Increment Width Research Articles

Spatiotemporal analysis of the daily growth traits of the prerecruits of a small pelagic fish in response to environmental drivers

AbstractA comparative analysis of daily growth patterns was carried out for prerecruits (PR) of Engraulis ringens, collected from spring to summer (2015–2016) in northern (18º25'S–24º40'S) and southern nursery areas (32º40'S–41º00'S) off the Chilean coast. Prerecruits ranged from 2.2 to 7.3 cm TL (4.27 ± 0.88) and from 27 to 102 days (54.68 ± 15.92) of age and were hatched mainly in spring 2015. Growth traits were addressed through otolith microstructure analysis to determine the increment width profiles (IW), back‐calculated growth rates (BIGR), and overall absolute growth rates (AGR), whereas the Chl–a and sea‐surface temperature (SST) variations were assessed by analyzing satellite and field‐based data. The IWs (5.42 ± 1.94 µm versus 1.02 ± 0.37 µm), BIGRs (1.02 ± 0.37 versus 0.72 ± 0.26 mm·day−1), and AGRs (0.93 ± 0.15 versus 0.62 ± 0.08 mm·day−1) were significantly higher in the northern than in the southern stocks. The SST ranged from 17°C to 23°C (19.42 ± 1.45) and from 12°C to 18°C (14.81 ± 1.31) and varied significantly between stocks and months, whereas the higher concentration of Chl–α (~8 mg/m3), occurred close to the shallow coastal areas irrespective of stocks. A parabolic relationship between the recent otolith growth rates (ROGR) (as a proxy of recent daily somatic growth rates) and SST recorded at the date of capture estimated a maximum ROGR of 13.4 µm·day−1 at 18°C. These results demonstrated that water temperature seemed to be an important daily growth controller for early juveniles of E. ringens in the Humboldt Current System and that the field‐based growth–temperature relationship obtained will contribute to future potential bioenergetics models for this important forage species.

Growing Up Down South: Spatial and Temporal Variability in Early Growth of Fuegian Sprat Sprattus fuegensis From the Southwest Atlantic Ocean

The Fuegian sprat Sprattus fuegensis represents one of the most important pelagic resources in the Southwest Atlantic Ocean (SWAO), exerting a crucial ecological role as an intermediary link in Patagonian food webs. Otolith microstructure of 217 age-0 sprats were analyzed aiming to characterize growth patterns and possible environmental effects over them. Samples were gathered during three oceanographic surveys (spring 2014; autumns 2016, 2017) in Tierra del Fuego (TDF) and the Marine Protected Area Namuncura-Burdwood Bank (MPAN-BB), the first Argentinian open-sea marine protected area. Daily growths (DG) of larvae and post-larvae were estimated by individually modeling size and otolith radius relationships through back-calculation procedures using potential and linear functions respectively. Increment widths (IW) and DG values and trajectories were assessed for older sprats (i.e. survivors) sampled in the autumn surveys considering the habitat, year sampled and sprats’ hatching seasons, and were additionally evaluated in relation to sea-surface temperature (SST). IW and DG trajectories differed primarily according to the habitat sampled and sprats’ hatching seasons. Overall, strong coupling was detected between IW and DG trajectories with SST in both habitats. However, statistical assessment on particular comparisons showed that this general trend is not strictly invariant. Even though several results pinpointed a positive correlation between IW and DG with SST, the highest DG were estimated for summer- and autumn-born sprats sampled in 2016 in the MPAN-BB, period and habitat with the lowest SST values. These results unveil a complex relationship between spatial and temporal variability during early growth of Fuegian sprats, supplying relevant information that could be used in the creation of adequate ecosystem based management strategies in the SWAO.

