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

Abstract

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.

In utero elemental tags in vertebrae of the scalloped hammerhead shark Sphyrna lewini reveal migration patterns of pregnant females

“…The mean percentage of the elemental concentration data below the limits of detection (LOD) was ≤10% for all elements (i.e. 7 Li, 24 Mg, 55 Mn, 57 Fe, 59 Co, 85 Rb, 88 Sr, 89 Y, 114 Cd, 118 Sn, 137 Ba, 208 Pb), except for 45 Sc (42.9%), 51 V (57.1%), 53 Cr (64.3%), 72 Ge (71.4%), 89 Y (64.3%), 114 Cd (57.1%), 197 Au (71.4%), 232 Th (63.3%) and 238 U (78.6%) which were not regularly detected in the vertebrae of embryos and pregnant females. For more details on the mean (±standard deviation) element:Ca ratios (µmole⋅mole −1 ) quantified at the vertebral focus and edge of embryos and pregnant females, please refer to Table S1 from the Supplementary Information.…”

“…The elemental composition of the vertebrae of S. lewini was quantified using a Photon-Machines Analyte 193 excimer UV laser ablation system (LA), connected to an Agilent Technologies 7500CX quadrupole inductively coupled plasma-mass spectrometer (ICP-MS). Raw data of the ion counts per second (cps) were collected for the following 21 elements: 7 Li, 24 Mg, 43 Ca, 45 Sc, 51 V, 53 Cr, 55 Mn, 57 Fe, 59 Co, 63 Cu, 72 Ge, 85 Rb, 88 Sr, 89 Y, 114 Cd, 118 Sn, 137 Ba, 197 Au, 208 Pb, 232 Th and 238 U with 43 Ca being quantified for use as internal standard. These were screened in the vertebrae of S. lewini because this combination of masses minimizes potential interferences that can arise from isobaric spectral overlap, sample matrix effects, and the presence of molecular ions 39 and was successfully used in previous studies for inferring the life history of sharks 19,20,[23][24][25][26][27] .…”

“…time of the pregnant female habitat shift), R t corresponds to the vertebral transect distance from the focus to the elemental shift identified in utero at age t, R V is the vertebrae centrum radius, L C the total length at the time of capture of the individual (i.e. young-of-the-year or embryo) and a is intercept of an established linear relationship between R V and L C 54 , which is L C = 17.349 R V + 14.516 for juvenile specimens of S. lewini in the Mexican Pacific 55 .…”