Cephalopod Remains from Stomachs of Sperm Whales
CEPHALOPOD REMAINS FROM STOMACHS OF SPERM WHALES
THAT MASS-STRANDED ON THE OREGON COAST
A Thesis Presented to the Faculty of Califomia State University, Stanislaus through Moss Landing Marine Laboratories
In Partial Fulfillment of the Requirements for the Degree of Master of Science in Mmine Science
By Theresa Friend January 2004 DEDICATION
To my partner and source of strength and love, without whose constant support and patience this project would not have happened. Thank you for believing in me.
iii ACKNOWLEDGMENTS
In an undertaking such as this there are so many people to thank. First, I sincerely thank my committee members, Dr. James Harvey, Dr. Pamela Roe, Dr. Gregor
Cailliet and Dr. Stacy Kim for their guidance, support, helpfi.1l comments and encouragement. Jim, thank you for the second chance when my first project fell through.
I especially thank Dr. Roe for her countless trips to the graduate office to ensure that all of the proper paperwork was in place and for the many phone calls of encouragement when I was sure that this project would not happen.
A very special thanks goes to Bill Walker for his immense generosity in helping to identify and verify cephalopod beaks and in training me to identify beaks. It was a tremendous experience.
My deepest appreciation goes out to my mom, dad and brother for their constant support and love. Much love and thanks also go out to my extended family (Autumn,
Jane, Tam, Kat, and Tom) without whose encouragement and many, many hours of beak measurements, data entry and library searches this project would not have happened.
Thank you to Joan Parker and the entire library staff for their assistance in obtaining reference materials. Thank you to Josh Adams and Mike Weise for assistance with questions regarding beak identification and data analysis.
iv Many thanks go to Jeff Rutter for his invaluable assistance with the statistics, graphs and pivot tables.
Finally, to my partner and best friend, Lisa Scheff, I owe you the world. Your constant support, encouragement, patience and work on this project kept me motivated and on track. You rarely complained about the never-ending piles of squid beaks, papers, books, calipers, microscopes and computer equipment that covered our second bedroom and kitchen table. I can't even begin to thank you for the hours of beak identification and editing you undertook for me.
This project was made possible by funding from the David and Lucile Packard
Foundation, the Ray Cannon Scholarship, and the Graduate Equity Fellowship from
CSU-Stanislaus.
v TABLE OF CONTENTS
PAGE
Dedication ll1
Acknowledgments ...... IV
List of Tables ...... VII
List of Figures ...... IX
Abstract ...... x
Introduction ...... 1
Current Study ...... 8
Methods...... 10
Results ...... 14
Discussion ...... 22
Literature Cited ...... 39
Tables ...... 48
Figures ...... 61
vi LIST OF TABLES
TABLE PAGE
1 Sex, age and number of lower beaks in the stomach contents ...... 49 of 32 sperm whales (ages from Rice et al., 1986) stranded off the Oregon coast.
2 Regression equations used in estimating body lengths and ...... 50 masses of cephalopod prey species in the diet of sperm whales stranded off the Oregon coast.
3 Number and frequency of cephalopodoccurrence of prey recovered 51 from 32 stomachs of 41 sperm whales that stranded off the Oregon coast.
4 Two-dimensional indices of relative importance (IRI) calculated .... 52 by multiplying averaged %N by %FO of cephalopod prey items recovered from 32 stomachs of 41 sperm whales stranded off the Oregon coast.
5 Percentage contribution by mass including minimum, maximum, ... 53 and mean mass of cephalopod prey recovered from 32 stomachs of sperm whales stranded off the Oregon coast.
6 Two-dimensional indices of relative importance (IRI) for each ...... 54 sex and age group of sperm whales, calculated by multiplying averaged %N by %FO of cephalopod prey items recovered from the stomach contents of 32 sperm whales stranded off the Oregon coast.
7 Minimum, maximum and mean dorsal mantle lengths (DML) ...... 56 of cephalopod prey recovered from 32 stomachs of sperm whales stranded off the Oregon coast.
8 Small, medium, med-large and large size classes of cephalopods .... 57 recovered from the stomach contents of 32 sperm whales stranded off the Oregon coast.
vii 9 Statistical results for One-Way ANOVA comparison of mean ...... 58 lengths for twelve prey species of cephalopod prey.
10 Cephalopod species recovered from the stomach contents ...... 59 of sperm whales from the Northeastern Pacific Ocean.
viii LIST OF FIGURES
FIGURE PAGE
1 Location of mass stranding of sperm whales, June 16, 1979, that.. .. 62 stranded off the Oregan coast near the Siuslaw River mouth.
2 Cumulative species curves for 32 spetm whales stranded off the ..... 63 Oregon coast.
3 Total number of beaks for each cephalopod prey item averaged ...... 64 within each whale to detetmine a percentage representation of the prey item for the whole group of whales.
4 Length distributions for 6 cephalopod species recovered from ...... 65 stomach contents of 32 sperm whales stranded off the Oregon coast.
5 Length distributions for 4 cephalopod species recovered from ...... 66 stomach contents of 32 sperm whales stranded off the Oregon coast.
6 Length distributions for Moroteuthis robusta recovered from ...... 67 stomach contents of 32 sperm whales stranded off the Oregon coast.
7 Length distributions for Taningia danae recovered from ...... 68 stomach contents of 32 sperm whales stranded off the Oregon coast.
8 Comparison of the %N represented by the major cephalopod prey .. 69 items consumed by male and female sperm whales.
9 Distribution in the water column of the major cephalopod species .. 70 eaten by the 32 sperm whales that stranded off the Oregon coast.
ix ABSTRACT
On 16 June 1979, a school of 41 sperm whales stranded on a shallow sloping beach near the mouth of the Siuslaw River in Florence, Oregon. A sample of the stomach contents from 32 of the whales was collected, identified, enumerated, and measured. In the 32 stomachs, 20,247 cephalopod lower beaks were recovered. These beaks represented 24 species from 14 different families. The most numerous species represented were
Histioteuthis lwylei (24.4%), Galiteuthis phyllura (13.1 %), Taonius borealis (12.1 %),
Moroteuthis robust a (11.1 %), and Gonatopsis/Berryteuthis type (10.9% ). Estimations of contribution by mass to the sperm whales' diets indicated that the dominant species were
M. robust a (42.98 % V) followed by Gonatopsis/Benyteuthis type (20.0 1 % V) and H. lwylei (12.26% V). Statistical analysis determined that there was no difference in the overall lengths of the dominant species eaten by male and female sperm whales, however, there was a significant difference in the importance of different species between the diets of male sperm whales (ages 15 to 21), and female sperm whales (ages 11 to 21) and between females of different age groups (ages 11 to 21 and 22 to 58). Based on species composition the sperm whales in this study were feeding in the lower mesopelagic to bathypelagic zones off the Oregon coast.
X INTRODUCTION
The sperm whale (Physeter macrocephalus Linnaeus, 1758) is an odontocele cetacean (toothed whale) in the family Physeteridae. The family Physeteridae is comprised of two genera: Physeter (sperm whale) and Kogia (pygmy sperm whale;
Berzin, 1972). Although there is no doubt that sperm whales are monotypic (Thomas,
1911; Berzin, 1972) there has been some confusion as to the correct species name.
Currently, the more widely used name for sperm whales has been P. macrocephalus
(Rice, 1998).
The body of the sperm whale is streamlined and massive in comparison with other members of the order Cetacea (Berzin, 1972). The species is easily distinguished from other whales by its gigantic and distinctive head. The head is box-like and can constitute from one quarter to one third of the length of the body (Berzin, 1972; Leatherwood &
Reeves, 1983; Gordon, 1998). The lower jaw of the sperm whale has up to 30 pairs of conical teeth, whereas the upper jaw has up to 18 pairs of teeth that are rudimentary stumps and no longer functional (Berzin, 1972; Kawakami, 1980; Gordon, 1998). The bottom teeth are firmly attached within sockets in the mandible, and fit snugly into
sockets in the upper jaw when the jaw is closed (Gordon, 1998). The teeth of the lower ja\V as well as the white lining around the mouth may play a role in attracting and catching squid, their main prey (Wray, 1979; Kawakami, 1980; Gordon, 1998). Current research indicates that sperm whales may stimulate bioluminescense from prey remains
1 caught between their teeth to Jure prey items to their mouths and may actively pursue
prey using vision (Fristrup & Harbison, 2002).
Other distinguishing features include dark grayish brown wrinkled skin that is
sometimes lighter or spotted on the belly or under the jaw, and a rounded or triangular dorsal hump (about two thirds of the way back) followed by knuckles along the spine
(Berzin, 1972, Wray, 1979; Leatherwood & Reeves, 1983). Sperm whales also have a
distinct bushy blow that is usually Jess than 2.4 m long and projects obliquely forward
(Leatherwood & Reeves, 1983). Berzin (1972) stated that the characteristic that
distinguishes the sperm whale from other species is the asymmetrical arrangement of the nostrils on the left distal end of the head. The distinct bushy blow is due to the blowholes resemblance to a letter "S." Sexual dimorphism in sperm whales is far more evident than in other species of whales (Berzin, 1972; Best, 1979; Gordon, 1998). Berzin (1972)
stated that male sperm whales may attain lengths of 19.5 to 20.7 m, but noted that few
males were larger than 17.5 m. In comparison, adult females are smaller and rarely reach
12m in length (Berzin, 1972; Leatherwood & Reeves, 1983; Gordon 1998).
Sperm whales may be solitary or in groups of 50 or more individuals (Caldwell et
al., 1966; Ohsumi, 1971; Berzin, 1972; Leatherwood & Reeves, 1983). Recent studies
(Whitehead eta!., 1991; Christal et al., 1998; Lyrholm eta!., 1999; Jaquet et al., 2000) indicated the average size of a "family unit," i.e. an association of adult females and
immature whales of both sexes, was 11 to 13 members. In some instances several of
these groups may combine to form a herd of more than 100 individuals (Whitehead eta!.,
1991; Christal eta!., 1998; Lyrholm eta!., 1999; Jaquet et al., 2000).
2 Several authors have described numerous types of associations, but the three most common include solitary males, bachelor males, and harems (Clarke, 1956; Caldwell et al., 1966; Gaskin, 1968; Ohsumi, 1971; Berzin, 1972; Gambell, 1972; Rice, 1977; Best,
1979; Wray, 1979; Leatherwood & Reeves, 1983; Mate, 1985). Bachelor schools are comprised of pubertal male sperm whales, ranging in size from 10.1 to 13.8 m, and immature males (Gaskin, 1968). These groups of males tend to have less social cohesion than harems and a decrease in sociality with age (Lyrholm et al., 1999). In contrast,
Goold (1999) found that one group of bachelor males studied in Scapa Flow (Orkney
Islands) displayed an unusually great amount of social cohesion.
Harems consist of sexually immature females, pregnant females, lactating females with calves, and immature and mature males up to 11 m long (Caldwell et al., 1966;
Berzin, 1972). During the breeding season, sexually mature males also associate with these harems in ratios ranging from 1 male to 4 females (Clarke, 1956; Pike, 1956;
Gaskin, 1968) up to 1 male to 12 females (Gambell, 1972). The immature males usually will exit these groups before puberty and join bachelor groups (Best, 1979; Lyrholm et al., 1999).
Cunent research indicates that individuals within a harem actually have two types of associations: "constant companions" and "casual acquaintances" (Whitehead et al.,
1991; Christal et al., 1998; Lyrholm et al., 1999; Jaguet et al., 2000). These groups are made up of adult females and immature whales of both sexes. The "constant companions" form a stable social unit that is usually based upon matrilineal lines
(Christal et al., 1998; Lyrholm & Gyllensten, 1998), whereas "casual acquaintances" are formed by members of other units forming short term associations with one another
3 (Christal eta!., 1998). Christal eta!. (1998) examined the dynamics of these two groups
and indicated that through time there were fluctuations in group membership based on
mergers and transfers between groups, and splitting of social units. They estimated that
sperm whales have a 6.3% chance each year of being involved in unit change by way of
splitting, merger, or transfer. Splitting was often caused by loss of the matriarchal
female, mortality of several group members, or large group size. Transfers often
occurred when whales sought nonrelated and potentially superior mates, attempted to reduce intragroup competition, and sought better habitats.
