Calving rates, long-range movements and site fidelity of southern right whales (Eubalaena australis) in south-eastern Australia

Within New Zealand and eastern Australia, over 58,000 southern right whales were harvested by commercial whalers between 1790 and 1980, with approximately 19,000 harvested from south-eastern Australia. Local extirpation is believed to have led to a loss of cultural memory of calving areas, contributing to the limited recovery of the south-eastern Australian population. While the number of whales observed using the south-eastern Australian coastline is increasing, there has been no change over three decades in the annual abundance of cow-calf pairs at Logans Beach in Warrnambool, Victoria, the only established calving ground in the region. Knowledge of life history parameters of the south-eastern Australian population is lacking. Here, we examine sightings and photo-identification data from southern Australia to investigate calving intervals, long range movements and fidelity to the Logans Beach nursery ground. Sightings data revealed at least 93 calves were born at Logans Beach between 1980 and 2018 (an average of 2.6 per year) with a mean calving interval of 3.5 ± 1.0 years (± SE, n = 34). Comparison between photo-identification catalogues compiled for south-eastern and south-western Australian populations shows that southern right whales are wide ranging within southern Australian waters. Females can be sighted at locations as far apart as 3,800 km across seasons and there is overlap in the wintering range of the south-eastern and south-western populations, with at least 7% of whales using both regions. We also provide the first report of an Australian southern right whale female with strong site fidelity to a calving area in one region relocating long-term to a calving area in another region. This work highlights several knowledge gaps, such as; the location of feeding and conception grounds for this population as well as the degree of mixing between the two Australian populations outside their wintering areas. In addition, the proportion of female calves born at Logans Beach returning to their natal site to calve remains unclear. Our work provides the first assessment of calving rates, movement and site fidelity within the south-eastern Australian population, critical for understanding constraints to recovery and informing conservation management of southern right whales in Australia. Targeted, long-term monitoring programs across the south-eastern Australian region are needed to provide demographic information on which to base predictions of the impacts of anthropogenic threats such as noise disturbance, entanglement and vessel strike.

Predicting suitable coastal habitat for sei whales, southern right whales and dolphins around the Falkland Islands

Species distribution models (SDMs) are valuable tools for describing the occurrence of species and predicting suitable habitats. This study used generalized additive models (GAMs) and MaxEnt models to predict the relative densities of four cetacean species (sei whale Balaeanoptera borealis, southern right whale Eubalaena australis, Peale’s dolphin Lagenorhynchus australis, and Commerson’s dolphin Cephalorhynchus commersonii) in neritic waters (≤100 m depth) around the Falkland Islands, using boat survey data collected over three seasons (2017–2019). The model predictor variables (PVs) included remotely sensed environmental variables (sea surface temperature, SST, and chlorophyll-a concentration) and static geographical variables (e.g. water depth, distance to shore, slope). The GAM results explained 35 to 41% of the total deviance for sei whale, combined sei whales and unidentified large baleen whales, and Commerson’s dolphins, but only 17% of the deviance for Peale’s dolphins. The MaxEnt models for all species had low to moderate discriminatory power. The relative density of sei whales increased with SST in both models, and their predicted distribution was widespread across the inner shelf which is consistent with the use of Falklands’ waters as a coastal summer feeding ground. Peale’s dolphins and Commerson’s dolphins were largely sympatric across the study area. However, the relative densities of Commerson’s dolphins were generally predicted to be higher in nearshore, semi-enclosed, waters compared with Peale’s dolphins, suggesting some habitat partitioning. The models for southern right whales performed poorly and the results were not considered meaningful, perhaps due to this species exhibiting fewer strong habitat preferences around the Falklands. The modelling results are applicable to marine spatial planning to identify where the occurrence of cetacean species and anthropogenic activities may most overlap. Additionally, the results can inform the process of delineating a potential Key Biodiversity Area for sei whales in the Falkland Islands.

The missing whales: relevance of “struck and lost” rates for the impact assessment of historical whaling in the southwestern Atlantic Ocean

The massive impact that open-boat historical whaling (18th to 20th centuries) had on whale populations has been traditionally estimated from records of oil and baleen plate production. However, an unknown proportion of hunted whales were struck, wounded, eventually killed, but lost, and not included in these records, suggesting that whaling impact may be critically underestimated. Whaling logbooks provide a key source for assessing past catches and losses. Here, we extract detailed records of 19875 days of activity in the southwestern Atlantic Ocean from 255 logbooks of offshore whaling voyages. During the period considered (1776–1923), whalers first targeted southern right whales (Eubalaena australis, 2497 sightings and 658 catches), gradually substituted by sperm whales (Physeter macrocephalus, 1157 sightings and 843 catches) after 1840. Loss rate factors, calculated to account for the number of “struck and lost” whales, decreased across time for both species, and were particularly high (ranging 1.09–1.6) for the southern right whale, whose population was drastically reduced by whaling, as compared to previous estimates based on rough catch records. Accurate accounting for these “lost” individuals is essential for reconstructing the impact of whaling on cetacean populations and for a proper assessment of their initial population size and demographic trends.

