Growth Band Counts Research Articles

Re-estimation of juvenile's Isurus oxyrinchus growth in the Mexican Pacific through a multi-model inference approach and verification of growth band periodicity.

An update of the age and growth for juveniles of shortfin mako shark (Isurus oxyrinchus) from the Mexican Pacific is presented, based on the analysis of growth band counts from dorsal vertebrae of 198 individuals (110 females 74-231 cm of total length, TL, and 88 males 72-231 cm TL) caught during 2008-2018. New available information on vertebral growth band periodicity (biannual deposition in juveniles) and the convenience of using vertebrae form the dorsal region over cervical region to count growth bands, as well as a multi-model approach, were used. The von Bertalanffy growth model (VB), Gompertz, logistic and the two parameters of VB were fitted to the length-at-age. Only the ages ≤ 6 years were used for the fitting of the models and their performance was compared with the small-sample bias-corrected form of Akaike information criterion (AICc), their differences and weights . Following a multi-model inference approach, the model averaged asymptotic length , length-at-age 0 and their unconditional standard error , were estimated for each sex scenario using the 3-parameters version of each model.The precision of growth band counts was acceptable for the different methods used and by two different readers. The Centrum edge analysis (CEA) and marginal increment analysis (MIA) did not support the hypothesis of biannual band pair formation for juveniles, likewise for adults the periodicity could not be verified due to the low sample of large animals. Still, age was estimated assuming the formation of two pairs of growth bands per year during the first five years of age and one pair of bands per year afterwards considering direct validation information. The estimated ages ranged from 0-14 for females and 0-6 for males. The Kimura's likelihood ratio test showed no differences in the growth curves of juveniles by sex (P>0.05). According to the AICc, the 2-VB better fitted the length-at-age data for sex combined (Linf = 386.4 cm, k = 0.12 yr-1 , L0 = 70 cm). The model averaged and were 378.3 cm ( = 64.5) and 69.5 cm = 6.3) respectively. The growth parameters determined for juveniles of I. oxyrinchus are similar with those estimated in other regions, showing relatively fast growth rate as previously reported, medium longevity in comparison to other shark species and natural mortality close to those reported in the last stock assessment for the North Pacific Ocean. These life-history parameters should be considered to evaluate the population in the region to develop better fishery management and conservation measures.

A rapid and precise method of establishing age model for coral skeletal radiocarbon to study surface oceanography using coupled X-ray photos and ICP-AES measurement

A high-precision age model is a critical component of coral skeletology. Here we propose a rapid and precise method, coupling coral growth band counting based on X-ray photo and Sr/Ca measurement using inductively coupled plasma atomic emission spectroscopy (ICP-AES) to establish the high-resolution age model. We measured Sr/Ca ratio of the Kikai coral, southeast of Japan using ICP-AES and compared the results with a previous study using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Sr/Ca values in 1947–2009 obtained by ICP-AES measurement were well correlated with Sr/Ca values obtained by LA-ICP-MS. Therefore, our study once again proved the feasibility of establishing age models by using Sr/Ca of temperate corals, and a smaller sample amount was applied for ICP-AES measurement to obtain higher-resolution data. The age model established by both Sr/Ca ratio and X-ray photo of corals will be contributed to the high-resolution coral skeletology, such as reconstructing high-resolution paleoceanography using coral skeletal radiocarbon.

Preliminary investigation of age analysis in crustacean species from the Indian coast, using growth bands

Abstract The present study represents the first information on direct age determination based on band counts in the mesocardiac ossicle (gastric mill) and eyestalk, in Aristeus alcocki, Penaeus monodon, Penaeus indicus, Panulirus homarus, and Portunus sanguinolentus from India. The determination of growth bands is important in understanding the accurate age of a specimen for the effective management strategies for stock sustainability of the natural resource. Longitudinal sections of the eyestalk and meso-cardiac ossicle of the gastric mill were observed for growth band counts in all species except for P. homarus, where the growth bands were recorded only in the ossicle. Growth bands count five in females and four in males of A. alcocki, respectively. In the case of inshore prawns, two growth bands were observed in P. monodon and one growth band in P. indicus, five growth bands in P. homarus, and three in P. sanguinolentus.

