Reproduction, growth, mortality and yield of Tilapia mariae Boulenger 1899 (Cichlidae) in a Nigerian rainforest wetland stream

The biology and fisheries of Tilapia mariae, the only tilapiine cichlid fish in the Iba Oku (Uyo, Nigeria) wetland stream was studied. There were more females than males in the population. The smallest sexually mature female fish was 11.0 cm total length (TL) while the size at 50% maturity was 17.1 cm TL. Absolute fecundity (F_e) ranged from 953 to 3200 eggs and was positively correlated with TL. The fish bred year‐round with peaks in November, March–April and July–September. The seasonalized von Bertalanffy growth function (VBGF) was fitted to the 12 consecutive months length–frequency data (n = 2439) to obtain a VBGF with the following parameters: L∞ (asymptotic length) = 30.4 cm TL, K (growth coefficient) = 0.4 year^?1, C (amplitude of growth oscillation) =0.4, and WP (winter point) = 0.9. The seasonalized length‐converted catch curve method gave Z (instantaneous total mortality coefficient) as 1.75 year^?1, M (instantaneous natural mortality coefficient) was 0.99 year^?1 while F (instantaneous fishing mortality coefficient) was 0.76 year^?1 and E (=F/Z the current exploitation rate) was 0.43. Length at first capture (Lc) was 17.7 cm TL. The fish was recruited to the fishery year‐round with two pulses. From the Beverton and Holt relative yield per recruit analysis via the selection ogive procedure, E_max (predicted maximum exploitation rate) was 0.54. The stock was not overexploited, since E < E_max. This study also showed that the fish is an r‐selected species with a few K‐selected traits.     

A seminal study of the dynamics of a mudskipper (Periophthalmus papilio) population in the Cross River,Nigeria

A seminal study was conducted in which the population dynamics (growth, mortality and recruitment) of the mudskipper (Periophthalmus papilio) in the Cross River, Nigeria, was elucidated for the first time using length frequency data and the ELEFAN software. The allometric relationship was: Weight=0.012(Length)^2.940, n=415, r²=0.939, P <0.0005. The seasonalized Von Bertalanffy growth parameters were L=19.39 cm, K=0.51 y^–1, C=0.3, and WP=0.4. The instantaneous total mortality coefficient Z was 2.208 y^–1 while the instantaneous natural mortality coefficient was 1.341 y^–1. The instantaneous fishing mortality coefficient of 0.867 y^–1 yielded the expectedly low exploitation rate E of 0.393. Our estimate shows that the species could reach an average maximum life span of about 6 years in the Cross River system. These results are used in quantitative elucidation of the state of exploitation of the population and will serve as input for the proper and scientific management of the fish resource.Alfred Wegener Institute Contribution nr. 1090.     

Comparative demography of commercially important parrotfish species from Micronesia

Fishery‐independent sampling was used to determine growth patterns, life span, mortality rates and timing of maturation and sex change in 12 common parrotfishes (Labridae: tribe Scarinae) from five genera (Calotomus, Cetoscarus, Chlorurus, Hipposcarus and Scarus) in Micronesia. Interspecific variation in life‐history traits was explored using multivariate analysis. All species displayed strong sex‐specific patterns of length‐at‐age among which males reached larger asymptotic lengths. There was a high level of correlation among life‐history traits across species. Relationships between length‐based and age‐based variables were weakest, with a tenuous link between maximum body size and life span. Cluster analysis based on similarities among life‐history traits demonstrated that species were significantly grouped at two major levels. The first grouping was driven by length‐based variables (lengths at maturity and sex change and maximum length) and separated the small‐ and large‐bodied species. Within these, species were grouped by age‐based variables (age at maturity, mortality and life span). Groupings based on demographic and life‐history features were independent of phylogenetic relationships at the given taxonomic level. The results reiterate that body size is an important characteristic differentiating species, but interspecific variation in age‐based traits complicates its use as a life‐history proxy. Detailed life‐history metrics should facilitate future quantitative assessments of vulnerability to overexploitation in multispecies fisheries.     

