Life-stage-dependent supergene haplotype frequencies and metapopulation neutral genetic patterns of Atlantic cod,Gadus morhua,from Canada's Northern cod stock region and adjacent areas

Among highly migratory fish species, nursery areas occupied by juveniles often differ from adult habitats. To better understand the spatial dynamics of Canada's Northern cod stock, juveniles caught off the east coast of Newfoundland and Labrador were compared to adults from the same region as well as individuals from other areas in Atlantic Canada using double-digest restriction site-associated DNA sequencing–derived single nucleotide polymorphisms. A reduced proportion of homozygotes with a chromosomal inversion located in linkage group 1 (LG1) was detected between juvenile and adult samples in the Northern cod stock region, potentially indicating age-dependent habitat use or ontogenetic selection for attributes associated with the many genes located in LG1. No selectively neutral genetic differences were found between samples from the Northern cod stock; nevertheless, significant differences were found between some of these samples and cod collected from St. Pierre Bank, Bay of Fundy, Browns Bank and the southern Scotian Shelf. Clustering analysis of variants at neutral loci provided evidence for three major genetic units: (a) the Newfoundland Atlantic Coast, (b) eastern and southern Gulf of St. Lawrence and Burgeo Bank and (c) the Bay of Fundy, Browns Bank and southern Scotian Shelf. Both adaptive and neutral population structure within the Northern cod stock should be considered by managers to promote demographic rebuilding of the stock.     

Predicting variability in catch-per-effort in Atlantic cod, Gadus morhua, trap and gillnet fisheries

The relationships between catch rates and fish abundance, hydrographic conditions and fishing effort, for Atlantic cod caught by trapnets (fixed gear) and gillnets (non-fixed gear) in the northern Gulf of St Lawrence have been quantified. Daily changes in trap catch rates were accounted for by changes in salinity, currents and mean local cod densities in 1985 ( R ²= 0.78), and predicted 1986 trap catch rate changes (by 1985 model) were correlated significantly with those observed ( r = 0.60, P < 0.05). In contrast, the daily changes in 1985 gillnet catch rates were determined by currents, maximum (not mean) local cod densities, and fishing effort (negative) ( R ²= 0.68), while predicted 1986 gillnet catch rates (by 1985 model) were significantly correlated with those observed ( r = 0.35, P < 0.05). Seasonal catchability coefficients of the traps were similar in 1985 and 1986, but for gillnets this index was an order of magnitude higher in 1986 than in 1985.     

Reproductive biology of hardhead catfish Ariopsis felis: evidence for overwintering oocytes

Hardhead catfish Ariopsis felis are a common marine catfish in the coastal waters of the Gulf of Mexico (GOM). The low economic value of this species has depressed interest and research, and although the species is known for its extremely low fecundity and large oocytes, little else is known about this catfish species. A total of 1230 samples across all months of the year from 2016 to 2018 resulted in 681 females, and analysis of gonado-somatic index (I_G) revealed 1% to be a clear cut-off indicating maturity. Females are considered capable of spawning from April to June when I_G averaged 4–8%. Both atresia and post-ovulatory follicles were present in July, suggesting that spawning ends in July in the northern GOM. The 1% I_G cut-off was used to designate maturity, and from that an L₅₀ of 253 mm was estimated. Batch fecundity from 41 females estimated a mean batch size of 36 oocytes. Perhaps the most interesting finding was the presence of secondary growth stage oocytes (e.g., cortical alveoli) from July through November, well outside the spawning capable period. Furthermore, 78% of females had some early vitellogenic oocytes present during the non-spawning season, and the distribution of these relatively large (2–5 mm) oocytes did not change over time. The results here are not only important as reproductive biology information for a common and abundant species, but also present interesting and unusual patterns of non-spawning season oocyte development that is not commonly seen in Western Hemisphere subtropical fish species.     

