Different growth trends of whitefish (Coregonus lavaretus) forms in the northern Baltic Sea

The sea growth of two whitefish forms, anadromous (Coregonus lavaretus lavaretus) and sea‐spawning (Coregonus lavaretus widegreni), was analysed using samples collected from the commercial sea catch in the Gulf of Bothnia (GoB) in the northern Baltic Sea during 1998–2014. In the GoB area, these two forms are possible to identify because the gill‐raker number and size at maturity vary between forms. The growth rate of the forms is linked to their feeding area. Sea‐spawning whitefish, which has a feeding migration near its home site, was shorter in the northern GoB (66°N–64°N) at the ages of 3–11 than those in the southern GoB (64°N–60°30′N). In the data, most whitefish were caught with gill nets in the GoB. The mesh sizes of gill nets capturing the anadromous form were mostly 35–45 mm, while those capturing the sea‐spawning form were <35 mm in the northern GoB. It is likely that the different growth trends for small and large whitefish were connected with differences in their recruitment for fishing. The length of anadromous females at the age of four sea years increased significantly, but the length of six‐year‐old anadromous female whitefish decreased over the catch years from 1998–2014. In contrast, the length of slow‐growing sea‐spawning whitefish of six years or older increased significantly in relation to the catch year in the gill‐net catch. The increase in the growth of young age groups in both forms was probably associated with the increasing temperature and the low fishing pressure on small fish. The decreasing age at capture for both forms and the depression of the mean size of old anadromous whitefish are signs of high fishing pressure with a high gill‐net effort that selectively removes the largest and oldest individuals of both forms.     

The distribution and some biological features of Stichaeus grigorjewi (Stichaeidae) in the waters of northern Primorye (The Sea of Japan)

Stichaeus grigorjewi is a common species, but in the waters of northern Primorye it is comparatively rare. It occurs at depths down to 465 m for the greater part of the year, except for the spawning period, staying in deep-water masses with relatively stable temperature conditions. The widest bathymetric distribution of S. grigorjewi is observed from spring-early summer. After the completition of spawning, it shifts to depths larger than 100 m and winters in the upper section of the continental slope. During each season maximum concentrations of S. grigorjewi along the coasts of Primorye are observed in water from Povorotnyi Cape to the Olga Gulf. Males and females of this species have close rates of growth and reach an age of not less than 12+ years. Most individuals of S. grigorjewi in catches had a length of 37 to 44 cm and fed mainly on fish.     

Omitted spawning in compensatory-growing perch

Individual growth trajectories of perch Perca fluviatilis in a Swedish forest lake (sampled in March) revealed growth depression at intermediate sizes, followed by enhanced, compensatory growth at larger sizes. All males of age ≥3+ years had mature, almost ripe testes. The proportion of spawning females was higher at age 3+ years (79%) than at older ages (44%), indicating that older females with non-developing ovaries were resting rather than immature juveniles. Resting females were 175–247 mm in total length ( L _T), and they were usually in a state of increasing annual growth. Spawning females were of more variable size (123–418 mm), and the larger ones had entered the faster growing state ≥2+ years before catch. Detectable growth costs of spawning indicated that resting females made a trade-off between current and future reproduction, rather than being constrained by poor feeding conditions.     

Diel periodicity of spawning activity in a permanently territorial damselfish: a test of adult feeding hypotheses

Synopsis Among species of damselfish in which both sexes defend individual feeding territories, spawning nearly always begins at first light and is completed within 2 h. According to the anti-competitor hypothesis, such dawn spawning occurs because it minimizes the rate of intrusion by diurnally active food competitors while the female is away from her territory. An alternative hypothesis pertaining to adult feeding biology is that dawn spawning minimizes interference with the female's own feeding activity. Diel patterns of spawning and mate-searching activity were documented for a population of garibaldi damselfish, Hypsypops rubicundus, and compared with their diel feeding patterns and those of their food competitors. Female garibaldi spawned at approximately constant levels from dawn through late afternoon and showed peaks in mate-searching activity in the late morning or in the afternoon. However, feeding activity of both female garibaldi and their food competitors increased significantly from dawn to early afternoon. Thus, there was no inverse relationship between garibaldi spawning activity and feeding activity as predicted by these hypotheses.     

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.     

