Otolith Readings Research Articles

Comparison between Otoliths and Length Based Ageing and Growth of African Armoured Searobin (Peristedion cataphractumL. 1758; Teleostei, Peristediidae) off the Southern Coasts of Sicily (Mediterranean Sea)

The recovering ofPeristedion cataphractumotoliths collected between 1991 and 1992 from specimens sampled off the southern coasts of Sicily has allowed a direct ageing and growth estimation to be compared with the length based method estimates produced in successive years. Overall, 855 left otoliths (sagittae) were recovered, measured, and read as a whole surface. The core and rings distances were also measured to perform back-calculation. The otolith length-body length relationships were allometric. Back-calculated lengths at age were in agreement with the lengths estimated with otolith readings. Present results showed a good congruency between otoliths and length based method.

An integrated Bayesian modeling approach for the growth of Indian Ocean yellowfin tuna

The Indian Ocean Tuna Tagging Program provided a unique opportunity to collect demographic data on the key commercially targeted tropical tuna species in the Indian Ocean. In this paper, we focused on estimating growth rates for one of these species, yellowfin (Thunnus albacares). Whilst most growth studies only draw on one data source, in this study we use a range of data sources: individual growth rates derived from yellowfin that were tagged and recaptured, direct age estimates obtained through otolith readings, and length-frequency data collected from the purse seine fishery between 2000 and 2010. To combine these data sources, we used an integrated Bayesian model that allowed us to account for the process and measurement errors associated with each data set. Our results indicate that the gradual addition of each data type improved the model's parameter estimations. The Bayesian framework was useful, as it allowed us to account for uncertainties associated with age estimates and to provide additional information on some parameters (e.g., asymptotic length). Our results support the existence of a complex growth pattern for Indian Ocean yellowfin, with two distinct growth phases between the immature and mature life stages. Such complex growth patterns, however, require additional information on absolute age of fish and transition rates between growth stanzas. This type of information is not available from the data. We suggest that bioenergetic models may address this current data gap. This modeling approach explicitly considers the allocation of metabolic energy in tuna and may offer a way to understand the underlying mechanisms that drive the observed growth patterns.

Age, growth and natural mortality of the Patagonian sprat Sprattus fuegensis (Jenyns, 1842) in Chiloe inland sea, southern Chile

Growth parameters (L∞, K, and t0) and natural mortality of the Patagonian sprat (Sprattus fuegensis) Chiloe inland sea were estimated. This area corresponds to the northern limit of the species distribution in the South Pacific Ocean. A total of 1,584 otolith were analyzed between July 2005 and December 2006. A covariance analysis ruled out significant differences (P = 0.654) in the otolith size-fish length relationship between males and females. The otoliths showed high monthly proportion of hyaline edge type in August 2005 and from July to October 2006. The hyaline band formation from mid-winter to spring coincided with the breeding season extending from September to December. This suggests an annual periodicity of annuli formation, likely as a consequence of channeling energy into reproduction. The growth parameters were L∞= 17.71 cm; K = 0.78 yr -1 ; and t0 = -0.46 yr, while the maximum observed age was 6 years. Natural mortality given growth parameters and species maturity, was estimated at 1.0 yr -1 . The modal decomposition of monthly length distribution, analyzed by a statistical-numerical algorithm (MIX approach) gave similar results to those obtained from otolith readings.

Estimating growth of tropical tunas in the Indian Ocean using tag-recapture data and otolith-based age estimates

A growth model from which the expected age of a fish can be estimated based on its length is a key component to most stock assessments. For the three tropical tuna species in the Indian Ocean – yellowfin (YFT; Thunnus albacares), bigeye (BET; T. obesus) and skipjack (SKJ; Katsuwonus pelamis) – information about growth has been very limited until recently, when data from a large-scale Indian Ocean tuna tagging program became available. In this paper, parametric growth models were fit to tag-recapture data for all three species using a maximum likelihood method that models the joint density of release and recapture lengths as a function of age by treating age at tagging as a random variable. The method allows for individual variability in growth by modelling the asymptotic length parameter as a random effect. Direct age and length data from otolith readings were also included in the analysis for YFT and BET. The results support two-stanza growth models for all three species; however, the growth patterns for YFT and BET differ from SKJ. YFT and BET exhibit a transition in growth between age 2 and 3, with faster growth in the second stanza than the first, whereas SKJ exhibit a transition in growth around age 1, with much faster growth in the first stanza than the second. Most likely, YFT and BET also experience a phase of rapid growth directly following hatching, but lack of data for fish less than 50cm for these species precludes its estimation. Differences in growth between sexes were found for YFT and BET, with males growing to a larger size; information on sex was not available for SKJ.

