Population biology and status of exploitation of introduced garfish Belone belone euxini (Günther, 1866) in the Black Sea

The garfish Belone belone euxini (Günther, 1866) is a commercially important pelagic fish species in Sinop artisanal fishery, which is showing a decreasing trend in catch results. As a basis for fisheries management a sampling program was carried out between October 2000 and September 2001 along the Turkish coast of the Black Sea, to study the population structure, growth, and reproduction cycle of garfish in the area, and to achieve a rough estimate of exploitation. The length–weight relationship and von Bertalanffy growth parameters were estimated as W = 0.00076 L^3.137, L_∞ = 74.64 cm, K = 0.13 year^?1, t_o = ?3.67, respectively. First sexual maturity was estimated at age 2 and at a total length of 38.8 cm for females. The spawning period was from May to September. The total fecundity–length relationship was estimated as F = 0.0041 L^4.1086 (r² = 0.92). Mortality rates were Z = 1.24 year^?1, M = 0.23 year^?1and F = 1.01 year^?1 for total, natural, and fishing mortality, respectively. The exploitation ratio E = 0.81 indicates that the population is heavily exploited.     

Age, growth, mortality and sex ratio of sand smelt, Atherina boyeri Risso, 1810 (Pisces: Atherinidae) in the estuary of the Mala Neretva River (middle-eastern Adriatic, Croatia)

The present study investigated the age, growth, mortality and morphometry of the sand smelt, Atherina boyeri, in the Mala Neretva River estuary (mid‐eastern Adriatic Sea). The study of scale annuli showed that the population is up to 4 years of age. However, most sand smelt are in their first and second year; the numbers of older individuals are very low because they migrate upstream and are heavily fished. The von Bertalanffy parameters for the total sample of sand smelt were found to be L_∞ = 13.5 cm, K = 0.37 year^?1 and t₀ = ?0.97. Overall total mortality was estimated at 1.81 year^?1, natural mortality was 0.90 year^?1 and fishing mortality was 0.91 year^?1.     

Distribution, standing stock, growth, mortality and production of Strongylocentrotus pallidus (Echinodermata: Echinoidea) in the northern Barents Sea

The regular sea urchin, Strongylocentrotus pallidus (G.O. Sars, 1871), is a widespread epibenthic species in high-Arctic waters. However, little is known about its distribution, standing stock, population dynamics and production. In the northern Barents Sea, S. pallidus was recorded on seabed still photographs at 10 out of 11 stations in water depths of 80–360?m. Mean abundances along photographic transects of 150–300 m length ranged between <0.1 and 14.7?ind. m^?2 yielding a grand average of 3.6?ind.?m^?2. The small-scale distribution along the transects was patchy, with densities varying from nil to an overall maximum of 25.5 ind. m^?2, and exhibited a significant relation to the number of stones present. Sea urchin test diameters, measured on scaled photographs, extended from 7 to 90?mm. Median values at single stations varied from 14 to 46?mm, showing a significant inverse relationship to water depth. Biomass, estimated by combining photographic abundances, size frequencies and a size-mass function established with trawled specimens, ranged between <0.1 and 3.0?g ash-free dry mass m^?2, averaging about 1.0?g ash free dry mass m^?2. An analysis of skeletal growth bands in genital plates was carried out with 143 trawled individuals ranging in test diameter (D) from 4 to 48?mm. Assuming these bands to represent annual growth marks, the ages of the specimens analysed ranged between 3 and 42 years. A von Bertalanffy function was fitted to size-at-age data to model individual growth pattern (D_∞?=?102.3?mm, k?=?0.011 year^?1, t₀?=?0.633?year). The annual mortality rate Z of the population in the northern Barents Sea was estimated from a size-converted catch curve to be 0.08 year^?1. Applying the weight-specific growth rate method, the average P/B ratio and the mean annual production of this population were estimated as 0.07 year^?1 and 0.076?g AFDM m^?2 year^?1, respectively. In conclusion, S. pallidus is characterized by slow growth, low mortality, high longevity and low productivity. Because of its relatively high biomass, it is considered to contribute significantly to total benthic standing stock and carbon flux in the study area.     