Reproductive biology and implications for management of the spangled emperor Lethrinus nebulosus in the southern Arabian Gulf

The reproductive biology of the spangled emperor Lethrinus nebulosus in the southern Arabian Gulf was determined from the examination of 781 individuals collected between September 2008 and August 2009. There was no histological evidence of adult sex change, and sex ratios did not differ significantly from unity across all size and age classes. Testes had an ovarian structure and a remnant lumen which was not used for sperm transport; furthermore, residual oocytes were observed in the testes of some immature, resting and developing males. A dramatic change in the sex ratio of the smallest and youngest size and age classes suggested that juvenile female to male sex change occurred between 21·0 cm fork length (L(F)) and 24·0 cm L(F) at 1 year of age. The combination of histological evidence with the sexual composition of the size and age structures suggests a non-functional protogynous hermaphroditic sexual pattern, which is analogous to functional gonochorism. The spawning season was well defined, occurring once a year during March, April and early May. Peaks in spawning occurred after full moons, there was a cessation in spawning activity after new moons and spawning was completed within three lunar cycles. The distribution of males over the entire size and age ranges and the absence of inactive mature females during the spawning season suggested that the population was not constrained by sperm limitation. Size-specific and age-specific reproductive potential indicated that conventional regulations that equate the mean size at first capture to sexual maturation are unsuitable for the management of L. nebulosus. The maximum recorded age (11 years), small mean size and young age at sexual maturation (L(m50) = 26·7 cm L(F), 2·1 years, for females and 19·4 cm L(F), 0·5 years, for males) may be a direct result of intensive demersal fishing in the southern Arabian Gulf.     

Warm winters and cool springs negatively influence recruitment of Atlantic salmon (Salmo salar L.) in a southern England chalk stream

Previous work suggests that juvenile salmon recruitment in rain-fed rivers is negatively influenced by warm and wet winters and cool springs. We tested whether this is generally applicable to a southern England chalk stream characterized by comparatively stable discharges and temperatures. We found that warm spawning and cool emergence temperatures negatively influenced juvenile recruitment between 2015 and 2020. Together these findings suggest an ability to predict juvenile productivity from water temperature records around spawning and fry emergence, thereby allowing time for management interventions in years of unfavourable temperatures.     

Morphological and ecological differentiation of sympatric whitefish species of the genus <Emphasis Type="Italic">Coregonus</Emphasis> from Lake Taymyr

Results of the morphological analysis of ecology and feeding of two sympatric forms of whitefishes (lacustrine and lacustrine–riverine) inhabiting Lake Taymyr (the Taymyr Peninsula) are presented in the article. It is revealed that these forms do not differ in the number of gill rakers on the first branchial arch and in the number of perforated scales in the lateral line, but they do differ in plastic characters, spawning periods, and area. At the age of 2–3 years they become separate in regards to feeding type. It is assumed that both forms of whitefishes inhabited Lake Taymyr simultaneously with the filling of the lake basin. Apparently the taxonomic status of the sympatric whitefishes from Lake Taymyr is broader than the term “ecological form.”     

A critical period for nutritional control of early gametogenesis in female winter flounder, Pleuronectes americanus (Pisces: Teleostei)

When female winter flounder ( Pleuronectes americanus ) were subjected to periods of satiation feeding alternating with starvation it was found that the first part of their normal six-month feeding period could be associated with subsequent gametogenesis, whereas feeding in the later part of the normal feeding period was not necessary. Conversely if females were not fed during the first part of the normal feeding season they were likely to become non-reproductive, although high condition fish or a non-spawner could become gametogenic in spite of starvation at this time. Feeding restricted to the later part of the normal feeding season was therefore not generally associated with successful gametogenesis for the following year's spawn. When the first part of the feeding period was further subdivided with satiation feeding limited to one or more months within it, most fish became non-reproductive. The exceptions which became reproductive were females which had high post-spawn condition maintained in the month following the immediate spawning period for the individual fish. A nutritionally sensitive period for early gametogenesis in female winter flounder therefore appears to occur in the early part of the normal feeding season, close to the normal spawning period. The experimentally produced non-reproductive females were generally halted in a previtellogenic stage of development for the most advanced oocytes which is consistent with a nutritionally related inhibition of gametogenesis close to the previous spawning period.     

