Elemental chronologies of Ba and Sr were constructed for statoliths of Doryteuthis gahi using LA-ICP MS. Temporally distinct spawning cohorts had unique elemental chronologies. Elemental chronologies displayed significant variation throughout ontogeny. Cohort-specific chronologies were most dissimilar during 80-160 d post-hatching.
Nursery grounds are valuable habitats providing sources of food and refuge during early life stages for many commercially caught marine fish. Distinguishing between different nursery grounds and identifying habitat origin using trace elemental concentrations in aragonite structures of teleost fish have proved valuable in fish ecology and fisheries. This study aimed to (1) compare chemical signatures (elemental fingerprints) within sagittal otoliths of juvenile European plaice Pleuronectes platessa sampled from known nursery habitats in the southeastern Irish Sea and (2) assess their potential and robustness as natural tags for identifying nursery grounds for the putative southeastern Irish Sea plaice stock. Otoliths from juvenile plaice ('1-group', 6 to 15 cm total length) were obtained from 8 nursery grounds in coastal areas off northwest England and north Wales (including Anglesey) between June and August 2008. Solution-based inductively coupled plasma-mass spectrometry determined the concentrations of 10 elements (Li, Na, Mg, K, Mn, Zn, Rb, Sr, Sn, Ba), with significant differences in otolith element composition observed between all nursery grounds. Cross-validation linear discriminant function analysis (CV-LDFA) classified fish to their nursery ground of capture (46.2 to 93.3%), with a total group CV-LDFA accuracy of 71.0%. CV-LDFA between regions (north-west England and north Wales) classified fish with 82% accuracy. The discrimination of juvenile plaice from all 8 nursery grounds within the southeastern Irish Sea using otolith microchemistry offers significant opportunities in the development of future effective fisheries management strategies through understanding the supply of juveniles from specific nursery grounds and adult plaice in the southeastern Irish Sea.
Southern blue whiting (Micromesistius australis australis) was one of the largest fisheries in the Southwest Atlantic with the peak in total annual catches attaining 258.000 tonnes. Intense exploitation over the past 30 years critically decreased its abundance and forced the implementation of a suite of conservation measures to save and rebuild the stocks. Recently improved recruitment levels require more information on the early life history stages of this fish. Using complimentary investigations into otolith microstructure and trace elemental composition by LA-ICPMS, larval, metamorphic and post-metamorphic periods of the early ontogeny were studied. The timing and completion of metamorphosis were estimated at 30.5 ± 0.3 and 60.7 ± 1.8 days after the first increment formation respectively. The timing of a newly defined 'juvenile transition-mark' (corresponding to the transition from the epipelagic larval habitat to a deeper juvenile habitat was estimated to form at age of 76.5 ± 2.0 days.
*Manuscript including abstract Click here to view linked ReferencesThe movement of juveniles into deeper waters post-metamorphosis were further confirmed by significant shifts in the element: 42 Ca ratios (for elements 24 Mg, Mn, 88 Sr and Ba).Elemental 'fingerprints' for each of the three otolith zones were further found to be distinct through high classification accuracies of the random Forest model (81.1 ± 0.1%). Holistic approach investigating both otolith microstructure and elemental composition provides further evidence that ontogeny could be a confounding factor in natal (geographic) origin studies if (1) otolith 'core' samples are taken from different ontogenetic otolith zones and (2) if elements predominantly controlled by physiology are included in the respective classification analyses.
Chronologies generated from core profiles to apply dates to environmental changes commonly use the measurement of the activity of radionuclides deposited and stratified with physical environmental material. The most commonly reported nuclide to define chronologies covering the last 150 years is Pb-210, for which accepted data processing methodologies in the literature have focussed on the constant rate of supply (CRS) model and the more recently published Bayesian Plum model. This short communication describes a validation approach using defined sediment layers referred to as ‘varve’ counting, which provide known points of reference to account for uncertainty between generated dates from each model using published Pb-210 measurements. A significant improvement in the chronologies was observed when applying reference date corrections to the models. This was shown to be essential in providing confidence in reported datasets and accuracy of predicted chronologies, which will better inform the interpretation of environmental change, e.g. sedimentation rates, climate change, pollution pathways and land degradation. Generated chronologies from both the CRS and Plum methods showed good agreement with the established varve dates (typically < 4-year difference).
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