Spawning Periodicity, Spawning Migration, and Size at Maturity of Green Sturgeon, Acipenser medirostris, in the Rogue River, Oregon

The Rogue River, Oregon represents one of three important spawning systems for green sturgeon, Acipenser medirostris, in North America. In this paper we describe the spawning migration, spawning periodicity, and size at maturity for green sturgeon caught in the Rogue River during 2000–2004. Green sturgeon were caught by gill net or angling; 103 individuals were tagged with radio or sonic transmitters (externally or internally). Green sturgeon caught by gill net and angling ranged from 145 cm to 225 cm total length. Histological and visual examinations of gonad tissues indicated that most green sturgeon were spawning or post-spawning adults that entered the Rogue River to spawn. Ripe individuals were caught when water temperature was 10–18°C. Specimens carrying transmitters migrated 17–105 km up river; reaches consisting of likely spawning sites were identified based on sturgeon migratory behavior. Most green sturgeon remained in the Rogue River until late fall or early winter when flows increased, after which they returned to the ocean. Eight green sturgeon (males and females) returned to the Rogue River 2–4 years after leaving, entering the river during March, April, and May when water temperatures ranged from 9°C to 16°C. None of the 103-tagged individuals entered the Rogue River during successive years. There appear to be few known natural threats to adult green sturgeon in the Rogue River. However, our data suggest that a high percentage of adults that spawn in the Rogue River (particularly males) were susceptible to harvest by commercial, Tribal, and sport fisheries after leaving the system because they were not adequately protected by maximum size limits during the period of this study. The implications of maximum size limits (or lack of size limits) to green sturgeon are discussed, and recent actions taken by Oregon and Washington Fish and Wildlife Commissions to manage green sturgeon more conservatively are presented.     

Evidence of spawning by green sturgeon, Acipenser medirostris, in the upper Sacramento River, California

This study reports the only direct evidence of spawning of green sturgeon, Acipenser medirostris, in the upper Sacramento River, CA. Two green sturgeon eggs were collected with substrate mats immediately below Red Bluff Diversion Dam. One green sturgeon larva was collected with a larval net at Bend Bridge. We concluded that green sturgeon spawn in the upper Sacramento River, both above and below RBDD. Temperature ranges in the study area (10–15°C) are similar to conditions used in successful artificial rearing of green sturgeon and do not appear to be a limiting factor to successful spawning of green sturgeon; however, suitable habitat upstream of RBDD is inaccessible when dam gates are lowered.     

Members of opposite sex mutually regulate gonadal recrudescence in the lizard Calotes versicolor Agamidae)

Adult males and females of the seasonally breeding lizardCalotes versicolor were subjected to various social situations under semi-natural conditions to explain the role of socio-sexual factors in gonadal recrudescence. They were grouped as: (i) males and females, (ii) males and females separated by a wire mesh, (iii) same sex groups of males or females, (iv) castrated males with intact females and (v) ovariectomized (OvX) females with intact males from postbreeding to breeding phase. Specimens collected from the wild during breeding season served as the control group. Plasma sex steroid levels (testosterone in male and 17β-estradiol in female), spermatogenetic activity and vitellogenesis were the criteria to judge gonadal recrudescence. In intact males and females that were kept together, gonadal recrudescence and plasma sex steroids levels were comparable to those in wild-caught individuals. Gonadal recrudescence was at its least in all male and all female groups, and plasma sex steroids were at basal levels. Association with OvX females initiated testicular recrudescence but spermatogenetic activity progressed only up to the spermatid stage while males separated from females by wire mesh showed spermatogenetic activity for a shorter period. Females grouped with castrated males and those separated from males by wire mesh produced vitellogenic follicles. However, the total number and diameter of vitellogenic follicles, and plasma estradiol levels were lower than in the females grouped with intact males. The findings indicate that association with members of the opposite sex with progressively rising titers of sex steroids is crucial in both initiating and sustaining gonadal recrudescence in the lizard. Thus, members of the opposite sex mutually regulate gonadal recrudescence in theC. versicolor.     

