Future Directions in Research on Bryde's Whales

One of the lesser known species of baleen whales, the Bryde's whale, also known as Eden's whale (Balaenoptera edeni edeni and B. edeni brydei), although hunted as part of a North Pacific Japanese research programme1, was not heavily exploited by commercial whaling and remains a data deficient species. Their taxonomic status is not fully resolved and they are often mistaken for other species leading to uncertainty about their true distribution, behavior and conservation status. Some populations are critically endangered, whilst others are small but have high genetic diversity suggesting wider connectivity. The species' unpredictable coastal and offshore global distribution throughout warm-temperate waters has led to populations with unknown genetic variation, and facing different threats. Few areas are well-studied, but each study reveals often contrasting movement patterns, foraging strategies, and vocal repertoires; there are considerable knowledge gaps for Bryde's whales. There are few Bryde's populations with abundance estimates but they typically number in the mid- to high-hundreds of individuals, with other populations small, <100 mature individuals, and exposed to high levels of anthropogenic impacts. Future research should focus on understanding the diversity within and between populations. Here, we suggest an integrative, comparative approach toward future work on Bryde's whales, including acoustic monitoring, trophic interactions, telemetry tools, understanding their novel behaviors, and resolving their species status. This will inform conservation management of this unusual species of whale vulnerable to anthropogenic impacts

Abundance and degree of residency of humpback dolphins Sousa plumbea in Mossel Bay, South Africa

Indian Ocean humpback dolphins Sousa plumbea inhabit nearshore waters from South Africa to eastern India. Humpback dolphins are vulnerable to conservation threats due to their naturally small population sizes and use of nearshore habitats, where human activities are highest. We investigated the abundance and residency of this species inhabiting Mossel Bay, South Africa, using photographic mark-recapture. Data were collected during 81 surveys in Mossel Bay between 2011 and 2013. Open population modelling using the POPAN parameterisation produced a ‘super-population’ estimate of 125 individuals (95% CI: 61–260) and within-year estimates of between 33 and 86 individuals (2011: 71 [95% CI: 30–168]; 2012: 33 [15–73], 32 [15–70]; 2013: 46 [20–108]). Although less appropriate, closed capture models were also run for comparison with previous studies in the region and generated similar, but slightly smaller, population estimates within each year. We compared our catalogue with opportunistic data collected from East London, Plettenberg Bay, De Hoop and Gansbaai. The only catalogue matches attained were between Plettenberg Bay (n = 44 identified) and Mossel Bay (n = 67 identified), separated by 140 km. Population exchange was moderate, with nine individuals resighted in multiple years between these two areas. This study supports previous findings of long-range movements for this species and provides a baseline from which to assess future impacts on the population.http://www.tandfonline.com/loi/tams202017-04-30hb201

Rostrum abnormalities in the endangered Indian Ocean humpback dolphin (Sousa plumbea) in South Africa

SUPPORTING INFORMATION : Appendix 1. Photographs of the abnormal rostrum conditions characterized in this study with corresponding ID number (if available), locality, time, and credits.Morphological abnormalities in wild animals can be indicators of the underlying health of a population and may be determined through routine photographic surveys. Here, we assess unusual rostrum conditions in Indian Ocean humpback dolphins (Sousa plumbea) inhabiting South African coastal waters to understand the rate of prevalence of abnormal rostrums and formulate hypotheses on potential causes. Photographic data were collated from systematic boat surveys and opportunistic sightings, obtained between April 1998 and March 2021 in various regions along the South African coast. Overall, 31 unique individuals were found with abnormal rostrum conditions, varying from slight misalignments to severe wounds and/or aberrant morphologies. In most cases, injuries were likely caused by natural events during the animal's life history such as interactions with sharks and/or reef-associated hunting strategies. Mark–recapture data indicated that individuals had survived with these injuries for up to 10 years. This study reports the highest incidence of rostrum abnormalities in the species. As numbers reflect only those that have survived their injuries, they are considered a minimum estimate. A better understanding of the cause(s) of these injuries is important given the endangered status of this species.National Research Foundation; The Rufford Foundation; The Society for Marine Mammalogy.https://onlinelibrary.wiley.com/journal/17494877hj2023Mammal Research InstituteZoology and Entomolog

Energetic and physical limitations on the breaching performance of large whales

The considerable power needed for large whales to leap out of the water may represent the single most expensive burst maneuver found in nature. However, the mechanics and energetic costs associated with the breaching behaviors of large whales remain poorly understood. In this study we deployed whale-borne tags to measure the kinematics of breaching to test the hypothesis that these spectacular aerial displays are metabolically expensive. We found that breaching whales use variable underwater trajectories, and that high-emergence breaches are faster and require more energy than predatory lunges. The most expensive breaches approach the upper limits of vertebrate muscle performance, and the energetic cost of breaching is high enough that repeated breaching events may serve as honest signaling of body condition. Furthermore, the confluence of muscle contractile properties, hydrodynamics, and the high speeds required likely impose an upper limit to the body size and effectiveness of breaching whales

