High concentrations of nutrients, phytoplankton and other organisms essential for the food chain in the Dome turn it into an important carbon sink and a highly prominent region for multiple species. Likewise, connectivity between habitats in the high seas and the coastal areas in Central America is critical for migratory species such as sharks, cetaceans, rays, billfish, and sea turtles, among others, including species in commercially important fisheries such as tuna, mahi-mahi and squid. Some of these species that benefit from nutrient rich waters of the Dome are described below.
Yellow fin tuna (Thunnus albacares)
IUCN Red List: Near Threatened
The yellow fin tuna is one of the most commercially important species worldwide due its use in the canning industry. In spite of its large distribution and high growth rate, it is catalogued as Near Threatened due to inefficient fisheries management.
They can reach up to 2.39 meters in length and weigh more than 200 kilograms. They feed primarily on fish, crustaceans and squid. Tuna are highly migratory and are commonly found in areas with temperatures between 18°C and 31°C but during spawning season they search for temperatures higher than 24°C, usually tropical equatorial regions. They hardly tolerance low oxygen concentrations, and as such are usually not found in depths greater than 250 meters in the tropics1.
Figure 6. Annual average yellow fin tuna catch.
In Figure 6 average annual rates of yellow fin tuna catch in the Eastern Tropical Pacific can be observed. The darker zones show higher annual catch. In the region, greater catch areas are concentrated in the Costa Rica Thermal Dome and its areas of influence.
In the Eastern Tropical Pacific, close to 200,000 tons of yellow fin tuna is caught annually making it the most significant fishery species in the region.2.
Blue Whale (Balaenoptera musculus)
IUCN Red List: Endangered
The blue whale is the largest animal that has inhabited the Earth, it can reach more than 33.6 meters in length and weigh 3,600 kilograms. It feeds almost exclusively on krill and can be found in all oceans expect for the Arctic.
The blue whale is considered endangered due to past indiscriminate fishing, which caused a drastic decline in its population. Even though it has been protected internationally since 1986, its population remains reduced.
Figure 7. Annual blue whale migration from the West Coast of the United States to the Costa Rica Thermal Dome.3.
Little is known about their migrations but both stationary and migratory populations have been observed. It is believed that populations that inhabit high latitudes migrate during winter in search of areas with higher temperatures and abundance of krill, while those that inhabit lower latitudes do not embark on long migrations.4.
Blue whales that visit the Costa Rica Thermal Dome come from California, United States, and Baja California, Mexico.5.
Common Dolphin (Delphinus delphis)
IUCN Red List: Least Concern
This species can reach 2.7 meters in length and weigh 150 kilograms. It generally forms groups of thirty individuals or less. Nevertheless, congregations of hundreds or thousands of common dolphins can be observed.
They generally feed on squid and small shoal forming fish, feeding on small groups at dusk.
Figure 8. Common dolphin sightings from NOAA/NMFS/SWFSC databases (1971-1999).6.
This species is classified as least concern by IUCN, incidental bycatch in fisheries being its main threat. There is an estimated three million common dolphins in the Eastern Tropical Pacific. In this same area the species tends to be associated with yellow fin tuna (Thunnus albacares), explaining its susceptibility to becoming bycatch in purse seines7,8.
Spotted Dolphin (Stenella attenuata)
IUCN Red List: Least Concern
This species can reach 2.57 meters in length and weigh 120 kilograms. Though the population has been significantly reduced in some areas due to massive bycatch, it is one of the most abundant cetaceans on the planet.
Its name comes from its dark back and light colored belly covered with a range of spots. Spotted dolphin feed primarily on at least 18 species of small pelagic fish, such as cephalopods and crustaceans that ascend to the surface. Groups of several hundreds or thousands can be observed in open waters. This species tends to be associated with spinner dolphin (Stenella longirostris), yellow fin tuna (Thunnus albacares) and sea bird flocks. Grouping helps improve its chance at feeding, offers protection from predators or simply helps them stay oriented in open waters.
Figure 9. Spotted Dolphin sightings from NOAA/NMFS/SWFSC databases (1971-1999).9.
This species is classified as least concern. Incidental bycatch in fisheries is its main threat. There are an estimated two million spotted dolphins in the Eastern Tropical Pacific. Even though they are not at risk of extinction, tuna purse seine fisheries reduced their populations during the sixties and seventies to 25% of their original size.10.
Sailfish (Istiophorus platypterus)
IUCN Red List: Least Concern
Sailfish is one of the most attractive fish in sport fishing. The species can measure up to 3.6 meters and habitually feeds on fish, crustaceans and cephalopods. They habitually migrate to tropical Pacific areas to reproduce. In Costa Rica they are commonly found from July to October.