Age and growth of the smooth hammerhead,Sphyrna zygaena,in the Atlantic Ocean: comparison with other hammerhead species

The smooth hammerhead Sphyrna zygaena (Sphyrnidae) is a pelagic shark occasionally caught as bycatch in pelagic longline fisheries, but is one of the least studied of all pelagic sharks. Age and growth of S. zygaena was studied along a wide Atlantic region covering both the northern and southern hemispheres. Data from 304 specimens, caught between October 2009 and September 2014, ranging in size from 126 to 253?cm fork length (FL), were analysed. Growth models were fitted using the three-parameter von Bertalanffy growth function (VBGF) re-parameterized to calculate L₀ (size at birth). Growth models were fitted to the sample data and data from several back-calculation models. The model fit to the quadratic modified Dahl-Lea back-calculated data seems to be the most appropriate to describe growth in this species, with resulting growth parameters of L_inf?=?285?cm FL, k?=?0.09 year^?1 for males and L_inf?=?293?cm FL, k?=?0.09 year^?1 for females. Compared with other species of the same genus, estimated growth coefficients for S. zygaena seem to fall in the low to middle range. Although further work is still needed, this study adds to knowledge of the vital life-history parameters of smooth hammerheads in the Atlantic Ocean, which can be used in the management and conservation of this species.     

Growth and mortality of the brushtooth lizardfish (Saurida undosquamis) in Iskenderun Bay (eastern Mediterranean Sea) using length frequency analysis

The growth and mortality of brushtooth lizardfish Saurida undosquamis (Richardson, 1848) in Iskenderun Bay (eastern Mediterranean Sea) were investigated based on length frequency data using the fisat software. Total length of the sampled 4711 fish ranged from 6.0 to 39.0 cm. The von Bertalanffy growth function estimates were L_∞ = 42.00 cm, k = 0.51 year^‐1, t₀ = −0.29 years. Total mortality rate (Z) was computed as 1.76 year^‐1 and the exploitation ratio was 0.51, indicating that the brushtooth lizardfish stock is on the verge being overfished.     

Mediterranean warming triggers seagrass (Posidonia oceanica) shoot mortality

Rapid warming of the Mediterranean Sea threatens marine biodiversity, particularly key ecosystems already stressed by other impacts such as Posidonia oceanica meadows. A 6‐year monitoring of seawater temperature and annual P. oceanica shoot demography at Cabrera Archipelago National Park (Balearic Islands, Western Mediterranean) allowed us to determine if warming influenced shoot mortality and recruitment rates of seagrasses growing in relative pristine environments. The average annual maximum temperature for 2002–2006 was 1 °C above temperatures recorded in 1988–1999 (26.6 °C), two heat waves impacted the region (with seawater warming up to 28.83 °C in 2003 and to 28.54 °C in 2006) and the cumulative temperature anomaly, above the 1988–1999 mean annual maximum temperature, during the growing season (i.e. degree‐days) ranged between 0 °C in 2002 and 70 °C in 2003. Median annual P. oceanica shoot mortality rates varied from 0.067 year^?1 in 2002 to 0.123 year^?1 in 2003, and exceeded recruitment rates in all stations and years except in shallow stations for year 2004. Interannual fluctuations in shoot recruitment were independent of seawater warming (P>0.05). P. oceanica meadows experienced a decline throughout the study period at an average rate of ?0.050±0.020 year^?1. Interannual variability in P. oceanica shoot mortality was coupled (R²>0.40) to seawater warming variability and increasing water depth: shoot mortality rates increased by 0.022 year^?1 (i.e. an additional 2% year^?1) for each additional degree of annual maximum temperature and by 0.001 year^?1 (i.e. 0.1% year^?1) for each accumulated degree water temperature remained above 26.6 °C during the growing season. These results demonstrate that P. oceanica meadows are highly vulnerable to warming, which can induce steep declines in shoot abundance as well indicating that climate change poses a significant threat to this important habitat.     