Life history parameters of the crocodile shark, Pseudocarcharias kamoharai, in the tropical Atlantic Ocean

AbstractThe crocodile shark (Pseudocarcharias kamoharai) is a small lamniform shark that is occasionally by-caught in pelagic longline fisheries targeting tunas and swordfish. Due to its biological features, this species is highly vulnerable to overexploitation. However, at present, the crocodile shark is not evaluated for its stock status by any of the Regional Fisheries Management Organizations. In this study, the biology of 391 specimens (220 females and 171 males), ranging from 44.2 cm to 101.5 cm fork length (FL), collected from the tropical region of the Atlantic Ocean, was examined. Ages were assigned from growth band counts in vertebral sections, with the modified von Bertalanffy growth model, using a fixed size at birth (L0) at 32 cm FL, producing the best fit: Linf = 105.6 cm FL and k = 0.14 y−1 for females; Linf = 94.6 cm FL and k = 0.18 y−1 for males. Maturity ogives were fitted to both length- and age-based data. The size (L50) and age (A50) at 50% maturity was estimated at 67.2 cm FL (5 years) and 81.6 cm FL (8 years) for males and females, respectively. Mean uterine fecundity was 3.7 pups per litter with a 1:1 embryonic sex ratio. Further work is needed regarding crocodile shark life-history characteristics, especially because there are no age validation studies of the band pair deposition periodicity. However, the parameters now presented can contribute to future evaluations of this species, which is especially important given its potentially vulnerable life history.

A historical record of the impact of nuclear activities based on 129I in coral cores in Baler, Philippines: An update

In a previous study in 2016, we presented how 129I in coral cores from the east (Baler) and west (Parola) sides of the Philippines recorded the impacts of human nuclear activities, including nuclear weapons testing, nuclear fuel reprocessing, and nuclear accidents. However, the 2016 Baler dataset only had a two-year time resolution and a crude age model based on growth band counting. Here we present a new 2020 Baler 129I/127I atomic ratio dataset that features at least annual time resolution and a more accurate age model constructed using 3D X-ray Computed Tomography. Results show that the bomb peaks in Baler primarily came from the Pacific Proving Grounds or PPG with a time lag of about 1.8 years (or more specifically, between 1.3 and 2.4 years). Moreover, a review of the Parola dataset shows that PPG signals may have been transported to Parola in the West Philippine Sea via two pathways: the northward and southward bifurcations of the North Equatorial Current, reaching Parola about 4.5 and 8.5 years after detonation, respectively. Moreover, a prominent peak in the year 2014.7 in Baler possibly came from the 2011 Fukushima Accident, transported by the Kuroshio Recirculation Gyre and the North Pacific Mode Waters with a 3.5-year time lag. This study contributes to the understanding of the impact and transport of human-made radionuclides to the Philippines and the relevant oceanographic processes in the Western Equatorial Pacific region.

Periodicity of the growth-band formation in vertebrae of juvenile scalloped hammerhead shark Sphyrna lewini from the Mexican Pacific Ocean.

The age of 296 juvenile scalloped hammerhead sharks Sphyrna lewini caught by several fisheries in the Mexican Pacific Ocean from March 2007 to September 2017 were estimated from growth band counts in thin-sectioned vertebrae. Marginal-increment analysis (MIA) and centrum-edge analysis (CEA) were used to verify the periodicity of formation of the growth bands, whereas elemental profiles obtained from LA-ICP-MS transect scans in vertebrae of 15 juveniles were used as an alternative approach to verify the age of the species for the first time. Age estimates ranged from 0 to 10+ years (42-158.7 cm total length; LT ). The index of average percentage error (IAPE 3.6%), CV (5.2%), bias plots and Bowker's tests of symmetry showed precise and low-biased age estimation. Both MIA and CEA indicated that in the vertebrae of juveniles of S. lewini a single translucent growth band was formed during winter (November-March) and an opaque band during summer (July-September), a period of faster growth, apparently correlated with a higher sea surface temperature. Peaks in vertebral P and Mn content spatially corresponded with the annual banding pattern in most of the samples, displaying 1.19 and 0.88 peaks per opaque band, respectively, which closely matched the annual deposition rate observed in this study. Although the periodicity of growth band formation needs to be verified for all sizes and ages representing the population of the species in the region, this demonstration of the annual formation of the growth bands in the vertebrae of juveniles should lead to a re-estimation of the growth parameters and productivity of the population to ensure that it is harvested at sustainable levels.

