A part of the Japan Sea form of the threespine stickleback, Gasterosteus aculeatus, spawns in the seawater tidal pools of western Hokkaido Island, Japan

The Japan sea form of the threespine stickleback, Gasterosteus aculeatus, was found to spawn in the seawater tidal pool of the Cape Benkei, western Hokkaido Island, Japan, in 2001 and 2003. Nest-guarding males, adult females and juveniles of this form were also observed in four tidal pools of the Capes Benkei, Kabuto and Kamui, in 2001–2003. Otolith Sr:Ca ratios in sticklebacks collected from these tidal pools were relative high from the core to the edge, suggesting they lived in seawater environments throughout its life cycle. These findings suggest that a part of the Japan Sea formȁ9s individuals in western Hokkaido Island have the potential to breed in the coastal sea and the life history style has evolved in dependence on the seawater environment.     

Life history and ecology of the elusive European short‐snouted seahorse Hippocampus hippocampus

To improve the understanding of the life history and ecology of one of Europe's most elusive fishes, the short‐snouted seahorse Hippocampus hippocampus, data from wild populations in a shallow coastal lagoon in southern Portugal were analysed. The data were collected from 17 tagged seahorses on a focal‐study grid as well as from >350 seahorses encountered during underwater visual surveys and a fishery‐independent study using beach seines. These populations of settled juveniles and adults had a mean population density of 0·009 m^?2. During the study period (2000–2004), reproduction peaked in July and August. Juveniles recruited to the lagoon at c. 66 mm standard length (L_S) and 0·5 years of age and established small home ranges (0·8 to 18·2 m²). First reproduction was estimated at 100 mm and 1 year of age. Based on a fitted von Bertalanffy model, H. hippocampus grew quickly (growth coefficient K = 0·93) to a maximum theoretical size L_∞ = 150 mm and have a maximum lifespan of c. 3·2 years. Courtship behaviours were consistent with the maintenance of pair bonds and males brooded multiple batches of young per year. Estimated annual reproductive output averaged 871 young (±632). Together these analyses provide the first life‐history parameters for this species and indicate that H. hippocampus bears characteristics of opportunist and intermediate strategists. Such populations are predicted to exhibit large fluctuations in abundance, making them vulnerable to extended periods of poor recruitment.     

Life‐history traits of the long‐nosed skate Dipturus oxyrinchus

This work investigates life‐history traits of the long‐nosed skate Dipturus oxyrinchus, which is a common by‐catch in Sardinian waters. The reproductive variables were analysed from 979 specimens sampled during scientific and commercial hauls. Females (10·4–117·5 cm total length, L_T) attained larger sizes than males (14·5–99·5 cm L_T). To evaluate age and growth, a sub‐sample of 130 individuals (76 females and 54 males) were used. The age was estimated by annuli counts of sectioned vertebral centra. Four models were used for the length‐at‐age data: the von Bertalanffy, the exponential, the Gompertz and the logistic functions. According to the Akaike's information criterion, the Gompertz model seemed to provide the best fitting curve (L_∞ mean ± s.e. : 127·55 ± 4·90 cm, k: 0·14 ± 0·09, IP: 3·97 ± 0·90 years). The oldest female and male were aged 17 (115·5 cm L_T) and 15 years (96·0 cm L_T), respectively. Lengths at maturity were 103·5 cm for females and 91·0 cm for males, corresponding to 90% of the maximum observed length in both sexes. The monthly distribution of maturity stages highlighted an extended reproductive cycle, with spawning females and active males being present almost throughout the year, as confirmed by the gonado‐somatic index. Ovarian fecundity reached a maximum of 26 yolked follicles with a mean ± s.e. size of 19·7 ± 6·5 mm.     

