Aquatic Mammals 2008, 34(1), 9-20, DOI 10.1578/AM.34.1.2008.9
First Case of a Monitored Pregnancy of a Harbour Porpoise
(Phocoena phocoena) Under Human Care
Marie-Anne Blanchet,1 Tiffany Nance,1 Colleen Ast,1
Magnus Wahlberg,1 and Mario Acquarone2
1Fjord&Baelt, Margrethes Plads 1, DK-5300 Kerteminde, Denmark
2NAMMCO, Polar Environmental Centre, N-9296 Tromsø, Norway
Current Addresses: Audubon Zoo, 6500 Magazine Street, New Orleans, LA 70118, USA (M-AB)
The Mirage, Dolphin Habitat, 3400 Las Vegas Boulevard South, Las Vegas NV 89109-8907, USA (TN)
Most of the data collected on the reproduction of
harbour porpoises (Phocoena phocoena) comes
from by-caught or stranded animals and is there-
fore opportunistic in nature. Harbour porpoises
kept in a human-controlled environment offer
a unique opportunity to gather data on the same
individual with a known history over a long period
of time. At Fjord&Baelt in Kerteminde, Denmark,
Freja, a 10-y-old female harbour porpoise, became
pregnant in September 2005 and gave birth during
the night between 24 and 25 July 2006. Routinely
sampled parameters, such as food intake, weight,
blubber-thickness, body-girth measurements, and
respiration rates, did not follow the seasonal pat-
terns observed the preceding years at the facil-
ity. These variables either increased or remained
stable during the pregnancy.
As the first sign of the approaching parturition,
a dramatic drop in food intake occurred 8 d prior to
her giving birth followed by a decrease in body tem-
perature of 1º C at about 62 h before giving birth.
Freja’s intermammary distance also increased as the
date of the birth approached, although this parameter
cannot be used for immediate diagnosis of impend-
ing parturition. The newborn calf was found dead
a few hours after the birth and appeared to be the
result of a full-term gestation. This study describes
some observable changes in behavioural, physical,
and physiological parameters occurring in a prim-
iparous harbour porpoise during gestation, which
could be used in animal husbandry for this species.
Key Words: pregnancy, husbandry, birth, parturi-
tion, harbour porpoise, Phocoena phocoena
The harbour porpoise (Phocoena phocoena) is a
relatively common cetacean living in coastal and
continental shelf waters (Haug et al., 2003) and
widely distributed in the northern hemisphere
(Read et al., 1997). It is one of the smallest ceta-
ceans found close to areas inhabited by humans
and is very vulnerable to anthropogenic distur-
bances. Concerns have been expressed regarding
the status of harbour porpoise populations in the
Baltic and the North Seas and the effects of pol-
lutants on their reproductive success (Desportes
et al., 2003; Hasselmeier et al., 2004). The repro-
ductive cycle of harbour porpoises is gener-
ally poorly understood (Read & Gaskin, 1990;
Kastelein et al., 1997), and most data come from
stranded or by-caught animals. The paucity of in
vivo information on reproductive parameters is
a major obstacle both in population modelling
for this species and for the design of effective
management procedures. Having animals under
human care is thus a unique opportunity to collect
data on the same individuals over long periods of
time and throughout different physiological states
(Desportes et al., 2003).
Pregnancy in harbour porpoises has never been
formally described in nature nor in a human-con-
trolled environment. The primary objective of this
study is to describe the behavioural, physiologi-
cal, and anatomical development of a captive har-
bour porpoise throughout pregnancy. This work
includes observations of food intake and physical
changes of the mother’s body and compares these
to the same data collected over previous years
from the same animal.
Materials and Methods
The study animal (Freja) was approximately
10 y old at the time of the study (Lockyer et al.,
2003b) and was housed at the Fjord&Baelt Centre
in Kerteminde, Denmark, together with two other
harbour porpoises: an 11-y-old male (Eigil) and
10 Blanchet et al.
a 3-y-old female (Sif). The age of the animals
is estimated on the basis of extrapolating their
growth curves back to a birth size of 70 cm in June
(Lockyer et al., 2003). These three animals were
taken under human care after having been rescued
from pound nets set in the inner Danish waters.