Sclerochronological basis for growth band counting: A reliable technique for life-span determination of Crassostrea virginica from the mid-Atlantic United States

Widely used sclerochronological methods for biologically aging fossilized oysters, such as δ18O and Mg/Ca analyses, are costly, time-consuming, and not always practical for population-level analyses. A method that relies on visible morphological features, such as growth bands, to determine the lifespan of Crassostrea virginica would provide a cost-efficient and reliable alternative. Previous studies have assessed whether counting growth bands can be used to biologically age C. virginica from the southeastern U.S. but have produced conflicting results. For this study, we conducted subseasonal sclerochronological analyses on Pleistocene C. virginica from the mid-Atlantic U.S. to determine whether growth band counting could be used to reliably measure oyster lifespan.A highly significant correlation exists between δ18O peaks and major (annual) grey growth bands in these oysters. Major grey and white growth bands differ significantly with respect to δ18O values. These data suggest that, for C. virginica from the Pleistocene of the mid-Atlantic U.S., major grey growth bands are accreted during the colder months of the year and can be used as annual markers to biologically age specimens. The results presented here differ from previous studies that reported no link between growth bands and δ18O values, possibly because the latter focused on lower latitude regions with different seasonal temperature regimes and sampled only the early stages of growth, which contain morphological features that could be confused with major growth bands. While growth band counting of oysters shows promise as a method for biologically aging oysters that experience high seasonal temperature variability, future studies are needed to assess its applicability over a broader geographic range.

Age determination in crustaceans: a review

Crustaceans, a commercially important class of arthropods in fisheries and aquaculture, represent a major worldwide food component for human consumption. Recently, growing interest regarding the ageing and longevity of crustaceans has led to advancement in the field of age determination methods, including the use of lipofuscin and growth band counts, veering from the classic approach of size modal analysis. This manuscript provides a comprehensive overview of literature published between 1990 and 2016 on popular age determination methods (length–frequency analysis, lipofuscin analysis, and growth band counts) applied to five main crustacean taxa (shrimp, krill, crayfish, crabs and lobsters). Of the 231 studies examined, 83% used length–frequency analysis, 13% used lipofuscin and 4% used growth bands. Validation, a necessary step to support results provided by age estimation studies, was included in 71% and 56% of the reviewed published papers that used lipofuscin and growth band counts, respectively. So far, growth band counts have been the only direct method of determining crustacean age. This method requires validation in all species before routine application in stock assessment and/or conservation purposes.

Bomb radiocarbon analyses validate and inform age determination of longnose skate (Raja rhina) and big skate (Beringraja binoculata) in the north Pacific Ocean

Age and growth estimates based on growth band counts of sectioned vertebrae have been produced for longnose skate (Raja rhina) and big skate (Beringraja binoculata [formerly Raja binoculata]) populations in the Gulf of Alaska, British Columbia and California. Previous growth studies involving estimates from different laboratories in the USA (Alaska Fisheries Science Center, AFSC; Pacific Shark Research Center, PSRC at Moss Landing Marine Laboratories) and Canada (Fisheries and Oceans Canada, DFO) have produced dissimilar results for either species, highlighting the need for development of a consistent age determination protocol and more importantly an age validation study. Archived large specimens of longnose skate and big skate collected in Monterey Bay, CA, in 1980 and 1981 had minimum preliminary age estimates from vertebral growth band counts old enough to suggest that radiocarbon (14C) signals from bomb testing conducted in the late-1960s could be used to establish dates of growth band formation. To this end, we micro-milled skate vertebral thin sections, measured Δ14C using mass spectrometry, and estimated year of growth band formation based on the estimated age from growth band counts using both unstained and stained preparation methods Non-linear random effects modeling, implemented in a Markov Chain Monte Carlo (MCMC) simulation, was used to compare the skate Δ14C data set to a marine teleost otolith reference chronology for the California Current System. Results showed Δ14C measurements for big skate were non-informative as none of the archived samples were old enough for comparison to the reference curve, hence validation of the age estimation approach was not possible. However, for longnose skate, Δ14C data were more informative to fit pulse function models and compare results to the reference chronology. Modeling results indicated longnose skate age estimates based on unstained vertebral thin sections were less biased (overestimated to a smaller degree) than estimates based on stained vertebral thin sections. The degree of bias depended on agency ageing criteria, with the least biased age estimates produced by age readers from the AFSC. The AFSC age estimates had about a 70% probability that age estimates of longnose skate was within+/− 2 years of the expected age based on the radiocarbon assays. We were able to validate the age estimation methodology for longnose skate and establish criteria for growth band counts, which should now be useful to generate region-specific accurate growth and life history parameters required for more reliable stock assessment approaches.

