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Maui 2023 humpback whale field season review

Written by Lewis Evans

Why are we here? Over the winter months, around 10,000-12,000 humpback whales complete a 3,000+ mile migration from feeding areas spanning from Alaska to Russia to the subtropical waters of Hawai’i. Hawai’i serves as the main breeding ground for the North Pacific population of humpback whales with most of the migrating population residing within Maui Nui waters. In addition to the high density of whales within the Au’au channel the, West Maui mountains and Haleakala offer a lee from prevailing trade winds creating one of the best areas in the world to capture aerial photogrammetry (use of drone photography for measuring an object) from unoccupied aerial systems (UAS) of humpback whales. Utilizing drones, we can measure the length and size (aka body condition) of the whales to ascertain their health. Using a picture of the ventral side of their fluke (Figure 1), we can then determine the identity of the whale using HappyWhale (it’s like Facebook for whales – check it out! Link - Happywhale). The introduction of HappyWhale means we can track individual whales throughout the breeding season and across years with just a fluke image! HappyWhale can be especially useful with this project as we have summer field seasons in southeast Alaska in collaboration with the Alaska Whale Foundation (AWF). Here, we collect body condition measurements which we can link to the same whales in Hawai’i to better understand the population’s health.

Figure 1: Fluke image of a humpback whale. Photo credit to Paul Schofield. (Whale in frame – HW-MN0441282)

Who is involved and what can we do with the information?

The MMRP in collaboration with AWF (Dr Andy Szabo) and PWF (Jens Currie and Stephanie Stack), just completed their 5th consecutive year of this long-term health monitoring project. The goal of generating a long-term monitoring database is to assess changes within the population over large spatial and temporal scales. This research will allow us to track body condition variations over time, entanglement rates, and calving rates, as well as answer a multitude of questions. As humpback whales are a sentinel species, we can quantify the effect of anthropogenic impacts, such as climate change on the health of the ecosystems in which they reside. A better understanding of all these metrics informs on whale population health and can, in turn, inform policymakers. This blog will review the special encounters, highlights, and achievements from the fifth consecutive year of this long-term monitoring project.

Figure 2: MMRP and PWF teams starting off the season strong! Photo credits to Emily Gregory.

The beginning of our 2023 field season:

At the beginning of January, I made my own migration from Marlow, England to Maui, Hawaii for my second successive year. It is always a good feeling to escape the English winter for the Hawaiian winter! From 11th - 20th January we had our first days on the water in collaboration with the Pacific Whale Foundation. Ten days of incredible weather and a hard-working team resulted in over 300 individual whale measurements and 18 successful biopsy attempts. Biopsy sampling will improve our understanding of variation patterns in whale health, genetics, toxicology, and hormones (both reproductive and stress-related). Within this period, we saw some interesting behavior, including what we believe to be a mother weaning off her year-old calf. We had seen this mother on the 12th and 13th of January swimming tightly together. However, on the way back to the Lahaina harbor on the 15th, we saw the mother using techniques that we thought were to separate herself from the yearling. This included peduncle throws, and extended pectoral fin posturing (see video below). This was the first time I had seen such behavior, I felt incredibly grateful to be able to watch in real-time. Nevertheless, I could not help but feel sorry for the yearling as I knew the remarkable journey it would have to undertake for the first time without its mother.

Bad weather:

The 2022 season comprised low winds and limited cloud cover, which led to excellent measurements from the air. This is important as we can only measure animals when the contours of the animal are clear and we can see a distinct middle line with minimal water distortion (Example A). However, when glare and cloud cover interact with windier conditions our measurement accuracy decreases (Example B). The 2023 season was the season of perseverance as we had wind shifts leading to less-than-ideal conditions for measurements. This was partly welcomed as the land days allowed us to complete most of our data processing. Even so, we were itching to get back out on the water to collect as much data as possible.

Figure 3: Example A – shows a suitable image to measure due to great weather conditions. Example B – shows a poor image to measure due to bad weather conditions.