Age determination,growth and mortality of Gerres subfasciatus Cuvier, 1830 in southeast Australia

Commercial beach‐seine (30–50 mm cod‐end mesh) catches of Gerres subfasciatus in Lake Macquarie southeast Australia were sampled monthly between December 2000 and April 2002 to investigate species age, growth and mortality characteristics using sectioned sagittal otoliths. Inclusion of fishery‐independent length data of young‐of‐the year collected from littoral seagrass beds with fine meshed beach seines augmented growth analyses. Fifty otoliths each month (total 448 female and 402 male) were examined with sections displaying alternating opaque and translucent zonation. Formation of otolith opaque zones occurred annually between August and December as determined by monthly marginal increment analyses. Spawning occurred between October and February, and a universal birth date of 1 December was assigned that allowed counts of opaque zones to be converted to age estimates in years and months (decimal ages). The von Bertalanffy growth function identified that both genders grew fast for their initial 2 years, but thereafter slowed. Females grew faster, had a greater mean fork length‐at‐age, estimated L_∞ and an observed greater maximum fork length in samples compared to males. Nevertheless, observed longevity was 10⁺ years for both genders. Commercial catches of both genders were dominated by the 2⁺ and 3⁺ year age classes. Catch curve analyses identified the instantaneous rate of total annual mortality to be ~0.8 and an exploitation rate of <0.5 for both genders. The data form a basis for developing assessment and management strategies of G. subfasciatus fisheries.     

Population parameters of the fish fauna in a long‐established Amazonian reservoir (Amapá, Brazil)

The present study focused on the fish fauna of the 44‐year‐old Coaracy Nunes reservoir in the northern Amazon basin, producing estimates of the growth constant (k), maximum and asymptotic body lengths and weights, natural mortality (M), the consumption/biomass ratio (QB) (intake of food by a group over a year), the Aspect ratio (Ar) of the caudal fin, growth performance (Φ), longevity, and trophic level for 45 fish species. Species collection was divided into eight sampling campaigns between May 2009 and July 2010. Gillnets were used in four of the sampling sites. The results revealed that (i) the most predominant species are Ageneiosus ucayalensis, Hemiodus unimaculatus, Serrasalmus gibbus and Geophagus proximus; (ii) small and medium‐sized fishes predominated in the community, characterized by high rates of growth and natural mortality, consistent with a predominance of r‐strategists; (iii) the body lengths of the detritivore species were similar to those of the piscivores, which are normally larger, but with higher growth rates, more similar to those recorded for the omnivores; (iv) consumption/biomass ratio (QB) × body length relationship is higher in the detritivores than in the omnivores and piscivores (which were similar to each other). Overall, the reservoir habitat appears to be advantageous to detritivorous fish species.     

Growth and mortality of two small fishes,Toxabramis swinhonis Günther, 1873 and Hyporhamphus intermedius (Cantor, 1842), in a Yangtze shallow lake (China) assessed by length frequency analysis

This study examined the growth and mortality of two widespread small fish species, Toxabramis swinhonis (Cyprinidae) and Hyporhamphus intermedius (Hemiramphidae), from a shallow lake (Niushan Lake, China) along the Yangtze River, by analyzing monthly length frequency data (July 2005 to June 2006) with the FAO‐ICLARM stock assessment tool (FiSAT). Estimated von Bertalanffy growth equation parameters were: L_∞ (asymptotic length) = 145 mm TL, and K (growth coefficient) = 0.66 year^?1 for T. swinhonis; L_∞ = 189 mm TL, and K = 0.68 year^?1 for H. intermedius. The instantaneous rates of natural mortality (M) calculated for T. swinhonis and H. intermedius were 1.35 and 1.28 year^?1, respectively. The length‐converted catch curve method gave the total annual instantaneous mortality rate (Z) of 2.92 year^?1 for T. swinhonis and 1.53 year^?1 for H. intermedius. Recruitment patterns of both species were continuous, displaying a single major peak event per year. Despite not being of direct fishing interest, T. swinhonis, with high abundance and productivity as indicated by a high Z‐value, can be an important species in fisheries management as an excellent food source for aquatic organisms, especially for larger fishes of economic value. These results represent the first information on population characteristics of T. swinhonis and H. intermedius, and constitute a comparison base for future growth studies in other lake environments.     

