Humpback whales returning to Hawaiʻi face entanglement, vessel collisions
Humpback whales from Alaska travel to the warm shallow waters of Hawaiʻi every winter to mate, give birth and raise their calves.
Researchers from the Hawaiian Islands Humpback Whale Marine National Sanctuary have been tracking the whales by tagging them or listening to their calls.
The whales are tagged with cameras to study their socialization behavior.
Tagging whales got a lot easier with the introduction of drones. The drones fly over whales swimming at the surface of the ocean and drop a small camera that sticks onto the whale's skin.
Scientists use acoustic monitoring to get an idea of when and where humpback whales are present. The males sing during the breeding season, although the exact cause is unknown.
"We do see continuous presence of humpback whales between January and March at all locations. Maui had the highest levels of chorusing. We do see high levels of chorusing off of Hawaiʻi Island, but also the French Frigate Shoals in the Northwestern Hawaiian Islands," sanctuary research ecologist Marc Lammers said.
The ʻAuʻau channel between Maui and Lānaʻi has the biggest abundance of humpback whales. The calm, protected ocean makes the channel the perfect place for whales to give birth.
Humpback whale presence off the coast of Oʻahu and Kauaʻi is more intermediate.
Knowing where whales are present can help avoid contact with ships. There have been 144 confirmed whale-vessel collisions in the past 43 years.
"When it comes to whale-vessel contact, the calves and the juveniles are especially vulnerable. Calves represent two-thirds of the reports — way beyond the proportion of the population," said Ed Lyman, the sanctuary’s natural resource specialist.
The average reported speed of the vessels that experience whale collisions are 10.5 knots, about 12 miles per hour. Lyman recommends reducing vessel speeds to 6 knots or less when approaching a humpback whale, and maintain a speed of 15 knots or less during whale season from November to May.
Whale-vessel collisions have increased. Although the humpback whale population also increased, the number of threats did not make up for the population change.
Fishing gear entanglement is another threat to humpback whales.
Over the past 20 years there have been more than 200 reports of entanglement and over 15,000 feet of fishing line removed from whale's bodies.
Almost 40% of entangled fishing gear were stationary pots and traps. The sanctuary found 14 instances of local gear and 20 from Alaska and Canada caught on humpback whales between 2002 to 2022.