Other groups that have been described include pairs of males (Gaskin, 1968;
Ohsumi, 1971), schools consisting predominantly of pregnant females (Clarke, 1956),
immature whales of both sexes (Gaskin, 1978; Ohsurni, 1971; Leatherwood & Reeves,
1983), and nursery schools (Gaskin, 1968; Ohsumi, 1971; Leatherwood & Reeves, 1983).
Whereas the forces promoting transfers and splits were easy to determine,
mergers were not as easily explained (Christal eta!., 1998) Several authors have
suggested that the formation of units by sperm whales arises from a sense of alloparental
care, which also gives rise to increased fitness among related individuals (Whitehead et
a!., 1991; Christal eta!., 1998). Thus, if whales associate in groups to promote the fitness
of their own bloodlines, one would not expect units of different bloodlines to form
mergers. Christal eta!. (1998) found that different groups did merge, and their
explanation was that benefits provided by an "optimal" group size may play a more
important role than the inclusive fitness benefits provided by association with related
individuals.
4 There are often different migratory patterns between females and males, but both
are dependent on the distribution of their major prey item, cephalopods, and on suitable
breeding conditions (Berzin, 1972). Berzin (1972) noted that most species of
Cephalopoda are relatively thermophilic and fairly stenohaline animals. Thus, like their prey items, the greatest abundance of sperm whales is found in tropical to subtropical
seas between a zone bounded by 40" N and 40" S (Berzin, 1972; Leatherwood & Reeves,
1983; Gordon, 1998), but they can sometimes be found in waters ranging from 60" N to
70" S (Leatherwood & Reeves, 1983). Sperm whales also are "associated with oceanographic fronts, steep bottom topography, and areas of high productivity" (Lyrholm
et al., 1999). Males range more northward and will move farther poleward than females,
which tend to remain between 40" N and 40" S. Males usually return to tropical and
subtropical waters mainly for breeding (Lyrholm et al., 1999). All sperm whales,
however, regardless of sex or age, shift poleward during the spring and summer and
return to more temperate and tropical waters during fall (Slijper, 1962; Berzin, 1972;
Leatherwood & Reeves, 1983). During their southward migration, the ranges of males
and females overlap.
Sperm whales generally dive deeper and for a greater duration than other whales
(Caldwell et al., 1966). Sperm whales are capable of reaching depths of 2000 m or more
(Berzin, 1972; Clarke, 1976; Gordon, 1998), but most dives are between 400 and 700 m
(Leatherwood & Reeves 1983; Watkins et al., 1993). Several accounts of deep diving
have been verified by the discovery of dead whales tangled in telegraph wires on the sea
floor and by damage to these wires (Heezen, 1957); by the accounts of whalers as to the
amount of line fed out on harpoons during capture (Caldwell et al., 1966); by sonar
5 observations from submarines (Gordon, 1998); and by species of squid, fish, and other items found in stomach contents that are inhabitants of deeper waters or near sea floor habitats (Nemoto & Nasu, 1963; Berzin, 1972; Clarke, 1980). Duration of dives for larger male sperm whales can be 90 minutes (Caldwell eta!., 1966), 83-82 min (Clarke,
1976), 75 min (Clarke, 1954), and 65 min (Beane, 1905). In contrast, females dive for shorter durations and Jess deep (Caldwell et al., 1966).
Sperm whales feed primarily on squid (Pike, 1950; Rice, 1963; Berzin, 1972;
Clarke & MacLeod, 1974; Fiscus & Rice, 1974; Clarke, 1976; Clarke & MacLeod, 1976;
Clarke & MacLeod, 1980; Kawakami, 1980; Clarke & MacLeod, 1982; Leatherwood &
Reeves, 1983; Nemoto et al., 1988; Fiscus et al., 1989), but also eat octopus and a variety of fishes, including salmon, rockfish, and skates (Berzin, 1972; Kawakami, 1980;
Leatherwood & Reeves, 1983). Clarke (1976) also found two benthic sharks (Scymnodon sp.) in the stomach of a sperm whale.
To date, studies of sperm whale food habits in the Pacific Ocean have included areas in the Galapagos (Whitehead et al., 1989), California (Fiscus & Rice, 1974; Fiscus eta!., 1989), western Canada (Clarke & MacLeod, 1980), the Bering Sea and Alaskan
Gulf (Okutani & Nemoto, 1964) and Japan (Okutani et al., 1976; Okutani & Satake,
1977). In the Atlantic, work has been conducted off Spain (Clarke & MacLeod, 1974),
Madeira (Clarke, 1962a), the Azores (Clarke, 1954; Clarke, 1956) and Iceland (Clarke &
MacLeod, 1976). Studies also have been conducted in the Tasman Sea (Clarke &
MacLeod, 1982) and off Durban in the Indian Ocean (Gambell, 1972).
Sperm whale distribution is closely related to the distribution patterns of cephalopods. By understanding which taxa of cephalopods are eaten by sperm whales,
6 scientists can begin to map sperm whales' movements through different water systems.
Food habits of sperm whales also can provide important information on their prey items,
such as the presence of cephalopod species in areas where they had not previously been
found, the presence of new species of cephalopods, and information on size classes of
various species of cephalopods. Clarke and MacLeod (1980) reported that few studies of
sperm whale food habits were conducted off the western side of North America south of
the Gulf of Alaska, which led to this current study of food habits of sperm whales
stranded on the Oregon coast.
7 CURRENT STUDY
On 16 June 1979, a school of 41 sperm whales stranded on a shallow sloping beach near the mouth of the Siuslaw River in Florence, Oregon (43°59'N, 124°08'W;
Fig. 1). The whales stranded on a high tide and individuals were spread out along a two kilometer stretch of the beach. This was the fourth largest recorded stranding of sperm whales that has been reported world wide (Mate, 1985; Snow & Mate, 1979). The school consisted of 13 males and 28 females (Rice et al., 1986). Rice et al. (1986) determined that the males were all subadults (14-21 yrs. old) ranging in length from 9.3 to 11.5m long, and the females were 9.3 to 11.4m long, ranging in age from 11 to about 58 years old (Table 1). A sample of the stomach contents from 32 of the whales was collected and stored in alcohol by Dr. James T. Harvey pending identification and enumeration.
Questions
First I sought to describe the species of cephalopods eaten by these sperm whales, and the importance of each cephalopod species in the sperm whale diet. I hoped to determine the species of cephalopods represented in the geographical region where the group was stranded. Previous research in western Canada and California indicated that the most numerous cephalopod species in sperm whale diets were Moroteuthis robusta,
Berryteuthis magister, Gonatopsis borealis, and Histioteuthis hoylei (previously described as H. dofleini). As the whale stranding in the current study occurred between those two regions, the stomach contents of these specimens were expected to reflect similar dietary habits.
8 I also sought to answer whether there were differences in prey composition between males (age 15-21) and females (age 11-21), and in the diets of females of different age categories (ages 11-21 and 22-58). Male sperm whales dive deeper than females, therefore, may have access to different species. The depth of dives, however, is determined largely by the size of the individual (Caldwell et al., 1966), and because the sperm whales in the subject stranding were all in the same size range regardless of sex, no difference in composition of prey items between sexes was expected. Several authors have compiled data indicating that there is no difference in the size of prey captured by males and females (Clarke, 1956; Okutani & Nemoto, 1964; Kawakami, 1980), which also indicated that no difference in size composition of the food would be found.
However, I expected a difference in the composition and number of prey items in the diets of females of different age groups, with older females having a greater diversity of prey and greater quantities captured, because experience in hunting would give the older females an advantage in finding food.
9 METHODS
Identification and Measurement
Stomach contents of 32 of the 41 stranded sperm whales were collected by Dr.
James T. Harvey in 1979. At the time of sampling, the stomach contents of each whale were emptied into individual 10-liter buckets and immediately stored in 50% isopropyl alcohol. The buckets were then transported to a laboratory where the stomach contents were washed with water, rinsed through a 0.5 mm sieve, emptied into a tray and sorted into categories. Once sorted, the contents were again placed in 50% isopropyl alcohol for storage to ensure that the beaks did not become dry or distorted. Several of the whales had stomach contents that were too voluminous to collect in their entirety and the stomach contents of these individuals were subsampled. Before subsampling, the contents were well mixed to ensure that a representative subsample would be collected.
For the current study, I separated and counted upper and lower cephalopod beaks.
Lower beaks represented a greater number of recovered beaks than upper beaks; therefore, lower beaks were used to estimate the minimum number of cephalopods present in the diets of these sperm whales. The present collection consists entirely of cephalopod beaks. No otoliths were discovered in the samples. For this reason, all references to "prey," "species" and "prey species" are to cephalopod species.
Lower beaks were identified to the lowest taxon using the reference collection at
Moss Landing Marine Laboratories (MLML), several published identification guides
(Clarke, 1962b; Iverson & Pinkas, 1971; Wolff, 1984; Clarke, 1986), and were visually
10 verified by William Walker of the National Marine Mammal Laboratory in Seattle, WA.
Walker also aided in the identification of several of the samples. Measurements of the
lower rostral length (LRL) of cephalopod beaks and the lower hood length (LHL) of
octopod and Vampyromorpha beaks were conducted using digital and vernier calipers to
the nearest 0.1mm. Beaks that were damaged were identified to the lowest taxon possible
and used only in determining frequency of occurrence and total number. For all other beaks that were deemed in good condition and measured, the LRL and LHL
measurements were used in mathematical regressions to determine dorsal mantle length
(DML) and mass of the prey items (Clarke, 1980; Wolff, 1984; Clarke, 1986; Walker et
al. 2002; Table 2).
Statistical Analysis
Often the cumulative number of prey species plotted against the cumulative
number of stomachs analyzed (in a random order) is used to determine if enough samples
have been collected to adequately describe the prey composition of the population
(Cailliet & Barry, 1978; Ferry & Cailliet, 1996). However in this study, because this
population of sperm whales did not represent a random sampling of the population, the
cumulative species curves were used to determine whether or not the spectrum of species
identified from the stomach contents encompassed all species that were expected to be
found in the diet of these sperm whales at the time of the stranding.
Relative prey importance was calculated using numerical abundance and
frequency of occurrence. Numerical abundance as defined by Hyslop (1980) determines
the proportion of a particular prey item in the diet, i.e. (number of individuals of each
species/total number of all prey items consumed) x 100. Frequency of occurrence is
II defined as the (number of stomachs containing each species/total number of stomachs containing food) x 100. Both of these measures provide valuable information about the food habits of predators but can be inherently misleading. Oftentimes a third measure of volumetric importance is included to complete the dietary picture (Hyslop, 1980: Cailliet et al., 1986). There were some biases associated with determining volumetric analyses because some stomachs were subsampled. Therefore, I only calculated relative contribution by mass. The contribution by mass of each species was determined using
(number of items of each species x mean prey mass/total mass of all prey items consumed) x 100 (Recchia & Read, 1989). The mean prey mass was calculated by averaging the estimated mass of each prey species. Hyslop (1980) noted that these three measures used together can provide a reasonable examination of the relative importance of prey species in the diets of predators. No regression equations were available for
Alloposus mollis, thus it was excluded from any volumetric or length analysis.
Two-dimensional indices of relative importance (IRI) (Laroche, 1982) were calculated by multiplying percent frequency of occurrence (%FO) by the averaged percent of numerical representation (%N). This latter number (%N) was calculated to eliminate any biases towards stomachs that were subsampled. To accomplish this, the total number of a particular species in a particular whale was divided by the total number of beaks collected from that whale. This calculation produced the percentage representation of a species for each whale. That number was then totaled for each prey species for all whales and divided by the total number of whales, which produced the average %N. Total IRI values were then expressed as %IRI (expressed as IRI for each
12 prey item divided by the sum of all IRI values for all prey items) to allow for the
determination of prey item importance.
A Spearman's rank correlation based on the %IRI values was calculated to determine if there was a difference in the importance of prey items in the diets of males and females and in the diets of females of different age groups. A Percent Similarity
Index (PSI) was calculated to determine the amount of similarity in the diets of males and
females and in the diets of females of different age groups (%S =2: min pi).
The estimated maximum, minimum, and mean dorsal mantle length of each species consumed were calculated using regression equations and LRL or LHL. For cephalopod species where regressions were unavailable, the length regressions for the genus or family were used. Length distribution graphs were generated for prey items that were considered major constituents of the diet of these whales.
Finally, a One-Way AN OVA was used to determine if there was any difference in
the mean length of major prey items captured by males and females and by females of
different age groups.