Growth and production of a tropical predatory shrimp, Macrobrachium hainanense (Palaemonidae), in two Hong Kong streams

1. Macrobrachium hainanense is a predatory palaemonid shrimp (total length >7 cm) that can be abundant [density 3–5 m^?2; biomass 484–606 mg ash‐free dry mass (AFDM) m^?2] in forest streams in Hong Kong, China. This study investigated the growth and production of M. hainanense during 2001 and 2002 in pools of two forested streams (one third‐ and one fourth‐order). 2. The growth of tagged individuals was recorded in situ and compared with that of tagged and untagged shrimps in laboratory tanks. Field and laboratory estimates yielded similar growth rates of 0.7 mm carapace length (CL) per month, and instantaneous growth rate was 0.004 g AFDM g^?1 day^?1. Tagging did not affect growth in the laboratory. Cohort analysis of field populations produced similar estimates of growth to that of tagged individuals, and the growth of M. hainanense was generally slower than has been reported for other Macrobrachium species. Mass‐specific growth rate of M. hainanense in the field varied with size and was two to five times higher in small individuals (<10 mm CL). In addition, growth rate varied with season and was 40% lower in the dry season when temperature was at the annual minimum. 3. Males grew bigger than females (36 versus 25 mm CL). The minimum lifespan of M. hainanense in the field, calculated from size‐specific growth rates, ranged from 29.3 months (females) to 47.6 months (males). Male lifespan derived from cohort analysis was estimated as 48 and 46 months in the two streams. Females reached maturity in 17–18 months (at 15–17 mm CL) while males matured at 24–26 months (at 18–22 mm CL). Females bred twice (at 2 and 3 years of age) while males probably bred three times (at 2, 3 and 4 years) in both streams. 4. Macrobrachium hainanense production in the fourth‐order stream, calculated by the size‐frequency method, was 900 and 1096 mg AFDM m^?2 year^?1 (for 2001 and 2002, respectively) with a production/biomass (P/B) of 2.1–2.3 year^?1. In the third‐order stream, production was 987 and 1304 mg AFDM m^?2 year^?1 (for 2001 and 2002, respectively) with a P/B of 1.7–2.1 year^?1. Production estimates based on the instantaneous growth method were half of those obtained by the size‐frequency method. 5. Although M. hainanense production at the third‐order stream exceeded that in the fourth‐order, growth rates showed the opposite pattern and were 0.31–0.43 mm CL month^?1 and 0.56–0.65 mm CL month^?1 in the third‐ and fourth‐order streams, respectively. Greater mortality in the latter may account for low production at a site where growth rate was high. 6. Production of M. hainanense in both streams was lower during 2001 when rainfall was higher. This may reflect the influence of spates associated with monsoonal rains, which could have reduced M. hainanense production through spate‐induced mortality or by reducing the abundance of prey. This study provides the first in situ estimate of secondary production by a non‐commercial Macrobrachium species in Asia or elsewhere. It involved a whole‐pool approach to sampling that allowed the estimation of production and population parameters on a realistic scale.     

Population parameters of stargazer (Uranoscopus scaber Linnaeus, 1758) in the southeastern Black Sea region during the 2011–2012 fishing season

The population parameters of stargazer (Uranoscopus scaber Linnaeus, 1758) were studied regarding age composition, sex ratio, growth, survival and mortality rates, and the exploitation rate in the southeastern Black Sea near the coast of Turkey during the 2011–2012 fishing season. According to ageing analysis of the samples, age group 1 is the most abundant (47.76%), followed by age 2 (41.04%), age 3 (9.33%), age 0 (1.12%) and age 4 (0.75%). Mean totals as well as total lengths and weights for males and females were 14.5 ± 0.22 cm and 12.9 ± 0.19 g, 16.6 ± 0.24 cm and 62.1 ± 2.76 g, and 37.2 ± 1.92 cm and 87.1 ± 3.88 g, respectively. The mean condition factor was K = 0.0167, while the sex ratio was 53.98% female, 38.75% male and 7.27% immature. Length‐weight, age‐length and age‐weight equations were W = 0.014 × L^3.059, L_(t)=44.5*[1?e^{?0.148*(t +1.242)}] and W_(t)=1544.4*[1?e^{?0.148*(t + 1.242)}]^3.059, respectively. The computed survival rate (S), instantaneous total mortality rate (Z), annual mortality rate (A), natural mortality rate (M) and fishing mortality rate (F) were S = 28.94%, Z = 1.24 year^?1, A = 71.06%, M = 0.26 year^?1 and F = 0.98 year^?1, respectively. The exploitation rate was 0.79, which is above the optimum exploitation levels.     

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).     

