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Navigating the migratory path:

Protecting Humpback Whales in the Sargasso Sea

By IW:LEARN

January 28^th, 2025

Each year, hundreds of humpback whales transit past Bermuda on their way from breeding grounds in the West Indies to feeding grounds in more northern latitudes.

The numbers are increasing every year, and Grove et al. report that

“up to 1434 whales visited Bermuda annually from 2011-2020.”

The whales feed all summer in areas off New England, Eastern Canada, and Greenland when those areas experience the most sunlight and biological productivity. They stock up on food reserves to migrate thousands of miles to warmer waters near the equator during the winter, where they can breed in areas where there are fewer predators to threaten humpback calves.

The whale season in Bermuda is in spring, with whale watching peaking in March and April. Of course, the animals pass by the island twice – once on their way to breeding grounds in December and January, when they are moving fast to join the fray, and a second time in March and April when they are moving slower, feeding, and able to be observed more easily.

Nutrient-rich water from the deep is driven up the sides of the Bermuda platform, creating ideal conditions for the humpback whales to feed. This is important because, by the time they reach Bermuda, males who have put on energy-intensive courtship displays and females who have just given birth are hungry from fasting during the breeding season. The upwelling from the Bermuda platform means that Bermuda serves as an incredibly important stopover site for humpbacks during their migration.

Capture-recapture, the practice of photographing humpback whale flukes in one area and matching those photographs to flukes of the same whale in another area, and satellite telemetry tagging can elucidate humpbacks' global movements.

Photo by Michele Roux / Ocean Image Bank

As part of the North West Atlantic Ocean and Wider Caribbean Important Marine Mammal Area (IMMA) workshop in May 2024, geographer Bea Smith, then part of Duke Marine Geospatial Ecology Laboratory, synthesized multiple studies on the migratory routes of North Atlantic humpbacks to create a visual map on behalf of the Sargasso Sea Commission. This map was submitted as one of 46 candidate IMMAs (cIMMAs) as part of the workshop.

Data sources contributing to cIMMA proposal: sighting (record in OBIS 2023b; putative calving site and tagging data from 2019 for Theresia (Kettemer et al. 2022); tagging data from 2019 for tag 111869 (Coyne and Godley 2005; Halpin et al. 2009; Robbins, 2022c); connections as described from the literature (Dunn et al. 2019; Migratory Connectivity in the Ocean 2023); breeding and feeding, wintering extents (Riede 2000, 2004); A subset of humpback whale sightings (records) in OBIS (2023) were used to develop the Robbins (2022) tracking data.

IMMAs are defined as discrete portions of habitat important to marine mammal species that have the potential to be delineated and managed for conservation. They are designated by the Marine Mammal Protected Areas Taskforce, supported by the International Union for the Conservation of Nature (IUCN). Like the Convention on Biodiversity (CBD) process for the description of Ecologically or Biologically Significant Areas (EBSAs), the IMMA process is science-led and carries no legal status or management obligations – though the designation can be used to justify arguments for conservation. cIMMAs are put through a rigorous scientific peer review process, and those that stand up to scrutiny are added as spatial delineations to the IMMA e-Atlas, a hands-on tool for use by conservation scientists, policymakers, the wider scientific community, and the general public to view important areas for marine mammals at a glance. Each IMMA on the map also comes with an accompanying fact sheet, explaining its importance to marine mammals and its justification for inclusion as an IMMA.

The initial draft of the North Atlantic Humpback Whale Migratory Corridor cIMMA prepared by Bea Smith on behalf of the Sargasso Sea Commission (SSC) Secretariat, with support from Fae Sapsford, SSC marine research fellow, benefitted from the review of the workshop participants, in particular the expertise of partners to the Sargasso Sea project Andrew Stevenson, a Bermuda whale researcher, and Dr Lea-Anne Henry, a reader in Marine Ecology at the University of Edinburgh. The proposed area was so large that it went beyond the boundaries of the workshop, with the migratory route extending into the Barents Sea. This prompted a discussion of how IMMAs that span multiple regions should be handled, and it was ultimately decided that the entire migratory route should be viewed as one unit rather than splitting up between IMMA workshop regions.

Proposed North Atlantic Humpback Whale Migratory Corridor IMMA boundaries. Credit: Bea Smith.

The proposal was revised slightly after the peer review stage to exclude areas incorporated in a separate West Indies Humpback Whale Breeding Ground cIMMA, keeping the breeding grounds and migratory route as two distinct areas. The migratory cIMMA also overlaps with another proposed cIMMA – the Somers Isles and Adjacent Seamounts cIMMA proposed by Andrew Stevenson and Lea-Anne Henry based on their research in Bermuda, which focused on the upwelling phenomenon created by the Bermuda platform and its importance for several species of marine mammals including Cuvier’s beaked whales, bottlenose dolphins, and sperm whales as well as humpback whales.

The North Atlantic Humpback Whale Migratory Corridor cIMMA has now been accepted in principle. It is expected to be formally recognized as an IMMA in early 2025 and uploaded to the eATLAS

This designation carries important implications for the conservation of the Sargasso Sea. Research from Duke MGEL shows that the shipping routes that have emerged in the Sargasso Sea intersect with humpback whale migratory routes, with obvious risks of collisions with cetaceans and of noise pollution which impedes whale communication.

Annual summary of vessel traffic in the Sargasso Sea (vessel time in hours) in 2019 (left), 2020 (center) and 2021 (right). Credit: Duke MGEL.

Duke’s research also shows that mean vessel speed has slightly increased over time. At 15 knots, the probability of lethal injury to cetaceans is ~80% (Vanderlaan and Taggart 2006), meaning that keeping ships below that speed threshold would have beneficial outcomes when ships come into contact with cetaceans at the surface.

Mean vessel speed based on AIS records for all vessels in the Sargasso Sea from 2019-2021. Credit: Duke MGEL.

As part of its stakeholder engagement strategy under its GEF-financed project, the Sargasso Sea Commission has held two workshops with shipping industry members to explore voluntary measures that could strengthen the stewardship of the Sargasso Sea.

An IMMA designation would also contribute to the conversation on the importance of this area for cetaceans and possibly lead to the enactment of conservation measures for their benefit in the Sargasso Sea.

About the Project

The Global Environment Facility, funded Common Oceans Sargasso Sea project, is committed to facilitating a collaborative, cross-sectoral, and sustainable stewardship mechanism to put in place a comprehensive conservation framework to protect the unique ecosystem of the Sargasso Sea. Led by UNDP, implemented by IOC UNESCO, and supported by a comprehensive network of partners, it brings together regional fisheries management organizations, national agencies, intergovernmental organizations, initiatives, the private sector, civil society, and academia.

Funded by the French Facility for Global Environment, and supported by the University of Western Brittany, Mar Viva, and the Sargasso Sea Commission, the ‘SARGADOM’ project focuses on two remarkable high seas sites – the Sargasso Sea in the North Atlantic (‘SARGA’) and the Thermal Dome in the Eastern Tropical Pacific (‘DOM’). The project aims to contribute to the protection of biodiversity and ecosystem services and facilitate the development of hybrid ocean governance approaches for the two sites.