Saturday, April 7, 2018

Basking Sharks Aggregations - North America Northeast Coast

Groups of basking sharks, ranging from as few as 30 to nearly 1,400 animals, have been observed aggregating in waters from Long Island to Nova Scotia.

Individual basking shark sightings are fairly common, but large groups are not, according to NOAA Fisheries.

In a recent study reported in the Journal of Fish Biology, researchers analyzed aggregations of basking sharks (Cetorhinus maximus) recorded off the northeastern United States coast to learn more about the phenomenon.

During decades of aerial surveys for right whales, large basking shark aggregation events were recorded and photographed on several occasions.

Comparing this information with that collected in a number of satellite and oceanographic databases and by the NEFSC’s ecosystem monitoring (EcoMon) cruises in the same region, researchers obtained more insight into this behavior.

The researchers found the aggregations occurred in summer and fall when sea surface temperatures ranged between 55 and 75 degrees F (13 to 24 degrees C). In the largest event, data were available to indicate there was a high concentration of zooplankton prey present.

Ten large aggregations of basking sharks were identified between June 1980 and November 2013, ranging from 36 to at least 1,398 animals within an 11.5-mile (18.5-kilometer) radius of the central point in the aggregation.

Data on breaching, circular swimming movements, and/or apparent feeding behavior were recorded in seven of the ten largest aggregations.

The largest aggregation ever recorded on the aerial survey was at least 1,398 animals photographed on November 5, 2013 in southern New England waters.

Given the apparent presence of juveniles and an abundance of zooplankton on the continental shelf at the time of the event, the study authors say it is likely foraging played a role in the formation of that aggregation.

The study also suggests that the animals may be aggregating to draft off each other for more efficient feeding given the immense drag from having their mouths open.

Basking Shark Facts

Basking sharks are highly migratory, slow-moving fish. They are often sighted close to the surface with their large mouths open to filter zooplankton from seawater.

Reaching 32 feet or more in length and weighing more than five tons, the basking shark is the world's second largest fish. The whale shark, a close relative, is larger.

Basking sharks, whale sharks, and megamouth sharks are the only shark species that feed on plankton.

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source: NOAA Fish News

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