Reproduction of the duck catfish Ageneiosus ucayalensis in a ria river system

A total of 1006 duck catfish Ageneiosus ucayalensis were collected from a ria river system of eastern Amazonia, of which 733 were females and 273 males, a sex ratio 2·69:1. Condition factors of males were higher than those of females and size at first sexual maturity (L₅₀) was 12·8 cm for females and 11·8 cm for males. The relative frequency of mature specimens and gonad condition indices indicate that the breeding season is short and coincides with the rainy season.     

Reproductive aspects of the Atlantic angel shark Squatina dumeril in the southern Caribbean Sea

The maturity and reproduction of the Atlantic angel shark Squatina dumeril were assessed using 77 females (29·2–110·4 cm total length; L_T) and 269 males (58·7–108·2 cm L_T) harvested by artisanal gillnetters off Venezuela. The biased sex ratio implied segregation or sex‐specific gear selectivity. Based on the development of the reproductive tract, 50% L_T at sexual maturity (L_T50, mean ± s.e .) for females and males were estimated at 86·14 ± 0·64 and 81·55 ± 0·12 cm, respectively. Uterine fecundity ranged between one and six and with a maximum embryo size of 25·7 cm L_T. Gravid females were observed from August to December, including those close to parturition and while the gestation period was not confirmed, the size of ovarian follicles among some specimens implied protraction. The low fecundity of the species supports close monitoring of catches.     

Comparison of electrofishing and trammel netting variability for sampling native fishes

The variability in size structure and relative abundance (CPUE; number of fish ≥200 mm total length, L_T, collected per hour of electrofishing or trammel netting) of three native Colorado River fishes, the endangered humpback chub Gila cypha, flannelmouth sucker Catostomus latipinnus and bluehead sucker Catostomus discobolus, collected from electrofishing and trammel nets was assessed to determine which gear was most appropriate to detect trends in relative abundance of adult fishes. Coefficient of variation (CV) of CPUE ranged from 210 to 566 for electrofishing and 128 to 575 for trammel netting, depending on season, diel period and species. Mean CV was lowest for trammel nets for humpback chub (P = 0·004) and tended to be lower for flannelmouth sucker (P = 0·12), regardless of season or diel period. Only one bluehead sucker >200 mm was collected with electrofishing. Electrofishing and trammel netting CPUE were not related for humpback chub (r = ?0·32, P = 0·43) or flannelmouth sucker (r = ?0·27, P = 0·46) in samples from the same date, location and hour set. Electrofishing collected a higher proportion of smaller (<200 mm L_T) humpback chub (P < 0·001), flannelmouth suckers (P < 0·001) and bluehead suckers (P < 0·001) than trammel netting, suggesting that conclusions derived from one gear may not be the same as from the other gear. This is probably because these gears fished different habitats, which are occupied by different fish life stages. To detect a 25% change in CPUE at a power of 0·9, at least 473 trammel net sets or 1918 electrofishing samples would be needed in this 8 km reach. This unattainable amount of samples for both trammel netting and electrofishing indicates that detecting annual changes in CPUE may not be practical and analysis of long‐term data or stock assessment models using mark‐recapture methods may be needed to assess trends in abundance of Colorado River native fishes, and probably other rare fishes as well.     

Reproductive parameters of the Pacific angel shark Squatina californica (Selachii: Squatinidae)

Reproductive characteristics of the Pacific angel shark, Squatina californica, were evaluated from 420 specimens obtained from the artisanal fishery in La Paz Bay, Gulf of California, Mexico. Females (99 cm, 6000 g) were larger than males (95 cm, 5000 g) in terms of both total length (L_T) and body mass (M_T). The overall sex ratio was significantly different from the expected 1:1, suggesting sexual segregation of mature individuals in La Paz Bay. Males had developed reproductive organs and calcified claspers from 72 cm L_T; the median size at maturity (L_T50) was 75·6 cm. In females, only the left ovary was functional and mature ovarian follicles were present from 77 cm L_T; the estimated L_T50 was 77·7 cm. For the 10 gravid females sampled, uterine fecundity was between two and 10 embryos. Mature, non‐gravid females with small and large ovarian follicles appeared simultaneously with gravid females with follicles that did not exceed 1·9 cm diameter.     

