Abundance & Distribution Discovery

Deepwater skate specimens collected along the Mid-Atlantic Ridge may change how scientists describe the colonization of the North Atlantic.

Referred to as "batoids" due to their wide, flat shape, skates and rays are relatives of sharks and therefore have cartilaginous skeletons. Found inhabiting most oceanic environments world-wide, these fish also have groups within their ranks that live far up rivers, and some species live exclusively in freshwater. While, as a group, skates and rays appear to be fairly common, some species remain relatively unknown. The skates that inhabit the deep ocean areas of the North Atlantic fall within this group of under-studied batoids. Many of the deep-water species of skates that are known were only discovered within the last half of the 20th century, and many are only represented by small numbers of collected specimens.

In 2004, the Mid-Atlantic Ridge Ecosystem (MAR-ECO) project of the Census of Marine Life conducted studies of deep bottom dwelling fish along the Mid-Atlantic ridge from the Azores to Iceland in the Northeast Atlantic Ocean. From the R.V. G.O. Sars bottom trawls were conducted down to depths of 3,500 m and from the longlining vessel the M.S. Loran, bottom longlines were deployed at depths down to 4,500 m. The results of these studies and the specimens collected are now suggesting that formerly accepted hypotheses of how skates and rays populated the North Atlantic Ocean may need to be revised. Past studies were focused on continental shelf and slope areas surrounding the North Atlantic basin and have been described by researchers as "inadequate". These studies generated the theory that skates and rays spread across the North Atlantic by following the continental shelf regions.

MAR-ECO researchers found that along the Mid-Atlantic ridge, certain species of skates were much more common than previously thought and have even found both juveniles and breeding/spawning adult populations. This suggests that these species are resident in the area and that the Mid-Atlantic Ridge could serve as a colonization pathway through the deep sea. In the past, it was believed that specimens encountered along the ridge were transient visitors and not members of resident populations. These new data are initiating a new look at the biogeography of these animals and may provide new understanding of how their populations have evolved. Future research may provide further insight into how these fish have become so successful and widespread.

What: The presence of both juvenile and spawning adult skates along the Mid-Atlantic Ridge suggests that colonization of the North Atlantic ocean may involve different pathways than previously thought.
Who: MAR-ECO Scientists --> A. Orlov, C. Cotton, and I. Byrkjedal
When: 2004
Where: Mid-Atlantic Ridge, North East Atlantic Ocean
How: Specimens collected via bottom trawl (at depths down to 3500 m) and bottom longlines (at depths down to 4500m).
Reference: Orlov, A., C. Cotton, and I. Byrkjedal. 2006. Deepwater skates (Rajidae) collected during the 2004 cruises of R.V. "G.O. Sars" and M.S. "Loran" in the Mid-Atlantic Ridge area. Cybium 30(4) suppl.: 35-48.

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