Humpback whales visiting coast earlier each year – study

Humpback whales are visiting the Irish coastline, earlier each year, correlating with rising global ocean temperatures, according to new academic research.

The research was led by ATU Galway PhD student Miguel Blásquez, who studied approximately 20 years of humpback whale data collected through the Irish Whale and Dolphin Group.

The first humpback whale sighting of the season advanced from 15 September in 1999 to 2 May in 2015 and to 2 March in 2023, the research found.

The IWDG has been collecting sightings and photo identification since 1999 as part of a citizen science project named Whale Track Ireland.

Images were submitted by naturalists, citizen scientists, and observers. Sightings were then validated, following strict methodologies to ensure data quality.

A total of 1,127 humpback whale photo identification sightings were recorded between 1999 and 2023 by 226 different contributors.

Humpback whales, ranging in size from 12-18 metres in length, are found in all major oceanic basins and can travel thousands of kilometres.

The study published in the Marine Mammal Science Journal indicates that the first annual sightings have shifted at a rate of approximately nine days earlier per year between 1999 and 2023.

The researchers said, to their knowledge, such steep rates have not been documented elsewhere. They added the last sighting of the season remained stable.

The study indicates that Ireland and adjacent UK waters may serve as a feeding ground for a subset of humpbacks that mainly reproduce in breeding grounds off Cape Verde.

Researchers found that 70% of identified humpbacks were recorded again across different calendar years, and 25% of those were resighted in five or more years.

Modelling suggested that the identified humpbacks spent a minimum 20 days, patrolling, hunting and feeding within a 100km range while in Irish waters.

The study, recognised as the most comprehensive analysis to date of humpback movement patterns in Irish waters, was supported by Fundación Mutua Madrileña and the Government's postgraduate scholarship program.

The findings align with predictions on climate change effects in marine environments, in that rising sea temperatures can alter prey availability and distribution.

The research suggested that area-based protection measures could help mitigate the impacts of human activities on the humpback whales who feed in Irish coastal waters.

'Humpback Whale Site Fidelity, Residency, and Movement Patterns in Ireland Based on Citizen Science Data’ was published in the Marine Mammal Science.

Dr Simon Berrow of the IWDG said when the project began, the first whales were sighted off the Cork coastline, but in recent years, they’re appearing more frequently in Donegal Bay.

"We’ve loosely correlated this to sea surface temperatures.We know the seas are warming and this has profound impacts on the prey and how the whales behave," he said.

He added: "It’s not all about sea temperature. It’s probably more about the distribution of food; pelagic fish and foraged fish. The whales are here to feed."

Alongside this pattern, the first and last seasonal sightings of humpback whales, noted by the IWDG, expanded from 47 days in 1999 to 241 days in 2023.

Dr Miguel Blásque’s research has estimated that there are 154 humpback whales in Irish waters, a number that’s increasing, according to Dr Berrow.

He said their own research has found that most humpback whales in Irish waters breed in Cape Verde off west Africa; while some breed in the Caribbean.

"We’ve measured an increase in their body condition when they’re here, so it’s a crucial time for the whales to build body reserves, to be able to return to the breeding grounds.

"These whales are feeding on foraged fish, mainly sprat and sand eels at this time of year. It’s critical that we protect foraged fish, not just for whales, but for other predators and other commercial fish species," he said.

Dr Berrow described the presence of humpback whales in Irish waters as fantastic, supporting marine tourism along the coastline.

"We’ve seen it expanding rapidly in the last few years, especially in Donegal Bay, where people are enjoying world class whale watching.

A humpback whale identified in Donegal Bay this week was sighted off Cork and Kerry in recent years.

Dr Berrow has said it’s important that a balance is achieved between protection, conservation and opportunities to see the "incredible species".

"We need to find that balance between protecting the prey, not disturbing them and providing amazing opportunities for people to see these incredible species because Ireland is providing world-class whale watching for the period, they’re in Ireland," he concluded.