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.publishedVersio

Observation of gravitational waves from the coalescence of a 2.5–4.5 M ⊙ compact object and a neutron star

We report the observation of a coalescing compact binary with component masses 2.5–4.5 M ⊙ and 1.2–2.0 M ⊙ (all measurements quoted at the 90% credible level). The gravitational-wave signal GW230529_181500 was observed during the fourth observing run of the LIGO–Virgo–KAGRA detector network on 2023 May 29 by the LIGO Livingston observatory. The primary component of the source has a mass less than 5 M ⊙ at 99% credibility. We cannot definitively determine from gravitational-wave data alone whether either component of the source is a neutron star or a black hole. However, given existing estimates of the maximum neutron star mass, we find the most probable interpretation of the source to be the coalescence of a neutron star with a black hole that has a mass between the most massive neutron stars and the least massive black holes observed in the Galaxy. We provisionally estimate a merger rate density of 55−47+127Gpc−3yr−1 for compact binary coalescences with properties similar to the source of GW230529_181500; assuming that the source is a neutron star–black hole merger, GW230529_181500-like sources may make up the majority of neutron star–black hole coalescences. The discovery of this system implies an increase in the expected rate of neutron star–black hole mergers with electromagnetic counterparts and provides further evidence for compact objects existing within the purported lower mass gap

Ultralight vector dark matter search using data from the KAGRA O3GK run

Among the various candidates for dark matter (DM), ultralight vector DM can be probed by laser interferometric gravitational wave detectors through the measurement of oscillating length changes in the arm cavities. In this context, KAGRA has a unique feature due to differing compositions of its mirrors, enhancing the signal of vector DM in the length change in the auxiliary channels. Here we present the result of a search for U(1)B−L gauge boson DM using the KAGRA data from auxiliary length channels during the first joint observation run together with GEO600. By applying our search pipeline, which takes into account the stochastic nature of ultralight DM, upper bounds on the coupling strength between the U(1)B−L gauge boson and ordinary matter are obtained for a range of DM masses. While our constraints are less stringent than those derived from previous experiments, this study demonstrates the applicability of our method to the lower-mass vector DM search, which is made difficult in this measurement by the short observation time compared to the auto-correlation time scale of DM

Isotope profiles of supplementary feeders from both populations.

<p>Each horizontal zone is created using isotopic coordinates consistent with prey values and corrected for trophic fractionation. The whale isotope data plots within the zone appropriate to the prey consumed by the individual. Food zones: Antarctic Krill (dashed line), Australian Krill (full line), average Australian fish species (dotted line). Time flows from left to right.</p

Isotope profiles for temperate zone feeders.

<p>Each horizontal zone is created using isotopic coordinates consistent with prey values and corrected for trophic fractionation. The whale isotope data plots within the zone appropriate to the prey consumed by the individual. Food zones: Antarctic Krill (dashed line), Australian Krill (full line), average Australian fish species (dotted line). Time flows from left to right.</p

Isotope profiles for D population classical feeders.

<p>Each horizontal zone is created using isotopic coordinates consistent with prey values and corrected for trophic fractionation. The whale isotope data plots within the zone appropriate to the prey consumed by the individual. Food zones: Antarctic Krill (dashed line), Australian Krill (full line), average Australian fish species (dotted line). Time flows from left to right.</p

Migration, feeding grounds and breeding grounds of the Australian humpback whale populations.

<p>Approximate feeding grounds of the D and E1 populations are the historical stock boundaries Area IV and V, as defined by the International Whaling Commission. Approximate breeding grounds are represented by the dotted areas, and migration routes are indicated by arrows.</p

Bivariate comparison of whale and prey isotope values corrected using two sets of TFs.

<p>Each prey source is plotted twice depending on the set of TFs: rectangles a, c, and e represent the generic set of TFs: + 3.4‰ for δ¹⁵N and + 0.5‰ for δ¹³C, while rectangles b, d, and f represent the fin whale-specific set of TFs: +2.77‰ for δ¹⁵N and +2.26‰ for δ¹³C. Sources: Antarctic Krill (dashed line), Australian Krill (full line), average Australian fish species (dash-dot line). Each zone is therefore created using isotopic coordinates consistent with prey values and corrected for trophic fractionation. The whale isotope data should plot within the zone appropriate to the prey consumed by the individual.</p

Isotope profiles for E1 population classical feeders.

<p>Each horizontal zone is created using isotopic coordinates consistent with prey values and corrected for trophic fractionation. The whale isotope data plots within the zone appropriate to the prey consumed by the individual. Food zones: Antarctic Krill (dashed line), Australian Krill (full line), average Australian fish species (dotted line). Time flows from left to right.</p