Otolith Core Research Articles

Diet and size at birth affect larval rockfish condition and survival

Feeding success and maternal effects on larval size have long been hypothesized to be important contributors to interannual recruitment variability in marine fishes. This study examined the feeding ecology and influences of diet and size at birth on length and growth of larval rockfishes (Sebastes spp.). Prey carbon biomass and selection were calculated from gut contents, size at birth was estimated using otolith core size, and recent growth was derived from outer otolith increment widths. Biomass contributions of preferred prey and otolith data were integrated into Bayesian hierarchical models predicting length and growth. Larvae primarily fed on and selected for copepod nauplii and calanoid copepodites, modulating feeding with ontogeny and in response to prey availability. Based on carbon weight, the relative contribution of calanoid copepodites to the diet was more strongly and positively correlated with length and growth than that of nauplii. Younger larvae experienced faster growth in association with calanoid copepodite consumption than older larvae. Positive effects of core radius suggest that initial larval size, believed to be mediated by maternal provisioning, increases the likelihood of survival, larger size, and faster growth. These findings ultimately provide evidence that selective feeding and size at birth mediate rockfish survival in early life stages.

Otolith elemental composition indicates differences in the habitat use for larvae and early juveniles of Japanese jack mackerel (Trachurus japonicus) in the waters around Japan

AbstractTrace element analysis of otoliths from core to edge was used to reveal differences in habitats of larvae and early juveniles of Japanese jack mackerel (Trachurus japonicus) caught in the East China Sea (ECS), Pacific Ocean, and Sea of Japan. Multi‐element signatures (Sr:Ca, Mg:Ca, Na:Ca, K:Ca, and Ba:Ca) were analyzed with multivariate statistics to determine whether these element signatures provide insight into regional population structure. The median values of elements: Ca ratios in otolith core region differed significantly among areas, with most elements between the ECS and the Pacific Ocean or Sea of Japan showing significant differences. The Sr:Ca ratios exhibited a V‐shaped trend from the otolith core to the edge, which was likely related to the vertical habitat layer shift of larvae and early juveniles of T. japonicus. Canonical analysis of principal coordinates using the element: Ca ratios and the hatching day were re‐classified according to the sampling area with higher accuracy in the ECS (88–95%) and the Sea of Japan (76–83%) compared to the Pacific Ocean (69–72%). These results indicate that the proportion of eggs, larvae, and early juveniles transported by the Kuroshio Current from the southern ECS—the main spawning ground—to the Pacific Ocean or the Sea of Japan is low and that juveniles distributed in the coastal waters off southwestern Japan may have originated from local spawners. These results suggest that determining the elemental composition of larvae and juveniles of T. japonicus is effective in determining the habitat differences of this species in the three regions. These findings will help to understand population structure and recruitment process of this species around Japan.

Age validation of yellowfin and bigeye tuna using post-peak bomb radiocarbon dating confirms long lifespans in the western and central Pacific Ocean

Abstract Age-reading protocols for tuna species using annual growth zones in thin-cut transverse otolith sections have produced greater age estimates than previous methods. Lifespan estimates for yellowfin (YFT) and bigeye (BET) tuna (Thunnus albacares and T. obesus) were validated up to 16–18 years in the western North Atlantic Ocean using bomb 14C dating and the current study extends the approach to YFT and BET of the western and central Pacific Ocean (WCPO). Archived otoliths from young-of-the-year (YOY) tuna caught in the WCPO were analysed for 14C to establish a reference chronology covering 30 years (1989–2019). This YOY 14C time series exhibited strong concordance with existing coral-otolith 14C references for the tropical-subtropical Pacific Ocean and was combined as a single chronology. Otolith cores from YFT aged 1–14 years and BET aged 1–13 years from presumed annual counts were analysed for 14C. These measurements aligned with the reference chronology for the calculated hatch years for both species. These findings provide strong evidence that growth zones in thin-sectioned otoliths are deposited annually for YFT and BET of the WCPO and that age interpretation is correct using the current age reading protocol with little to no bias.