Reproductive strategy of Labeo senegalensis Valenciennes 1842 (Teleostei: Cyprinidae) in the Ouémé basin,Benin

Aspects of the reproductive biology and population structure of Labeo senegalensis were investigated in the Ouémé River between April 2005 and March 2006. Reproductive strategy was investigated using gonadosomatic index, ovarian structure and fecundity. Average size-at-first-maturity (L ₅₀) was estimated at 29 cm TL for females and 25.7 cm TL for males. The average sex ratio (1:0.96) was not significantly different from unity. Oocyte diameter frequency distribution suggests synchronous development with a single total spawning. Absolute fecundity ranged between 12 948 and 74 832 eggs. Labeo senegalensisis a highly fecund fish that presents a seasonal cycle of reproduction from May to October during the rainy season.     

Life‐history strategies of the rock hind grouper Epinephelus adscensionis at Ascension Island

Epinephelus adscensionis sampled from Ascension Island, South Atlantic Ocean, exhibits distinct life‐history traits, including larger maximum size and size at sexual maturity than previous studies have demonstrated for this species in other locations. Otolith analysis yielded a maximum estimated age of 25 years, with calculated von Bertalanffy growth parameters of: L_∞ = 55·14, K = 0·19, t₀ = ?0·88. Monthly gonad staging and analysis of gonad‐somatic index (I_G) provide evidence for spawning from July to November with an I_G peak in August (austral winter), during which time somatic growth is also suppressed. Observed patterns of sexual development were supportive of protogyny, although further work is needed to confirm this. Mean size at sexual maturity for females was 28·9 cm total length (L_T; 95% C.I. 27·1–30·7 cm) and no females were found >12 years and 48·0 cm L_T, whereas all confirmed males sampled were mature, >35·1 cm L_T with an age range from 3 to 18 years. The modelled size at which 50% of individuals were male was 41·8 cm (95% C.I. 40·4–43·2 cm). As far as is known, this study represents the first comprehensive investigation into the growth and reproduction of E. adscensionis at its type locality of Ascension Island and suggests that the population may be affected less by fisheries than elsewhere in its range. Nevertheless, improved regulation of the recreational fishery and sustained monitoring of abundance, length frequencies and life‐history parameters are needed to inform long‐term management measures, which could include the creation of marine reserves, size or temporal catch limits and stricter export controls.     

Three decades of longlining in Bimini,Bahamas, reveals long‐term trends in lemon shark Negaprion brevirostris (Carcharhinidae) catch per unit effort

In Bimini, Bahamas, the consistent employment of longlines, beginning in 1982, provided a rare opportunity to explore population trends for large resident sharks. This study assessed three shallow water longline survey periods at this location; 1982–1989, 1992–2002 and 2003–2014, with the aim of determining trends in annual catch per unit effort (CPUE) for an IUCN listed near‐threatened species, the lemon shark Negaprion brevirostris. A general additive model (GAM) was used to analyse the non‐linear annual CPUE values over the entire 32‐year research period. The GAM displayed high variability of annual CPUE, with a peak value of 0·026 N. brevirostris per hook day (hooks day^?1) in 2000. The temporal pattern of CPUE indicated an abundance trend with a complete cycle, from trough to trough, occurring over a period of approximately 18 years. The 1982–1989 survey period saw the highest proportion of mature individuals (19·8%) and the smallest average pre‐caudal length (L_PC; 124·8 cm). The 1992–2002 survey period had the highest average annual CPUE (0·018 hooks day^?1), while the 2003–2014 research period saw largest average L_PC size (134·8 cm) and the lowest average CPUE values (0·009 hooks day^?1) of the entire research period. The long‐term trend identified in this study provides a baseline for future assessment.     