Rapid changes in growth, condition, size and age of small pelagic fish in the Mediterranean

Since 2007, the ecosystem of the Gulf of Lions has shifted to a different regime, characterised by a low anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) biomass and a remarkably high sprat (Sprattus sprattus) biomass. Surprisingly, the abundance and recruitment of anchovy and sardine remained high. To understand which processes (bottom-up or top-down control, etc.) could have caused this shift, we studied the changes in body condition, growth and size and age of anchovy, sardine and sprat over 1984–1985 and 1992–2012, using data from scientific surveys. The annual age structure of anchovy and sardine was estimated using Bayesian mixture models based on size frequency data with priors on the age–length relationship derived from independent otolith readings. The results indicated periods during which anchovy and sardine were in an average (1992–2004), good (2005–2007) or poor (2008–2012) overall state of condition. For sardine, the shift towards smaller fish observed during these past 4 years was explained by a combination of slower growth and the disappearance of older individuals (ages 2+). Despite the increase in biomass of sprat since 2008, indications were found that sprat was also smaller than in the past. As growth and condition decreased and overexploitation has not been documented or suspected for those three species in this area, we propose that the current decline in sardine and anchovy biomass could be due to qualitative and/or quantitative modifications in the planktonic production (i.e. a bottom-up control) or mass mortalities of adults due to an epidemic disease.

Improved growth estimates from integrated analysis of direct aging and tag–recapture data: An illustration with bigeye tuna (Thunnus obesus) of the eastern Pacific Ocean with implications for management

The growth modeling framework to integrate age-at-length and tag–recapture length-increment data sources is well established in fishery science. Surprisingly, the use of the so-called “Laslett–Eveson–Polacheck (LEP)” statistical approach has been infrequent since its development in the early 2000s. Likely, this is due to the complex treatment of process error by the methodology and its resulting high computational demands. Using bigeye tuna in the eastern Pacific Ocean as an example, this research presents a modified LEP method to strengthen the benefits of integrating the two sources of data into a single-step modeling approach. The bigeye tuna case study is typical in the tuna world in which age estimates from direct otolith readings commonly cover the young segment of the species life-cycle only, causing growth model predictions extrapolated beyond the data to be unreasonably high and contain uncertain values of the asymptotic length parameter L∞.In the case of bigeye, several improvements resulted from integration of an auxiliary tag–recapture dataset containing recoveries from large (older) fish: the estimated growth curve “bent” over toward a much lower and more plausible value of L∞ in order to explain the tag–recapture observations from older adult bigeye and the uncertainty (precision) of most growth parameters was greatly reduced (increased). The estimate of variability of the length-at-age was lower and estimated with greater precision. It is argued that it is reasonable to relax the complex assumptions made in the original LEP approach of treating L∞ as a random variable and assuming dependency between the lengths at tagging (l1) and recovery (l2) while treating the unknown age at release (A) for each tagged fish as a random variable. These modifications greatly reduce computational demand, potentially making the LEP approach more widely used, and simplifying the interpretation of variation of length-at-age for use in stock assessment models that fit to length composition data. In addition, opportunities are opened to integrate the methodology inside modern statistical stock assessment models.

Spawning, pelagic and metamorphosis stage duration in European flounder (Platichthys flesus): a latitudinal approach

