Southern Hemisphere Humpback Whales Research Articles

Bioenergetic Shifts in Humpback Whale Fibroblasts Upon Chemical Exposure.

Southern Hemisphere humpback whales accumulate persistent and toxic chemicals, which are transported to Antarctica through distant sources and in situ usage. The extreme seasonal migration-associated fast of humpback whales results in the remobilization of persistent and lipophilic environmental contaminants from liberated fat stores. Mitochondria play a key role in lipid metabolism, and any disruption to mitochondrial function is expected to influence whole-organism bioenergetics. It is therefore of interest to advance understanding of the impact of known contaminants of the Antarctic sea-ice ecosystem upon humpback whale cellular bioenergetics. Using cell line-based in vitro testing, this study employed the Seahorse Extracellular Flux Analyzer to study cellular metabolic activity in live humpback whale fibroblast cells. The assay, based on oxygen consumption rate, provides insights into the cause of cellular bioenergetic disruption. Immortalized skin fibroblasts were exposed to four priority environmental chemicals found in the Antarctic sea-ice ecosystem. Our findings reveal chemical-dependent functional alterations and varying bioenergetic profile responses. Chlorpyrifos was observed to decrease mitochondrial basal oxygen consumption; dieldrin increased basal oxygen consumption; trifluralin's impact was dose-specific, and endosulfan displayed no effect. Our results provide unique insights into environmental chemical mechanisms of action on cellular bioenergetics, generating much-needed taxa-specific chemical effect data in support of evidence-based conservation policy and management.

Southern Hemisphere humpback whales (Megaptera novaeangliae) (Artiodactyla: Balaenopteridae) singing activity at Caño Island Biological Reserve, Costa Rica before, during, and after COVID-19 lockdowns

Introduction: Boat traffic is recognized as a major contributor of underwater noise. Increasing presence of boats in coastal habitats is predicted to have important repercussions on the communication of marine mammals. In Costa Rica, the waters of the Caño Island Biological Reserve are an important breeding area for humpback whales from the Breeding-Stock G (BSG). Their predicted and abundant presence has fueled the development of whale watching activities as an important component of the local economy, and while the country has norms of conduct for this activity, whales often interact with multiple boats at the same time. The lockdowns associated with the COVID-19 pandemic provided a unique opportunity to study the potential impacts of noise associated with boat traffic on the singing activity of humpback whales.
 Objective: Determine whether noise levels and boat acoustic presence around Caño Island Biological Reserve changed during the COVID-19 lockdowns, and if it did, what is the impact on song detection of BSG humpback whales.
 Methods: Acoustic recordings were made using a bottom-mounted autonomous underwater recorder for 30 days in September 2019, 2020, and 2021, resulting in a total recording effort of 480 hours.
 Results: Our results show that broadband underwater noise levels (dBRMS) during pre-lockdown were significantly higher, particularly at frequencies below 1kHz, than during and post-lockdown. This is likely due to a decrease in the proportion of boat acoustic presence during the lockdown. Although the proportion of whale songs detected did not vary among years, whale songs were detected similarly throughout the day during the lockdown, compared to pre-and-post lockdown where the proportion of whale song presence decreased during hours when more boats were present.
 Conclusions: This study shows a clear change in underwater noise levels during the COVID-19 lockdown, likely due to a decrease in boat presence. The study also highlights the potential impact of noise associated with boat traffic on humpback whale singing activity. The results of this study can inform the Conservation Areas of Osa (ACOSA) in charge of managing Caño Island Biological Reserve, to develop and implement mitigation measures to regulate underwater anthropogenic noise associated with tour boats.

A review of post-whaling abundance, trends, changes in distribution and migration patterns, and supplementary feeding of Southern Hemisphere humpback whales

Southern Hemisphere humpback whales (Megaptera novaeangliae) were heavily targeted during modern commercial whaling operations, with some 216,000 individuals killed between 1903 and 1973. That impacted the abundance of all the seven breeding stocks of the species. Most of these stocks have been recovering from whaling pressure although the understanding of the current growth rates of some stocks, and how the rates compare across stocks are lacking. Updated information is fundamental for understanding the species’ current status, and to support the review of management plans promoting its protection and recovery, especially considering current changes in ocean environments due to climate change. This work offers a comprehensive overview of the current knowledge on Southern Hemisphere humpback whales breeding stocks’ status. The aim is to provide information on their post-whaling growth trends and changes in distribution and migration patterns. Within that, records of supplementary feeding records (i.e. feeding beyond their formally described feeding grounds) are described. We have also identified knowledge gaps and note that the establishment of research collaborations, as well as standard methodologies for data collection can be important steps for the acquisition of better comparable data sets for the analysis of the current status of humpback whales and to fill such gaps. The compiled information provided can be used as part of an In-Depth Assessment of the species by the International Whaling Commission.

