Much of the research reviewed in this paper is that
of Dr. Peter Ross of the Institute of Ocean Sciences
in British Columbia and he refers to the northeastern
Pacific killer whales as being "sentinels of a
contaminated planet; indicators of global contamination".
The northeastern Pacific killer whales serve as such
powerful indicators for the following reasons:
- Marine mammals, generally, are highly susceptible
to the bioaccumulation of organochlorine pollutants.
Most PCBs will end up in the marine environment and,
with PCBs being fat-soluble, the marine mammals, with
their thick blubber layers and poor ability to excrete
and metabolize these pollutants, are ideal candidates
for bioaccumulation.
- Of the marine mammals, the killer whales are superior
indicators of bioaccumulation and biomagnification
due to their position at the top of marine food webs
(high trophic level) and their coastline habitats.
The findings of the Whale And Dolphin Conservation
Society are, in fact, that "Orca have high levels
of bioaccumulation and are regarded as amongst the
most vulnerable wildlife to chemical pollution."
- The populations of killer whales in the northeast
Pacific are specifically ideal for the study of bioaccumulation
since more than 3 decades of research on these animals
allows for bioaccumulation data to be analyzed in
light of previously acquired knowledge. These populations
are amongst the most thoroughly studied group of cetaceans
in the world. Photo-identification studies have been
conducted since 1973 and the extensive study of feeding
patterns, social structure, acoustics and genetics,
allows for the reliable study of differences in PCB
accumulation in relation to age, gender, diet
and population.
The natural history of killer whales in the northeastern
Pacific
The killer whales referred to in this work are those
frequenting the waters of the western coast of North
America from 44 to 61 degrees N. They comprise 3 different
sympatric populations: residents, transients and offshores.
For the purposes of this paper, the relatively unstudied
offshore killer whales are not included.
The studies of the late Dr. Michael Bigg, Dr. John Ford
and Graeme Ellis have determined that resident and transient
populations are distinct in diet, language, behaviour
and social organization. They are, therefore, ecotypes
filling distinct ecological niches. The DNA research
of Dr. Lance Barrett-Lennard has confirmed that resident
and transient populations do not interbreed.
The residents feed solely on fish, predominantly salmon.
Salmon, through their spawning behaviours, are a highly
predictable prey. Their predictability appears to have
allowed the residents to be able to "afford"
evolving into highly social and vocal animals. They
have a matrilinear social structure in which there is
no dispersal from natal groups. Their vocalizations
do not handicap their success in hunting, as salmon
cannot hear within the acoustic range of the calls.
Indeed, vocalizations have differentiated to the extent
of forming distinct dialects found to be a vehicle in
inbreeding avoidance. The resident population is comprised
of two parapatric sub-populations. The northern resident
population consists of some 215 animals. The southern
resident population only has 81 members. Interbreeding
between these two subpopulations does not occur, believed
to be as a result of the divergence in dialects. Note
that population estimates for resident orca are highly
reliable as a result of their matrilinear social structures
and ranges.
The +/- 220 transients eat marine mammals and their
evolution appears to have been guided to ensure success
in hunting such challenging prey. Transients travel
in small non-static groups, have considerably longer
dives, appear to have greater ranges (reflected in the
designation "transient"), have only one
language and vocalize infrequently. Hypothetically,
the latter is to increase success in hunting since marine
mammals hear within the frequency range of these calls.
Supporting this hypothesis, calls appear to be far more
frequent after a successful kill. Even echolocation
is used infrequently in order to avoid detection, resulting
in the transients having a far greater reliance on passive
noise to find prey. Population estimates for the transients
are less conclusive due to their fluid social associations.
Transient orca - http://www.uaf.edu/seagrant/nosb/papers/2002/seward-orcas.html
Plight of the northeastern Pacific killer whales
With these killer whales populations being the subject
of much study, alarming stresses and population decline
have been noted. The Committee on the Status of Endangered
Wildlife in Canada (COSEWIC) upgraded the status of
the northeastern Pacific killer whale populations in
November of 2001. The southern resident population has
been upgraded to the status "endangered",
meaning that there is the threat of "imminent extinction".
Transient and northern resident killer whale populations
have been upgraded to the status "threatened"
indicating that, if conditions are not reversed, the
populations are likely to become endangered.
There are great differences in survival rate between
the different populations of killer whales. Also, male
killer whales have considerably shorter life expectancies
than do the females. These issues will be examined in
light of the bioaccumulation of PCBs.
PCBs' impact on male vs. female life expectancy
Average life expectancy for male resident killer whales
is 29 years with maximum life span being from 50 to
60 years. Average longevity for females is 50 with maximum
age being 80 to 90 years.