Growth, mortality and stock assessment of kelee shad, Hilsa kelee (Fam: Clupeidae) in the coastal waters of Pakistan

Growth of kelee shad, Hilsa kelee, in the coastal waters of Pakistan was estimated from the lengthfrequency samples. The von Bertalanffy growth equation was L _t = 23.10 (1 ? exp (?0.94(t + 0.18))). Estimated parameters of total mortality (Z), natural mortality (M) and fishing mortality (F) were 2.08 year^?1, 1.78 year^?1, and 0.30 year^?1 respectively. The length-at-first capture was Lc = 10.88 cm. Biomass per recruitment (B/R) and yield per recruitment (Y′/R) were 0.87 and 0.031 respectively. The annual exploitation rate was U = 0.12. The exploitation ratio for maximum yield per recruit E _max = 0.73 and fishing mortality for maximum yield per recruit F _max = 1.52; biological reference point F _opt = 0.89 year^?1 and F _limit = 1.18 year^?1. Present estimations showed that the natural mortality was higher than fishing mortality in Hilsa kelee, indicating that the state of the stock is sustainable and the fishery of kelee shad should not be increased beyond current levels in the coastal waters of Pakistan.     

Some aspects of the biology of the stargazer mountain catfish,Amphilius uranoscopus (pfeffer); (Siluriformes: Amphiliidae) indigenous to Kenya streams

A study on some biological parameters of the mountain catfish, Amphilius uranoscopus Pfeffer 1889 (Silurifomes: Amphiliidae), was carried out in the Thego stream on the slopes of Mount Kenya from February to December 2002. Physical and chemical profiles of the Thego show that the water quality parameters is typical of high altitude streams with temperatures rarely exceeding 18°C, DO ranging from 7.9 to 8.2 mg l^?1 and relatively high conductivity (97–137 μS cm^?1) typical of perturbed lotic environments. A total of 1010 fish were caught by an electro‐fisher, with sizes ranging between 8 and 24 cm fork length. The population structure had a unimodal distribution with maxima at 14–16 cm. The length–weight relationship showed relatively narrow range in the slope ranging from 2.61 in April to 2.98 in February 2002, thereby suggesting isometric growth pattern. The fitted growth pattern of A. uranoscopus showed an asymptotic length (L_∞) of 28.5 cm and a growth curvature (K) of 0.56 year^?1 resulting in an estimated natural mortality coefficient (M) of 0.90 year^?1. The Fulton’s condition factor (K) was also relatively stable with a peak in April (0.92 ± 0.21) and lowest value in June (0.86 ± 0.10). As A. uranoscopus is not under commercial exploitation, the seemingly depressed population is possibly attributed to the introduced exotic rainbow trout that heavily predates on the species and environmental perturbations arising from changes in land use. The implications of such changes on A. uranoscopus are discussed.     

Population dynamics of the venerid bivalve Tawera gayi (Hupé, 1854) in the Ushuaia Bay, Beagle Channel

Growth, productivity and potential for exploitation of the clam Tawera gayi from shallow waters (3–5 m) of Ushuaia Bay, Beagle Channel were investigated. Mean abundance and biomass in the study area were 1091 ± 737 ind. m^?2 and 901.83 g SFWM m^?2 (shell‐free wet mass), respectively. Individual growth was described best by the von Bertalanffy growth model with the parameter values H_∞ = 28.03 mm, K = 0.288 year^?1, t₀ = ?0.34 (r² = 0.83). Annual production of the population was estimated to be 120.45 g SFWM m^?2 year^?1, corresponding to a production‐to‐biomass ratio (P/B) of 0.134 year^?1. The single negative exponential mortality model does not fit the population mortality pattern, but predation by gastropods (Xymenopsis muriciformis, Trophon geversianus, Natica sp.) appears to be the major cause of mortality. These highly mobile predators together with the comparatively slow growth and low turnover of T. gayi in Ushuaia Bay limit its potential for sustainable commercial exploitation.     

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.     

Length–weight relationship,parameters of growth and mortality for the hardhead halfbeak Chriodorus atherinoides Goode & Bean, 1882 (Beloniformes: Hemiramphidae) from Yucatan Peninsula,Mexico

This study reports length–weight relationships and growth parameters for Chriodorus atherinoides from La Carbonera, a karstic tropical coastal lagoon on the northwestern coast of the Yucatan Peninsula, Mexico. A total of 667 specimens were collected between April 2009 and March 2010. The length‐weight relationship obtained was W = 0.0034Lt^3.22. This study presents the first estimation of the model parameters of the von Bertalanffy growth equation (L_∞ = 27.30 cm, k = 0.76 year^?1 and t₀ = ?0.178 years), the instantaneous total mortality (2.51 year^?1) and the maximum length record (26.0 cm total length), which is greater than previously recorded.     