The annual marine feeding aggregation of Atlantic sturgeon Acipenser oxyrinchus in the inner Bay of Fundy: population characteristics and movement

Atlantic sturgeon Acipenser oxyrinchus aggregate to feed from May to October in Minas Basin (45° N; 64° W), a large, cul‐de‐sac embayment of the inner Bay of Fundy. The aggregation consists mainly of migrants from the Saint John, NB and Kennebec Rivers, ME (99%). During 2004–2015, 4393 A. oxyrinchus were taken as by‐catch by commercial fish trawlers or at intertidal fishing weirs, and 1453 were marked and/or sampled and released. Fork length (L_F) ranged from 458 to 2670 mm, but 72·5% were <1500 mm. Mass (M) ranged from 0·5 to 58·0 kg. The mass‐length relationship for fish ≤50 kg was log₁₀M = 3·32log₁₀L_F ? 5·71. Observed growth of unsexed A. oxyrinchus recaptured after 1–8 years indicated fish of 90–179 cm L_F grew c. 2–4 cm a year. Ages obtained from pectoral spines were from 4 to 54 years. The Von Bertalanffy growth model predicted K = 0·01 and L_∞ = 5209 mm L_F. Estimated annual mortality was 9·5–10·9%. Aggregation sizes in 2008 and 2013 were 8804 and 9244 individuals, respectively. Fish exhibited high fidelity for yearly return to Minas Basin and population estimates indicated the total at‐sea number utilizing the Basin increased from c. 10 700 in 2010 to c. 37 500 in 2015. Abundance in the Basin was greatest along the north shore in spring and along the south shore in summer, suggesting clockwise movement following the residual current structure. Marked individuals were recaptured in other bays of the inner Bay of Fundy, north to Gaspé, Quebec, and south to New Jersey, U.S.A., with 26 recoveries from the Saint John River, NB, spawning run. Fish marked at other Canadian and U.S. sites were also recovered in Minas Basin. Since all A. oxyrinchus migrate into and out of the Basin annually they will be at risk of mortality if planned tidal power turbines are installed in Minas Passage.     

Age and growth of mangrove red snapper Lutjanus argentimaculatus at its cool‐water‐range limits

This study investigates the age and growth of Lutjanus argentimaculatus at its southern (cooler) range limits in eastern Australia. Specimens were collected from New South Wales and southern Queensland between November 2011 and December 2013. Fork lengths (L_F) ranged from 190 to 1019 mm, and ages ranged from 2+ to 57+ years. Growth was described by the von Bertalanffy growth function with coefficients L_∞ = 874·92 mm, K = 0·087 year^?1 and t₀ = ?2·76 years. Estimates of the instantaneous natural mortality rate (M) ranged from 0·072 to 0·25. The L_F (mm) and mass (W; g) relationship was represented by the equation: . The maximum age of 57+ years is the oldest reported for any lutjanid and comparisons with tropical studies suggest that the age‐based demography of L. argentimaculatus follows a latitudinal gradient. High maximum ages and low natural mortality rates indicate considerable vulnerability to overexploitation at the species' cool‐water‐range limits. These results demonstrate the need to identify underlying processes driving latitudinal gradients in fish demography.     

Freshwater and coastal migration patterns in the silver‐stage eel Anguilla anguilla

The unimpeded downstream movement patterns and migration success of small female and male Anguilla anguilla through a catchment in north‐west Europe were studied using an acoustic hydrophone array along the River Finn and into the Foyle Estuary in Ireland. Twenty silver‐stage A. anguilla (total length, L_T, range: 332–520 mm) were trapped 152 km upstream from a coastal marine sea‐lough outlet and internally tagged with acoustic transmitters of which 19 initiated downstream migration. Migration speed was highly influenced by river flow within the freshwater (FW) compartment. Anguilla anguilla activity patterns were correlated with environmental influences; light, tidal direction and lunar phase all influenced the initiation of migration of tagged individuals. Migration speed varied significantly between upstream and lower river compartments. Individuals migrated at a slower speed in transitional water and sea‐lough compartments compared with the FW compartment. While 88·5% survival was recorded during migration through the upper 121 km of the river and estuary, only 26% of A. anguilla which initiated downstream migration were detected at the outermost end of the acoustic array. Telemetry equipment functioned efficiently, including in the sea‐lough, so this suggests high levels of mortality during sea‐lough migration, or less likely, long‐term sea‐lough residence by silver A. anguilla emigrants. This has important implications for eel management plans.     

