation landscape structure. Reproductive and morphological data of specimens were recorded. Although populations had a similar mean length of mature snakes, the frequency of some size classes tended to be different. Size at sexual maturity differed between populations for females, generating variations in the proportion of mature individuals. Reproductive threshold and follicular size also varied, but female reproductive frequency was similar between populations. Reproductive frequency of males varied between populations although their body condition was similar. We discussed two major issues: (1) implications of size at sexual maturity for body size and fecundity; (2) trade-offs in reproductive characters.

Interference of asexual and sexual reproduction in the green hydra

AbstractThe green hydra, Hydra viridissima, has three sexes: hermaphrodite, male, and female. I investigated the reproductive strategies of the green hydra and the relationship between asexual budding and sexual reproduction. The proportion of mature individuals in the asexually reproducing population increased with increasing temperature. Sexual reproduction did not interrupt asexual budding in hermaphrodites or males; sexual reproduction did interrupt asexual budding in females. Sexual reproduction also resulted in exponential population growth during the reproductive season. The number of asexual buds on each parental individual was positively correlated with the parental individual size in asexual individuals and in males. The same positive correlation was found between the number of testicles and the size of males. These correlations reflect a common tendency in asexual and sexual reproduction: larger parental individuals have a greater number of propagules or gametes. No correlation was found between size and buds or size and gonads in hermaphrodites; hermaphrodites had at most one asexual bud and were significantly larger than males, females, and asexual individuals. The larger size of hermaphrodites supports the hypothesis that producing both female and male gonads is more energetically costly than producing only one type of gamete (gonochorism).

Spatio-temporal variability in reproductive ecology of sand flathead,Platycephalus bassensis, in three Tasmanian inshore habitats: potential implications for management

Temporal and spatial variability in gonad development, duration of spawning period, and size ⁄ age at maturity were investigated in sand flathead, Platycephalus bassensis. A 3-year study (2001–2003) revealed that variation in gonad weight with somatic weight was a function of an interaction between season and study location (Coles Bay, Georges Bay, and Tamar River estuary). Highest gonad weight was recorded in Coles Bay in early summer, which in comparison to Georges Bay, was approximately 50% higher and occurred 3 months later. Tamar River mature individuals were reproductively inactive during the spawning season. The proportion of mature individuals at different stages of maturity differed significantly among the three locations across all times. Coles Bay individuals were reproductively active from October to March, while in Georges Bay females with hydrated oocytes were seen in September but were absent from the population by November. Interannual variation in initiation and duration of spawning activity was evident in each location. Apart from male size at maturity, for both sexes the size and age at maturity (L50) was higher in Georges Bay compared to Coles Bay. The results emphasize the necessity of temporal and spatial management based on population differences in reproductive ecology.

Intrapopulation variation in life history traits of Boa constrictor occidentalis in Argentina

AbstractWe provide data on intrapopulation variation of life history traits of Boa constrictor occidentalis in the District of Pocho, Córdoba, Argentina. A total of 153 individuals were captured. The distribution of individuals among four size classes differed significantly among the five years of study. The proportion of mature individuals did not differ between sexes but it showed variation among years. Females were longer and heavier than males. The mean litter size of the species was 24 and there was a linear relationship between litter size and maternal snout-vent length. Most boas were captured during the dry season. There were no significant sex differences in the time of capture and air temperature in either the wet or the dry seasons. However, we found significant differences in the time of capture and air temperature between the seasons. The long-term monitoring of wild populations should be a priority for the development of conservation and management plans for this boid.

Variability in maturity and growth in a heavily exploited stock: whiting ( Merlangius merlangus L.) in the Irish Sea

This paper examines the relationships between maturity, length and age of whiting sampled on a length-stratified basis from groundfish surveys of the Irish Sea during spawning in spring 1992–2001. Maturity, defined by the triggering of vitellogenesis or milt production, was a function of both length and age. Proportions of mature individuals in 1-year-old males increased successively from almost zero in length classes below 15 cm to around 0.9 at 25 cm, whilst almost all 2-year-old males were mature from their smallest length of around 19 cm. Maturity in females was more strongly linked to age than to length. Most 1-year-old females were immature, the proportion of mature individuals not exceeding 0.3 in any length class. Most 2-year-old females were mature and immature fish were found in the smallest length classes only (20–25 cm). Almost all 3-year-olds of both sexes were mature in all length classes. Proportions of mature individuals in 1-year-olds increased substantially after 1997, particularly in males. Significant positive cross-correlation between proportion mature and mean length was found for 1-year-olds of both sexes. Length at 50% maturity ( L 50 ) averaged around 19 cm in males and 22 cm in females. Variability in L 50 was negatively cross-correlated with average sea surface temperature in the preceding year. There is no evidence for substantial changes in maturity of whiting since the 1950s, despite an order-of-magnitude reduction in biomass caused by high fishing mortality. Concomitant decreases in mean length-at-age and weight-at-age in recent decades indicate that conditions may have been unfavourable for compensatory changes in maturation.