Paul Ensor

Blue whale vocalizations recorded around New Zealand: 1964–2013

Previous underwater recordings made in New Zealand have identified a complex sequence of low frequency sounds that have been attributed to blue whales based on similarity to blue whale songs in other areas. Recordings of sounds with these characteristics were made opportunistically during the Southern Ocean Research Partnerships recent Antarctic Blue Whale Voyage. Detections of these sounds occurred all around the South Island of New Zealand during the voyage transits from Nelson, New Zealand to the Antarctic and return. By following acoustic bearings from directional sonobuoys, blue whales were visually detected and confirmed as the source of these sounds. These recordings, together with the historical recordings made northeast of New Zealand, indicate song types that persist over several decades and are indicative of the year-round presence of a population of blue whales that inhabits the waters around New Zealand. Measurements of the four-part vocalizations reveal that blue whale song in this region has changed slowly, but consistently over the past 50 years. The most intense units of these calls were detected as far south as 53°S, which represents a considerable range extension compared to the limited prior data on the spatial distribution of this population.

Re-constructing historical Adélie penguin abundance estimates by retrospectively accounting for detection bias

Seabirds and other land-breeding marine predators are considered to be useful and practical indicators of the state of marine ecosystems because of their dependence on marine prey and the accessibility of their populations at breeding colonies. Historical counts of breeding populations of these higher-order marine predators are one of few data sources available for inferring past change in marine ecosystems. However, historical abundance estimates derived from these population counts may be subject to unrecognised bias and uncertainty because of variable attendance of birds at breeding colonies and variable timing of past population surveys. We retrospectively accounted for detection bias in historical abundance estimates of the colonial, land-breeding Adélie penguin through an analysis of 222 historical abundance estimates from 81 breeding sites in east Antarctica. The published abundance estimates were de-constructed to retrieve the raw count data and then re-constructed by applying contemporary adjustment factors obtained from remotely operating time-lapse cameras. The re-construction process incorporated spatial and temporal variation in phenology and attendance by using data from cameras deployed at multiple sites over multiple years and propagating this uncertainty through to the final revised abundance estimates. Our re-constructed abundance estimates were consistently higher and more uncertain than published estimates. The re-constructed estimates alter the conclusions reached for some sites in east Antarctica in recent assessments of long-term Adélie penguin population change. Our approach is applicable to abundance data for a wide range of colonial, land-breeding marine species including other penguin species, flying seabirds and marine mammals.

Fur seals over the Kerguelen Plateau and elsewhere in the Southern Ocean

Two species of southern fur seal range into the Southern Ocean south of 50~ (Bonner and Laws 1985), the Antarctic fur seal Arctocephalus gazella and the Subantarctic fur seal A. tropicalis. Pinnipeds rarely are seen at sea (Bonner and Laws 1985). Most sightings of southern fur seals at sea are from the vicinity of their breeding grounds. For example, Hunt et al. (1986) sighted fur seals off South Georgia in February-March 1986. Few pelagic sightings of fur seals have been reported. Shaughnessy and Burton (1986) reported three from the South Indian Ocean (possibly A. gazella). This note reports sightings of fur seals over the Kerguelen Plateau within the Australian Fishing Zone near Heard Island in the winter of 1987, and additional sightings elsewhere in the Indian sector of the Southern Ocean in the period September 1985 to February 1988.

Observations of blue whales feeding in Antarctic waters

Abstract There are no published accounts of blue whales (Balaenoptera musculus) feeding in Antarctic waters. This note describes the behaviour of two groups of blue whales feeding in Antarctic pelagic waters. Whales were observed during the 18th IWC/IDCR southern hemisphere minke whale assessment cruise. Feeding behaviour in both cases resembled those described previously for both northern hemisphere blue whales and fin whales (B. physalus). These observations suggest that a programme of comparative behavioural observations could be developed to test the “feeding competition” hypothesis, which suggests that recovery of populations of blue whales will be impeded by feeding competition with sympatric minke whales.

New Zealand Blue Whales: Residency, Morphology, and Feeding Behavior of a Little-Known Population

Abstract: Blue whales are infrequently reported from New Zealand and their taxonomic status is unclear. Here we present new information on the residency, external morphology, and habitat use of blue whales encountered in New Zealand waters. Thirty-one blue whales were photo-identified around the North and South Islands of New Zealand from 2004 to 2014 in seven different months of the year. One photographic match was found between June 2011 and March 2013: the first evidence that an individual blue whale has remained in or returned to New Zealand waters in different years and seasons. Observations of the external morphology of blue whales encountered off the South Island confirm that there is a shorter, non-Antarctic form of blue whale occurring near New Zealand. Body length and proportion, head shape, body condition, and skin condition were similar to Australian but not Antarctic blue whales. In 2013, feeding behavior was observed off the South Islands west coast and strong evidence of feeding was observed off the east coast and is the first reported occurrence of feeding for these locations. Feeding behavior was also observed in the Hauraki Gulf in November 2010. Feeding in these widely spread locations, in addition to the recently reported foraging ground in the South Taranaki Bight, suggest that New Zealand coastal waters are a feeding area for blue whales.

Low-frequency vocalizations of sei whales (Balaenoptera borealis) in the Southern Ocean

Simultaneous sightings and acoustic detections of sei whales (Balaenoptera borealis) are scarce, and there are few published data describing their vocalizations. Analysis of recordings from directional frequency analysis and recording sonobuoys in the presence of sei whales in the Southern Ocean in March 2013 identified both downsweep and upsweep calls. Sound frequencies within all calls were between 34 and 87 Hz with an average call duration of 1.1 s. These very low-frequency sounds share characteristics with sei whale calls recorded near the Hawaiian Islands and off Cape Cod in winter and summer, respectively, but are the first documented sei whale calls in the Southern Ocean that are clearly less than 100 Hz.

Modelling the effects of environmental conditions on the acoustic occurrence and behaviour of Antarctic blue whales

Harvested to perilously low numbers by commercial whaling during the past century, the large scale response of Antarctic blue whales Balaenoptera musculus intermedia to environmental variability is poorly understood. This study uses acoustic data collected from 586 sonobuoys deployed in the austral summers of 1997 through 2009, south of 38°S, coupled with visual observations of blue whales during the IWC SOWER line-transect surveys. The characteristic Z-call and D-call of Antarctic blue whales were detected using an automated detection template and visual verification method. Using a random forest model, we showed the environmental preferences pattern, spatial occurrence and acoustic behaviour of Antarctic blue whales. Distance to the southern boundary of the Antarctic Circumpolar Current (SBACC), latitude and distance from the nearest Antarctic shores were the main geographic predictors of blue whale call occurrence. Satellite-derived sea surface height, sea surface temperature, and productivity (chlorophyll-a) were the most important environmental predictors of blue whale call occurrence. Call rates of D-calls were strongly predicted by the location of the SBACC, latitude and visually detected number of whales in an area while call rates of Z-call were predicted by the SBACC, latitude and longitude. Satellite-derived sea surface height, wind stress, wind direction, water depth, sea surface temperatures, chlorophyll-a and wind speed were important environmental predictors of blue whale call rates in the Southern Ocean. Blue whale call occurrence and call rates varied significantly in response to inter-annual and long term variability of those environmental predictors. Our results identify the response of Antarctic blue whales to inter-annual variability in environmental conditions and highlighted potential suitable habitats for this population. Such emerging knowledge about the acoustic behaviour, environmental and habitat preferences of Antarctic blue whales is important in improving the management and conservation of this highly depleted species.