Age validation and variation in growth,mortality and population structure of Liza argentea and Myxus elongatus (Mugilidae) in two temperate Australian estuaries

This study investigated variation in the rates of growth and mortality, and age and fork‐length (L_F) compositions of two exploited species of Mugilidae, Liza argentea and Myxus elongatus, in two south‐east Australian estuaries (Lake Macquarie and St Georges Basin). An ageing protocol was developed by counting opaque growth zones on sectioned otoliths which was validated by periodically examining the otoliths of captive‐reared young‐of‐the‐year fishes, and marginal increment analysis of wild fishes. The maximum recorded age was 17 years for L. argentea and 12 years for M. elongatus, which is greater than generally observed in other species of mugilids. Growth models of each species significantly differed between sexes and, except for male L. argentea, between estuaries. Fishes from Lake Macquarie generally had a greater mean L_F at age than those from St Georges Basin and females of both species generally attained a greater maximum L_F and age than males. Gillnet catches of L. argentea were of similar L_F and age compositions in both estuaries, whereas the age composition of catches of M. elongatus in Lake Macquarie contained a greater proportion of younger fish. Estimates of total, natural and fishing mortality were greater for M. elongatus than L. argentea across both estuaries, and estimates of total mortality were greatest for both species in Lake Macquarie. The data indicate that neither species has been overfished in these estuaries.     

Population biology and assessment of the white-spotted spinefoot, Siganus canaliculatus (Park, 1797), in the southern Arabian Gulf

The age, growth, mortality, reproduction and resource status of Siganus canaliculatus in the southern Arabian Gulf were investigated using a combination of size frequency, biological and size‐at‐age data. Defined structural increments consisting of alternating translucent and opaque bands in transverse sections of sagittal otoliths were validated as annuli. The maximum absolute age estimate was 7.8 years. Parameter values of the von Bertalanffy growth function fit to size‐at‐age data (males and females combined) were: k = 1.0, L_∞ = 24.8 cm (L_F), t_o = −0.1 years. Fish in spawning condition were only observed between April and July although patterns in gonadosomatic indices suggested a second but less well defined spawning event in November. The mean sizes and ages at first sexual maturity were 21.5 cm L_F (1.9 years) for males and 25.7 cm L_F (2.1 years) for females. Fish were fully recruited to the fishery at a size (L₁₀₀ = 19.7 cm L_F) that was smaller than the sizes at which sexual maturity was attained. The annual instantaneous rate of fishing mortality (F = 0.85 year⁻¹) (0.26–1.44 year⁻¹ 95% CI) was considerably greater than the target (F_opt = 0.33 year⁻¹) and limit (F_limit = 0.44 year⁻¹) biological reference points, indicating that the stock is overexploited.     

Variation in growth,mortality, length and age compositions of harvested populations of the herbivorous fish Girella tricuspidata

Commercial gillnet and beach‐seine catches of Girella tricuspidata from seven estuaries in eastern Australia were examined for differences in fork length (L_F), sex and age composition, and populations were assessed for growth and mortality. Fish 220–350 mm L_F dominated landings across all estuaries sampled, regardless of gear type. Few fish >10 years of age were observed in the catches, with fish aged 3–5 years, and 4–7 years, being most abundant in the catches in the four most northern estuaries and three southern estuaries, respectively. There was considerable variation in the L_F of G. tricuspidata at any given age and the oldest male and female were 21 and 24 years, respectively. There were no consistent differences between sexes or latitudinal regions in the growth and mean L_F at age of fish in each individual age class between 3 and 8 years. Growth of females was greater than males in the northern region, but not elsewhere. Estimates of the instantaneous rate of total mortality (Z) were dependent on estuary and year, ranging from 0·30 to 1·01, whereas the corresponding estimates of fishing mortality (F) ranged from 0·12 to 0·90. Populations of G. tricuspidata appear to have been heavily exploited, primarily relying on young fish recruiting to the fishery. The ecosystem‐wide effects of harvesting this dominant mobile teleost herbivore need to be assessed further.     