Biology of the rainbowfish,Glossolepis multisquamatus (Melanotaeniidae), from the Sepik River floodplains,Papua New Guinea

Synopsis G. multisquamatus is abundant in the Sepik River, preferring floodplain lakes and marginal areas of floodplain with moderate turbidity. It is the only rainbowfish documented to inhabit river floodplains. Migrations onto and off the floodplain occur in response to changes in flood conditions. Seasonality is evident in reproduction, condition factor and fat deposit and stomach fullness indices; all increasing in the flood season. Fecundity is high compared with stream dwelling rainbowfish species mainly due to decreased egg size. The reproductive strategy ofG. multisquamatus is interpreted as a response to increased adult mortalities encountered on floodplains in comparison to more stable stream habitats occupied by related species.G. multisquamatus is carnivorous, its diet being similar to other rainbowfishes, consisting of a variety of small invertebrates taken from mid-water or the water surface. The ecology and behaviour ofG. multisquamatus is explained as a partial colonisation of newly developed floodplains in this river.     

Population demographics of American eels Anguilla rostrata in two Arkansas,U.S.A., catchments that drain into the Gulf of Mexico

The goal of this study was to compare American eel Anguilla rostrata life history in two inland river systems in Arkansas, U.S.A., that ultimately discharge into the Gulf of Mexico via the Mississippi River and the Red‐Atchafalaya catchments. From 21 June 2011 to 24 April 2014, 238 yellow‐phase A. rostrata were captured in the middle Ouachita River and tributaries using boat electrofishing and 39 in the lower White River using multiple sampling gears. Most of them were caught downstream of dams in both basins (61%). Medium‐sized A. rostrata ranging from 225 to 350 mm total length (L_T) were the most abundant size group in the Ouachita River basin, but they were absent from the White River. Mean L_T at age 4 years (i.e. youngest shared age) was 150 mm greater for the White River than the Ouachita River basin. Anguilla rostrata appeared to have a greater initial L_T (i.e. minimum size upon arrival) in the White River that allowed them to reach a gonado‐somatic index (I_G) of 1·5 up to 4 years earlier, and downstream migration appeared to occur 5 years earlier at 100 mm greater L_T; these differences may be related to increased river fragmentation by dams in the Ouachita River basin. Growth and maturation of A. rostrata in this study were more similar to southern populations along the Atlantic coast than other inland populations. Adult swimbladder nematodes Anguillicoloides crassus were not present in any of the 214 swimbladders inspected. Gulf of Mexico catchments may be valuable production areas for A. rostrata and data from these systems should be considered as range‐wide protection and management plans are being developed.     

Age, growth, and sexual maturity of the yellownose skate Dipturus chilensis in the south‐eastern Pacific

The age and growth parameters of Dipturus chilensis were estimated by counting growth rings from thin sections of vertebral centra from 400 fish (246 females and 154 males), ranging from 23 to 124 cm total length (L_T), and backcalculating fish lengths at previous ages. Marginal increment analysis lent support to the hypothesis of annual deposition of band‐pairs, which formed during the winter months. The oldest female D. chilensis aged in this study was 21 years and 117 cm L_T, whereas the oldest male was 18 years and 93 cm L_T. A 4·7% index of average per cent error (I_APE) suggested that this is a precise method for calculating the age of D. chilensis. Observed L_T were lower than backcalculated L_T, which implies the influence of Lee's phenomenon. The von Bertalanffy growth equations, based on mean length‐at‐age data, were estimated as L_t = 128·3 (1 ? e^{?0·112 (t + 0·514)}) for females and L_t = 107·8 (1 ? e^{?0·134 (t + 0·862)}) for males where t is age (years). Growth was significantly different between sexes: females reached a larger adult size. Ages and lengths at 50% maturity were estimated at 14 years of age and 106 cm L_T for females and 11 years of age and 86 cm L_T for males. At c. 14 years, there was a decline in growth rates in females. The factor most likely responsible for this was sexual maturity, which caused a discontinuity in growth of female fish. These results show that this species is slow‐growing, long‐lived, relatively large and of delayed maturity, characteristics that make it vulnerable to exploitation.     

