Opaque Zones Research Articles

Misadventure in Little Lon: augmented reality and the question of historical ’presence’

ABSTRACT True Crime Games is an award winning Melbourne-based game company headed by artist and designers Andy Yong and Emma Ramsay. This paper explores the first of their games–Misadventure in Little Lon – a case study that brings to light local histories that have been lost, elided or marginalized in traditional accounts of Melbourne and its development around the time of Federation. Drawing upon the phenomenology of Vivian Sobchack and the microhistory of Carlo Ginzburg, the article argues that implementing AR in historically driven game contexts allows for an improved grasp of the microhistory of a specific area. It does this by bringing the agency to the ‘ghost in the machine’ –characters in the AR game who enable players to resituate themselves and reorientate themselves to city streets through game play. This method of resituating historical sources so that players discover ‘opaque zones’, new ways of viewing located history that encourages reading ‘against the grain’ , is coincidental with important archaeological work that has been undertaken in the Little Lon district of Melbourne. Misadventure in Little Lon therefore joins a larger effort to reveal, circulate and celebrate the communities, individuals, and stories that traditional histories have ignored.

The Generation of Equal-Intensity and Multi-Focus Optical Vortices by a Composite Spiral Zone Plate

We propose a new vortex lens for producing multiple focused coaxial vortices with approximately equal intensities along the optical axis, termed equal-intensity multi-focus composite spiral zone plates (EMCSZPs). In this typical methodology, two concentric conventional spiral zone plates (SZPs) of different focal lengths were composited together and the alternate transparent and opaque zones were arranged with specific m-bonacci sequence. Based on the Fresnel–Kirchhoff diffraction theory, the focusing properties of the EMCSZPs were calculated in detail and the corresponding demonstration experiment was been carried out to verify our proposal. The investigations indicate that the EMCSZPs indeed exhibit superior performance, which accords well with our physical design. In addition, the topological charges (TCs) of the multi-focus vortices can be flexibly selected and controlled by optimizing the parameters of the zone plates. These findings which were demonstrated by the performed experiment may open new avenues towards improving the performance of biomedical imaging, quantum computation and optical manipulation.

Puzzling parrotfishes: Radiocarbon age validation and updated longevity estimates for western Atlantic species in support of sustainable fisheries management

For management efforts to succeed in Caribbean fisheries, local fishers must support and be willing to comply with fishing regulations. This is more likely when fishers are included in a stock assessment process that utilizes robust scientific evidence, collected in collaboration with fishers, to evaluate the health of fish stocks. Caribbean parrotfishes are important contributors to coral reef ecosystem health while also contributing to local fisheries. Scientifically robust stock assessments require regional species-specific information on age-based key life history parameters, derived from fish age estimates. Evaluation of the accuracy of age estimation methods for fish species is a critical initial step in managing species for long-term sustainable harvest. The current study resulted from a collaborative research program between fish biologists and local fishers investigating age, growth, and reproductive biology of the seven parrotfish species landed in U.S. Caribbean fisheries; specifically, we validated age estimation for stoplight parrotfish Sparisoma viride and queen parrotfish Scarus vetula. This is the first study to directly validate age estimation for any parrotfish species through analysis of Δ14C from eye lens cores. Our age estimation validation results show that enumeration of opaque zones from thin sections of sagittal otoliths for a Sparisoma and a Scarus species provides accurate age estimates. The oldest stoplight parrotfish and queen parrotfish in the Δ14C age estimation validation series were 14 y and 16 y; while the oldest stoplight parrotfish and queen parrotfish we aged to-date using the Δ14C validated age estimation method were 20 y and 21 y, respectively. Fish longevity (maximum age attained/life span) is a key life history parameter used for estimation of natural mortality, survivorship, and lifetime reproductive output. Past reviews on parrotfishes from the Pacific and Atlantic concluded that most Caribbean/western Atlantic parrotfish species are relatively short-lived with estimated maximum ages ranging from 3–9 y. However, information from our collaborative research in the U.S. Caribbean combined with recently published age estimates for Brazilian parrotfish species indicate that many western Atlantic parrotfishes are relatively long-lived with several species attaining maximum ages in excess of 20 y.