Validated annual band‐pair periodicity and growth parameters of blue‐spotted maskray Neotrygon kuhlii from south‐east Queensland,Australia

Age and growth parameters were derived for blue‐spotted maskray Neotrygon kuhlii from Moreton Bay in subtropical eastern Australia. Maximum age estimates of 13 and 10 years were obtained from female (n = 76) and male (n = 44) N. kuhlii, respectively. Estimated ages at maturity for 50% of females and males were 6·32 and 3·95 years, respectively. A three‐parameter power function provided the best statistical fit to size at age data in both sexes, providing parameter estimates of y⁰ = 163·13, a = 58·52 and b = 0·58 for females and y⁰ = 165·13, a = 59·02 and b = 0·54 in males. The two‐parameter von Bertalanffy growth function was used to estimate biological parameters based on disc width (W_D) for both female (W_D∞ = 465·81 mm, K = 0·13 year^?1, b = 0·63) and male N. kuhlii (W_D∞ = 385·19 mm, K = 0·20 year^?1, b = 0·54). Annual band‐pair deposition was observed in three calcein‐injected N. kuhlii after periods of liberty ranging from 631 to 1081 days. Centrum edge analysis indicated that annual band‐pair formation was generally consistent within this population, with translucent bands formed over spring and summer and opaque bands formed in autumn and winter. Individual growth rates obtained from tagged specimens were similar to power function growth predictions. These results support previous characterizations of this common trawl by‐catch species as comparatively resilient to non‐targeted catches, although higher catch rates outside Australia infer a need for cautious management.     

Migratory behaviour and survival rates of wild northern Atlantic salmon Salmo salar post‐smolts: effects of environmental factors

To study smolt behaviour and survival of a northern Atlantic salmon Salmo salar population during river descent, sea entry and fjord migration, 120 wild S. salar were tagged with acoustic tags and registered at four automatic listening station arrays in the mouth of the north Norwegian River Alta and throughout the Alta Fjord. An estimated 75% of the post‐smolts survived from the river mouth, through the estuary and the first 17 km of the fjord. Survival rates in the fjord varied with fork length (L_F), and ranged from 97·0 to 99·5% km^?1. On average, the post‐smolts spent 1·5 days (36 h, range 11–365 h) travelling from the river mouth to the last fjord array, 31 km from the river mouth. The migratory speed was slower (1·8 L_F s^?1) in the first 4 km after sea entry compared with the next 27 km (3·0 L_F s^?1). Post‐smolts entered the fjord more often during the high or ebbing tide (70%). There was no clear diurnal migration pattern within the river and fjord, but most of the post‐smolts entered the fjord at night (66%, 2000–0800 hours), despite the 24 h daylight at this latitude. The tidal cycle, wind‐induced currents and the smolts' own movements seemed to influence migratory speeds and routes in different parts of the fjord. A large variation in migration patterns, both in the river and fjord, might indicate that individuals in stochastic estuarine and marine environments are exposed to highly variable selection regimes, resulting in different responses to environmental factors on both temporal and spatial scales. Post‐smolts in the northern Alta Fjord had similar early marine survival rates to those observed previously in southern fjords; however, fjord residency in the north was shorter.     

Validated age,growth and maturity of the bonnethead Sphyrna tiburo in the western North Atlantic Ocean

The age, growth and maturity of bonnetheads Sphyrna tiburo inhabiting the estuarine and coastal waters of the western North Atlantic Ocean (WNA) from Onslow Bay, North Carolina, south to West Palm Beach, Florida, were examined. Vertebrae were collected and aged from 329 females and 217 males ranging in size from 262 to 1043 mm and 245 to 825 mm fork length, L_F, respectively. Sex‐specific von Bertalanffy growth curves were fitted to length‐at‐age data. Female von Bertalanffy parameters were L_∞ = 1036 mm L_F, k = 0·18, t₀ = ?1·64 and L₀ = 272 mm L_F. Males reached a smaller theoretical asymptotic length and had a higher growth coefficient (L_∞ = 782 mm L_F, k = 0·29, t₀ = ?1·43 and L₀ = 266 mm L_F). Maximum observed age was 17·9 years for females and 16·0 years for males. Annual deposition of growth increments was verified by marginal increment analysis and validated for age classes 2·5+ to 10·5+ years through recapture of 13 oxytetracycline‐injected specimens at liberty in the wild for 1–4 years. Length (L_F50) and age (A₅₀) at 50% maturity were 819 mm and 6·7 years for females, and 618 mm and 3·9 years for males. Both female and male S. tiburo in the WNA had a significantly higher maximum observed age, L_F50, A₅₀ and L_∞, and a significantly lower k and estimated L₀ than evident in the Gulf of Mexico (GOM). These significant differences in life‐history parameters, as well as evidence from tagging and genetic studies, suggest that S. tiburo in the WNA and GOM should be considered separate stocks.     