Age,growth, mortality and sex ratio of the inshore population of the edible crab,Cancer pagurus (Linnaeus 1758) in South Wales (UK)

Age, growth, and mortality of the edible crab, Cancer pagurus, were determined for the native population in South Wales (UK). Sampling was carried out on a monthly basis between February 2001 and September 2002. Carapace width ranged between 10.4 and 163 mm. Based on the carapace width frequency distribution, the Swansea and Gower population was composed mainly of males belonging to the first and second age‐class (1 and 2), and of females belonging to the third and fourth age‐class (3 and 4). Sex ratio was 1.126 ± 0.27 in favour of males. Carapace width frequency distributions and weight‐at‐age data were used to estimate the von Bertalanffy growth equation parameters. For the population as a whole, these were: L∞ = 199 mm, W∞ = 1179.56 g, K = 0.24 year^?1, t₀ = ?0.1004 years. The overall carapace width–weight relationship was: W = 0.38(CW^2.69). Analysis of covariance indicated a significant difference in the carapace width–weight relationship between males and females in the study area. Total mortality Z and natural mortality M rates for combined sexes were 1.245 year^?1 and 0.567 year^?1, respectively. The exploitation ratio E was estimated to be 54.43%.     

Age,growth and reproduction of the black sea bream Spondyliosoma cantharus (Linnaeus, ) (Sparidae) in the Gulf of Annaba (Algeria)

The objective of this study was to determine the basic population‐specific parameters necessary for fish stock assessment in the Gulf of Annaba and to compare these with data from other Mediterranean regions. Black sea bream Spondyliosoma cantharus (Linnaeus, 1758) (N = 501) were collected monthly from January to December 2008 along the Algerian eastern coasts. More than 22 fish were collected each month and ranged in size from 13.4 to 40 cm total length, weighing from 36 to 1080 g eviscerated weight. Biological sampling included weighing and measuring the fish, gonad weighing, sex and maturity stage determination, and age estimation through otolith readings. Validity of the otolith readings for estimating age and growth was supported using the back‐calculation method. Estimated parameters of the von Bertalanffy model are: L_∞ = 33.54 cm, W_∞ = 633.46 g, k = 0.52 year^?1 and t_o = ?0.04 year. The growth performance index (φ) is: 2.76. The length‐weight relationship is: EW = 4.4.10^?6 TL^3.23. The spawning period occurred from February to May, while the gamete emission peaked in April. Females reached sexual maturity at 19.3 cm (2 years) and males at 21.3 cm (3 years). Sexual inversion occurs at approximately 24.3 cm. Spondyliosoma cantharus was characterized as being a protogynic hermaphrodite.     

Soil Carbon Storage by Switchgrass Grown for Bioenergy

Life-cycle assessments (LCAs) of switchgrass (Panicum virgatum L.) grown for bioenergy production require data on soil organic carbon (SOC) change and harvested C yields to accurately estimate net greenhouse gas (GHG) emissions. To date, nearly all information on SOC change under switchgrass has been based on modeled assumptions or small plot research, both of which do not take into account spatial variability within or across sites for an agro-ecoregion. To address this need, we measured change in SOC and harvested C yield for switchgrass fields on ten farms in the central and northern Great Plains, USA (930 km latitudinal range). Change in SOC was determined by collecting multiple soil samples in transects across the fields prior to planting switchgrass and again 5 years later after switchgrass had been grown and managed as a bioenergy crop. Harvested aboveground C averaged 2.5?±?0.7 Mg C ha^?1 over the 5 year study. Across sites, SOC increased significantly at 0–30 cm (P?=?0.03) and 0–120 cm (P?=?0.07), with accrual rates of 1.1 and 2.9 Mg C ha^?1 year^?1 (4.0 and 10.6 Mg CO₂ ha^?1 year^?1), respectively. Change in SOC across sites varied considerably, however, ranging from ?0.6 to 4.3 Mg C ha^?1 year^?1 for the 0–30 cm depth. Such variation in SOC change must be taken into consideration in LCAs. Net GHG emissions from bioenergy crops vary in space and time. Such variation, coupled with an increased reliance on agriculture for energy production, underscores the need for long-term environmental monitoring sites in major agro-ecoregions.     