Eigil and Freja arrived together at the Centre on 7
April 1997 and Sif on 23 July 2004.
Harbour porpoises are known to become sexu-
ally mature between 3 and 4 y old for females
and between 2 and 3 y old for males (Lockyer &
Kinze, 2003). Mating behaviour between Eigil and
Freja has been observed since 1997 (Desportes
et al., 2003). However, Freja never conceived to our
knowledge until 2003 when Freja suffered a mis-
carriage in October.
The animals were housed in an outdoor, open-sea
enclosure forming a pool in the Kerteminde Fjord.
The environment is subject to the seasonal varia-
tions of light, temperature, and weather conditions.
The winter months were defined as December
through February and the summer months as June
through August. The rectangular enclosure was
approximately 15 m × 36 m and had an average
depth of 3.5 m, with a natural sandy and rocky
bottom. The habitat was subject to a strong daily
tidal flow, causing a water level variation of 1 m
Various types of data were gathered from Freja’s
life at the Center both before and during her preg-
nancy: food intake, physical parameters (girth,
weight, blubber thickness, intermammary dis-
tance), and physiological parameters (i.e., plasma
progesterone, body temperature, and respiration
All the samples requiring close contact with the
animal were collected using voluntary husbandry
behaviours (VHB), which were trained using oper-
ant conditioning (for a definition, see McFarland,
2006) and positive reinforcement (Pryor, 1984;
Ramirez, 1999). This method allowed collecting a
wide variety of biological samples without undue
capture-related stress to the animal (Lacinak et al.,
1996; Desportes et al., 2007).
Progesterone—The plasma progesterone levels
were measured opportunistically during routine
blood sampling. The blood was collected from
the dorsal fluke vessels with a butterfly needle
(Nipro scalp vein set 21G*3⁄4”) and was trans-
ferred into a 5-ml Luer syringe. After a centrifuga-
tion (in NH4-heparin tubes, 10 min at 2,000 rpm),
the separated plasma was frozen at -20º C until
assayed. The laboratory (Veterinary Department,
Rotterdam Zoo, P.O. Box 532, 3000 Rotterdam,
The Netherlands) used an Immulite 1000 system
by Siemens Medical Solutions Diagnostics. The
progesterone assay was a sequential competitive
immuno-assay. The intra- and inter-assay tests
were based on humans but also have been used
on Asian elephants (Elephas maximus) (de Boer
& Schaftenaar, 2004). They have a variation of
17.4% (inter-assay based on 52 different runs) and
15.7% (intra-assay based on one run analyzed 18
times). Similar data were currently not available
for harbour porpoises.
Food Intake—The three porpoises were fed
whole fish with a diet combining mackerel
(Scomber scombus), herring (Clupea harengus),
sprat (Sprattus sprattus), capelin (Mallotus villo-
sus), and sand eels (Hyperoplus sp. and Ammodytes
sp.).The quantity in kilograms and kilocalories of
fish eaten daily was routinely recorded. All batches
of fish were analyzed for protein, fat content, and
energy by the methods described by the Nordic
Nutrition Recommendations (Nordic Council of
Ministers, 2004) at the State Laboratory of the
Ministry of Food, Agriculture and Fisheries or at the
Steins Laboratory (Eurofins Steins Laboratorium,
Hjaltesvej 8, DK-7500 Holstebro).
The assumption was made that the quantity
of live fish caught by the animals in the enclo-
sure outside of training sessions was negligible
since the mesh size (10 cm × 10 cm) and the
algae growth on the double-net barrier does not
allow a significant passage of wild fish.
The porpoises were fed according to their
motivation in training, their general appetite,
and their physical status (i.e., weight).