Critical swimming speeds of wild‐caught sand‐smelt Atherina presbyter larvae

Swimming abilities of wild‐caught sand‐smelt Atherina presbyter larvae were assessed as critical swimming speed (U_crit) throughout ontogeny. The mean U_crit increased with size, ranging from 3·6 to 18·7 cm s^?1, over the size range of 6·6–21·0 mm L_T. This indicates that at hatching A. presbyter larvae, far from being passive floaters, are already capable of active behaviours, which may influence their dispersal patterns.     

Reproductive parameters of rhinobatid and urolophid batoids taken as by‐catch in the Queensland (Australia) east coast otter‐trawl fishery

Reproductive variables are provided for batoids regularly taken as by‐catch in the east coast otter‐trawl fishery on the inner‐mid continental shelf off the south‐east and central coasts of Queensland, Australia. Total length at maturity (L_T50 and 95% c.i .) for the eastern shovelnose ray Aptychotrema rostrata was 639·5 mm (617·6–663·4 mm) for females and 597·3 mm (551·4–648·6 mm) for males. Litter size (n = 9) ranged from nine to 20 (mean ± s.e. = 15·1 ± 1·2). This species exhibited a positive litter size–maternal size relationship. Disc width at maturity (W_D50 and 95% c.i .) for the common stingaree Trygonoptera testacea was 162·7 mm (155·8–168·5 mm) for females and 145·9 mm (140·2–150·2 mm) for males. Gravid T. testacea (n = 6) each carried a single egg in the one functional (left) uterus. Disc width at maturity (W_D50 and 95% c.i .) for the Kapala stingaree Urolophus kapalensis was 153·7 mm (145·1–160·4 mm) for females and 155·2 mm (149·1–159·1 mm) for males. Gravid U. kapalensis (n = 16) each carried a single egg or embryo in the one functional (left) uterus. A single female yellowback stingaree Urolophus sufflavus carried an embryo in each uterus. A global review of the litter sizes of shovelnose rays (Rhinobatidae) and stingarees (Urolophidae) is provided.     

Growth, sex differentiation and gonad and plasma levels of sex steroids in male‐ and female‐dominant populations of Dicentrarchus labrax obtained through repeated size grading

Starting from 66 days post hatching (dph), European sea bass Dicentrarchus labrax were graded successively to create a fast growing (L‐extreme) and a slow growing (S‐extreme) population. The L‐extreme population grew significantly larger (ANOVA, n = 89–101, P < 0·01) attaining twice the wet mass of the S‐extreme population at 300 dph (130·9 ± 1·8 v. 66·7 ± 0·9 g, mean ± s .e .). When the two populations were sexed, the L‐extreme consisted of 96·5% and the S‐extreme of 30·2% females, while the ungraded control had 59·2% females. Sex differentiation began first in females at a total length (L_T) of 97 ± 4 mm and wet mass of 9·4 ± 1·2 g (150 dph), and was completed when fish reached 166 ± 6 mm and 53·4 ± 6·4 g (250 dph) in both sexes. Precocious maturation in males was positively correlated to growth. Gonad oestradiol (E₂) was significantly higher in the female‐dominant population at the onset of ovarian differentiation (ANOVA, n = 10, P < 0·05) and in the plasma after the appearance of the first primary oocytes (P < 0·01). Gonad testosterone (T) increased in both populations after sex differentiation (ANOVA, n = 10, P < 0·05), while plasma levels were significantly higher in the male‐dominant population (P < 0·001). Both gonad and plasma 11‐keto testosterone (11‐KT) were significantly higher in the male‐dominant population (ANOVA, n = 10, P < 0·01) reaching maximal values at spermiation. The results suggest that E₂ is closely related with ovarian differentiation and the onset of oogenesis, while T and 11‐KT is more related to spermatogenesis and precocious maturation.     