Event Abstract Back to Event Spawning, pelagic and metamorphosis stage duration in European flounder (Platichthys flesus): a latitudinal approach Filipe Martinho1*, Henk W. Van Der Veer2, Henrique N. Cabral3 and Miguel A. Pardal1 1 Centre for Functional Ecology - CFE, Portugal 2 Royal Netherlands Institute for Sea Research - NIOZ, Netherlands 3 Centro de Oceanografia, Portugal The spawning, pelagic and metamorphosis stage duration were evaluated in European flounder (Platichthys flesus) along a latitudinal gradient in the European Atlantic coast. The main objective was to determine latitudinal trends in the estuarine nursery habitat colonization processes, considering a wide geographical range: from the southernmost population in the Mondego estuary (Portugal), the French coasts (Vilaine and Slack estuaries), the Wadden Sea (Netherlands) to the northern populations in the Sørfjord (Norway). Flounder 0-group juveniles were captured in June/July 2010. Otolith microstructure was used to account for the duration of each stage by analysing daily growth increments. The spawning period took place between mid-January and early-July over the species’ distribution range, with a gap of nearly two months between the Mondego estuary and the Sørfjord populations, as a consequence of warmer water temperature earlier in the season in the southern areas. Both pelagic and metamorphosis stages were longer at the middle of the distribution range, and lasted in total up to two months after hatching. Results also suggested the existence of a counter-gradient growth compensation mechanism in the northernmost populations. Apart from temperature (proxy for the latitudinal gradient), which regulates species’ basal metabolic rates, differences between sites were also related with local features, such as the extension of the continental platform and adaptations to transport and retention mechanisms. Acknowledgements The authors would like to thank Daniel Crespo, Dániel Nyitrai, João Rito, Cláudia Moreira, Rita Guillot and Hans Witte for the help in the sampling campaigns; to Louis Quiniou and Rachid Amara for providing flounder samples from the French estuaries; to Catarina Vinagre and Audrey Geffen for helping with the otolith reading procedures. Filipe Martinho is funded by the Portuguese Foundation for Science and Technology (FCT) through a research contract (IF/01410/2012). Keywords: Flounder, spawning, larval development time, counter gradient growth compensation, latitudinal cline Conference: IMMR | International Meeting on Marine Research 2014, Peniche, Portugal, 10 Jul - 11 Jul, 2014. Presentation Type: Poster Presentation Topic: BIODIVERSITY, CONSERVATION AND COASTAL MANAGEMENT Citation: Martinho F, Van Der Veer HW, Cabral HN and Pardal MA (2014). Spawning, pelagic and metamorphosis stage duration in European flounder (Platichthys flesus): a latitudinal approach. Front. Mar. Sci. Conference Abstract: IMMR | International Meeting on Marine Research 2014. doi: 10.3389/conf.fmars.2014.02.00013 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 30 May 2014; Published Online: 18 Jul 2014. * Correspondence: Dr. Filipe Martinho, Centre for Functional Ecology - CFE, Coimbra, 3000-456, Portugal, fmartinho@gmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Filipe Martinho Henk W Van Der Veer Henrique N Cabral Miguel A Pardal Google Filipe Martinho Henk W Van Der Veer Henrique N Cabral Miguel A Pardal Google Scholar Filipe Martinho Henk W Van Der Veer Henrique N Cabral Miguel A Pardal PubMed Filipe Martinho Henk W Van Der Veer Henrique N Cabral Miguel A Pardal Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Age and maturation of jack mackerel Trachurus japonicus in the East China Sea

Growth and reproductive characteristics of jack mackerel Trachurus japonicus collected in the East China Sea were determined based on otolith readings and gonad histology, respectively. Translucent and opaque zones on sectioned otoliths were identified and opaque rings counted. Von Bertalanffy growth parameters did not significantly differ between males and females, and the combined growth curve was: Lt = 401{1 − exp[−0.275 (t + 1.149)]} (0.8 < t < 6.9), where Lt is fork length (mm) at age t. The calculated lengths at age 1 in our study were larger than those reported 50 years ago from the East China Sea. The spawning period was evaluated to be from December to June, but primarily from February to May, based on the monthly changes in the gonadosomatic index and histological observations. The minimum size and age at first maturity were smaller and younger, respectively, than those reported in previous studies.

Comparing growth and maturity of sympatric Atlantic (Gadus morhua) and Greenland (Gadus ogac) cod in coastal Newfoundland

Growth and maturity of two sympatric gadids were examined from 48 Atlantic (Gadus morhua L., 1758) and 42 Greenland (Gadus ogac Richardson, 1836) cod ranging from 17 to 74 cm in length collected from an inshore area of Trinity Bay, Newfoundland, Canada, during 2009 and 2010. Ages estimated from otolith readings ranged from 2 to 7 for both species. Age and size at 50% maturity differed between species, being 2.3 years and 28.2 cm for G. ogac and 4.6 years and 48.8 cm for G. morhua. von Bertalanffy growth models did not differ between species with parameters L∞ = 91 cm, k = 0.16 year−1, t0 = –0.02 years for G. ogac and L∞ = 112 cm, k = 0.13 year−1, t0 = 0.18 years for G. morhua. Length (L) – mass (W) relationships differed; W = 0.000005 kg·cm−b × L3.17 for G. ogac and W = 0.000011 kg·cm−b × L2.91 for G. morhua suggested slightly positive and negative allometric growth, respectively. For G. morhua, growth curves, length–mass relationships, and maturity rates did not differ between fish collected during this and earlier studies. Differences in maturity schedules and growth may decrease resource competition and help facilitate coexistence of these species.