Reproductive demographics,intersex, and altered hormone levels in shortnose sturgeon,Acipenser brevirostrum,from Delaware River,USA

Non‐lethal sampling techniques were used to document the reproductive structure of the shortnose sturgeon (Acipenser brevirostrum) population at a fish aggregation site (near Bordentown, New Jersey) in the Delaware River. A total of 68 fish were captured using gill nets (100 × 1.8 m, 12.7 or 15.2 cm mesh) and examined laparoscopically in May–June, and 61 additional fish captured and examined in November during 2006–2011. Six stages of reproductive development were identified in females and five stages were identified in males, encompassing differentiation through maturity in both sexes. Fish captured in the spring were predominantly immature with a higher proportion of females (1 : 1.2 M : F sex ratio), while mature males predominated in the autumn (5.7 : 1 M : F), indicating that the Bordentown area serves as an overwintering/pre‐spawn aggregation site. Three distinct forms of intersex were noted in gonads of 11.6% of fish examined: ovo‐testis, consisting of scattered spermatic cysts in predominantly immature ovary (3.9%); testis‐ova, consisting of ovarian lamellae projecting from a predominantly immature testes (4.7%); and zonal distribution, consisting of multiple, nearly‐homogenous pockets of either testicular or ovarian tissues along the gonad (3%). The hormone profile in fish with ovo‐testis was similar to that of immature males, while the hormone profile in fish with testis‐ova was similar to that of immature females. The relatively high prevalence of intersex raises concerns regarding potential reproductive effects and long‐term impacts on shortnose sturgeon in the Delaware River.     

Age and growth of ocellated icefish, Chionodraco rastrospinosus DeWitt and Hureau, 1979, from the South Shetland Islands

Age and growth of ocellated icefish, Chionodraco rastrospinosus, were investigated using counts of annual growth increments from sagittal otoliths. Samples were collected during research surveys by benthic trawl carried out around Elephant and South Shetland Islands in January–February 2002 and December 2006–January 2007. A total of 290 specimens were selected for the study, consisting of 120 females and 170 males. The age of fish was estimated by counting annuli on transverse sections obtained by grinding and polishing whole otoliths embedded in epoxy resin. The precision-of-age estimates within and between readers were tested applying both the average percent error (APE) and the coefficient of variation (CV). The estimated age-range was 1–12 for both sexes of C. rastrospinosus. Applying the von Bertalanffy growth function to the age–length data, a growth curve was obtained for each sex. The estimated values of VB growth parameters L _∞ and k were, respectively, 47.9 cm and 0.28 for females and 42.9 cm and 0.36 for males. Compared to other congeneric species, the growth performance of C. rastrospinosus was relatively high, being 2.82 and 2.81 in males and females, respectively. Age at sexual maturity was estimated to be about 4 years in both sexes. C. rastrospinosus captured in the studied area consisted mainly of adult specimens between 3 and 8 years, with few older fish.     

On occurrence and biology of Berg wrymouth <Emphasis Type="Italic">Cryptacanthodes bergi</Emphasis> (Cryptacanthodidae) in the north-western part of the Sea of Japan

With consideration of the data obtained in the period from 1981 to 2009, the occurrence of Berg wrymouth Cryptacanthodes bergi is estimated in the north-western part of the Sea of Japan. Almost all captures of wrymouth were made in Peter the Great Bay (only once was it caught in the Northern Primor’e) in a bathymetric range 18–60 m. Captures of Berg wrymouth are confined to aleurite bottom sediments. The size of captured specimens varied from 11 to 29 cm. The ratio of males and females in collections was close to 8: 1. In July–September, the gonads of females were at maturity stages III and IV and gonadosomatic index varied from 3 to 14%; in males, gonads were at stages II–III and III and gonadosomatic index varied from 0.5–2.7%, respectively.     