Age,growth and maturity of tub gurnard (Chelidonichthys lucerna Linnaeus 1758; Triglidae) in the inshore coastal waters of Northwest Wales,UK

The tub gurnard Chelidonichthys lucerna has been identified by ICES as a potential commercial species in the northeast Atlantic with recommendations made to monitor landings and discards and to derive information on population biology for stock assessment purposes, however, data are lacking for the species in the northeast Atlantic. Therefore, aims of this study were to provide data on the size/age‐structure and patterns of growth, maturity and mortality of C. lucerna in Northwest Wales, UK, and in doing so to provide data on the biological characteristics of the most northerly population studied to date for comparison with the existing data for southerly Mediterranean populations. Data on the age, growth and maturity of C. lucerna were collected by otter trawling (73 mm cod‐end stretched mesh size) in the coastal waters of Northwest Wales, UK in October (2000–2011, excluding 2006). Total length (TL) of fish sampled ranged between 10.5–41.0 cm (males) and 10.4–57.5 cm (females). The majority of the female fish were between 20–30 cm TL (60.2%) and the majority of the male fish between 20–30 cm TL (58.3%) respectively. TL/weight (W) relations for male and female fish were similar and the combined data was described by W = 0.0067 TL^3.10. Age of fish ranged between 1–7 years old for female fish and 1–5 years old for male fish respectively with the majority of female fish 3 years old (40%) and the majority of male fish 3 years old (37%). The age structures of female and male tub gurnards were not significantly different with the older age classes consisting predominantly of female fish. Both males and females exhibited similar asymptotic growth patterns and the combined von Bertalanffy growth function was TL_t = 51.6 (1 ? e ^{[?0.25(t + 0.41)]}). Instantaneous rates of total mortality were calculated as 1.04 year^?1 for males and 1.11 year^?1 for females. The size (L₅₀) and age at first maturity (A₅₀) were estimated to be 29.1 cm TL and 2.8 years for males, 27.7 cm TL and 2.7 years for females and 28.0 cm TL and 2.8 years for both sexes combined. The results of this study provide the first information on the biology and population dynamics of C. lucerna in the Irish Sea, the first data collected in the northeast Atlantic since 1985 and the most northerly population studied to date.     

Distribution, growth and mortality of young rough scad, Trachurus lathami, in the south-eastern Brazilian Bight

Distribution, growth and mortality of larval and juvenile rough scad Trachurus lathami Nichols, 1920, were studied, based on samples collected during December 1991 in the south-eastern Brazilian Bight. Young rough scad were widespread throughout the region surveyed, but spawning was more intensive in the northern area and tended to be greater in areas of low temperature and high salinity. The length class distribution of the rough scad larvae and juveniles ranged from 2.25 to 32.25 mm body length (BL), and the preflexion larvae of size categories from 2.25 to 3.25 mm BL were the most abundant. Net avoidance was detected for early larvae (2.25 mm length class) and for juveniles larger than 12.25 mm BL length class. Two models were applied to estimate growth and daily growth rate: a linear regression and a Gompertz curve. Both curves showed similar results and a good fit to the data. The mean growth rate estimated by linear regression was 0.44 mm per day (SD=0.008 mm). In small larvae up to 25 mm BL the linear and Gompertz curves showed similar estimated lengths. The hypothetical length at age zero ( L ₀) was estimated as 1.5 mm. The instantaneous daily mortality coefficient estimated from the slope of the regression of log-transformed values of relative production rates ( P _t/ d _t) against age ( t_i ) was Z=0.1888 for larval and juvenile rough scad. This corresponds to a daily mortality rate of 17.2%.     