Hibernation Records on the Incisor Surface in the Turkish Hamster (Mesocricetus brandti) (Rodentia, Cricetidae)

The teeth of an adult female of the Turkish hamster (Mesocricetus brandti) after hibernation in semi-natural conditions were examined to reveal a relationship between the hibernation pattern on the incisor surface and the data of a temperature logger. The female spent the winter in a burrow prepared by herself inside a wintering cage from October 2018 till May 2019. A temperature logger was implanted to the animal intraperitoneally to record body temperature at 20-min intervals. Regular bouts of hypothermia started in mid-October. The longevity of each hypothermia bout increased whereas the minimum body temperature decreased and reached its lowest value in March. Later, the process proceeded backwards until the end of the heterothermia period. In the apical region of the incisor, daily increments were wide and well-distinguished which indicates that they had formed before the onset of the heterothermal period. In the basal region, closer to the growth zone, the increments were narrow and distinct, and their number corresponded in general to the number of normothermia episodes bouts. At the very base of the incisor as well as at its apical part, typical daily increments were revealed again. However, no correlation between the longevity of normothermia bouts and the width of increments was found. These data varied greatly from two other hamsters. In the Ciscaucasian hamster (Mesocricetus raddei) the number and character of increments comply with the number and duration of normothermia bouts, in the Common hamster (Cricetus cricetus), the “hibernation zone” was not recorded on the incisor surface. The Turkish hamster demonstrate an intermediate pattern, which we explain by quite different hibernation conditions of these species.

Otolith oxygen isotope analysis and temperature history in early life stages of the chub mackerel Scomber japonicus in the Kuroshio–Oyashio transition region

To determine the temperature history of early life stages of chub mackerel (Scomber japonicus), otolith stable oxygen isotope ratios (δ18Ootolith) of larval and juvenile fish collected in the Kuroshio–Oyashio transition area during 2004–2015 were analyzed, and experienced temperatures were estimated accordingly. The δ18Ootolith values decreased with otolith growth during the larval stage, whereas those for juveniles were positively correlated with otolith radius and increased with increasing otolith size. Combinations of δ18Ootolith values, average otolith daily increment width, and daily age were representative of the differences between better and poorer recruitment years, the former being characterized by earlier spawning and faster growth (resulting from cooler experienced temperatures), and the latter by slower growth. Analyzed fish were sorted into larval and early juvenile growth stages by cluster analysis; the high-growth cluster exhibited higher δ18Ootolith values than the low-growth cluster. The conversion of δ18Ootolith values to water temperature indicated that the higher growth cluster experienced a water temperature ca. 2.0 °C cooler during the later juvenile stage. Therefore, our results suggest the presence of a growth positive spiral, wherein individuals with high initial growth proactively enter cooler water temperature areas, accessing a highly nutritious diet resulting in further rapid growth.

Effects of water temperature and prey density on recent growth of chub mackerel Scomber japonicus larvae and juveniles along the Pacific coast of Boso–Kashimanada

The effects of temperature and prey density on the recent growth rate (RGR) of chub mackerel, Scomber japonicus, were examined. Scomber spp. larvae and juveniles were collected along the Boso–Kashimanada Pacific coast in Japan between March and July in 2015 and 2016. Larvae and juveniles identified as S. japonicus using DNA were subjected to stomach-content and otolith-increment analyses. The effects of temperature and prey density on RGR were analyzed using a generalized linear mixed model (GLMM), which showed that temperature positively affected the RGR of larvae in the body length (BL) classes 11 mm classes and effects of prey density on RGR for larger (> 11 mm) larvae and juveniles were stronger than those for smaller (< 9 mm) larvae. S. japonicus larvae transform into juveniles at around 12 mm BL, and the increased feed demands of juveniles likely lead to prey-density-dependent growth. The otolith increment widths of larvae and juveniles were significantly narrower than those during the same stages in 1-year-old S. japonicus collected from purse seine fisheries operated in the Joban or Kashimanada areas, suggesting growth-dependent mortality.

