Loss of Mitochondrial Genetic Diversity in Overexploited Mediterranean Swordfish (Xiphias gladius, 1759) Population

Microplastic characterization in the stomachs of swordfish (Xiphias gladius) from the western Mediterranean Sea

In this study, we aimed to quantify the presence of microplastics (MPs) in the stomachs of large pelagic fish (swordfish, Xiphias gladius, Linnaeus, 1758) sampled in the western Mediterranean Sea, and assess temporal trends (2011-2012 vs. 2017-2019) in MP ingestion. MPs were extracted from stomachs and characterized by μ-Fourier transform infrared spectroscopy. Results highlighted the ingestion of MP in 39 out of 49 stomachs analysed. Ingested MPs consisted mostly of small (<1 mm) fibers (88.6 %, mean ± standard deviation = 2.5 ± 6.1 particles per stomach), with a greater frequency of occurrence (FO) in the second period (FO = 90 %, 3.3 ± 8.0 particles per stomach). The predominant colours were purple, black and blue, and polyethylene terephthalate was the most frequently detected polymer. These results are crucial for the development of management actions aimed at the conservation of swordfish in the Mediterranean Sea and the prevention of health risks to humans.

Age estimates derived from hard parts of swordfish Xiphias gladius from the north-western Mediterranean Sea

Accurate age estimates for fish are critical for properly understanding stock dynamics and health; this is particularly true for larger billfishes. Here we determined the most accurate aging estimation methods for swordfish (Xiphias gladius). We compared age estimates obtained from fin-ray sections, otolith sections, whole otoliths, and vertebrae collected from 87 swordfish off the east coast of Corsica. Age estimates from otolith sections were most consistently estimated across different readers (lowest average percentage error), followed by fin-ray sections, third vertebrae, and whole otoliths. When the age estimates from the otolith sections were compared with the other three age sclerochronological methods, we found the average percentage error to be lowest between the otolith section and fin-ray methods. However, age estimates from fin rays proved most useful for estimating swordfish younger than 6 years, as the fin ray-based age diverged from that of the otolith sections as the swordfish aged. Combining fin ray and otolith section techniques, we estimated the growth parameters of 1-12-year-old females (L∞  = 259.412, k = 0.113, t0  = -2.499) and 1-7-year-old males (L∞  = 175.543, k = 0.202, t0  = -2.239). We found that females grew significantly faster than males after 3 years and remained larger thereafter. Our calculated growth rates for this region of the north-western Mediterranean Sea were lower than those of the Atlantic, Pacific, and eastern Mediterranean Sea swordfish populations, and similar to growth rates recorded for the western Mediterranean Sea populations. Our study provides critical knowledge on biological-related parameters to serve as a guide for preserving the swordfish population in the Mediterranean Sea.

Cross-Amplification in Strigiformes: A New STR Panel for Forensic Purposes

Strigiformes are affected by a substantial decline mainly caused by habitat loss and destruction, poaching, and trapping. Moreover, the increasing trend in bird trade and the growing interest in wild-caught rather than captive-bred birds are expected to encourage illegal trade. The biomolecular investigation represents a valuable tool to track illegal trade and to explore the genetic variability to preserving biodiversity. Microsatellite loci (STRs) are the most used markers to study genetic variability. Despite the availability of species-specific microsatellite loci in Strigiformes, a unique panel permitting the description of the genetic variability across species has not been identified yet. We tested 32 highly polymorphic microsatellite markers to evaluate the reliability of a unique microsatellite panel in different species of Strigiformes and its use for conservation and forensic purposes. We included in the study 84 individuals belonging to 28 parental groups and 11 species of Strigiformes. After screening polymorphic microsatellite loci, the description of genetic variability, and the kinship assessment, we characterized a final panel of 12 microsatellite loci able to identify individuals in 9 Strigiformes species. This STR panel might support the authorities in the forensic investigation for suspected smugglers and false parental claims; moreover, it can be useful to evaluate relatedness among individuals in captive-bred populations and to implement research projects finalized to the description of the genetic variability in wild populations.