Reproductive biology and feeding habits of the prickly dogfish Oxynotus bruniensis

The reproductive biology and diet of prickly dogfish Oxynotus bruniensis, a deep‐sea elasmobranch, endemic to the outer continental and insular shelves of southern Australia and New Zealand, and caught as by‐catch in demersal fisheries, are described from specimens caught in New Zealand waters. A total of 53 specimens were obtained from research surveys and commercial fisheries, including juveniles and adults ranging in size from 33·5 to 75·6 cm total length (L_T). Estimated size‐at‐maturity was 54·7 cm L_T in males and 64·0 cm L_T in females. Three gravid females (65·0, 67·5 and 71·2 cm L_T) were observed, all with eight embryos. Size‐at‐birth was estimated to be 25–27 cm L_T. Vitellogenesis was not concurrent with embryo development. Analysis of diet from stomach contents, including DNA identification of prey using the mitochondrial genes cox1 and nadh2, revealed that O. bruniensis preys exclusively on the egg capsules of holocephalans, potentially making it the only known elasmobranch with a diet reliant solely upon other chondrichthyans. Based on spatial overlap with deep‐sea fisheries, a highly specialized diet, and reproductive characteristics representative of a low productivity fish, the commercial fisheries by‐catch of O. bruniensis may put this species at relatively high risk of overfishing.     

Trophic size‐structure of sailfish Istiophorus platypterus in eastern Taiwan estimated by stable isotope analysis

To examine trophic dynamics over different size classes, an isotopic study of sailfish Istiophorus platypterus life‐history stages was carried out. Samples were collected from eastern Taiwan and the South China Sea during April 2009 and February 2012. A total of 263 samples (111–245 cm, lower jaw fork length, L_LJFL) were examined for changes in trophic structure in relation to L_LJFL by using stable isotope analysis of carbon (δ¹³C) and nitrogen (δ¹⁵N). The δ¹⁵N values for I. platypterus ranged from 7·51 to 14·19‰ (mean ± s.d . = 12·06 ± 1·16‰) and the δ¹³C values ranged from ?22·04 to ?15·48‰ (mean ± s.d . = ?17·62 ± 1·10‰). The δ¹⁵N values were positively dependent on L_LJFL (r² = 0·377), whereas δ¹³C were negatively dependent on L_LJFL (r² = 0·063). There were significantly different seasonal changes in nitrogen and carbon isotopic concentration, but no significant differences in concentrations between eastern Taiwan and the South China Sea were reported. The trophic level (T_L) of each L_LJFL class was correlated, starting from 2·84 T_L for size class I (L_LJFL < 140 cm) and reaching 5·03 T_L for size class VI (L_LJFL > 221 cm). The mean ± s.d . T_L was 4·43 ± 0·19 for all samples. The results reveal that I. platypterus occupies a wide range of trophic levels and different size classes occupy different trophic positions in the pelagic ecosystem.     

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.     

Catch composition,reproductive biology and diet of the bramble shark Echinorhinus brucus (Squaliformes: Echinorhinidae) from the south‐eastern Arabian Sea

Fishery and biological data are presented for the poorly known bramble shark Echinorhinus brucus (Squaliformes: Echinorhinidae), from the deep waters of the south‐eastern Arabian Sea. A total of 5318 individuals from by‐catch landings of deep‐water bottom set longlines, gillnets and shrimp trawl fisheries operating at depths of 200–1200 m were recorded between January 2008 and December 2011 at the Kochi Fisheries Harbour (Kerala). A total of 431 individuals, from 46 to 318 cm total length (L_T) and 0·8 to 132 kg total mass (M_T), were examined to determine biological data for this species. The L_T at which 50% were mature (L_T50) for females and males was estimated at 189 and 187 cm L_T. Litter size ranged from 10 to 36 and size at birth was between 42 and 46 cm L_T. Dietary analysis of stomach contents revealed E. brucus feeds on a variety of prey including crustaceans (69% index of relative importance, I_RI), teleosts (25·8% I_RI), cephalopods (1·7% I_RI) and elasmobranchs (0·7% I_RI). This study provides the first detailed biological data for this species and also highlights the extent of the by‐catch fishery for this species in Indian waters.     