Weight —Freja’s weight was recorded weekly
by her voluntarily beaching onto a scale (Kruuse
model PS250), which was located behind a slide-
out platform. However, from February 2006, this
behaviour was stopped, assuming that the pressure
of Freja’s weight on her belly while hauled out
would be hazardous to the fetus. Thereafter, her
body weight was estimated using a formula ini-
tially developed by Lockyer (1995) and Lockyer
et al. (2003b) for stranded British Isles data, and
for by-caught pregnant and nonpregnant females
from West Greenland (Lockyer et al., 2003a). This
formula was derived from data on animals from
a population geographically distant from Freja’s
wild Danish population. Still, when comparing
with formulas from other populations as described
in Lockyer (1995) and Lockyer et al. (2003b), it
seems to be the best one to fit Freja’s measure-
ments collected previously to the pregnancy.
The formula was
W = 0.00028 * L1.713 * G 0.782
Where, W = weight and G = mid-body girth
Monitoring the Pregnancy of a Harbour Porpoise (Phocoena phocoena) 11
Girth Measurements—The girths G2, G3, and
G4 (Lockyer, 1995; Lockyer et al., 2003b) were
measured every week with the animal in the
water. A soft, inextensible nylon rope was placed
around the body of the animal at the three posi-
tions successively and then measured. Lockyer
et al. (2003b) found these measurements to be
variable due to the movements of the animal like
the expansion of the chest while breathing when
taken on land. But, in the present case, the animal
remained calmly in the water during the proce-
dure, holding its breath.
Blubber Thickness—The full blubber thickness
was measured weekly; it was measured dorsally,
laterally, and ventrally in three positions along the
body (Lockyer et al., 2003b) by means of a porta-
ble ultrasonic subdermal fat scanner (Lean Meter
by Renco) designed for use in domestic pig hus-
bandry and used with success in precedent stud-
ies (Desportes et al., 2003). The blubber thickness
measurements were taken once a month until the
diagnosis of the pregnancy and then once a week.
Intermammary Distance—The distance at the
middle of the genital opening from the outer side
of one slit to the other was measured twice a week
from March until June and then every day until the
parturition using a ruler placed against the body
Body Temperature—The core body temperature
was measured at least once a week until 31 May,
then opportunistically until the delivery. The irreg-
ularity in the data collection was due to the unwill-
ingness of Freja to cooperate during some of the
training sessions as the delivery approached. The
temperature was taken rectally using a soft probe
(DM 852, Ellab Ltd. Copenhagen, Denmark)
inserted up to the bowel wall to guarantee a con-
sistency in the measurements (N. Van Elk, DVM,
Breathing Rate—The breathing rate of all three
animals was monitored once every day between
0830 h and 1600 h over a 10-min interval. The
observer would stand at a position overlooking
the whole pool and would record every surfacing
of the animals during which both expiration and
The pregnancy was detected by an ultrasono-
graphic examination on 22 February 2006 using
an ALOKA 500 machine and a 3.5 MHz convex
The birth date (25 July 2006) is denoted as B,
the number of days (x) prior to the parturition as
B-x and number of days after the parturition as
Freja gave birth between 2200 h on 24 July and
0500 h on 25 July to a fully formed female calf
that was recovered from the enclosure at 0600 h
but was dead. The 7-h gap was a nighttime period
when the staff was unable to observe the animals.
Back-calculating by using the rectal temperature
of the calf and the ambient water temperature, the
birth was estimated to have occurred around 0200
h on 25 July (N. Van Elk, DVM, pers. comm.). A
necropsy was performed the next day on the fresh
neonate. The calf had reached full-term both mor-
phologically and histologically. It weighed 8 kg
and measured 76 cm in length. It is impossible to
say whether the animal was born dead or alive,
but the calf never took a breath since the lungs
had not been inflated (N. Van Elk, DVM, prelimi-
nary pathology report PP060725, University of
Rotterdam, The Netherlands).
