Abundant species are typically also viewed as ecologically dominant, and are frequently used to characterize the communities in which they live. Such characteristic assemblages may also be used as indicators of environmental conditions, such as relative stability. Fossil and modern turritelline gastropods are often the most abundant species in the marine assemblages and communities in which they occur, forming ‘turritelline-dominated assemblages’ (TDAs). We use data on modern Turritella bacillum from waters around Hong Kong as a case study to analyse fluctuations in abundance over 25 years. While turritellines were not always dominant in the area surveyed (~1650 km2), populations were notably persistent, and rebound after decline of abundances occurred within ~5 years at some sites. δ18O sclerochronology suggests that individuals were ~1–2 years old. It is also notable that T. bacillum was found to be abundant at salinities as low as 10–15 psu, despite the general characterization of turritellines as fully marine. Comparison with data on modern T. communis in the western English Channel corroborates this pattern, as localized sites of high abundance also appear transient. These results have implications for the interpretation of TDAs in the fossil record: they may signify the cumulative result of short-lived, spatially restricted populations, possibly resulting from essentially stochastic larval settlement. This suggests that the palaeoenvironmental setting of fossil TDAs does not always control their occurrence on short temporal scales.

Although the red striped mullet is one of the main target fish of the Hellenic demersal fisheries, information about its biology is limited. The aim of this study was to describe the reproductive biology and growth of the species in the south Aegean Sea based on 1032 individuals sampled under the Data Collection Framework Program in 2016. According to the monthly variation of the maturity stages and the gonadosomatic index, spawning activity took place from March to July, although it appeared to occur throughout the year. Length at 50% maturity (L50) was 153.3 and 139.2 mm in females and males, respectively. Individual ages were determined by counting the annuli of otoliths macroscopically. Marginal increment analysis (MIA) combined with complementary information derived from otolith edge analysis, the assessment of the reproductive period and the length–frequency distribution modes of the population showed that annulus formation occurs between February and April. The length–weight relationship revealed a significant sex effect and was described by the parameters α = 0.0155 and b = 2.915 in females, and α = 0.0032 and b = 2.976 in males. The von Bertalanffy growth function (VBGF) parameters for sexes combined were Linf = 346.1 mm, k = 0.299 year−1 and t0 = −0.984 years. Longevity (tmax) was estimated at 11.75 years. This study provides valuable data for the stock assessment of M. surmuletus in one of the major Hellenic fishing grounds located in the south Aegean Sea.

The geographical distribution of the two species of the genus Parachaenichthys is allopatric and restricted to the inner shelves of South Georgia–South Sandwich Islands (P. georgianus) and South Orkney Islands–South Shetland Islands (P. charcoti). To evaluate the consistency between the geographical patterns of adult distribution and early life history traits of P. charcoti, sagittal otoliths were used to estimate growth rate and pelagic duration in larvae and juveniles of this species collected in the Bransfield Strait in winter and summer, respectively. Individual age was determined through microincrement counts, assuming they were daily increments. The Gompertz model was fitted to age–length estimates, providing a mean growth rate of 0.22 mm day-1 estimated for 28–204-day-old individuals. Larval hatching was spread over a relatively wide period, lasting from July throughout September. The pelagic larval duration of P. charcoti was about six months based on ageing data of larvae and juveniles, as reported for P. georgianus from South Georgia. The strong dependence of larvae on the inshore habitat may hamper their dispersal at large spatial scale limiting the connectivity among distant populations, providing clues to interpret the present geographical distribution of the two species.

Early life history traits of the blackfin notothen, Trematomus scotti, were investigated through otolith microincrement pattern and stomach content analyses. Post-larval specimens of 12–20 mm standard length (SL) were collected in the Bransfield Strait and adjacent waters during the 2010–11 summer. Catches were unevenly distributed across the surveyed area, yielding a relative abundance of 0.3–3.6 specimens per 1000 m3 of filtered sea water. Age estimates ranged from 34 to 67 days, with good consistency and no apparent bias between readings. Based on an exponential model fitted to the age-length dataset, the growth rate was 0.17 mm day-1, corresponding to a daily percentage increment in size of 1.07% SL. In agreement with previous studies, larval hatching occurred at a mean size of 9.0 mm and was spread over a relatively short period, lasting from late December to late January. Prey composition consisted exclusively of copepods, mainly larval stages of copepodites. Feeding intensity ranged from 1–14 prey items per stomach, being positively correlated with larval fish size. In summary, T. scotti shares a common early life history strategy with several other notothenioids, consisting of small larvae hatching in summer and overwintering as pelagic early juveniles until the following summer season.

