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Variation in otolith elemental fingerprints was investigated in albacore tunas (Thunnus alalunga) sampled in the southwest Indian Ocean (SWI) and along the Atlantic coast of South Africa (SA). A total of 72 otoliths were selected, from 46 adult fish captured around the Reunion Island (SWI) and 26 juvenile and sub-adults sampled at two locations off the South African coast (SA-N and SA-S, n = 13 per location). LA-ICP-MS was used to assess the signatures in 15 chemical elements at all otolith cores (to investigate potential differences in fish spawning origin among regions) and along all otolith edges (to characterize the chemical signatures of fish capture areas). Among the 15 chemical elements analysed, only Mg, P, Zn, Sr, Ba, B and Cu were above detection limits and significantly contributed to the variation in otolith composition. Based on differences in these elements, two groups of distinct multi-elemental signatures, denoting potentially discrete spawning origins (SpO), were identified at the otolith cores using hierarchical clustering based on Euclidian distances. Each of the two potential SpO contributed to the tuna sampled in all three areas, suggesting a common origin in some fish caught in the Atlantic and in the Indian Ocean and important trans-oceanic migrations between these two Oceans. The possible location of the two spawning areas is discussed based on the signatures recorded on the otolith edges before the final capture of the fish, in both oceans. This study was part of a collaborative project on the population structure of tuna, billfish and sharks of the Indian Ocean (PSTBS-IO).

Natal origin of 92 Albacore tuna (Thunnus alalunga) from the West Indian Ocean was investigated using trace elements in otoliths. Otoliths were collected from (i) 46 juveniles caught in 2 locations in South Africa (SA-North and SA-South) in 2018 and Tasmania (SWTS) in 2019, which are both known to be nurseries areas for the species, and (ii) 46 older fish caught in the Reunion island (SWI) during 3 sampling events in 2018. Otolithsconcentrations in seven chemical elements (B, Mg, P, Cu, Zn, Sr and Ba) were analysed by LA-ICP-MS at two points, near the core and at the edge, providing an elemental signal from the material deposited while the fish were close to their spawning grounds and from material deposited while they were in (or close) to their capture areas, respectively. Core and edge signatures for the same otolith were significantly different for most elements.At the edge, PCA identified different signatures (in Sr, Ba, and B) between the 3 main capture areas. Multi-elemental signatures for the Reunion samples were stable over the 3 sampling events. Those for South Africa samples split into 2 groups, the group of juveniles sampled in the Atlantic (SA- North) exhibiting signatures in B statistically different from those of all the juveniles from the Indian Ocean (SA-South and SWTS).The PCA on core signatures (from West Indian ocean and Atlantic ocean samples) identified some variation in spawning origin according to fish capture location. Based on the most relevant number of clusters, 2 putative spawning origins (SpO) with distinct chemical signatures in B and P were identified. All two SpO apparently contribute to the 3 sampling events investigated, but in varied proportions. Interestingly, although someoverlap was found between SA-North and SA-South signatures, the two juvenile sampling locations mostly had different spawning origin. SpO-2 was identified as the main spawning source for the albacore analysed (52%), principally in SA-S (76%), SWI-May18 (62%) and SWI-Dec18 (70%). SpO-1 apparently provides 47% of the fishsampled, principally in SA-N (69%) and SWI-Feb18 (85%). The samples collected do not allow to prove that these different spawning origins correspond to spatially discrete zones in the Indian or Atlantic Ocean. Nonetheless, these results bring evidence for trans-oceanic migrations in T. alalunga, which has strong implications for the management of its stocks