The arrival of the tag team:

A collaborative tag project from MMRP (Professor Lars Bejder, Dr. William Gough, Augusta Hollers, Martin van Aswegen, and myself), PWF (Jens Currie)), and AWF (Dr. Andy Szabo) aims to apply suction cup tags to humpback whales to present a better understanding of lactation rates in correspondence with drone measurements. The tag team stayed on Maui for ten days albeit bad weather days limited the time on the water and hindered the tagging effort. On 15th February we got a call from Kohala (NOAA) about a sighting of false killer whales (FKW). FKW are fast-moving species that can be difficult to track, and as a result, if a call comes in we have to drop what we are doing and go find them as quickly as possible. Fortunately, we managed to find these elusive predators and capture photo ID and drone measurements of them. We tracked this fast-moving dispersed cluster for an hour until the tag team could make their way out. A collaborative tagging effort on Lanai consisting of PWF and MMRP (Tag Team takeover: 2022 Lānaʻi Fieldwork ( has tried to tag a false killer whale with a CATS tag previously. Despite the tremendous efforts on Lanai and a few tagged pilot whales, the false killer whales escaped being tagged! As luck would have it, on this day, the moment finally happened, and Jens Currie was the first person to put a CATS tag on a false killer whale (go read his blog for more information!). The information we can gather from this will provide valuable insights into understanding behavior, ecology, and vocalizations which can be used to better understand the threats facing this species and how we can mitigate them.

Familiar faces:

The MMRP field season spanning February 6th – March 20th presented some great weather days and a tremendous effort from everyone involved. We managed to obtain 1046 individual whale body condition measurements - many of which were repeat measurements from previous years. Two very distinctive examples are Moira HW-MN0443816 (Figure 4 - A and B) and Breadloaf (Figure 4 - C and D). Moira had been seen and measured multiple times in 2022 with a calf, so seeing her the following year with another calf was an exciting surprise! Breadloaf (which we named after the distinctive propeller scarring) was measured multiple times in 2021 with a calf and was again seen this year with a new calf. This animal was both seen in 2021 and 2023 with a calf. These individuals are very important as it allows us to quantify how the body condition of mothers changes over multiple years and how this could potentially affect calving rates. This gives us a unique insight into the health and productivity of this population of humpback whales.

Figure 4: A) Moira (HW-MN0443816) measured in 2022 B) Moira measured in 2023. C) Breadloaf (HW-MN0400268) measured in 2021. D) Breadloaf measured in 2023.

The special thing about spending so much time in the field year after year is that we can capture these valuable repeat sightings between years. It is exciting to see the previous work coming together as a foundational database to help assess and protect this humpback whale population in the years to come. The repeat measurements can help us; assess the productivity of feeding grounds across the North Pacific, increase our understanding of humpback bioenergetics across the entire migratory cycle, and track body condition variation across years.

Finishing strong!

The last portion of our field season from 22nd – 29th of March was spent collaborating with the Pacific Whale Foundation on their new research vessel, Kaiao (Figure 5). The new vessel was equipped with everything a marine mammal scientist could want for collecting field data! On the 25th of March, we happily surpassed our goal for the season (1,500 body condition measurements) despite the setbacks from the weather throughout the season.

Figure 5: Research team on Kaiao.

The season ended with 1630 humpback whale body condition measurements from 709 drone flights over 45 field day attempts. As the whales were migrating back up to their feeding grounds it was time, I made my own back to the UK. But since I got my confirmation letter, I will be back in Hawaii to start grad school with the MMRP!

Such a project could only be accomplished with the help of many passionate and hardworking people. I would like to thank these people for their hard work and contributions to this year’s field season: Martin van Aswegen, Jens Currie, Stephanie Stack, Shannon Barber, Florence Sullivan, Grace Olson, Brian Stirling, Elizabeth Beato, Emily Gregory, Seth Bartusek, Liah McPherson, Paul Schofield, Ella Samaha, Madison Kosma, Abigael Jacka, Cameron Nemeth, Elizabeth Fry, Jessie Hoffman, Brianna Law, Stephanie Vlachos, Karen Harper, Patrick and Naomi Guth, Joshua Guth, Sandee Crossland, Anthony DelleFave, Ted Cheeseman. We would also like to thank the Marine Mammal Commission and Dolphin Quest for funding this field season.

That is it for the 2023 Maui field season. It was an incredible season filled with great people, plenty of laughs, and a whole bunch of whales measured! Until next time.

All research was conducted in accordance with NOAA permits 21476-02 and 21321. All UAS activities were conducted in compliance with FAA part 107 regulations.


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