El Niño-induced changes in grey whale abundance & residency patterns on the Central Coast of British Columbia: Possible Ecosystem Shift? William Megill 1,2 , Lei Lani Stelle 1,3 , Michelle Kinzel 1,4 , Deborah Randall 1,2 1. Coastal Ecosystems Research Foundation 2. Dept. of Zoology, University of British Columbia 3. Dept. of Organismic Biology and Evolution, UCLA 4. Moss Landing Marine Laboratories El Niño-induced changes in grey whale abundance & residency patterns on the Central Coast of British Columbia: Possible Ecosystem Shift? William Megill 1,2 , Lei Lani Stelle 1,3 , Michelle Kinzel 1,4 , Deborah Randall 1,2 1. Coastal Ecosystems Research Foundation 2. Dept. of Zoology, University of British Columbia 3. Dept. of Organismic Biology and Evolution, UCLA 4. Moss Landing Marine Laboratories
Transcript
El Niño-induced changes in grey whale abundance &
residency patterns on the
Central Coast of British Columbia: Possible Ecosystem
Shift?William Megill 1,2, Lei Lani Stelle 1,3, Michelle Kinzel 1,4, Deborah
Randall 1,2
1. Coastal Ecosystems Research Foundation 2. Dept. of Zoology, University of British Columbia 3. Dept. of Organismic Biology and Evolution, UCLA
4. Moss Landing Marine Laboratories
El Niño-induced changes in grey whale abundance &
residency patterns on the
Central Coast of British Columbia: Possible Ecosystem
Shift?William Megill 1,2, Lei Lani Stelle 1,3, Michelle Kinzel 1,4, Deborah
Randall 1,2
1. Coastal Ecosystems Research Foundation 2. Dept. of Zoology, University of British Columbia 3. Dept. of Organismic Biology and Evolution, UCLA
4. Moss Landing Marine Laboratories
The California grey whale (Eschrichtius robustus) undertakes the longest migration of any mammal: Baja California - Alaska and back annually (Pike 1962, Rice & Wolman 1971, Braham 1984, Clarke et al. 1989). Some don’t complete the migration, staying instead in southern areas off British Columbia, Washington, Oregon, and northern California (Pike 1962, Pike & MacAskie 1969, Hatler & Darling 1974, Darling 1984).
Vancouver Island grey whales are well documented. Hatler & Darling (1974) reported resident animals, present throughout the summer months. Using photographs of the animals flanks & flukes, Darling (1984) identified individual whales returning annually to the same area. Estimated population size: 35-50. Animals range from Victoria to Cape Scott, apparently moving between feeding sites.
Previous studies have documented the presence of grey whales along the BC mainland coast north of Vancouver Island (Darling 1978, Darling et al. 1998). We present here the first detailed study of abundance, distribution and habitat use by grey whales off Cape Caution, BC.
Our observations were made between 1994 and 1999. During that time, we were provided with an interesting ecological experiment, namely the perturbation in the ocean temperature and nutrient supply caused by the 1997-98 El Niño Southern Oscillation Event.
Objectives of this study1. Estimate the abundance of grey whales off the Central Coast of British Columbia;
2. Determine the spatial and temporal distribution of grey whales;
3. Document habitat use patterns of the population; and
4. Describe the effects of the 1997-8 El Niño on the resident grey whales of BC.
Introduction
Study Area
Mainland Coast of British Columbia, Canada.
36 miles, Allison Harbour - Rivers Inlet
Generally rocky coastline, with some sandy beaches. Many nearshore rocks & kelp beds.
Whales distributed along the coast, almost always within 1/2 naut. mile of shore.
Single transect through study area, from Allison Harbour NW to Cape Caution, then due N to Rivers Inlet.
Area divided into 13 zones following natural boundaries, such that a whale in the zone could be seen from anywhere in the zone.
Canada -
British Columbia
USA - Washington State
Map 1. Vancouver Island, British Columbia, Canada, showing the study area north of Port Hardy.
Record location/movements of whales relative to kelp beds.
94 - 96 Occasional diver observations of prey in kelp beds.
97 - 99 Systematic sampling (Bertrand et al.1997, Bisson et al. 1997, Stelle & Megill 1999)
Photo-identificationFollow transect until whale spotted, then
1. Break off to identify individual2. Record ventilation rate, behaviour data3. Resume transect
Photography1. Ease up to whale, approach parallel2. Wait for appropriate lighting, whale posture3. Repeat until obtain good photos of both sides, fluke.4. Attempt visual ID by comparison to catalogue.
Mark-recapture1. Jolly - Seber open population model (Hammond 1986)2. Each year = sampling period.
