Bellwethers of change: population modelling of North Pacific humpback whales from 2002 through 2021 reveals shift from recovery to climate response

For the 40 years after the end of commercial whaling in 1976, humpback whale populations in the North Pacific Ocean exhibited a prolonged period of recovery. Using mark-recapture methods on the largest individual photo-identification dataset ever assembled for a cetacean, we estimated annual ocean-basin-wide abundance for the species from 2002 through 2021. Trends in annual estimates describe strong post-whaling era population recovery from 16 875 (± 5955) in 2002 to a peak abundance estimate of 33 488 (± 4455) in 2012. An apparent 20% decline from 2012 to 2021, 33 488 (± 4455) to 26 662 (± 4192), suggests the population abruptly reached carrying capacity due to loss of prey resources. This was particularly evident for humpback whales wintering in Hawai'i, where, by 2021, estimated abundance had declined by 34% from a peak in 2013, down to abundance levels previously seen in 2006, and contrasted to an absence of decline in Mainland Mexico breeding humpbacks. The strongest marine heatwave recorded globally to date during the 2014-2016 period appeared to have altered the course of species recovery, with enduring effects. Extending this time series will allow humpback whales to serve as an indicator species for the ecosystem in the face of a changing climate.

Migratory destinations and spatial structuring of humpback whales (Megaptera novaeangliae) wintering off Nicaragua

Understanding the migratory patterns of large whales is of conservation importance, especially in identifying threats to specific populations. Migration ecology, including migratory destinations, movements and site fidelity for humpback whales (Megaptera novaeangliae) remain poorly studied in parts of the range of the Central America population, considered endangered under the United States Endangered Species Act. This study aimed to investigate the migratory destinations of humpback whales sighted at two study sites in Nicaragua, which are part of the Central America population. A ten-year photographic database of humpback whales observed off Nicaragua was combined with citizen science contributions and sightings from dedicated research programs. The resulting image collection was compared with available historical photo identifications and databases using an automated image recognition algorithm. This approach yielded 36 years of photographic identification totaling 431 recaptures in Nicaragua (2006-2008 and 2016-2021) and 2539 recaptures (1986-2020) in both feeding and breeding grounds of 176 unique individuals sighted in Nicaragua. Our results showed that photo-identified whales were recaptured between October and April in breeding grounds and year-round in feeding grounds between British Columbia and California, with peak recaptures between June and October. Our study provided first-time evidence on fine-scale site affinity of individual humpback whales within Nicaraguan waters and to other breeding and feeding grounds.

A collaborative and near-comprehensive North Pacific humpback whale photo-ID dataset

We present an ocean-basin-scale dataset that includes tail fluke photographic identification (photo-ID) and encounter data for most living individual humpback whales (Megaptera novaeangliae) in the North Pacific Ocean. The dataset was built through a broad collaboration combining 39 separate curated photo-ID catalogs, supplemented with community science data. Data from throughout the North Pacific were aggregated into 13 regions, including six breeding regions, six feeding regions, and one migratory corridor. All images were compared with minimal pre-processing using a recently developed image recognition algorithm based on machine learning through artificial intelligence; this system is capable of rapidly detecting matches between individuals with an estimated 97-99% accuracy. For the 2001-2021 study period, a total of 27,956 unique individuals were documented in 157,350 encounters. Each individual was encountered, on average, in 5.6 sampling periods (i.e., breeding and feeding seasons), with an annual average of 87% of whales encountered in more than one season. The combined dataset and image recognition tool represents a living and accessible resource for collaborative, basin-wide studies of a keystone marine mammal in a time of rapid ecological change.

Interactions between marine megafauna and plastic pollution in Southeast Asia

Southeast (SE) Asia is a highly biodiverse region, yet it is also estimated to cumulatively contribute a third of the total global marine plastic pollution. This threat is known to have adverse impacts on marine megafauna, however, understanding of its impacts has recently been highlighted as a priority for research in the region. To address this knowledge gap, a structured literature review was conducted for species of cartilaginous fishes, marine mammals, marine reptiles, and seabirds present in SE Asia, collating cases on a global scale to allow for comparison, coupled with a regional expert elicitation to gather additional published and grey literature cases which would have been omitted during the structured literature review. Of the 380 marine megafauna species present in SE Asia, but also studied elsewhere, we found that 9.1 % and 4.5 % of all publications documenting plastic entanglement (n = 55) and ingestion (n = 291) were conducted in SE Asian countries. At the species level, published cases of entanglement from SE Asian countries were available for 10 % or less of species within each taxonomic group. Additionally, published ingestion cases were available primarily for marine mammals and were lacking entirely for seabirds in the region. The regional expert elicitation led to entanglement and ingestion cases from SE Asian countries being documented in 10 and 15 additional species respectively, highlighting the utility of a broader approach to data synthesis. While the scale of the plastic pollution in SE Asia is of particular concern for marine ecosystems, knowledge of its interactions and impacts on marine megafauna lags behind other areas of the world, even after the inclusion of a regional expert elicitation. Additional funding to help collate baseline data are critically needed to inform policy and solutions towards limiting the interactions of marine megafauna and plastic pollution in SE Asia.