Demographic Variation between Colour Patterns in a Temperate Protogynous Hermaphrodite, the Ballan Wrasse Labrus bergylta

Fish populations are often treated as homogeneous units in typical fishery management, thereby tacitly ignoring potential intraspecific variation which can lead to imprecise management rules. However, intraspecific variation in life-history traits is widespread and related to a variety of factors. We investigated the comparative age-based demography of the two main colour patterns of Labrus bergylta (plain and spotted, which coexist in sympatry), a commercially valuable resource in the NE Atlantic. Individuals were aged based on otolith readings after validating the annual periodicity of annuli deposition. The relationships between the otolith weight and fish age and between otolith length and fish length were strong but differed between colour patterns. The fit of the growth models to the age and length data resulted in divergent growth curves between colour morphotypes and between sexes. Males and spotted individuals attained larger mean asymptotic sizes (Linf) than females and plain individuals, respectively, but converged to them more slowly (smaller k). Estimates of mortality based on catch curves from two independent datasets provided a global total mortality (Z) of 0.35 yr–1, although Z was larger in plain and female individuals. Overall, the results of this research have direct implications for management of L. bergylta and, as a precautionary measure, we recommend considering both colour patterns as two different management units.

Age, growth and reproduction of the lizard fish Saurida undosquamis from the Gulf of Suez, Red Sea, Egypt

The lizard fish Saurida undosquamis represents one of the most commercial fish in the Gulf of Suez. The growth and reproductive biology of the species were studied. The age was determined from otolith readings of the collected specimens from the Attaka Harbor through the period from September 2011 to April 2012. The results show that the life span of the sampled fish was seven years. The estimated von Bertalanffy growth equation was Lt=51.252 (1-e -0.131(t+1.45) ), the calculated lengthweight relationship was W= 0.004 L 3.107 . Seasonally distribution of gonado-somatic index (GSI) values showed that the main peak of GSI was in spring. The results of gonad development stages show that, Saurida undosquamis is a synchronous spawner. The size at which 50% of fishes are mature was 15.0 cm for males and 15.5 cm for females, which indicates that all individuals over one year of age were sexually mature. The results indicated that juvenile individuals are one of the targets of the fishery and the protection of the juveniles is probably the key factor for the sustainability of the resources.

Accounting for Age Uncertainty in Growth Modeling, the Case Study of Yellowfin Tuna (Thunnus albacares) of the Indian Ocean

Age estimates, typically determined by counting periodic growth increments in calcified structures of vertebrates, are the basis of population dynamics models used for managing exploited or threatened species. In fisheries research, the use of otolith growth rings as an indicator of fish age has increased considerably in recent decades. However, otolith readings include various sources of uncertainty. Current ageing methods, which converts an average count of rings into age, only provide periodic age estimates in which the range of uncertainty is fully ignored. In this study, we describe a hierarchical model for estimating individual ages from repeated otolith readings. The model was developed within a Bayesian framework to explicitly represent the sources of uncertainty associated with age estimation, to allow for individual variations and to include knowledge on parameters from expertise. The performance of the proposed model was examined through simulations, and then it was coupled to a two-stanza somatic growth model to evaluate the impact of the age estimation method on the age composition of commercial fisheries catches. We illustrate our approach using the saggital otoliths of yellowfin tuna of the Indian Ocean collected through large-scale mark-recapture experiments. The simulation performance suggested that the ageing error model was able to estimate the ageing biases and provide accurate age estimates, regardless of the age of the fish. Coupled with the growth model, this approach appeared suitable for modeling the growth of Indian Ocean yellowfin and is consistent with findings of previous studies. The simulations showed that the choice of the ageing method can strongly affect growth estimates with subsequent implications for age-structured data used as inputs for population models. Finally, our modeling approach revealed particularly useful to reflect uncertainty around age estimates into the process of growth estimation and it can be applied to any study relying on age estimation.