Size-independent growth in fishes: patterns, models and metrics

A combination of a dynamic energy budget (DEB) model, field data on Atlantic salmon Salmo salar and brown trout Salmo trutta and laboratory data on Atlantic salmon was used to assess the underlying assumptions of three different metrics of growth including specific growth rate (G), standardized mass‐specific growth rate (G_S) and absolute growth rate in length (G_L) in salmonids. Close agreement was found between predictions of the DEB model and the assumptions of linear growth in length and parabolic growth in mass. Field data comparing spring growth rates of age 1+ year and 2+ year Atlantic salmon demonstrated that in all years the larger age 2+ year fish exhibited a significantly lower G, but differences in growth in terms of G_S and G_L depended on the year examined. For brown trout, larger age 2+ year fish also consistently exhibited slower growth rates in terms of G but grew at similar rates as age 1+ year fish in terms of G_S and G_L. Laboratory results revealed that during the age 0+ year (autumn) the divergence in growth between future Atlantic salmon smolts and non‐smolts was similar in terms of all three metrics with smolts displaying higher growth than non‐smolts, however, both G_S and G_L indicated that smolts maintain relatively fast growth into the late autumn where G suggested that both smolts and non‐smolts exhibit a sharp decrease in growth from October to November. During the spring, patterns of growth in length were significantly decoupled from patterns in growth in mass. Smolts maintained relatively fast growth though April in length but not in mass. These results suggest G_S can be a useful alternative to G as a size‐independent measure of growth rate in immature salmonids. In addition, during certain growth stanzas, G_S may be highly correlated with G_L. The decoupling of growth in mass from growth in length over ontogeny, however, may necessitate a combination of metrics to adequately describe variation in growth depending on ontogenetic stage particularly if life histories differ.     

Age and growth of three species of clupeids from Kiribati, tropical central south Pacific

The age and growth of three widely distributed tropical clupeids, Amblygaster sirm, Herklotsichthys quadrimaculatus and Spratelloides delicatulus at four sites in Kiribati were examined by otolith increment counts. Amblygaster sirm grew to 230 mm s.l. and 130 g and lived for up to 2 years at all sites. Herklotsichthys quadrimaculatus grew to 110 mm and 15 g and lived up to 1 year; white S. delicatulus grew to 66 mm and 2.5 g and lived for 4-5 months. There was little difference in the rate of growth in length of any of the species at the sites, except for S. delicatulus at one site. All species grew rapidly in length at the expense of growth in weight during the early life-stages when mortality is highest, hence reducing the time they spend in this life-stage. The relationship between weight and age varied between the sites for H. quadrimaculatus and S. delicatulus, but these differences narrowed as fish size increased. Herklotsichthys quadrimaculatus also grew more rapidly in weight during the first 3 months than the other species. Growth comparisons between the three species showed that all grew in length at similar rates for the first 2 months. Spratelloides delicatulus became sexually mature at 2 months of age and subsequently grew more slowly than the other species. After 4 months A. sirm grew faster than H. quadrimaculatus. The rates of growth in length and weight of these species from Kiribati were compared with those from other regions of the Indo-Pacific. There were significant differences: A. sirm grew to a larger size in Kiribati than elsewhere; H. quadrimaculatus grew at a similar rate at all sites during the first 2 months, but then the growth rate of Kiribati fish declined and they reached a smaller asymptotic size than elsewhere; S. delicatulus from Kiribati grew in length at similar rates to Solomon Islands fish, but were significantly lighter in weight at the same age. The relative growth performance of these short-lived tropical species was compared to that of temperate clupeids. All species showed similar growth performance despite the slower growth rates of temperate species, which suggests that the clupeoids' phylogenetic conservatism in some life history traits extends to growth. Regional and local differences in growth rates of some tropical clupeids are as large as those found among most clupeid species.     

Do the maximum sizes,ages and patterns of growth of three reef‐dwelling labrid species at two latitudes differ in a manner conforming to the metabolic theory of ecology?