Study on Carapace Width Growth Band Counts Relationship of Orange Mud Crab, Scylla olivacea (Herbst, 1796) from Terengganu Coastal Waters, Malaysia.

Orange mud crab Scylla olivacea is one of the most important fisheries resources. A new development in ageing technique of crustaceans has been introduced. The detection of growth band deposited in hard structure of gastric mill in the cardiac stomach are found retained after moulting process can be used as age indicator and growth estimation. This study was carried out to determine the comparison between carapace width and growth band count of S. olivacea in Malaysia. Samples were collected from Setiu Wetlands, Terengganu, Malaysia from February until August, 2016. Samples were categorized based on their morphological measurements. The mesocardiac and zygocardiac ossicles in the gastric mill of S. olivacea was dissected out and preserved in solutions and underwent a cross sectioning process. A total of 76 of wild S. olivacea ranging from 6.56 to 12.84 cm in carapace width were analysed. The growth band counts were examined for each individual and ranging from 1 to 3 band counts. A positive linear relation was observed between CW and GBC with r2 = 0.5178, p<0.01. Overall, there was a strong, positive correlation between CW and GBC. Increase in CW were correlated with increases in GBC respectively for this species. Therefore, the carapace width, growth band counts and body weight can be used to improve data on growth, recruitment, maturation and mortality. Thus, this study would able to improve new ageing technique and contribute greatly to improve the conservation and management of S. olivacea in Setiu Wetlands, Terengganu, Malaysia.

Preliminary investigation of direct age determination using band counts in the gastric mill of the blue swimmer crab (Portunus pelagicus Linnaeus, 1758) in two salt-water lakes in the Eastern Mediterranean

The blue swimmer crab, Portunus pelagicus (Linnaeus, 1758), is an important component of the crustacean fisheries in Egypt. This fishery occurs mainly in two salt-water lakes in the Eastern Mediterranean, the coastal Lakes Bardaweel and Timsah, which is located about 100 km further south. We investigated for the first time the applicability of using growth band counts in thin sections of two gastric mill ossicles (mesocardiac and zygocardiac) as age indicator in the blue swimmer crab collected from the two lakes. There was no significant difference in band counts in thin sections of the two ossicles, although the zygo-cardiac ossicles were easier to process. Three growth bands were observed in the ossicles suggesting three years as the species life span. Meanwhile, size modal analysis suggested that the longevity of the species in the two lakes is only two years. Mean carapace width (mm) of the first two presumed year-classes obtained from the band counts and size modal analysis ( y 1 72.8 and 76.2 mm and y 2 91.5 and 97.8 mm, respectively) were not significantly different in Lake Timsah. In Lake Bardaweel, however, the mean size observed at the first two years was different ( y 1 78.5 and 102.2 mm and y 2 94.5 and 128.0 mm for the band count and size modal analysis, respectively). Sex-specific size-at-band counts (estimated age) was demonstrated for the species in both lakes. The models were fitted by power equations and there was no significant difference in the growth models between sexes in the two lakes. Further validation needs to be done to confirm the annual deposition of the growth bands before using the results on a routine basis.