Biological traits of a sub-Antarctic nototheniid,Patagonotothen ramsayi,from the Burdwood Bank

The rock cod Patagonotothen ramsayi (Regan 1913) is the most abundant species of the genus Patagonotothen, occurring along the Patagonian shelf. It plays an important role in the demersal food web both as prey and predator, showing an increasing importance for the local finfish and squid trawl fisheries. Age structure and the reproductive traits were investigated from the population inhabiting the eastern shelf of Burdwood Bank, which represents the southernmost area of its geographical distribution. Adult specimens of P. ramsayi were collected during bottom trawling carried out in the austral summer. The specimens were aged by otolith readings, and their reproductive characteristics were assessed by macroscopical and histological analyses. Age was similar between sexes, ranging from 4 to 7 and from 4 to 8 years in males and females of comparable size, respectively. GSI was relatively low in females (<1.5 %), as fish were sampled far from the reported spawning season (June–August). Females were all in the early developing stage (III) on the macroscopic maturity scale, with the most advanced oocytes being in early vitellogenesis. The oocyte size distribution was bi-modal, with two partially overlapping modes consisting of oocytes of a maximum size of 0.66 mm. A few large atretic oocytes (diameter > 1 mm) were found in three females. Absolute fecundity ranged from approximately 30 to 120 thousands of eggs. No relationship was found between female size and fecundity, probably due to the relatively narrow range of the investigated fish sizes. Males were in the spent (VII) or resting (II) stages.     

Maturation and Reproductive Biology of Female Wild Carp, Cyprinus carpio, in Victoria, Australia

The reproduction of carp Cyprinus carpio L. (Family: Cyprinidae), from Victorian waters in Australia, is studied with detailed analysis of gonad maturation, spawning season, fecundity and oocyte diameter. Results show that carp has a high annual fecundity (AF) (0.12–1.54 million oocytes per fish), which is positively correlated with caudal fork-length (L, mm) and total weight (W, kg) but not age. The relationships between length or weight and AF were statistically significant and best described with the simple linear or quadratic regressions. Mean relative fecundity was 0.163 million eggs kg^–1 whole weight. Egg size was estimated from oocyte diameter in carp from eight stocks. Egg size was proportional to maternal size but not age. Seasonal trends in gonadosomatic indices, together with the changes in the macroscopic and microscopic condition of ovaries, demonstrated that spawning generally peaks during spring–early summer, but also occurs through until autumn and can even start in late winter at some sites. In Victoria, this species is a multiple spawner with asynchronous oocyte development and a protracted spawning season. Stocks generally contain both females that spawn once, and females that spawn repeatedly, within a spawning season. Implications for management for the control of feral carp stocks are discussed.     

Life history of the cownose ray, <Emphasis Type="Italic">Rhinoptera bonasus</Emphasis>, in the northern Gulf of Mexico,with comments on geographic variability in life history traits

Synopsis We determined age and growth, size at maturity, and fecundity for cownose rays, Rhinoptera bonasus, collected from the northern Gulf of Mexico. Vertebral age estimates ranged from 0+ to 18+ years for females and 0+ to 16+ years for males. Annual deposition of growth increments was verified with marginal increment analysis. Likelihood ratio tests indicated that the growth of the cownose ray was best described by a combined sexes Gompertz model. Median size at 50% maturity was determined to be 642 mm DW for males and 653 mm DW for females, or 4–5 years of age. Median pup size-at-birth was estimated to be 350 mm DW, with a gestation period of 11–12 months. In all cases, gravid females contained only one pup. Statistically significant differences were detected between growth curves for the Gulf of Mexico and the western Atlantic Ocean. Cownose rays in the Gulf of Mexico had lower estimates of DW_∞ and K, and a higher theoretical longevity than their conspecifics in the western Atlantic Ocean. Cownose rays in the Gulf of Mexico also attain maturity at a smaller size and earlier age than their counterparts in the western Atlantic Ocean.     