Interpretation of southern hemisphere humpback whale diet via stable isotopes; implications of tissue-specific analysis.

Blubber and skin are commonly used tissues in stable isotope analysis for the purpose of investigating cetacean diet. Critical comparison of tissue-specific isotopic signals is, however, lacking resulting in uncertainty surrounding the representativeness and therefore utility of different tissues for accurate determination of recent foraging. This study used remotely biopsied blubber and skin tissues from southern hemisphere humpback whales for strategic comparison of δ13C and δ15N values. Samples were collected between 2008-2018 as part of long-term monitoring under the Humpback Whale Sentinel Program. Blubber tissues were lipid-extracted prior to analysis, whilst mathematical lipid-correction was performed on skin samples. Isotopic values from paired blubber and skin samples from the same individuals were compared to assess whether tissues could be used interchangeably for isotope analysis and dietary interpretation. Significant differences were observed for both δ13C and δ15N, flagging previously undocumented methodological considerations, and the need for method validation and standardisation in application of these approaches. This study therefore advances methodological aspects of cetacean dietary analysis. This is of elevated importance in the context of rapidly changing ocean ecosystems.

Interchange of Southern Hemisphere humpback whales across the South Atlantic Ocean

The cosmopolitan distribution of humpback whales (Megaptera novaeangliae) is largely driven by migrations between winter low-latitude breeding grounds and summer high-latitude feeding grounds. Southern Hemisphere humpback whales faced intensive exploitation during the whaling eras and recently show evidence of population recovery. Gene flow and shared song indicate overlap between the western (A) and eastern (B1, B2) Breeding Stocks in the South Atlantic and Indian Oceans (C1). Here, we investigated photo-identification evidence of population interchange using images of individuals photographed during boat-based tourism and research in Brazil and South Africa from 1989 to 2022. Fluke images were uploaded to Happywhale, a global digital database for marine mammal identification. Six whales were recaptured between countries from 2002 to 2021 with resighting intervals ranging from 0.76 to 12.92 years. Four whales originally photographed off Abrolhos Bank, Brazil were photographed off the Western Cape, South Africa (feeding grounds for B2). Two whales originally photographed off the Western Cape were photographed off Brazil, one traveling to the Eastern Cape in the Southwestern Indian Ocean (a migration corridor for C1) before migrating westward to Brazil. These findings photographically confirm interchange of humpback whales across the South Atlantic and Indian Oceans and the importance of international collaboration to understand population boundaries.

Winter distribution and abundance of humpback whales (Megaptera novaeangliae) off Northeastern Brazil

The Brazilian coast is recognised as a Southern Hemisphere humpback whale (Megaptera novaeangliae) wintering ground (IWC breeding stock ‘A’). The northeastern coast of Brazil was an important whaling ground in the 20th century. Shipboard sighting surveys were conducted in this area to evaluate large whales’ distribution and density in 1999 and 2000. Humpback whale sightings (n = 81, 153 individuals) were recorded using line transect methodology. Data from the 2000 survey were used to estimate abundance over the continental shelf from 5 to 12°S (20,040km2 ). A total of 872.1km were surveyed on effort. Humpback whales were distributed from nearshore to the 800m isobath, but 93.5% of sightings were recorded shoreward of the 300m isobath. The relatively high density off northeastern Brazil suggests that the species is reoccupying historical areas of distribution and the presence of newborn individuals indicates that calving and nursing occur in the area. The hazard rate model best fit perpendicular distance data. Abundance was estimated at 628 individuals (CV = 0.335, 95% CI = 327-1,157). This estimate probably corresponds to only a portion of the breeding population. Therefore, additional studies must be conducted to estimate the total size of the humpback whale population wintering off Brazil.