Improved filters for angular filter refractometry

Angular filter refractometry is an optical diagnostic that measures the absolute contours of a line-integrated density gradient by placing a filter with alternating opaque and transparent zones in the focal plane of a probe beam, which produce corresponding alternating light and dark regions in the image plane. Identifying transitions between these regions with specific zones on the angular filter (AF) allows the line-integrated density to be determined, but the sign of the density gradient at each transition is degenerate and must be broken using other information about the object plasma. Additional features from diffraction in the filter plane often complicate data analysis. In this paper, we present an improved AF design that uses a stochastic pixel pattern with a sinusoidal radial profile to minimize unwanted diffraction effects in the image caused by the sharp edges of the filter bands. We also present a technique in which a pair of AFs with different patterns on two branches of the same probe beam can be used to break the density gradient degeneracy. Both techniques are demonstrated using a synthetic diagnostic and data collected on the OMEGA EP (extended performance) laser.

Towards plastics circular economy: sustainability assessment of mono-material design for recycling

Plastic pollution is a pressing global concern due to its severe environmental impacts. Thus, the adoption of sustainable practices in product design and end-of-life management has become paramount towards a plastic's circular economy. This study delves into the transformative potential of design for recycling by examining the replacement of a multi-material skillet lid with a mono-material plastic injected solution featuring opaque and translucent zones. Through a life cycle cost and life cycle assessment, this research evaluates and compares the environmental and economic implications of both solutions. The analysis encompasses crucial life cycle phases, including raw material extraction and transformation, manufacturing, and end-of-life. The results highlight the considerable benefits of the mono-material design approach, particularly enhanced recyclability and a reduction of 31.39% and 10.97% of the total environmental and economic impact, respectively. Additionally, the environmental impact further reduces when considering a potential waste management scenario for 2035 defined based on European directives. This research not only contributes to the field of life cycle engineering by emphasizing the economic and environmental advantages of the mono-material design for recycling in a particular application but also fosters informed sustainable decision-making within the plastics industry. Furthermore, this study underscores the utmost importance of adopting design for recycling to foster a plastics circular economy.

Antimicrobial and quorum sensing inhibitory activity of epiphytic bacteria isolated from the red alga Halymenia durvillei.

Halymenia durvillei is a red alga that is commonly utilized in the Philippines as food and as a source of high-value natural products for industrial applications. However, there are no studies regarding the microbial community associated with H. durvillei and its potential applications. This study aimed to isolate and identify the epiphytic bacteria of H. durvillei and determine their antimicrobial and quorum sensing inhibitory (QSI) effects. The thalli of H. durvillei were collected at the shores of Santa Fe, Bantayan, Cebu, Philippines. Bacterial isolates were identified using 16S rRNA, and their ethyl acetate (EtOAc) extracts were subjected to antimicrobial susceptibility tests against representative species of yeast and Gram-negative and Gram-positive bacteria. Their QSI activity against Chromobacterium violaceum was also determined. Fourteen distinct bacterial colonies belonging to four genera, namely Alteromonas (3), Bacillus (5), Oceanobacillus (1) and Vibrio (5), were successfully isolated and identified. All 14 bacterial isolates exhibited antibacterial effects. EPB9, identified as Bacillus safensis , consistently showed the strongest inhibition against Escherichia coli , Staphylococcus aureus and Staphylococcus epidermidis , with minimum inhibitory concentrations (MICs) ranging from 0.0625 to 1.0 mg ml-1. In contrast, all 14 isolates showed weak antifungal effects. Both B. safensis (EPB9) and Bacillus australimaris (EPB15) exhibited QSI effects at 100 mg ml-1, showing opaque zones of 3.1±0.9 and 3.8±0.4 mm, respectively. This study is the first to isolate and identify the distinct microbial epiphytic bacterial community of H. durvillei and its potential as an abundant resource for new antibacterial and QSI bioactives.

A capacitive method and experiment for measurement of sedimentation of magnetorheological fluid

Sedimentation is one of the key issues in the practical engineering applications of magnetorheological fluids (MRFs). Testing and evaluation of the suspension stability of MRFs should be a prerequisite procedure before their applications. There are a few reported methods of measurement of sedimentation of MRFs. The opaque zone below the mudline, especially the sediment zone at the bottom in the MRF column, is the true key factor that affects the applications of MRF due to the possible irreversibility caused by the caking of the sediment zone. This study proposes a novel capacitive method on the basis of the change in dielectric constant resulting from the change in concentration of the magnetic metal particles of MRF upon sedimentation. First, an analytic model was established to present a positive correlation between the dielectric constant and volume fraction of particles throughout the entire MRF column and the theoretical expression of the dielectric constant of MRF in a test tube was obtained. Second, a capacitive sensor and the relevant experimental set-up were designed and fabricated. Especially, the effect of eccentricity error of the capacitor sensor structure on the measurement was analyzed. Then, a sedimentation experiment for prepared MRF samples was carried out, and the testing results were discussed and verified by a visual mudline observation of the supernatant zone, indicating the feasibility of testing and evaluating the suspension stability of MRF by the capacitive method.