Food consumption and diet composition of cod,Gadus morhua,inhabiting the southwestern Gulf of St. Lawrence

Synopsis Stomach content analysis of commercial size cod, Gadus morhua, inhabiting the southwestern Gulf of St. Lawrence are presented for the period May to November 1980. Season- and size-related changes in the diet composition are indicated and the results compared to those of earlier studies. The extent of cod predation on major prey groups is evaluated by estimating their consumption by cod age-groups 3–15. The evaluation is based on the estimate of food intake by individual cod of different ages derived with the aid of a procedure based on Ursin growth theory, estimates of numbers-at-age from cohort analysis and the results of stomach content analysis.With the exception of American plaice, Hippoglossoides platessoides, and snow crab, Chionoecetes opilio, the consumption of commercially important species was relatively low and restricted to older cod. Commercially important species accounted for less than 12% of the total food biomass consumed by cod during the study period. The remainder consisted of other fish (18%), decapods (22%), euphausiids (15%), molluscs (11%), annelids (8%), and other invertebrates (15%). Methods are suggested to improve the above estimates of total and individual prey biomasses consumed by the fish population.     

The reproductive biology of the two-banded sea bream (Diplodus vulgaris) from the southwest coast of Portugal

The study of the reproduction of Diplodus vulgaris (Geoff.) as part of a base‐line study of the fishery resources of the south‐west coast of Portugal, was based on the analysis of the spawning season, gonad maturation, size at maturity, fecundity and hermaphroditism. The spawning season is relatively long, from December to March, with peaks in January and February. No significant differences were found either in the sex ratio (M : F = 1.01) over the year or by size. The size at first maturity (L₅₀) for all sexes and undetermined individuals combined was 18.33 cm total length (TL), with no significant differences between males and females. The estimated L₅₀ is considerably greater than the minimum legal size in Portugal of 15.0 cm. Mean absolute fecundity (F_a) was 131 127 oocytes, ranging from 31 523 to 250 608. The relationship between absolute fecundity and total length (TL) (F_a = 25 398 TL – 484 426) and somatic weight (SW) (F_a = 878.8SW – 71 416) was of the linear type. The mean number of oocytes per gram of somatic weight was 526, ranging from 194 to 887. The reproductive strategy of this species is characterized by a rudimentary hermaphroditism with possible protandry, as evidenced by the existence of individuals in sexual transition.     

Reproductive strategies of a temperate Australian sciaenid (teraglin,Atractoscion atelodus)

Worldwide there have been declines in stocks of exploited sciaenids. Despite a long history of exploitation, there has been no study of the life history characteristics of the fishery-important sciaenid, teraglin, Atractoscion atelodus. This study describes the reproductive characteristics of A. atelodus within the major area of its distribution and fishery, New South Wales (NSW) Australia. Characteristics studied included the size and age at maturity, fecundity, spawning mode and season, and these are compared to congeneric species. Atractoscion atelodus displays year-round batch spawning behaviour with asynchronous oocyte development and indeterminate fecundity. This is unusual for sciaenids, which typically display spring-summer spawning and only over a few months. The length and age at which 50% of the population matures for both males and females is 36 cm fork length (FL) and 1 year, a smaller size compared to other closely related sciaenids. While the species displays resilient reproductive characteristics such as protracted year-round spawning, constant supply of vitellogenic oocytes and relatively small/young age at maturity, there are also characteristics that make it susceptible to over-exploitation. These include highly female skewed sex ratios, as well as their schooling and voracious feeding behaviour leading to the potential for high catch rates.     

Sexual size dimorphism,growth, and maturity of the fluvial eight-barbel loach in the Kako River,Japan

The maturation and growth pattern of the fluvial eight-barbel loach Lefua sp. (Japanese name: nagare-hotoke-dojo), an endangered species, was investigated using an individual identification-recapture method from 1995 to 1998 in an upper reach of a headwater tributary of the Kako River, Hyogo Prefecture, Japan. Based on observations of the gonads through the abdominal skin, the loach was estimated to breed mostly from May to July. All the males matured by age 1⁺, and all the females matured by age 2⁺. Gamete release in all individuals of both males and females was predicted from recaptured loaches during each breeding season. The standard length of mature females was significantly larger than that of males, showing sexual size dimorphism (SSD). The maximum sizes recorded were 75.4 mm SL for females and 61.2 mm SL for males. Both males and females of immature specimens grew mainly from May to November, including the breeding season, with no significant differences in growth rates between them. After sexual maturity, both males and females grew mainly from July to October (or November), after the breeding season, and the females exhibited higher growth rates than males. Therefore, SSD of the species seems to be attributable to the different growth rates after maturity. The longevity of the loach was estimated to exceed ten years based on individual growth patterns of various sizes during the survey period. It is likely that the loach has an iteroparous life history, breeding every year, and moderate growth rates after maturity.     