Patterns of gametic investment by female stream-and ocean-type chinook salmon

Investment in fecundity and egg size is compared among two types of chinook salmon Oncorhynchus tshawytscha : stream-type, which undertake long, arduous oceanic and upstream migrations and often return to their natal rivers (where they do not feed)months before spawning, and ocean-type, which undertake relatively short oceanic and upstream migrations and remain at sea feeding and accumulating energy until a few days or weeks before spawning. The coefficient of variation in egg size for both life-history types was significantly less than variation in fecundity, reflecting the expected strong selection on egg size relative to egg number. Total investment in the gonad varied significantly among years in both life-history types, apparently reflecting variation in oceanic feeding conditions. Stream-type chinook were smaller in total body size and more than 1 year older than ocean-type. Stream-type also invested relatively less of their total body energy in eggs and produced smaller eggs than ocean-type, reflecting the greater energetic cost of their longer migration and freshwater maintenance. These differences suggest that stream-type chinook pay a considerable fitness penalty in reproductive output. This may be offset by the fact that stream-type go to sea at larger size and migrate far offshore, thereby avoiding some of the mortality costs of oceanic migration.     

Climate change impacts on potential recruitment in an ecosystem engineer

Climate variability and the rapid warming of seas undoubtedly have huge ramifications for biological processes such as reproduction. As such, gametogenesis and spawning were investigated at two sites over 200 km apart on the south coast of Ireland in an ecosystem engineer, the common cockle, Cerastoderma edule. Both sites are classed as Special Areas of Conservation (SACs), but are of different water quality. Cerastoderma edule plays a significant biological role by recycling nutrients and affecting sediment structure, with impacts upon assemblage biomass and functional diversity. It plays a key role in food webs, being a common foodstuff for a number of marine birds including the oystercatcher. Both before and during the study (early 2010–mid 2011), Ireland experienced its two coldest winters for 50 years. As the research demonstrated only slight variation in the spawning period between sites, despite site differences in water and environmental quality, temperature and variable climatic conditions were the dominant factor controlling gametogenesis. The most significant finding was that the spawning period in the cockle extended over a greater number of months compared with previous studies and that gametogenesis commenced over winter rather than in spring. Extremely cold winters may impact on the cockle by accelerating and extending the onset and development of gametogenesis. Whether this impact is positive or negative would depend on the associated events occurring on which the cockle depends, that is, presence of primary producers and spring blooms, which would facilitate conversion of this extended gametogenesis into successful recruitment.     

Diet and condition of wild boar, Sus scrofu scrofu, without supplementary feeding

From 1987 to 1992 diet and condition of two populations of wild boar which received no supplementary feeding were studied in the Veluwe area, a large area of heathlands and forests in The Netherlands, and were compared with those obtained in a previous study (1974–1976), when supplementary food was provided. Composition of stomach contents depended mainly on season, mast availability, and area-specific factors, whereas sex and age were of little or no importance. Density dependence was found for the decrease in mast (tree seed) consumption from autumn to winter. In autumn, and in winters of rich mast years, mast was the main constituent of the diet. In winters of poor mast years this was replaced by broadleaved grasses in one area and by broadleaved grasses, wavy hairgrass, and roots in the other. We found no important differences between the stomach contents of animals receiving no supplementation, and the natural fraction during a period of supplementary feeding. Variation in body weight was related mainly to age and sex, but also to mast availability. Judged by relative loss of body weight and decrease of bone marrow fat, juveniles seemed to suffer more from poor mast availability than adults. The decrease in body weight from autumn to winter was greater when population density was high. In poor mast years, recruitment into the population receiving no supplementation depended on the availability of broadleaved grasses; in rich years, recruitment was still lower than in populations receiving supplementary feeding. In populations receiving supplementary feeding, recruitment seemed independent of mast availability.     

Aspects of the biology of Scomberomorus maculatus (Mitchill) in Trinidad

A study was made of the biology of S. maculatus . Results of gonadal examination of 347 males and 409 females suggest spawning takes place from October to April, a period associated with low salinities. First spawning takes place at ages I1 and/or III for both sexes. Sex ratio results suggest spawning may be promiscuous, males outnumbering females. Egg counts from 12 ripe females ranged from 26 057 to 149 736. A period of abundance from May to September may be associated with a post-spawning feeding migration encompassing the island, possibly in a clockwise direction. Otolith were used to age 817 fish. Opaque and translucent rings are formed yearly. The translucent ring, representing a period of slow growth, is laid down during the spawning season. The fish can live for nine years with females growing faster than males. Growth parameters are compared with those obtained for Brazilian and Florida fish. Mortality rates were investigated and gill nets effected higher mortality rates than beach seines. Full recruitment takes place at age III for gill nets, and ages II and III for beach seines.     