Changing patterns of habitat use by southern right whales (Eubalaena australis) on their nursery ground at Península Valdés, Argentina, and in their long-range movements

Southern right whales (Eubalaena australis) have been studied on their nursery ground at Península Valdés, Argentina, every year since 1970. Since 1990, 1,208 individuals have been identified from photographs taken during annual aerial surveys; 618 whales were seen in two or more years. Patterns of habitat use have changed during the study in ways which suggest that right whales may be capable of substantial behavioral and ecological flexibility. One male and three females from Península Valdés have been sighted on other nursery grounds (Tristan da Cunha and southern Brazil). Three individuals from Península Valdés were sighted on feeding grounds off Shag Rocks and South Georgia. Some right whales from Península Valdés showed carbon and nitrogen isotope ratios very similar to those seen in right whales off South Africa, while others showed distinctive isotope ratios indicating that they fed in a different area. Whales of all ages and both sexes moved frequently between three major regions of concentration on the Península Valdés nursery ground. Subadults and adult females with calves were resighted at higher rates than adult males and females in non-calf years. Changes in the geographic distribution of whales at the Península include: (1) abandonment of a major region of concentration; (2) establishment of a nursery area adjacent to thecentre of a growing whalewatching industry; and (3) small-scale shifts in distribution, possibly in response to natural and human disturbances.

Estimates of demographic parameters for southern right whales (Eubalaena australis) observed off Pen´ınsula Vald´es, Argentina

Photographs of the right whales which occur between June and December in the waters surrounding Pen´ınsula Vald´es, Argentina, have been obtained from aerial surveys conducted each year from 1971 to the present. Resightings of previously catalogued individuals enable various demographic parameters to be estimated. From analyses of multiple resightings of females accompanied by calves, estimates of the following demographic parameters were obtained, based on the data collected during 1971-90: mean calving interval 3.35 yrs (SE = 0.05 yrs); mean age at first calving 9.1 yr (SE = 0.3 yr); adult female annual mortality rate 0.019 (SE = 0.005); annual percentage rate of population increase 6.9% (SE = 0.7%); reproductive female population size in 1990: 328 animals (SE = 21). No evidence of any trend with time in mean calving interval, mortality rate or rate of population increase was found.

Stranding events of southern right whales, Eubalaena australis, in southern Brazil

Although international protection has been granted since 1935, southern right whales have only recently shown signs of recovery, possiblydue to anthropogenic factors. Off Brazil, illegal hunting of right whales occurred until 1973. This paper reports on surveys conducted alongthe southern Brazilian coast and the information recovered on right whale strandings for this area from 1977-1995. In the first 10 years ofthis period only four cases were registered. However, in contrast, 20 cases were counted during the last nine years. These results arediscussed in relation to marine traffic and the fisheries in the area that produce risks of collision and entanglement. Further, the possibilityof storm surges being a preponderant factor in the mortalities in this area is presented. These yearly rates are compared with neighbouringareas that are also inhabited by the right whales. Both possibilities fit the hypothesis that the right whales using the Brazilian coast forbreeding may finally be showing signs of recovery.

A note on an automated system for matching the callosity patterns on aerial photographs of southern right whales

Photographs showing the callosity patterns of southern right whales (Eubalaena australis) are currently compared by eye to identifyindividuals and monitor their occurrence within certain areas. This paper describes software designed to reduce the number of by eyecomparisons required to maintain each of the existing local photo-identification catalogues. The software is used to extract, from eachphotograph, a viewpoint-independent description of the shape and location of each callosity which generates a parallel catalogue of extracts.This is then compared with the description extracted from each new photograph to generate a list of similarity scores and thus highlightlikely matches. The software can also be used to compare the different catalogues of extracts with each other. Using a test set of 67photographs of 23 whales taken from 1974 to 1986, the software reduced the number of by eye comparisons required to identify allindividuals by 93% when compared with a purely random search.