Reproductive biology of brown trout, Salmo trutta macrostigma Dumeril 1858, in a tributary of the Ceyhan River which flows into the eastern Mediterranean Sea

The study describes some key elements of the reproductive biology, including spawning season, age at sexual maturity, fecundity and egg diameter of the native brown trout, Salmo trutta macrostigma, in a tributary of the Ceyhan River. A total of 197 brown trout (118 females and 79 males) were captured in 2000–2001 by electric fishing. In observations on monthly changes, the gonadosomatic index (GSI) and the monthly frequency distribution of egg diameter confirmed that spawning lasted from November to January. Some 27.7% of the females and 62.5% of the males attained sexual maturity in their second year. The smallest fork length (FL) of brown trout attaining sexual maturity was 17.4 cm for males and 17.8 cm for females. Mean fecundity in age groups II, III, IV and V were 360, 452, 693 and 1283 eggs per female, respectively. One 9‐year‐old female had a unique 3232 egg count. The mean fecundity of the sampled population was 554 eggs per fish, positively correlated with the FL (mm) (R = 0.8227 ) and body weight (R = 0.8130). The diameter of mature eggs in the spawning season ranged from 3.250 to 5.930 mm, with a 4.146 mm average. Mean egg diameter in age groups II, III, IV and V in the spawning season were 0.813, 3.799, 4.663 and 5.243 mm, respectively. Fecundity, egg weight and diameter were statistically different in all age groups.     

Burst and coast use, swimming performance and metabolism of Atlantic cod Gadus morhua in sub-lethal hypoxic conditions

Prolonged swimming capacity (critical swimming speed, U _crit, protocol) and metabolism were measured for 14 Atlantic cod Gadus morhua exposed to seven oxygen levels within the non-lethal range normally encountered in the Gulf of St Lawrence (35 to 100% saturation). Burst-and-coast swimming was triggered earlier (at lower speeds) in hypoxia, and burst-and-coast movements were more frequent in hypoxia than in normoxia at low speeds. Furthermore, the metabolic scope beyond the metabolic rate at which Atlantic cod resorted to burst-and-coast movements decreased gradually as ambient oxygen concentration dropped. Overall, fewer burst-and-coast movements were observed in hypoxia while the distance swum in burst-and-coast mode remained c . 1% of the total distance swam in all tests. Oxygen availability had no effect on the rate of increase in metabolic rate with increasing velocity <50 cm s⁻¹_, but limited swimming performances and metabolic rate at higher speeds. The prevailing low oxygen tensions on the bottom in the deep channels may impair the swimming capacity of Atlantic cod in the estuary and northern Gulf of St Lawrence.     

Seasonal distribution of juvenile Atlantic cod in the southern Gulf of St Lawrence

Seasonal changes in the geographic distribution of juvenile (ages 1–4) Atlantic cod Gadus morhua were determined from research surveys conducted in the southern Gulf of St Lawrence during 1986–87, 1990–91, and 1994. From late June to early October, juvenile cod were most abundant in shallow water (<50 m deep). By early November, all age groups (adults and juveniles) had migrated to deep (>100 m) offshore waters for the winter. For most juveniles, this represented a minimum migration of >225 km (each way). Age 3 and 4 cod migrated greater distances than age 1 and 2 fish. Some age 3 and 4 cod migrated as far as 650 km from their summer and early autumn areas. Although there was partial geographic segregation of juvenile and adult fish during summer and winter, all age groups were found together during the migration. No cod were present in the shallow waters (<80 m deep) of the south-western Gulf during April due, in part, to later than average ice-melt. Large numbers of all age-classes were present in most of the south-eastern Gulf by mid-May.     