Paired Li/Ca and δ18O peaks in bivalve shells from the Gulf of Panama mark seasonal coastal upwelling

Paired lithium-to-calcium (Li/Cashell) and oxygen isotope (δ18Oshell) ratios were measured in four aragonitic Megapitaria aurantiaca bivalve shells from the tropical Eastern Pacific and evaluated with respect to their linkage to seasonal coastal upwelling. The Li/Cashell and δ18Oshell of two specimens from the upwelling-dominated Gulf of Panama are positively correlated and consistently reveal large seasonal variations of up to ~300 μmol/mol and ~3‰, respectively. The Li/Cashell and δ18Oshell of two shells from the adjacent non-upwelling Gulf of Chiriquí are not correlated and show a reduced seasonal variability rarely exceeding 20 μmol/mol and ~1.0‰, respectively. In some M. aurantiaca specimens the Li/Cashell shows a weak positive correlation with growth increment width, indicating that physiological growth rate effects might in part control the ‘background’ Li/Cashell. Unambiguous seasonal δ18Oshell signals, used for a precise chronology for a live-collected specimen from the Gulf of Panama, imply that distinct parallel peaks in Li/Cashell and δ18Oshell mark the cold and highly productive coastal upwelling season during February to April. A comparison with environmental data reveals a negative correlation between Li/Cashell and water temperature, and a strong positive correlation between Li/Cashell and chlorophyll a in the Gulf of Panama. While a causal link between Li/Cashell and temperature remains uncertain, we argue that Li/Cashell peaks in M. aurantiaca are consistent with the concept of an incorporation of additional Li provided by diatom-dominated phytoplankton blooms during coastal upwelling. Our findings suggest that Li/Cashell in M. aurantiaca may serve as a new proxy for seasonal coastal upwelling, the potential of which should be tested for other mollusk species and upwelling regions.

Influences of life history and environment on lake trout (Salvelinus namaycush) growth and longevity in the Husky Lakes of the Western Canadian Arctic

The interaction between an organism and its environment is a major determinant of an individual’s growth rate, longevity, and fitness. Such interactions and resultant variation in growth is particularly prevalent in salmonids where a diversity of life history types and morphotypes can be observed within a single ecosystem. Lake trout, Salvelinus namaycush, are typically considered freshwater residents. However, three life history types within the Husky Lakes estuary and connected lakes, NWT were recently documented, including semi-anadromous, brackish-water resident, and freshwater resident. To understand how use of brackish-water environments influences growth and longevity in lake trout, we assessed otolith increment widths, as a proxy for annual fish growth, and age-at- capture among life history types. Assessment of increments indicated that growth increased in brackish water for semi-anadromous lake trout, and that growth was faster for semi-anadromous and brackish-water residents than for freshwater residents (70 mm larger on average at age 15). In addition, age at capture was significantly older in brackish-water residents (3.8 years older) when compared to the other life histories. Together these results indicate that life in brackish water can have positive effects on growth and longevity for lake trout.

An integrated carbon and oxygen isotope approach to reconstructing past environmental variability in the northeast Atlantic Ocean

The combined influence of temperature and the isotopic composition of the seawater (δ18Ow) often precludes the use of oxygen isotope (δ18O) records, derived from marine carbonates, to reconstruct absolute seawater temperatures, without the application of an independent δ18Ow proxy. Here we investigate the application of carbon isotope records (δ13Cshell), derived from the long-lived marine bivalve Glycymeris glycymeris, as a proxy for δ18Ow variability. Our analyses indicate G. glycymeris δ13Cshell data derived from growth increments >20 years of age contain strong ontogenetic trends (−0.013‰ yr−1, R = 0.98, P < 0.001, N = 51). These analyses demonstrate that, coupled with the ontogenetic trends, 54% of the variability in G. glycymeris δ13Cshell records can be explained by a combination of the marine Suess effect and physical (salinity and riverine input) and biological processes (primary production). The application of these δ13Cshell data in conjunction with co-registered δ18Oshell and growth increment width series, each of which have been shown to be sensitive to seawater temperature and primary productivity respectively, can therefore provide new insights into past environmental variability and help constrain uncertainties on reconstructions of past seawater temperature variability.