Life‐history characteristics of the large Amazonian migratory catfish Brachyplatystoma rousseauxii in the Iquitos region,Peru

The main life‐history traits of the dorado Brachyplatystoma rousseauxii, a large Amazonian catfish undertaking the largest migration known for a freshwater fish species (from the nursery area in the estuary of the Amazon to the breeding zones in the head waters of the western Amazon basin close to the Andes), were determined from a 5 year sampling of >15 000 specimens in the Peruvian Amazon. The breeding season occurred during the falling and low‐water periods, which is hypothesized to be an adaptation to maximize the chances of young stages to reach the estuary. The size at first sexual maturity was slightly larger for females than males, c. 91 and 83 cm standard length (L_S), respectively. Both males and females reproduce for the first time at >3 years old. The fecundity per spawning event ranged from 481 734 to 1 045 284 oocytes for females weighing 25 and 34 kg, respectively. Seasonal variations of body condition were similar among sexes, but differed between immature specimens that had a higher condition during the low‐water period and lower condition during rising waters, and mature individuals that showed the opposite pattern. The growth characteristics were estimated by L_S frequency analysis. For females, the best fitting models gave a mean birth date in August, during the height of the breeding cycle, with the following von Bertalanffy growth function parameters: L_S∞ = 153·3, K = 0·29 and t₀ =– 0·37 years. For males, the best fitting model gave a mean birth date in July, also during the height of the breeding period, with L_S∞ = 142, K = 0·30 and t₀ =– 0·36 years. At a given age, females were systematically larger than males and the size difference increased with age. The largest females sampled (148 cm L_S) was 11 years old and the largest male (134 cm L_S) was 9 years old. The mortality estimates were higher for males total (Z) = 1·34, natural (M) = 0·52 and fishing (F) = 0·82 than for females (Z = 0·98, M = 0·50, F = 0·48). The life‐history patterns of B. rousseauxii are discussed in light of the available knowledge about this species and the understanding of its complex life cycle.     

Age‐based demographic and reproductive assessment of orangespine Naso lituratus and bluespine Naso unicornis unicornfishes

Bluespine unicornfish Naso unicornis and orangespine unicornfish Naso lituratus were sampled in Pohnpei and Guam, Micronesia, over 13 months to identify reproductive and age‐based demographic features necessary for informed management. Age and reproductive information were derived from analysis of sagittal otoliths and gonads. Both species had moderate life spans [maximum ages of 23 (N. unicornis) and 14 years (N. lituratus)] compared with published estimates of conspecifics from other locations (>30 years) and of other Naso species. Length at maturation for N. unicornis was similar between Pohnpei and Guam while females consistently matured at a larger size [c. 30 cm fork length (L_F)] than males (c. 27 cm L_F). This sex‐specific pattern was reversed in N. lituratus for which estimates of maturation length (females: 15 cm L_F; males: 18 cm L_F) were only obtained from Guam. Developmental patterns in female gonads of both species suggested that initiation of maturation occurs very early. Growth patterns of N. lituratus displayed rapid asymptotic growth compared with N. unicornis and other congeners as well as slight sex‐specific patterns of length‐at‐age. Results highlight the considerable spatial variation that may occur in the population biology of these species across various scales. Additionally, proper management remains complicated without improved knowledge of fishery trends and reproductive behaviour in unicornfishes, species that are prime fishery targets in Micronesia and elsewhere.     

Reproduction,growth and mortality of the exploited sillaginid,Sillago ciliata Cuvier, 1829

The goal of this study was to examine the age and size composition, growth, reproductive biology and mortality of Sillago ciliata Cuvier, 1829 in one of the largest estuarine commercial fisheries in south‐eastern Australia. The study also aimed to present a qualitative comparison of latitudinal variations in some of these characteristics along the eastern Australian coastline. The sampled population contained fish aged up to 10 years with a maximum size of 39.2 cm fork length (L_F), and was dominated by 1–5 year olds. Sexual divergence in both the age and size structure of the population was recorded. Female S. ciliata grew slightly faster and attained a greater maximum size (L_∞ = 33.79 cm L_F, k = 0.50 year^?1 and t₀ = ?0.57 years) than males (L_∞ = 29.73 cm L_F, k = 0.49 year^?1 and t₀ = ?0.67 years). Females also matured at a significantly larger size (19.13 cm) and older age (1.63 years) than males (size: 17.07 cm, age: 1.10 years). Reproductive activity was highest between September and March. There were no differences between males and females in terms of mortality rate; the estimated total population, natural and fishing mortality rates were Z = 0.64, M = 0.42 and F = 0.22, respectively. Although these mortality rates suggest that S. ciliata in the Clarence River are relatively resilient to current rates of exploitation, regular monitoring of their commercial and recreational catch as well as their population structure is recommended in order to maintain sustainable fisheries. Potential latitudinal shifts in the spawning period, age structure and growth of S. ciliata along eastern Australia were also revealed.     