The interaction of season length and development time alters size at maturity

An end-of-season penalty, with late-maturing individuals being smaller than early-maturing individuals, has been observed in a variety of univoltine terrestrial arthropods. The current study extends these observations, utilizing multiple populations of a single sexually dimorphic species to examine the ecological correlates and fitness consequences of late maturation at a small size. The orb-weaving spider, Nephila clavipes, inhabits a broad range of habitats that vary from mild to strong seasonality. Because males mature several instars earlier than females, they can reach maturity much earlier in the growing season. Within a cohort, I found that female size at maturity was negatively correlated with timing of maturation in strongly seasonal sites. At a less seasonal site, there was no correlation between female size and timing of maturation within a cohort. In most populations studied, male size was not correlated with the timing of maturation within a cohort. Within populations in strongly seasonal sites, late-maturing females had reduced fecundity. The probability of copulation, survivorship from maturity to first clutch, clutch size relative to female size, and the number of possible clutches were all reduced with delayed maturation. The probability of pre-reproductive death for late-maturing females was strongly affected by stochasticity in the timing of the end of the growing season. Received: 30 December 1998 / Accepted: 1 September 1999     

Effects of experimental manipulations on the life history pattern of Lymnaea stagnalis appressa say (pulmonata: lymnaeidae)

Field sampling of an Iowa population of Lymnaea stagnalis appressa Say indicated an annual generation pattern, with survivorship to maturity of i percent or less. Estimates of adult fecundity ranged from about 300 to 800 eggs.Density and food manipulations were performed to determine whether density dependent limitation of growth rates, maturation, or fecundity occurs in this fresh water pulmonate snail. Addition of a high quality food resource, spinach, accelerated growth rates, but did not drastically accelerate maturity, nor increase fecundity. Density increments lowered growth rates, delayed maturity, and lowered fecundity, and the addition of spinach did not counteract high densities. Adult densities are fairly low in the field population, and adults are randomly dispersed, indicating little density dependent regulation of fecundity in this population. However, the low survivorship to maturity, response in growth rates with food addition, and increasing survivorship with age and size indicate that juvenile mortality may play an important role in structuring life history patterns in this population.     

THE EVOLUTION OF PHENOTYPIC PLASTICITY IN LIFE-HISTORY TRAITS: PREDICTIONS OF REACTION NORMS FOR AGE AND SIZE AT MATURITY

We used life-history theory to predict reaction norms for age and size at maturation. We assumed that fecundity increases with size and that juvenile mortality rates of offspring decrease as ages-at-maturity of parents increase, then calculated the reaction norm by varying growth rate and calculating an optimal age at maturity for each growth rate. The reaction norm for maturation should take one of at least four shapes that depend on specific relations between changes in growth rates and changes in adult mortality rates, juvenile mortality rates, or both. Most organisms should mature neither at a fixed size nor at a fixed age, but along an age-size trajectory. The model makes possible a clear distinction between the genetic and phenotypic components of variation. The evolved response to selection is reflected in the shape and position of the reaction norm. The phenotypic response of a single organism to rapid or slow growth is defined by the location of its maturation event as a point on the reaction norm. A quantitative test with data from 19 populations and species of fish showed that predictions were in good agreement with observations (r = 0.93, P < 0.0001). The predictions of the model also agreed qualitatively with observed phenotypic variation in age and size at maturity in humans, platyfish, fruit flies, and red deer. This preliminary success suggests that experiments designed to test the predictions directly will be worthwhile.     

Movements and diving of grey seal females (Halichoerus grypus) in the Gulf of St. Lawrence, Canada

Five female grey seals were tracked with satellite-linked time-depth recorders during September to April 1993-1994. Seals remained in the northern Gulf of St. Lawrence (Gulf) for 1-2.5 months after capture. Four females dove primarily to depths <10 m and 20-70 m, while all dives of the fifth female, a blind animal, were <10 m. During October/November, all animals moved into the southern Gulf or onto the Scotian Shelf. This migration lasted 6-10 days, during which time animals covered 350-800 km. During that migration, all females, including the blind animal, dove up to 100 m, but the majority of dives were to depths of 40-70 m. Two seals stayed in the southern Gulf through the winter while the others left the Gulf in January. When in the southern Gulf and on the Scotian Shelf, dive depths and bathymetry information indicated that dives were to the bottom.     