Calcium regulation in wild populations of a freshwater cartilaginous fish, the lake sturgeon Acipenser fulvescens

Lake sturgeon, Acipenser fulvescens, are one of a few species of cartilaginous fishes that complete their life cycle entirely in freshwater. Sturgeons maintain very low concentrations of circulating calcium (Ca²⁺) compared with other vertebrates, and therefore, face unique challenges in regard to Ca²⁺ regulation, which are likely to be magnified during vitellogenic stages of the reproductive cycle. In the present study, Ca²⁺ concentrations and associated hormones of female and male lake sturgeon were examined in two wild populations, and were related to reproductive stage. In both populations, free, bound and total Ca²⁺ were low, peaking in mid-late vitellogenic females. Internal Ca²⁺ and phosphate (PO₄³⁻) concentrations were inversely related to environmental concentrations, suggesting that these ions are preferentially retained and that mechanisms for mobilization are up-regulated under diminished environmental concentrations. Plasma 17β-estradiol, 11-ketotestosterone and testosterone, peaked in mid-late vitellogenic females, while the androgens peaked in spawning males. Urine Ca²⁺ was more tightly regulated than other divalent ions and decreased in spawning fish. Therefore, the increases in free plasma Ca²⁺, the very low circulating concentrations of free and total Ca²⁺, and the increase in PO₄³⁻ and bound Ca²⁺ in low Ca²⁺ environments indicate unique adaptations to Ca²⁺ regulation in the lake sturgeon.     

Movements of green sturgeon, Acipenser medirostris, in the San Francisco Bay estuary, California

Synopsis The green sturgeon, Acipenser medirostris, is a long-lived, iteroparous, anadromous acipenserid that is native to the San Francisco Bay Estuary, California. Sub-adult and adult fish are oceanic, but enter the estuary during the spring and remain through autumn. Little is known about green sturgeon distribution within the estuary or what, if any, physical parameters influence their movements. We report the results of a telemetry study conducted between September 2001 and November 2002. Five sub-adult and one adult green sturgeon were captured by trammel net in the San Pablo Bay region of the estuary. We implanted depth-sensing, ultrasonic transmitters within the peritoneum of individuals and tracked them from a boat for 1 – 15 h per day over periods ranging from 1 to 12 days. Salinity, temperature, and dissolved oxygen profiles of the water column were measured hourly. Observed movements were categorized as either non-directional or directional. Non-directional movements, accounting for 63.4% of observations, were closely associated with the bottom, with individuals moving slowly while making frequent changes in direction and swim speed, or not moving at all. Directional movements consisted of continuous swimming in the top 20% of the water column while holding a steady course for extended periods. Four of the five sub-adult fish remained within the confines of San Pablo Bay for the duration of their tracking period. The remaining sub-adult moved over 45 km up-river into Suisun Bay before contact was lost. The adult fish exited the bay and entered the ocean 6 h after release near Tiburon, CA, a movement of approximately 10 km. The sub-adult fish typically remained at the shallower depths (<10 m) of the estuary, but there were no apparent preferences for temperature, salinity, or dissolved oxygen, with the fish moving widely and rapidly across the range of these physical parameters. Activity is believed to be independent of light level with no discernable crepuscular, nocturnal, or diurnal peaks in activity.     

Seasonal and sexual variation in diel activity rhythms of pine martenMartes martes in the Białowieża National Park (Poland)

From 1991–1996, the activity rhythms of 14 radio-collared pine martensMartes martes (Linnaeus, 1758) (6 males and 8 females) were studied in the pristine deciduous and mixed forests of the Białowieża National Park. Tracking data (5823 h) indicated that the activity rhythms of pine martens varied between sexes and seasons. In spring, male activity peaked at 20.00–00.00 h, whereas in summer and autumn-winter, activity was bimodal, peaking at 18.00–22.00 h and 02.00–04.00 h. Female activity in spring was more evenly distributed than that of males, but in summer their activity peaked at 20.00–00.00 h, while in autumn-winter females had a bimodal rhythm with peaks at 18.00–20.00 h and 02.00–06.00 h. In breeding females, activity rhythms changed in the course of pregnancy and nursing. On average, martens started their activity 73±209 (SD) min before sunset and finished 87±245 min after sunrise. Females became active earlier than males but both sexes terminated activity at the same time. For both males and females the daily activity rhythm was not related to the diurnal course of temperature.     

