ORCID Profile
0000-0001-5308-8745
Current Organisation
UNSW Sydney
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Publisher: Frontiers Media SA
Date: 16-09-2021
DOI: 10.3389/FMARS.2021.671145
Abstract: There are multiple blue whale acoustic populations found across the Southern Hemisphere. The different subspecies of blue whales feed in separate areas, but during their migration to lower-latitude breeding areas each year, Antarctic blue whales become sympatric with pygmy and Chilean blue whales. Few studies have compared the degree of this overlap of the Southern Hemisphere blue whale subspecies across ocean basins during their migration. Using up to 16 years of acoustic data, this study compares the broad seasonal presence of Antarctic blue whales, Chilean blue whales, and Southeast Indian Ocean (SEIO) pygmy blue whales across the Pacific and Indian Oceans. Antarctic blue whales were sympatric with the other two blue whale subspecies during the migrating season of every year. Despite this overlap, Chilean and pygmy blue whale detections peaked earlier during the austral autumn (April–May) while Antarctic blue whale detections peaked later during the austral winter (June). Chilean (Pacific Ocean) and SEIO (Indian Ocean) pygmy blue whales showed similar seasonal patterns in detections despite occurring in different ocean basins. Though we have shown that Antarctic blue whales have the potential to encounter other blue whale subspecies during the breeding season, these distinct groups have remained acoustically stable through time. Further understanding of where these whales migrate will enable a better insight as to how these subspecies continue to remain separate.
Publisher: Frontiers Media SA
Date: 20-03-2023
DOI: 10.3389/FMARS.2022.850162
Abstract: Oceans across the globe are warming rapidly and marine ecosystems are changing as a result. However, there is a lack of information regarding how blue whales are responding to these changing environments, especially in the Southern Hemisphere. This is because long term data are needed to determine whether blue whales respond to variability in environmental conditions. Using over 16 years of passive acoustic data recorded at Cape Leeuwin, we investigated whether oceanic environmental drivers are correlated with the migration patterns of eastern Indian Ocean (EIO) pygmy blue whales off Western Australia. To determine which environmental variables may influence migration patterns, we modelled the number of acoustic call detections of EIO pygmy blue whale calls with broad and fine scale environmental variables. We found a positive correlation between total annual whale call detections and El Niño Southern Oscillation (ENSO) cycles and the Indian Ocean Dipole (IOD), with more whale calls detected during La Niña years. We also found that monthly whale call detections correlated with sea surface height around the hydrophone and chlorophyll-a concentration at a prominent blue whale feeding aggregation area (Bonney Upwelling) where whales feed during the summer before migrating up the west Australian coast. At the interannual scale, ENSO had a stronger relationship with call detections than IOD. During La Niña years, up to ten times more EIO pygmy blue whale calls were detected than in neutral or El Niño years. This is likely linked to changes in productivity in the feeding areas of the Great Australian Bight and Indian Ocean. We propose that in lower productivity years whales either skipped migration or altered their habitat use and moved further offshore from the hydrophones and therefore were not detected. The frequency and intensity of ENSO events are predicted to increase with climate change, which is likely to impact the productivity of the areas used by blue whales. These changes in productivity may affect the physical condition and reproductive success of in idual whales. A reduction in reproductive success could have a significant impact on blue whale recovery from historical whaling and their ability to adapt to a changing environment.
Publisher: Frontiers Media SA
Date: 23-06-2022
DOI: 10.3389/FMARS.2022.843875
Abstract: Marine ecosystems are experiencing rapid shifts under climate change scenarios and baleen whales are vulnerable to environmental change, although not all impacts are yet clear. We identify how the migration behaviour of the Chagos whale, likely a pygmy blue whale ( Balaenoptera musculus brevicauda ), has changed in association with shifts in environmental factors. We used up to 18 years of continuous underwater acoustic recordings to analyse the relationships between whale acoustic presence and sea surface temperature (SST), chlorophyll-a concentration, El-Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). We compared these relationships between two independent sites Diego Garcia southeast (DGS) and Diego Garcia northwest (DGN) where Chagos whales are detected and are suspected to move interannually across the Chagos-Lacca e ridge. We showed that the number of whale songs detected increased on average by 7.7% and 12.6% annually at DGS and DGN respectively. At the DGS site, Chagos whales shifted their arrival time earlier by 4.2 ± 2.0 days/year ± SE and were detected for a longer period by 7.3 ± 1.2 days/year ± SE across 18 years. A larger number of songs were detected during periods of higher chlorophyll-a concentration, and with positive IOD phases. At the DGN site, we did not see an earlier shift in arrival and songs were not detected for a longer period across the 13 years. Whale presence at DGN had a weaker but opposite relationship with chlorophyll-a and IOD. The oceanic conditions in the Indian Ocean are predicted to change under future climate scenarios and this will likely influence Chagos whale migratory behaviour. Understanding how environmental factors influence whale movement patterns can help predict how whales may respond to future environmental change. We demonstrate the value of long-term acoustic monitoring of marine fauna to determine how they may be affected by changing environmental conditions.
Publisher: CSIRO Publishing
Date: 2016
DOI: 10.1071/MF14208
Abstract: A widely documented impact of ocean warming is the poleward shift in species’ distributions. This includes the global movement of tropical fishes into temperate rocky reefs. The ecological impacts of such range extensions are, however, largely unknown. We compared the feeding habits of herbivorous tropical surgeonfishes (Acanthuridae) to that of warm-temperate surgeonfishes near Sydney, Australia. The abundance of tropical surgeonfishes peaked during warmer months before they became locally extinct in winter. Comparisons of bite rates in the field between tropical (Acanthurus triostegus, Acanthurus dussumieri) and warm-temperate (Prionurus microlepidotus, Prionurus maculatus) surgeonfishes showed a significant effect of schooling, with both groups feeding most intensely in monospecific schools. In aquarium feeding trials, tropical surgeonfishes consumed more algae than their warm-temperate counterparts at both high and low temperatures (25 and 20°C), and had higher bite rates at 25°C than at 20°C. A. dussumieri also had significantly higher consumption rates on brown algal recruits at warmer temperatures. We further compared gut indices and jaw-lever ratios among the four focal species, and found no consistent pattern between tropical and warm-temperate fishes. This study suggests that the continued intrusion of tropical surgeonfishes in temperate reefs will result in increased herbivory, as a result of both higher herbivore abundance and higher consumption rates per capita by tropical species.
No related grants have been discovered for Gary Truong.