Scaling of swimming performance in baleen whales

The scale dependence of locomotor factors has long been studied in comparative biomechanics, but remains poorly understood for animals at the upper extremes of body size. Rorqual baleen whales include the largest animals, but we lack basic kinematic data about their movements and behavior below the ocean surface. Here, we combined morphometrics from aerial drone photogrammetry, whale-borne inertial sensing tag data and hydrodynamic modeling to study the locomotion of five rorqual species. We quantified changes in tail oscillatory frequency and cruising speed for individual whales spanning a threefold variation in body length, corresponding to an order of magnitude variation in estimated body mass. Our results showed that oscillatory frequency decreases with body length (proportional to length(-0.5)(3)) while cruising speed remains roughly invariant (proportional to length(0.08)) at 2 m s(-1). We compared these measured results for oscillatory frequency against simplified models of an oscillating cantilever beam (proportional to length(-1)) and an optimized oscillating Strouhal vortex generator (proportional to length(-1)). The difference between our length-scaling exponent and the simplified models suggests that animals are often swimming non-optimally in order to feed or perform other routine behaviors. Cruising speed aligned more closely with an estimate of the optimal speed required to minimize the energetic cost of swimming (proportional to length(-1)). Our results are among the first to elucidate the relationships between both oscillatory frequency and cruising speed and body size for free-swimming animals at the largest scale

Indian Ocean humpback dolphin (Sousa plumbea) movement patterns along the South African coast

1. The Indian Ocean humpback dolphin was recently uplisted to ‘Endangered’ in the recent South African National Red List assessment. Abundance estimates are available from a number of localized study sites, but knowledge of movement patterns and population linkage between these sites is poor. A national research collaboration, the SouSA project, was established in 2016 to address this key knowledge gap. Twenty identification catalogues collected between 2000 and 2016 in 13 different locations were collated and compared. 2. Photographs of 526 humpback dolphins (all catalogues and photos) were reduced to 337 individuals from 12 locations after data selection. Of these, 90 matches were found for 61 individuals over multiple sites, resulting in 247 uniquely, well‐marked humpback dolphins identified in South Africa. 3. Movements were observed along most of the coastline studied. Ranging distances had a median value of 120 km and varied from 30 km up to 500 km. Long‐term site fidelity was also evident in the data. Dolphins ranging along the south coast of South Africa seem to form one single population at the western end of the species' global range. 4. Current available photo‐identification data suggested national abundance may be well below previous estimates of 1000 individuals, with numbers possibly closer to 500. Bearing in mind the poor conservation status of the species in the country, the development of a national Biodiversity Management Plan aimed at ensuring the long‐term survival of the species in South Africa is strongly recommended. At the same time, increased research efforts are essential, particularly to allow for an in‐depth assessment of population numbers and drivers of changes therein. 5. The present study clearly indicates the importance of scientific collaboration when investigating highly mobile and endangered species.This collaborative research project was funded by the South African Network for Coastal and Oceanic Research (SANCOR), the National Research Foundation (NRF), and the University of Pretoria.http://wileyonlinelibrary.com/journal/aqc2019-02-01hj2018Mammal Research Institut

Key Challenges in Advancing an Ecosystem-Based Approach to Marine Spatial Planning Under Economic Growth Imperatives

In 2017, South Africa became the first African country to draft Marine Spatial Planning (MSP) legislation. The underlying legal framework supports the achievement of ecological, social and economic objectives, but a national policy to fast track the oceans economy provides a challenge for ecosystem-based approaches to MSP. During the 2018 International Marine Conservation Congress, we convened a session to present particular challenges that will likely apply to any developing country seeking to increase profits from existing, or proposed, marine activities. Here we present six multi-disciplinary research projects that support ecosystem-based approaches to MSP in South Africa, by addressing the following knowledge gaps and specific key challenges: (1) the lack of data-derived measurements of ecosystem condition (and the need to validate commonly-used proxy measures); (2) the need to develop models to better understand the potential impacts of climate change on food webs and fisheries; (3) the slow implementation of an ecosystem approach to fisheries management, and the need to implement existing legal instruments that can support such an approach; (4) the paucity of evidence supporting dynamic ocean management strategies; (5) the requirement to manage conflicting objectives in growing marine tourism industries; and (6) the need to adopt systems thinking approaches to support integrated ocean management. We provide examples of specific research projects designed to address these challenges. The ultimate goal of this research is to advance a more integrated approach to ocean management in South Africa, using tools that can be applied in countries with similar socio-political and environmental contexts

Phylogenetic relationships in southern African Bryde's whales inferred from mitochondrial DNA : further support for subspecies delineation between the two allopatric populations