Behavioural responses of humpback whales (Megaptera novaeangliae) to whalewatching boats near Isla de la Plata, Machalilla National Park, Ecuador

Machalilla National Park, on the coast of mainland Ecuador, supports a growing whalewatching industry that focuses on Southern Hemisphere humpback whales, which spend the austral winter (June-September) in this area. This study was designed to measure short-term reactions of whales to the whalewatching vessel activity typically seen in this area for two reasons: (1) to identify the nature of whales’ avoidance response, if any, in order to draft whalewatching guidelines that help local mariners identify when they may be disturbing whales; and (2) to quantify the magnitude of any avoidance response, to examine how this relatively understudied population behaves around boats compared with whales in other whalewatching areas. A shore-based theodolite tracking team created a ‘natural’ experiment to observe relationships between whalewatching traffic and whale behaviour in 1998 and 1999. Swim speed and path directness of humpback whales were measured in the absence of boats, and how those parameters changed when boats arrived was recorded. When whales entered the study area accompanied by boats, a record was made of how their behaviour changed after the boats left. Humpback whales reacted to the approach of whalewatching boats by increasing swim speed significantly, and adopted a much more direct path after boats left. Future research is needed to determine whether responses vary with number, proximity or type of vessel. Similarly, future studies are recommended to determine whether different age-sex classes vary in vulnerability to disturbance. Meanwhile, this study enables provision of much-needed, practical advice to local operators who are concerned that they may be disturbing whales: one way that mariners can tell if they are causing disturbance is if they need to increase their vessel’s speed to keep pace. The average behavioural responses measured were strong enough to recommend that Machalilla National Park adopt precautionary management procedures to limit number and proximity of vessels.

A note on the movement of a humpback whale from Abrolhos Bank, Brazil to South Georgia

Most models of population structure for Southern Hemisphere humpback whales (Megaptera novaeangliae) assume that individuals feeding in the Scotia Sea migrate primarily to breeding and calving areas off Brazil. However data to support this are few and mostly indirect. Abrolhos Bank, Brazil, is the largest breeding and calving ground for humpback whales in the western South Atlantic Ocean. Historically, the waters near South Georgia held the largest concentrations of humpback whales in Antarctic Area II and were among the largest in the Southern Ocean. Photographs of individually distinctive natural markings on humpback whale flukes collected from the Scotia Sea (n=9) were compared with two collections of photographs from Brazilian waters (n=829 and n=735) to identify re-sightings. A humpback whale photographed in August 2000 at Abrolhos Bank was subsequently photographed in December 2004 near Shag Rocks off South Georgia. The migratory distance between these sightings is 3,945km. This finding constitutes the first long-distance individual resighting to be documented from either of these areas.

A note on the spatial and temporal distribution of humpback whales (Megaptera novaeangliae) off Venezuela, Southeastern Caribbean

This paper presents information on the spatial and temporal distribution of humpback whales in Venezuelan waters. Using a relational database containing information from the museums of Venezuela, published and unpublished records were incorporated into a Geographical Information System (MapInfo Professional 7.0). A total of 53 records were gathered, of which sightings made up 72%, followed by acoustic sampling (9%) intentional capture (6%), stranding (6%) and unknown records (8%). Humpback whales were mainly sighted over the continental shelf of the northeastern region in shallow waters of 0-100m in depth. The date on which each record was made supports the seasonal occurrence of North Atlantic humpback whales off the Venezuelan coast. Opportunistic sightings and stranding records from the austral winter months do not give conclusive proof that Southern Hemisphere humpback whales are present during this time, but lead to the hypothesis that whales migrate from Brazil. Systematic research effort (especially photo-identification) is recommended in order to better understand humpback whale movements, distribution and identity.

Song recordings suggest feeding ground sharing in Southern Hemisphere humpback whales

The Atlantic sector of the Southern Ocean (ASSO) has one of the highest densities of Antarctic krill (Euphausia superba) compared to other polar and subpolar regions, which attracts migratory baleen whale species to aggregate in this area for feeding. Humpback whales (Megaptera novaeangliae) also sing extensively while on the Southern Ocean feeding grounds which allows for the exploration of song similarity between feeding grounds and breeding populations which helps to understand population mixing. The results of comparative song analyses between the ASSO and the Ecuadorian and Brazilian breeding populations and recordings from the Chilean, South African and Namibian migration routes/mid-latitude feeding grounds revealed that individuals from at least three humpback whale breeding populations most likely migrate to shared feeding grounds in the ASSO. Humpback whales from different populations potentially mix at different times (i.e., years) at feeding hotspots in variable locations. The ASSO seems to provide sufficient prey resources and seems to present an important area for both cultural and maybe even genetic exchange between populations supporting the maintenance of large gene pools. Assuming that multi-population feeding hotspots are also suitable habitat for krill and other krill-dependent predators, these areas in the ASSO should be carefully managed integrating population, ecosystem and fisheries management.

