The Roles of Introduced Rats and Commercial Fishing
in the Decline of Ancient Murrelets on Langara Island,,
British Columbia
DOUGLAS F. BERTRAM
University of Washington, Friday Harbor Laboratories, 620 University Road, Friday Harbor, WA 98250, U.S.A.
Abstract: I e x a m i n e d the decline o f A n c i e n t Murrelets (Synthliboramphus antiquus), a small, burrou>nesting
seabird, at Langara Island. The island's seabird colony w a s historically one o f the largest colonies o f A n c i e n t
Murrelets in British C o l u m b i a - - p e r h a p s in the w o r l d - - w i t h a n estimated 200,000 nesting pairs. I reviewed
historical i n f o r m a t i o n a n d c o m p a r e d the results o f surveys f r o m 1981 a n d 1988 that employed the s a m e census protocol. The extent o f the colony, a potential index o f p o p u l a t i o n size, declined f r o m 101 ha in 1981 to 4 8
h a in 1988. B u r r o w density increased during the s a m e period, however, suggesting that the colony h a d consolidated. In 1988, the p o p u l a t i o n estimate w a s 24,200 +- 4 0 0 0 (S.E.) breeding p a i r s c o m p a r e d to 22,000 +_
3 7 0 0 in 1981. In 1988, 29% o f the b u r r o w s that were completely searched contained bones o f A n c i e n t Murrelets. Bones were m o s t c o m m o n in b u r r o w s located in a b a n d o n e d areas o f the colony a n d were least c o m m o n
where b u r r o w occupancy w a s high. The discovery o f adult A n c i e n t Murrelets killed in their b u r r o w s by introduced rats, c o m b i n e d w i t h the high proportion o f b u r r o w s w i t h bones, suggests that rats (Rattus rattus a n d R.
norvegicus) have contributed significantly to the decline o f the population. In addition, the presence a n d activities o f a salmon-fishing fleet in the 1950s a n d 1960s m a y also be linked to the decline o f the Langara Ancient Murrelet p o p u l a t i o n during that period because these fisheries are k n o w n to h a v e caused h e a v y mortality through f a t a l light attraction a n d d r o w n i n g in gill nets. The c o m b i n e d effects o f ongoing predation by
introduced rats a n d - - t o a lesser extent--previous, episodic fishery-induced mortality are probable causes f o r
the p o p u l a t i o n decline.
E1 papel de las ratas introducidas y la pesca comercial en la declinaci6n de Synthliboramphus a n t i q u u s en la Isla
Langara, en la Columbia Britfinica
Resumen: En el presente trabajo e x a m i n d la d e d i n a c i 6 n de Synthliboramphus antiquus, u n a p e q u e ~ a ave
m a r i n a que anida en cuevas, en la Isla Langara. La colonia de aves m a r i n a s de la isla f u e hist6ricamente
u n a de las mtis grandes de la C o l u m b i a Britdnica y quizdLs la m ~ s grande en el m u n d o con unos 200,000
p a r e s de anidadores. Revis~ la i n f o r m a c i 6 n hist6rica y compard los resultados de las evaluaciones realizadas
en 1981 y 1988 que utilizaron el m i s m o protocolo de censo. La extenci6n de la colonia, u n indice potencial
dei t a m a ~ o poblacional, declin6 de 101 ha. en 1981 a 48 ha. en 1988. Sin embargo, la densidad de cuevas se
increment6 durante el m i s m o perfodo, lo que sugiere que la colonia se ha consolidado. En 1988, la estim a c i 6 n p o b l a c i o n a l f u e de 24,200 +__4 0 0 0 (S.E.) pares de reproductores en c o m p a r a c i 6 n con 22,000 +__3 7 0 0
en 1981. En 1988, u n 29% de las cuevas que f u e r o n revisadas c o m p l e t a m e n t e contenian huesos de Synthliboramphus antiquus. Los huesos f u e r o n mdts c o m u n e s en cuevas localizadas en dreas a b a n d o n a d a s de la colonia y f u e r o n m e n o s c o m u n e s en areas d6nde el grado de ocupaci6n era alto. El descubrimiento de adultos
m u e r t o s de Synthliboramphus antiquus en sus cuevas p o r ratas introducidas, c o m b i n a d o con la alta proporci6n de cuevas con huesos sugiere que las ratas (Rattus rattus y R. norvegicus) h a n contribuido significativam e n t e a la declinaci6n de la poblaci6n. Adicionalmente, la presencia de actividades de la ]Iota p e s q u e r a del
Present address: Environment Canada, Canadian Wildlife Service, Pacific Wildlife Research Center, RR 5421, Robertson Road, Delta, B.C. V4K
3N~, Canada, emaa bertram@fhLwashtngton.edu
Paper submitted March 21, 1994; revised manuscript accepted September 29, 1994.