Location,size and age at onset of metamorphosis in the Japanese eel Anguilla japonica

This study clarifies the location, size and age at the onset of metamorphosis in Japanese eels Anguilla japonica through oceanic surveys, rearing experiments and analyses of the morphology and otoliths of leptocephali and glass eels. Twenty‐eight metamorphosing leptocephali were collected in the mesoscale eddy region to the east of Taiwan during research expeditions in 2004. Rearing experiments showed that the total length (L_T) of leptocephali decreased by an average of 12·5% during metamorphosis and 13·9% during the 2–12 h after death. Thus, the mean back‐calculated L_T at the onset of metamorphosis for 630 glass eels from Taiwan and Japan was estimated at 67·8 ± 2·7 mm (mean ± S.D.). The estimated mean ante‐mortem size of the fully grown pre‐metamorphic leptocephali collected in 2004 was 64·6 ± 3·4 mm, which was consistent with the L_T estimate for glass eels. Otolith analysis showed that the mean age at the onset of metamorphosis was 137 ± 15 days and indicated that Japanese eels may have a recruitment route through the mesoscale eddies to the east of Taiwan in addition to the direct transfer route from the North Equatorial Current to the Kuroshio Current.     

Age and growth of Carcharhinus leucas in the northern Gulf of Mexico: incorporating variability in size at birth

Age and growth rates of bull shark Carcharhinus leucas[n = 255; 555–2230 mm fork length (L_F)] from the northern Gulf of Mexico were estimated from ring counts on vertebral sections collected from fishery‐dependent and ‐independent surveys. Two growth models were fitted to observed data: the von Bertalanffy growth model (VBGM) with t₀ as the third parameter and a modified version of the VBGM using a fixed size‐at‐birth intercept as the third parameter. To address the variability in size‐at‐birth, a Monte Carlo simulation was incorporated into the size‐at‐birth intercept. The sex‐specific growth models were not significantly different, allowing a sexes combined model to be generated. The traditional VBGM predicted a theoretical maximum size (L_∞) of 3007·1 mm L_F, a growth coefficient (K) of 0·042 year^?1 and a theoretical age at zero length (t₀) of –6·844 years. The modified VBGM with a fixed size‐at‐birth intercept of 565 mm L_F predicted an L_∞ of 2289·2 mm L_F and a K value of 0·089 year^?1. When comparing model estimates to previously published information, the traditional VBGM predicted a significantly lower theoretical maximum size and a higher growth coefficient than those produced using data collected during the 1980s. Overall, results obtained using the VBGM with a fixed size‐at‐birth produced more biologically realistic parameters than that of the VBGM with t₀. The Monte‐Carlo simulation incorporating variability in size‐at‐birth produced similar results to the VBGM using a fixed size‐at‐birth. This study provides the first attempt to incorporate variability at size‐at‐birth and provide measurements of variability around the individual parameter estimates for an elasmobranch.     

Changes in growth and maturation parameters of Pacific sardine Sardinops sagax collected off California during a period of stock recovery from 1994 to 2010

Whether fluctuation in density influenced the growth and maturation variables of three aggregated cohorts (fish born during the 1986–1993, 1996–2003 and 2004–2008 periods) of Pacific sardine Sardinops sagax caeruleus collected off the Californian coast from 2004 to 2010 was investigated. Using a von Bertalanffy mixed‐effects model with aggregated cohorts as covariates, estimated growth rate significantly covaried with aggregated cohorts. Growth rate (K) was modelled as a fixed effect and estimated to be 0·264 ± 0·015 (±s.e ). Statistical contrasts among aggregated cohorts showed that the 1996–2003 cohorts had a significantly lower growth rate than the other two aggregated cohorts. The theoretical age at length zero (t₀) and the standard length at infinity (L_S∞) were modelled as random effects, and were estimated to be ?2·885 ± 0·259 (±s.e ) and 273·13 ± 6·533 mm (±s.e ). The relation of ovary‐free mass at length was significantly different among the three aggregated cohorts, with the allometric coefficient estimated to be 2·850 ± 0·013 (±s.e ) for the S. sagax population. The age‐at‐length trajectory of S. sagax born between 1986 and 2008 showed strong density dependence effects on somatic growth rates. In contrast to the density‐dependent nature of growth, the probability to be mature at‐size or at‐age was not significantly affected by aggregated cohort density. The size and the age‐at‐50% maturity were estimated to be 150·92 mm and 0·56 years, respectively. Stock migration, natural fluctuations in biomass and removal of older and larger S. sagax by fishing might have been interplaying factors controlling growth parameters during 1986–2010.     

