This report provides the first confirmed identifications of wahoo (Acanthocybium solandri) and striped marlin (Kajikia audax) in the Red Sea, expanding the known ranges of these species into the basin. Potential mechanisms responsible for the lack of regional documentation of the two species are further discussed. These findings illustrate the need for systematic biodiversity surveys of pelagic fish assemblages in the Red Sea.

Blue marlin are sexually dimorphic in size-at-age and other biological characteristics. However, few studies have examined the possible impact of sexual dimorphism on the population parameters and the ratios of fishing to total mortality (the exploitation ratios) for this species. We analyzed sex-specific catch-at-length data for blue marlin collected from the Taiwanese tuna longline fishery in the northwest Pacific Ocean, ranging between 100–311 cm in eye to fork length (EFL) for females and 100–236 cm EFL for males, and show that the proportion of females in the catch (the sex ratio) increases with length, with females reaching larger body sizes than males. Minor differences in fishery sex ratios among months were observed. Growth parameters, length structures, and natural mortality rates were estimated to differ between males and females, while fishing mortality rates were found to be similar. Nevertheless, the exploitation ratio for females was higher than that for males. We suggest that growth parameters and natural mortality rates should be sex-specific when assessments for sexually-dimorphic species such as blue marlin are conducted, and that management of blue marlin fisheries could be developed based on size limit regulations for large individuals.

Uncertainty about reporting rates of tags returned by fishermen has often prevented tagging data from being used in stock assessments. In this study we conduct a meta-analysis to estimate tag reporting rates of commercial tuna fleets by comparing their tag return data with those of the USA longline pelagic observer program. The longline fleets of Venezuela and the USA are estimated to report about 0.8% of tags caught, compared with less than 0.1% for Canadian, Spanish and Japanese longline fleets. For some fleets with sparse return data or for those that do not overlap often with the observer fleet, reporting rate estimates are sensitive to changes in the spatio-temporal resolution over which comparisons are made. Regardless of these sensitivities, the estimated reporting rates are low and there are likely to be large differences in reporting rate between different combinations of flag and gear.

The present study attempts to give information on the resource partitioning between the Mediterranean spearfish (Tetrapturus belone) and the swordfish (Xiphias gladius). The contents of 53 T. belone and 95 X. gladius non-empty stomachs were analysed from specimens caught in the central Mediterranean Sea (Strait of Messina), from 2004 to 2006, by the harpoon fishery. Daily catches (expressed as number of fish) showed the contemporary occurrence of both species in the studied area then allowing direct comparison of diets. Epipelagic fish were the dominant prey (%IRI = 99.1) of T. belone. Eight families were identified among them, with the dominance of Belonidae and Clupeidae, which represented 40.9% and 36.8%, respectively, of the total preyed items in terms of %IRI and were mostly composed of Sardinella aurita and Belone belone.

Xiphias gladius preyed mainly on teleosts and cephalopods, which represented 59% and 39.1%, respectively, of the total preyed items in terms of %IRI. Eleven teleost and five cephalopod families were recognized among them with the dominance of Trichiuridae (IRI% = 30.5) and Ommastrephidae (IRI% = 27.6). The first was represented only by Lepidopus caudatus (IRI% = 30.5), while the latter by the squid Todarodes sagittatus (IRI% = 21.1) and Illex coindettii (IRI% = 6.5). Results of a multivariate statistical analysis demonstrated that the dietary compositions differed significantly between swordfish and spearfish. Diet overlap analysed with the Schoener and Horn indices showed low values (0.23 and 0.21 for the two indices) underlining a food partitioning that prevents competitive exclusion. Our results highlight a feeding strategy that is more related to the habitat of the species than to the food availability. In fact, migration patterns of the two predators are quite different. Swordfish show vertical migrations from 0 to 800 m while spearfish are characterized by limited migrations, ranging between 0 and 200 m depths. The observation of specific prey items in the stomach content of both billfish confirmed the bathymetric range of their migrations.

The stomach contents of 69 Mediterranean spearfish Tetrapturus belone collected in the Strait of Messina, central Mediterranean Sea were examined. Of the total specimens, caught by harpoon, only three stomachs were empty. Their diet consisted mainly of pelagic fish and cephalopods. The most important piscine prey belonged to the families of Belonidae, Clupeidae and Scomberesocidae. Cephalopods were mainly represented by Tremoctopus violaceus in terms of per cent weight and by Illex coindetii in terms of per cent frequency of occurrence. Tetrapturus belone is an active predator on epipelagic fast-moving prey and school-forming species. Its ecological role is similar to that of other large pelagic species which share the same environment.