Challenges of Monitoring Endangered Bryde's Whales During a Period of Rapid Environmental Change

Vessel collisions are considered an important source of mortality for some cetacean species, and this is likely for the New Zealand Bryde's whale (Balaenoptera brydei), a species currently classified as “nationally critical”. Nevertheless, the occurrence and frequency of vessel strikes involving whales in New Zealand waters is yet to be systematically evaluated. Herein, we document the use of radiography as a diagnostic tool to examine the pectoral nippers of a Bryde's whale carcass recovered from Hauraki Gulf, New Zealand. To determine age class, radiographs were used to assess the degree of epiphysial fusion in the pectoral flippers. Additionally, evidence of bone damage and repair was examined in an attempt to clarify cause of mortality. Radiographs were definitive for age‐class determination, revealing the specimen to be a juvenile, as evidenced by open physes, incompletely ossified epiphyses, and incompletely ossified cuboidal bones of the carpus. The degree of epiphyseal development of the distal radial and ulnar secondary ossification centres suggests a late stage two or early stage three degree of development. Radiographs were less definitive in clarifying cause of mortality. Bilateral distal antebrachial fractures were observed on both the left and right pectoral flippers. The fractures evident in the distal right antebrachium of the left flipper were considered atypical of acute blunt trauma. The fracture fragment ends were not sharp edged as expected, but instead exhibited the appearance of remodelled and/or pulverised fracture fragment ends. Regardless of cause, the degree of bone remodelling and callus formation is evidence that the whale likely survived any initial trauma, thus suggesting mortality was not immediate. However, the absence of appropriate histopathology sampling and a systematic necropsy prevent confirmation of this hypothesis.

The Hauraki Gulf is a large, shallow embayment located north of Auckland City (36°51′S, 174°46′E), New Zealand. Bryde's whales (Balaenoptera edeni) are the most frequently observed balaenopterid in these waters. To assess the use of the Hauraki Gulf for this species, we examined the occurrence and distribution in relation to environmental parameters. Data were collected from a platform of opportunity during 674 daily surveys between March 2003 and February 2006. A total of 760 observations of Bryde's whales were recorded throughout the study period during 371 surveys. The number of Bryde's whales sighted/day was highest in winter, coinciding with the coolest median sea‐surface temperature (14.6°C). Bryde's whales were recorded throughout the Hauraki Gulf in water depths ranging from 12.1–59.8 m (mean = 42.3, SD = 5.1). Cow–calf pairs were most frequently observed during the austral autumn in water depths of 29.9–53.9 m (mean = 40.8, SD = 5.2). Data from this study suggest Bryde's whales in the Hauraki Gulf exhibit a mix of both “inshore” and “offshore” characteristics from the Bryde's whales examined off the coast of South Africa.

Bryde’s whales (Balaenoptera brydei) are the least known of the large baleen whales and there are still some questions about their taxonomy and the number of species (Kato 2002). Indeed, previous studies of Bryde’s whale feeding ecology were based only on observational events (e.g., Siciliano et al. 2004) and on stomach contents (e.g., Kawamura 1980, Murase et al. 2007). Rorqual whales are known to display lunge feeding behavior (Werth 2000); however, there has been no evidence of Bryde’s whales lunge feeding at depth. Apart from a few studies that have used time depth recorders (TDRs) to analyze the dive profiles and feeding behaviors of fin whales in the Mediterranean Sea (Panigada et al. 1999) and of fin and blue whales in the Gulf of California (Croll et al. 2001), knowledge of the dive profiles of other Balaenoptera species is unknown. Watkins et al. (1979) successfully tracked separately two adult Bryde’s whales with radio tags, providing some surfacing data; however, no dive data were obtained. This study is the first to analyze dive data from TDRs attached to Bryde’s whales to examine foraging behavior from dive profiles. Data on individual associations over consecutive years, which is scarce for any baleen whale species, are presented and new insights into foraging behavior given. In the waters around Madeira Island (southeast North Atlantic, 32◦N, 17◦W) Bryde’s whales can frequently be found alone or in groups of two to five individuals between the months of June and November. During tagging surveys, carried out using the Madeira Whale Museum’s (MWM) 6.5 m inflatable boat Roaz in 2006, two individual adult Bryde’s whales were tagged on 27 June at 6 km off the southeast coast of the island. The tags used were Mk9 mold 161 (up to 1,000 m) TDR (Wildlife Computers, Redmond, WA) set to sample once per second and very high-frequency (VHF) radio transmitters with a 34 cm semirigid wire antenna (Telonics, Mesa, AZ)

