Species in the Spotlight: Humpback Whales

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Written by Isobel Chaudhuri, our recent school intern, as part of her work experience with Restore Blue.

The humpback whale is often called the gentle giant, the singer of the sea, and one of the ocean's greatest travellers. Its size, intelligence and curiosity have captivated people all over the world, and it is increasingly seen closer to home, in Irish waters.

As offshore wind expands, there is growing interest in how projects can be planned, built and operated in ways that minimise harm to these remarkable animals. The good news is that the risks are increasingly well understood, and there are ways to manage them alongside renewable energy development.

What are humpback whales?

Humpback whales (Megaptera novaeangliae) are baleen whales found in every major ocean basin around the world. Adults average around 14 to 15 metres in length and 25 to 35 tonnes, with females slightly larger than males. They are best known for their long pectoral fins, their acrobatic breaching, and their beautiful song.

• The song: male humpbacks sing complex songs, each lasting around 20 minutes and repeated for hours.
• The diet: humpbacks filter-feed on krill and small schooling fish, sometimes working together to trap prey with "bubble nets".
• The journey: many populations migrate thousands of kilometres each year, between cold, productive feeding grounds in summer and warm breeding grounds in winter.

Humpbacks are also a growing presence off Ireland. Since 1999, the Irish Whale and Dolphin Group has used photo-identification to record at least 140 individual humpback whales in Irish waters, some returning year after year to feed off the south and west coasts.

Offshore wind and whale habitat

Offshore wind farms are a long-term feature of our seas, so it is important to understand how they could affect whales and how those effects can be managed. Without the right measures in place, the main potential pressures are:

Supporting coexistence

Around the world, projects now use a range of measures to protect whales while allowing offshore wind to grow:

• Bubble curtains: a ring of air bubbles released around the pile during installation, which dampens sound before it spreads. During construction of a German North Sea wind farm, a big bubble curtain reduced the area where harbour porpoises were disturbed by around 90%.
• Soft starts: pile driving begins at low power and builds up gradually, giving animals time to move away before full-power work begins.
• Marine mammal observers and acoustic monitoring: trained observers and underwater microphones check that no whales are nearby before and during noisy work.
• Vessel speed limits and set routes: slower speeds and agreed shipping routes reduce the risk of collisions.
• Careful timing and siting: early planning in the project to avoid sensitive areas and seasons, such as key feeding periods.

In Ireland, the National Parks and Wildlife Service publishes guidance for managing the risk to marine mammals from man-made underwater sound. For pile driving, this includes a soft start and a trained marine mammal observer, who must watch for at least 30 minutes and confirm no marine mammals are within 1,000 metres before work begins.

Looking ahead

Offshore wind is central to cutting greenhouse gas emissions, and climate change is one of the greatest long-term threats to ocean wildlife. When protections are designed into projects from the outset, we can expand renewable energy and safeguard humpbacks at the same time.

With humpbacks returning to Irish waters in growing numbers, they are certainly a species to keep in the spotlight!