Effect of spatial differences in growth on distribution of seasonally co‐occurring herring Clupea harengus stocks

The mechanisms most likely to determine the distribution of the two major herring Clupea harengus stocks in their common early summer feeding ground in the eastern North Sea, Skagerrak and Kattegat were investigated through analysis of acoustic survey data from six consecutive years. No change was detected in biomass of North Sea autumn spawning C. harengus (NSAS) over time, whereas the biomass of western Baltic spring spawning C. harengus (WBSS) declined severely. Analyses of centre of abundance by stock showed no change in NSAS distribution, whereas the WBSS changed to a more western distribution over time. Contrary to previous perception of the juvenile migration, NSAS were found to leave the study area at the age between 1 and 2 years and WBSS 1 year olds were encountered in the Skagerrak. The estimated parameters of von Bertalanffy growth equations showed marked differences between areas with fish in the eastern part of the area having the lowest size at age at all ages. Further, their growth conditions appeared to deteriorate progressively over the period studied. Both NSAS and WBSS showed the highest condition in the North Sea and Skagerrak while condition was substantially lower in age Kattegat. The westward movement of spring spawners over time suggests that growth rate and possibly density of conspecifics influence the migration pattern and distribution of C. harengus in the area. In contrast, there was no evidence to suggest that distribution was constant over time within stocks or that distribution reflected size‐dependent limitations on migration distance.     

A review of the likely effects of climate change on anadromous Atlantic salmon Salmo salar and brown trout Salmo trutta,with particular reference to water temperature and flow

The present paper reviews the effects of water temperature and flow on migrations, embryonic development, hatching, emergence, growth and life‐history traits in light of the ongoing climate change with emphasis on anadromous Atlantic salmon Salmo salar and brown trout Salmo trutta. The expected climate change in the Atlantic is for milder and wetter winters, with more precipitation falling as rain and less as snow, decrease in ice‐covered periods and frequent periods with extreme weather. Overall, thermal limits for salmonids are species specific. Scope for activity and growth and optimal temperature for growth increase with temperature to an optimal point before constrain by the oxygen content of the water. The optimal temperature for growth decreases with increasing fish size and varies little among populations within species, whereas the growth efficiency may be locally adapted to the temperature conditions of the home stream during the growth season. Indirectly, temperature influences age and size at smolting through its effect on growth. Time of spawning, egg hatching and emergence of the larvae vary with temperature and selective effects on time of first feeding. Traits such as age at first maturity, longevity and fecundity decrease with increasing temperature whilst egg size increases with temperature. Water flow influences the accessibility of rivers for returning adults and speed of both upstream and downstream migration. Extremes in water flow and temperature can decrease recruitment and survival. There is reason to expect a northward movement of the thermal niche of anadromous salmonids with decreased production and population extinction in the southern part of the distribution areas, migrations earlier in the season, later spawning, younger age at smolting and sexual maturity and increased disease susceptibility and mortality. Future research challenges are summarized at the end of the paper.     

Coping with resource variation: Effect of constant and variable intervals between feeding on reproductive performance at first spawning of female three-spined sticklebacks

Female three-spined sticklebacks Gasterosteus aculeatus exposed to spring conditions (14) C and a photoperiod of 16L: 8D), and fed 6% of initial body weight per day of enchytraeid worms (controls) over 56 days, or either at regular 3-day or variable 1–5-day intervals between feeds, did not differ significantly in the proportion spawning (72%), in time to first spawning (24·5 days), in fecundity at first spawning (34) or in egg diameter (1·4 mm) at first spawning. There was no significant effect of feeding regime on lipid concentration of females immediately after first spawning (18·8% dry weight), but the experimental females had a slightly lower dry matter content and lower fresh and dry liver weight than controls. Eggs of females on the variable-interval regime had a higher lipid content than eggs from other groups. Days to spawning was correlated inversely and fecundity positively with initial length. Females adjusted their food intake to compensate for short periods of food deprivation, allowing them to maintain their reproductive performance at first spawning.     