Accurate abundance estimates are essential for the development of effective conservation management strategies, yet they are difficult to produce for small populations that are elusive and sparsely distributed throughout their range. For such populations it is challenging to collect a representative dataset sufficient for robust estimation of detectability and abundance. Over a one‐year study, we used two methods to estimate abundance of a Nationally Critical, widely dispersed Bryde's whale population in the Hauraki Gulf, Aotearoa/New Zealand; (i) distance sampling from systematic line‐transect aerial surveys (n = 22 surveys, 9,944 km, total sightings 21–24 whales), and (ii) mark‐recapture (MR) using photo‐identification images collected from a platform‐of‐opportunity and small‐boat surveys (218 sampling occasions, 27 whales). From the aerial surveys, we estimated an average of 15 whales (95% CI = 6, 30; CV = 37%) at the sea‐surface at any time. For the boat‐based surveys, we developed a custom MR model to address seasonal and individual heterogeneity in capture probabilities and obtained an estimate of 72 distinct whales (95% CI = 38, 106; CV = 24%) in the population. These two approaches provide different perspectives on the abundance and dynamics of Bryde's whales. The aerial surveys estimate the average number of individuals present at any one time, whereas the MR model estimates the total number of animals that used the Gulf during the study. Although neither sampling method is optimal for estimating the abundance of this small, dispersed population, the use of two complementary approaches informs conservation managers about patterns of abundance and distribution over different temporal and spatial scales. It is common to have limited resources for marine research where model assumptions cannot be met. Here, we highlight pragmatic strategies showing how models can be customized to the population of interest to assist with monitoring species of conservation concern.

Here we present the first data describing the behavior of common dolphins (Delphinus sp.) in the Hauraki Gulf, New Zealand. Activity budgets are used to assess the effects of diel, season, depth, sea surface temperature, group size, and composition on dolphin behavior. Additionally, the presence/absence of Bryde's whale (Balaenoptera brydei) and Australasian gannet (Morus serrator) is examined in relation to dolphin behavior. Behavioral data were collected from 686 independent dolphin groups during boat-based surveys conducted between February 2002 and January 2005. Foraging (46.7%) and social (7.2%) were the most and least frequently observed behaviors, respectively. Travel (28.9%), mill (9.5%), and rest (7.7%) accounted for the remainder of the activity budget. Behavior varied seasonally, with the highest proportion of foraging and resting groups observed during the spring and autumn, respectively. Behavior also varied with water depth, with foraging animals observed in the deepest and resting groups recorded in the shallowest regions of the Hauraki Gulf. A correlation between group size and behavior was evident, although behavior did not vary with the composition of dolphin groups. Resting, milling, and socializing animals were more frequently observed in smaller group sizes. Foraging behavior was prevalent in both small and large group sizes, suggesting foraging plasticity exists within this population. Behavior differed between single- and multispecies groups, with foraging more frequent in multispecies groups. Resting, milling, or socializing was rarely observed in the presence of any associated species, indicating the primary mechanism for association is likely prey related.

The establishment of marine protected areas (MPAs) for cetaceans is an important strategy to mitigate human disturbance and protect biodiversity. Despite abundant cetacean species, there are only a few MPAs dedicated to cetacean conservation in China, all of which are for inshore dolphins. Bryde's whales, the only nearshore baleen whale population in mainland China, are conflicting with intensive human activities, yet an effective conservation strategy is lacking. This study used species distribution models to analyze distribution patterns and suitable habitats of Bryde's whales in the Beibu Gulf and proposes the first baleen whale MPA in China. Our results showed Bryde's whales have a seasonal distribution pattern in the Beibu Gulf, and that the waters around Weizhou Island and the southeastern coast of Vietnam were their core habitats. The seasonal nighttime light data indicated a negative relationship between the number of ship lights and Bryde's whale sightings and suggest that Bryde's whales might be threatened by fisheries. We proposed an MPA based on the results, suggesting that the waters within 20 km around Weizhou Island should be declared a protected area. Furthermore, we recommend that anthropogenic activities in the waters around Weizhou Island are better managed to reduce negative impacts on marine life.

A genetic analysis based on mitochondrial DNA control region sequences was conducted to investigate both species identity and populations genetic structure of South American Bryde's whales. The genetic analysis was based on historical, biopsy and stranding samples from Chile (n= 10) and Brazil (n= 8). For comparative purposes published sequences of the Bryde's whales from different localities of the Indian and Pacific Oceans (including Peru, n= 24) were incorporated into the analysis. Results of the phylogenetic analysis identified the Bryde's whales of South Ameri ca as Balaenoptera brydei. No statistically significant genetic differentiation was found between Chilean and Peruvian Bryde's whales. However, striking differences were found between western South Atlantic (Brazil) and eastern South Pacific (Peru and Chile) animals. In addition, striking genetic differences were found between all South American localities and those from the western North Pacific, Fiji and Java. These results suggest movement of B. brydei in the eastern South Pacific in the latitudinal range corresponding to Chile and Peru. These results also suggest no or very limited mov ement of whales between the South Pacific and the South Atlantic Oceans. This is consistent with the notion that B. brydei is not distributed further south of approximately 40oS on both sides of South America.