It is believed that males may not live as long as females
since females rid themselves of the toxins BUT at a
cost to their young. PCB levels in females were found
to decrease significantly around age 15, when they are
believed to have their first calf, and were found to
increase again when the females were post-reproductive
(+/- 50 years). The toxins are downloaded to the calves
via the placenta and through the very fatty milk during
lactation. Female killer whales have been found to lose
45 to 50 percent of their PCB loads per calf with first-born
calves having four times higher toxin loads than subsequent
calves. The displacement of PCBs from mother to calf
leads to great concern about the "generational
effect". As a result of downloading, calves start
off with toxin levels comparable to their mother's
but will gain toxins throughout their lives, potentially
leading to their calves having higher toxin loads -
and so on.
Males have no opportunity to get rid of their PCB loads
as they do not have calves. Therefore, the older the
male is, the greater the PCB load. Gender appears to
be such a significant factor in bioaccumulation that
reproductive females have been found to have only half
the toxin levels of males of the same age.
PCBs in transient vs. resident populations
It is startling to contrast the PCB concentrations in
transients to that of the beluga whales (Delphinapterus
leucas) of the heavily polluted St. Lawrence River population
(central Canada). Research on this beluga population
did much to bring global attention to the reality of
bioaccumulation. There used to be at least 5,000 in
the population. Now, there are only around 700 despite
their having been protected under the Fisheries Act
since 1962 and being listed as endangered (COSEWIC)
since 1997. The beluga are plagued by many toxins. Tumours
and skeletal abnormalities are often found, beluga carcasses
need to be treated as toxic waste and there have even
been documented cases of true hermaphroditism in the
population. Yet, the PCB levels found in 2 populations
of the northeastern Pacific killer whales far exceed
those of the beluga (data of Muir et al = 78.9 mg/kg;
data of Letcher et al =86 mg/kg).
Beluga -142.179.94.212/Gallery_4/beluga.html
Dr. Peter Ross et al found male transients to have
a stunning 251 ppm of PCBs. Even more startling are
the loads found in a female transient
washed ashore near Dungeness Spit, Washington in 2002.
Gina Ylitalo, researcher for the National Marine Fisheries
Service (US), reported that the levels were so high,
that the standard instruments could not be used with
accuracy and the initial test had to be aborted. The
PCB levels were about 1,000 ppm. This is the highest
level of PCBs ever found in a killer whale and the highest
found in any cetacean. It is interesting to note that
this particular transient had never been sighted in
British Columbia before, only California. Another population
of transient killer whales, in southern Alaska, were
found to have comparable high levels at 230 ppm by Craig
O. Matkin of the North Gulf Oceanic Society. This collective
data indicates that transients have in the area of 3
to 12 times the PCB loads of the highly contaminated
beluga population, making the transients the most contaminated
animals on the planet.
With transients feeding on marine mammals, they feed
at a higher trophic level than do the fish-eating residents.
Predictably then, transient PCB loads have been found
to be far higher than those of the sympatric resident
populations. The northeastern Pacific transients have
up to almost 7 times more PCBs than do the resident
killer whales.
Resident Orca - http://www.orcanetwork.org/habitat/habitat.html
PCBs in southern resident vs. northern resident
populations
Between the two genetically isolated resident subpopulations,
there is also a great difference in survivability. The southern population is in great trouble while the northern
population is stable. There has been an 18 percent decrease
in the southern residents in the last 7 years. The southern
residents comprise a very small gene pool indeed, now
with only 81 while there are some 215 northern residents.
Furthermore, in the southern population, there are fewer
calves and there is concern that the males may enter
puberty later. Currently, there are only 4 mature males
in the southern population (there are several "sprouters"
soon to reach sexual maturity).
Many urban factors surely influence the survival rate
of the southern resident killer whales. One could consider
decreased availability of prey, boat traffic stresses
and the historical depletion of the southern population
due to more of these animals having been taken for aquaria.
However, toxins likely have a considerable effect with
the southern residents having at least 4 times higher
levels of PCBs than the northern residents do. The impact
of PCBs is likely compounded by the aforementioned factors,
e.g. reduced food stock would increase the concentration
of PCBs in blubber stores.
Highly significant is that the southern and northern
resident populations are parapatric; they have different
ranges. The southern residents are most often found
off the southern half of Vancouver Island and in Puget
Sound. This is an area of great urbanization with approximately
5 million people residing in the area. By contrast,
the northern residents are often in the waters of the
far less urbanized northern Vancouver Island.
The habitat of the southern residents has been found
to have significantly higher levels of PCBs than that
of the northern residents. Dr. Ross' research has proven
that seals in Washington's Puget Sound have 7
to 8 times higher levels of PCBs than even the seals
in the near Strait of Georgia in British Columbia. This
reflects that Puget Sound receives little flushing and
has even been referred to as containing "toxic
soup".
The population viability analysis of the southern residents,
conducted by the Centre of Biological Diversity (Taylor),
reports that with the current population trend, "the
most plausible scenario predicted a median extinction
time of 74 years with 33-121 years 95% confidence interval".
Maps - on-line Atlas of Canada &
www.sidneymuseum.ca/vanisle5.htm