Fish community characteristics of the lower Gambia River floodplains: a study in the last major undisturbed West African river

1. The Gambia River is the last major West African river that has not been impounded. However, a hydroelectric dam is being constructed and substantial changes to the hydrology and ecology of the system are expected. 2. Little information is available on the impact of water impoundments in semi‐arid regions on downstream floodplain fish communities, due to the scarcity of pre‐intervention data. Because profound impacts on physical habitat, salinity and nutrient transport can occur downstream of such impoundments, a knowledge of the species‐habitat associations of biota such as fishes is necessary for understanding likely changes and how to limit them. 3. Fish were sampled using cast and hand nets along two transects on the floodplain, and with fyke nets in two ‘bolongs’ (creeks) from May to November 2005 and 2006 in the lower reaches of the Gambia River, close to the salt water front where ecological changes due to the construction of the dam are likely to be pronounced. 4. Greatest fish species richness was associated with low conductivity, low pH and deep water. Bolongs held greater species richness compared with other floodplain habitats, probably because they acted as conduits for fish moving on and off the floodplain. Species richness and catch biomass increased rapidly following the first rains and then declined. 5. Using a multivariate analysis, three main species groups were identified on the floodplain; one associated with deeper water, one with less brackish water and one with shallow, open water. Tilapia guineensis was the commonest species on the floodplains. 6. The floodplains provide nursery habitats as many fish captured were immature, particularly for species where adults are mainly encountered in the main channel. Several small‐sized floodplain specialists were also represented by a high proportion of mature individuals. 7. Impoundment is expected to reduce seasonal flooding of the floodplain in the lower Gambia River, downstream of the impoundment, resulting in reduced occurrence of aquatic habitats, especially bolongs, together with lower dissolved oxygen and increased salinity, leading to alteration of the floodplain fish communities, benefiting salt‐tolerant species, reducing overall species richness and probably reducing floodplain fish production.     

Reproductive strategy and recruitment dynamics of amphidromous goby Sicyopterus japonicus as revealed by otolith microstructure

The daily ages of 312 of 879 newly recruited postlarvae of Sicyopterus japonicus, collected from the Shuang‐Chi Estuary in north‐eastern Taiwan during February 1996 to April 1997, were determined from daily growth increments in their otoliths. Pelagic larval duration, growth rate of the marine larval stage and hatching dates were estimated, and recruitment timing was linked to environmental factors. The mean ±s .d . total length (L_T) and daily ages of S. japonicus at recruitment to the estuary were estimated to be 33·95 ± 1·31 mm (range 30·7 to 38·1, n = 317) and 163·72 ± 12·79 days (range 130 to 198, n = 312), respectively. The recruitment of S. japonicus larvae is size dependent not age dependent because L_T of the larvae is independent of age at recruitment. Periodic analysis indicated that L_T and growth rate of the larvae were inversely correlated with the age at recruitment, which means that the fast‐growing individuals recruited earlier. The growth rate of S. japonicus in the marine larval stage was synchronous with marine productivity in this subtropical area, i.e. the spring cohort recruited in the autumn had a higher growth rate than the autumn cohort recruited the following spring. The main spawning season of S. japonicus as backcalculated from otolith daily increments was in autumn, a relatively low productivity period compared with spring. During this season, there were fewer competitors and predators than in the more productive spring. The recruitment of 95% of postlarva coincided with low salinity (14) and low water temperature (23° C) in the river mouth that provided a buffer area for the adaptation of the larvae for upstream migration. This unique reproduction strategy and prolonged larval duration facilitated the widespread distribution of the fish along the coasts of East Asia.     