An unknown nocturnal call type in the Mariana Archipelago

In spring/summer of 2018 and 2021, the Pacific Islands Fisheries Science Center Cetacean Research Program deployed drifting acoustic recorders in the U.S. Exclusive Economic Zones surrounding the Mariana Archipelago. Manual assessments revealed a low-frequency (median 473-554 Hz), short-duration (median 0.596 s), stereotypic tonal nocturnal call throughout the Mariana Archipelago. Based on time of year, spatiotemporal patterns, clear division among calls (i.e., no chorusing), comparisons with known vocalizations of whales, turtles, and fish, and presence of Bryde's whale calls, and because the call has not been detected elsewhere, we hypothesize this 500-Hz pulsed call is produced by Bryde's whales (Balaenoptera brydei).

Interchanges and movements of humpback whales in Japanese waters: Okinawa, Ogasawara, Amami, and Hokkaido, using an automated matching system

Humpback whales in the western North Pacific are considered endangered due to their small population size and lack of information. Although previous studies have reported interchanges between regions within a population, the relationship between the geographic regions of a population in Japan is poorly understood. Using 3,532 fluke photo IDs of unique individuals obtained from four areas in Japan: Hokkaido, six IDs (2009-2019); Ogasawara, 1,477 IDs, from two organizations (1) Everlasting nature of Asia (1987-2020) and (2) Ogasawara Whale Watching Association, (1990-2020); Amami, 373 IDs (1992-1994, 2005-2016); Okinawa, 1,676 IDs (1990-2018), interchanges were analyzed. The ID matchings were conducted using an automated system with an 80.9% matching accuracy. Interchange and within-region return indices were also calculated. As a result, number of matches and interchange indices follow locations, Hokkaido-Okinawa (3, 0.31), Amami-Ogasawara (36, 0.06), Amami-Okinawa (222, 0.37), and Okinawa-Ogasawara (225, 0.08), respectively. Interchange indices among Japanese areas were much higher than the indices between Ogasawara/Okinawa and Hawaii (0.01) and Mexico (0.00) reported in previous studies, indicating that the Japanese regions are utilized by the same population. At the same time, the frequency of interchanges among the three breeding areas vary, and the high within-region return indices in respective breeding areas suggest the site fidelity of the whales in each area at some level. These results indicate the existence of several groups within the population which are possibly be divided into at least two groups based on geographical features: one tend to utilize Ogasawara and the Mariana Archipelago; the other utilize Amami, Okinawa, and the Philippines, migrating along the Ryukyu and Philippine Trench. The matching results also suggest that Hokkaido is possibly be utilized as a corridor between northern feeding areas and southern breeding areas at least by individuals migrating to Okinawa area.

Tidal effects on periodical variations in the occurrence of singing humpback whales in coastal waters of Chichijima Island, Ogasawara, Japan

Marine organisms inhabiting coastal waters are known to be driven by periodic cycles such as diel, tidal, and seasonal changes. Humpback whales (Megaptera novaeangliae) breed in shallow and warm coastal waters, with males singing complex songs during the breeding season. To investigate periodic variations in humpback whale singing activities, we conducted fixed passive acoustic monitoring in the Ogasawara (Bonin) Islands, Japan, from winter to spring during 2016-2018. The singing activity and individual number of singers were observed throughout the day and night using a very long baseline passive acoustic array. The occurrence of singers peaked before sunrise and in the evening and was reduced during the daytime. The frequency of song reception depended on the tidal phase. A generalised additive model demonstrated that the occurrence of singers increased during the flood tide and decreased during the ebb tide in the waters west of Chichijima Island. These results suggest that the singing behaviour of humpback whales in breeding areas is affected by the diel and tidal cycles. Male humpback whales may change their behaviour or singing location depending on the strength and direction of the tidal current, considering that the selection of a stable location is beneficial for singing whales.