Content area
Full Text
Introduction
The Red Sea, located between Africa and Asia, is a long, narrow saltwater inlet dominated by extensive shallow-water shelves (Bosworth et al., 2005). These shallow waters house abundant coral reefs, which are a popular draw for both tourists and scientific study (Gladstone et al., 2013). The Red Sea provides an unusual case study as the water below the subsurface depths of ~137–300 m remains warm (~21.5 °C; Yao & Hoteit, 2018), highly saline and oligotrophic throughout the water column, both horizontally and vertically (Thiel, 1979; Zajonz, 2007). The water column is slightly stratified into two layers by a weak thermohalocline, with the deep water being homogeneous down to its maximum depth of ~2900 m (Woelk & Quadfasel, 1996). This unusual phenomenon occurs as the Red Sea is largely cut off from the Gulf of Aden and the Indian Ocean, connected only by the narrow and shallow Strait of Bab el Mandeb, which prevents cold bottom water from entering (Woelk & Quadfasel, 1996) and also limits colonization of the Red Sea by primary deep-sea species from the older Indian Ocean (Zajonz, 2007). Despite these unique conditions, few investigations into the deeper depths of the Red Sea have been conducted beyond deep-sea corals and meiofauna (Thiel, 1979; Roder et al., 2013). The elevated temperatures throughout the water column appear to allow littoral species to live far deeper in the Red Sea than where they are found elsewhere (Khalaf & Zajonz, 2007), a phenomenon observed in other enclosed warm basins such as the Mediterranean Sea (Linley et al., 2018).
The bigeye hound shark, Iago omanensis (Norman, 1939) (Carcharhiniformes, Triakidae), also known as the Oman shark, is the best studied shark in the Red Sea, and may be the only deep-water or bathypelagic shark in the area (Spaet, 2019). This is largely due to its prevalence in Red Sea commercial fisheries, where it is considered bycatch (Henderson et al., 2006). However, along the coast of Oman, I. omanensis is a target species and is one of the most abundant and frequently landed fish (Henderson et al., 2007). Although this species is not considered to be threatened, as it currently listed as of Least Concern by the IUCN Red List, there is evidence...