Interaction between migration behaviour and estuarine mortality in cultivated Atlantic salmon Salmo salar smolts

Migration behaviour and estuarine mortality of cultivated Atlantic salmon Salmo salar smolts in a 16 km long estuary were studied using two methods: (1) acoustic telemetry and (2) group tagging in combination with trap nets. Progression rates of surviving individuals through the estuary were relatively slow using both methods [0·38 L_T (total length) s^?1 v. 0·25 L_T s^?1]. In 2012, the progression rate was slow from the river to the estuary (0·55 L_T s^?1) and the first part of the estuary (0·31 L_T s^?1), but increased thereafter (1·45–2·21 L_T s^?1). In 2013, the progression rate was fast from the river to the estuary (4·31 L_T s^?1) but was slower thereafter (0·18–0·91 L_T s^?1). Survival to the fjord was higher in 2012 (47%) compared to 2013 (6%). Fast moving individuals were more likely to migrate successfully through the estuary compared to slower moving individuals. Adult recapture of coded‐wire‐tagged S. salar was generally low (0·00–0·04%). Mortality hot spots were related to topographically distinct areas such as the river outlet (in 2012) or the sill separating the estuary and the fjord (in 2013). At the sill, an aggregation of cod Gadus morhua predating on cultivated smolts was identified. The results indicate that slow progression rates through the estuary decreases the likelihood of smolts being detected outside the estuary. The highly stochastic and site‐specific mortality patterns observed in this study highlight the complexity in extrapolating mortality patterns of single release groups to the entire smolt run of wild S. salar.     

Life history of the river goby Glossogobius callidus (Teleostei: Gobiidae)

The river goby Glossogobius callidus is native to freshwater and estuarine habitats in South Africa. Individuals [21.1–144.4 mm total length (L_T)] were sampled from impoundments in the Sundays River Valley, Eastern Cape, from February 2014 to March 2015. The largest female was 137.2 mm L_T, and the largest male was 144.4 mm L_T. Length-at-50% maturity was 75.2 ± 2.1 mm L_T for males and 76.2 ± 2.0 mm L_T for females. Absolute fecundity was 1028.2 ± 131.7 oocytes per fish, and relative fecundity was 50.1 ± 18.1 oocytes per gram. The spawning season extended from October to December. Fish were aged using sectioned sagittal otoliths. The growth zone periodicity was validated using edge analysis. Longevity was more than 7 years for females and more than 6 years for males. Length-at-age was similar for the two sexes and was best described using the von Bertalanffy growth model as L_t = 74.7(1 − e^{–1.0(t + 0.1)}) mm L_T for the entire population. Using the population age structure, the mortality rate was estimated at 1.3 per year.     

Aspects of reproductive biology of Labeo horie Heckel (Pisces: Cyprinidae) in Lake Chamo, Ethiopia

Labeo horie Heckel is increasingly becoming commercially important in Lake Chamo but its reproductive biology in the lake is not well enough to guide its management. Sex ratio, breeding season, length at first maturity and fecundity of L. horie were studied from 1197 fish samples collected between August 1998 and October 1999 in Lake Chamo, Ethiopia. The sex ratio was significantly different (χ ² = 12.12, P < 0.001). The peak‐breeding period was during the rainy months of March to May, during which time more than 90% of both sexes had ripe gonads. The size at maturity ( L _m50 ) of males was 52 cm while the L _m50 of females was 62 cm. The smallest ripe male in the catch was 46.7 cm and weighed 890 g while the smallest ripe female caught was 49.5 cm and weighed 1145 g. The weight of ripe ovaries ranged from 54.3 g to 991.8 g and contained between 68,400 and 1,320,400 eggs. Relative fecundity ranged between 60 and 290 eggs per g of body weight. The relationships between fecundity and total length and between fecundity and total weight were curvilinear, while the relationship between fecundity and ovary weight was linear. L. horie conformed to the general pattern of reproduction in a tropical environment where peak‐breeding activity occurred during the rainy season. In order to protect the spawning population, fishing pressure should be minimized during breeding time at the shallower littoral regions.