Carbon balances in US croplands during the last two decades of the twentieth century

Carbon (C) added to soil as organic matter in crop residues and carbon emitted to the atmosphere as CO₂ in soil respiration are key determinants of the C balance in cropland ecosystems. We used complete and comprehensive county-level yields and area data to estimate and analyze the spatial and temporal variability of regional and national scale residue C inputs, net primary productivity (NPP), and C stocks in US croplands from 1982 to 1997. Annual residue C inputs were highest in the North Central and Central and Northern Plains regions that comprise ~70% of US cropland. Average residue C inputs ranged from 1.8 (Delta States) to 3.0 (North Central region) Mg?C?ha^?1?year^?1, and average NPP ranged from 3.1 (Delta States) to 5.4 (Far West region) Mg?C?ha^?1?year^?1. Residue C inputs tended to be inversely proportional to the mean growing season temperature. A quadratic relationship incorporating the growing season mean temperature and total precipitation closely predicted the variation in residue C inputs in the North Central region and Central and Northern Plains. We analyzed the soil C balance using the crop residue database and the Introductory Carbon Balance regional Model (ICBMr). Soil C stocks (0–20?cm) on permanent cropland ranged between 3.07 and 3.1?Pg during the study period, with an average increase of ~4?Tg?C?year^?1, during the 1990s. Interannual variability in soil C stocks ranged from 0 to 20?Tg?C (across a mean C stock of 3.08?±?0.01?Pg) during the study period; interannual variability in residue C inputs varied between 1 and 43?Tg C (across a mean input of 220?±?19?Tg). Such interannual variation has implications for national estimates of CO₂ emissions from cropland soils needed for implementation of greenhouse gas (GHG) mitigation strategies involving agriculture.     

Exploitation and mortality rates of European hake (Merluccius merluccius) in the Aegean Sea (Izmir Bay,Turkey)

Experimental trawl surveys in Izmir Bay (Aegean Sea) were taken seasonally between 2007 and 2009. A total of 1353 specimens were sampled ranging from 5.9 cm (1.4 g) to 44.4 cm (670 g). The main size group of Merluccius merluccius was between 14 and 25 cm total length (TL). In total, the mean catch per unit effort (CPUE) for hake by number and weight was 101.4 ± 18.4 ind h^?1 and 10.7 ± 1.5 kg h^?1, respectively. Highest mean CPUE by number and biomass was determined as 257.1 ± 15.1 ind h^?1 and 15.1 ± 4.9 kg h^?1 in summer. Mortality (M, F, Z) ratios of hake were 0.58 year^?1, 1.66 year^?1 and 2.24 year^?1, respectively. Because of the many smaller specimens caught in this study, this seems to indicate that there may be heavy fishing pressures on the hake population; the high exploitation rate (E = 0.74) appears to confirm this conclusion.     

Age, growth and mortality of a semi-isolated lagoon population of sand smelt, Atherina boyeri (Risso, 1810) (Pisces: Atherinidae) in an estuarine system of northern Greece

Age, growth and mortality of the sand smelt, Atherina boyeri (Risso, 1810), were studied in the Vistonis estuarine system in northern Greece from February 1989 to August 1990. Overall male : female sex ratio was 1 : 2.5, statistically different from unity. Total lengths ranged between 13 and 105 mm. Age determination based on scale readings showed that the population comprised five age‐groups. Sand smelt grew allometrically (b = 3.22) and rapidly during the first year, achieving 60% of their growth. Growth parameters of the population were: L_∞ = 116.97 mm, K = 0.35 year⁻¹ and t_o = −0.99 years. Growth index ϕ′ was 3.69 of all individuals studied. The mean growth index was significantly lower for the Mediterranean lagoon (ϕ′ = 3.73, SD = 0.1) than for Atlantic populations (ϕ′ = 3.92, SD = 0.06). Total mortality rate was Z = 1.29 year⁻¹ and natural mortality M = 0.95 year⁻¹. Males had a lower life span than females, the latter dominating length classes >60 mm. Exploitation rate of the studied population was E = 0.26, suggesting that stock size might increase and generate improved possibilities for exploitation.