13 RESULTS
From the 32 stomachs, 20,247 cephalopod lower beaks (last column of Table 1) were recovered, representing 24 cephalopod species of 14 different families (Table 3).
An additional 6 groupings of beaks were identified to species types and 4 remaining groups were identified to a generic level. Other items recovered from the stomach contents included upper beaks, parasites, squid pens, mud, and ropes. Cumulative species curves for the entire group of stranded whales and for the different age and sex groups gradually reached an asymptote (Fig. 2). This indicated that the number of stomachs analyzed for this stranding of sperm whales adequately assessed the number of prey species expected in the diet of this grouping of whales.
Four families contributed a majority of the total number of beaks: Histioteuthidae
(%N=32.8, %FO=l00), Cranchiidae (%N=25.5, %F0=96.9), Gonatidae (%N=15.8,
%F0=96.9) and Onychoteuthidae (%N=l5.6, %F0=93.8). When percent N was averaged across all whales to eliminate any biases towards stomachs that were subsampled, Histioteuthidae still represented the majority of beaks recovered (averaged
%N = 32.6; Table 4 ). Histioteutlzis lzoylei represented the most numerous species (%N =
24.4, averaged % N = 25.9, Figure 3).
The relative total mass of prey consumed by this group of stranded whales was
10,758.6 kg (Table 5). Based on the prey items recovered for this study, the contribution by mass to the sperm whales diet indicated that the dominant species was Moroteutlzis
14 robusta (42.9 %V) followed by Gonatopsis/Berryteuthis type (20.0 %V) and
Histioteuthis lzoylei (12.3 %V).
The most important species by %IRI were H. lzoylei (27.0 %), Taonius borealis
(13.4 %), Galiteuthis plzyllura (11.8 %), Gonatopsis/Berryteutlzis type (11.7 %),
Octopoteutlzis deletron (10.5 %) and M. robusta (10.4%). These numbers were similar to the ran kings based on %N alone (Table 5). The most dominant species eaten by males
(ages 15-21) were H. lzoylei (25.1 %IRI), M. robusta (18.6 %IRI) and G. phyllura (14.1
%IRI; Table 6). The dominant species eaten by females (ages 11-21) were H. hoylei
(23.2 %IRI), T. borealis (17.0 %IRI), Gonatopsis/Berryteutlzis type (13.7 %IRI), G. phyllura (12.6 %IRI), and 0. deletron (12.1 %IRI). The dominant species eaten by females (ages 22-58) were H. lzoylei (32.6%), 0. deletron (13.1 %IRI),
Gonatopsis/Benyteuthis type (12.6 %IRI), and T. borealis (12.1 %IRI).
The following section of results is intended to examine the make-up of the major prey items that contributed to the diets of these sperm whales (Figs 4-7) in order to build an understanding about what they were eating on and where they were feeding. As stated above, the family Histioteuthidae represented 32.8% of the beaks recovered and identified. Members of this family were present in all of the stomachs examined. Two species were identified definitively from the samples as H. hoylei Goodrich, 1896 and H. heteropsis Ben·y, 1913. One beak was described as Histioteutlzis sp. cf H. hoylei because the beak was very similar to H. hoylei with only minor differences that raised questions as to its identity. A fourth grouping of beaks had similar questions of identity and were classified as Histioteutlzis sp. cf H. corona (per the advice of Bill Walker at the NMML in
15 Seattle). Finally, several beaks were simply classified as Histioteuthis spp because they were too damaged to identify more specifically.
Histeoteuthis hoylei was the most numerous species recovered in this study. It represented 24.4 % of the total beaks recovered and was found in 96.8 % of the stomachs
(27 .0 %IRI). Histeoteuthis hoylei also was the most dominant species eaten by males of this group (25.1 %IRI), young females (23.2 %IRI) and older females (32.6 %IRI). The
DML for these squids ranged from 63.3 mm to 215.8 mm, with a mean length of 133.1 mm (95% CI =0.6; Fig. 4a). This species contributed 12.3 %of the total mass of prey items recovered in this group of whales.
Beaks described as Histioteuthis sp. cf H. corona were the second most common histoteuthid beak identified from the stomachs of this group of sperm whales (7 .1 %N,
87.5 %FO, 5.6 %/RI). Histioteuthis sp. cf H. corona had an 8.1 %IRI in the diet of male whales, a 4.6 %IRI in the diet of younger females, and a 4.8 %IRI in the diets of older females. The mean DML was 139.0 mm (95% CI = 1.1), with a range of 82.5 to 206.8 mm (Table 4b). These squids contributed 3.7% of the total mass of prey items recovered for this group of whales.
The family Cranchiidae represented 25.5 %of the beaks recovered and identified.
Members of this family were present in 96.9 %of the stomachs. Two species were identified definitively from the samples as Taonius borealis Nesis, 1972 and G. phyllura
Berry, 1911. One group of beaks was described as Galiteuthis sp. cf G. pacifica because the beaks were very similar to G. pacifica but had some minor differences that raised questions as to their identity. The remaining beaks were divided into three groups:
16 Megalocranchia spp, Galiteuthis sp. A, and an unidentified Galiteuthis type (per recommendation of William Walker, NMML Seattle, W A.).
The most common species of the Cranchiidae family by number of beaks was G. phyllura (13.1 %N, 96.9 %FO, 11.7 %IRI). Galiteuthis phyllura also was a dominant species in the diets of male sperm whales (14.1 %IRI) and young females (12.6 %IRI).
These squids contributed 3.4 %of the total mass of prey items recovered for this group of whales. The DML for G. phyllura ranged from 142.7 mm to 346.6 mm, with a mean
DML of 257.8 mm (95% Cl = 1.2; Fig. 4c).
Taonius borealis closely followed G. phyllura in number of beaks recovered (12.1
%N, 96.9% FO), but it had a greater %IRI value (13.4 %). Taonius borealis was more dominant in the diets of both groups of female sperm whales (17 .0 %IRI for younger females and 12.1 %IRI for older females) than in the male sperm whales (9.6 %IRI).
These squids contributed 3.6 %of the total mass of prey items recovered in these sperm whales. The mean DML forT. borealis was 331.4 mm (95% CI = 1.3), with a range in
DML from 195.3 mm to 438.4 mm (Table 4d).
The family Gonatidae represented 15.8 %of the beaks recovered. Members of this family were present in all of the stomachs examined. Three species were identified definitively from the samples as Gonatus benyi Naef, 1923, Gonatus onyx Young, 1972, and Gonatus pyros Young, 1972. One group of beaks was described as Gonatus madokai/middend01jfi because the beaks were very similar to both G. madokai and G. middend01:ffi. Another group of beaks was describes as Gonatopsis/Berryteuthis type because Gonatopsis borealis and Benyteuthis magister cannot be differentiated based on beaks alone (Fiscus 1982; Hacker, 1986; William Walker pers. Comm.). A fifth group of
17 beaks was described as Gonatus sp. A (William Walker pers. comm.) and two beaks were only identified to the genus level.
The most numerous group of the Gonatidae family encountered was the
Gonatopsis/Berryteuthis type. Members of this type represented 10.9 % of the beaks identified from the stomachs of this group of sperm whales, and occurred in 96.9 % of the stomachs examined (11.4 %IRI). This group contributed the second greatest percentage volume (20.0 %V) based on the prey items recovered. Specimens of
Gonatopsis/Berryteuthis type were more dominant in the diets of both groups of females
(13.7 %/RI in younger females and 12.6 %in older females) than in males (5.4 %/Rl).
The mean DML of this group was 316.0 mm (95% CI = 10.4), with DMLs ranging between 162.6 mm to 442.0 mm (Fig. Sa).
All other groups in this family represented less than 6 %of the total beaks identified. Gonatus berryi Naef, 1923 and Gonatus sp. A represented 2 %and 3 %of the beaks respectively. Gonatus berryi was found in 84.4 %of stomachs analyzed (1.6
%IRI) whereas Gonatus sp. A was found in 90.6 % of the stomachs (2.5 %IRI).
Combined, both species contributed less than 4 % of the total mass of prey items recovered from the stomachs of these whales. Gonatus sp. A had a DML between 145 and 376 mm (mean DML 291.3 mm, 95% CI = 3.5; Fig. 5b), whereas Gonatus benyi had a DML between 124 mm and 334 mm (with a mean DML of 206.7 mm, 95% CI = 3.1;
Fig. 5c).
The family Onychoteuthidae represented 15.6 %of the beaks recovered.
Members of this family were present in 93.8 %of the stomachs examined. Two species were identified from the beaks: Onychoteuthis borealijaponica and M. robusta.
18 Moroteutlzis robusta Verrill, 1876 was the most numerous member of the family
Onychoteuthidae, representing 11.1 % of the beaks recovered. This species was found in
90.6 %of the stomachs examined (10.4 %IRI). Moroteuthis robusta was the second
most dominant species in the diet of male sperm whales (18.6 %IRI), but was of less
importance in the diets of female sperm whales (7 .0 %IRI in younger females and 8.2
%IRI in older females). Overall this species contributed the most mass of all prey items recovered (42.9 %V). The mean DML for this species was 621.5 mm (95% CI= 5.1), with a range of 326.7 to 942.7 mm (Fig. 6).
Onyclzoteutlzis borealijaponica Okada, 1927 was less frequent in the stomachs of this group of sperm whales. It represented 4.5 % of the total beaks recovered and occurred in only 84.4 %of the stomachs analyzed (3.54 %IRI). Onyclzoteuthis borealijaponica was more dominant in the diets of male sperm whales (8.4 %IRI) than in female sperm whales (2.9 %IRI in younger females and 1.5 %IRI in older females). The mean DML for this species was 340.3 mm (95% CI = 1.8), with a range of 123.6 and
434.7 mm DML (Fig. 4e). This species represented 3.4% of the total mass of prey items recovered in this study.
The family Octopoteuthidae represented 7.6% of the beal(s recovered and identified. Two species of this family were identified from the lower beaks recovered, 0. deletron Young, 1972 and Taningia danae Joubin, 1931. Octopoteutlzis deletron represented 7.2 % of the total number of beaks identified and was found in 96.8 % of the stomachs (10.5 %IRI). This squid was a major constituent of the diets of older female whales (11. 7 %IRI), but represented a lesser percentage of the diets in younger females
(7.3 %IRI) and males (2.5 %IRI). The DMLs for these squids were 40.3 mm to 218.0
19 mrn, with a mean DML length of 126.6 mm (95% CI = 0.8; Fig. 4f). There was a significant difference in the size of the 0. deletron eaten by male sperm whales versus young female sperm whales (t = 2.24, p = 0.047), with males taking slightly larger individuals. These squids contributed 1.6% of the total mass of prey items recovered for this group of whales.
Taningia danae represented only 0.5 %of the total number of beaks identified but was found in 67.7% of the stomachs (0.4 %IRI). The DML for specimens of this species ranged from 22.3 mm to 669.2 mm, with a mean DML of 415.0 mm (95% CI = 26.3; Fig.
7). This species contributed 2.1 % of the total mass eaten by this group of whales.
In the order Vampyromorpha, Vampyroteutlzis infemalis represented 0.8% of the beaks recovered and was found in 71.9 % of the stomach examined (0.63 %IRI). It contiibuted 1.0 %of the total mass of prey items recovered in this study, and had a mean
DML of 97.7 mm (95% CI = 2.5; 58.2 mm to 145.7 mm DML; Table 5d).
The lengths of squid eaten by the sperm whales that stranded in Oregon were between 22.3 and 1318.1 mm in DML (mean= 265.7, SD = 158.1; Table 7).
Cephalopods were divided into four size groups: small (20-600 mm), medium (600-900 mm), medium-large (900-1300 mm), and large (1300 mm and greater). Male sperm whales fed primarily on cephalopods in the small size group (90.8 %), as did females of all age groups (females aged 11-21 had a %N of 95.5, and females aged 22-58 had a %N of 95.2; Table 8). Males fed more in the medium size class than did females (males with
%N of 8.9 and females aged 11-21 with %N of 4.3 and females aged 22-58 with a %N of
4.7). There was no significant difference in size classes of squid among sexes or age classes of sperm whales (Table 9).
20 There was a significant difference in the importance of prey items in the diets of males and females (rs = 0.908, p <0.001) and in the diets of females of different age groups (r, = 0.896, p <0.001). However, when a PSI (%S) was generated for the major prey items consumed, the difference was not that significant (%S for males and females=
76.1, %S for females of different age groups= 88.2, Fig. 8). Hence, differences were produced by the appearance of infrequent prey species.