Otolith chemistry reveals ontogenetic movement of the Antarctic toothfish (Dissostichus mawsoni) in the Amundsen Sea polynya, Antarctica

The Amundsen Sea polynya is one of the richest areas of primary productivity in Antarctica. The Antarctic toothfish (Dissostichus mawsoni, TOA) is a commercially valuable circum-Antarctic fish that undertakes ontogenetic movements on the continental shelf. However, the movement and distribution of this species remain unclear in the polynya, especially in the data-poor Amundsen Sea polynya. Along with hydrological and fishery survey data in the Amundsen Sea polynya, the otolith chemistry of TOA from three areas along the ice shelf of the Dotson–Getz Trough was analyzed to explore the movement pattern of this species. The elemental composition deposited during early life in the otolith core did not show significant differences, indicating that TOA in the Amundsen Sea polynya probably experienced a similar hydrological environment at the early life stage or might originate from the same spawning ground. However, the elemental composition deposited at the otolith edge showed that SrCa−1 and LiCa−1 differ in otolith chemistry between areas along the Amundsen Sea coast. In conjunction with additional data from the fish sampled in these areas, this study reveals that TOA show an ontogenetic movement from westward along the ice shelf in the Amundsen Sea polynya. A deeper area (with a depth of over 1000 m) in the west box provides a fish pool for TOA, which needs to be conserved in the fishery management of toothfish populations.

Network connectivity contributes to native small‐bodied fish assemblages in the upper Mississippi River system

Abstract Effective management and conservation of fishes requires understanding habitat use across multiple life stages while ensuring necessary habitats are both available and accessible. Tributary habitats may play an important role in recruitment and dispersal of fishes in anthropogenically modified rivers such as the Mississippi and Illinois Rivers of the Midwest U.S.A. Identifying source locations that contribute to recruitment of fish populations can determine the importance of connectivity within river networks and pinpoint critical habitats that sustain fish populations. In the Upper Mississippi River System (UMRS), the environments that fish use in early life stages (i.e., natal origin) can be identified using otolith trace element analysis due to stability and distinctness in water chemistry (strontium: calcium [Sr:Ca]) among water bodies that is reflected in otoliths. Here, we used trace element analysis to determine natal origin of six small‐bodied fishes including bullhead minnow (Pimephales vigilax), emerald shiner (Notropis atherinoides), gizzard shad (Dorosoma cepedianum), bluegill (Lepomis macrochirus), orangespotted sunfish (Lepomis humilis), and yellow perch (Perca flavescens) across six reaches of the UMRS (Pools 4, 8, 13, 26, the Open River of the Middle Mississippi River, and the La Grange Pool of the Illinois River). Otolith core Sr:Ca for fishes was quantified using laser ablation inductively coupled plasma mass spectrometry. Using the resulting Sr:Ca chemical signatures of otolith cores, natal origin (tributary, immigrant, or potential resident) was determined for individual fish based on family‐specific relationships between otolith and water chemistries. We found that all species originated from tributaries and other reaches (i.e., were immigrants) to varying extents, which acted as evidence for network connectivity. Specifically, tributaries contributed up to 48% of individuals at a given reach. In certain reaches, Pool 26 and the Open River reach, up to 80% of individuals in a species immigrated from another mainstem river reach. Network connectivity was also important in both upstream and downstream directions. Contributions from network connectivity varied among species: bullhead minnow used less whereas orangespotted sunfish used more network connectivity than when all species were combined. Further, the use of network connectivity varied spatially where individuals captured in Pool 8 and the La Grange Pool less often and those from Pool 26 and the Open River more often originated from network connectivity compared to the whole assemblage across reaches. These results indicate that species' life history traits probably interacted with the physical environment, which differs spatially, to yield observed recruitment source patterns. Our results show that network connectivity contributes to established assemblages of native small‐bodied fishes throughout the UMRS and underscore the role of interjurisdictional management in maintaining network connectivity to sustain fish populations.