Planktonic larval duration, early growth, and the influence of dietary input on the otolith microstructure of Scolopsis bilineatus (Nemipteridae)

The pelagic larval phase represents a critical period in the early life history of fishes, since larval growth and development can contribute substantially to patterns of survival, dispersal and connectivity. The microstructure of otoliths was examined to investigate events during the early life history of the bridled monocle bream Scolopsis bilineatus (Nemipteridae) on the Great Barrier Reef. We validated a distinct settlement mark, characterized by a rapid transition from wide to narrow increments. The time fish spent in the plankton (Pelagic Larval Duration; PLD) ranged from 17 to 27 days (mean = 21.3 days), which is similar to many other fish families. Three distinct early life history stages occurred: pre-settlers (larvae), newly settled fish, and settled juveniles. Increment width (a proxy for growth) was sequentially narrower with each life history stage; pre-settlers>newly settled>settled juveniles, and growth was reduced as fish approached and underwent settlement to reef habitats. Evidence is provided for a “search phase”, whereby growth was reduced in the three to four days preceding settlement; this pattern may be indicative of changes in the behaviour of larvae immediately prior to settling. Two manipulative experiments investigated the effects of diet ration on otolith increment widths. Reduced food intake resulted in significantly narrower increment widths, with a possible lag effect of at least six days. Experiment results indicated that increment widths can be a reliable proxy of somatic growth, and results from this study overall highlight the utility of otoliths as a tool for investigating the early life history of fishes.

Sclerochronological approach for the identification of herring growth drivers in the Baltic Sea

Long-term datasets developed based on measurements of archived fish otoliths may help in the evaluation of climatic impacts on marine resources. The objective of the present study was to identify the factors that influence interannual variations in the somatic growth rate of herring (Clupea harengus) in the Baltic Sea. This work covers otolith samples collected from commercial catches and during scientific surveys from 1951 to 2017 in the Polish zone of the southern part of the Baltic. Otolith increment widths, which represent changes in fish growth, were analyzed with linear mixed models to investigate different intrinsic and extrinsic sources of fish growth variation. The stock biomass of pelagic species (herring and sprat Sprattus sprattus), sea surface temperature, Baltic Sea Index and land precipitation over the catchment area were considered potential predictors of herring growth. Methods to identify the optimal time window for environmental factors were incorporated in the modeling. Moreover, a wavelet coherence analysis, tests for identification of regime shifts in fish growth and a spatial correlation analysis were applied to the data. The developed multidecadal otolith-based biochronology showed that the growth of Baltic herring is under the strong influence of interspecific competition between herring and sprat, but the biochronology also indicated a high correlation with precipitation patterns over the runoff area and hydrological conditions within the Baltic Sea. A detailed investigation revealed that the relationships between herring growth and abiotic conditions or other ecosystem components can vary over time. The recognized complex ecological effects on herring growth necessitate the application of holistic ecosystem-based approaches for sustainable management and exploitation of small pelagic fish resources.

The revolution of crossdating in marine palaeoecology and palaeoclimatology.

Over the past century, the dendrochronology technique of crossdating has been widely used to generate a global network of tree-ring chronologies that serves as a leading indicator of environmental variability and change. Only recently, however, has this same approach been applied to growth increments in calcified structures of bivalves, fish and corals in the world's oceans. As in trees, these crossdated marine chronologies are well replicated, annually resolved and absolutely dated, providing uninterrupted multi-decadal to millennial histories of ocean palaeoclimatic and palaeoecological processes. Moreover, they span an extensive geographical range, multiple trophic levels, habitats and functional types, and can be readily integrated with observational physical or biological records. Increment width is the most commonly measured parameter and reflects growth or productivity, though isotopic and elemental composition capture complementary aspects of environmental variability. As such, crossdated marine chronologies constitute powerful observational templates to establish climate-biology relationships, test hypotheses of ecosystem functioning, conduct multi-proxy reconstructions, provide constraints for numerical climate models, and evaluate the precise timing and nature of ocean-atmosphere interactions. These 'present-past-future' perspectives provide new insights into the mechanisms and feedbacks between the atmosphere and marine systems while providing indicators relevant to ecosystem-based approaches of fisheries management.