Prey found in sperm whales off California and western Canada were similar to those reported here (Table 10). Fiscus et al. (1989) found the predominant prey families in sperm whales (n = 157) in California included: Gonatidae (31.42 %N, 68.8 %FO),
Onychoteuthidae (24.93 %N, 75.8 %FO), Histioteuthidae (15.45 %N, 46.5 %FO), and
Cranchiidae (9.93 %N, 43.3 %FO). In their study the most numerous species were, G. borealis (26.3 %N), M. robusta (23.3 %N), and H. dojleini (H. hoylei) (12.2 %N). In western Canada, Clarke and MacLeod (1980) found the predominant families in sperm whales (n = 20) were Gonatidae (34.2 %N, 80 %FO), Onychoteuthidae (24.3 %N, 80
%FO), Cranchiidae (15.1 %N, 55 %FO), and Histioteuthidae (5.9 %N, 25 %N). The two most dominant species from the western Canada study were B. magister (28.9 %N, 17.6
%V) and M. robusta (24.3 %N, 61.9 %V).
21 DISCUSSION
Berzin (1972) stated that members of the family Physeteridae were primarily squid-eaters, and as such their morphological and physiological characteristics were largely determined and affected by the deep-sea mode of life of their major prey items.
By identifying prey items, we begin to understand the biology, diving and foraging patterns, distribution, and migration of these whales. Analysis of stomach contents has indicated the presence of cephalopod species in areas where these species had not previously been found (Clarke & MacLeod, 1976; Gales & Pemberton, 1992). Such studies also provided greater knowledge of the size composition of living cephalopods because undigested squid and squid beaks recovered from the stomachs of sperm whales indicated the existence of cephalopods larger than those normally caught in nets (Clarke,
1977; Clarke, 1980; Fiscus eta!., 1989).
Biases
There are several inherent biases associated with stomach content analysis.
Among these biases are differential rates of digestion, differences in stomach retention time among prey species, and difficulty in identification due to erosion and regurgitation of prey from the stomach because of over-accumulation or stress (Caldwell eta!., 1966,
Clarke, 1980, Hyslop, 1980; Harvey, 1987; Fiscus, 1990; Finley & Gibb, 1982; Harvey &
Antonelis, 1994; Santos et. al, 2001). Finley and Gibb (1982) provided evidence for the differential rates of digestion among calcareous fish otoliths and the hard chitinous squid beaks. In an experiment in which they simulated the acidic conditions of the typical marine mammal stomach, after a 24-hour period the squid beaks had little damage,
22 whereas the otoliths underwent considerable deterioration. The fact that no otoliths were found in the stomach contents of the whales examined in this current study does not imply that these whales were not eating fish. The absence of otoliths may be attributed to their susceptibility to erosion in the stomachs of these predators. Two other factors also may explain the lack of otoliths. First, the stomach contents for these sperm whales were not collected until three days after they stranded, which may have allowed for total erosion of the otoliths (Dr. James T. Harvey, pers. comm.). Secondly, the whales may not have eaten days before they stranded.
Many authors have reported that squid beaks were poorly digested and often accumulated in the stomachs of predators, which may cause overrepresentation of cephalopods in the diets of marine mammals (Fiscus & Baines, 1966; Miller, 1978;
Hyslop, 1980; Pitcher, 1980; Finley & Gibb, 1982; Selzer et. a!, 1986; Harvey, 1987;
Harvey & Antonelis,1994; Santos et. a!, 2001). Fiscus and Baines (1966) and Finley and
Gibb (1982) stated that squid beaks often remain in the stomach contents through several feedings, thus may not be an accurate record of recent ingestion unless flesh is present on the beaks.
Relatively few studies have examined the retention times of prey items in stomach contents of larger marine mammals, especially whales. Based on mathematical regressions estimating the amount of food required per day by a sperm whale and the
amount of food found in his collection of sperm whale stomach contents, Clarke (1980) suggested that the average retention time of beaks in female sperm whales was 2.1 to 2.5 days and the average time for males was 1.2 to 1.6 days. In a series of controlled feeding experiments, several authors have suggested other retention times for cephalopod beaks.
23 Bigg and Fawcett (1985) reported that in fur seals, squid beaks may be retained up to 33 hours after feeding. Ross (1979) determined that cephalopod beaks may be retained in the stomachs of bottlenose dolphins for 3 days or more. In feeding studies with elephant seals, Harvey and Antonelis (1994) found that beaks could remain up to 9 days, and often remained in the stomachs of the seals after continuous lavages.
Although erosion may be a factor in the identification of otoliths, it seems that the passage of squid beaks through the digestive system of marine mammals has little effect on the appearance of the beaks (Bigg & Fawcett, 1985). The use of beaks to estimate the dorsal mantle length (DML) and the mass of the cephalopods at the time that they were ingested, therefore, should not underestimate the size disttibutions. Because the beaks were not digested, the number of cephalopod taxa as indicated by the presence of their beaks also was fairly representative. However, sperm whales have a tendency to regurgitate when they are under stress or when the accumulation of beaks in the stomach becomes excessive (Caldwell eta!., 1966; Clarke, 1980). Thus, the numbers represented in this study may not reflect the actual quantities of cephalopods ingested by these sperm whales. However, the relative frequency of occurrence of each cephalopod species should not be affected if it is assumed that the beaks of different species have an equal chance of being regurgitated.
In this study, the majority of beaks were free of any flesh at the time that they were collected (Dr. James T. Harvey, pers. comm.), indicating that this group of sperm whales had not fed immediately before stranding. Clarke (1980) suggested that stomach contents of sperm whales could represent at least 3 days of food. However, due to the large array of cephalopod beaks recovered in the stomach contents, it is likely that the
24 stomach contents of these sperm whales represented several days', if not weeks' worth of food. Whereas the beaks found in sperm whale stomachs may not be indicative of recent feeding, they may still give a true indication of the species composition of cephalopods that recently were eaten by the whales (Clarke, 1980).
Where these whales may have fed can be inferred from the distribution of the prey items upon which they fed. In the results section, size classes for each of the major prey items were given, and these measurements can be con·elated to age classes of cephalopods. Additionally, the distribution of the cephalopod species in the water column often is based upon age. Based on these data, the discussion that follows looks at the geographic distribution as well as the vertical distribution of cephalopod species, in an attempt to determine where these whales were feeding.
Specific families of cephalopods
Histioteutlzidae
The family Histioteuthidae represented the majority of beaks recovered and identified (32.8 %). Among all cephalopods, H. hoylei was the most numerous species recovered (%N =24.4). In the family Histioteuthidae, it was followed in number by
Histioteuthis sp. cf H. corona (%N =7.1) and H. lzeteropsis (%N =0.3). Based on the
DMLs that were calculated for the Histioteuthidae taken, these whales were feeding mostly on adult H. hoylei, Histioteuthis sp. cf H. corona and H. heteropsis.
Hisrioteuthis hoylei is described as a medium-sized squid, with adult females having a DML between 140 mm and 236 mm and males reaching sizes between 100 mm and 210 mm (Voss et al. 1998). It is considered to be a cosmopolitan species widely distributed among tropical and subtropical waters (Young, 1972; Nesis, 1987; Voss et al., 25 !992a). In the Pacific H. hoylei is found from 45 °N to 40-45 °S (Nesis, 1987; Voss et a!., 1998). Jefferts (1983) reported H. lwylei as common in the California Current.
In the water column, H. lwylei occurs primarily in the mesopelagic but also can be found along the lower epipelagic to bathypelagic (Fig. 9). Juveniles and subadults captured in open and closing nets displayed vertical distributions of -50 m to 850 m depth. These squid migrate at night, when they are found at depths between 50 m and
500 m. During the day they are mostly found between 375 m and 850 m, with adults being found slightly deeper than juveniles (Young, 1978; Voss et al., 1992a). The adults of this species also occur at depths greater than 1,000 m (Voss et al., 1992a).
There are four subspecies of H. corona currently recognized (Voss et al., 1998).
Of these, the only subspecies found in the North Pacific is H. corona berryi Voss, 1969
(Voss, 1969). To date the only specimens of this species captured in the North Pacific have been juveniles with DMLs between 35 mm and 47 mm (Voss et al., 1998). The geographical distribution of this species is poorly known, with only eight specimens collected in the California Current and fringing waters (Voss et al. 1992a; Voss et al.,
1998). Its vertical distribution is between 300m and 800 m (Voss et al., 1992a; Voss et al., 1998).
Histeoteuthis heteropsis is a small to medium sized squid, with adult males having a DML of 54 mm to 89 mm (Voss et al., 1998). The range in female sizes is not known, but the largest known specimen is 132 mm. It is considered to be an east Pacific transitional species, and in the northeast Pacific is restJicted to the California Current system between 24 °N and 45 °N (Voss et al., 1998). Histeoteuthis heteropsis often occurs in areas of high productivity and upwelling, and is found in the transition waters
26 between two eastern boundary currents in the Pacific, both of which are characterized by having a complex hydrography (Voss eta!., 1998). In the California Current system it is the most common histioteuthid (Jefferts, 1983). Histioteuthis heteropsis is mesopelagic
(Nesis, 1987). Capture data in the California Current system indicated that members of this species stay between 300 m and 900 m during the day and between the surface and
400m at night (Roper & Young, 1975; Voss et al., 1998).
Based on the discussion of the major histioteuthids eaten by this group of sperm whales, we can infer that this group of whales was feeding on members of this family primarily in the lower mesopelagic of the California Current system.
Cranchiidae
The family Cranchiidae represented 25.5 %of the beaks recovered and identified.
Galiteuthis phyllura was the most common species of this family represented in these whales (%N = 13.1). Tao1zius borealis closely followed G. phyllura in number of beaks recovered (%N = 12.1), but it had a greater %IRI value (13.4% vs. 11.7 %). The remaining groups in this family (Megalocranchia spp, Galiteuthis sp. cf G. Pacifica,
Galiteuthis sp. A and the unidentified Galiteuthis type) represented about 0.3% of the beaks identified and were not major constituents in the diets of these sperm whales.
At 60 mm the larval development of G. phyllura is complete and they are considered subadults (Roper & Young, 1975). Because the DMLs estimated in this study for this species ranged from 142.7 mm to 346.6 mm, these squid were most likely subadults and adults. Galiteuthis phyllura typically is found in the temperate northeast
Pacific, but has a distribution that extends from Baja California to the Bering Sea (Nesis,
1987). It has been desczibed by Nesis (1987) as a meso-bathypelagic and benthic-bathyal
27 species. Juveniles and subadults of this species are usually found between approximately
700 m and 2,000 m, with no evidence of die! vertical migration (Roper & Young, 1975;
Voss et al., 1992b). Roper & Young (1975) reported this species as undergoing an ontogenetic descent "whereby increasingly larger larvae occupy successively greater depths."
Taonius borealis adults can reach a DML of 660 mm (Voss, 1980). In this study the estimated DMLs (195.6 mm to 438.4 mm) indicated that the sperm whales were feeding on subadults and adults. The distribution ofT. borealis is subarctic Pacific (Voss
1980, Voss et al., 1998). Juveniles are found at depths between 400 m and 600 m. The species also displays ontogenetic descent with maturity occurring at depths of greater than 2,000 m (Young, 1975; Voss et al., 1992b). If die! vertical migration is displayed in this species, it is only slight (Young, 1975; Voss et al., 1992b).
The remaining groups in this family were Megalocranchia spp, Galiteuthis sp. cf
G. pacifica, Galiteuthis sp. A, and the unidentified Galiteuthis type. Megalocranchia species occur worldwide and are usually found in tropical to subtropical waters (Voss et al, 1992b). Some species can reach lengths of 1,800 mm (Tsuchiya & Okutani, 1993).
They display a die! vertical migration, with subadults found at depths of greater than
2,000 m during the day and migrating to depths between 100m and 700 mat night. This genus is considered mesopelagic (Young, 1978). Galiteuthis pacifica Robsen, 1948 was found in the California CuiTent to- 34 °N (Voss et al., 1992b). This species, like G. phyllura, has an ontogenetic migration with subadults found between approximately 700 and 2,000 m, with no evidence of die! vertical migration (Young 1978; Voss et al.,
1992b).