The size and age data and patterns of growth of three abundant, reef‐dwelling and protogynous labrid species (Coris auricularis, Notolabrus parilus and Ophthalmolepis lineolata) in waters off Perth at c. 32° S and in the warmer waters of the Jurien Bay Marine Park (JBMP) at c. 30° S on the lower west coast of Australia are compared. Using data for the top 10% of values and a randomization procedure, the maximum total length (L_T) and mass of each species and the maximum age of the first two species were estimated to be significantly greater off Perth than in the JBMP (all P < 0·001) and the maximum ages of O. lineolata in the two localities did not differ significantly (P > 0·05). These latitudinal trends, thus, typically conform to those frequently exhibited by fish species and the predictions of the metabolic theory of ecology (MTE). While, in terms of mass, the instantaneous growth rates of each species were similar at both latitudes during early life, they were greater at the higher latitude throughout the remainder and thus much of life, which is broadly consistent with the MTE. When expressed in terms of L_T, however, instantaneous growth rates did not exhibit consistent latitudinal trends across all three species. The above trends with mass, together with those for reproductive variables, demonstrate that a greater amount of energy is directed into somatic growth and gonadal development by each of these species at the higher latitude. The consistency of the direction of the latitudinal trends for maximum body size and age and pattern of growth across all three species implies that each species is responding in a similar manner to differences between the environmental characteristics, such as temperature, at those two latitudes. The individual maximum L_T, mass and age and pattern of growth of O. lineolata at a higher and thus cooler latitude on the eastern Australian coast are consistent with the latitudinal trends exhibited by those characteristics for this species in the two western Australian localities. The implications of using mass rather than length as the indicator variable when comparing the maximum sizes of the three species and the trends exhibited by the instantaneous growth rates of those species at different latitudes are explored. Although growth curves fitted to both the L_T and masses at age for the males of each species lay above those for their females, this would not have influenced the conclusions drawn from common curves for both sexes.     

Age,growth, mortality and population structure of silver croaker Pennahia argentata (Houttuyn, 1782) and red bigeye Priacanthus macracanthus Cuvier, 1829 in the north‐central Taiwan Strait

The main objectives of this study were to estimate the age, growth, mortality and population structure of silver croaker Pennahia argentata (Houttuyn, 1782) and red bigeye Priacanthus macracanthus Cuvier, 1829 and to explore the factors causing the fluctuation of the fish populations and the ecological parameters. The two species were randomly sampled, with 80~120 individuals of each species captured every month from a single trawler fishery (mesh size 250 mm), March to November 2006, in the north‐central Taiwan Strait. A total of 994 speciments of silver croaker and 851 speciments of red bigeye were collected. Compared with previous studies, the mean length and weight, mean age, the minimum size at first sexual maturity, the asymptotic length (L_∞) and weight (W_∞) of the two species has decreased in recent decades, indicating that the populations were younger, smaller and earlier in sexual maturity. Meanwhile, the growth coefficient (K) increased, the mortality coefficients (Z, F, M) were higher, and the exploitation rate (E) indicated overfishing. Fishing is a key driving force that can cause abundant fluctuations and changes in ecological characteristics in these two demersal fishes in this area. Accordingly, the traditional fishery management approach, such as the reduction in fishing effort, coupled with the Ecosystem‐based Fishery Management (EBFM) should be implemented to achieve sustainable demersal fisheries.     

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.     

Are fish early growth and condition patterns related to life-history strategies?