Age and growth of black seabream Acanthopagrus schlegelii (Sparidae) in Hong Kong and adjacent waters of the northern South China Sea

Age and growth of the black seabream Acanthopagrus schlegelii (family Sparidae) from the northern South China Sea (NSCS) were studied by reading growth rings in sectioned sagittal otoliths. Ring formation frequency was determined to be annual by using marginal increment analysis. The von Bertalanffy growth function parameters were estimated as: L_∞ = 43.7 cm L_S; K =0.22 year; t₀ = ?1.59 years. Functional males are significantly younger than functional females, with sexually transitional individuals between the modal ages of males and females supporting protandry in this species. Males become sexually mature within 1 year and 50% age at sex change is at 2 years. The maximum age recorded for both males and females sampled was 9 years which is lower than for conspecifics elsewhere and may reflect high fishing pressure in the study area when compared with conspecifics in other areas or could reflect latitudinal effects. Otolith mass was significantly and positively related to age, providing a cheap and quick alternative method for approximating age. Acanthopagrus schlegelii is a relatively fast‐growing and rapidly maturing species attaining a similar asymptotic length to conspecifics. A need for fishery management is indicated to protect both young juveniles and older adults, especially females, to increase reproductive output and safeguard fishery production.     

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.     

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.     

Growth and derived life-history characteristics of the Brazilian electric ray Narcine brasiliensis

The majority of batoids are listed as Threatened (20.4%) or Data Deficient (41%) by the IUCN Red List. A key challenge to assessing Data-Deficient species is obtaining estimates of key life-history characteristics. Here, a Bayesian approach was used to estimate derived life-history characteristics from a growth model applied to the Data-Deficient Brazilian electric ray Narcine brasiliensis. The age of 170 specimens (107 females, 63 males) was estimated from vertebral centra, and total length, disc width, total weight and birth size were used in a joint estimation of sex-specific length-weight models and two-dimensional von Bertalanffy growth models. Estimates of age at length zero, age at maturity, longevity and mortality at age were derived simultaneously. The Bayesian joint modelling approach was robust to small sample sizes by adding a likelihood to constrain L₀ and sharing parameters, such as Brody growth coefficient between length measurements. The median growth parameter estimates were a shared L₀ = 38.8 mm, female L_∞ = 515 mm, 𝑘 = 0.125 and male L_∞ = 387 mm, 𝑘 = 0.194. Age at maturity was estimated to be 7.40–7.49 years for females and 4.45–4.47 years for males, whereas longevity was 22.5–22.6 years for females and 14.2 years for males depending on length measurement. Age-1 natural mortality was estimated to be 0.199–0.207 for females and 0.211–0.213 for males. The derived life-history characteristics indicate N. brasiliensis is earlier maturing, but slower growing relative to other Torpediniformes. These characteristics along with the species’ endemism to southern Brazil and high by-catch rates indicate that one of the IUCN Red List threatened categories may be more appropriate for the currently Data-Deficient status. The Bayesian approach used for N. brasiliensis can prove useful for utilizing limited age-growth data in other Data-Deficient batoid species to inform necessary life characteristics for conservation and management.     

Age,growth and mortality of invasive sharpbelly,Hemiculter leucisculus (Basilewski, 1855) in Erhai Lake,China

The sharpbelly Hemiculter leucisculus, an invasive species, has expanded its range throughout much of Asia and into the Middle East. However, little is known of its adaptive changes regarding life history traits such as age, growth and mortality that could possibly explain its success as an invasive species. A detailed study of the invasive sharpbelly was conducted based on 4539 samples collected from July 2009 to June 2011 in Erhai Lake, China. Standard length ranged from 4.3–19.1 cm for females and 4.6–12.3 cm for males. Length–weight relationships for females and males were significantly different and described as W = 0.0076SL^3.2608 and W = 0.0084SL^3.1901, respectively. Otoliths are ideal for age determination because of the single annulus formed each year. Based on marginal increment analysis, the total mean CV for age estimate between two readings was 3.55%. The von Bertalanffy growth curves computed by observed length‐at‐age data were expressed as L_t = 25.6 (1 ? e^{?0.176 (t + 1.347)}) for females and L_t = 16.4 (1 ? e^{?0.354 (t + 0.819)}) for males. According to the age, growth and mortality data, there are three possible reasons for H. leucisculus attaining such dominance within a short time in Erhai Lake. First, because of the simple age structure of this species: 97.58% of males were 1–2 years old with a maximum age of only 3 years; 93.14% of females were 1–3 years old, with a maximum age of 6 years. Second, females grew larger than males at any age. Third, instantaneous mortality rates were much higher for males (4.22 year^?1) than for females (1.17 year^?1).     

