Saturday, June 28, 2008


This post fell behind "schedule" thanks to the status of Hyperoodon ampullatus as the best known ziphiid and apparently a fairly well known cetacean. Completely contrary to other ziphiids, H. ampullatus will actually approach boats (Reeves et al. 2002) and was hunted in substantial numbers as a result. Currently the species also seems well known in terms of population studies and I wonder if B. bairdii and other giant ziphiids could be studied similarly. I bring this up because the genera share latitude preferences in the north Pacific (Berardius), north Atlantic (Hyperoodon) and southern oceans (both genera) and do not appear to overlap with Indopacetus (much? oceanic ID is difficult) (MacLeod et al. 2006) - do they occupy the same niche? H. planifrons apparently migrates to warmer waters from the Antarctic with sighting peaks in South Africa in October (early spring) and February (mid-summer) [see here] and they apparently calve off there in spring/early summer (Reeves et al. 2002) but data for the genera seems too scant to make many inferences. Plus seasons in that other hemisphere are confusing. Great, I've already digressed...

While giant ziphiid genera may be functionally similar, none appear to be closely related and one morphological study placed Hyperoodon rather unexpectedly: within the genus Mesoplodon. Superficially Hyperoodon is much larger than mesoplodonts, has a rotund rather than laterally compressed body and has a much more prominent melon (Reeves et al. 2002) - I don't think anybody has suspected this close a relation before. Bianucci et al. 2007 used 18 osteological characters in their ziphiid phylogeny and the data (Appendix 3) shows that while 15 of those characters are shared, only one was both shared and derived - apical teeth. However, only 5 of 14 extant mesoplodonts were included and I'm pretty sure that M. perrini and M. hectori also have what can be considered apical teeth (Dalebout et al. 2002 - Fig. 3). The limited number of characters led Bianucci et al. to recommend that a morphological and molecular study could resolve the paraphyletic Mesoplodon issue but current mtDNA analyses seem best used for taxonomic purposes (species identification) than phylogenetic ones (Dalebout et al. 2007). Apparently Dalebout et al. have some unpublished data from slower evolving nuclear markers that would be better suited to phylogeny, I'll have to keep my eye open. While a decently resolved phylogeny for ziphiids is a bit beyond the horizon, I think the data in Bianucci et al. 2007 can at least be taken to indicate close relation between Hyperoodon and Mesoplodon. The Hyperoodon-like (and also Berardius-like, apparently) Indopacetus appears to be in the same subfamily as Hyperoodon (Hyperoodontinae) but data in Bianucci et al. suggests numerous fossil taxa are more closely related to Hyperoodon and it would seem any similarities are convergence.

Unlike Berardius, the anti-tropically distributed Hyperoodon species have traits that can convincingly distinguish them. Mead 2007 mentions H. planifrons* is sufficiently distinctive to warrant a different subgenus (Frasercetus) and that while only the stomach anatomy of H. ampullatus was described by Mead, he predicted that there would be differences. The book Australian Mammalogy (available here in part) reports that the stomach of H. planifrons has three major compartments with the last and largest having five sub-compartments; most ziphiids (including H. ampullatus) have a generalized anatomy with two compartments (one main, one pyloric) and derived mesoplodonts and B. bairdii stomachs have two main and two pyloric stomachs. Hopefully future publications by Mead will address (and diagram) this feature - phylogenetic and functional implications will probably not be known for some time. According to Hardy 2005 other differences in the species include an apparently denser skull and higher temporal fossa in H. planifrons and much larger, narrower and abruptly ending maxillary crests in H. ampullatus. The sample size in that study was very small (4) and none of the specimens had a determinate gender so it seems that speculating on the implications of the apparent lack of enlarged premaxillary crests in H. planifrons is a bit preliminary.

*Dalebout et al. 1998 noted that H. planifrons sequences differed more from each other than the Berardius species. It probably doesn't have multiple "Evolutionarily Significant Units" but is just diverse (since it is so populous).