Life-history studies provide a global framework for comparison of fish species responses and trade-offs facing ecological and environmental constrains. A broad comparison among fishes’ early growth and condition traits is performed in order to determine ecological patterns of early development regarding latitudinal distribution, habitat use and life-history strategies. Based on Winemiller and Rose (1992) classification of life-history strategies, data on early growth and condition indices of 46 fish species worldwide was analysed. Available information on fishes’ early features, namely first year length percentage (relative to species maximum theoretical length), age at maturation and Fulton’s condition index (K), provided a good segregation of species by latitudinal distribution and habitat use, and evidenced the categories of the three-endpoint model. Higher larvae and juvenile growth rates and condition indices (K, mean RNA–DNA ratios and protein contents) were associated with tropical and temperate fish species that occur in complex or variable habitats (respectively coral reefs and estuaries). These species selected for the opportunistic and periodic strategies, investing highly in rapid growth in order to increase survival probability to counter high mortality rates during early stages or unstable habitat conditions. Later age at maturation, slower larvae and juvenile growth as well as lower mean condition indices were consistent with fish species from more stable or predictable environments, as polar regions and freshwater habitats, which selected for the equilibrium strategy. Nonetheless, differences in energy allocation strategies during early stages were not observed, evidencing the scarcity of available data regarding condition indices and/or the importance of integrating life-history intermediate strategies. Future research into condition indices and other physiological processes, for a broader set of species and for a wider latitudinal and habitat range including seasonal variability (particularly for species from tropical and polar regions), is essential to better understand or test current theories of species ecological patterns. The use of direct quantitative measures of young fishes’ metabolic investment and fitness constitutes a new approach for life-history studies, and should be fundamental for predicting species’ responses to acute environmental or human constrains, especially in a global climate change scenario that is expected to affect distribution and abundance of fish species worldwide.     

The potential use of scales for estimating age and growth of Mediterranean albacore (Thunnus alalunga)

The ability to accurately estimate the age of fishes is critical for conducting stock assessments and developing fishery management policies. Scales were collected from albacore, Thunnus alalunga, caught in the Mediterranean Sea during the years 1989–1995 to estimate their age and growth. Ages, which ranged from 1+ to 6+ years, were estimated from the interpretation of the concentric rings on the scales of 473 individuals that ranged in fork length from 55.5 to 89 cm. Males reached a greater size and age than females. The relatively close agreement in the mean lengths at ages estimated by scales and other techniques constituted a preliminary verification of the method. The von Bertalanffy growth model was fitted to mean lengths at estimated ages, resulting in the following growth parameters for the combined sexes: L_∞ = 86 cm, K = 0.4, t_o = ?0.8 years. Parameter estimates were in agreement with what is known about life history of the species in the Mediterranean. Moreover, the growth rates were consistent with length increment observations from five tag returns, which lend support to our working hypothesis that the scale‐rings are annual structures. When the Mediterranean albacore growth parameters were compared with those of Atlantic Ocean albacore using scale age estimates, there were significant differences between the two populations, and Mediterranean albacore remain significantly smaller than Atlantic Ocean albacore.     

Growth and mortality of exploited fishes in China's coastal seas and their uses for yield‐per‐recruit analyses

Given the scarcity of information suitable for other forms of fish stock assessments, the growth, and mortality of 10 important marine exploited fishes in China's coastal seas were estimated, based on published length‐frequency data and the ELEFAN approach and software. The resulting parameters, complemented with growth curves from FishBase were then used for yield‐per‐recruit analyses. These 10 species were both traditional commercial species (Trichiurus lepturus, Larimichthys polyactis, Scomber japonicus) and less commercial interest species (Coilia nasus, Engraulis japonicus, Decapterus maruadsi, Psenopsis anomala, Coilia mystus, Setipinna tenuifilis, Harpadon nehereus). The yield‐per‐recruit analyses indicated that the fishing mortality experienced by these 10 fish species was very high, especially in view of the extremely small cod‐end mesh sizes deployed by Chinese trawlers, of about 10 mm or less (vs. 25 mm as minimum legal size). More precisely, all 10 species suffered from growth overfishing, which was very pronounced in large species. Indeed, enlarging cod‐end mesh size, by increasing mean sizes at first capture, would increase yield‐per‐recruit for all 10 fish species by a factor of up to 2.5. Obviously, such increases in mesh size would have to be in tandem with other management measures designed to ensure the sustainability of China's marine fisheries resources.     