Maturity,size at age and predator–prey relationships of winter skate Leucoraja ocellata in the southern Gulf of St Lawrence: potentially an undescribed endemic facing extirpation

The goals of this study were to document the size and age structure, size at maturity, ovarian fecundity and diet of the endangered population of winter skate Leucoraja ocellata that resides in the southern Gulf of St Lawrence (SGSL). The maximum size observed for SGSL L. ocellata was 68 cm total length (L_T) but >99% of animals caught were <60 cm L_T. Fifty per cent of male and female L. ocellata were fully mature at 40 and 42 cm L_T, respectively, age c. 5 years. The oldest individual caught was age 11 years, but 98% of the 561 individuals examined were ≤age 8 years, indicating a short reproductive life span. Ovarian fecundity was low; no more than 29 ova >10 mm diameter were ever observed. At 40 cm L_T, the diet changed from one dominated by shrimp Crangon septemspinosa and gammarid amphipods to one dominated by fishes (mainly sand lance Ammodytes spp. and rainbow smelt Osmerus mordax) and Atlantic rock crab Cancer irroratus. Sufficient differences were observed between SGSL L. ocellata and other populations in their size‐at‐maturity pattern and maximum size to propose the taxonomic re‐evaluation of the population.     

Reproductive traits of the “ocellated killifish” Floridichthys polyommus Hubbs, 1936 (Pisces: Cyprinodontidae) inhabiting estuary of the Champotón River (Campeche,Mexico)

This study explores the reproductive biology and the influence of environmental factors on the reproductive traits of Floridichthys polyommus inhabiting the estuary of the Champoton River. The analysis included population structure, gonadal developmental stages, reproductive period, size at first sexual maturity, fecundity, sex ratio, and somatic indexes. A spatio‐temporal pattern in the distribution of the seven size classes was detected. The species showed a positive allometric growth. Sex ratio was 1.21:1 (females:males). Size at first maturity was 42.23 mm (females) and 47.8 mm (males). A higher absolute and relative fecundity was detected in Puente Champotón estuary (PCH) with lower salinities than those detected in the Delta (DE). The adaptive significance of this trait could be in response to the heavy osmotic constraint imposed by extreme salinities in the DE. Floridichthys polyommus prefers PCH for spawning, and as a result a higher number of ripe individuals was observed in this site, characterized by the highest nutrient levels, which can boost productivity and food availability for fish. Hepatosomatic index was negatively correlated with gonadosomatic index, suggesting energy transfer from the liver towards gamete production. Floridichthys polyommus exhibits an opportunistic strategy (early maturity, small oocytes, small clutches) suggesting that energy is allocated towards reproduction to compensate for the unpredictable hydrological conditions imposed by the estuary (particularly during the hurricane season). Floridichthys polyommus shows a reproductive strategy exhibited by fish living in unstable systems. A seasonal divergence was observed in the reproductive traits of F. polyommus, while differences between study sites were for fecundity.     

Reproductive biology of wahoo, Acanthocybium solandri, off eastern Australia

A dearth of basic biological information for wahoo, Acanthocybium solandri, currently hinders the ability of scientists and managers to assess population sustainability and appropriately manage the dramatically increasing global catch. This study examined the gonads of 382 wahoo collected off eastern Australia during 2008–2011 to quantify their reproductive biology in the region. The overall sex ratio of the sample was 3.2:1 (females:males), however this differed significantly among fishing sectors and areas. The estimated fork length at which 50 % of female wahoo reach maturity was 1,046 mm. Similar to the Atlantic Ocean, female wahoo have a protracted summer spawning season during October-February. The mean spawning frequency of female wahoo was uncertain but may be approximately 2–3 days, with evidence of fish actively spawning on consecutive days. Batch fecundity of females was positively correlated with fish size and estimates ranged between 0.65 and 5.12 million oocytes. Relative fecundity was estimated at 122.0 (±9.7) oocytes per gram of ovary free body weight and did not differ with fish size or throughout the spawning season. Estimation of reproductive parameters such as size- and age-at-maturity may facilitate the construction of per-recruit stock assessments of wahoo in the region.