28 The members of the family Cranchiidae are found primarily in the lower mesopelagic to bathypelagic region of the water column. The majority of this family also displays ontogenetic descent with adults being found at depths greater than 1,000 m. As the sperm whales in this study were feeding primarily on subadult and adult members of this family, they were most likely feeding in the bathypelagic region. Also, because G. phyllura was a major constituent in the diets of these whales, it is likely that they were feeding along the sea floor bottom in this region.
Gonatidae
The family Gonatidae represented 15.8 %of the prey items recovered and identified. The most numerous group of this family encountered was
Gonatopsis!Berryteuthis type (10.9 %N). This species contributed 20.0 %of the total mass eaten by these sperm whales.
Gonatopsis borealis is capable of reaching DMLs between 250 mm and 450 mm, whereas B. magister can reach a DML of 380 mm (Nesis, 1987). The juveniles of both these species range between 5 mm and 16 mm DML (Okutani & Clarke, 1992). The majority of the Gonatopsis/Benyteuthis types recovered from the stomachs of this group of sperm whales were adults. Gonatopsis borealis Sasaki, 1923 can be found in the
North Pacific from Japan (37 °N) to California (33 °N) whereas B. magister Pearcy and
Voss, 1963 is commonly found in the pansubarctic Pacific (Okutani & Clarke, 1992).
Pearcy (1965) found G. borealis in the waters off the Oregon coast. Members of the gonatid family are found principally along the continental slope seaward and also may be found in some inshore deepwater localities such as Prince William Sound (Fiscus, 1982).
Off Oregon, G. borealis displays vertical a migration (Pearcy eta!., 1977). Gonatopsis
29 borealis specimens were captured off California primarily between 400 m and 700 m during the day and at night they were found distributed throughout the upper 400 m
(Roper & Young, 1975). Berryteuthis magister captured in the Auke Bay region of
Alaska did not display vertical migration, and were found between 165 m and 310m during day and night (Roper & Young, 1975). Data from Japan and Korea indicated that
B. magister can be found at depths of 1,000m (Roper & Young, 1975). Nesis (1987) described B. magister as often near the bottom between 100 m and 200 m, and between
600 m and 800 m depth with juveniles ascending into midwater and to the surface.
Gonatopsis borealis occurs from the epipelagic to the bathylpelagic and in bathyl and abyssal zones (Nesis, 1987).
Gonatus spA and G. berryi juveniles are between 8 mrn and 30 mrn DML
(Okutani & Clarke, 1992). Nesis (1987) described G. benyi as mesopelagic to
bathypelagic, capable of reaching a DML of 190 mrn. Gonatus sp. A has been described to closely resemble Gonatusfabricii Lichtenstein, 1818, but it is more appropriate to
label them as Gonatus sp. A (William Walker pers. comm.). These squid also have been
grouped as Gonatus sp. A by Jefferts (1983) and Okutani and Clarke (1992). The family
Gonatidae has been described by Jefferts (1983) as being the most important cephalopod
group in the subarctic Pacific. Gonatus berryi is found in the northeast Pacific from 30
0 N to 40 °N, as is Gonatus sp. A (Jefferts, 1983; Okutani & Clarke, 1992). Gonatus
benyi has a distribution between 300m and 1200 m depth during the day and exhibits a
slight vertical migration at night (Roper & Young, 1975).
The estimated DMLs for G. benyi and Gonatus sp. A indicate that both species
present in this study were adults. Based on the above discussion of the distribution of
30 Gonatidae members and the fact that majmity of gonatids eaten were adults, we can infer that the spenn whales in this study were eating primarily in the mesopelagic to bathypelagic region. Also, as G. borealis and B. magister are known to be associated with the bathyl region, these sperm whales were likely feeding on Gonatids along the seafloor.
Onychoteuthidae
The family Onychoteuthidae represented 15.6 %of the beaks recovered and identified. Moroteuthis robusta was the most numerous species (11.1 %N) of this family and it contributed the most mass of all prey items recovered in the diets of all 32 sperm whales (42.9 %V).
Moroteuthis robustct may reach a DML of 2,300 mm, but the largest specimen recovered to date had a DML of 1,000 mm (Nesis, 1987; Clarke, 1992). Based on the estimated DMLs, sperm whales in this study were feeding on all age classes of this species. Moroteuthis robusta is a Pacific boreal species, found in waters extending from the Bering Sea and Gulf of Alaska to Japan and southern California (Nesis, 1987;
Kubodera et al., 1998). It is often found near the bottom in the lower sublittoral and upper bathyl (Nesis, 1987). Currently, few data are available to determine the full vertical distribution of this species. Reports from fishermen indicate that this species occurs between 100m and 375 m depth, with 100m most likely representing their upper limit (Roper & Young, 1975). Roper and Young (1975) also reported that there is little indication that this species undergoes a vertical migration.
Males of the species Onychoteuthis borealijaponica mature at about 250 mm
DML, whereas females reach maturity at a DML of 300 mm to 350 mm (Kubodera et al.,
31 1998). 0. borealijaponica is found in the far northem Pacific 30 °N to 55 °N, migrating to subarctic waters during the summer, and retuming to subtropical waters during fall and winter (Clarke, 1992; Kubodera eta!., 1998).
The majority of 0. borealijaponica eaten by this group of sperm whales were adults. Based on the above discussion of the distribution of Onychoteuthidae members, we can infer that the sperm whales in this study were eating primarily in the mesopelagic along the bottom in the lower sublittoral and upper bathyl.
Octopoteuthidae
Members of the family Octopoteuthidae represented 7.6% of the beaks recovered and identified. The most numerous member of this family was 0. deletron (7.2 %N) followed by T. danae (0.5 %N). Octopoteuthids can be found worldwide between 56 °N and 50 °5. Octopoteutlzis deletron occurs in the Pacific from Washington to Baja
California (Nesis, 1987). Juveniles of the species often have a vertical distribution that ranges from 0 to 300m depth, whereas adults occupy the meso- to bathypelagic zones
(Stephen & Jefferts, 1992). Roper and Young (1975) showed that the daytime range for
0. deletron was between 200m and 1200 m depth. They stated that 200m was a definite upper limit that was not exceeded during their sampling, but that the lower range was much more difficult to assess as this squid could go as deep as 1,200 m. At night the vertical distribution of 0. deletron was 100m and 500 m, with only a few species captured below that depth.
Taningia danae is of particular interest in this study, because previously it has only been recorded in the northeastem Pacific twice, both times along the California coast. Fiscus et al. (1989) found one lower beak ofT. danae among sperm whale
32 samples, and Condit and Leboeuf (1984) also recorded finding one lower beak of that species among elephant seal samples. In this study, this species was found in 65.6 %of the stomachs examined. Also, to date most samples ofT. danae have come from the
stomachs of predators, most notably sperm whales (Nesis, 1987; Roper & Vecchione,
1993). This species is considered cosmopolitan in distribution, and is found primarily in
tropical to subtropical waters, but also occurs in boreal and notalian waters (Nesis, 1987;
Roper & Vecchione, 1993). Its vertical distribution is "mesopelagic and at the bottom in
bathyi"(Nesis, 1987). The deepest occurrence reported forT. danae comes from Clarke
& Merrett (1972). They reported finding T. danae remains in the stomach contents of a
bottom dwelling shark captured at 1,246 m. Others have reported capturing a small
sample of juveniles between 300 and 10m depth at night and between 203 and 102 m
depth during the day (Clarke,1967; Clarke & Lu, 1974; Lu & Clarke, 1975). From the
compilation of data represented in the literature, Roper and Vecchione (1993)
summarized the vertical descent of T. danae as: "the young undergo ontogenetic descent
and the adults become benthopelagic, associated with but not limited to the bottom."
Sperm whales in this study were most likely feeding on subadults and adults of
this family, indicating that they were feeding in the mesopelagic and bathypelagiz zones.
The presence oft. danae in this study indicated that these sperm whales were also
feeding in the bathyl region.
Other Families
The remaining families represented less than 3% of the total beaks recovered and
had a combined %IRI of <2. The only species that will be mentioned here is V. infemalis
Chun, 1903 since it is the only representative of the order Vampyromorpha.
33 Vampyroteuthis infemalis can range in size from 8 mm to 110 mm DML, with juveniles usually reaching 20 mm (Roper & Young, 1975; Hochberg & Nixon, 1992).
Vampyroteuthis ill{emalis is cosmopolitan in distribution, found in tropical and temperate waters between 40 °N and 40 as (Young, 1972; Hochberg & Nixon, 1992). Pearcy
(1965) found this species in the waters off of Oregon at about 44°N. It is associated with the lower mesopelagic to bathypelagic zones and have a vertical migration centered between 600 m and 1200 m depth (Roper & Young, 1975; Hochberg & Nixon, 1992).
The adults of this species are usually found below 900 m. This species displays ontogenetic descent (Hochberg & Nixon, 1992).
The DMLs estimated for this species indicated that this group of whales were primarily feeding on adult V. illfemalis. Because the sperm whales in this study were feeding on adult V. infemalis, we can infer that they were feeding on Vampyroteutlzis primarily in the lower mesopelagic to bathypelagic zones (Fig. 9).
Vertical and geographic distribution
Because a majority of the prey items eaten were adults (as indicated from the estimated DML) and because the species displays ontogenetic distribution, these sperm whales were likely feeding between 500 m and 2,000 m depth. Several of the major prey items were associated with the bathyl benthic area of the ocean from 200m to 2,000 m.
This finding is consistent with the fact that sperm whales feed in the bathypelagic to bathybenthic regions (Roper & Vecchione, 1993). The distributions in the northeastern
Pacific of these prey items falls between 26 °N and 55 °N, with the majority found in the
California Cunent system between 30 °N and 45 °N. The California Cunent system is the boundary in the northeastern Pacific of temperate-subtropical waters and runs south
34 along the western coast of North America from the US and Canadian border to Baja
California (Jefferis, 1983; Pi net, 1992). Some of the prey items in this study are found in the subarctic Pacific. A portion of this subarctic current system can be found around 43
0 N (Jefferis, 1983). Based on the fact that the majority of the species eaten in this study are temperate to subtropical in distribution with a few being subarctic, these sperm whales likely had fed before their deaths in waters along the Oregon coast extending from around 43 °N to the Oregon and California border.
Size classes
There were no significant differences in the lengths of individual squids and size classes of squids taken by male and female sperm whales and between female whales of different age groups. This finding is corroborated by several authors who have compiled data indicating that there is no difference in the size of prey captured by males and females (Clarke, 1956; Okutani & Nemoto, 1964; Kawakami, 1980).
Male sperm whales fed primarily on cephalopods in the small size group (90.8%), as did females of all age groups (females aged 11-21 had a %N of 95.5, and females aged
22-58 had a %N of 95.2; Table 8). In this study, the small size group was defined as cephalopods having a DML between 20 mm and 600 mm. The group of whales as a whole fed in this size group 92% of the time.
Considering how large these sperm whales were, it is surprising that they ate so many small cephalopods (n = 18,543). Several authors have documented the fact that sperm whales tend to eat smaller squids, ranging in size from 600 mm to 900 mm, more regularly than larger sized squids (Matthews, 1938; Clarke, 1956; Kawakami, 1980).
Clarke et al. (1993) estimated that only 23 %of the diets of sperm whales examined in
35 the Azores were comprised of fast-swimming, large cephalopods. The sperm whale diets in the Azores were comp1ised primarily of small, neutrally buoyant, luminescent species.
Bioluminescence
Fristrup and Harbison (2002) proposed two hypothesis for how sperm whales catch cephalopods. The first hypothesis is that sperm whales locate their prey items visually, either silhouetted against light from the midwater, or by searching for bioltJminescence emitted from their prey. The second hypothesis holds that they create a
"zone of biolumeniscence" around their mouths that attract prey items. They concluded that these two hypothesis may not be mutually exclusive and that sperm whales may indeed, use a combination of both methods to catch cephalopod prey ..
In this current study from Oregon, a majority of the prey items are bioluminescent. These species include, but are not limited to, H. hoylei, H. heteropsis, G. phyllura, T. borealis, 0. deletron, T. danae, 0. borealijaponica and V. infemalis
(Church, 1970; Young, 1972; Voss et al., 1992a; Voss et al., 1992b; Roper & Vecchione,
1993; Kubodera et al., 1998; Voss eta!., 1998; Robison eta!., 2003). If these whales
were using a variety of techniques to capture their prey as suggested by Fristrup and
Harbison (2002), it may help to explain the large number of beaks recovered for this
group of sperm whales. In any event, it would appear as if these whales were able to
locate and capture their prey items efficiently.