Use of otolith microchemistry signatures to assess the habitat use of Centropomus undecimalis in lagoon systems of the southwest Atlantic

The common snook, Centropomus undecimalis, is a catadromous species that is economically important for the southwest Atlantic artisanal and recreational fisheries. Their complex movement patterns and habitat use preferences are not fully understood in the Brazilian Atlantic waters, raising some issues regarding the rational and sustainable management of the fisheries. The present study aimed to identify the habitat use by C. undecimalis individuals captured in four coastal lagoon systems in the Eastern Rio de Janeiro state, Brazil. Sixty individuals were collected in the lagoon systems of Itaipu, Maricá, Saquarema and Araruama, between November 2019 and March 2020. A selection of 15 individuals per site from the same age group (3 years old), following age estimation by counting the annual growth increments, were used. Elemental signatures of the otolith’s cores and edges were obtained using laser ablation inductively coupled-plasma mass spectrometry (LA-ICP-MS). Data were analyzed using univariate and multivariate statistics to assess the degree of separation among individuals regarding the natal origin (otolith cores) and moment of capture (otolith edges) from the sampling sites. Elemental signatures exhibited distinct spatial patterns, driven by Ba/Ca, Li/Ca and Sr/Ca in the otolith cores and Ba/Ca, Li/Ca, Mn/Ca and Sr/Ca in the edges. A low reclassification was recorded for the otolith’s core (overall: 45%; by lagoon: 53% Saquarema, 53% Maricá, 47% Itaipu and 27% Araruama). However, a highest overall reclassification was observed for the otolith’s edge (overall: 65%; by lagoon: 73% Itaipu, 73% Saquarema, 60% Maricá, and 53% Araruama). Differences between otolith core and edge signatures within locations were detected for Ba/Ca, Cu/Ca, Li/Ca, Mn/Ca and Sr/Ca ratios. The results obtained indicate an ontogenetic habitat shift, with a similar natal origin of the individuals probably due to marine water influence, and discrimination of heterogeneous juvenile fish groups driven by distinct phenotypic characteristics of the lagoons.

Trace elemental and stable isotopic signatures to reconstruct the large-scale environmental connectivity of fish populations

Animal movements and connectivity across different environments constitute essential components of virtually all ecological and evolutionary processes. In the present study, we measured multiple trace-element profiles and stable isotopes to reconstruct life cycle patterns of Eleutheronema rhadinum, and patterns of connectivity among populations of E. rhadinum across 3 distinct ecoregions in the eastern China Sea. Our results indicated that E. rhadinum larvae from different regions exhibited distinct otolith core levels of trace elements and stable isotopes, serving as discriminative markers of geographical origin. We used the maximum likelihood approach and linear discriminant analysis to trace back the origins of the mixed adult fish stocks. After leaving their nursery areas, juvenile fish from colder northern regions migrated south to overwinter in the South China Sea, where they mixed with the local populations. After overwintering, the adult fish began their long journey north, with the migrating population including individuals of both East China Sea and South China Sea origins. Meanwhile, fish in the Beibu Gulf exhibited a lower degree of interaction with the South China Sea populations and minimal interaction with those in the East China Sea. Trace elements and stable isotopes revealed the spatiotemporal connectivity of E. rhadinum across the 3 different ecoregions. This study provides critical information on how marine connectivity supports temperature-mediated fish community movement patterns within coastal ecosystems.