Boats
94 95 96 97 98 99
M/V Lagtime 16’ motorboat
x x x x x
S/V Feel Free 51’ sailboat
x
S/V Dagon 40’ sailboat
x x x
M/V Etta Pace 18’ motorboat
x
M/V Seabreeze 35’ forestry boat
x
F/V Stardust 38’ fishboat
x
M/V Theodore 24’ crewboat
x
Table 1. Boats used for grey whale surveys on the Central Coast of BC, 1994-1999.
Figure 1. Some of the boats used: Lagtime in the foreground, Seabreeze stern-to, and Stardust against the wharf.
Effort
We used days of observation as an overall measure of effort, since hours was dependent on the abundance of whales: the more animals, the longer it took to photograph them, but the time spent surveying was no different.
Except for the first two years, effort in the study area was fairly constant. To avoid biases due to unequal survey effort, data from those years was discarded for some of our analyses.
Beginning in 1996, we attempted to cover the entire study area reasonably evenly, attempting to visit every zone at least once per week.
Table 2. Survey effort for grey whales off the southern Central Coast of BC, 1994-1999.
94 95 96 97 98 99
Period of observation24 Jul -
10 Sep
9 Jul -
2 Sep
16 Jun -
7 Sep
29 Jun -
13 Sep
21 Jun -
12 Sep
26 Jun -
10 Sep
Weeks of observation 7 7 12 11 12 11
Days of observation 11 37 58 64 57 70
Hours of observation 38 226 366 468 307 358
Mean ( SE) hrs. of observation per week
5 26 36 40 25 33
Results
Abundance
0
10
20
30
40
50
60
1995 1996 1997 1998 1999
Year
Num
ber
of W
hale
s Id
enti
fied
0
10
20
30
40
50
60
70
80
90
100
Obs
erva
tion
eff
ort (d
ays)
Identified whales
New whales
Sighting Effort
0
10
20
30
40
50
60
14-Jun 4-Jul 24-Jul 13-Aug 2-Sep
Date
Nu
mb
er
of
ind
ivid
ua
ls
ide
nti
fie
d
1997
19961998
1999
0
30
60
90
1994 1995 1996 1997 1998 1999
Jolly - Seber (Hammond 1986) mark-recapture model for open populations estimates overall size of population using the area at about 65 animals.
Year-to-year abundance shown in Figure 2 is defined as simply the number of animals identified in a given year.
Abundance peaked in 1997, then, despite increased observation effort, declined during the El Niño - La Niña events of 1998-1999.
The dropping numbers of new animals discovered (solid bars, Figure 2; inset, Figure 3) suggest that most of the population has been accounted for.
Discovery rates were high in July every year, then leveled off during August before rising again in early September. The weekly abundance (data not shown) followed a similar trend.
Figure 2. Grey whale abundances, per year. Line shows overall effort, in days.
Figure 3. Discovery rates. Main figure: per year. Inset: (blue) overall discovery, (red) new individuals.
Residency
0
1
2
3
4
5
1996 1997 1998 1999Year
Res
iden
cy (
wee
ks)
33 5127
22
Residency Classes
0
5
10
15
20
25
1996 1997 1998 1999
Year
Num
ber
of W
hale
s
0-4
4-8
8-12
Defined as the number of weeks individuals were sighted in the study area during the summer interval.
Mean residency time almost differed significantly (Kruskal-Wallis p=0.08), with the shortest mean residency time during the 1998 ENSOE.
Overall mean residency was 4.6 0.2 weeks.
Numbers inside the bars refer to the total number of whales observed in each year.
Three residency classes were apparent: sometimes (0-4 weeks), often (4-8 wks), always (>8 wks).
During most years, the ratio of sometimes to often was about even. During the 1998 El Nino, there was a huge shift to shorter residency times. There were no whales in the always class in 1998.
Figure 4. Mean (±SE) residency times, per year
Figure 5. Residency classes, per year. Sizes in number of weeks.
Home ranges
26 44 17 180
10
20
1996 1997 1998 1999Year
Hom
e Ran
ge S
ize
(nau
t. m
iles)Defined as 90% Confidence Interval
Only calculated for animals sighted more than 5 times
1998 slightly longer range, though not significant (Kruskal-Wallis non-parametric test p=0.43)
Total average Home Range size = 9.9 naut. miles
Four home range classes 1. “Local” 0-10 naut. miles. 2. “Resident” 10-20 naut. miles. 3. “Transient” >20 naut. miles. 4. “Offshore” less than five visits
Usual pattern was that most whales were “Local”, except during the ENSOE in 1998, when “Residents” & “Locals” were equally abundant, consistent with the shift to larger home range sizes that year.
Generally, though individual whales might change the location of their home range from year to year, they did not change class - if they were local one year, they tended to be so every year.