Microstructure comparison of hard tissues (statoliths, beaks, and eye lenses) of Uroteuthis chinensis in the South China Sea

In the present study, the microstructure features and the number of growth increments in the statoliths, beaks, and eye lenses of the mitre squid, Uroteuthis chinensis (Gray, 1849), were examined. Growth increments in three regions of the statolith [the dorsal dome (SDD), lateral dome (SLD), and rostrum] were observed; those of the SLD had the most stable increment widths. The SLD and SDD had a similar number of growth increments. Increment number in the rostrum sagittal section (RSS) of the upper beak was lower (about 30 increments) and that of the eye lens was many times higher (about 3–5 times) than those in the statolith and the beak. The best fits against mantle length were the number of growth increments of the beak, SLD, and eye lens. The relationship between mantle length and growth increments of SLD could be described with two separate equations, possibly indicating that two different cohorts were sampled. Based on the growth increments of SLD, the maximum age of U. chinensis in our study was inferred to be 169 d.

Moonlight enhances growth in larval fish.

Moonlight mediates trophic interactions and shapes the evolution of life-history strategies for nocturnal organisms. Reproductive cycles and important life-history transitions for many marine organisms coincide with moon phases, but few studies consider the effects of moonlight on pelagic larvae at sea. We evaluated effects of moonlight on growth of pelagic larvae of a temperate reef fish using "master chronologies" of larval growth constructed from age-independent daily increment widths recorded in otoliths of 321 individuals. We found that daily growth rates of fish larvae were enhanced by lunar illumination after controlling for the positive influence of temperature and the negative influence of cloud cover. Collectively, these results indicate that moonlight enhances growth rates of larval fish. This pattern is likely the result of moonlight's combined effects on foraging efficiency and suppression of diel migrations of mesopelagic predators, and has the potential to drive evolution of marine life histories.

Hibernation Records on the Surface of Incisors in Radde’s Hamster (Mesocricetus raddei, Rodentia, Cricetidae) from Dagestan

Abstract—The lower incisors of ten hamsters from the Khunzakh region of Dagestan were studied. One hamster implanted with a temperature data logger successfully survived one winter in natural conditions, and its body temperature curve revealed 25 episodes of hypothermia with the body temperature dropping to 1–9°C, i.e., the period of hibernation. On the surface of the incisors, against a background of very indistinct increments, a zone with more distinct increments was observed. From the apical part of the zone to its basal part, the width of these increments decreased to very narrow, almost indistinguishable increments, and then increased. A comparison of the number of increments formed after this zone with the number of days the hamster survived after arousal from hibernation indicated that the zone was formed during hibernation. The pattern of variation in the increment width in the “zone of hibernation” corresponded to that observed in the episodes of normothermia during hibernation. A similar “zone of hibernation” was seen on the incisor surface in six of nine specimens caught in the field in June to early July. The date of their arousal was calculated from the number of increments corresponded to the date of arousal of the hamsters in this region, according to field observations. The pattern of the hibernation record on the incisors of these hamsters was mainly similar to that in the hamster with the temperature data logger and also demonstrated individual variations. Due to the poor contrast of increments on the incisor surface of these hamsters, it is difficult to use this record of hibernation for precise calculation of the data of arousal or for estimation of the duration of every episode of normothermia during hibernation. However, it is possible among the animals caught in spring to early summer to distinguish specimens aroused earlier or later using the position of the “zone of hibernation” on the incisor. It is also possible to estimate the relative duration of periods with short or long episodes of normothermia using the ratio of fragments with different widths of the increment in the “zone of hibernation.”

Size-selective mortality of laboratory-reared Atlantic bluefin tuna larvae: evidence from microstructure analysis of otoliths during the piscivorous phase

Atlantic bluefin tuna (Thunnus thynnus) larvae show strong piscivorous feeding behavior at the very early larval stage and this enables them to grow at high rates. We conducted a laboratory experiment in which Atlantic bluefin tuna larvae were offered larval prey for the first time at different ages to simulate the early onset of piscivory at three treatments: yolk-sac larvae (YSL), delayed onset of piscivory (DYSL) and a solely planktivorous diet (Rotifers). The otolith microstructure was then used to compare the larval size distribution at the onset of the experiment with the estimated previous size-at-age of the survivors at the end of the experiment by back-calculation. Within a cohort, our results show size-selective mortality of the largest larvae independent of the differences in the timing of onset of piscivory and differences in growth patterns. The results also corroborate the rapid response of Atlantic bluefin tuna to piscivory in terms of growth reflected in the otolith increment widths. Being bigger did not infer a survival advantage and mortality rates did not decline with increasing larval size. Smaller size at a given age could under certain conditions and stages of development confer a survival advantage of individual members of a larval cohort when suitable small-sized prey is available.