Connectivity of Greenland halibut in the northwestern Atlantic Ocean inferred from otolith chemistry

Greenland Halibut (Reinhardtius hippoglossoides) is a deepwater flatfish having a circumpolar distribution. Understanding the spatial connectivity and migratory patterns of this commercially valuable species is essential for ensuring a sustainable fishery; nonetheless, this information remains relatively scarce for many Greenland Halibut populations. Here we evaluate the connectivity and the population structure of halibut along coastal Greenland and Canada to better characterize the contribution of each production zone to the various stocks found in the northwestern Atlantic Ocean. In 2014 and 2016, we sampled 411 large Greenland Halibut from coastal Nunavut, Labrador, and Greenland. We used the elemental fingerprint (magnesium, strontium, and barium) from the otolith core and margin of the sampled fish to determine spatial differentiation of the source areas of the collected halibut. From the 17 sample sites, margin elemental fingerprint delineated four “elemental sectors”, representing pooled adjacent sites having similar chemistry. Overall, 62% of Greenland Halibut were correctly assigned to their sampled coast. Elemental fingerprint of the otolith cores indicated three chemically distinct natal sources for the captured halibut. The chemical record in the otolith cores suggested a high connectivity of Greenland Halibut in the northwestern Atlantic and a main natal source located potentially along the west coast of Greenland. Given that our results suggest the presence of a large nursery around Disko Bay–Hellefiske Bank, protection measures should be considered for this area.

Caribbean deepwater snappers: Application of the bomb radiocarbon age estimation validation in understanding aspects of ecology and life history.

Reef fishes have been utilized as food fish throughout the U.S. Caribbean and Gulf of Mexico waters for centuries, with increasing fishing effort in recent decades. As a result, many species have experienced declines in landings, including deepwater snappers such as queen snapper Etelis oculatus and blackfin snapper Lutjanus buccanella. However, little to no peer-reviewed published research exists on basic life history parameters for either species. Confirming the accuracy of an age estimation method for a fish species is essential for ensuring sustainable fisheries management. This is because in the assessment of fisheries species population age-based parameters, including longevity, age at sexual maturity, growth rate, mortality, age-specific reproductive output, and lifetime reproductive output, are important in understanding overall life history strategies of managed stocks. The past stock assessment on U.S. Caribbean queen snapper utilized an estimated longevity of 8 y, derived from length frequencies for fish from St. Lucia. Blackfin snapper has an estimated longevity of 27 y based on a relatively small study from offshore waters of the southeastern U.S. The focus of our investigation was to estimate maximum longevity of two data-poor species in the U.S. Caribbean. The accuracy of ageing methods was tested via bomb radiocarbon age estimation validation and effects of depth on Δ14C in otolith cores and eye lens core values were examined. Results from our work indicate a maximum validated age of 45 y for queen snapper, and 43 y for blackfin snapper. Our findings indicate queen snapper and blackfin snapper are long-lived (> 40 y). The resulting Δ14C comparison between eye lens cores and otolith cores has important implications for the study of age validation, specifically when deepwater species are involved.

Momma's larvae: Maternal oceanographic experience and larval size influence early survival of rockfishes

AbstractIdentifying factors that affect larval mortality is critical for understanding the drivers of fish population dynamics. Although larval fish mortality is high, small changes in mortality rates can lead to large changes in recruitment. Recent studies suggest maternal provisioning can dramatically affect the susceptibility of larvae to starvation and predation, the major sources of early‐life mortality. We measured otolith core width‐at‐extrusion and validated that this is a proxy for larval size‐at‐extrusion for eight species of rockfishes (genus Sebastes) to examine the influence of initial larval size on larval growth and survival and to understand how oceanographic conditions experienced by gestating females affect larval size (i.e., quality). Otolith core width‐at‐extrusion was significantly positively related to larval rockfish recent growth rate (5/7 species with sufficient sample size) and survival (all eight species). This suggests that individuals that are larger at extrusion generally grow faster and are more likely to survive early life stages. Otolith core width‐at‐extrusion was positively related to higher presence of Pacific Subarctic Upper Water and was negatively related to warmer, saline waters at the depths gestating mothers inhabited during the months prior to larval collection. In addition, otolith core width was larger further from fishing ports, possibly because these locations were historically less fished, contained more older, larger females, and/or had inherently better habitat quality (higher Pacific Subarctic Upper Water) than sites closer to shore. These results indicate that the environmental conditions female rockfish experience during gestation drive the size of the larvae they produce and impact larval growth and survival.