Species composition
The Spearman's rank correlation indicated that there were differences in the
importance of prey items in the diets of the different sex and age groups of this group of
36 sperm whales. However, percent similarity indices indicated that this difference was not
as significant when only the major prey items were examined.
LeBoeuf et al. (1993) stated that species that have extreme sexual dimorphism, as
is the case in sperm whales, will exhibit sexual difference in foraging. Male sperm
whales tend to dive deeper than females, therefore, they may have access to different
species (Caldwell et al., 1966). Jaquet et al. (2000) suggested that the different dive
durations and depth of dives displayed by sperm whales may be due to different foraging behavior. I did not expect to see a difference in the diets of males and females since the
depth of dives is determined largely by the size of the individual (Caldwell et al., 1966),
and the sperm whales in this study were all in the same size range. However, examining
the %IRI values for some of the species that are more benthopelagic (M. robusta and T.
danae), it would appear that male sperm whales were feeding more along the bottom than
the females. The %IRI values also indicated that older female sperm whales had a more
diverse diet than younger females, which may be attributed to more experienced foraging
habits.
Conclusion
Spe1m whale distribution is closely related to the distribution patterns of their
major prey items, cephalopods. By understanding which taxa of cephalopods are eaten
by sperm whales, we can begin to map sperm whales' movements through different water
systems. In this study, I was able to show that this group of sperm whales was feeding in
the lower mesopelagic to bathypelagic and along the lower sublittoral to bathyl zones,
and m the California Current system. Sperm whale feeding studies also can provide
important information on their prey items, such as the presence of cephalopod species in
37 areas where they previously had not been found (as is the case of the T. danae found in this study), the presence of new species, and infonnation on the size composition of members of these species.
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47 TABLES Table l. Sex, age and number oflower beaks in the stomach contents of32 sperm whales stranded offthe Oregon coast (ages from Rice eta/., 1986).
Specimen no. Sex Age based on No. of No. of dentinal layers • Beaks
2 Female 33' 47 5 Male 15 662 6 Female 22+ 3 7 Male 17 183 8 Female 16 31 10 Female II 189 II Female 49' 163 12 Female 20 80 13 Female 17 317 14 Female 23 417 15 Female 31 + 19 16 Male 18' 49 17 Female 15 271 18 Female 25' 361 19 Female 16 1525 20 Female 28 71 21 Female 22 1304 22 Female 22' 510 23 Female 18 2909 24 Female 22 800 25 Male 18 1145 26 Female 14 156 27 Female 40' 1323 28 Female 55 362 29 Male 18 1025 30 Male 18 201 32 Male 20 1039 33 Male 21 449 34 Female 19 52 38 Female 28 1420 39 Female 16 64 40 Female 20 1695
'Per Rice et al., 1986, a plus-sign ( +) indicates that the tip of the tooth used for aging the whale was worn.
49 Table 2. Regression equations used in estimating body lengths and masses ofcephalopod prry species in the diet ofsperm whales stranded offthe Oregon coast. w ~wet weight (g), I~ dorsal mantle length (mm), r ~lower rostra/length (mm) and h ~hood length (*) Walker eta/., 2002. All other values were taken fi"orn Clarke, /986.
Family Species Equation for mass Equation for length
Octopoteuthidae Octopoteuthis deletron In w~ 0.166 + 2.3lln r I~-0.4+17.33 r Taningia danae In w ~ -0.874 + 3.42 ln r I~ -556.9 + 75.22 r Onychoteuthidae Onychoteuthis borealijaponica In w ~ 0.576 + 3.00 In r I~ -28.9 + 61.0 r Moroteuthis robusta ln w ~ -0.068 + 3.50 ln r I~ 4.7 + 70.00r Gonatidae Gonatus benyi In w ~ -0.655 + 3.33 ln r I~ -43.4 + 42.87 r Gonatus onyx ln w ~ 0.086 + 2.13 In r I~ 12.82 + 19.02 r Gonatus pyros In w ~ -0.655 + 3.33 In r I~ -43.4 + 42.87 r Gonatus sp. A ln w ~ -0,655 + 3.33 ln r I~ -43.4 + 42.87 r Gonatus sp. ln w ~ -0.655 + 3.33 In r I~ -43.4 + 42.87 r Gonatus madokailmiddendorffi ln w ~ -0.655 + 3.33 ln r I~ -43.4 + 42.87 r Gonatopsis/Benyteuthis type ln w ~ -8,66 + 2.70 ln l (*) I~ 11.4 + 36.00 r (*) Architeuthidae Architeuthis japonica ln w ~ -l. 773 + 4.57 ln r I~-180.4+109.38r Architeuthis spp. In w ~ -1.773 + 4.57ln r I~-180.4+109.38r Histioteuthidae Histioteuthis hoylei ln w ~ 1.342 + 2.44 In r I~-15.9+20.61 r Histioteuthis sp. cf H. hoylei ln w ~ 1.342 + 2.44 ln r I~ -15.9 + 20.61 r Histoteuthis heteropsis ln w ~ 1.35 + 2.64 In r I~ 2.04 +20.57 r Histioteuthis sp. cf H. corona In w ~ 1.594 + 2.31 In r 1~ 13.6+22.21 r Histioteuthis sp. In w ~ 1.594 + 2.31 ln r I~ 13.6 + 22.21 r Ommastrephidae Ommastrephes bartrami lnw~0.48+3.15lnr 1~52.7+27.61 r Chiroteuthidae Chiroteuthis calyx In w ~ -0.241 + 2.7ln r I~ 11.4 + 24.46 r Mastigoteuthidae Mastigoteuthis sp. A In w ~ 0.184 + 2.88ln r I~ -1.8 + 29.08 r Mastigoteuthis sp. B In w ~ 0.184 + 2.88ln r I~ -1.8 + 29.08 r Mastigoteuthis sp. cf M pyrodes Inw~O.I84+2.881nr I~ -1.8 + 29.08 r Cranchiidae Taonius borealis ln w ~ 0.786 +2.19ln r I~ 45.29 + 40.53 r (*) Megalocranchia sp. ln w ~ -0.108 + 2.73 In r I~ -70.9 + 68.13 r Ga/iteuthis phyllura In w ~ 0.728 + 2.34 In r I~ 12.2 + 40.78 r Galiteuthis sp. cf G pacifica In w ~ 0.728 + 2.34 In r I~ 12.2 + 40.78 r Galiteuthis sp. A In w ~ 0.728 + 2.34 In r I~ 12.2 + 40.78 r Unidentified Ga/iteuthis type In w ~ 0.728 + 2.34 In r I~ 12.2 + 40.78 r Enoploteuthidae Ancistrocheirus lesueuri In w ~ -0.194 + 3.561n r I~-41.3 +40.75r Pholidoteuthidae Pholidoteuthis boschmai In w ~ 0.976 + 2.83 In r I~ 11.3 + 41.09r Cycloteuthidae Cyc/oteuthis akimushkini In w ~ 1.89 + 1.95 In r I~ 31 r Vampyroteuthidae Vampyroteuthis itifernalis In w ~ -2.88 + 3.71 In h I~-5.8+9.02h Allopsidae Alloposus mol/is no regressions available
50 Table 3. Number and frequency ofoccurrence ofcephalopod prey recovered from 32 stomachs of41 sperm whales that stranded offthe Oregon coast.
Number Occurrence No. %of Total No. %Frequency
Total Prey 20247 100 32 100 Octopoteuthidae 1548 7.6 32 100 Octopoteuthis dele/ron 1451 7.2 31 96.9 Taningia danae 97 0.5 21 65.6 Onychoteuthidae 3159 15.6 30 93.8 Onychoteuthis borea/ijaponica 910 4.5 27 84.4 Moroteuthis robusta 2249 11.1 29 90.6 Gonatidae 3208 15.8 31 96.9 Gonatus benJ'i 396 2.0 27 84.4 Gonatus onyx 5 <0.1 3 9.4 Gonatus pyros 4 <0.1 2 6.3 Gonatus madokai/middendorjfi 3 <0.1 3.1 Go1wtus sp. A 600 3.0 29 90.6 Go1wtus spp 2 <0.1 2 6.3 Gonatopsis!Bmyteuthis type 2198 10.9 31 96.9 Enoploteuthidae Ancistrocheirus lesueuri 25 0.1 8 25.8 Architeuthidae 10 <0.1 5 15.6 Architeuthis japonica I <0.1 I 3.1 Architeuthis spp 9 <0.1 5 15.6 Histioteuthidae 6642 32.8 32 100 Histioteuthis hoylei 4940 24.4 31 96.9 Histioteuthis sp. H. hoylei I <0.1 I 3.1 Histeoteuthis heteropsis 55 0.3 9 28.1 Histioteuthis sp. cf H corona 1437 7.1 28 87.5 Histioteuthis spp 209 1.0 15 46.9 Ornrnastrephidae Ommastrephes bartrami <0.1 3.1 Chiroteuthidae Chiroteuthis calyx 139 0.7 22 68.8 Mastigoteuthidae 127 0.6 16 50.0 !vfastigoteuthis sp. A Il5 0.6 14 45.2 !vfastigoteuthis sp. B 5 <0.1 5 15.6 !vfastigoteuthis sp. cf M pyrodes 7 51 Table 4. Two-dimensional indices ofrelative importance (JRI) calculated by multiplying averaged %N by o/oFO ofcephalopod prey items recoveredfi"om 32 stomachs of41 sperm whales stranded offthe Oregon coast. %N %FO IRI o/o!Rl Total Prey 20247 100 9293.2 100 Octopoteuthidae Octopoteuthis dele/ron 10.1 96.9 976.8 10.5 Taningia danae 0.5 65.6 32.1 0.4 Onychoteuthidae Onychoteuthis borealijaponica 3.9 84.4 329.2 3.5 Moroteuthis robusta 10.7 90.6 966.7 10.4 Gonatidae Gonatus benyi 1.8 84.4 150.2 1.6 Gonatus onyx 0.1 9.4 0.7 <0.1 Gonatus pyros 0.1 6.3 0.4 <0.1 Gonatus madokai/middendorffi <0.1 3.1 <0.1 <0.1 Gonatus sp. A 2.6 90.6 234.7 2.5 Go110tus spp 0.1 6.3 0.3 <0.1 Gonalopsis/Berryteuthis type 10.9 96.9 1058.2 11.4 Enoploteuthidae Ancistrocheirus lesueuri 0.1 25.8 2.3 <0.1 Architeuthidae Architeuthis japonica <0.1 3.1 <0.1 <0.1 Architeuthis spp <0.1 15.6 0.3 <0.1 Histioteuthidae Histioteuthis hoylei 25.9 96.9 2512.6 27.0 Histioteuthis sp. H. hoylei <0.1 3. I <0.1 <0.1 Histeoteuthis heteropsis 0. I 28.1 3.9 <0.1 Histioteuthis sp. cf H. corona 6.0 87.5 523.3 5.6 Histioteuthis spp 0.6 46.9 26.3 0.3 Ommastrephidae Ommastrephes bartrami <0.1 3.1 <0.1 <0.1 Chiroteuthidae Chiroteuthis calyx 0.8 68.8 55.0 0.6 Mastigoteuthidae Mastigoteuthis sp. A <0.1 45.2 14.5 0.2 Mastigoteuthis sp. B <0.1 15.6 0.5 <0.1 