Reproductive biology of albacore Thunnus alalunga

Reproductive variables in albacore Thunnus alalunga were evaluated by gonad histology in samples of 132 males (58–118 cm fork length, L_F) and 112 females (59–101 cm L_F) that were collected from the western North Pacific Ocean from 2001 to 2006. In the sex ratio examination, males greatly outnumbered females in large adult fish (L_F > 100 cm). Thunnus alalunga exhibited a protracted spawning period from March to September in the waters off eastern Taiwan and the Philippines, and the peak spawning activity occurred in March and April. Minimum sizes associated with the classification of mature fish were 78 and 83 cm L_F for males and females, respectively. In addition, the largest L_F of immature fish were 93 cm for males and 94 cm for females. The spawning frequency estimate in April was 1·7 days. Batch‐fecundity estimates of 21 females (89–99 cm L_F) ranged between 0·17 and 1·66 million eggs (mean ±s.d . = 0·94 ± 0·43). The relative fecundity estimates of the 21 females ranged between 9·2 and 92·4 oocytes g^?1 body mass (mean ±s.d . = 50·5 ± 22·8). The results presented in this study provide increased information regarding this species' reproductive‐related characteristics than are currently available in stock status determinations.     

Growth and maturation of the redlip parrotfish Scarus rubroviolaceus

This study presents age‐based life‐history information for the red lip parrotfish Scarus rubroviolaceus based on a 5 year sampling programme from the commercial fishery of American Samoa. Females reached sexual maturity at 31·9 cm fork length (L_F) and 2·6 years and sex change occurred at 42·3 cm L_F, although not all females change sex through their ontogeny. The maximum observed age was 14 years and c. 65% of the fishery harvest was above the median L_F at sex change.     

Age,growth and mortality of scaldfish (Arnoglossus laterna Walbaum, 1792) from the Adriatic Sea

The population dynamics parameters of scaldfish, Arnoglossus laterna, from the Adriatic Sea were studied. Specimens ranging from 4.5 to 17.1 cm in total length were collected from commercial bottom‐trawl catches (2000–2006). Spawning from April through the end of August with a peak in May, A. laterna is one of the non‐target species usually present in mixed bottom trawl catches. The overall male to female ratio was 1.00 : 0.61. The oldest individual was 6 years of age. Length–weight relationships showed positive allometric growth (b = 3.36 for males and b = 3.39 for females). Parameters of the von Bertalanffy growth equation were: L_∞ = 17.3 cm; K = 0.258 per year; t₀ = ?1.0026 year; R² = 0.925. The relatively low value of total mortality (Z = 0.90) and relatively high value of constant rate of natural mortality (M = 0.64) was estimated. Presumed calculated fishing mortality (F = 0.26) and the consequently estimated exploitation ratio (E = 0.29) indicated no danger of an over‐exploitation of this species in the study area at the current level of fishing pressure. The low T max and correspondingly high M suggest that this small benthic predator plays an important role in the Adriatic ecosystem as a prey species for large benthic predators. However, the estimates include uncertainties and require further confirmation, especially with regard to natural mortality.     

Gonadosomatic index‐based size at first sexual maturity of the catfish Eutropiichthys vacha (Hamilton, 1822) in the Ganges River (NW Bangladesh)

This study describes the size at first sexual maturity, length–weight relationships (LWR) in relation to size at first sexual maturity, and Fulton’s condition factor (K_F) of Eutropiichthys vacha in the Ganges River, northwestern Bangladesh. Sampling was done using traditional fishing gear including cast nets, square lift nets and conical traps during January and April, and July to December 2010. For each individual, total length (TL) was measured to the nearest 0.01 cm, and total weight (BW) was determined to the nearest 0.01 g. The gonadosomatic index (GSI) was calculated by the equation, GSI (%) = (Gonad weight in g/BW) × 100. The size at first sexual maturity of males and females was estimated by the relationship between gonadosomatic index and total length. A total of 583 specimens (289 males; 294 females) ranging from 8.30 to 27.00 cm TL and 3.16 to 159.50 g BW were analyzed. Sizes at first sexual maturity for male and female E. vacha were 13.15 and 14.00 cm TL, respectively. The analysis of covariance (ancova ) revealed significant differences in slope and intercept between early and late phases for males (F = 4.532, P < 0.001) and females (F = 21.984, P < 0.001). The K_F was not significantly correlated with TL for males (r_s = 0.052; P = 0.378), but was highly correlated for females (r_s = ?0.165; P = 0.005). This study establishes a strong base for monitoring changes in length at first sexual maturity attributable to high fishing pressures or other reasons within the Ganges and associated river ecosystems.     