Food Intake During Pregnancy
The proportion of each dietary fish in kilocalories
is shown in Figure 1.
During the pregnancy, the food intake decreased
at first until November and then increased until
July (Figure 2). On average, the minimum food
intake was 4,529 kcal/d in November 2005 and the
maximum was 7,650 kcal/d in July 2006. Some
peaks were observed in July at up to 9,086 kcal/d
between 10 July and 15 July. The average of food
intake during the pregnancy was 5,982 kcal/d (SD
= 1,098 kcal).
Food Intake Around Parturition
The food intake from B-12 became irregular
(Figure 3), swinging between 8,306 kcal/d (her
steady diet in July 2006) and 5,666 kcal/d. It
decreased to zero kcal/d at B-1. Freja resumed
eating (3,536 kcal/d) on the very afternoon after
giving birth and reached a regular diet on B+6
(3,600 kcal/d); however, she did not reach her pre-
birth diet of 8,306 kcal/d. It is interesting to note
that this post-birth diet was very similar to her diet
in July 2005.
Food Intake Before and During Pregnancy
Comparing the daily food intake between
September 2003 and July 2004 vs between
September 2004 and July 2005, there was no sta-
tistically significant trend over time (ANOVA on
the regression residuals of the difference in daily
food intake per month as a function of time: F =
0.16, df = 7, p = 0.7). During these periods, Freja
was not pregnant to our knowledge. In contrast, the
difference in daily food intake between September
2004 and July 2005 (nonpregnant) and September
2005 and July 2006 (pregnant) showed a signifi-
cant increase, with daily food intake increasing
12 Blanchet et al.
during the pregnancy (ANOVA: F = 91.52, df =
7, p < 0.01).
Between September 2003 and September 2005,
Freja’s weight varied seasonally between 47
and 64 kg (Figure 4) as described in Lockyer
et al. (2003b). The lowest weight was observed
in August-September (mean water temperature:
17.4º C, SD = 1.4º C; mean air temperature:
20.6º C, SD = 1.9º C), and the highest was observed
in February (mean water temperature: 3.6º C, SD
= 2º C; mean air temperature: 5.3º C, SD = 3.1º
C) during the coldest month. From September
2005, when the pregnancy was assumed to begin,
the weight increased through July 2006 to reach
a maximum of 68.9 kg on 9 July. Her average
weight in July 2003, 2004, and 2005 was 53.8 kg.
The weight gain at the end of the pregnancy was
estimated to be 15 kg.
Figure 1. Diet composition for a pregnant female harbour porpoise in kilocalories; the absence of certain fish species for
some months is due to a lack of fish supply.
Figure 2. Monthly food intake for a female harbour porpoise for 2003-2004, 2004-2005, and 2005-2006; the average daily
food intake in July was calculated until the 25th to compare similar periods before and during the pregnancy.
Monitoring the Pregnancy of a Harbour Porpoise (Phocoena phocoena) 13
Data on girth measurements from previous years
showed a seasonal trend, with the porpoise becom-
ing thicker in winter than in summer. During the
year of the pregnancy, there was a steady increase
in Freja’s girth throughout the gestation period
(Figure 5). A linear regression applied to these
data was highly significant (F = 97.31, df = 1, p <
0.01) and explained 84% of the variation in these
Figure 6 shows the fluctuations in the fat layer
thickness measured at the mid-dorsal position (D3)
between September 2003 and July 2006. A seasonal
variation was observed between summer and winter.
The fat layer was usually the thickest during January
and February (between 30 and 42 mm) and thinner
during July and August (between 16 and 25 mm).
These variations were similar to those described in
Lockyer et al. (2003b) on data collected from April
Figure 3. Daily food intake of a female harbour porpoise 30 days before and 30 days after parturition; the open circles rep-
resent the food intake at the same period the previous year. The food intake recorded in kilograms can be linked to the data
presented in Figure 1 recorded in kilocalories.
