Another source of threats in the Alboran Sea is the accumulation of heavy metals,
such as cadmium, lead, copper, and zinc, which have been detected in loggerhead
turtle tissue samples (García-Fernandez et al. 2008). Such heavy metals have also
been found in their main prey, Polybius henslowii, along the southern Portuguese
coast (Nicolau 2017) and in the strait of Gibraltar (Ocaña et al. 2005).
Observations of sea turtles are frequent on the north and south coasts of the
Alboran Sea due to the number of specimens that are stranded either alive, dead, or in
poor condition in these areas (Bellido et al. 2010a, b; Rojo-Nieto et al. 2011;
Benhardouze et al. 2012a). Each year, many injured turtles or their carcasses are
found on Andalusian coasts (Camiñas 2002; Bellido et al. 2010a, b). The high
frequency and steady rate of turtle strandings per year, as well as mortality/injury
rates, suggest that there is a high presence of sea turtles, particularly loggerheads and
leatherbacks, along the Andalusian coastline (Bellido et al. 2018a). According to
Rojo-Nieto et al. (2011), there are more loggerhead turtle strandings on the northern
Alboran coasts, whereas there are more leatherback turtle strandings on southern
Alboran coasts.
Regarding strandings for which it is possible determine the cause of death, up to
43% of loggerhead strandings, could be directly attributed to anthropogenic causes
such as trauma and interaction with fisheries. According to Bellido et al. (2007,
2018a), longline bycatch is not the main cause of loggerhead strandings on the
Alboran coast. Natural causes, such as debilitated turtle syndrome (Vallini et al.
2011), and disease account for the remaining 57% of loggerhead strandings. However, the cause of leatherback strandings is very difficult to determine. In most cases,
stranded specimens have been found dead and in an advanced state of decomposition, which makes it difficult to determine the cause of stranding. Nevertheless, in
some cases, the presence of net marks on flippers establishes the cause of death as
interactions with fisheries (Bellido et al. 2018a).
Regarding natural hazards in the Alboran Sea, sea turtles could be affected by
cold stunning (Bellido et al. 2008a), diseases driven by epibionts (Bellido et al.
2010a), and predation by large sharks (Bellido et al. 2018b). Although white sharks
rarely prey on loggerhead turtles, the proportion of sea turtles in the white shark diet
is the highest in the Mediterranean area (Morey et al. 2003).
21.4 Seabirds
The Gibraltar-Alboran Sea region is one of the most important corridors for seabirds
in the Palearctic, because it connects continental Europe and Africa as well as the
Atlantic Ocean and Mediterranean Sea (e.g. see Arcos et al. 2009). The numbers of
seabird inhabiting in Alboran Sea varies across years and seasons. There are
49 species including resident, migrant, wintering, occasional, and vagrant birds
(Table 21.1). Ornithological interest in this biogeographic region arose in the
nineteenth century (e.g. Irby 1875; Garrido Sánchez 2017), when naturalists frequently visited the area to collect specimens and eggs and to conduct research on
21 Marine Megafauna and Charismatic Vertebrate Species
717
such as cadmium, lead, copper, and zinc, which have been detected in loggerhead
turtle tissue samples (García-Fernandez et al. 2008). Such heavy metals have also
been found in their main prey, Polybius henslowii, along the southern Portuguese
coast (Nicolau 2017) and in the strait of Gibraltar (Ocaña et al. 2005).
Observations of sea turtles are frequent on the north and south coasts of the
Alboran Sea due to the number of specimens that are stranded either alive, dead, or in
poor condition in these areas (Bellido et al. 2010a, b; Rojo-Nieto et al. 2011;
Benhardouze et al. 2012a). Each year, many injured turtles or their carcasses are
found on Andalusian coasts (Camiñas 2002; Bellido et al. 2010a, b). The high
frequency and steady rate of turtle strandings per year, as well as mortality/injury
rates, suggest that there is a high presence of sea turtles, particularly loggerheads and
leatherbacks, along the Andalusian coastline (Bellido et al. 2018a). According to
Rojo-Nieto et al. (2011), there are more loggerhead turtle strandings on the northern
Alboran coasts, whereas there are more leatherback turtle strandings on southern
Alboran coasts.
Regarding strandings for which it is possible determine the cause of death, up to
43% of loggerhead strandings, could be directly attributed to anthropogenic causes
such as trauma and interaction with fisheries. According to Bellido et al. (2007,
2018a), longline bycatch is not the main cause of loggerhead strandings on the
Alboran coast. Natural causes, such as debilitated turtle syndrome (Vallini et al.
2011), and disease account for the remaining 57% of loggerhead strandings. However, the cause of leatherback strandings is very difficult to determine. In most cases,
stranded specimens have been found dead and in an advanced state of decomposition, which makes it difficult to determine the cause of stranding. Nevertheless, in
some cases, the presence of net marks on flippers establishes the cause of death as
interactions with fisheries (Bellido et al. 2018a).
Regarding natural hazards in the Alboran Sea, sea turtles could be affected by
cold stunning (Bellido et al. 2008a), diseases driven by epibionts (Bellido et al.
2010a), and predation by large sharks (Bellido et al. 2018b). Although white sharks
rarely prey on loggerhead turtles, the proportion of sea turtles in the white shark diet
is the highest in the Mediterranean area (Morey et al. 2003).
21.4 Seabirds
The Gibraltar-Alboran Sea region is one of the most important corridors for seabirds
in the Palearctic, because it connects continental Europe and Africa as well as the
Atlantic Ocean and Mediterranean Sea (e.g. see Arcos et al. 2009). The numbers of
seabird inhabiting in Alboran Sea varies across years and seasons. There are
49 species including resident, migrant, wintering, occasional, and vagrant birds
(Table 21.1). Ornithological interest in this biogeographic region arose in the
nineteenth century (e.g. Irby 1875; Garrido Sánchez 2017), when naturalists frequently visited the area to collect specimens and eggs and to conduct research on
21 Marine Megafauna and Charismatic Vertebrate Species
717