Condrictios del atolón Albuquerque durante la Expedición Seaflower 2018 - Proyecto Colombia BIO

Study Extent

Isla Cayo Albuquerque, Reserva de la Biósfera Seaflower, Colombia.

Sampling

In response to population declines noted for many sharks and other elasmobranch species around the world, protecting them from overexploitation has become a global priority. However, the necessary data to assess the diversity and abundance of elasmobranchs has often hindered efforts to effectively restore and protect such species. Many reef surveys around the world have been conducted by scuba divers, although many studies have exposed the flaws and biases of this type of surveys for species such as elasmobranchs. Sampling of these species has traditionally been resource and time intensive due to the need to capture sharks or rays on lines. Recently, advances in video technology and molecular tools have allowed the deployment BRUVs and conduct eDNA surveys. The video (BRUV) technique involves positioning a bait source in front of an underwater video camera and quantifying the fish that are observed in the field of view over a standard sampling period and are an ideal way to quickly, and inexpensively, sample populations of relatively low-density predators like sharks and rays. Due to the remote location of Isla Cayos de Albuquerque in the southern most region of the Seaflower Biosphere Reserve, there is a lack of knowledge of elasmobranch species and their abundance in the area. The environmental DNA (eDNA) technique involves collecting 4Lts of water from the bottom of the reef and passing it through a filter to concentrate the suspended DNA in the water and conduct next generation sequencing with shark-specific primers to detect the presence of these organisms in the reef. The catch-and-release technique involves five weights at the bottom with baited hooks to catch the elasmobranchs present on the back reef and inner lagoon. Once a shark is caught, length measurements and sex are recorded and a DNA samples is taken for future population genetics analyses.

Method steps

1. Elasmobranch diversity and abundance was surveyed on the fore-reef, back-reef, and the inner lagoon selecting sites randomly within the defied boundary of the study reef. Forty-nine BRUVs were deployed consisting of a video camera (GoPro) mounted on a metal frame with a cage with pre-weighted bait source (e.g. 1 kg of sardines) attached to a metal pole in the camera’s field of view. Each BRUV was deployed using a 50 m rope from the boat and in-water personnel to orient the BRUV facing down current between 5 to 30 m of depth. Cameras recorded for standardized 90 minutes after settling to the bottom. No BRUVs were simultaneously deployed within 1000m of one another. Units were manually retrieved using the rope, which terminates in a small buoy to aid in relocation. At both the start and end of each deployment environmental variables such as underwater visibility, temperature, salinity, wind speed and wind direction, bottom depth, cloud cover and surface wave (chop), were recorded.
2. Twenty eDNA samples were taken on the fore-reef using 2 Neskin bottles of 2 Lt each. The volume of water was passed through a filter on-board to concentrate the DNA suspended in the water column and stored in a freezer with silica beads until analysis at the lab. Molecular analysis consists on using shark-specific primers and running next-generation sequencing to reconstruct the DNA left behind by the shark species present in reef.
3. Thirty-three drumlines were deployed in the back-reef to catch and release elasmobranchs. Drumline consisted on 5 weights at the bottom with one baited hook at the end of a 7 m line attached to each weight. Drumlines were manually retrieved using a rope, which terminated in a small buoy to aid in relocation. Once a shark was caught, catch time, species, sex, and length were recorded and a tissue sample was collected from the free rear tip of the second dorsal fin. At the moment of release, the hook was removed from the shark.

106 registros pertenecientes a 5 ordenes.

1. Carcharhiniformes
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2. Testudines
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3. Orectolobiformes
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4. Mammalia
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5. Myliobatiformes
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Isla Cayo Albuquerque, Reserva de la Biósfera Seaflower, Colombia.