Figure 4. The body weight of a female harbour porpoise between September 2003 and July 2006; the weight from February
2006 is an extrapolation from the formula linking body weight and mid-body girth G3 (see text for details).
14 Blanchet et al.
1997 to January 2000 on the same animal. However,
during the pregnancy (September 2005 to July
2006), these seasonal variations decreased in mag-
nitude. The blubber thickness remained between 30
and 40 mm during the whole pregnancy.
The intermammary distance remained constant (5
cm) up to B-46, and a fluctuation between 5 and 6
cm was observed until B-9. The distance increased
from B-9 to reach 8 cm at B-2 (Figures 7, 8 & 9).
Figure 5. Change in a female harbour porpoise’s mid-body girth G3 measurement between October 2003 and July 2006;
the lack of measurements between October 2004 and June 2005 is due to a breakdown of the trained behavior for taking
the measurement. More girth measurements were taken towards the end of the pregnancy because the trained behavior was
A linear regression of the girth’s data during the pregnancy data (September 2005 to July 2006) was y = 1.00033 × -37,804
with R2 = 0.8366.
Figure 6. The dorsal mid-body blubber thickness of a female harbour porpoise between September 2003 and July 2006; the
seasonal pattern observed in 2003-2004 and 2004-2005 disappears during the pregnancy.
Monitoring the Pregnancy of a Harbour Porpoise (Phocoena phocoena) 15
During the last days of pregnancy (B-8 to B-2),
there is an almost significant linear trend in the
increase of the intermammary distance (F-test:
F = 14.6, df = 3, p = 0.06), which explains 100%
of the variation in these data.
Breathing rate from February 2003 until July 2006
showed seasonal variation (Figure 10), increasing
during winters and decreasing during summers.
However, during the pregnancy, this seasonal pat-
tern disappeared and was substituted by a constant
Core Body Temperature
The body temperature varied between 36º C and
37.7º C during the pregnancy (Figure 11). The
average temperature was 36.7º C (SD = 0.4º C).
At B-1, the temperature fell to 35.6º C. During the
last 24 d before the birth, there was a significant
linear trend in falling rectal temperature (F-test: F
= 64.79, df = 10, p < 0.01), which explained 88%
of the variation.
A plasma progesterone level was measured on 30
August 2005 and was 1.34 nmol/l. The next level
available was on 14 March 2006, and it was 40.89
nmol/l this time. The progesterone level remained
high (between 47.22 nmol/l and 55.86 nmol/l)
during the rest of the pregnancy and dropped dra-
matically after the birth to 4.17 nmol/l on 2 August
2006 (Figure 10).
Figure 7. Measurements of the intermammary distance during the pregnancy of a female harbour porpoise
Figure 8. Genital opening of a female harbour porpoise in a
normal state; the intermammary distance is 5 cm.
Figure 9. Genital opening of a female harbour porpoise
two days prior to the delivery (23 July 2006); the intermam-
mary distance is 8 cm.
16 Blanchet et al.
Duration of Gestation and Calving Period
Gestation in harbour porpoises lasts 10.5 to 10.6 mo
(Read, 1990; Sørensen & Kinze, 1994), according
to studies on Danish and Canadian populations.
The body length of the newborn calf (76 cm) and
the results of the necropsy indicated that Freja had
been through a full-term gestation (e.g., Read,
1990; Sørensen & Kinze, 1994; Lockyer, 1995;
Halldórsson & Víkingsson, 2003; Hasselmeier
et al., 2004) and indicated that Freja carried the
calf to term (25 July 2006). The back-calculation
of the time of conception indicated a date between
7 September and 10 September. Progesterone
analysis indeed showed that Freja became preg-
nant after 31 August. Thus, it is very likely that
conception did take place in early September.