Migration of green sturgeon, Acipenser medirostris, in the Sacramento River

Adult green sturgeon, Acipenser medirostris, were collected in San Pablo Bay, California, and surgically implanted with ultrasonic acoustic tags from 2004 to 2006. An array of automated acoustic monitors was maintained in the Sacramento River to record movements of these fish. We presumed movements to known spawning areas (based on previous green sturgeon egg collections) or areas with potential spawning habitat (characterized by substrate, flow, and temperature criteria) represented a “spawning migration.” Three separate annual “spawning migrations” were recorded involving 15 individuals. The majority of the Sacramento River migrants entered the system in the months of March and April. Two different patterns of “spawning migration” and out-migration were observed. Six individuals potentially spawned, over-summered and moved out of the river with the first fall flow event. This is believed to be the common behavior of the green sturgeon. Alternatively, nine individuals promptly moved out of the Sacramento River before 1 September, and any known flow or temperature cue. Some green sturgeon appeared to be impeded on their upstream movement by the 15 May closure of the Red Bluff Diversion Dam, and at least five passed under the dam gates during downstream migration. A delay in the closure of the Red Bluff Diversion Dam would likely allow upstream passage of spawning green sturgeon, further, the potential mortality affects of downstream passage beneath the Red Bluff Diversion Dam should be assessed. Specific protection should be also given to the large aggregation of green sturgeon located in the reach of the Sacramento River adjacent to the Glen Colusa Irrigation District pumping facility.     

Lake sturgeon population attributes and reproductive structure in the Namakan Reservoir,Minnesota and Ontario

Quantified were the age, growth, mortality and reproductive structure of lake sturgeon (Acipenser fulvescens) collected in the US and Canadian waters of the Namakan Reservoir. The hypotheses were tested that (i) age and growth of lake sturgeon in the Namakan Reservoir would differ by sex and reproductive stage of maturity, and (ii) that the relative strength of year‐classes of lake sturgeon in the reservoir would be affected by environmental variables. To quantify age, growth and mortality of the population, existing data was used from a multi‐agency database containing information on all lake sturgeon sampled in the reservoir from 2004 to 2009. Lake sturgeon were sampled in the Minnesota and Ontario waters of the Namakan Reservoir using multi‐filament gillnets 1.8 m high and 30–100 m long and varying in mesh size from 178 to 356 mm stretch. Reproductive structure of the lake sturgeon was assessed only during spring 2008 and 2009 using plasma testosterone and estradiol‐17β concentrations. Ages of lake sturgeon >75 cm ranged from 9 to 86 years (n = 533, mean = 36 years). A catch‐curve analysis using the 1981–1953 year classes estimated total annual mortality of adults to be 4.8% and annual survival as 95.2%. Using logistic regression analysis, it was found that total annual precipitation was positively associated with lake sturgeon year‐class strength in the Namakan Reservoir. A 10 cm increase in total annual precipitation was associated with at least a 39% increase in the odds of occurrence of a strong year class of lake sturgeon in the reservoir. Plasma steroid analysis revealed a sex ratio of 2.4 females: 1 male and, on average, 10% of female and 30% of male lake sturgeon were reproductively mature each year (i.e. potential spawners). Moreover, there was evidence based on re‐captured male fish of both periodic and annual spawning, as well as the ability of males to rapidly undergo gonadal maturation prior to spawning. Knowledge of lake sturgeon reproductive structure and factors influencing recruitment success contribute to the widespread conservation efforts for this threatened species.     

Does rumen–reticulum capacity correlate with body size or age in black-tailed deer?

To accommodate an increased food intake with greater body size, rumen–reticulum capacity must become larger to allow heavier digesta loads. Recently, digesta load was found to correlate with age more strongly than body size. It was suggested that older animals had compromised mastication efficiency due to tooth wear and compensated for larger particles by increasing rumen–reticulum capacity to extend retention time. Herein, we constructed models and used Akaike Information Criteria corrected for small sample size to determine if digesta load was related with age or body weight in 80 female and 105 male black-tailed deer (Odocoileus hemionus columbianus). We also assessed if the presence of fetuses influenced relationships in females. Females were collected in spring, 1985–1988, and males were collected in autumn, 1980, 1982–1984, and 1988, from Hopland Research and Extension Center, Mendocino County, California. Digesta loads, fetuses, and carcasses were weighed, and animal ages were estimated. Digesta load was related to age in females and body weight in males. Our study shows that body size and age-related factors may both influence rumen–reticulum capacity.     