Biology of santer seabreamCheimerius nufar(Val. 1830) from the Arabian Sea off Oman

Summary The declining trend in the catches of santer seabream, Cheimerius nufar (Val. 1830), and sizable capture of immature and mature fish from the Arabian Sea at the coast of Oman have led to questioning the hypothesis that the fishery is in a state of decline due to inappropriate management. The lack of data on the basic biology and landing statistics for exploited fish species have made the management of fish resources in western Indian Ocean complicated. This paper presents data on the population biology of C. nufar in the Arabian Sea, with a view to contributing towards the development of management plans for a sustainable exploitation. A total of 4132 fish were obtained from the artisanal hand-line fishery catch at the Lakbi and Salalah landing sites from April 2005 to March 2007. Size distribution ranged from 16 to 64 cm [total length (TL)]. About 67.5% of the catch was composed of fish measuring <32 cm TL. Neither sex dominated the population nor were there significant differences in the monthly and annual sex-ratios tested by chi-squared. Spawning is from May to October. The declining trend in the hepatosomatic indice (HPI) values from September to February was almost identical to the declining trend in the gonado-somatic indice (GSI) values. The rise and fall in the condition factor (CF) values could not be related to the spawning period. Females and males mature at 31.9 and 33.7 cm TL, respectively. Otolith readings indicated the life span to be about 13 years. The instantaneous rate of natural mortality was estimated with M = 0.62 year−1.

Review of the literature on age and growth of grenadiers in the Mediterranean and new data on age of Trachyrincus scabrus (Macrouridae) in the Ionian Sea

This paper reviews the existing literature on the age and growth of grenadiers in the Mediterranean Sea and provides new data on ageing of Trachyrincus scabrus in the Northwestern Ionian Sea (Central Medi� terranean). Most studies have been carried out through otolith readings. Seasonal otolith formation also appears to be a general trend in grenadier fish in the Mediterranean even though it seems to be related to fluc� tuations in feeding and activity patterns. From examined literature age ranges of macrourids in the Mediter� ranean Sea varied from youngoftheyear (age 0) to a maximum ages of 23 years. There is a general agree� ment on the growth pattern of the species in the different geographic areas. T. scabrus was collected in the Northwestern Ionian Sea at depths between 400 and 1200 m during four seasonal trawl surveys. The mini� mum and maximum sizes of the whole sampled population were between 58 and 217 mm PAL. Otoliths were removed from 216 specimens. Backcalculation was performed and a maximum age of 10 years was deter� mined. The following von Bertalanffy growth parameters were estimated for the whole sampled population: L ∞ = 247.44 ± 8.39 mm PAL; k = 0.125 ± 0.010/year; t 0 = -1.921 ± 0.127.

Age determination of Atlantic halibut (Hippoglossus hippoglossus L.) along the coast of Norway: status and improvements

Abstract Karlson, S., Michalsen, K., and Folkvord, A. 2013. Age determination of Atlantic halibut (Hippoglossus hippoglossus L.) along the coast of Norway: status and improvements. – ICES Journal of Marine Science, 70:50–55. This study re-evaluates the current ageing methodology for the Atlantic halibut, Hippoglossus hippoglossus. The traditional method is through surface readings of otoliths, but, based on new experiments with different preparation treatments and techniques, a more accurate and cost-efficient procedure for the age determination of Atlantic halibut is proposed.

Age, growth and reproduction of the white seabreamDiplodus sargus sargus(Linneaus, 1758) off the eastern coast of Algeria

Summary The objective of this study was to determine the basic population-specific parameters necessary for fish stock assessment in the area and to compare these with data from other Mediterranean regions. White seabream Diplodus sargus sargus (n = 449) were caught along the Algerian coast between December 2005 and December 2006. Total length ranged from 12.2 to 34.6 cm, representing age classes between 0 and 10 years. Validity of the otolith readings for estimating age and growth was supported using the back-calculation method. The von Bertalanffy growth parameters for all fish were calculated as: TL = 36.3 cm, k = 0.154 year−1, t0 = −0.488 year. The growth performance index (φ) showed a relatively slow growth of the local population. The length-weight relationship showed an isometric growth (b = 2.98; r = 0.98). Subspecies Diplodus sargus sargus was characterized as being a proterandric hermaphrodite. Overall ratio of males to females was 1 : 1.4, with males predominant in the smaller size intervals and females in the larger ones. The reproductive season extended from January to May, with a March–April peak in spawning activity. Fifty per cent maturity of the tested cohort was reached at a total length of 20.2 cm for males and 20.0 cm for females.