Climate-driven synchrony in growth-increment chronologies of fish from the world's largest high-elevation river

Understanding how sensitive aquatic ecosystems respond to climate change is essential for effective biodiversity conservation and management. The Tibetan Plateau (TP) is one of the most globally sensitive areas to climate change with potentially serious implications for resident fish populations and aquatic food webs. However, how the growth of TP fish responds to climate change, and how this response varies with the trophic level of different species remain unknown. We established growth-increment chronologies of two important Schizothoracinae fishes that are endemic to the TP (e.g., the omnivorous Schizopygopsis younghusbandi and the carnivorous Oxygymnocypris stewartii) from the Yarlung Tsangpo River, using otolith increment width measurements and dendrochronological methods. These growth chronologies were correlated with key indicators of environmental variation (temperature, precipitation, and river discharge) to examine the potential effects of climate change. The two chronologies displayed synchronous responses to recent climate change. In this glacial-fed river, the growth of both fish species was significantly and negatively correlated with the mean annual air temperature, while it was positively but not significantly correlated with precipitation and discharge. The higher trophic level species O. stewartii was more sensitive to climate than was the lower trophic level species S. younghusbandi, with temperature variables explaining a higher proportion of growth variability in O. stewartii (64.6%) than in S. younghusbandi (46.4%). The results collectively indicate that both species are highly sensitive to climate change, which may affect fish growth by altering water environment, fish physiological fitness and food availability. This study provides further empirical evidence of the utility of growth-increment chronologies for investigating the effects of climate change on aquatic ecosystems across different basins and water body types of the TP. These findings can inform conservation and management actions related to addressing climate change on the TP and other high-elevation temperate systems found worldwide.

Ligament, hinge, and shell cross-sections of the Atlantic surfclam (Spisula solidissima): Promising marine environmental archives in NE North America.

The Atlantic surfclam (Spisula solidissima) is a commercially important species in North American waters, undergoing biological and ecological shifts. These are attributed, in part, to environmental modifications in its habitat and driven by climate change. Investigation of shell growth patterns, trace elements, and isotopic compositions require an examination of growth lines and increments preserved in biogenic carbonates. However, growth pattern analysis of S. solidissima is challenging due to multiple disturbance lines caused by environmental stress, erosion in umbonal shell regions, and constraints related to sample size and preparation techniques. The present study proposes an alternative method for describing chronology. First, we analyzed growth patterns using growth lines within the shell and hinge. To validate the assumption of annual periodicity of growth line formation, we analyzed the oxygen isotope composition of the outer shell layer of two specimens (46°54'20"N; 56°18'58"W). Maximum δ18Oshell values occurred at the exact same location as internal growth lines in both specimens, confirming that they are formed annually and that growth ceases during winter. Next, we used growth increment width data to build a standardized growth index (SGI) time-series (25-year chronology) for each of the three parts of the shell. Highly significant correlations were found between the three SGI chronologies (p < 0.001; 0.55 < τ < 0.68) of all specimens. Thus, ligament growth lines provide a new method of determining ontogenetic age and growth rate in S. solidissima. In a biogeographic approach, the shell growth performance of S. solidissima in Saint-Pierre and Miquelon was compared to those in other populations along its distribution range in order to place this population in a temporal and regional context.