Population characteristics of pallid sturgeon (Scaphirhynchus albus (Forbes & Richardson, )) in the Lower Missouri River

Population characteristics of pallid sturgeon Scaphirhynchus albus in the lower Missouri River are relatively unknown. Therefore, data collected from the Nebraska Game and Parks Commission Pallid Sturgeon Population Assessment Program was synthesized to (i) document the population structure of pallid sturgeon by origin (hatchery‐reared or wild), gender, and reproductive readiness, (ii) document the minimum size and age‐at‐maturity by gender, and (iii) document the fecundity rates of the fish that were successfully spawned in the hatchery. During this 4‐year study (2008–2011), relative abundance for wild and hatchery‐reared pallid sturgeon collected with gill nets did not significantly change whereas relative abundance for wild fish using trot lines declined significantly. The proportion of hatchery‐reared pallid sturgeon increased annually, with the population being composed primarily of hatchery‐reared fish. The proportion of reproductively ready females to non‐reproductively ready females was 1 : 2.0, compared to male ratios at 1 : 0.9. Minimum fork length‐at‐maturity was estimated for females at 788 mm and for males at 798 mm. Minimum age‐at‐maturity for hatchery‐reared released fish was age‐9 for females and age‐7 for males. Highest relative fecundity, based on the ovosomatic index, was 10% with an overall mean of 7%. The number of eggs per ml (egg size) was not correlated with fork length (P = 0.0615) or weight (P = 0.0957). Relative condition factor (Kn) for females was significantly different by reproductive condition (P = 0.0014) and Kn for males did not differ between reproductive conditions (P = 0.2634). Detecting shifts in population characteristics are essential not only to understand population dynamics since hatchery inputs and natural perturbations continue to change the population structure but also to assess species recovery efforts to ensure long‐term species sustainability.     

Observations on the reproductive cycle of cultures white sturgeon, Acipenser transmontanus

Males and females of cultured white sturgeon, Acipenser transmontanus, mature at an average age of 4 and 8 years, respectively. However, the onset of ovarian vitellogenesis and puberty are highly asynchronous in the female stock. Gonadal cycles are annual in males and biennial in females, and gametogenesis is influenced by season. Neuroendocrine regulation of reproduction appears to involve a dual gonadotropin system controlling gonadal development and spawning. Labile puberty and sex-specific duration of the gonadal cycle are distinct characteristics of cultured and wild sturgeon. Photoperiod and temperature play a significant role in environmental regulation of the reproductive cycle, but further studies are necessary to elucidate the roles of endogenous and environmental factors in sturgeon reproduction which is critically important for both aquaculture and conservation of endangered wild stocks.     

Migration and Movement Patterns of Green Sturgeon (Acipenser medirostris) in the Klamath and Trinity rivers, California, USA

Green sturgeon, Acipenser medirostris, movement and migration within the Klamath and Trinity rivers were assessed using radio and sonic telemetry. Sexually mature green sturgeon were captured with gillnets in the spring, as adults migrated upstream to spawn. In total, 49 green sturgeon were tagged with radio and/or sonic telemetry tags and tracked manually or with receiver arrays from 2002 to 2004. Tagged individuals exhibited four movement patterns: upstream spawning migration, spring outmigration to the ocean, or summer holding, and outmigration after summer holding. Spawning migrations occurred from April to June, as adults moved from the ocean upstream to spawning sites. Approximately 18% of adults, those not out mignation in the spring, made spring post-spawning outmigrations. The majority of adults, those not outmigrating in the spring, remained in discrete locations characterized as deep, low velocity pools for extended periods during the summer and early fall. Fall outmigration occurred when fish left summer holding locations, traveled rapidly downstream, and exited the river system. High river discharge due to the onset of winter rainstorms and freshets appear to be the key environmental cue instigating the fall outmigration.     