Samples of common two-banded seabream Diplodus vulgaris (N = 1097), used in this study, were caught in the Gulf of Gabès (Tunisia) from March 2008 to February 2010. Total length ranged from 7 to 25 cm. Diplodus vulgaris is a protandric hermaphrodite. The overall ratio of females to males was 1:1.66. The reproductive season extended from October to February, and the peak spawning activity occurred in December–January. The total length at which 50% of the population reached maturity was 14.14 ± 0.16 cm for females and 13.57 ± 0.01 cm for males. Parameters of the length–weight relationship (TW = aTLb) for all individuals were a = 0.0185 and b = 2.9319. The youngest specimen in this study was 0+ years, whereas the oldest one was 9 years. The von Bertalanffy growth parameters for the whole sample were: L∞ = 25.4 cm, k = 0.179 and t0 = −1.631 year. The instantaneous rate of natural mortality was: M = 0.333 year−1.

Age, growth and feeding habits of early life stages of Chionodraco rastrospinosus Dewitt & Hureau, the most abundant channichthyid in the larval fish assemblages of the Bransfield Strait, were studied by otolith microincrement counts and stomach content analyses. Individuals measuring 39–69 mm standard length were caught in the uppermost depth strata down to 300 m from Brabant to Joinville islands along the northern Antarctic Peninsula. The sample consisted of post-larvae and juveniles aged 105–211 days, with a mean growth rate of 0.25 mm day-1. Larval size at hatching was estimated to be c. 17.2 mm. Hatching was spread over a relatively long period from August–November. Sagittal otoliths were characterized by a strong check located at 23–52 microincrements of distance from the core, tentatively associated with the onset of first exogenous feeding. The relatively long period during which larvae can rely on yolk reserves and the large size at hatching enable them to utilize a wide size range of prey, as well as cope with occasional food shortages. The stomach contents consisted exclusively of euphausiids (furcilia and adults) and larvae of Pleuragramma antarcticum Boulenger. Based on growth rate, the residence time in pelagic waters of juvenile C. rastrospinosus was estimated to be about a year and a half.

Based on the samples collected in Chinese scientific surveys off the Costa Rica Dome from July to August in 2009, statolith microstructure of the jumbo flying squid, Dosidicus gigas, was analysed for studying their age, growth and population structure. Three typical growth zones (postnuclear, dark and peripheral zones), abnormal increments (checks) and aberrant microstructure (additional centre and additional rings) were found in the statoliths examined. Squid sizes ranged from 205 to 429 mm dorsal mantle length (ML) with ages no more than 10 months for females and 8 months for males. Back-calculated hatching dates were from November 2008 to April 2009. Growth in ML was best described by a linear function for both the sexes, while growth in body weight was best quantified by an exponential function for females and a power curve for males. The maximum absolute daily growth rates and instantaneous growth rate in ML were reached during 181–210 and 151–180 days for females and males, respectively. The Costa Rica Dome and its adjacent waters were considered as a potential spawning ground because of presence of not only high proportion of mature squid but also rhynchoteuthion paralarvae, and high primary productivity from the strong upwelling. This study suggests that D. gigas have complicated intra-specific population structure and large spatial variability in the key life history parameters.

The bigeye thresher, Alopias supercilious,is commonly caught as bycatch in pelagic longline fisheries targetingswordfish. Little information is yet available on the biology ofthis species, however. As part of an ongoing study, observers sentaboard fishing vessels have been collecting set of information thatincludes samples of vertebrae, with the aim of investigating ageand growth of A. supercilious. A total of 117 specimenswere sampled between September 2008 and October 2009 in the tropicalnortheastern Atlantic, with specimens ranging from 101 to 242 cmfork length (FL) (176 to 407 cm total length). The A. supercilious vertebraewere generally difficult to read, mainly because they were poorlycalcified, which is typical of Lamniformes sharks. Preliminary trialswere carried out to determine the most efficient band enhancementtechnique for this species, in which crystal violet section stainingwas found to be the best methodology. Estimated ages in this sampleranged from 2 to 22 years for females and 1 to 17 years for males.A version of the von Bertalanffy growth model (VBGF) re-parameterisedto estimate L0, and a modified VBGF using a fixed L0 were fittedto the data. The Akaike information criterion (AIC) was used tocompare these models. The VBGF produced the best results, with thefollowing parameters: Linf = 293 cm FL, k = 0.06 y–1 and L0 = 111 cmFL for females Linf = 206 cm FL, k = 0.18 y–1 and L0 = 93 cm FLfor males. The estimated growth coefficients confirm that A. supercilious isa slow-growing species, highlighting its vulnerability to fishingpressure. It is therefore urgent to carry out more biological researchto inform fishery managers more adequately and address conservationissues.