Population biology and vulnerability to fishing of deep‐water Eteline snappers

Deep‐water fish in the tropical and sub‐tropical Pacific Ocean have supported important fisheries for many generations. Observations of localised depletions in some fisheries have raised concerns about the sustainability of current fishing rates. However, quantitative assessments of deep‐water stocks in the Pacific region have been limited by the lack of adequate biological and fisheries data. Estimates are provided of age‐based demographic parameters for two important deep‐water snapper species in the Pacific, Etelis carbunculus and E. coruscans. A spawner biomass‐per‐recruit (SPR) model was applied to determine fishing mortality rates for each species that would achieve specified biological targets (40% unexploited levels, SPR₄₀) and limit (30% unexploited levels, SPR₃₀) reference points, and examine the sensitivity of the model to variation in natural mortality and age at first capture. The maximum observed age, based on increment counts from sectioned otoliths, was 21 years for E. carbunculus and 18 years for E. coruscans. Total mortality (Z), estimated from the Hoenig regression, was 0.21 year^?1 for E. carbunculus and 0.25 year^?1 for E. coruscans. The best approximating growth models were the von Bertalanffy model (L_∞ = 896 mm fork length, k = 0.28, t₀ = 0.51) for E. carbunculus and the logistic model (L_∞ = 879 mm fork length, k = 0.32 year^?1, t₀ = 3.42) for E. coruscans. The spawner biomass‐per‐recruit analysis demonstrated that lower rates of fishing mortality were required for E. coruscans than for E. carbunculus to maintain spawning biomass above estimated biological reference points. Estimates of spawner biomass‐per‐recruit were more sensitive to variation in natural mortality than in the age at first capture, suggesting that regulating fishing mortality rather than gear selectivity would be a more effective management measure for both species. Maintaining fishing mortality <0.1 for both species is recommended as a cautious approach to management, given the uncertainty in estimates of natural mortality and mixed fishery considerations.     

Life history of the red-banded seabream Pagrus auriga (Sparidae) from the coasts of the Canarian archipelago

Red‐banded seabream Pagrus auriga (N = 615) were caught off the Canary Islands from January 2003 to December 2004. Total length ranged from 120 to 780 mm. The species was characterized by protogynous hermaphroditism. The male :female ratio was in favour of females (1 : 8.2). The reproductive season extended from September to February, with a peak in spawning activity in October–November. Fifty percentage maturity was reached at 387 mm total length by females and 533 mm by males. The length–weight relationship for all individuals was described by the parameters: a = 0.0086 and b = 3.014, when length is given in mm and weight in grams. Otolith age readings indicated that the population consists of 19 age groups, including a very high proportion of individuals between 0 and 7 years old. Growth analysis reveals that the species is slow‐growing and relatively long lived (18 years). The von Bertalanffy growth parameters for the entire population were: L_∞ = 803 mm, k = 0.081 year⁻¹ and t₀ = −2.17 year. Growth differed between males and females. The instantaneous rate of natural mortality for all fish was: M = 0.164 year⁻¹.     

Length‐ and age‐based demographics of exploited populations of stout whiting,Sillago robusta Stead, 1908

This study assessed variability in the length and age compositions, longevity, length‐at‐age and rates of growth and mortality of the east Australian stout whiting Sillago robusta Stead, 1908 population harvested by demersal trawl fisheries. Sampling was done over 2 years and was spatially stratified across three depth strata between 11 and 90 m at two locations approximately 400 km apart. There were no consistent depth‐related differences in length and age compositions, but the mean and median length and age of the population was greater at the lower latitude location. Age classes 2 and 3 years dominated samples in the north, and 1 and 2 years in the south. Observed longevity was 10 years in the north, and 6 years in the south. Mean length‐at‐age was not consistently different between sexes, years or locations, nor did the von Bertalanffy growth function differ significantly between sexes, even though females had a greater estimated L_∞ (23.45 cm FL) compared to males (22.36 cm FL). Estimated natural mortality (M) ranged between 0.42 and 0.77, using age‐ and length‐based methods. Age‐based catch‐curve analyses identified the instantaneous rate of total mortality (Z) to range between 1.48 and 2.70, with subsequent estimates of fishing mortality (F) ranging between 1.15 and 2.00, being greater than M. Exploitation rates (E) were greater than 0.7, indicating that S. robusta at the study locations was heavily fished. The data provided here can be used as a basis to evaluate future fishery‐ and climate‐related changes in the population demographics of east Australian S. robusta.     

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.