Movements of scalloped hammerhead sharks (Sphyrna lewini) at Cocos Island, Costa Rica and between oceanic islands in the Eastern Tropical Pacific

Abstract

Many species of sharks form aggregations around oceanic islands, yet their levels of residency and their site specificity around these islands may vary. In some cases, the waters around oceanic islands have been designated as marine protected areas, yet the conservation value for threatened shark species will depend greatly on how much time they spend within these protected waters. Eighty-four scalloped hammerhead sharks (Sphyrna lewini Griffith & Smith), were tagged with acoustic transmitters at Cocos Island between 2005–2013. The average residence index, expressed as a proportion of days present in our receiver array at the island over the entire monitoring period, was 0.52±0.31, implying that overall the sharks are strongly associated with the island. Residency was significantly greater at Alcyone, a shallow seamount located 3.6 km offshore from the main island, than at the other sites. Timing of presence at the receiver locations was mostly during daytime hours. Although only a single individual from Cocos was detected on a region-wide array, nine hammerheads tagged at Galapagos and Malpelo travelled to Cocos. The hammerheads tagged at Cocos were more resident than those visiting from elsewhere, suggesting that the Galapagos and Malpelo populations may use Cocos as a navigational waypoint or stopover during seasonal migrations to the coastal Central and South America. Our study demonstrates the importance of oceanic islands for this species, and shows that they may form a network of hotspots in the Eastern Tropical Pacific.

Catch composition and life history characteristics of sharks and rays (Elasmobranchii) landed in the Andaman and Nicobar Islands, India

“…Significantly more females than males for C. amblyrhynchos, S. lewini, and P. jenkinsii suggests that females of these species dominate the populations in these waters. These are also aggregating species often exhibiting some degree of side fidelity [52–56] another ecological character that needs to be considered in spatial management. Similarly, for L. macrorhinus, and H. leoparda, significantly more males were landed than females, whereas parity was recorded for C. falciformis .…”

Residency and diel movement patterns of the endangered scalloped hammerhead Sphyrna lewini in the Revillagigedo National Park

“…The high residency of female hammerheads in the southern area of SBI constitutes an important refuge as shown for this species at a seamount in the Gulf of California (Klimley & Nelson, ), which may relate to the magnetic properties of the site (Klimley, ) as well as the occurrence of cleaning stations (Bessudo et al ., ; Ketchum et al ., ). In the southern area of SBI, the strong currents could allow low‐energy swimming for the scalloped hammerheads during their aggregation in schools, as it has been suggested in other localities like Malpelo (Bessudo et al ., ), Galapagos (Hearn et al ., ; Ketchum et al ., ) or Cocos (Nalesso et al ., ).…”

“…The scalloped hammerheads remain at SBI during the day, whereas at night the lower number of detections may be due to the movement of sharks to offshore areas. This pattern has been suggested as part of the feeding behaviour and diel movements of S. lewini in other areas of the Eastern Tropical Pacific (Hearn et al ., ; Ketchum et al ., ,b; Nalesso et al ., ).…”

DNA Analysis of Juvenile Scalloped Hammerhead Sharks Sphyrna lewini (Griffith, 1834) Reveals Multiple Breeding Populations and Signs of Adaptive Divergence in the South Pacific

“…The scalloped hammerhead shark, Sphyrna lewini (Griffith, 1834), is a viviparous high trophic level predator, circumglobally distributed in tropical and warm temperate waters over both, neritic and adjacent pelagic waters, with fecundities ranging from 13 to 31 neonates of 42-55 cm total length per litter after a gestation period of 9-10 months (Compagno, 1984). The species is known to use coastal embayments and river mouths for parturition and juvenile development where they can grow and mature protected from large predators (Daly-Engel et al, 2012) and is known to form large femaledominated aggregations around oceanic islands with some degree of site fidelity and residency to these archipelagos (Nalesso et al, 2019). Juveniles are demersal and gregarious, while adult females form seasonal pelagic aggregations, and males appear to be more solitary and more common in open waters.…”

“…In the Eastern Pacific Ocean, males, juvenile and neonate scalloped hammerhead sharks are uncommon at oceanic aggregations. Pupping grounds for the Cocos, Galapagos, Malpelo, Revillagigedo and Gulf of California island populations are thought to be located mainly along continental shores of southern-North, Central and South America (Nalesso et al, 2019). For example, important nursery grounds have been documented in the western Pacific in the Golf of California (Torres-Huerta et al, 2008) and in the Golf of Tehuantepec in Mexico (Bejarano-Álvarez et al, 2011), and in the Golf of Nicoya in Costa Rica (Zanella et al, 2009).…”