Nursery origin of yellowfin tuna in the western Atlantic Ocean: significance of Caribbean Sea and trans-Atlantic migrants

Natural geochemical markers in the otolith of yellowfin tuna (Thunnus albacares) were used to establish nursery-specific signatures for investigating the origin of fish captured in the western Atlantic Ocean (WAO). Two classes of chemical markers (trace elements, stable isotopes) were used to first establish nursery-specific signatures of age-0 yellowfin tuna from four primary production zones in the Atlantic Ocean: Gulf of Mexico, Caribbean Sea, Cape Verde, and Gulf of Guinea. Next, mixture and individual assignment methods were applied to predict the origin of sub-adult and adult yellowfin tuna from two regions in the WAO (Gulf of Mexico, Mid Atlantic Bight) by relating otolith core signatures (corresponding to age-0 period) to baseline signatures of age-0 fish from each nursery. Significant numbers of migrants from Caribbean Sea and eastern Atlantic Ocean (EAO) production zones (Gulf of Guinea, Cape Verde) were detected in the WAO, suggesting that fisheries in this region were subsidized by outside spawning/nursery areas. Contributions from local production (Gulf of Mexico) were also evident in samples from both WAO fisheries, but highly variable from year to year. High levels of mixing by yellowfin tuna from the different production zones and pronounced interannual trends in nursery-specific contribution rates in the WAO emphasize the complex and dynamic nature of this species’ stock structure and population connectivity. Given that geographic shifts in distribution across national or political boundaries leads to governance and management challenges, this study highlights the need for temporally resolved estimates of nursery origin to refine assessment models and promote the sustainable harvest of this species.

Using otolith microchemistry to determine natal origin of Black Sea Bass off the coast of Maine

AbstractObjectiveA recent expansion of the northern stock of Black Sea Bass Centropristis striata into the northern Gulf of Maine raises questions about this species’ movement and population dynamics in this region. Determining the origin of these fish is essential, as dramatic changes in migration patterns or current population boundaries could have profound effects on stock assessment estimates and subsequent management regulations.MethodsIn this study, we measured otolith core concentrations of stable isotopes (δ18O, δ13C) and trace element:calcium ratios (Mg:Ca, Mn:Ca, Cu:Ca, Zn:Ca, Ba:Ca, Sr:Ca) to assess the natal origin of Black Sea Bass that were caught off the coast of Maine. Spawning condition adults from southern New England (SNE) and the mid‐Atlantic Bight (MAB) were used to characterize the chemical fingerprint of these known spawning regions.ResultUnique chemical fingerprints were identified for fish from SNE and the MAB, with high reclassification success using random forest analysis (16% error rate). The classification of Black Sea Bass of unknown origin that were caught in Maine waters indicated that 85% of the samples matched to SNE and 13% to the MAB, whereas one sample remained unclassified.ConclusionResults from this study support the current management population separation of the northern stock of Black Sea Bass between SNE and the MAB and lends additional information to the understanding of this species’ movement into the northern Gulf of Maine. As fish stocks around the world continue to shift into new regions due to climate change, knowledge of their natal origin will be critical to long‐term sustainable management of this species.

Exploring European Eel Anguilla anguilla (L.) Habitat Differences Using Otolith Analysis in Central-Western Mediterranean Rivers and Coastal Lagoons from Sardinia