Birefringence analysis of collagen supraorganization in cat corneas with tropical keratopathy.

To evaluate the birefringent properties of the cornea and examine the supraorganizational aspects of collagen fibers in cats with tropical keratopathy. In this study, 10-micrometer-thick sections of corneal tissue from cats with tropical keratopathy were examined, both in the opaque and transparent areas of the anterior stroma. Control samples were obtained from healthy cat corneas. Polarized light microscopy was employed to evaluate the birefringent properties using two distinct methods. The first method involved measuring the optical retardation associated with corneal birefringence, while the second method assessed the alignment/waviness of the birefringent collagen fibers. Differences were significant when p < .05. Tropical keratopathy resulted in a significant rise (p < .05) in optical retardation in both opaque and transparent regions of the cat cornea. In the anterior stroma, both the opaque zones and transparent tissue exhibited a higher degree of collagen fiber packing than the control corneas. However, no significant differences (p > .05) in alignment were observed between the transparent tissue of the diseased cornea and the healthy corneas. Supraorganizational changes in collagen fiber packing are not restricted to lesion zones in cat corneas affected by tropical keratopathy. Such alterations also occur in the corneal tissue of the anterior stroma adjoining the lesions. Therefore, it is plausible that the transparent tissue of the anterior stroma in corneas affected by the disease may have functional abnormalities, despite its macroscopic healthy appearance. Additional investigations are required to clarify the implications of these potential defects and their conceivable contribution to tropical keratopathy.

Eye lens-derived Δ14C signatures validate extreme longevity in the deepwater scorpaenid blackbelly rosefish (Helicolenus dactylopterus)

Many members of the scorpaenid subfamily: Sebastinae (rockfishes and their relatives) exhibit slow growth and extreme longevity (> 100 y), thus are estimated to be vulnerable to overfishing. Blackbelly rosefish (Helicolenus dactylopterus) is a deepwater sebastine whose longevity estimates range widely, possibly owing to different regional levels of fisheries exploitation across its Atlantic Ocean range. However, age estimation has not been validated for this species and ageing for sebastines in general is uncertain. We performed age validation of northern Gulf of Mexico blackbelly rosefish via an application of the bomb radiocarbon chronometer which utilized eye lens cores instead of more traditional otolith cores as the source of birth year Δ14C signatures. The correspondence of eye lens core Δ14C with a regional reference series was tested with a novel Bayesian spline analysis, which revealed otolith opaque zone counts provide accurate age estimates. Maximum observed longevity was 90 y, with 17.5% of individuals aged to be > 50 y. Bayesian growth analysis, with estimated length-at-birth included as a prior, revealed blackbelly rosefish exhibit extremely slow growth (k = 0.08 y−1). Study results have important implications for the management of blackbelly rosefish stocks, as extreme longevity and slow growth imply low resilience to fishing pressure.

Age Determination of the Azov Anchovy Engraulis encrasicolus maeoticus (Engraulidae) Based on the Otolith Image Analysis

To specify the age determination of the Azov anchovy Engraulis encrasicolus maeoticus, the length of otoliths of the age 0+ fish and the radii of annual rings in the otoliths of individuals of different age groups have been analysed. The otoliths of 380 fish caught in the Sea of Azov in October–November 2018 and off the northwestern coast of the Caucasus in February 2019 have been analyzed. The ImageJ software has been used for measuring the maximum otolith length and plotting the reflected light intensity profiles along the length of the otolith transect. In the fingerlings (0+) with an average total length of 70.9 ± 6.7 mm, in October–November, the otolith radius averaged 0.95 ± 0.08 mm, while in February, with an average 66.6 ± 10.6 mm, it was 0.86 ± 0.15 mm. In the smallest fish (48–55 mm), the distance from the core of the otolith to the edge of the white opaque zone varied from 0.54 to 0.72 mm (on average, 0.63 ± 0.04 mm). According to the averaged data, the radii to the center of the dark hyaline zone of otoliths for different age groups of anchovy are: R1, 0.94 ± 0.09; R2, 1.23 ± 0.08; and R3, 1.40 ± 0.07 mm. The present study is aimed at developing automatic methods for determining the age of fish from light intensity profile peaks on otolith images.