Life histories of two deep-water Australian endemic elasmobranchs: Argus skate Dipturus polyommata and eastern spotted gummy shark Mustelus walkeri.

Two Australian endemic elasmobranchs, the Argus skate Dipturus polyommata and the eastern spotted gummy shark Mustelus walkeri, were collected from the by-catch of a prawn Melicertus plebejus trawl fishery off Queensland. Age and growth parameters were estimated from growth band counts in vertebral sections of 220 D. polyommata and 44 M. walkeri. Dipturus polyommata males and females had an observed maximum age of 10 years and reached maximum sizes of 369 and 371 mm total length (LT ), respectively. Mustelus walkeri lived longer, with the oldest female aged 16 years and measuring 1050 mm stretched total length (LST ), and oldest male aged 9 years and 805 mm LST . Dipturus polyommata grew relatively fast with a von Bertalanffy growth completion parameter of k = 0·208 year(-1) with males reaching maturity at 4·0 years (c. 278 mm LT ) and females at 5·1 years (c. 305 mm LT ). Mustelus walkeri grew more slowly with k = 0·033 year(-1) with males estimated to mature at 7-9 years (670-805 mm LST ) and females at 10-14 years (833-1012 mm LST ). Length at birth inferred from neonate D. polyommata was 89-111 mm LT while for M. walkeri it was estimated to be 273 LST based on the value of L0 from the von Bertalanffy growth model. Both species appeared to have continuous reproductive cycles and low fecundity with an average ovarian fecundity of eight follicles for D. polyommata and a litter size of five to seven pups for M. walkeri. Based on these life-history traits, D. polyommata is more resilient to fishing pressure than M. walkeri.

Age and growth of the tiger shark Galeocerdo cuvier off the east coast of Australia.

Total lengths (L(T)) at age and growth rates for south-west Pacific Galeocerdo cuvier were estimated from vertebral growth-band counts of 202 sagitally sectioned centra from 112 females (71-430 cm L(T)), 79 males (72-351 cm L(T)) and 11 of unknown sex. Captive growth data were also examined to complement vertebral age estimations. The sexes combined modelled growth coefficient (k = 0.08) was smaller than previously reported for G. cuvier populations elsewhere. Split-band and narrow banding patterns were identified as potential sources of age underestimation in this species.

Feasibility of using growth band counts in age determination of four crustacean species in the Northern Atlantic

The age information of commercially important species is crucial in fisheries management. Age of various fish and molluscan species has routinely been determined by counting annual growth bands deposited within the hard structures. In crustaceans such structures were previously believed to be lost and replaced due to molting. However, a technique was recently developed to use growth bands deposited in hard structure retained through molting as an age indicator. In the present study, the applicability of the novel technique is investigated for four crustacean species collected from Northern Atlantic for the first time: European lobster, Homarus gammarus (Linnaeus, 1758); Norway lobster, Nephrops norvegicus (Linnaeus, 1758); Atlantic rock crab, Cancer irroratus Say, 1817; and northern shrimp, Pandalus borealis (Kroyer, 1838). The gastric mill ossicles in the first three species were processed to show the growth bands while the eyestalk was used in the shrimp species. Four growth bands were visible in European lobster hatched in a Norwegian hatchery and maintained alive for four years before prior processing. Band counts in the other three species were identical to size-at-age interpretation determined from length-frequency analysis. Validation of the periodicity of annual deposition of growth bands is essential before applying the technique on a wider scale.

Direct age determination by growth band counts of three commercially important crustacean species in Chile

Management of commercially important crustacean stocks has been hindered by the inability to directly determine individual age. A lack of comprehensive age information leads to poor understanding of life history schedules, difficulty in estimation of parameters necessary for modeling population dynamics, and uncertainty in the determination of appropriate harvest levels. This study applied a novel direct age determination method based on band counts to three Chilean crustacean species: red squat lobster (Pleuroncodes monodon), yellow squat lobster (Curvimunida johni), and nylon shrimp (Heterocarpus reedi) for the first time. The growth bands were observed and counted in the endocuticle layer in thin longitudinal sections of the meso-cardiac ossicles of the gastric mills in the two squat lobster species and in the eyestalks of the nylon shrimp. Comparison of growth band counts with independent estimates of age strongly suggests that the bands form annually, thus providing a direct and accurate method of age determination in all of the species examined. Sex-specific growth curves were produced and demonstrated that the females grow at a slower rate than the males in the three species. Size and age-at-sexual maturity were also estimated. Application of this technique to known-age individuals will be necessary to validate band counts as indicators of chronological age.

