Bermuda Humpbacks Feature In New Study

April 27, 2013

Research published this week in the journal “Science” involving a population of humpback whales which spends time in Bermuda’s waters every year adds further evidence to the theory the giant mammals are able to learn from one other, in this case passing on a hunting technique suited to a particular type of prey.

The authors of the study found, via analysis of a database collected over three decades, that since it was first recorded this particular behaviour has spread across 40 per cent of the population concerned.

This population of humpback whales spend their summers in the Gulf of Maine. The whales arrive there every year to spend the summer feeding before making the return journey to breed in the Silver Bank off the Dominican Republic and in Bermuda.

Dr. Luke Rendell, a Marine Alliance for Science and Technology Scotland [MASTS]-supported lecturer in the School of Biology at the University of St. Andrews, Scotland spoke to ScienceOmega.com’s Katy Eddington about the innovative hunting strategy and its implications for cultural transmission in humpback populations.

humpback-whale

Humpbacks around the world have been observed herding shoals of fish with underwater nets of bubbles, but ‘lobtail feeding’ involves the whale hitting the water with its tail before diving. It then blows bubbles below the disturbance it’s created before swimming up through the centre. It has been hypothesised that the surface disruption helps to herd the fish in some way, but it remains unclear whether this is the true purpose of the behaviour.

“It was first recorded in 1980 as part of a study of feeding behaviour in that population that was mostly done from an aeroplane,” Dr Rendell stated. “Around 150 incidences of humpbacks feeding were observed. One incident, it was noticed, used this technique, although it wasn’t described as lobtail feeding at the time. The behaviour first appears in the records of the whale-watching observers in the following year – 1981 – when it was recorded five times.”

Dr. Rendell explained that it is difficult to pinpoint what necessitated the invention of lobtail feeding because researchers are not certain what the functional significance of the behaviour is. However, it is believed to be an adaptation for feeding on sand lance.

“There seems to be an uptick in the rate of individuals performing this behaviour when sand lance adundance is relatively high, and it was initially seen when the stock of herring in the area had crashed and the stock of sand lance was entering a boom period,” Dr Rendell continued. “There was an ecological shift and we believe lobtail feeding was a response to that.”

If behaviour is passed on by cultural transmission, it follows that the more you ‘hang out with’ a particular individual, the more likely you are to adopt the behaviours that they display. From the data collected over 30 years by the New England whale-watchers, the authors were able to build up a picture of the social network of the whales, including which ones spent most time together.

“We were able to determine when the behaviour was first observed in individual whales, and assumed that was some index of when they actually learned it,” Dr. Rendell said. “The analysis technique assumes that, if cultural transmission is responsible, you would expect animals which are socially connected to other animals that already know the behaviour to be more likely to learn it.”

The technique quantifies the strength of that relationship, allowing the investigators to compare models describing what would be expected if there was no social transmission going on, and what would be expected if the social network influenced the learning rate of individual whales.

The cultural transmission model was the best fit for the data. Since it was first observed, lobtail feeding has spread through 40 per cent of the New England humpbacks via this process.

“There has been a lot of debate and discussion about cultural processes in whales and dolphins over the last ten years,” said Dr. Rendell. “To my mind, this study highlights how crucial these learning processes are for the animals to be able to spread new feeding behaviours – which we think are responses to ecological change – through their population. This goes some way to explaining why the humpback whale is a particularly successful animal in its ecosystem. We think cultural transmission plays a vital role in their success.”

Humpback whales filmed in Bermuda’s waters by Andrew Stevenson

The Bermuda Humpback Whale Project has been compiling a photo-ID catalogue of the island’s greatest return visitors since 2007 — documenting at least 150 of the magnificent migratory animals in the island’s waters between February and May every year.

Headed by conservationist and filmmaker Andrew Stevenson, the Humpback Whale Project researches and collect visual and acoustics data on the great sea creatures.

Last year Bermuda’s Exclusive Economic Zone [EEZ] was declared a Marine Mammal Sanctuary with particular emphasis on the endangered humpback whale.

Then Environment, Planning and Infrastructure Strategy Minister Marc Bean announced on Sept 21, 2012 that: “The area of the new Bermuda Marine Mammal Sanctuary will be more than 170,000 square nautical miles, approximately circular in shape with Bermuda at its centre.

“Although by no means the biggest Marine Mammal Sanctuary in the world, it is a very substantial size and we hope it will be a great contribution to marine mammal conservation in the Atlantic Ocean.”

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