Stomach contents of sperm whales Physeter macrocephalus stranded in the North Sea 1990-1996

Abstract

Stomach contents of 17 sperm whales Physeter rnacrocephalus stranded in Scotland and Denmark during 1990-96 were analysed. All were sub-adult or adult males and stranded between November and March. They had presumably entered the North Sea during their southward migration from feeding grounds in Arctic waters. Other studies indicate that the majority of the whales were apparently healthy. The diet of these whales was found to consist almost entirely of cephalopods, principally squid of the genus Gonatus (hereafter 'Gonatus', but probably G. fabncii, an oceanic species characteristic of Arctic waters). The other prey species identified were also mostly oceanic cephalopods: the squids Hjstioterlthis bonnellii, Teuthowenia megalops and Todarodes sagjttatus and the octopus Hahphron atlanticus. Although these results are consistent with other recent studies in the area based on single stranded whales, they chffer from results of work on whales caught during commercial w h a h g operations in Icelandic waters (1960s to 1980s) in that little evidence of predation on fish was found in the present study. Remains of single indviduals of the veined squid LoLigo forbesi, the northern octopus Eledone cirrhosa and the saithe PoUachius virens provided the only possible evidence of feeding in the North Sea. We infer that sperm whales do not enter the North Sea to feed. The timing, and large and uniform sizes of the Gonatus species eaten (most had mantle lengths in the range 195 to 245 mm), as estimated from measurements of the lower beaks, and the seasonality of the strandings is consistent with the whales having fed on mature squid, possibly spawning concentrations-as has recently been reported for bottlenose whales. Assuming that the diet recorded in this study was repre sentative of sperm whales during the feeding season, as much as 500000 t of Gonatus could be removed by sperm whales in Norwegian waters each year and up to 3 times that figure from the eastern North Atlantic as a whole. Evidence from other studies indicates that Gonatus is an important food resource for a wide range of marine predators in Arctic waters.

Breaking symmetry: The marine environment, prey size, and the evolution of asymmetry in cetacean skulls

“…Between 1 and 177 stomachs were measured per species depending on availability (Table 1). These stomachs had been analyzed as part of an ongoing program looking at dietary preferences in cetaceans (e.g., Santos et al, 1999Santos et al, , 2001aSantos et al, ,b, 2004. From these data, a maximum predatorprey size ratio (PPSR) was calculated for each individual cetacean by dividing the size of the prey item with the largest size (estimated from hard remains such as otoliths or squid beaks using standard regression equations; fish: Hä rkönen, 1986; cephalopods: Clarke, 1986) by the body length of that individual cetacean.…”

Summer spatial distribution of cetaceans in the Strait of Gibraltar in relation to the oceanographic context

“…Within the second group of cetaceans, pilot whales and sperm whales are known to be mainly squid eaters (Desportes & Mouritsen 1993, Gannon et al 1997, Santos et al 1999) and deep divers (Watkins et al 1993, Baird et al 2002. Thus, the spatial summer distribution of these 2 species within the strait is likely to be indicative of the distribution of larger squid species encountered in the strait.…”

Marine mammals from the southern North Sea: feeding ecology data from δ13C and δ15N measurements

“…Stable carbon isotope ratios have proved most useful in identifying the feeding grounds of particular organisms, as δ 13 C values are typically higher in species from coastal or benthic food webs than in those of offshore food webs (Hobson 1999, Lesage et al 2001). No food was found in the digestive tract of the sperm whales, which seems to indicate that they had not been feeding within the southern North Sea prior to stranding (Jauniaux et al 1998, Santos et al 1999.…”

“…However, despite regular and new observations in the southern North Sea, few data dealing with the diets of marine mammals within this area are available (Desportes 1985, Prime & Hammond 1990, Santos 1998, Santos et al 1999, Santos & Pierce 2003. Strandings offer a good opportunity for scientists to collect biological data but, in most cases, either the stomachs of stranded animal are empty, or digested material is not suitable for dietary research (Santos et al 1994, Jauniaux et al 2002.…”