Bryde’s whales (Balaenoptera edeni) are medium-sized balaenopterids with tropical and subtropical distribution. There is confusion about the number of species, subspecies and populations of Bryde’s whale found globally. Two eco-types occur off South Africa, the inshore and offshore forms, but with unknown relationship between them. Using the mtDNA control region we investigated the phylogenetic relationship of these populations to each other and other Bryde’s whale populations. Skin, baleen and bone samples were collected from biopsy-sampled individuals, strandings and museum collections. 97 sequences of 674 bp (bp) length were compared with published sequences of Bryde’s whales (n = 6) and two similar species, Omura’s (B. omurai) and sei (B. borealis) whales (n = 3). We found eight haplotypes from the study samples: H1–H4 formed a distinct, sister clade to pelagic populations of Bryde’s whales (B. brydei) from the South Pacific, North Pacific and Eastern Indian Ocean. H5–H8 were included in the pelagic clade. H1–H4 represented samples from within the distributional range of the inshore form. Pairwise comparisons of the percentage of nucleotide differences between sequences revealed that inshore haplotypes differed from published sequences of B. edeni by 4.7–5.5% and from B. brydei by 1.8–2.1%. Ten fixed differences between inshore and offshore sequences supported 100% diagnosability as subspecies. Phylogenetic analyses grouped the South African populations within the Bryde’s-sei whale clade and excluded B. edeni. Our data, combined with morphological and ecological evidence from previous studies, support subspecific classification of both South African forms under B. brydei and complete separation from B. edeni.PostprintPeer reviewe

Scaling of maneuvering performance in baleen whales: larger whales outperform expectations

Despite their enormous size, whales make their living as voracious predators. To catch their much smaller, more maneuverable prey, they have developed several unique locomotor strategies that require high energetic input, high mechanical power output and a surprising degree of agility. To better understand how body size affects maneuverability at the largest scale, we used bio-logging data, aerial photogrammetry and a high-throughput approach to quantify the maneuvering performance of seven species of free-swimming baleen whale. We found that as body size increases, absolute maneuvering performance decreases: larger whales use lower accelerations and perform slower pitch-changes, rolls and turns than smaller species. We also found that baleen whales exhibit positive allometry of maneuvering performance: relative to their body size, larger whales use higher accelerations, and perform faster pitch-changes, rolls and certain types of turns than smaller species. However, not all maneuvers were impacted by body size in the same way, and we found that larger whales behaviorally adjust for their decreased agility by using turns that they can perform more effectively. The positive allometry of maneuvering performance suggests that large whales have compensated for their increased body size by evolving more effective control surfaces and by preferentially selecting maneuvers that play to their strengths.We thank the crews of many research vessels including the R/V John Martin, R/V Fluke, ARSV Laurence M. Gould, R/V Sanna, M/V Antonie, M/V Northern Song, the Cascadia Research Collective and the Shallow Marine Surveys Group; in particular, we thank John Douglas, Andrew Bell, Shaun Tomlinson, Steve Cartwright, Tony D'Aoust, Dennis Rogers, Kelly Newton, Heather Riley, Gina Rousa and Mark Rousa. We also thank Brandon L. Southall, Alison K. Stimpert and Stacy L. DeRuiter for their role in collecting data as part of the SOCAL-BRS project. We thank Matt S. Savoca, Julian Dale and Danuta M. Wisniewska for assistance with data collection. Finally, we thank John H. Kennedy, Michael A. Thompson and the NSF Office of Polar Programs.Ye

The biology of South African Bryde's whales

The biology of South African Bryde’s whales (Balaenoptera brydei/edeni), with a focus on the inshore form, was investigated through estimates of abundance and survival rate, seasonality of occurrence and variation in mitochondrial and nuclear DNA. Photographs, sightings data and biopsy samples were collected in Plettenberg Bay, on the south-east coast of South Africa. Additional genetic material was obtained from the Iziko South African Museum, Marine and Coastal Management, and the Port Elizabeth Museum. Mark-recapture methods applied to photo-identification data were used to estimate abundance and survival rate. Estimates of abundance ranged from 130 to 250 (CV = 0.07 - 0.38) and the estimated annual survival rate was 0.93 (CV = 0.047, 95% CI = 0.852 - 1.0). Seasonal increases in the encounter rate and number of individual whales were observed during summer and autumn, with a peak in April, which corresponded to increased feeding activity and larger average aggregation sizes. Chlorophyll-a, sea surface temperature and wind speed were all significant factors in explaining the variability in the occurrence of whales. No seasonality in the occurrence of calves was detected. Mitochondrial DNA control region sequences (685bp) were compared to published sequences. This confirmed the offshore form as Balaenoptera brydei and the inshore form as closely related to B.brydei, possibly at the sub-specific level, but excluded it as B.edeni. Phylogenetic analyses support complete separation between the two forms. The use of 10 polymorphic microsatellite loci revealed no population structure among the inshore samples (FST = 0.006). Pairwise estimates of relatedness found most individuals to be unrelated, with only a few distant relatives detected