Deadly interaction between a swordfish Xiphias gladius and a bigeye thresher shark Alopias superciliosus
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Deadly interaction between a swordfish Xiphias gladius and a bigeye thresher shark Alopias superciliosus Patrick L. Jambura1 · Julia Türtscher1 · Jürgen Kriwet1 · Sara A. A. Al Mabruk2 Received: 18 June 2020 / Revised: 23 September 2020 / Accepted: 24 September 2020 © The Ichthyological Society of Japan 2020
Interspecific aggressive behaviour has been reported for a number of fish species, including not only coral reef fishes that compete for territory (Myrberg Jr and Thresher 1974; Eurich et al. 2018), but also large pelagic fishes, such as billfishes (Istiophoridae and Xiphiidae), which are known to exhibit aggressive behaviours towards other species. The swordfish Xiphias gladius, which is a highly mobile, predatory fish is known to attack sharks (e.g. Starck 1960; Penadés-Suay et al. 2017, 2019; Romeo et al. 2020), whales (Machida 1970), sea turtles (Frazier et al. 1994), humans (e.g. Gooi et al. 2007; Georgiadou et al. 2010), and even inanimate objects, e.g. boats and submarines (Zarudski and Haedrich 1974; Romeo et al. 2017). The resulting impact can lead to a transverse fracture of the bill, with the distal segment often remaining embedded in the victim. Aggressive behaviour towards thresher sharks (Lamniformes, Alopiidae), however, was only suggested once before in a conference contribution (Vacchi et al. 1999). Here, we present the first verified illustrated documentation of a stranded bigeye thresher Alopias superciliosus that was fatally wounded by a swordfish and discuss this incidence within the context of a possible accidental collision or interspecific aggression. In April 2020, a dead female thresher shark was found washed ashore on the Libyan coast near the town of Brega (30°25′18.1"N, 19°37′38.9"E). Videos and photos of the animal were taken on April 1st and April 4th and sent to the citizen science initiative “Marine biology in Libya”. The species was identified based on the following features (sensu Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10228-020-00787-x) contains supplementary material, which is available to authorized users. * Patrick L. Jambura [email protected] 1
Department of Palaeontology, University of Vienna, 1090 Vienna, Austria
Zoology Department, Omar Al-Mokhtar University, El Bayda, Libya
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Ebert et al. 2013): (1) long curving upper tail lobe nearly as long as the rest of the shark; (2) body grey-brown on the dorsal surface and light grey to white ventrally, not extending above pectoral fin bases; (3) huge eyes, orbits expanded onto dorsal head surface; (4) deep horizontal groove above gills; (5) very long narrow pectoral fins (Figs. 1 and S1). A total length (TL) of 445 cm was measured by one of the citizen scientists, which was supported by analysing the images and comparing the dimensions of the shark with an object of known size (i.e. the right hand of the observer). Female bigeye threshers mature at a TL of 330-350 cm (Ebert et al. 2013). Therefore, the examined specimen is regar
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