Age, growth and maturity of the pelagic thresher Alopias pelagicus and the scalloped hammerhead Sphyrna lewini.

Indonesia has the greatest reported chondrichthyan catches worldwide, with c.110,000 t caught annually. The pelagic thresher (Alopias pelagicus) and scalloped hammerhead (Sphryna lewini) together comprise about 25% of the total catches of sharks landed in Indonesia. Age and growth parameters were estimated for A. pelagicus and S. lewini from growth-band counts of thin-cut vertebral sections. Alopias pelagicus (n = 158) and S. lewini (n = 157) vertebrae were collected from three Indonesian fish markets over a 5 year period. A multi-model analysis was used to estimate growth parameters for both species. The models of best fit for males and females for A. pelagicus was the three-parameter logistic (L∞ = 3169 mm LT , k = 0·2) and the two-parameter von Bertalanffy models (L∞ = 3281 mm LT , k = 0·12). Age at maturity was calculated to be 10·4 and 13·2 years for males and females, respectively, and these are the oldest estimated for this species. The samples of S. lewini were heavily biased towards females, and the model of best fit for males and females was the three-parameter Gompertz (L∞ = 2598 mm LT , k = 0·15) and the two-parameter Gompertz (L∞ = 2896 mm LT , k= 0·16). Age at maturity was calculated to be 8·9 and 13·2 years for males and females, respectively. Although numerous age and growth studies have previously been undertaken on S. lewini, few studies have been able to obtain adequate samples from all components of the population because adult females, adult males and juveniles often reside in different areas. For the first time, sex bias in this study was towards sexually mature females, which are commonly lacking in previous biological studies on S. lewini. Additionally, some of the oldest aged specimens and highest age at maturity for both species were observed in this study. Both species exhibit slow rates of growth and late age at maturity, highlighting the need for a re-assessment of the relative resilience of these two globally threatened sharks at current high levels of fishing mortality throughout the eastern Indian Ocean.

Eficiencia de la tinción de bandas de crecimiento con calceina y azul de coomassie, para estimar la edad de jóvenes de Pinctada mazatlanica (Pterioida: Pteriidae)

Age validation is the first step to determine shellfish species age determination. This information is vital for different inferential models used in marine ecosystem management activities. In spite that various validation techniques are used for marking carbon calcium structures, the calcein marking technique for oysters had never been used for age validation in Pinctada mazatlanica. Thus the objectives of this study included: the evaluation of calcein to mark a shell growing-edge, and the efficacy of Coomassie Blue staining on posterior shell growth, to produce visible micro growth-bands that would enable age validation of juvenile mother-of-pearl oysters. Oysters were collected and cultivated at The Perlas del Cortez S. de R. L. MI. pearl-farming operation, in Pichilingue, La Paz Bay, Baja California Sur, Mexico; a total of 36 oysters (shell height 11.5-36.4 mm) were injected with calcein (0.125 g/L), and another 50 oysters (shell height 14.8-42.7 mm) were submersed in calcein (0.4 and 0.7 g/L). Shell slices of calcein-marked oysters were posteriourly stained with Coomassie Blue R-25 for micro growth-band recognition. Our results showed that Calcein marking only worked by submersion and produced a concise bright lime-green florescent band along the growing-edge with clear boundaries for both concentrations. However, marks resulted better at the lower calcein concentration (0.4 g/L) with more "perfect" and "good" marks on the growing-edge (p = 0.0012). Commassie Blue staining technique was successful, and allowed to conclude that one micro growth-band was laid down per day, similar to other oyster species. Mean 15-d increment of shell growth height was slightly greater at the lower calcein concentration (= 0.735 mm) than at the higher one (= 0.577 mm) (not significant difference, p = 0.198). Calcein marking of shell growing-edges and Commassie Blue staining of posterior shell growth, as a method for age validation is recommended for shellfish shell growth-band counts. This will allow back-dating for estimation of very precise colonization dates, both spatially and temporally in future work.