An otolith shape and morphometric analysis was performed on European eel (Anguilla anguilla) subpopulations from five rivers and three coastal lagoons of Sardinia (central-western Mediterranean) to assess the role of different habitats on otolith development. Sagittal otolith shape was described by 11 harmonics from elliptic Fourier descriptors. Comparisons among the harmonics were run through canonical discriminant analyses (CDAs). The CDA reclassification rate (75.7%) demonstrated a spatial environmental discrimination among local eel subpopulations of Sardinia. The Euclidean distance values demonstrated a dissimilarity between the river and lagoon groups. The form factor and roundness shape indices were significantly higher in the river group than in the lagoon group. The distances of the first three rings to the otolith core revealed site-specific otolith development. Moreover, the annual otolith growth rate was faster in the lagoon group than in the river group. The differences among the studied sites in terms of sagittal otolith shape could relate to changes in different local stocks potentially related to environmental peculiarities. Establishing a direct correlation between otolith morphology and environmental factors is challenging, and further studies are needed to investigate the relationship between habitat type/environmental variation and growth/body characteristics of eels. Nevertheless, the achieved results suggest that this method can be considered to be a valuable tool for studying the ontogeny of the European eel.

Spatiotemporal variability in otolith elemental fingerprint and the potential to determine deepwater redfish (Sebastes mentella) origins and migrations in the Estuary and Gulf of St. Lawrence, Canada

Connectivity processes have major implications in defining the resiliency of fish populations to overexploitation. A preliminary estimate of population exchange rates can be done by identifying the natal origin of adult fish. In this study, otolith elemental fingerprints were used as natural marker of origins and movements of Deepwater redfish (Sebastes mentella) in the Gulf of St. Lawrence (GSL). We specifically targeted the strong 2011–2013 cohorts that supported the rapid recovery of the GSL stock after its collapse in the 1990s. Elemental fingerprints were extracted from the core (proxy for larval origin) and edge (proxy for capture location) of otoliths using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). We observed an East to West gradient in the multi-elemental fingerprint of the otolith edge in the GSL, as well as evidence of temporal variation between 2016 and 2018. Cluster analysis of the core fingerprint revealed the existence of two chemically distinct natal sources of variable contribution between the Saguenay Fjord, the western GSL and the eastern GSL. This new insight on the population structure of redfish in the GSL at an ecologically relevant scale constitutes important knowledge for the assessment and sustainable management of a key recovering resource.

Strontium isotope mapping and its application to study the fish life history (Salminus brasiliensis) in semi-fragmented rivers (La Plata Basin, South America)

Salminus brasiliensis is one of the largest and most important commercial and sporting fish species in South America, of which little is known about its habitat use, especially in semi-fragmented rivers. The aims of this study were to expand the water 87Sr/86Sr baseline of the La Plata Basin, and to study the migratory patterns of S. brasiliensis from Paraná dam-free stretch and a representative tributary semi-fragmented using otolith isotopic chemistry. Water samples were collected at 10 sites on the upper Paraná River and two sites on the middle and lower Carcarañá Basin (tributary of the lower Paraná River). Fourteen fish were caught in the upper Paraná River and 13 in two sites of the middle and lower Carcarañá Basin. 87Sr/86Sr was measured in water and otolith core-to-edge transect by MC-ICPMS and LA-MC-ICPMS, respectively. Water results were incorporated into a dataset with 53 other sampling points from the La Plata Basin and subjected to a cluster analysis, which resulted in nine differentiable chemical signatures. Discriminant analysis confirmed the presence of at least eight contrasting isotopic signals. Based on the otolith core 87Sr/86Sr, four individuals from the upper Paraná River were classified as originating from Paraguay sub-basin, while the rest were assigned to Paraná River. All fish from the Carcarañá sub-basin were classified as originating from the Paraná River, except two individuals which were assigned to the Carcarañá sub-basin. Results indicated that the fish run up the Carcarañá sub-basin overcoming up to three open spillways, and could live there for years and even reproduce. However, the Paraná River had the largest contribution to the fish caught in both the upper Paraná River and the Carcarañá sub-basin.