Highly variable length-at-age in vermilion snapper (Rhomboplites aurorubens) validated via Bayesian analysis of bomb radiocarbon

Vermilion snapper (Rhomboplites aurorubens) has been reported to exhibit highly variable length-at-age, while age estimates derived from otoliths are often imprecise (i.e., average percent error ≥ 8.0%). This has led to questions whether the observed variability in length-at-age is due to variability in growth or ageing error. The current study was conducted to address this by testing the accuracy of otolith-derived age estimates via age validation. Age was estimated by enumerating opaque zones in otolith thin sections observed under a dissecting microscope with transmitted light. Then, age validation was performed by applying the bomb radiocarbon (14C) chronometer, where vermilion snapper birth year Δ14C values were derived from eye lens cores for contemporary samples and otolith cores for archived samples. Otolith-derived age estimates were found to be accurate, with the maximum validated age being 28 years. Results of Bayesian regression modeling indicated there was no significant relationship between eye lens Δ14C variance and fish length (p = 0.93). Further Bayesian regression modeling demonstrated vermilion snapper do not exhibit sexually dimorphic growth (p = 0.91). Study results have important implications for vermilion snapper assessment and management, as variable growth reduces the accuracy in assigning age based on length. Moreover, the approach reported here could be applied to test the accuracy of highly variable length-at-age estimates in other marine fishes.

Age, Growth and Reproductive Cycle of the Jack Mackerel &lt;i&gt;Trachurus japonicus&lt;/i&gt; in the Southwestern Sea of Japan

The growth and reproductive cycle of the jack mackerel (Trachurus japonicus) that were caught in the southwestern Sea of Japan during 2016-2017 were examined based on otolith annuli and gonad histology. Translucent and opaque zones on transverse sections on otoliths were identified and opaque rings were counted. The von Bertalanffy growth curve was expressed as follows: FLt = 445{1 − exp (−0.149 (t + 1.74))} (0.250 < t < 7.67), where FLt is the fork length (mm) at age t. The estimated body length at age t in the growth model was smaller than that of jack mackerel in the East China Sea. The spawning period was evaluated from May to September based on the monthly changes in the gonadosomatic index and histological observations. The spawning period starts later than in the East China Sea, but the minimum size at first maturity was similar to that of the jack mackerel in the East China Sea. The information generated in this research can contribute to the sustainable management of the species in the Sea of Japan.

The age estimation of an extremely old Silver Drummer Kyphosus sydneyanus (Günther 1886) from southern Western Australia

Kyphosids are conspicuous members of temperate and tropical reef fish communities. Some species contribute to commercial and recreational fisheries but are vulnerable to capture in large numbers due to their schooling behaviour and site fidelity. Previous ageing studies of kyphosids have determined that some species are long-lived, with maximum ages &gt;40 years, which is a trait often associated with low natural mortality rates. Kyphosus sydneyanus is one of the largest kyphosids and has historically been caught in large numbers as a bycatch species in the demersal gillnet fishery in southern Western Australia. A large K. sydneyanus specimen was collected from that fishery in March 2021. A count of the growth (opaque) zones in the sectioned otoliths were used to determine that the age of this individual was 93 years, more than double the previous maximum age of a Kyphosus species and the longest-lived coastal species in southern Australia.

TROIS FEMMES PUISSANTES DE MARIE NDIAYE : LA GRÂCE DE LA RÉSILIENCETHREE STRONG WOMEN, BY MARIE NDIAYE: THE GRACE OF RESILIENCE

By taking "three strong women" as heroines, Marie NDiaye brings out the paradoxical strength of characters caught up in the destructive mechanisms of stories with uncertain endings. We perceive in these women the models of a resilience whose restorative grace is inscribed the intersubjective relations of which they are the hearths. This hypothesis invites us to observe how these relationships, threatened by an alienating confusion, get out of it, but also to locate the opaque zones of the narratives which designate the fragility of the process. Resilience could be the faculty of escaping from the dead life, that which makes them know the reflex of the withdrawal on oneself for a preservation without other goal than to flee the suffering. By refusing to collude with the deadly exercise of violence, the protagonists restore in themselves the dignity of the human person, concentrated in the faculty of answering to oneself and to the other. As for the reader, he is provoked by the ambivalences of the narratives to a hermeneutic choice reflecting the existential choice of the characters: the question is posed to him of the confidence to grant – or to refuse – to an original goodness of the human being and of life.