Swordfish, striped marlin and sailfish are the dominant billfish species caught in the Indian Ocean. These species are currently assessed and managed as single stocks. Evidence from population genetics studies to date has not provided evidence that a revision to this approach is warranted. Exploring and understanding the level of population heterogeneity is a priority for sustainable management of these fisheries. This paper presents results from a recent investigation of population structure of swordfish, striped marlin and sailfish using cutting-edge sequencing technology as part of a larger collaborative project "Population Structure of IOTC species and sharks of interest in the Indian Ocean (PSTBS-IO)". Sampling of striped marlin was challenging with only three individuals collected within the Indian Ocean, permitting only a rudimentary population comparison to a single outlier location in the Coral Sea, SW Pacific Ocean. Similarly, sailfish also proved difficult to obtain, however, sufficient samples were obtained to permit analysis from two Indian Ocean locations. No population structure was revealed for this comparison, which was consistent with sailfish representing a highly mixed Indian Ocean population. For both striped marlin and sailfish, sampling coverage was insufficient for the current study to unequivocally conclude whether there was evidence of sufficiently restricted gene flow to consider whether the Indian Ocean basin contains stocks of these species that are effectively isolated population(s) from the Atlantic and/or Pacific Oceans for fisheries management purposes. In contrast, swordfish samples permitted a broad spatial analysis that included 6 sampling locations within the Indian Ocean and an outlier sample location from the southwest Pacific in the Coral Sea. Differences in gene-frequencies of swordfish between the Indian and southwest Pacific Ocean, in the current study, and results from earlier studies from the southeast Atlantic Ocean support the assessment and management of swordfish within the Indian Ocean as an independent unit. Notwithstanding this conclusion, the potential for connectivity between the NE Indian and western Pacific Oceans requires further investigation. The indication of different northern and southern genetic groupings of swordfish, which may represent different reproductive populations, warrants targeted investigation via additional structured sampling and analysis that includes and expands the areas covered in this project and, ideally, includes sampling of spawning adults. For the three billfish species examined, insufficient sampling coverage was obtained for both sailfish and striped marlin to enable adequate assessment of population genetic structure. However, results for swordfish indicate consideration of management strategy refinement may be warranted, and highlights the need for targeted research to confirm the temporal stability of the results presented here, and in particular, further extending of sample coverage in the northern regions of the IO. Additional sampling both within and from locations outside the Indian Ocean should also be completed in order to provide a more comprehensive understanding of inter-ocean population boundaries for all three Indian Ocean billfish species.

Variation in otolith elemental fingerprints was investigated in the broadbill swordfish (Xiphias gladius) to complement genetic data obtained by next generation sequencing in the framework of a collaborative project on population stock structure of tuna, billfish and sharks of the Indian Ocean (PSTBS-IO). Swordfish specimens for this work were sampled in the southwest (SWI), west central (WCI) and southeast (SEI) regions of the Indian Ocean. A total of 70 otoliths (30 from SWI and 20 from each WCI and SEI) were selected and the elemental signatures of their cores were analysed by LA-ICP-MS to investigate potential differences in spawning origin among regions. Among the 15 chemical elements analysed, only Mg, P, Sr, Ba and B were above detection limits and significantly contributed to the variation in otolith core composition. Based on differences in these five elements, three groups of distinct multi-elemental signatures, denoting potentially discrete spawning origins (SpO), were identified using hierarchical clustering based on Euclidian distances. All SpO identified apparently contributed to the swordfish stocks of the three regions sampled, but in different proportions. SpO-1 was the most common spawning source among the fish sampled (49%); it probably corresponds to the swordfish spawning ground located between northeast Australia and Indonesia. SpO-3 was found to provide 34% of the total fish analysed, but mainly in SWI (53%) and WCI (35%). It could correspond to the spawning grounds reported for the species in the central and southwestern Indian Ocean. Lastly, SpO-2, which contributed to only 17% of the total fish analysed (mainly in SEI and WCI), may correspond to the spawning ground previously reported in the northwestern Indian Ocean, off the Somalian coast. Although our results show mixed origins in the fish sampled at each sampling location, the contrast in otolith core fingerprints between SWI and SEI otoliths suggests differences in main spawning origin, at least for the swordfish captured in these two regions of the Indian Ocean. Additional analyses are needed to consolidate these results, as well as information on the spatiotemporal distribution of chemical tracers in the water masses of the Indian Ocean to assign regions to otolith elemental signatures.

A series of substituted 1,4,7,10-tetraazacylcododecane ligands 1-4, possessing sensitizing nitrobenzene or naphthalene antennae, as one of the amide pendant arms, and their complexes with europium(III) were synthesised. The protonation constants and the metal ion stability constants of two of these ligands were determined by potentiometric titration. The pK(a) of the water molecules coordinated to the complexed metal ion were determined by both luminescent and potentiometric measurements. The luminescence pH dependence of a further three Eu(III) complexes, 5-7, which lack any antennae, were also studied with the aim of gaining a better understanding of the role of the metal bound water molecules in the luminescence properties of such complexes upon direct excitation of the lanthanide ion. The results from these luminescent measurements demonstrate that the Eu(III) emission was significantly modulated as a function of pH for all the complexes, which we assigned to changes occurring in the coordination environment of the ion within the cyclen system, caused by deprotonation of metal bound water molecules and/or deprotonation of pendent amide arms.