Short-term change in male sexually selected traits and female mate preference in the guppy Poecilia reticulata

Some recent theoretical studies predict the plasticity of female preferences for male sexual ornaments. However, only little empirical information is available regarding changes in female preferences within a short period in the wild. In this study, we examined the short-term change in the exaggeration of sexually selected traits in males and intensity of female preferences in the guppy Poecilia reticulata of a wild population in Okinawa, Japan. We collected adult guppies from a single collection site with an interval of 2–3 months. The results indicated that the degrees of exaggeration of male sexually selected traits, such as orange spot patterns and body size, changed with an interval of 2–3 months. The intensity of female preferences in each collection term was quantified by a laboratory experiment using an identical pair of digitally modified male images. The intensity of female preferences for the conspicuous male image also changed with an interval of 2–3 months. Males that were collected in July exhibited the greatest degree of exaggeration of sexually selected traits. On the other hand, males that were collected in April showed a smaller degree of exaggeration of these traits; however, females that were captured in April exhibited the greatest mate preferences for the conspicuous male image.     

Dispersal of the alien raccoon dog Nyctereutes procyonoides in Southern Brandenburg, Germany

The raccoon dog Nyctereutes procyonoides, an East Asian canid species, was introduced into the European part of the former USSR since 1928. Within 50 years (1935–1984), it colonised a territory of 1.4 million km² in Europe. A telemetry study took place in Southern Brandenburg in a 60 km² sized study area with a typical mosaic structured East German agricultural landscape. For catching raccoon dogs, 20 trap boxes were set there in an area of 46 km², and between February 2001 and July 2004, 15 (5 males, 10 females) adult and 46 (25 males, 21 females) juvenile raccoon dogs were eartagged and adults additionally fitted with radio collars (Biotrack, 150–151 MHz). Data on dispersal behaviour was collected by the relocation points of 11 juveniles (6 males, 5 females). Four juvenile males dispersed even more than 40 km from their trapping places. Additionally, dispersal of two adult males could be documented. This behaviour probably indicates that the German raccoon dog population still is in a process of colonising. This canid’s ability for colonising spacious and distant areas during comparative short periods of time and its preference for habitats with richness of water possibly make this species to be an important vector of fox tapeworm Echinococcus multilocularis—a very dangerous zoonosis.     

Serum levels of testosterone, 11‐ketotestosterone and oestradiol‐17β in three species of sturgeon during gonadal development and final maturation induced by hormonal treatment

Changes in serum concentrations of two androgens, testosterone (T) and 11‐ketotestosterone (11KT), and oestradiol‐17β(E2) in male and female giant sturgeon Huso huso , Russian sturgeon Acipenser gueldenstaedtii and stellate sturgeon Acipenser stellatus were studied at different stages of gonadal maturity and after final maturation induced by hormonal treatment. Both male and female fish displayed a distinct increase in serum steroid concentrations during gonadal development. 11KT levels were significantly higher in males than females, with a positive correlation detected between 11KT and T concentrations. In maturing males and females, higher values of both 11KT and T were observed in stellate sturgeon compared to giant and Russian sturgeons. Vitellogenesis and high E2 levels were correlated in maturing sturgeon females.     

Population structure and reproduction ofCalanus helgolandicus (Copepoda,Calanoida) along the iberian and Moroccan slope

During three cruises, carried out in March 1991, October 1991, and January 1992 off the Iberian Peninsula and Morocco, the abundant calanoid copepodCalanus helgolandicus (Claus) was collected from a depth of 1000 m to the surface. Differences in depth preference were correlated with the life stage and geographically differing vertical salinity structures. In autumn and winter, only stage V copepodids (CV) and adults were found, in spring also younger copepodid stages. Within the range of the Mediterranean outflow water (MOW), a sharp decline of abundances of all stages was evident during all cruises. In autumn 1991, the bulk of the population was recorded south of the MOW, in winter 1992 north of it. During winter, numbers had declined by 70%, supporting the idea that winter individuals represent the same generation as was encountered in autumn, and that they had been transported northwards. CV stages preferred the depth layer 400–800 m, in autumn and winter. Adults were found in autumn at the same depth south of the MOW, while they preferred the 0–400 m layers north of it. In winter, the abundance of adults increased, males preferred the 400–600 m depth layer, while females stayed at 200–400 m. In spring 1991, stages younger than CV were found in high densities, all stages concentrating in the upper 200 m. During the crosslope survey in spring off Portugal, an absolute abundance maximum of females was found. In contrast, offshore densities were very low. On the basis of these findings, the hypothesis of a Mediterranean centre of distribution and dispersal into the Atlantic is questioned. It is suggested that a separate, reproductively active population ofC. helgolandicus exists off NW. Africa.