The smooth hammerhead shark Sphyrna zygaena (Sphyrnidae) is regularlycaught as bycatch in pelagic longline fisheries, but is one of the least studied of allpelagic sharks. Recently, ICCAT (International Commission for the Conservation of AtlanticTunas) issued recommendations underlining the need for more studies on the life historyparameters of this and other pelagic shark species. To this end, the age and growth ofS. zygaena were studied in the Eastern Equatorial Atlantic Ocean, in anarea where growth parameters were not yet available for this species. Data from 139specimens, caught between June and September 2009, ranging in size from 136 to 233 cm forklength (FL), were analysed. Preliminary trials were carried out to assess the mostefficient growth band enhancement technique. These indicated that sectioning the vertebraeinto 500 μm sections followed by staining with crystal violet producedthe best results. Growth models were fitted using the traditional von Bertalanffy growthequation and a modification of this equation using a known size at birth. Growth modelswere compared using the Akaike information criterion (AIC). The von Bertalanffy growthequation seemed to be the most adequate model to describe growth in this species, withresulting growth parameters of Linf = 272 cmFL, k = 0.06 year for males andLinf = 285 cm FL,k = 0.07 year for females. In the first four years of life, S.zygaena grows 25 cm per year on average, but its growth slows down in laterlife. Future stock assessment models should incorporate these age and growth parametersfor species management and conservation.

The jumbo flying squid, Dosidicus gigas, support an important squid fishery off the Exclusive Economic Zone of Chilean waters. However, we only have limited information about their biology. In this study, age, growth and population structure of D. gigas were studied using statoliths from 533 specimens (386 females and 147 males) randomly sampled in the Chinese squid jigging surveys from 2007 to 2008 off the Exclusive Economic Zone of Chile. Mantle lengths (MLs) of the sample ranged from 206 to 702 mm, and their ages were estimated from 150 to 307 days for females and from 127 to 302 days for males. At least two spawning groups were identified, the main spawning peak tended to occur between August and November (austral spring group), and the secondary peak appeared during March to June (austral autumn group). The ML–age relationship was best modelled by a linear function for the austral spring group and a power function for the austral autumn group, and the body weight (BW)–age relationship was best described by an exponential function for both the groups. Instantaneous relative growth rates and absolute growth rates for ML and BW did not differ significantly between the two groups. The growth rate of D. gigas tended to be high at young stages, and then decreased after the sub-adult stage (>180 days old). This study suggests large spatial and temporal variability in key life history parameters of D. gigas, calling for the collection of more data with fine spatial and temporal scales to further improve our understanding of the fishery biology of D. gigas.

Age and growth of adult gilthead seabream, Sparus aurata were determined from 332 specimens (total N = 476), collected from purse-seiners, in the south-eastern Aegean Sea from November 2006 to January 2007. The fork length and body wet weight ranged from 26.5 to 51.5 cm (mean: 36.6 ± 0.18) and from 375 to 2600 g (mean: 1009.2 ± 14.16), respectively. Age groups were varied between 2 and 7. Growth parameters were estimated as L∞ = 64.97 ± 12.93 cm, K = 0.14 ± 0.07 year−1, t0 = −2.47 ± 1.09 year−1, and index of phi-prime was Φ′ = 2.772 ± 0.51. The length–weight relationship equation of all fish was calculated as W = 0.0515 × L2.737 (r2 = 0.95). The mean condition factor was estimated as 2.058. Mortalities (M, F and Z) and exploitation rate (E) of gilthead seabream from the Aegean Sea were 0.34 year−1, 0.77 year−1, 1.11 year−1and 0.69 year−1, respectively. The result of E indicated that the population was overexploited.