Global cultural evolutionary model of humpback whale song.

Humpback whale song is an extraordinary example of vocal cultural behaviour. In northern populations, the complex songs show long-lasting traditions that slowly evolve, while in the South Pacific, periodic revolutions occur when songs are adopted from neighbouring populations and rapidly spread. In this species, vocal learning cannot be studied in the laboratory, learning is instead inferred from the songs' complexity and patterns of transmission. Here, we used individual-based cultural evolutionary simulations of the entire Southern and Northern Hemisphere humpback whale populations to formalize this process of inference. We modelled processes of song mutation and patterns of contact among populations and compared our model with patterns of song theme sharing measured in South Pacific populations. Low levels of mutation in combination with rare population interactions were sufficient to closely fit the pattern of diversity in the South Pacific, including the distinctive pattern of west-to-east revolutions. Interestingly, the same learning parameters that gave rise to revolutions in the Southern Hemisphere simulations gave rise to evolutionary patterns of cultural evolution in the Northern Hemisphere populations. Our study demonstrates how cultural evolutionary approaches can be used to make inferences about the learning processes underlying cultural transmission and how they might generate emergent population-level processes.This article is part of the theme issue ‘Vocal learning in animals and humans’.

Assessing the effects of lipid extraction and lipid correction on stable isotope values (δ13 C and δ15 N) of blubber and skin from southern hemisphere humpback whales.

The coupled analysis of δ13 C and δ15 N stable isotope values of blubber and skin biopsy samples is widely used to study the diet of free-ranging cetaceans. Differences in the lipid content of these tissues can affect isotopic variability because lipids are depleted in 13 C, reducing the bulk tissue 13 C/12 C. This variability in carbon isotope values can be accounted for either by chemically extracting lipids from the tissue or by using mathematical lipid normalisation models. This study examines (a) the effects of chemical lipid extraction on δ13 C and δ15 N values in blubber and skin of southern hemisphere humpback whales, (b) whether chemical lipid extraction is more favourable than mathematical lipid correction and (c) which of the two tissues is more appropriate for dietary studies. Strategic comparisons were made between chemical lipid extraction and mathematical lipid correction and between blubber and skin tissue δ13 C and δ15 N values, as well as C:N ratios. Six existing mathematical normalisation models were tested for their efficacy in estimating lipid-free δ13 C for skin. Both δ13 C and δ15 N values of lipid-extracted skin (δ13 C: -25.57‰, δ15 N: 6.83‰) were significantly higher than those of bulk skin (δ13 C: -26.97‰, δ15 N: 6.15‰). Five of the six tested lipid normalisation models had small error terms for predicting lipid-free δ13 C values. The average C:N ratio of lipid-extracted skin was within the lipid-free range reported in other studies, whereas the average C:N ratio of blubber was higher than previously reported. These results highlight the need to account for lipids when analysing δ13 C and δ15 N values from the same sample. For optimised dietary assessments using parallel isotope analysis from a single sample, we recommend the use of unextracted skin tissue. δ15 N values should be obtained from unextracted skin, whereas δ13 C values may be adequately lipid corrected by a mathematical correction.

Large-scale spatial variabilities in the humpback whale acoustic presence in the Atlantic sector of the Southern Ocean.

Southern Hemisphere humpback whales (Megaptera novaeangliae) inhabit a wide variety of ecosystems including both low- and high-latitude areas. Understanding the habitat selection of humpback whale populations is key for humpback whale stock management and general ecosystem management. In the Atlantic sector of the Southern Ocean (ASSO), the investigation of baleen whale distribution by sighting surveys is temporally restricted to the austral summer. The implementation of autonomous passive acoustic monitoring, in turn, allows the study of vocal baleen whales year-round. This study describes the results of analysing passive acoustic data spanning 12 recording positions throughout the ASSO applying a combination of automatic and manual analysis methods to register humpback whale acoustic activity. Humpback whales were present at nine recording positions with higher acoustic activities towards lower latitudes and the eastern and western edges of the ASSO. During all months, except December (the month with the fewest recordings), humpback whale acoustic activity was registered in the ASSO. The acoustic presence of humpback whales at various locations in the ASSO confirms previous observations that part of the population remains in high-latitude waters beyond austral summer, presumably to feed. The spatial and temporal extent of humpback whale presence in the ASSO suggests that this area may be used by multiple humpback whale breeding populations as a feeding ground.