Eden's whale (Balaenoptera edeni), a poorly understood baleen cetacean, has long been shrouded in taxonomic ambiguity due to limited genomic resources, obscuring its distinction from closely related species and its position within the cetacean Tree of Life. In this paper, we present a high-quality chromosomal-level genome of B. edeni and conduct comparative genomic analyses to address long-standing taxonomic confusion and elucidate speciation of balaenopterids. Our phylogenomic analysis and demographic reconstruction reveal that B. edeni is a distinct sister to Bryde's whale (Balaenoptera brydei), sharing a common ancestor that diverged approximately 7.84 million years ago during the late Miocene. Their genetic divergence exceeds typical intraspecific variation in whales, supporting the reinstatement of B. brydei as a valid species. Chromosomal syntenic analyses suggest that macro-fragment inversions contributed to speciation in balaenopterid whales and uncover unexpected large-scale complex genome rearrangements in Bryde's whale, offering novel insights into cetacean genome evolution. Functional enrichment analysis of inverted regions between B. edeni and Balaenoptera musculus indicates their predominant association with metabolism and biosynthesis, as well as responses to various substances, stress, and stimuli. These genomic resources for B. edeni not only lay a critical foundation for comparative genetic and evolutionary research of cetaceans but also advance our understanding of the taxonomy and evolutionary dynamics of the Bryde's whale complex, with broader implications for baleen whale conservation and biodiversity.

Vessel collisions are an important threat to several cetacean species, both large and small. In addition to negatively affecting the animals themselves, collisions can also damage or sink vessels, threatening both human safety and marine industry economics. Larger cetaceans seem to be the most affected by vessel collisions, and vessel strikes with Bryde's whales (Balaenoptera brydei/Balaenoptera edeni) have been reported worldwide. Long‐term photo‐identification research on Bryde's whales off the northern coast of the state of São Paulo, Brazil, has been continuing since 2016. Of the 67 individuals that were photo‐identified between 2004 and January 2022, three (4%) presented scars compatible with injuries from vessel propellers. These data contribute towards an understanding of the long‐term effects of collision injuries on the behaviour and survival of Bryde's whales. This report is intended to help inform the future evaluation of the conservation status of B. brydei off Brazil.

Marine protected areas miss key habitats of Bryde's whales and bottlenose dolphins exposed to anthropogenic stressors.

Ship-based sighting surveys for cetaceans were conducted in the former whaling ground off the northeastern coast of Brazil. The cruises took place in winter and spring of 1998-2001 with the objectives of investigating current distribution and abundance of cetaceans, particularly large whale species taken during whaling. In 1998 the survey were conducted between the parallels 5°30'W and 9°S and the 200 m isobath and the meridian 033°W. A total of about 3,100 nm were surveyed between 1998 and 2001 Surveys were conducted using line transect methods from about 5-10°S, and from the coast to 33°W. A total of 151 sightings (203 individuals) of large whales were recorded on effort. The Antarctic minke whale - Balaenoptera bonaerensis (Burmeister, 1867) was the most frequently sighted species (97 groups/132 individuals; Sighting Rate [SR] = 0.031 groups/nm), being recorded only in offshore waters. Density gradually increased from August to October. Minke whales were distributed throughout the area, both to the north and the south of former whaling ground. Sighting data indicate this is the most abundant species, particularly in the area beyond the continental shelf break. Breeding behavior was observed for Antarctic minke whales, but few groups containing calves were recorded (4.3% of the groups sighted on effort). Three other large whale species were recorded in low numbers: the Bryde's whale - Balaenoptera edeni (Anderson, 1879)1; the sei whale, B. borealis (Lesson, 1828), and the sperm, Physeter macrocephalus (Linnaeus, 1758). Sei, Bryde and sperm whales were regularly caught during whaling operations, but are rare in the area, suggesting they were depleted by whaling and have yet to recover to their pre-explotation abundance. In contrast, minke whales are abundant in this area, suggesting that either they were not substantially depleted, or that they have recovered rapidly. Blue whale, Balaenoptera musculus (Linnaeus, 1758), and fin whale, B. physalus (Linnaeus, 1758), not recorded on our surveys, have always been extremely rare in the area.

Testing the efficacy of ship strike mitigation for whales in the Hauraki Gulf, New Zealand

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).

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).

In southern African waters, information about species distribution and habitat preferences of many cetacean species is limited, despite the recent economic growth that may affect them. We determined the relative importance of eight environmental variables (bathymetry, distance to shore, slope, chlorophyll-a, salinity, eastwards sea water velocity, northwards sea water velocity and sea surface temperature) as drivers of seasonal habitat preferences of Bryde’s whales (Balaenoptera brydei), humpback whales (Megaptera novaeangliae), southern right whales (Eubalaena australis) and sperm whales (Physeter macrocephalus). Using presence only data from multiple sources, we constructed predictive species distribution models (SDMs) consisting of ensembles of seven algorithms for these species during both summer and winter. Predicted distribution for all cetaceans was high in southern Africa and, in particular, within the South African Exclusive Economic Zone (EEZ). Predictive models indicated a more pronounced seasonal variation for humpback, sperm and southern right whales than for Bryde’s whales. Southern right whales occurred closer to shore during winter, humpback whales were more likely to occur along the east coast in winter and the west coast in summer, and sperm whales were more concentrated off the shelf in winter. Our study shows that ensemble models using historical, incidental and scientific data, in conjunction with modern environmental variables, can provide baseline knowledge on important environmental drivers of cetacean distribution for conservation purposes. Results of this study can further be used to help develop marine spatial plans and identify important marine mammal areas.