Characterization of a methane‐utilizing strain and its application for monitoring methane

Aims: To explore new resources of methane‐utilizing micro‐organism and develop a microbial biosensing system for monitoring methane released from natural and semi‐natural ecosystems. Methods and Results: A methane (CH₄)‐utilizing bacterial strain was isolated from paddy soil using CH₄ as the sole carbon source and identified as Klebsiella sp. ME17 by phenotyping and 16S rDNA sequence analysis. The efficiency of CH₄ utilization of strain ME17 was 83·2% by gas chromatography analysis. A microbial biosensing system for CH₄ detection was developed by combining immobilized cells of strain ME17 with a dissolved oxygen sensor. It was found that response time of the system to CH₄ was <90s. The dissolved O₂ consumption increased with increasing CH₄ from 0% to 16·0% (v/v) demonstrating a positive linear relationship with a low detection limit of 0·2% (v/v). The relative standard deviation is 3·48%. Conclusions: Klebsiella sp. ME17 isolate is capable of utilizing CH₄. The microbial biosensing system of strain ME17 has been successfully applied to measure standard CH₄ sample with satisfactory results. Significance and Impact of the Study: This study suggests that certain strains of Klebsiella genus are capable of utilizing CH₄. Our proposed method appears very attractive for CH₄ measurement in coal mine.     

Some observations on the biology of two rarely seen deep‐sea chimaerids,Chimaera carophila and Hydrolagus homonycteris

Chimaera carophila (n = 45) and Hydrolagus homonycteris (n = 11), two deep‐sea chimaerids rarely caught in the waters off New Zealand, were collected from research trawl catches and commercial fishery catches around New Zealand at depths between 400 and 1300 m, between 2014 and 2016. Additional preserved specimens of both species (n = 58) from museum collections were analysed for size, sex and maturity. External assessment of male claspers and a combination of internal assessments of female gonad mass and oviducal gland width, were used to determine maturity. For both species, length at first maturity was 0·70–0·82 of their maximum observed chimaera length (L_C), with females maturing at a larger size. Length at maturity for C. carophila (L_C range: 28·7–103·9 cm) was estimated at 72·5 cm L_C for males (n = 163) and 82·5 L_C for females (n = 58). In H. homonycteris, length at maturity (length range: 78·6–99·8 cm L_C) was estimated at 79·1 cm L_C for males (n = 51) and 80·1 cm L_C for females (n = 17). Ovarian fecundity was up to 31 for C. carophila and sperm storage was confirmed in the oviducal gland of this species. Both species preyed on benthic invertebrates. Some C. carophila and H. homonycteris inhabit depths beyond most current fisheries, but both species appear to be relatively rare and have reproductive parameters characteristic of low productivity, which may make these species vulnerable to population decline if mortality was to increase in the future.     

Estimated genetic parameters for growth‐related traits in large yellow croaker Larimichthys crocea using microsatellites to assign parentage

To estimate the heritabilities of growth‐related traits in large yellow croaker, Larimichthys crocea, three independent full‐factorial crosses were created by crossing four males × four females, seven males × three females and four males × three females (set 1, set 2 and set 3). At 13 months post‐hatch, the juveniles were collected from three cross sets and measured for body mass (M), standard length (L_S) and body height (H_B). In addition, the parentage of the juveniles was assigned by genotyping six or seven polymorphic microsatellite loci. Out of the 959 juveniles, 99·6% could be assigned to a single parental pair. Heritabilities of growth‐related traits were estimated for individual and combined sets with the pedigrees reconstructed by using microsatellite genotypes. The heritability estimates at 13 month‐old were 0·02–0·30 for M, 0·02–0·25 for L_S and 0·03–0·36 for H_B. These results showed that the heritabilities of M, L_S and H_B were different among three sets, which suggested that different breeding strategies should be adopted for different sets.