Birth periods may vary considerably between
populations (Read, 1990; Halldórsson &
Víkingsson, 2003; Gol’din, 2004; Hasselmeier
et al., 2004). In the Bay of Fundy in Canada,
harbour porpoise births occur during mid-May
(Read, 1990), while the parturition is calculated
to occur between 6 June and 16 July for the
North Sea population and one month later in the
Figure 10. Daily respiration rate of a female harbour porpoise between February 2003 and July 2006; the arrows show the
start and the end of the pregnancy.
Figure 11. The core body temperature of a female harbour porpoise during pregnancy
Monitoring the Pregnancy of a Harbour Porpoise (Phocoena phocoena) 17
western Baltic Sea (Hasselmeier et al., 2004).
Freja, coming from the area of southern Zealand
in East Denmark, followed the pattern of the latter
Food Intake Changes During Pregnancy
Food intake varies in numerous species of marine
mammals in relation to age, sex, season, and repro-
ductive status (e.g., Kastelein et al., 1994; Blanchet
et al., 2006). Seasonal variations are especially evi-
dent for harbour porpoises (Desportes et al., 2003;
Lockyer, 2003; Lockyer & Kinze, 2003; Lockyer
et al., 2003b). During the pregnancy monitored
here, though, the seasonal drop in food intake
normally observed from March to April did not
occur. This could be related to the extra demand
for energy from the fetus (Kastelein et al., 1994)
but also to the energy storage in blubber for the
milk production. Increased food intake during the
late stages of the gestation has been observed in
several species of cetaceans such as killer whales
(Orcinus orca) reported by Clark & Odell (2000),
beluga whales (Delphinapterus leucas) reported
by Kastelein et al. (1994), and bottlenose dolphins
(Tursiops truncatus) reported by Ridgway et al.
(1994). However, Kastelein et al. (1993) showed
the opposite tendency in Commerson’s dolphins
(Cephalorhynchus commersonii). It is interesting
to note that 7 d after the birth, Freja regained a
stable diet at the same level as the one from July
2004 and July 2005 when not pregnant.
Behavioural and appetite changes occur before
parturition in various species of marine mammals
such as harbour seals (Phoca vitulina) (Blanchet
et al., 2006), beluga whales (Dalton et al., 1991),
Commerson’s dolphins (Kastelein et al., 1993),
and bottlenose dolphins (Cornell et al., 1987;
Schroeder, 1990; Terasawa et al., 1999). Freja
seemed to follow this tendency; she had a dra-
matic decrease in food intake the day prior to the
parturition. Various hormonal mechanisms are
involved in appetite changes. In some species, like
mink (Mustela vison) (Tauson et al., 2004) and
cattle (Bos taurus) (Ingvartsen et al., 1999), leptin
is centrally involved. More studies are needed to
investigate if the same mechanism occurs in har-
bour porpoises and other marine mammals.
Physical, Behavioural, and Physiological Changes
Similar to food intake, morphological parameters
evolved during the pregnancy. Blubber thickness
at a mid-body position (D3) remained the same
throughout the pregnancy instead of decreasing
following the seasonal pattern observed the preced-
ing years (Figures 5 & 6; Lockyer, 1995; Lockyer
et al., 2003b). The blubber layer in harbour por-
poises appears to have two distinctive functions:
the thoracic and abdominal parts have energy stor-
age and insulation functions whereas the posterior
part plays a hydrodynamic role (Koopman, 1998).
A decrease in the thickness of the blubber layer
is linked to the increase in water temperature and
less need for insulation in nonreproductive ani-
mals. During a pregnancy, though, the blubber
layer can provide an extra energy source for use
during lactation (Kastelein et al., 1993). The blub-
ber layer can therefore remain thick throughout
a pregnancy even though the need for insulation
Similarly, the mid-body girth (G3) did not
follow the previously observed seasonal pattern
Figure 12. Serum progesterone levels of a female harbour porpoise between August 2005 and August 2006; the porpoise was
pregnant between September 2005 and July 2006.
18 Blanchet et al.
(see Figure 5; Lockyer, 1995; Lockyer et al.,
2003b). The G3 increased throughout the preg-
nancy reflecting the volume occupied by the fetus
and the thick blubber layer of Freja.