Age, growth, mortality, and yield‐per‐recruit of red spotted grouper Epinephelus akaara in the central Seto Inland Sea, Japan

The red spotted grouper Epinephelus akaara is important for commercial and recreational fishing in the coastal waters of East Asia. In Japan, approximately 850,000 juveniles are released annually for stock enhancement, and the catch in several release areas has increased. Life-history traits are important for fisheries management and stocking programmers. The age, growth, and mortality of fish collected from the central Seto Inland Sea from June 2012 to November 2014 were examined using 1022 sectioned sagittal otoliths, and the yield-per-recruit (YPR) was calculated. The opaque zones in the otoliths were confirmed to be annuli, formed mainly between June and July. The oldest fish was 16 years old. The percentage of those between two and five years was approximately 80%, whereas that of more than ten years was only 0.6%. The five parameters von Bertalanffy growth equation was calculated as: TLt = 390 {1 − 0.23[(t − 3.78)2 + 1]−1}{1 − exp [−0.34 (t + 0.28)]}, where TLt is the total length (mm) at t (year). The total, natural, and fishing mortality rates were calculated to be 0.80, 0.24–0.31 and 0.49–0.56 year−1, respectively. The YPR analysis indicated that the current fishing mortality rate (Fcurrent) was higher than F0.1 and Fmax, and that increasing the age at first capture is more effective than decreasing F for increasing the YPR. These results provide important information for fisheries management and the stocking of E. akaara.

Age and Growth Estimations of Decapterus Kurroides Using Otolith in the Waters of Eastern Taiwan

Aims: Redtail scad (Decapterus kurroides Bleeker, 1855) was once an economically important Carangidae species in Taiwan. This study determined age using otolith increments and re-evaluated the parameters of growth equations for this species.&#x0D; Place and Duration of Study: Fish samples were collected monthly off the coast of Taitung, eastern Taiwan.&#x0D; Methodology: A total of 367 specimens were observed in this study. To determine fish age, otolith age determination method was used. The largest and smallest otolith rings were seven and two, and their corresponding means of fork length (FL) were 29.2 and 12.2 cm, respectively.&#x0D; Results: Most samples had six otolith rings with a mean FL of 27.2 cm. The von Bertalanffy growth equation is FLt = 30.44 (1 – e −0.52 (t - 1.50)) for females and FLt = 32.45 (1 – e −0.39 (t – 1.18)) for males. The otolith opaque zone annually formed from September to October. The relationship of body weight (BW) and Fork Length (FL) differed significantly between genders: BW = 0.334 × 10-2 FL3.463 for females and BW = 0.469 × 10-2 FL3.349 for males. The sex ratio was 0.56 over a whole year and varied among the age groups.&#x0D; Conclusion: This study using the otolith method revises the estimations of age and growth parameters for the D. kurroides, which would be beneficial to manage and recover this species stock in the waters of Taiwan.

Age-based life history of Pacific longnose parrotfish Hipposcarus longiceps from New Caledonia.

The Pacific longnose parrotfish, Hipposcarus longiceps, is a medium‐ to large‐bodied scarine labrid that is among the most commonly harvested species in mixed reef fisheries across the Indo‐Pacific. Despite its ecological and fisheries importance, assessments of stock status and development of appropriate management strategies for the species have been limited by an absence of biological information. To date, the only detailed studies of the biology of H. longiceps have occurred in tropical regions. This study examined the biology of H. longiceps in southern New Caledonia, towards the southernmost extent of the species' distribution. In addition, resulting estimates of longevity and asymptotic length were compared against those derived for the species elsewhere in the Pacific, and regional patterns in these parameters were explored for correlation with sea surface temperature (SST). A total of 212 H. longiceps were collected from commercial fishers or fish markets between September 2015 and March 2017. Sampled individuals ranged from 28.2 cm fork length (L F) to 57.3 cm L F, and from 424 g to 3773 g. Examination of sectioned otoliths showed a clear pattern in increment formation, with opaque zones forming annually in most individuals between July and August (i.e., austral winter). Estimated longevities were similar between sexes, at ~18 years for females and ~19 years for males. These estimates extend the reported longevity of H. longiceps by at least 5 years. Despite this species being a diandric protogynous hermaphrodite, sex ratios were only slightly female biased, with 1 female:0.6 males. Primary males (i.e., those individuals that are male at first sexual maturity) constituted 30% of all sampled individuals and 79% of all males. A clearly defined, yet protracted, spawning season was evident, with peak spawning occurring from December–February, extending from November to April in some individuals. The estimated median length (L 50) and age (A 50) at female maturity were 38.9 cm L F and 5.7 years, respectively, while the estimated length at which females changed sex to secondary males was 52.5 cm L F. Reported longevity and asymptotic length were found to exhibit considerable regional variation, and both were negatively associated with SST. The results highlight the importance of geographically disparate studies into the species' biology, inform future assessments for the species, provide key baseline information for comparative work and improve understanding of spatial patterns of the life history of parrotfish species.