Home Range Types
0
5
10
15
20
25
30
1996 1997 1998 1999
Year
Fre
quen
cy
0-10
10-20
>20
Figure 7. Frequency of home range types, by year, in naut. miles.
Figure 6. Mean (±SE) home range size, by year. Sample size inside bars.
Habitat UseThe x-axis in this figure shows the distance along the transect, centered at Cape Caution, with negative numbers to the southeast and positive ones due north. Prominent geographical features are labeled on the figure.
Data are the first sightings of each individual whale each day, collected into two-mile bins. They have been corrected for effort by dividing the total number of whale observations per day by the number of days spent in each two-mile bin.
Four primary whale-use areas were identified: Allison Harbour, Silvester Bay, Hoop Bay, and Table Island. The biggest difference between years was that in 96-97 all of the habitat was used, while in 98-99, several areas never saw whales.
0
0.5
1
1.5
2
2.5
-20 -15 -10 -5 0 5 10 15 20
Location (naut. miles)
Fre
quenc
y (
sigh
ting
s pe
r day
of
obse
rvati
on)
1996 1997 1998 1999
Alli
son
Har
bour
Slin
gsby
Cha
nnel
Bur
nett
Bay
Cap
e C
autio
nH
oop
Bay
Tabl
e Is
land
Silv
este
r Bay
Figure 8. Habitat use along the linear transect of the study area.
El Niño & Queen Charlotte Sound
Sea surface temperature
Two stations: Egg Island (Queen Charlotte Sound), Nootka Island (West coast Vancouver Island). Data collected by lightkeepers for Fisheries & Oceans Canada (DFO, 1999).
Usual situation (1994-1997)
Alaska Current hits continental shelf
Resultant upwelling brings cold water, high oxygen & nutrient content, high zooplankton abundance.
El Niño (1998)
Alaska Current forced offshore by northbound warm water, particularly in spring 1998.
No upwelling, warmer water, smaller, less abundant zooplankton. Also, pilchard arrival: zooplankton predator absent for 40 years.
La Niña (1999)Cold spring time water, colder summertime water. Massive pilchard die-off. Also grey whale die-off. Mysids still smaller than in 1997 (Stelle & Megill, 1999; Bisson et al. 1999)
Sea surface temperature, Nootka I sland
6
8
10
12
14
16
18
20
Jan Feb
Mar
Apr
May
Jun Jul
Aug
Sep
Oct
Nov
Dec
Month
Tem
pera
ture
(C)
1994
1995
1996
1997
1998
1999
Sea surface temperature, Egg I sland
6
8
10
12
14
16
18
20
Jan Feb
Mar
Apr
May
Jun Jul
Aug
Sep
Oct
Nov
Dec
Month
Tem
pera
ture
(C) 1994
1995
1996
1997
1998
1999
Figure 9. Average monthly sea surface temperature at Egg Island, Queen Charlotte Sound, and Nootka Island, on the west coast of Vancouver Island.
DiscussionWe have clearly shown that the southern Central Coast is
currently an important area for grey whales. Darling et al. (1998) report a population of 35-50 animals living off the west coast of Vancouver Island. A similar number of individuals have made use of the much smaller range off Cape Caution over the last six years. Many of "our" animals have been seen off the southern coast of Vancouver Island (Megill 1998, J. Calambokidis, pers. comm.), indicating that the Cape Caution population is far from isolated, and indeed would seem to be an extension of the Vancouver Island population.
That said, many individuals did remain in our study area for quite significant lengths of time, with a mean of nearly five weeks. The exception was 1998, when the pattern shifted to most animals remaining only a few days in the area. While in the area, the animals tended to wander little, remaining for long periods in short home ranges less than 10 miles long (i.e. confined to one or two bays) – again, with the exception of 1998, when home range size increased. These observations would be in keeping with a decrease in prey abundance, making the area less attractive to grey whales, and forcing those that did choose to stay to forage over greater distances.
Discussion (cont.)Within our study area, we have documented four important
feeding areas, where the animals were seen feeding primarily on mysids around kelp beds during the summer months. In years where many whales were present at one time (1996, 1997), animals were distributed throughout the study area, with almost every kelp bed being visited at some point during the summer. In later years, with fewer whales in the area, intermediate feeding habitat was used much less, but the primary areas were still important. Incidental observations by locals and notes made by visitors recorded in the logbooks of several cabins in the area indicate that the kelp beds off Allison Harbour have been used by grey whales regularly at least since 1991.