Interannual variability in the lipid and fatty acid profiles of east Australia-migrating humpback whales (Megaptera novaeangliae) across a 10-year timeline

Southern hemisphere humpback whales are classified as high-fidelity Antarctic krill consumers and as such are vulnerable to variability and long-term changes in krill biomass. Evidence of heterogeneous feeding patterns of east coast of Australia migrating humpback whales has been observed, warranting a comprehensive assessment of interannual variability in their diet. We examined the lipid and fatty acid profiles of individuals of the east coast of Australia migrating stock sampled between 2008 and 2018. The use of live-sampled blubber biopsies showed that fatty acid profiles varied significantly among all years. The two trophic indicator fatty acids for Antarctic krill, 20:5ω3 and 22:6ω3 remained largely unchanged across the 10-year period, suggesting that Antarctic krill is the principal prey item. A distance-based linear model showed that 33% of the total variation in fatty acid profiles was explained by environmental variables and climate indices. Most of the variation was explained by the Southern Annular Mode (23.7%). The high degree of variability observed in this study was unexpected for a species that is thought to feed primarily on one prey item. We propose that the observed variability likely arises from changes in the diet of Antarctic krill rather than changes in the whale’s diet.

Migration and summer destinations of humpback whales (Megaptera novaeangliae) in the western South Atlantic Ocean

Southern Hemisphere humpback whales (Megaptera novaeangliae) migrate from wintering grounds in tropical latitudes to feeding areas in the Antarctic Ocean. In 2003 and 2005, satellite transmitters were deployed on humpback whales on their wintering grounds off the eastern coast of South America (Breeding Stock A). Seven whales were tracked for a period of 16 to 205 days travelling between 902 and 7,258km. The tracks of these whales provided partial or full information on the migratory schedule, migration routes and location of the feeding ground in the Southern Oceans. Whales departed from the coast of Brazil from late October to late December between 20˚ and 25˚S and gradually moved away from the South American coast as they moved towards high latitudes. They followed a somewhat direct, linear path, with an approximate geographic heading of 170˚. Satellite telemetry data indicated that the migratory corridors are restricted to a relatively narrow (~500–800km) strip in the South Atlantic Ocean. Migration speed to the feeding grounds averaged 80.2km/day and lasted from 40–58 days. Four individuals arrived at the feeding ground located to the north of the South Sandwich Islands, where they were tracked up to 102 days. Movements in this area were erratic at a mean travelling speed of 22.3km/day. Satellite telemetry data indicate that the main feeding grounds for the population wintering off eastern South America lie between 22˚W and 33˚W and in the southern South Atlantic Ocean south of the Antarctic Convergence but north of 60˚S. This is only partially consistent with the currently proposed stock boundaries for this population on the feeding grounds.

A description and summary of the Antarctic Humpback Whale Catalogue

The Antarctic Humpback Whale Catalogue (AHWC) is an international collaborative project investigating movement patterns of humpback whales in the Southern Ocean and corresponding lower latitude waters. The collection contains records contributed by 261 researchers and opportunistic sources. Photographs come from all of the Antarctic management areas, the feeding grounds in southern Chile and also most of the known or suspected low-latitude breeding areas and span more than two decades. This allows comparisons to be made over all of the major regions used by Southern Hemisphere humpback whales. The fluke, left dorsal fin/flank and right dorsal fin/flank collections represent 3,655, 413 and 407 individual whales respectively. There were 194 individuals resighted in more than one year, and 82 individuals resighted in more than one region. Resightings document movement along the western coast of South America and movement between the Antarctic Peninsula and western coast of South America and Central America. A single individual from Brazil was resighted off South Georgia, representing the first documented link between the Brazilian breeding ground and any feeding area. A second individual from Brazil was resighted off Madagascar, documenting long distance movement of a female between non-adjacent breeding areas. Resightings also include two matches between American Samoa and the Antarctic Peninsula, documenting the first known feeding site for American Somoa and setting a new long distance seasonal migration record. Three matches between Sector V and eastern Australia support earlier evidence provided by Discovery tags. Multiple resightings of individuals in the Antarctic Peninsula during more than one season indicate that humpback whales in this area show some degree of regional feeding area fidelity. The AHWC provides a powerful non-lethal and non-invasive tool for investigating the movements and population structure of the whales utilising the Southern Ocean Sanctuary. Through this methodical, coordinated comparison and maintenance of collections from across the hemisphere, large-scale movement patterns may be examined, both within the Antarctic, and from the Antarctic to breeding grounds at low latitudes.