Demography of spawning grayling (Thymallus arcticus) in the Beaverlodge River,Alberta

Changes in a grayling spawning population are described that occurred in relation to both natural and man-induced events. The spawning population was monitored from 1982 to 1987 with a trap on a fishway on the Beaverlodge River, Alberta. Most of the spawning run in each year was tagged with recaptures noted in subsequent years. Male grayling grew slightly faster than females. Growth rates were variable and appeared to be quite low in years of low water flow. Grayling first spawned at 2 to 6 years of age. The majority of tagged grayling would have returned to spawn a second time after a delay of one to two years were it not for the high adult mortality. It is hypothesized that the variable time to first maturity and the delay in the second spawning is a response to highly variable juvenile recruitment. Annual mortality rates increased with age, suggesting an increased vulnerability of larger fish to angling. The population appears highly sensitive to over-exploitation, because of the high mortality rates and the delayed time to spawning of the adults.Deceased.Deceased.     

Effects of an autocorrelated stochastic environment and fisheries on the age at maturity of Chinook salmon

Chinook salmon (Oncorhynchus tshawytscha) reproduce only once in their lifetime, and their age at reproduction varies among individuals (indeterminate semelparous). However, the factors that determine their spawning age still remain uncertain. Evidence from recent studies suggests that individual growth and reproduction of Chinook salmon are affected by the rate of coastal upwelling, which is shown to be positively autocorrelated between years. Therefore, the serially autocorrelated environmental is expected to play an important role in determining their spawning age. In the present study, I demonstrate the advantage of an indeterminate maturation strategy under a stochastic environment. I then present theoretical evidence for the advantage of adjusting the maturation probability based on the environment they experienced and demonstrate that fisheries reduce the fitness of the strategy to delay maturation. The results presented herein emphasize the importance of incorporating detailed life-history strategies of organisms when undertaking population management.     

Patterns of migration between feeding and spawning sites in a coral reef surgeonfish

Many coral reef fishes exhibit regular localised migrations between feeding and spawning areas, but the factors affecting these migration patterns, such as the distance, frequency and spawning site fidelity are poorly understood. The aim of this study was to investigate the patterns of migration to spawning sites of the surgeonfish, Ctenochaetus striatus (Acanthuridae). We explored relationships amongst an individual’s size and sex, the distance and frequency it migrated from its feeding area to spawning sites, fidelity to particular spawning sites and the number of individuals that aggregated to spawn. In order to achieve this, 406 C. striatus were captured and tagged on inshore reefs in Kimbe Bay (5°30′S 150°6′E), New Britain, Papua New Guinea. Tagged individuals were consistently observed within spatially discrete but overlapping feeding areas (maximum diameter averaging <13 m). The mean distance migrated was 58 m (ranging from 2 to 291 m). No tagged individuals were witnessed spawning at more than one site. Whilst most individuals (n = 88) migrated to the spawning site that was closest to their feeding areas, those that migrated to sites further away (n = 9) always spawned at sites where the number of conspecifics aggregating was larger. Neither the size nor the sex of individuals limited migration distance. However, males migrated significantly more frequently than females (on average once every 2 days vs. once every 3 days), and migration frequency was positively correlated with size in females. Migration distance did not affect the frequency with which individuals spawned. Whether patterns of migration are determined by cost-benefit optimisation, tradition, or an alternative mechanism is unknown.     

First maturity and spawning periodicity of hatchery‐origin pallid sturgeon in the upper Missouri River above Fort Peck Reservoir,Montana

The pallid sturgeon Scaphirhynchus albus conservation propagation program has augmented declining wild populations since the 1990s and the older age classes of hatchery‐origin fish are beginning to reach sexual maturity in the wild. Currently, the majority of the information available on the age and size at first maturity and spawning periodicity for pallid sturgeon in the upper basin is from captive hatchery‐origin pallid sturgeon (i.e. age and size at first maturity and spawning periodicity) or from wild pallid sturgeon artificially spawned in the propagation program (i.e. spawning periodicity). The purpose of this study was to document age and size at first maturity and spawning periodicity of known age hatchery‐origin pallid sturgeon that have reached maturity in the wild. Radio‐tagged pallid sturgeon in the upper Missouri River upstream of Fort Peck Reservoir were serially sampled in the early‐spring over multiple years and assigned to reproductive classifications each year based on sex‐steroid concentrations. The youngest reproductively‐active male hatchery‐origin pallid sturgeon sampled was 14.5 years old and the youngest female was 18. Hatchery‐origin males were observed having annual (N = 3) and biennial (N = 2) reproductive cycles. The observed spawning periodicity was similar to what has been reported elsewhere for the species. The youngest mature fish in this study are older and larger than what has been reported for those retained in captivity, indicating that body size alone is not a reliable predictor of maturity for pallid sturgeon.