Bomb radiocarbon dating reveals 40‐year lifespan of Shovelnose Sturgeon (Scaphirhynchus platorynchus)—Implications for stock assessments of long‐lived, primitive fishes

AbstractStock assessments for Shovelnose Sturgeon have largely been limited to age and growth analyses using pectoral fin rays despite potential underestimation of age and lack of age validation. Fisheries stock assessments rely on accurate estimates of vital rates for effective fisheries management, within which fish age and lifespan are of primary importance. Age was estimated using pectoral fin rays and otolith sections, and bomb radiocarbon (14C) dating was applied to otolith cores to determine lifespan and validate ages. Age reading of fin rays was straightforward, whereas most otolith thin sections provided two age‐reading scenarios: lumping (primary increments) or splitting (finer increments) presumed annuli. While fin‐ray estimates led to a maximum age of 14 years, otolith estimates led to maximum ages of 27 and 42 years.14C dating provided support for a combination of lumping early in life, to splitting in later years, and validation of a ~40‐year lifespan. Age reading of otoliths was imprecise and resulted in ~40% of thin sections that were not age scoreable. However, scoreable otolith sections, coupled with14C dating, resulted in growth and lifespan information that are the most accurate to date for Shovelnose Sturgeon and can be used as a baseline toward stock assessment refinements.

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.

Lebranche mullet Mugil liza population structure and connectivity patterns in the southwest Altantic ocean using a multidisciplinary approach

Previous meristic analysis of the oblique scale counts (OSC) of Mugil liza showed a bimodal pattern within the southern stock, between São Paulo, Brazil (−24°S), and Samborombón Bay, Argentina (−35°S), allowing the identification of two morphotypes (BR1 and BR2). The Brazilian group with lower number of OSC was represented by morphotype 1 (BR1), while the group with higher number of OSC was referred as morphotype 2 (BR2), which could represent distinct subpopulation-units. This study aims at evaluating 1) the population structure of M. liza in Brazilian waters through meristics and body morphometrics from individuals captured by the industrial purse seine fishery, and 2) to assess the possible connectivity between individuals collected off southeast-south Brazil with specimens sampled in Argentinean waters (AR) through otolith shape and microchemistry analyses. Combined meristic and morphometric analyses of fish bodies captured in Brazilian waters allowed to discriminate morphotypes (BR1 and BR2) characterized by different body proportions, head profiles and relative positions of the eye. BR1 presented on average 34 OSC, contrasting with 36 of BR2. For mullets born in two-time distinct intervals, (i) 2008–2011 and (ii) 2011–2014, otolith shape analyses associated AR to BR2, and evidenced a distinct otolith outline from BR1, while multi-elemental otolith core analyses showed no significant differences between AR and BR2. It suggests that the mechanisms responsible for the elemental deposition during the early life history for these two sub-populations (AR + BR2) were significantly different compared to BR1. Univariate analyses of the otolith fingerprints (core and edge) showed higher significant levels in Cd/Ca, Cu/Ca, Fe/Ca, Li/Ca, Mn/Ca, Ni/Ca and Zn/Ca for BR1 compared to AR and BR2. The hereby morpho-meristic data and univariate elemental fingerprints suggest distinct environments inhabited by fish along the western coast of South America. Furthermore, the multi-elemental otolith core results suggested the existence of more than one nursery area for the species. In conclusion, the two morphotypes identified (BR1 and BR2+AR) should be considered as two sub-populations within the mullets southern stock for fisheries management purposes.

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.

Application of the bomb radiocarbon chronometer with eye lens core Δ14C for age validation in deepwater reef fishes

Eye lens core Δ14C of Gulf of Mexico outer shelf and upper slope reef fishes matched a regional Δ14C reference time series, but otolith cores were depleted in 14C relative to the reference series. This is due to C in eye lens protein being derived from metabolic sources, with the ultimate source being epipelagic phytoplankton. In contrast, otolith C is derived mainly (70%–80%) from dissolved inorganic C, which is depleted in 14C beyond the epipelagic. Analyzing Δ14C in eye lens cores provides a novel approach for validating age estimates of deepwater (>200 m) fishes, which were unresolved in earlier applications of the bomb 14C chronometer.