This years ECS conference was a comparatively quiet one with regards to ziphiid research from those of recent years. Nevertheless, some interesting work concerning beaked whales was still presented.

Recent research on Cuvier’s beaked whale, Ziphius cavirostris, featured in a few posters. Pavan et al. produced results of acoustic recordings of Z. cavirostris obtained from a wideband array of towed hydrophones deployed in the Ligurian Sea, whilst both Causer et al. and Ballardini et al. both displayed their relevant findings concerning the use of photo-identification techniques within this species by using the recognition of natural marks such as scarring patterns – a particular characteristic of Z. cavirostris.

Data concerning ziphiid distribution in various localities were also presented. The results of photo-identification and line transect methods in the Canary Islands were presented by Tejedor and Carrillo. Their findings illustrate that at least 3 species of beaked whale are present throughout the survey area, including: Blainville’s beaked whale, Mesoplodon densirostris, Cuvier’s beaked whale, Ziphius cavirostris, and Gervais’ beaked whale, Mesoplodon europaeus. 81% of the ziphiid sightings recorded were attributed to M. densirostris, 64.9% of which were recorded during the period of August through October, although sightings of this species were recorded all year round. Many of these late summer/autumn sightings were of females with calves. Their findings indicate that these islands may be an important location for ziphiid populations and researchers alike.

The results of boat-based surveys along pre-determined transects, that took place during the 1999-2004 period throughout the Azores Archipelago, were used by Seabra et al. to model beaked whale habitat preferences against a number of environmental variables (depth, sea-bottom slope, aspect, sea-surface temperature and ocean colour) – the first time an attempt has been made to describe beaked whale habitats in this region. Sightings of Mesoplodon spp. northern bottlenose whale, Hyperoodon ampullatus, Cuvier’s beaked whale, Ziphius cavirostris, and non-identified ziphiids were made. The results produced, indicate a similar general pattern for habitat preference for all species, especially for deep canyons. The application of GIS software was found to be useful for highlighting and visualising ziphiid habitat hot-spots in the Azores.

Two related posters concerning odontocete diversity and distribution in the Bay of Biscay, included observations of ziphiids. In the South-Eastern region of the Bay of Biscay, results of shipboard visual surveys between April 2004 and October 2005 (presented by Marcos-Ipiña and Salazar-Sierra) revealed that Cuvier’s beaked whale, Z. cavirostris, were observed on 5 occasions (5% of total toothed whale sightings). These sightings all corresponded to the deepest-water areas between 1000m and 2300m. In their other poster concerning odontocete sightings in the Bay of Biscay, Salazar-Sierra and Marcos-Ipiña, report on cetaceans observed and reported by fisherman from the Basque country. From 185 sightings, Z. cavirostris represented the third most frequently observed cetacean from the nine odontocete species recorded, with a total of 38 sightings collected (representing 13% of the total sightings made).

The distribution and occurrence data of cetaceans off the Madeira Archipelago (NE Atlantic) was presented by Freitas et al. This study examined sightings data from both nautical (2001-2002) and aerial surveys (2002-2004). From a total of 148 sightings, beaked whales (categorised as a single group) formed a surprisingly high percentage of the total sightings – 5% of total nautical sightings, and 9% of total aerial sightings.

Two associated posters presented by MacLeod, Hardy and Goold concerned studies on the evolution and function of sexually dimorphic structures used for intraspecific combat in ziphiids. The first (MacLeod et al.) examined the form and development of these bizarre and highly characteristic structures found in the head of beaked whales, and described their association with intraspecific agonistic interactions. For this study northern bottlenose whale, Hyperoodon ampullatus, Cuvier’s beaked whale, Ziphius cavirostris, Sowerby’s beaked whale, Mesoplodon bidens, and Blainville’s beaked whale, Mesoplodon densirostris, were examined in detail, whilst information on other species was obtained from published sources. The findings indicate that ziphiids can be separated into three conditions based on their respective modes of combat, and the type of sexually dimorphic structures exhibited. These are ‘jousting’ using large apical tusks (e.g. Z. cavirostris) – hypothesised by the authors as being the ancestral condition in beaked whales, and one that evolved from the ‘bite and rake’ exhibited in other odontocete species. To protect the melon from excessive damage during these encounters, a thick dermal ‘shield’ of connective tissue developed to protect the melon and its echolocatory capabilities – a feature that gives such species their characteristically bulbous and rounded forehead. From this condition the two other derived conditions seem to have arisen. The first, as noted in some Mesoplodon species (e.g. M. densirostris), involved the shifting of the tusks to a more posterior position, to bypass the dense forehead ‘shield’. This resulted in the loss of this now ‘unnecessary’ and resource-heavy structure – thus leading to a more sloping forehead shape.

The final condition, described in Hardy et al., is that found in the bottlenose whales, Hyperoodon spp. Here, the melon ‘shield’ has increased into massive proportions in mature males, and the ‘shield’ itself becomes the sexually dimorphic primary weapon used in these intraspecific combative encounters, changing the mode of combat from ‘jousting’ to ‘head-butting’. In the northern bottlenose whale, H. ampullatus, the ‘shield’ of tissue becomes further reinforced into a more effective weapon by the development of the enormous and bony maxillary crests found on the dorsal surface of the skull. The findings also indicate that within this species, it would appear that only once the forehead shield and the maxillary crests within have developed to their largest extent, does the forehead change its external colouration – from grey to white – perhaps acting as a ‘badge of quality’ to receptive females and prospective opponents alike, that the individual is now morphologically mature with a fully reinforced forehead weapon.

Butti et al. presented a comparative study of the distribution of bone density and mechanical stresses in the rostrums of selected ziphiid and delphinid species. The Bone Mineral Density (BMD) of the rostra was measured through the use of Dual-Energy X-ray Absorptiometry (DEXA) device. The findings allowed mathematical models to be created that analysed the mechanical stresses that act on each rostrum in relation to three different behaviours: swimming, fighting, and foraging. The results showed that the BMD distributions between the two families (Ziphiidae and Delphinidae) were found to be consistently different.

Mathew D. Hardy, April 2006.

References (All poster presentations from the 20th Annual Conference of the European Cetacean Society, held in Gdynia, Poland, 1st – 6th April 2006):