Mastigoteuthis sp. cf M pyrodes <0.1 9.4 0.1 <0.1 Cranchiidae Taonius borealis 12.9 96.9 1246.1 13.4 Megalocranchia spp 0.3 31.3 10.0 0.1 Galiteuthis phyllura 11.2 96.9 1083.3 11.7 Galiteuthis sp. cf G. pacifica 0.2 21.9 4.2 <0.1 Galiteuthis sp. A <0.1 6.3 0.1 <0.1 Unidentified Galiteuthis type 0.1 18.8 2.4 <0.1 Pholidoteuthidae Pholidoteuthis boschmai <0.1 3.1 <0.1 <0.1 Cyc1oteuthidae Cycloteuthis akimushkini <0.1 6.3 <0.1 <0.1 Vampyroteuthidae Vampyroteuthis inferno/is 0.8 71.9 58.2 0.6 Allopsidae Alloposus mol/is 0.1 15.6 0.8 <0.1 52 Table 5. Percentage contribution by mass including minimum, mCL"timum~ and mean rnass of cephalopod prey recovered from 32 stomachs qfsperm whales stranded offthe Oregon coast. Minimum Maximum Mean(SD) %V Mass (g) Mass (g) mass (g) Total Volume of all species~ 10,758,614.27g Octopoteuthidae Octopoteuthis dele/ron 40.1 411.1 120.2 (32.3) 1.6 Taningia danae 449.0 5835.9 2819.8 (1126.0) 2.1 Onychoteuthidae Onychoteuthis borealijaponica 27.8 780.9 40l.l (88.6) 3.4 Moroteuthis robusta 195.0 8228.8 2236.6 (1543.5) 42.9 Gonatidae Gonatus benyi 48.3 725.6 196.4 (98.8) 0.7 Gonatus onyx 17.7 36.5 28.5 (7.0) <0.1 Gonatus pyros 33.7 77.8 57.7 (19.1) <0.1 Gonatus madokailmiddendot:ffi 251.3 292.7 278.9 (23.9) <0.1 Go1Jatus sp. A 72.2 I 034.8 517.3 (189.2) 2.9 Gonatus spp 251.3 292.7 272.0 (29.3) <0.1 Gonatopsis/Berryteuthis type 161.8 2407.4 991.2 (224.8) 20.0 Enoploteuthidae Ancistrocheirus lesueuri 95.5 1748.1 726.3 (395.4) 0.2 Architeuthidae Architeuthis j aponica 26595.5 26595.5 26595.5 (--) 0.3 Architeuthis spp. 9753.5 16250.3 13001.9 (4594.0) 0.2 Histioteuthidae Histioteuthis hoylei 29.2 978.5 279.1 (119.7) 12.3 Histioteuthis sp. H. hoylei Histeoteuthis heteropsis 62.4 277.3 159.2 ( 46.5) <0.1 Histioteuthis sp. cf H. corona 67.2 728.7 279.0 (108.8) 3.7 Histioteuthis spp 119.0 709.5 382.3 (137.3) 0.7 Ommastrephidae Ommastrephes bartrami 2662.0 2662.0 2662.0 (--) <0.1 Chiroteuthidae Chiroteuthis calyx 26.9 215.6 109.5 (36.2) 0.1 Mastigoteuthidae Mastigoteuthis sp. A 60.6 885.8 276.0 (117.6) 0.3 Mastigoteuthis sp. B 241.0 810.7 421.5 (227.8) <0.1 Mastigoteuthis sp. cf M pyrodes 80.2 146.5 119.4 (24.5) <0.1 Cranchiidae Taonius borealis 38.5 318.0 161.1 (39.2) 3.6 Megalocranchia spp 329.6 3068.9 1201.4 (491.4) 0.4 Galiteuthis phyllura 31.5 284.8 141.5 (38.2) 3.4 Galiteuthis sp. cf G. pacifica 148.0 284.8 215.1 (38.0) <0.1 Galiteuthis sp. A 137.1 318.3 268.7 (87.8) <0.1 Unidentified Galiteuthis type 56.2 641.2 296.8 (180.4) <0.1 Pholidoteuthidae Pholidoteuthis boschmai 211.8 211.8 211.8 (--) <0.1 Cycloteuthidae Cycloteuthis akimushkini 247.1 1421.7 834.4 (830.6) <0.1 Vampyroteuthidae Vampyroteuthis inferno/is 80.8 1973.0 550.1 (340.9) l.O Allopsidae Al/oposus mol/is 53 Table 6. Two dimensional indices ofrelative importance (lRI} for each sex and age group ofsperm whales, calculated by multiplying averaged %N by %FO of cephaloeod e.rey items recovered from the stomach contents qf32 se.erm whales that stranded offthe Oregon coast. Males (15-21 yrs old) Females (11-21 yrs old) Females (22-58 yrs old) (n = 8) (n = 11) (n = 13) %N %FO !Rl %1Rl %N %FO IRI %1Rl %N %FO !Rl %!Rl Octopoteuthidae Octopoteuthis deletron 4.8 87.5 420.9 4.3 11.7 100 1167.0 12.1 12.0 100 1197.0 13.1 Taningia danae 1.1 100 114.0 1.2 0.2 54.6 8.7 0.1 0.4 53.9 20.5 0.2 Onychoteuthidae Onychoteuthis borealijaponica 8.1 100 814.0 8.4 3.1 90.9 280.0 2.9 2.0 69.2 138.5 1.5 Moroteuthis robusta 18.1 100 1811.0 18.6 7.4 90.9 673.6 7.0 8.9 84.6 749.7 8.2 Gonatidae Gonatus berryi 0.8 87.5 65.6 0.7 2.7 90.9 245.5 2.5 1.5 76.9 114.6 1.3 Gonatus ocyx <0.1 12.5 0.4 <0.1 0.2 18.2 3.3 <0.1 0.0 0.0 0.0 0.0 Gonatus pyros 0.0 0.0 0.0 0.0 0.2 18.2 3.5 <0.1 0.0 0.0 0.0 0.0 Gonatus madokailmiddendorffi 0.0 0.0 0.0 0.0 <0.1 9.1 0.2 <0.1 0.0 0.0 0.0 0.0 Gonatus sp. A 2.8 87.5 247.6 2.5 2.9 100 292.0 3.0 2.2 84.6 183.6 2.0 Gonatus spp 0.0 0.0 0.0 0.0 0.1 9.1 1.0 <0.1 <0.1 7.7 0.2 <0.1 Gonatopsis/Berryteuthis type 5.3 100 529.0 5.4 13.2 100 1323.0 13.7 12.4 92.3 1148.3 12.6 Enop1oteuthidae Ancistrocheirus lesueuri 0.1 37.5 2.3 <0.1 <0.1 9.1 0.1 <0.1 0.2 30.8 5.2 0.1 Architeuthidae Architeuthis japonica 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 <0.1 7.7 0.1 <0.1 Architeuthis spp 0.4 12.5 0.5 <0.1 <0.1 18.2 0.2 <0.1 <0.1 15.4 0.5 <0.1 Histioteuthidae Histioteuthis hoylei 24.4 100 2444.0 25.1 22.5 100 2249.0 23.2 29.8 100 2976.0 32.6 Histioteuthis sp. H hoylei 0.0 0.0 0.0 0.0 0.0 9.1 0.0 0.0 0.0 0.0 0.0 0.0 Histeoteuthis heteropsis <0.1 25.0 0.8 <0.1 0.2 36.4 8.4 0.1 0.1 23.1 3.0 <0.1 Histioteuthis sp. cf H. corona 7.9 100 792.0 8.1 4.9 90.9 448.2 4.6 5.7 76.9 436.2 4.8 54 Table 6 continued Males~(l)c21 yrs old) Females (11-21 yrs old) Females (22-58 yrs old) %N %FO lRl %IRJ o/oN %FO IRJ %1RI %N %FO IRJ %IRJ Histioteuthis spp. 1.0 75.0 77.3 0.8 0.2 18.2 3.6 <0.1 0.6 46.2 26.3 0.3 Ommastrephidae Ommastrephes bartrami 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 <0.1 7.7 0.2 <0.1 Chiroteuthidae Chiroteuthis calyx 0.4 50.0 17.5 0.2 0.6 63.6 38.8 0.4 1.2 84.6 104.1 1.1 Mastigoteuthidae Mostigoteuthis sp. A 0.4 50.0 22.0 0.2 0.2 27.3 4.4 0.1 0.4 53.4 20.5 0.2 Mastigoteuthis sp. B <0.1 25.0 0.8 <0.1 <0.1 9.1 0.3 <0.1 <0.1 15.4 0.3 <0.1 Mastigoteuthis sp. cf M pyrodes 0.0 0.0 0.0 0.0 <0.1 27.3 1.1 <0.1 0.0 0.0 0.0 0.0 Cranchiidae Taonius borealis 9.4 100 939.0 9.6 16.5 100 1645.0 17.0 12.0 92.3 1103.1 12.1 Mega/ocranchia spp 0.2 12.5 2.5 <0.1 0.1 36.4 2.6 <0.1 0.6 38.5 23.1 0.3 Galiteuthis phyllura 13.8 100 1375.0 14.1 12.2 100 1223.0 12.6 8.7 92.3 803.1 8.8 Galiteuthis sp. cf G. pacifica 0.2 25.0 0.1 <0.1 0.1 18.2 1.3 <0.1 0.3 23.1 6.9 0.1 Galiteuthis sp. A <0.1 12.5 0.1 <0.1 <0.1 9.1 0.1 <0.1 0.0 0.0 0.0 0.0 Unidentified Galiteuthis type 0.3 25.0 8.0 0.1 0.1 18.2 1.1 <0.1 0.1 15.4 0.9 <0.1 Pholidoteuthidae Pho/idoteuthis boschmai <0.1 12.5 0.1 <0.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Cycloteuthidae Cyc/oteuthis akimushkini 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 <0.1 7.7 0.1 <0.1 Vampyroteuthidae Varnpyroteuthis infernalis 0.7 75.0 52.5 0.5 0.7 72.7 50.2 0.5 1.0 69.2 68.5 0.8 Allopsidae Alloposus mol/is <0.1 12.5 0.3 <0.1 <0.1 18.2 0.6 <0.1 0.1 15.4 1.2 <0.1 55 Table 7. Minimum, maximum and mean dorsal mantle lengths (DML) of cephalopodprey recovered from 32 stomachs ofsperm whales stranded offthe Oregon coast. Minimum Maximum Mean Std. Dev. Length (mm) Length (mm) Length( nun) Octopoteuthidae Octopoteuthis deletron 79.3 218.0 126.6 15.2 Taningia danae 22.3 669.2 415.0 130.0 Onychoteuthidae Onychoteuthis borealijaponica 123.6 434.7 340.3 28.1 Moroteuthis robusta 326.7 942.7 621.5 122.3 Gonatidae Gonatus benyi 123.8 333.9 206.7 31.0 Gonatus onyx 83.2 111.7 100.3 10.7 Gonatus pyros 106.7 149.5 131.3 18.6 Gonatus madokailmiddendorffi 231.0 243.8 239.5 7.4 Gonatus sp. A 145.2 376.3 291.3 43.5 Gonatus spp 231.0 243.8 237.4 9.1 Gonatopsis/Berryteuthis type 162.6 442.0 316.0 28.7 Enop1oteuthidae Ancistrocheirus lesueuri 113.6 309.2 223.6 45.6 Architeuthidae Architeuthis japonica 1318.1 1318.1 1318.1 Architeuthis spp 1022.8 1165.0 1093.9 100.5 Histioteuthidae Histioteuthis hoylei 63.3 215.8 133.1 19.6 Histeoteuthis heteropsis 61.1 105.9 85.3 9.6 Histioteuthis sp. cf H. corona 82.5 206.8 139.0 20.4 Histioteuthis spp 101.8 204.6 157.2 24.2 Ommastrephidae Ommastrephes bartrami 342.6 342.6 342.6 Chiroteuthidae Chiroteuthis calyx 101.9 207.1 161.5 20.0 Mastigoteuthidae Mastigoteuthis sp. A 111.6 286.1 186.4 28.3 Mastigoteuthis sp. B 181.4 277.4 215.7 37.4 Mastigoteuthis sp. cf lvf. pyrodes 123.2 152.3 141.1 10.7 Cranchiidae Taonius borealis 195.6 438.4 331.4 32.4 Megalocranchia spp. 521.8 1271.3 863.1 143.0 Galiteuthis phyllura 142.7 346.6 257.8 30.3 Ga/iteuthis sp. cf G. pacifica 265.0 346.6 307.8 22.5 Galiteuthis sp. A 256.9 362.9 334.4 51.7 Unidentified Galiteuthis type 179.4 485.3 337.9 93.2 Pho1idoteuthidae Pholidoteuthis boschmai 204.4 204.4 204.4 Cycloteuthidae Cyc/oteuthis akimushkini 198.4 486.7 342.6 203.9 Vampyroteuthidae Vampyroteuthis infernalis 58.2 145.7 97.7 17.6 56 Table 8: Small, medium, med-large, and large size classes ofcephalopods recovered from the stomach contents of32 sperm whales that stranded offthe Oregon coast. Males Females Females Sizes classes DML(mm) ( 15-21 yrs old) (ll-21 yrsold) (22-58 yrs old) of Cephalopods (n= 8) (n = II) (n =13) No. of %N No. of %N No.of %N cephalopods cephalopods cephalopods Small 20-600 4244 90.8 7974 95.5 6325 95.2 Medium 600-900 414 8.9 361 4.3 310 4.7 Med-Large 900-1300 14 0.3 II 0.1 6 0.1 Large 13 00 and