Effects of habitat conditions at hatching time on growth history of offspring European anchovy, Engraulis encrasicolus, in the Central Mediterranean Sea

The knowledge of the growth history in young fishes represents an important aspect of fishery ecology. This is especially relevant in short-living species like European anchovy, since they suffer a high mortality rate in their early life stages until recruitment. Although it is well known that habitat condition significantly affects spawning dynamics of fishes, it is not yet clear if these conditions affect growth trajectories during the early life stage’s critical period. Otolith microstructure analysis has been proven a useful tool to back-calculate growth history of young fishes. Thus, we analysed the effect of habitat variability on their growth history using otolith microstructures and environmental variables obtained from satellite imagery. Growth trajectories in juvenile anchovies, collected in two recruitment surveys carried out in 2004 and 2005 in the Strait of Sicily, were characterized by means of three indices within the fast growing period: the maximum increment width, the mean value of increment width, and the time extension of the fast growing period. Obtained results evidenced a clear effect of environmental conditions, particularly of sea surface temperature and chlorophyll-a concentration, on the growth histories of juveniles of anchovy. Furthermore, delayed effects of environmental conditions at hatching time on the forthcoming growth dynamics were discussed.

Age-based life-history parameters of the mesopelagic fish Notoscopelus resplendens (Richardson, 1845) in the Central Eastern Atlantic

The mesopelagic fish Notoscopelus resplendens is distributed mainly between 500 and 1000 m of depth during the day, with diel migration to surface waters at night (<90 m). Fish move during their diel migrations across different water masses, which show strong changes in temperature with depth that can reach 7 °C in the first 300 m during the warm season. N. resplendens show a type of diel migration pattern of the “entire migrant”, showing a clear day-night habitat separation, with peak abundance above 200 m at night. The difference between sexes in maximum size was 1.97 mm SL (84.36 mm, males; 82.39 mm females). The spawning season can be determined from December to March by back calculating the hatching date from daily growth increments. Age at first maturity was 1.7 year for males and 2.05 years for females. The sex ratio showed a predominance of males (1:0.67). Males were significantly more abundant than females in the 1-year age class. In the rest of the age classes, no significant differences were observed. A sexually dimorphic nature in relation to the position of the accessory luminous glands was observed. Three growth regions were observed in the otolith corresponding to different rates of deposition during fish ontogeny. Daily growth increments were calculated as validation of the annuli pattern. The pattern of the increment formation showed that each annulus has a unimodal distribution. The increment width decreases with age from 1 to 4 years. A strong relationship was found between both diameters of the otolith and length and between otolith weight and age. Different growth models have been analysed to understand the growth of this species. Gomperzt and von Bertalanffy were the best models obtained and revealed differences in growth between sexes. The maximum age recorded was 4 years. The SL-TW relationship showed allometric positive growth. The natural mortality coefficient for the overall population derived from the age-frequency distribution was 0.579 year−1. M obtained from the length converted catch curve was very similar at M = 0.549 year−1.

Multi-decadal variation in cohort specific sex ratios and otolith increment growth characteristics of juvenile blue grenadier (Macruronus novaezelandiae)

This study presents inter-annual variability of otolith growth from 1993 to 2011 and cohort specific sex ratios from 1976 to 2011 in blue grenadier Macruronus novaezelandiae on the west coast of Tasmania. Length-at-age data highlighted that M. novaezelandiae females grow larger than males with mean length-at-age statistically diverging by three years of age and remaining separated thereafter. Statistical differences in both cumulative, and age specific otolith increment widths-at-age between sexes were detected at earlier ages, but these effects were variable and not consistent with the sexual dimorphism observed for mean length at age. No differences between sexes were evident for the ages 8–14 or 7–11 for cumulative increment widths or age specific otolith increment widths-at-age respectively. Inter-annual variation in mean otolith increment widths for the first five increment zones (juvenile zones) showed a trend of declining increment widths from 2006 to 2010. Inter-annual cohort sex ratio variation across year-of-birth was also significant displaying a similar trend to the first-year otolith increment growth profiles. Regression analysis of birth year sex ratio with mean otolith increment widths indicated a significant negative relationship for first year growth with increasing numbers of male offspring. The inter-annual variation in cohort specific sex ratio suggests that environmental factors may be involved with sex determination. When coupled with climate change these influences could have long term consequences for the fitness of the stock and corresponding flow-on effects into the stock assessment process and future management of the stock.