As with other toothed whales, the age of the animals can be determined by looking at the growth layer groups (GLGs) in the dentin and the cement of the teeth. In Faroese pilot whales (2,448 whales from 39 schools), longevity is greater in females which live up to 59 years, while males attain up to 46 yrs (Bloch et al. 1993b).
Growth layer groups in the dentin of three pilot whales aged 0, 6 and 18 years. Photos: Christina Lockyer.
Male pilot whales reach sexual maturity at 11 to 22 years of age (Desportes et al. 1993, 1994d), while females do so at age 5 to 15 and both sexes reach physical maturity at age 25 to 30 (Bloch et al. 1993b, Martin and Rothery 1993). Gestation lasts about 12 months (Martin and Rothery 1993), with a significant overall foetal mortality (Desportes et al. 1994b). The fertility of females declines with age, and whales older than 40 years rarely become pregnant (Martin and Rothery 1993, ICES 1996), although the phenomenon is less accentuated than in short-finned pilot whales (Foote 2008).
The mean size at birth is 178 cm and 75 kg. Although remains of prey, together with milk, are observed in calves only a few months old, young nurse on average for 3–4 years. Lactation can however last much longer; up to 7 years in males and 12 years in females. This protracted lactation period is believed to be of social rather than nutritional importance (Desportes and Mouritsen 1993), allowing for long-lasting mother-calf bonds. It is consistent with the stable matrilineal school structure described for the species (Andersen 1990, 1993, Amos et al. 1991, 1993a,b). Post-reproductive females possibly play important roles in the survival of their last young. As they can no longer bear young of their own, they invest in their current one and continue to lactate and nurse.
Pilot whales are primarily consumers of squid and are essentially oceanic and deep water feeders, but they seem to be opportunistic feeders that may exploit any locally abundant prey and both the oceanic and neritic (coastal) habitats.
Off the Faroe Islands, pilot whales are clearly squid specialists and feed mainly on the European flying squid (Todarodes sagittatus) and the harmhook squid (Gonatus spp.), although other species, some benthic, are present in the same areas. Fish such as greater argentine (Argentina silus), blue whiting (Micromisistius poutassou), Greenland halibut (Reinhardtius hippoglossoides) and pandalid shrimps are also consumed. Although cod, herring and mackerel are common species in the neritic zone around the Faroes and have been reported as pilot whale prey elsewhere, they do not appear in the diet (Desportes 1985, Desportes and Mouritsen 1993).
Off Scotland, the French Atlantic coast and the NW Iberian Peninsula, the main component of the diet is also cephalopods, although fish are also present in varying importance (Martin et al. 1987, Gonzáles et al. 1994, Pierrepont et al. 2005, Spitz et al. 2011, Santos et al. 2013). Scottish whales consumed oceanic squid species, while the benthic octopods constitute the most numerous prey off the Iberian Peninsula and France.
In the Northwest Atlantic, the short and long-finned squids Illex illecebrosus and Loligo pealei dominate the diet of pilot whales, the Atlantic mackerel (Scomber scombrus) and Atlantic herring (Clupea harengus) are also present (Overholtz and Waring 1991, Abend and Smith 1997, Gannon et al. 1997a, 1997b). The cod (Gadus morhua) was reported as a secondary prey in earlier studies (Sergeant 1962, Mercer 1975).
Pilot whales can thus feed on a wide variety of prey and consume both oceanic and neritic species and pelagic and benthic species. They adjust their diet in response to changes in prey abundance. Off the Faroes, in years where Todarodes is abundant on the Faroe shelf, the diet becomes nearly mono-specific, centered upon that species. In years where Todarodes is not abundant, the diet is more diverse and other species of squid and fish are consumed, species which were also abundant in Todarodes years but not preyed upon. They may feed predominantly on fish when squid are not readily available (Desportes and Mouritsen 1993).
This dietary plasticity is also illustrated in the fact that pilot whales can forage in, and occupy successfully or shift to and from both oceanic and neritic habitats (Desportes 1985, Desportes and Mouritsen 1993, Spitz et al. 2011, Santos et al. 2013). The use of ecological tracers reflecting longer-term diet, such as cadmium, carbon and nitrogen isotope ratios, and fatty acid signatures have also confirmed this foraging plasticity (Méndez-Fernandez et al. 2012, 2013, Monteiro 2013).
Did you know?
A pilot whale stomach used as a buoy
Pilot whale stomachs were used as buoys until the 70s. Pilot whale stomachs have three compartments. The first one, called mechanical stomach, is made of very strong tissues and acts as a grinder. This part was emptied, placed in brine, then tanned and inflated for use as buoys with the long-lines. (top)
In former days, thongs of the dried skin were used in the boats to tie the oars to the wooden tollars which take the places of rowlock. (bottom)
Photos: Faroese Museum of Natural History
As one of the most abundant cetaceans in the North Atlantic, pilot whales are important consumers in the marine ecosystem. They may be one of the most important marine mammal predators in the offshore waters of northwestern North America (Gannon et al. 1997ab). In the central North Atlantic around Iceland, pilot whales are likely the 4th most important marine mammal predator in the marine ecosystem, consuming 200 to 300 thousand tonnes of fish, and 900 to 1100 thousand tonnes of squid per year (Sigurjónsson and Víkingsson 1997). Much of this consumption is concentrated on species presently of little importance to commercial fisheries, so direct competition with fisheries is probably minimal.
Pilot whales have few predators besides humans, but may be preyed upon by killer whales (Orcinus orca) and large sharks. Striking changes in behaviour have been observed during playback of killer whale sounds (Miller et al. 2011, Curé et al. 2012).
Pilot whales are often infested with whale lice (Isocyamus delfini), cestodes and nematodes (Balbuena and Raga 1991, 1993, Raga and Balbuena 1993). The stomach parasites Annisakis simplex is particularly prevalent in pilot whales from the Faroes, the infestation beginning with the onset of feeding and increasing with age (Raga and Balbuena 1993).