Concomitant to the increase in girth, an increase
in weight was observed (Figure 4). At the end of
the pregnancy, it represented a 15-kg difference
in weight on the same date in the two preceding
years. This reflects the growth of the fetus, the
thickening of the blubber layer, and the develop-
ment of the embryonic annexes. In wild animals,
a female harbour porpoise reaches her asymptotic
length at the age of 7 y old (Lockyer, 2003). Thus,
the increase in weight was most likely caused by
the pregnancy and not by any body growth.
A decrease in body temperature is character-
istic of the prepartum events in several species
of mammals (Terasawa et al., 1999) and often is
associated with a decrease in the level of circulat-
ing progesterone (Katsumata et al., 1998). In bot-
tlenose dolphins (Terasawa et al., 1999) and killer
whales (Katsumata et al., 1998), a decrease in the
core body temperature was observed before the
delivery. A drop of 1º C is observed in bottlenose
dolphins 12 to 24 h prior to parturition. In killer
whales, the decrease in core body temperature
can start as early as 5 d before the birth. In Freja’s
case, it is interesting to notice that the drop of 1º C
occurred approximately 62 h prior to parturition
(Figure 11); however, the time of birth was some-
what uncertain. The body temperature just before
the parturition is unknown since Freja refused to
participate in medical behaviours 2 d prior to the
An increase of the intermammary distance is
a valuable indication for predicting the onset of
parturition in many cetacean species such as killer
whales, bottlenose dolphins, and beluga whales
(Dalton et al., 1991). In cetaceans, one mammary
slit is located on each side of the genital opening.
During parturition, a maximal dilatation of the
vagina and the cervix is necessary for the passage
of the neonate. Thus, the increase in the distance
between the two mammary slits can be consid-
ered a reliable indication of the magnitude of the
cervix dilatation. For Freja, a slight but notice-
able change in the intermammary distance first
appeared 46 d before the parturition. An accelera-
tion of the increase of the intermammary distance
indicated the imminence of the delivery.
Respiration rate can be related to activity level
and metabolic rate in harbour porpoises (Reed
et al., 2000). Breathing rate varies among seasons,
with higher rates in winter than in summer (Figure
12) and can be related to a higher heat production
in winter than in summer and/or to responses to the
environment (Lockyer et al., 2003b). During the
pregnancy, these seasonal variations disappeared
and the daily breathing rate even increased during
the summer months prior to delivery. This could
be due to an increase of the metabolic rate due to
the needs of the fetus or to the physical constraint
imposed by a growing fetus on the lungs. Without
any further information regarding metabolic rates
of porpoises, it is difficult to determine the cause.
There was an important at least forty-fold
increase in serum progesterone levels of the preg-
nant vs the nonpregnant harbour porpoise. This is
higher than the values measured in other cetacean
species, in which progesterone elevates ten-fold
during pregnancy (Sweeney, 2003). It is difficult,
however, to compare progesterone levels obtained
with different methods due to the risk of cross-
reactions with various circulating progesterone
Monitoring the pregnancy of a harbour porpoise
allowed the gathering of valuable information on
the morphological and physiological changes that
occurred during this sensitive period of the life
cycle. The seasonal fluctuations in body weight,
blubber thickness, girth, breathing rate, and food
intake are characteristic of nonparous females.
Some information can help to pinpoint the immi-
nence of parturition such as a dramatic loss of
appetite, a drop in core body temperature, and a
rapid increase of the intermammary distance.
More data are needed on Freja to determine
whether all pregnancies in the same individual
have comparable measures. Moreover, more data
are needed on other animals within the species to
verify if these observations can apply to all female
The authors would like to thank Niels Van Elk,
DVM, from Dolfinarium Harderwijk for perform-
ing the necropsy so quickly and Mark de Boer
from the Veterinary Department from Rotterdam
Zoo for analyzing the serum samples.
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