The 1998 ENSOE and consequent offshore shift of the Alaska Current did have a profound effect on the ecology of Queen Charlotte Sound. We suggest that it may have caused the dip in grey whale use of the Cape Caution area in 1998 through bottom-up control of zooplankton abundance (particularly mysids). The effects of ENSOEs are known to last several years (Whitney et al. 1998), and our data for 1999, showing only partial return to pre-El Niño levels of use, would certainly agree. These conclusions are difficult, especially in the light of the 26 year study reported by
Darling et al. (1998), where long-time, large-scale shifts in habitat use (and apparent local abundance) due to changes in the local ecosystem, were shown to be the norm for grey whales. Time will tell whether the 1998-9 dip was a one-off event, or whether we are on the edge of an ecosystem shift.
ReferencesBraham, H.W. 1984. Distribution and migration of gray whales in
Alaska. In The Gray Whale (eds.M.L. Jones, S. Swartz and S. Leatherwood), pp. 276 – 287, Academic Press, New York, NY.
Bertrand, Y., Megill, W.M., and J. Lafond. 1997. Contamination aux BPC de la ressource alimentaire des baleines grises (Eschrichtius robustus) de la côte du Pacifique canadien. Coastal Ecosystems Research Foundation, Vancouver, B.C.
Bisson, M., Megill, W.M., and J. Lafond. 1997. Étude sur le degré de contamination par le mercure dans l’alimentation de la baleine grise (Eschrichtius robustus) dans la région du Cap Caution, C.-B. Coastal Ecosystems Research Foundation, Vancouver, B.C.
Clarke, J.T., Moore, S.E., and D.K. Ljungblad. 1989. Observations of the gray whale (Eschrichtius robusutus) utilization patterns in the northeastern Chukchi Sea, July – October 1982-1987. Can. J. Zool. 67, 2646-2654.
Darling, J.D. 1984. Gray whales off Vancouver Island, British Columbia. In The Gray Whale (eds.M.L. Jones, S. Swartz and S. Leatherwood), pp. 276 – 287, Academic Press, New York, NY.
Darling, J.D. 1978. Aspects of the behavior and ecology of the Vancouver Island gray whales, Eschrichtius glaucus Cope. M.Sc. Thesis, Department of Biology, University of Victoria, Victoria, B.C. 200 pp.
Darling, J.D., Keogh, K.E., and T.E. Steeves. 1998. Gray whale (Eschrichtius robustus) habitat utilization and prey species off Vancouver Island, B.C. Mar. Mammal Sci. 14, 692-720.
Fisheries and Oceans Canada. 1999. Data from BC Lightstations. Institute for Ocean Sciences, Sidney, BC. http://www.ios.bc.ca/ios/osap/data/lighthouse/bcsop.htm
Hammond, P.S. 1986. Estimating the size of naturally marked whale populations using capture-recapture techniques. Rep. IWC Spec. Iss. 8, 253-282.
Hatler, D.F. and J.D. Darling. 1974. Recent Observations of the gray whale
in British Columbia. Can.Field. Nat. 88., 449- 459.
Megill, W.M. 1998. Minimum age estimates. Pale Whale Tales (CERF Newsletter) Vol.2. 96-97. Coastal Ecosystems Research Foundation.
Pike, G.C. 1962. Migration and feeding of the gray whale (Eschrichtius robustus). J. Fish. Res. Board.Can. 19, 815- 838.
Pike G.C. and I.B. MacAskie. 1969. Marine mammals of British Columbia.
Fish. Res. Board Can. Bull. 171, 1-54.
Rice, D.W. and A.A. Wolman. 1971. The life history and ecology of the gray whale (Eschrichtius robustus). Spec. Publ.- Am. Soc. Mammal. 13, 1-142.
Stelle, L. and W.M. Megill. 1999. Feeding ecology of gray whales in British Columbia. Poster presented to the 13th Biennial Conference on the Biology of Marine Mammals, Maui HI, December 1999.
Whitney, F.A., Wong, C.S., and P.W. Boyd. 1998. Interannual variability in nitrate supply to surface waters of the Northeast Pacific Ocean. Mar. Ecol. Prog. Ser. 170: 15-23.
Thanks
This work is the product of many people’s labours. Thank you to all who helped collect the data over the years, and to those individuals and organisations that helped fund the research. We owe especial thanks to:
Environment Youth Team, BC Ministry of Environment, Lands & ParksHuman Resources Development CanadaDepartment of National DefenseAdventure Spirit Travel Company / Tours of ExplorationUniversity Research Expeditions, University of California at Davis
Thanks also to the following people for scientific, moral and financial advice & support: Dr. Boye Ahlborn, Dr. John Gosline, Dr. R.W. Blake, Stan & Judy Westhaver, Susanne Megill, William K & Susan Megill, Bob & Sharon Davis, Josef Neumer.