Gowans and Rendell 1999 observed that H. ampullatus males have very little scarring and relatively (to other ziphiids) unmodified apical teeth, but greatly enlarged melons were present. Once in a 10 year study of the species in the Gully (off Nova Scotia) adult males showed what appeared to be ritualized head-butting in an aggressive context - as opposed to other cetaceans using this behavior in play or courtship. While the infrequence of observation seems a bit odd, morphological developments in mature males indicate that this behavior is of importance. The thesis of Hardy 2005 goes into much more detail and explained that the enlarged premaxillary crests form a "tube-like channel" which protects the actual melon organ which shrinks, shifts position and becomes more fibrous as the ziphiid matures. Development of a flattened melon from a bulbous one appears to occur before the development of the maxillary crests (at ~ 7.2 to 7.5 m and 9-11 years old) and an increasingly white patch in the largest males (>8.3 m) appears to signify that it is fully mature. While male H. ampullatus apparently reach larger sizes than females (9.8 vs. 8.7 m - Dalebout et al. 2006) an article by MacLeod cited by Hardy (I can't find or access it) notes that the median size is not significantly different and a person communication with MacLeod brought up the idea that larger size with hinder maneuverability. Sources like Reeves et al. 2002 cite female H. planifrons with a larger maximum size than males but presumably the cryptic paper by MacLeod also discounted this (only three mesoplodonts have significantly larger females) - I still would like to know if this species really is smaller than H. ampullatus (much like how the sympatric B. arnuxii is reportedly smaller than B. bairdii). I really wish I had that paper...*

*Post script: It was included in MacLeod's doctoral thesis. Although the mean values for H. ampullatus were similar for males and females (6.4 vs. 6.51), at least some males obtain larger sizes (10 m vs. 8.6 m). Mean values for H. planifrons were similar for males and females (6.425 m vs. 6.5 m) but maximum sizes were smaller (6.93 m vs. 7.45 m).

H. ampullatus in the Gully live at the southernmost consistent range for the species and are significantly smaller (0.7 m) than the next nearest population in Labrador (Whitehead et al. 1997) nearly 2000 kilometers away (Dalebout et al. 2006). The small population has been estimated to contain 163 individuals and suspicions that it was distinct (e.g. Whitehead et al. 2000) have been confirmed by mtDNA (Dalebout et al. 2001) and microsatellites with mtDNA control regions (Dalebout et al. 2006). The former study estimated that only two whales per generation will likely disperse to the Labrador population and there does not seem to be seasonal migration. Possible morphological distinctions (besides size) have been alluded to by Dalebout et al. 2006 but have yet to be described. 65,000 H. ampullatus were taken from the N. Atlantic from 1850 to the early 1970's but it does appear that the population is a fragment of a much larger one, but merely habitat preference (Dalebout et al. 2006). Dalebout et al. also note that the 87 H. ampullatus taken from the gully between 1962 and 1967 did not appear to cause a bottleneck but suggest that this population be regarded as endangered. Biopsy samples taken before and after major oil and gas development in the region show show that while health problems are not being caused, the fact that it was last carried out in 2003 and the population is so small is a potential concern (Hooker et al. 2008).

Ecologically, Hyperoodon is mainly a teuthivore that commonly preys on cephalopods over 0.5 kg and commonly over 1 kg (MacLeod et al. 2003). Stomach contents reviewed by MacLeod et al. 2003 reveal that H. ampullatus has a less diverse diet of smaller squids than H. planifrons but differences in the amount of fish consumed are unknown since fish digest more quickly than squid and are less frequently found in stranded specimens (H. planifrons) than ones caught by whalers (H. ampullatus). And for those interested, H. planifrons is yet another predator of the colossal squid Mesonychoteuthis, although the record is only a ~4 kg specimen. Hooker et al. 2002 estimate that the average Gully H. ampullatus is about 6.5 m long and weighs 5500 kg (~21' and 6 tons) and estimate that it needs to consume 110,000 kcals a day, equivalent to 300 Gonatus squid per day and 15-20 per dive. The number of prey items in the average Hyperoodon stomach was 1452 - much higher than Ziphius (454) and Mesoplodon (34) - so the small prey preferring H. ampullatus may be even busier on its dives than Hooker et al. estimate (or has a slower digestive system?). While we aren't even entirely clear on the coloration of H. planifrons, Kasamatsu and Joyce 1995 estimated that most of the Antarctic ziphiid population (~93%) was from that species; this presumably indicate that half a million individuals are present and that they equal the mass of all the other odontocetes combined (judging from Table IX). The fact that so little is written on such a major player in Antarctic ecology is a bit alarming, and hopefully by our decent knowledge of its northern cousin can help us learn basic information about it.