Maximum age and missing time in the vertebrae of sand tiger shark (Carcharias taurus): validated lifespan from bomb radiocarbon dating in the western North Atlantic and southwestern Indian Oceans

Bomb radiocarbon analysis of vertebral growth bands was used to validate lifespan for sand tiger sharks (Carcharias taurus) from the western North Atlantic (WNA) and southwestern Indian Oceans (SIO). Visual counts of vertebral growth bands were used to assign age and estimate year of formation (YOF) for sampled growth bands in eight sharks from the WNA and two sharks from the SIO. Carbon-14 results were plotted relative to YOF for comparison with regional Δ14C reference chronologies to assess the accuracy of age estimates. Results from the WNA validated vertebral age estimates up to 12 years, but indicated that ages of large adult sharks were underestimated by 11–12 years. Age was also underestimated for adult sharks from the SIO by 14–18 years. Validated lifespan for C. taurus individuals in the present study reached at least 40 years for females and 34 years for males. Findings indicated that the current age-reading methodology is not suitable for estimating the age of C. taurus beyond ~12 years. Future work should investigate whether vertebrae of C. taurus record age throughout ontogeny, or cease to be a reliable indicator at some point in time.

Assessment of radiometric dating for age validation of deep-water dogfish (Order: Squaliformes) finspines

Vertebrae of most deep-water sharks are too poorly calcified to record visible growth bands and therefore are not useful for age determination. Most dogfish species (Order: Squaliformes) possess dorsal finspines and several recent studies have shown that these structures offer potential for age determination. Age validation should be central to any age determination study, yet to date no age and growth study of deep-water sharks has included a complete validation of age estimates. In this study we sought to age two deep-water dogfish species by analyzing 210Pb and 226Ra incorporated into the internal dentin of the finspines. These radiometric age estimates were compared with counts of internal growth bands observed in the finspines. A pilot study indicated that dorsal finspines of Centroselachus crepidater are too small and thus offer insufficient mass for the radiometric techniques employed in this study. For ageing larger finspines of Centrophorus squamosus, the lead–radium disequilibria method (ingrowth of 210Pb from 226Ra) was found to be inapplicable due to exogenous uptake of 210Pb in the finspine. Therefore, to approximate age, we measured the decay of 210Pb within the dentin material at the tip of the finspine (formed in utero), relative to the terminal material at the base of the finspine. Results with this method proved to be inconsistent and did not yield reliable age estimates. Hence the use of 210Pb and 226Ra for radiometric age determination and validation using dorsal finspines from these deep-water dogfishes was deemed unsuccessful. This outcome was likely due to violations of the consistent, life-long isotopic uptake assumption as well as the provision that the finspine must function as a closed system for these radioisotopes. Future improvements in analytical precision will allow for smaller samples to be analyzed, potentially yielding a better understanding of the fate of these radioisotopes within finspine dentin throughout the life of the shark.

Direct determination of age in shrimps, crabs, and lobsters

The detection and measurement of annual growth bands preserved in calcified structures underlies the assessment and management of exploited fish populations around the world. However, the estimation of growth, mortality, and other age-structured processes in crustaceans has been severely limited by the apparent absence of permanent growth structures. Here, we report the detection of growth bands in calcified regions of the eyestalk or gastric mill in shrimps, crabs, and lobsters. Comparison of growth band counts with reliable, independent estimates of age strongly suggests that the bands form annually, thus providing a direct and accurate method of age determination in all of the species examined. Chemical tags in the lobster cuticle were retained through one or two molts that occurred over the duration of an experiment, as apparently was the mesocardiac ossicle containing the growth bands in the gastric mill. Growth bands are not the previously documented lamellae of the endocuticle, and their formation was not associated with molting. Sex-specific growth curves were readily developed from growth band examination in multiple species, suggesting that routine measurement of growth and mortality in decapod crustaceans may now be possible.