Age, growth, and reproductive characteristics of dolphinfish Coryphaena hippurus in the waters off west Kyushu, northern East China Sea

The growth and reproductive characteristics of dolphinfish Coryphaena hippurus collected in the waters off western Kyushu from May 2008 to April 2011 were determined based on scale and otolith readings and gonad histological examinations, respectively. Based on annual increments in scales and daily increments in sagittal otoliths, the von Bertalanffy growth curves in male and females were determined as $$ FL_{t} = 1049[1 - \exp \{ - 0.835(t + 6.975 \times 10^{ - 14} )\} ] $$ and $$ FL_{t} = 938[1 - \exp \{ - 1.029(t + 6.975 \times 10^{ - 14} )\} ] $$ , respectively, where FL t is the mean fork length (mm) at age t. The spawning period was found to last from June to August for dolphinfish, based on an examination of the monthly changes in the gonadosomatic index and histological observations. Therefore, based on the relationship between the fork length and the developmental stage of the testes or ovaries, male and female dolphinfish were found to reach sexual maturity by the following spawning season after hatching in the northern East China Sea.

OtolithsversusScales: Evaluating the Most Suitable Structure for Ageing Largemouth Bass,Micropterus salmoides, in South Africa

The suitability of scales for ageing Micropterus salmoides was determined by comparing the precision of growth zone counts on scales with those obtained from sectioned sagittal otoliths from a sample of 496 fish collected from Wriggleswade and Mankazana Impoundments in the Eastern Cape, South Africa. Otoliths (1.4% rejected) were more readable than scales (41.7% and 7.5% rejected) for Wriggleswade and Mankazana Impoundments respectively. Otolith readings were more precise (average percentage error (APE) = 13.6%; coefficient of variation (CV) = 15.8%) than scales (APE = 18.0%; CV = 21.9%) for the total sample. Growth zone counts between structures were not symmetrically distributed around the agreed ages (otolith age = scale age) of the fish from Wriggleswade Impoundment (Bowker's test H2: χ2= 136, d.f. = 27, P < 0.05) and graphical comparison showed that scales tended to underestimate age, particularly for fish older than five years. Scales are therefore not suitable structures for ageing South African M....

Early life behavioural differences in wild caught and domesticated sea bass (Dicentrarchus labrax)

Behavioural studies comparing hatchery and wild-caught fish are useful to improve selection for aquaculture and restocking programmes. We examined swimming behaviour characteristics in wild captured and domesticated sea bass juveniles before and after eliciting a startle response at 8 different ages and always on naive individuals. We specifically investigated whether domestication impacts juvenile sea bass behaviour and whether the first months of captivity induce behavioural modifications in wild juveniles. An apparatus was designed to mimic a predator attack by presenting a sudden visual and mechanical stimuli simultaneously in 8 arenas where single individuals were placed and video recorded. The reactivity response was evaluated and different swimming variables including angular velocity, total distance travelled, mean velocity, immobility and distance from stimulus point were analysed from videos taken 5min before stimulus actuation, 5 and 15min after. Otolith readings showed that wild and domesticated juveniles were of similar age (∼55 days at the start of the experiment and ∼125 at the end of experiment). There were consistent behavioural differences (e.g. higher angular velocity and distance from stimulus point in wild fish) demonstrating that domestication reduces flight response behaviour. There were also similarities between both fish origins (similar response to stimulus actuation: decrease of total distance travelled and mean velocity, increase of angular velocity and immobility). A decrease over time in reactivity and variability in swimming responses among fish of both origins showed that captivity only does not fully explain wild fish behaviour changes and ontogenic modifications are likely interplaying.

Statistical distribution of age readings of known-age sablefish (Anoplopoma fimbria)

A mark-recapture experiment provided a collection of 172 known-age sablefish from Alaska waters. Otoliths from each fish were read by three readers. The readings have a positive bias among young fish and a negative bias among older fish. Among otoliths of the same age, some tended to give consistently high or low annulus counts, so that the variance of age readings at each true age was about half due to variance among otoliths and half due to variance among replicate readings of individual otoliths. The statistical distribution of age reading errors is well described by an asymmetrical two-sided geometric distribution with age-varying parameters. For comparison, the error distribution was estimated with naive methods that do not use the known ages and that assume the readings are unbiased. These estimated distributions do not match the actual error distributions very well, but they do a surprisingly good job of predicting the distribution of age readings from a stock assessment model's internal estimate of a true age composition. They also produce estimates of recruitment and biomass close to those obtained with the actual error distributions when used in the present sablefish stock assessment.