Even though it is classified as a species of least concern by the IUCN on a worldwide level, its Costa Rican population has diminished by 80% since 1964. Its greatest threat is incidental bycatch. Although targeted fishing is forbidden in Costa Rica, it can be commercialized as incidental bycatch as long as sailfish does not exceed 15% of the total catch.
Sailfish has very high oxygen demand, reason it keeps away from the dome’s mayor productivity region, since high concentrations of phytoplankton reduce available oxygen. Nevertheless, it stays within the area of influence because the fish and squid they live off are abundant there, hence providing important nourishment to the species.
Sport fishing for which sailfish is the most important species is a growing industry in the region. Sport fishing in Guatemala generates an estimated income of at least 25 million dollars a year. 11. The University of Costa Rica calculated that sport fishing contributes 599 million dollars a year to the country’s national economy,12. while in Panama sport fishing contributes to 90.7 million dollars annually to the local economy.13.
Silky Shark (Carcharhinus falciformis)
IUCN Red List: Least Concern
This shark can measure up to 3.5 meters in length and weighs up to 346 kilograms. It lives in tropical waters around the world where it is a dominant species in fisheries, both as a targeted species and incidental bycatch.
Figure 10. Movements of tagged silky shark in the Eastern Tropical Pacific.14.
Silky shark is a pelagic species found near the continental shelf and islands at depths of 200 meters or more and is commonly associated with islands or deep-water reefs. Its young is found in coastal regions while adults head towards deeper open waters.
This species is caught in commercial and artisanal fisheries in the Eastern Tropical Pacific, especially with longlines or incidentally in purse seine fishing. Its population shows a decreasing tendency. Its abundance and biomass is calculated to have been reduced by more than 90% in the region.15.
Leatherback Turtle (Dermochelys coriacea)
IUCN Red List: Vulnerable
Leatherbacks are the world’s largest turtle. It can weigh up to 900 kilograms and measure 2 meters in length. Its nourishment consists of soft-bodied organisms, mainly jellyfish, salps and siphonophores.
Figure 11. Adult leatherback migration from Playa Grande, Costa Rica, after spawning.16.
Leatherback turtles have a wide distribution and are highly migratory. They move among different feeding zones and then migrate to tropical beaches where they nest. Every two years during their reproductive stage, these turtles go back to the beach they were born to nest. During the 8 to 12 day reproductive stage, each female can make 3 to 10 nests laying between 60 and 90 eggs in each.
The main threats this species faces is the recollection of its eggs for human consumption and drowning as incidental bycatch in longline fisheries. On a lesser scale the destruction and alteration of the coast, habitat where they nest, and climate change also affects the species’ population.17.
10 Folkens, P.A.; B.S. Stewart; P.J. Clapham & J.A. Powell. 2002. Guide to marine mammals of the world. National Audobon Society. 527pp.
11 Villagrán, G. 2015. Guatemala, con el reservorio más grande de pez vela. Diario de Centro América. http://www.dca.gob.gt/index.php/nacional/item/25847-guatemala-con-el-reservorio-m%C3%A1s-grande-de-pez-vela.
12 Yong-Chacón, M.; A. Gutiérrez-Li; C. Fernández-García; R. Lucke-Bolaños; F. Rojas & G. González (2010). Informe final: un análisis de la contribución económica de la pesca deportiva y comercial a la economía de Costa Rica. Instituto de Investigaciones en Ciencias Económicas de la Universidad de Costa Rica bajo el patrocinio de The Billfish Foundation. San José, Costa Rica: 166p.
13 Southwick, R.; R. Nelson; R. Lachman & J. Dreyfus. Sportfishing in Panama: Size, Economic Impacts and Market Potential. Produced for The Billfish Foundation. February, 2013.
14 Modificado de Kojin, S.; R. Arauz; D. Holts & R. Vetter. 2006. Preliminary results: behavior and habitat preferennces of silky sharks (Carcharhinus falciformis) and a big eye thresher shark (Alopias superciliosus) tagged in the Eastern Tropical Pacific. Memoria del primer seminario-taller del estado del conocimiento de la condrictiofauna de Costa Rica. Instituto Nacional de Biodiversidad INBIO. Santo Domingo de Heredia, Costa Rica.
16 Modificado de Shillinger, G. L.; D. M. Palacios; H. Bailey; S. J. Bograd; A. M. Swithenbank; P. Gaspar; B. P. Wallace; J. R. Spotila; F. V. Paladino & R. Piedra (2008). Persistent leatherback turtle migrations present opportunities for conservation. PLoS Biology Vol. 6(7): e171.