greater 0 0 0 0 0.0 Total 4672 100 8346 100 6642 100 Average size of cephalopod (± SD) 298.2 mm (182.4) 256.0 mm (142.9) 252.2 mm (154.7) 57 Table 9. One-Way ANOVA comparisons ofmean lengths for twelve species ofcephalopod species. Comparisons were made between male sperm whales (ages I 5-21, n~8),female sperm whales (ages II-21, n~II) and older female sperm whales (ages 22-58, n~/3). Comparison between males and females Species F p Octopoteuthis deletron 2.979 0.067 Taningia danae 1.017 0.384 Onychoteuthis borealijaponica 0.599 0.557 Moroteuthis robusta 1.955 0.162 Gonatus berryi 1.548 0.233 Go1wtus sp. A 2.813 0.078 Gonatopsis/Berl}1feuthis type 1.455 0.251 Histioteuthis hoylei 0.576 0.569 Histioteuthis sp. cf H. corona 3.211 0.057 Galiteuthis phy/lura 0.299 0.744 Taonius borealis 0.360 0.701 Vampyroteuthis infernalis 0.418 0.664 58 Table 10: Cephalopod species recoveredji-orn the stomach contents ofsperm whalesfi'om the North Eastern Pacific Ocean. Western Canada California Oregon (Clarke and (Fiscus et a!., 1989) (Current study) MacLeod, ~1980) Loliginidae Lo/igo opalescens X Octopoteuthidae Octopoteuthis deletron X X Octopoteuthis spp X Taningia danae X X Onychoteuthidae Onychoteuthis borea/ijaponica X X Nforoteuthis robusta X X X Gonatidae Gonatus berryi X X Gonatus onyx X Gonatus pyros X X Gonatus madokai!middendorffi X Ganatus sp. cf G~ fabricii X Gonatus fabricii X Gonatus sp. A X Gonatus spp X X Gonatopsis borealis X Gonatopsis/Benyteuthis type X Berryteuthis magister X Unidentified gonatids X Enoploteuthidae Abraliopsis felis X Ancistrocheirus lesueuri X Architeuthidae Architeuthis japonica X X Architeuthis spp X Histioteuthidae Histioteuthis hoylei X X X Histioteuthis sp~ H. hoylei X Histeoteuthis heteropsis X X Histioteuthis sp. cf H. corona X Histioteuthis spp X X Stigrnateuthis spp Ommastrephidae Dosidicus gigas X Ommastrephes bartrami X Unidentified ommastrephids X X 59 Table l 0 continued. Western Canada California Current study in (Clarke and (Fiscus et al., 1989) Oregon MacLeod, 1980) Chiroteuthidae Chiroteuthis calyx X X Chiroteuthis spp X Mastigoteuthidae Mastigoteuthis spp X X Mastigoteuthis sp. A X Mastigoteuthis sp. B X Mastigoteuthis sp. cf M pyrodes X Cranchiidae Taonius borealis X Taonius pavo X X Taonius/Galiteuthis X Megalocranchia spp X X Galiteuthis phyllura X X Galiteuthis pacifica X Galiteuthis sp. cf G. pacifica X Galiteuthis spp X Galiteuthis sp. A X Unidentified Galiteuthis type X Mesonychoteuthis hamiltoni X Unidentified cranchiids X Pholidoteuthidae Pholidoteuthis boschmai X Cycloteuthidae Cycloteuthis akimushkini X X Vampyroteuthidae Vampyroteuthis infernalis X X X Allopsidae Alloposus mollis X X Octopodidae Octopus dojleini X Unidentified octopod X 60 FIGURES 124"40' . 47"00'" 47"00' N A. Oregon 42"20' { 42"20' I California 124"40' 122"20' Figure 1: Location of mass stranding of sperm whales, June 16, 1979, that stranded along the Oregon coast near the Siuslaw River mouth. 62 34 32 3 0 28 .~ ..•0 26 ~ " ~.. :! 2 Q " 20 I 8 I 6 I 4 O I 0 15 20 25 J 0 35 #ofstomachs 26 " 22 M~Jes ages 15-21 l (n=S) F '" ::: 0 I ' ~ I 6 I 4 l llof5tomnchs Femnles nges l 1-21 '" {11"'11) 28 ~~~--r-H " 1 ·'~ " " -+++-1-r-~=L,.J ! (n"'J3) ~ " ' " ' " I 4 " #orstomnchs Figure 2: Cumulative species curves for 3 2 sperm whales that stranded along the Oregon coast. Each curve represents 100 iterations and the error bars are ± 1 SD. a: Cumulative species curve for all 32 whales. b: Cumulative species curve for male sperm whales (ages 15-21). c: Cumulative species curves for female sperm whales (ages 11-21 and 22- 58). 63 30.00% 25.00% 20.00% z •~ "C ~ 15.00% "'~ ~ ~ 10.00% - !- 1- 1- 5.00% - 1- 1- 1- - - 0.00% DD .... oo ..-. ~ ~ .§ ~ ,,it " ~ ~ ' ~ ·~ i' ~ 1 ' • ~ ~ .g' ~t • j ~· ~ • '[ .8 j I • I .g 1!' :§ • • ~ i· ~ ] <' I ·~ l ! :S ' j <" jl 1 I ~ ? 1 ~ t "'• ·~ ] j ~ G ~ " ~ 1 ' j '§ j ~ < ~ ~· ] ~ ' ' ~ " t5 ' .8 ~ ~ l <3 ' ' "• " ~ ~ " ~ •' " i "~ ,, k ~ ~' ~" i ' I ~ f " ' i ~ f ~ l. ' l ~ ~· ~ ] ~ I J Figure 3: Total number of cephalopod beaks for each prey item averaged within each whale to detetmine a percent representation of the prey item in that particular whales diet. This number was then averaged over all 32 whales to determine the averaged %N for each prey item for the whole group of sperm whales. 64 1200,------·------··------, 350,------~-~~=:'~--~------···------, 10001----- 300 +------ ~ 250+------"'§ 200 +------ z 150 ·------ 400t------~ 100 +------200t----- so+---- o+-.~~-rl' 0 +-.~,-,-,4 ro~ ""r:::;, "~>-r:::;, ::.r:::;, ~r:::;, r'j,r§'l ~r::;, ~r:::;, '?fl,f\::.1 "':J~r:::;, '? Gnliteuthis phyllura Taonius borealis 500r----···-----··--·-·-···------, 35QT------·----···------300t------.~ ~ 400 +------~ 250+------"'§ 300 +------'il= 200+------z :s 200 +------= ~ 150t------ ~ 100t------100t------= 50t------"' o~~~~~rn~~ o+-~~~~~~~rr~~~ i' "'" "'" """ ,•" .:;." i'" 1:'" '".§> '""'" "''"" "'"'" "'"'" •"" .}-" i' "'" "'" """ ,•" .:::-" i'" 1)" ~" ~" ,i' ,<:>" ,rp" •"" .}-" Slze Class (mm) Size Class (mm) Onychoteuthis borealijaponica Octopoteuthis deletl·on 600,----··------····------soo+------" i 400+------z 300 -1------ :s 200 +------100+----- "' 0 +-~~,.-!11' '"" "'" "'" """ ,p .:::-" i'" '""'" '""" '"<§> ,i' ,.J> "'"'" •"" .}-" Size Class (mm) Figure 4: Length distribution for 6 cephalopod species recovered from the stomach contents of32 sperm whales stranded off the Oregon coast. a: Histioteuthis /wylei (range 60-220 mm). b: H. sp. cf H. corona (range 80-210 mm). c: Galiteuthis phyllura (range 140-350 mm). d: Tam1ius borealis (range 200-440 mm). e: Onycoteuthis borea/ijaponica (range 120-430 mm). f: Octopoteuthis deletron (range 80-200 mm). 65 ------ Gonatupsis!Berryreuthi,~ type Gmwt1H .1p. A 500 90 80 400 70 .c" .c-" -s 60 s 300 = 50 z= z 40 200 :g 5 0 30 0 E- E- 20 100 10 0 0 'I" o.,cf' rv" n" <:;fb" t>l' rv" ~" ']; '), ']; ']; <:; dJ'" ~ ~~" ~" ']; ')) ']; ']; 4' <:; ~ ~ "" "'" "" " "" """ "'" "'" "" "" "" "'" "" ""'" "" """ "'" "'" "" " " Size Class " " Size Class Gonat1u berryi Vampymteutl!i.1· infemalis 100 50 80 40 .c"- .c-" s 60 s 30 z= i :g 40 20 0 ~ E- 20 E- 10 0 0 rv" ~" !0" n" t>l' rv& ')) ']; ']; <:; dJ'" ~ ~ fb" t>l' "" "'" """ " ""'" """ "'" """"" "" 17 ....~" rv& '), ']; ']; o.,cf' <:;n" <:; t>l Size Class "" "'" """ ""'" """ "'" "'" ~"" Size Class (mm) Figure 5: Length distribution for 4 cephalopod species recovered from the stomach contents of 32 sperm whales stranded off the Oregon coast. a: Gonatopsis/Berryteutlzis type (range 160-440 mm). b: Gonatus sp. A (range 150-380 mm). c: Gonatus berryi (range 120-330 mm). d: Vampyroteuthis infemalis (range 60-150 mm). 66 Moroteuthis robusta 120,------·------·-·------·------, 100\------·------···------ " ~ i 60 +------ 0 ---!"-- #$~#~~$~~~#$~#~$$##~~~~~~~$##~# Size Class Figure 6: Length distribution for Moroteutlzis robusta (330 to 940 mm) recovered from the stomach contents of 32 sperm whales stranded off the Oregon coast. 67 Taningia danae 0 ~~~~~~~$$#~~#~#~~$##~~$$##~$$##~$ Size Class (mm) Figure 7: Length Distribution for Taningia danae (20 to 670 mm) recovered from the stomach contents of 32 sperm whales stranded off the Oregon coast. 68 Males (ages 15·21) 30 25 20 z "$. 15 10 5 0 0 <( , g • • :;; J:l e J:l :;, ·~ ~ ·~ g. ;;- 1:; • • ;; .!l! ~ " E 0 {!l .Q• ~ ~ £ ,_; ~ e .a• " g.ro .Q "'"- (!j ,_; .s ci •0 .!c1 (!j "' • 0 u " e "' ;; 0 e (!} :3._.!!2 2 " .e" ~ u " ,g ci •8 (!} :f Females (ages 11-21) 30 25 20 z "$. 15 10 5 0 0 <( , g • • ~ J:l e J:l :;, ~ ·~ g. 1:; • • ;; ~ -~ .@ " e E 0 .. .Q £ {!l • ~ ,_; "- e .a• • a g.~ 2 "'"- .5 ci ~ (!j ,_; (!j •0 .!!): e "' • 0 ~"' ;; 0 e (!} a.\!2 " 0 " j! u .Q .e" " ci •8 ,g (!} :f Females (ages 22-58) 30 25 20 z "$. 15 10 5 0 <( • .. :;; 1!1 ~ ~ g •0 • % ·~ "'~ ~ g. J!! ;;- 1:; • • ;;-• {!l .Q E .. .Q " e 0 {!l 8. • ~ 0 ., ,_; e .a• " .Q t ~ (!j g.~ ,_; .s ci •0 .!!J. (!j • 0 e e (!} u " % 0 0 " .Q " R·• .e " 0 ci ,g •8 (!} ~ Figure 8: Comparison of the %N represented by the major cephalopod prey items consumed by male and female sperm whales. The percent similarity index (PSI) between males and females was 76.1 %. PSI between females of different age groups was 88.2 %. 69 Om 200m 1000 m 2000 m Mesopelagic Bathypelagic Abyssalpelagic 6000 m Hadalpelagic Figure 9: Distribution in the water column of the major cephalopod species eaten by the 32 sperm whales that stranded on the Oregon coast. The stars next to species names indicate that the species is found along the sea floor in the areas they are associated with. 70