Preliminary age-based life history characteristics of the dogtooth tuna, Gymnosarda unicolor (Ruppell, 1838), in the southwest Pacific Ocean

Dogtooth tuna, Gymnosarda unicolor were sampled off the east coast of Australia (southwest Pacific Ocean) from 2007 to 2012. Ages were determined by examining thin transverse sections of their sagittal otoliths and were based on counts of alternating opaque and translucent zones (annual growth increments). Growth was rapid during the first year of life, after which growth in length was much reduced. Parameters of the constrained von Bertalanffy growth function (fork length-at-age) were L∞ = 1164.77 (mm, FL) and K = 0.44 year−1. Preliminary estimates of longevity indicate a maximum observed age of at least 20 years. There was a high degree of variation in the observed length and age of sexual maturity for G. unicolor. Despite this variation, the size at 50% maturity for female G. unicolor estimated in this study was 713 mm FL (<2 years of age). The diet of G. unicolor is very broad and covers a range of fish species. The life history characteristics of G. unicolor overall, indicate that this species may be somewhat resilient to fishing. However, reports of localised depletions, in association with heavy targeting by sports fishers, low effective population sizes and patchy recruitment indicate that this species is particularly vulnerable to overfishing.

Demographics of Scomberomorus commerson in the Central Taiwan Strait

The narrow-barred Spanish mackerel Scomberomorus commerson is an economically essential species; however, few studies have investigated its demographic structure in the northwestern Pacific, which includes Taiwan’s waters. This study examined the growth parameters, age composition, mortality, and sex ratio of S. commerson catches by examining sagittal otoliths and other biological data collected in a 3-year project from June 2018 to June 2021. The transverse sections of sagittal otoliths exhibited alternating translucent and opaque zones, in annual cycles, and this observation was validated by otolith edge analysis. Opaque zones began to form in October; the growth peaked in December and lasted until March. Growth parameters were estimated for female (L∞ = 144.1 cm fork length [FL], k = 0.39 y−1, to = −0.85 y) and male (L∞ = 136.0 cm FL, k = 0.32 y−1, to = −1.49 y) specimens. The maximum recorded FL, body weight, and age were 159.0 cm, 27 kg, and 9.2 y for female and 135.0 cm, 17.8 kg, and 7.2 y for male specimens. Rapid growth was observed for both sexes, with FL reaching 66.8 ± 14.2 cm in female specimens and 70.1 ± 11.0 cm in male specimens during the first year of life. An age–length key based on the direct otolith aging and FL dataset (N = 646) was used to estimate the age composition of 3-year catches measured at landing (N = 16,133). The results verified that the S. commerson currently caught in the central Taiwan Strait are mainly young fish aged 1+ to 2+ y. The estimated fishing mortality (0.27 y−1) and exploitation rate (0.30) suggested that overfishing was not occurring in this stock. The findings of this study have helped clarify the population dynamics of the S. commerson in the Taiwan Strait, and the biological parameters reported herein can aid the management and conservation to ensure the sustainability of this species in this region.

Age, Growth and Mortality of Atlantic chub mackerel, Scomber colias Gmelin, 1789 in the Mediterranean Waters of Morocco

This work is a study of growth aspects and mortality of the Atlantic chub mackerel, Scomber colia, from the Mediterranean Moroccan coast. A total of 845 specimens were collected from commercial catches in M’diq Bay, whose total length ranged between 16.4 and 35.9 cm. The length-weight relationship was W = 0.0019 TL 3.4527 (r = 0.97) for the whole population. The Atlantic chub mackerel displays positive allometric growth. Otolith edge analysis indicated that opaque zones were formed between April and September and translucent ones during the remaining months of the year. The oldest individuals in the sample were 5 years old for both sexes. Von Bertalanffy growth parameters estimated for this species were: L ∞ = 37.30 cm, k = 0.26 year -1 and t 0 = - 2.19 year. The difference in growth between sexes is not significant. The estimated natural mortality was 0.59 per year.