Demography of swordfish (Xiphias gladius Linneus) populations from the coasts of Turkey, based on mitochondrial DNA and microsatellites

The genetic diversity of the Mediterranean swordfish (Xiphias gladius Linneus) has not been explored extensively at its easternmost range so far. In this study, modern X. gladius samples from the eastern part of the Mediterranean basin, north of the Aegean Sea (Aegean-2013, n = 26) and the Mediterranean coast of Turkey (N.Levantine-2013, n = 42) were studied genetically, along with ancient samples from Yenikapı excavation (n = 6). Partial mitochondrial DNA control region sequences (entire sequences, clade I and clade II) were evaluated spatially and temporally together with previously published sequences (Alvarado Bremer et al., Molecular Phylogenetics and Evolution, 2005, 36, 169-187; Viñas et al., ICES Journal of Marine Science, 2010, 67, 1222-1229; Righi et al., Diversity, 2020, 12, 170) from the rest of the Mediterranean Sea. Pair-wise F_ST and pair-wise AMOVA tests showed that, in general, groups of eastern populations and western Mediterranean populations have not genetically differed from each other significantly nearly in the past 20 years. Therefore, the results direct reconsideration of previous descriptions of population sub-structure within the Mediterranean and support high gene flow throughout the region. On the contrary, the results of this study confirmed the existence of genetic diversity differences between western and eastern Mediterranean, with eastern being low. One-tailed permutation tests revealed that θ, which is directly proportional to long-term female effective population size (Ne), decreased significantly (P < 0.05) in both regions over the past two decades. On the Turkish coasts, θ is not significantly different from that of the nearly contemporary eastern Mediterranean population. Nonetheless, θ of the ancient sample was consistently and significantly (P < 0.001) higher than those of the eastern and western Mediterranean populations in clade I and clade II. Furthermore, it contains two mitochondrial haplotypes that are not observed in modern samples, suggesting that the Ne of X. gladius in the eastern was high in Byzantium times. Eight microsatellite loci were also genotyped in modern samples. The microsatellite-based present Ne estimate of the pooled Aegean-2013 and N.Levantine-2013 populations was lower than 1000 according to the upper limit of 95% c.i. and possibly even lower than 100 according to the mean of posterior distribution of the present Ne estimate calculated by the software package MSVAR. These alarming genetic signals for the sustainability of X. gladius on the coasts of Turkey are in agreement with the nearly collapsing X. gladius fisheries as depicted also in the fisheries statistics. Overall, congruent with the previous studies, the data presented here show that sustainability of the X. gladius population in Mediterranean is under major threat. Therefore, X. gladius around the Turkish coasts need an immediate stringent action and management plan.

Historical and Current Diversity Patterns of Mediterranean Marine Species

The Mediterranean is a sea which, despite its peculiar geomorphological history and ecological–oceanographic features, still receives less attention than it ought to [...]

Mediterranean swordfish (Xiphias gladius Linnaeus, 1758) population structure revealed by microsatellite DNA: genetic diversity masked by population mixing in shared areas

Background

The Mediterranean swordfish stock is overfished and considered not correctly managed. Elucidating the patterns of the Mediterranean swordfish population structure constitutes an essential prerequisite for effective management of this fishery resource. To date, few studies have investigated intra-Mediterranean swordfish population structure, and their conclusions are controversial.

Methods

A panel of 20 microsatellites DNA was used to investigate fine-scale population structuring of swordfish from six main fishing areas of the Mediterranean Sea.

Results

This study provides evidence to reject the hypothesis of a single swordfish population within the Mediterranean Sea. DAPC analysis revealed the presence of three genetic clusters and a high level of admixture within the Mediterranean Sea. Genetic structure was supported by significant F_ST values while mixing was endorsed by the heterozygosity deficit observed in sampling localities indicative of a possible Wahlund effect, by sampling admixture individuals. Overall, our tests reject the hypothesis of a single swordfish population within the Mediterranean Sea. Homing towards the Mediterranean breeding areas may have generated a weak degree of genetic differentiation between populations even at the intra-basin scale.