Some biological parameters of the Mediterranean sand smelt Atherina (Atherina) hepsetus, Linnaeus, 1758 (Pisces: Atherinidae) from the middle eastern Adriatic (Croatian coast)

Data on the length–weight relationship, age, growth, sex ratio and mortality were analysed for the Mediterranean sand smelt, Atherina (Atherina) hepsetus L. (total = 2805; males = 1258; females = 1547) collected in the eastern middle Adriatic island area during the reproductive period (February to April) in 2002. The total length of sampled specimens ranged from 3.8 to 14.5 cm and the weight from 0.28 to 22.39 g. The overall sex ratio was 1.23 : 1 in favour of females, significantly different from the expected 1 : 1 ratio (χ² = 29.76; P < 0.05). All individuals >13.4 cm were females. The oldest collected male and female specimens were 5 years old. The von Bertalanffy growth formula was estimated for females (L_∞ = 15.79 (1−e^{−0.43(t+0.049)}) and males (L_∞ = 15.25 (1−e^{−0.43(t+0.018)}). The power values (b) of the length–weight relationship were very similar for both sexes (b = 3.14) and indicated a slightly allometric growth. The instantaneous rates of mortality for all collected fish were Z = 1.44 year⁻¹; M = 0.94 year⁻¹ and F = 0.50 year⁻¹. The exploitation ratio was E = F/Z = 0.35. The value for M is highly uncertain, however, as well as those values for F and E.     

Age,growth and mortality of common two‐banded seabream,Diplodus vulgaris (Geoffroy Saint‐Hilaire, 1817), in the eastern Adriatic Sea (Croatian coast)

Age, growth and mortality were analysed for the common two‐banded seabream, Diplodus vulgaris, collected in the eastern Adriatic (Croatian coast) from commercial fishery catches by ‘tramata’ fishing (2005–2006) to obtain growth estimation. The oldest female was estimated to be age 11, the oldest male age 10 years. The von Bertalanffy growth parameters estimated by reading scales were: L_∞ = 48.60 cm (SE = 1.101), K = 0.112 (SE = 0.005) and t₀ = ?2.366 (SE = 0.060) for all specimens; L_∞ = 51.96 cm (SE = 2.153), K = 0.095 (SE = 0.007) and t₀ = ?2.837 (SE = 0.120) for females and L_∞ = 56.25 cm (SE = 2.662), K = 0.084 (SE = 0.067) and t₀ = ?2.920 (SE = 0.117) for males. The overall sex ratio was 1.22 : 1 in favour of males. Total mortality, corresponding to the slope of the descending limb of the catch curve, was Z = 0.81 per year for females and Z = 0.85 per year for males. Exploitation ratios were E = 0.68 for females and E = 0.73 for males.     

Age,growth, reproduction and feeding of John Dory,Zeus faber (Pisces: Zeidae), in the Saros Bay (North Aegean Sea)

The age, growth, reproduction, sexual maturity and stomach content of John Dory (Zeus faber), caught in the Bay of Saros (North Aegean Sea) between September 2006 and September 2008, were investigated. The female‐male ratio was 1.6 : 1. The total length of females ranged from 13.8 cm to 52.8 cm, and of males from 12.2 cm to 42.9 cm. The length‐weight relationship was W = 0.0174*L^2.936. Age data derived from vertebral centra readings were used to estimate the growth parameters of the von Bertalanffy equation. Growth parameters for females were L_∞ = 58.50 cm K = 0.11 year^?1, t₀ = ?0.99 year and for males L_∞ = 45.01 cm, K = 0.13 year^?1, t₀ = ?1.17 year. Maximum age was 18 years for females and 17 years for males. Length at first maturity for both females and males was 25.4 cm. Monthly values of the gonadosomatic index indicated that spawning occurred mainly in two peaks: one between January and June, and the other from August to September. Stomach content analysis showed the most‐preferred prey to be Pisces (IRI% 97.3).