Bianucci, Giovanni et al. 2007. A high diversity in fossil beaked whales (Mammalia, Odontoceti, Ziphiidae) recovered by trawling from the sea floor off South Africa. A high diversity in fossil beaked whales (Mammalia, Odontoceti, Ziphiidae) recovered by trawling from the sea floor off South Africa. Geodiversitas 29 (4) : 561-618.

Dalebout, Merel L. et al. 2007. A divergent mtDNA lineage among Mesoplodon beaked whales: Molecular evidence for a new species in the tropical Pacific? Marine Mammal Science 23 (4) 954-966.

Dalebout, Merel L. et al. 2006. Nuclear and mitochondrial markers reveal distinctiveness of a small population of bottlenose whales (Hyperoodon ampullatus) in the western North Atlantic. Molecular Ecology 15, 3115–3129

Dalebout, Merel L. et al. 2002. A new species of beaked whale Mesoplodon perrini sp. n (Cetacea: Ziphiidae) discovered through phylogenetic analyses of mitochondrial DNA sequences. Marine Mammal Science 18 (3) 577-608.

Dalebout, Merel L. et al. 2001. Genetic diversity and population structure among northern bottlenose whales, Hyperoodon ampullatus, in the western North Atlantic Ocean. Can. J. Zool. 79: 478–484

Dalebout, Merel L. et al. 1998. Molecular genetic identification of southern hemisphere beaked whales (Cetacea: Ziphiidae). Molecular ecology 7, 687-694.

Dixon, Joan M. et al. 1994. New information on the Southern Bottlenose Whale, Hyperoodon planifrons (Cetacea: Ziphiidae) from a recent stranding in Victoria, Australia. Australian Mammalogy 17: 85-95. Available

Hardy, Mathew D. 2005. Extent, Development and Function of Sexual Dimorphisms in the Skulls of the Bottlenose Whales (Hyperoodon spp.) and Cuvier’s Beaked Whale (Ziphius cavirostris). Available

Gowans, Shannon et al. 2000. Population size and residency patterns of northern bottlenose
whales (Hyperoodon ampullatus) using the Gully, Nova Scotia. J. Cetacean Res. Manage. 2(3): 201–210

Gowans, Shannon and Rendell, Luke. 1999. Head-butting in northern bottlenose whales (Hyperoodon ampullatus): A possible function for big heads? Marine Mammal Science 15 (4) 1342-1350

Hooker, Sascha K. et al. 2008. Changes in persistent contaminant concentration and CYP1A1 protein expression in biopsy samples from northern bottlenose whales, Hyperoodon ampullatus, following the onset of nearby oil and gas development. Environmental Pollution 152 205-216

Hooker, Sascha K. et al. 2002. Ecosystem consideration in conservation planning: energy demand of foraging bottlenose whales (Hyperoodon ampullatus) in a marine protected area. Biological Conservation 104, 51–58

Kasamatsu, F. and Joyce, G. G. (1995). Current status of odontocetes in the Antarctic. Antarctic Science, 7: 365-379.

MacLeod, Colin D et al. 2006. Known and inferred distributions of beaked whale species (Cetacea: Ziphiidae). J. Cetacean Res. Manage. 7(3):271–286

MacLeod, C. D. et al. 2003. Review of data on diets of beaked whales: evidence of niche separation and geographic segregation. J. Mar. Biol. Ass. U.K. , 83, 651-665

Mead, James G. 2007. Stomach Anatomy and Use in Defining Systemic Relationships of the Cetacean Family Ziphiidae (Beaked Whales). The Anatomical Record 290:581–595

Reeves, Randall R. et al. 2002. National Audubon Society Guide to Marine Mammals, Alfred A. Knopf, New York.

Whitehead, Hal. 1997. Population analysis of northern bottlenose whales in the Gully, Nova Scotia. Marine Mammal Science. 13 (2) 173-185

1 comment:

Christopher Taylor said...

You know, if this is how much space you dedicate to just two species, I shudder to think what's going to happen when you reach _Mesoplodon_. Maybe you should skip the post and just go right ahead and publish it in book form ;-P.