Long term trends in abundance of humpback whales in Hervey Bay, Australia

Seasonal abundance estimates of humpback whales resident during the austral winter in Hervey Bay, Queensland, Australia between 1987 and 2007were obtained from a capture-mark-recapture study using photo-identification images of 3,155 individual whales. Hervey Bay is a major southboundstopover site for Breeding Stock E humpback whales returning to Antarctic waters from over-wintering in the vicinity of the Great Barrier Reef.Annual survival, recapture and abundance estimates were derived using a Cormack-Jolly-Seber modelling approach and a Horwitz-Thompson typeabundance estimator. The best-fit model was a 2-ageclass Brownie-Robson type model that estimated apparent annual survival for the non-transientwinter stopover ageclass at approximately 0.945 (95% confidence interval: 0.929–0.957). Apparent annual abundance of winter stopover humpbackwhales in Hervey Bay was estimated to have increased significantly over the past 21 years at ca. 13.4% per annum (95% CI 11.6–15.2). The mostrecent Hervey Bay winter stopover population (2007) was estimated to comprise ca. 6,246 post-yearlings (95% CI 5,011–7,482). This estimatedrate of population increase is similar to estimates for other surveys along the east Australian coast but significantly higher than the intrinsic rate ofincrease (rmax) estimated recently for several recovering Southern Hemisphere humpback whale stocks based on the feeding ground sampling.

Responses of humpback whales to a changing climate in the Southern Hemisphere: Priorities for research efforts

AbstractGlobally, baleen whales were severely depleted by historic whaling. Recovering populations have been observed to alter their behaviour. These changes have been attributed to climate change in some cases and raise concerns over the successful recovery of baleen whale populations. Current data‐driven statistical habitat and behavioural models have proven useful for addressing questions of whale distribution changes within their limitations. Given observed changes in oceanic conditions, a new approach to managing baleen whale population recovery is necessary. Model predictions of future whale movements and distributions under climate change scenarios are vital to enable adequate conservation management. This paper presents a new perspective on understanding the impacts of climate change on humpback whales, arguing the need for a system‐based multidisciplinary research approach. Our approach includes coupled, mechanistic models based upon robust ecological principles, and integrates key physical, biogeochemical, biological and ecological modules to address long‐term changes associated with climate change. To illustrate the need for this system‐based multidisciplinary approach, we focus on Southern Hemisphere humpback whales, the recovery of which may be impacted by rapid changes in habitat conditions brought about by anthropogenic climate change.

Northernmost records of Southern Hemisphere humpback whales (Megaptera novaeangliae) migrating from the Antarctic Peninsula to the Pacific coast of Nicaragua

Northernmost records of Southern Hemisphere humpback whales (<scp><i>Megaptera novaeangliae</i></scp>) migrating from the Antarctic Peninsula to the Pacific coast of Nicaragua

Feeding ecology and population delineation of south‐eastern Atlantic and south‐western Indian Ocean humpback whales using stable isotope analysis

Abstract Population delineation is vital for effectively managing and protecting populations of all at‐risk species. Population boundaries of Southern Hemisphere humpback whales on their breeding and feeding grounds have not been fully resolved. A number of methods have been used to delineate breeding stocks of Southern Hemisphere humpbacks, but ecological characteristics determined via stable isotope analysis provide valuable information to contrast other data sources. In this study, stable isotope analysis is used to investigate potential separation of humpback whale populations on Southern Hemisphere feeding grounds as evidenced by carbon and nitrogen isotope values in their skin as proxies of diet. One hundred samples of whale skin obtained from biopsies in sampling localities off the coasts of Gabon, Mayotte (Mozambique Channel), and Madagascar were analysed for carbon (δ13C) and nitrogen (δ15N) stable isotope ratios. The results showed a statistically significant difference in the mean δ15N values for whales between the populations from Gabon and Madagascar (7.0 ± 0.1‰ and 7.6 ± 0.1‰), and Gabon and Mayotte (7.6 ± 0.1‰ and 7.2 ± 0.1‰), indicating that these breeding stocks are potentially visiting different areas of the feeding grounds outside of the breeding season. The results from this study indicate that at least some breeding stocks may show fidelity to separate feeding areas and do not widely mix with individuals from other breeding stocks while feeding.