865
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Volume9, No. 4, August1995
866
AncientMurreletDeclineon LangaraIsland
Bertram
salm6n en las d~cadas de 1 9 5 0 y 1960 podrfa tambidn estar ligada a la declinaci6n de la poblact6n de Synthliboramphus antiquus de Langara durante dicho perfodo, puesto que se sabe que estas pesquerfas ban
causado una alta mortaltdad medtante la fatal atracci6n luminosa y sofocaminento en redes agaUeras. Los
efectos combinados de la de predaci6n actual p o r ratas introducidas y e n menor grado por la mortalidad
epis6dica inducida p o r la pesca son las causas probables de la declinaci6n poblactonal.
Introduction
Catastrophic population declines of numerous islandbreeding seabird species have occurred worldwide, and
seabird conservation is becoming an increasingly important issue as development extends to archipelagoes of all
oceans (Atkinson 1985; Bailey & Kaiser 1993; Lowe
1993). Moreover, human-introduced mammalian predators, particularly rats, have been implicated in many of
the documented declines. Langara Island in British Columbia, Canada, represents a classic case history of the
progress of seabird population decline. A study of the
seabird decline on Langara may therefore provide insight into a number of important general issues that relate to seabird conservation biology.
Langara, at the northeast tip of the Queen Charlotte Islands (Haida Gwah'), was historically one of the largest
seabird colonies in British Columbia (Drent & Gulguet
1961). The Ancient Murrelet ( S y n t h l t b o r a m p h u s ant i q u u s ) was believed to be the most numerous seabird
species on Langara (Green 1916; Darcus 1930), numbering about 200,000 birds (Gaston 1992), perhaps the
world's largest colony (Nelson 1990); "The whole island
is a warren of Ancient Murrelets . . . " (Green 1916);
"The numbers can only be described as astronomical"
(Beebe 1960); and "Immense numbers nesting here"
(Drent & Guiguet 1961). Peregrine Falcons (Falco pereg r i n u s pealet), specializing on seabird prey (Green
1916; Beebe 1960; Blood 1968; Nelson & Myers 1976),
were also found on the island in breeding densities unsurpassed in British Columbia (Blood 1968). At one
time, Langara supported several other species of burrow-nesting seabirds: Tufted Puffin (Fratercula cirrhata), Rhinoceros Auldet (Cerorhinca m o n o c e r a t a ) ,
Cassin's Auklet ( P t y c h o r a m p h u s aleutica), and Forktailed Storm Petrels ( O c e a n o d r o m a f u r c a t a ; Drent &
Guiguet 1961), but those species have virtually disappeared from the island (Campbell et al. 1990; Royal British Columbia Museum, unpublished data).
Despite the lack of rigorous estimates of the size of
past Ancient Murrelet populations on Langara, insight
into the historical population size can be obtained from
three sources: accounts of the colony extent, actual
counts of birds, and counts of the number of pairs of
Peregrine Falcons. On June 6, 1947, Guiguet observed
families of Ancient Murrelets making their way to the
sea at Henslung Cove. He remarked "The big hatch is on,
thousands of downies, escorted by parents, go d o w n to
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Volume 9, No. 4, August 1995
sea every night" (Drent & Guiguet 1961). On May 29,
1952, Guiguet observed birds on the water in Parry Passage, and his "extremely conservative estimate" was
60,000 birds in an area about 300 by 300 meters (C. J.
Guiguet Provincial Museum field notes, Royal British Columbia Museum, unpublished). Beebe (1960), w h o studied Peregrine Falcons on Langara from 1952 to 1958,
stated that " . . . the entire fringe forest seems to be one
continuous colony, extending to all parts of the island
that I know, from Cloak Bay around to Langara Point."
Signs that colony extent had diminished were evident in
1970, w h e n Sealy noted (cited in Nelson & Myres 1976)
that the colony near Dadens, which was "riddled with
burrows" in 1966 (Campbell 1969), had been abandoned. In retrospect, Sealy estimated 80,000 to 90,000
pairs of Ancient Murrelets in 1971 (Vermeer et al. 1984).
Total counts of occupied Peregrine Falcons nests on
Langara indicate that numbers declined from about 2123 pairs in the early 1950s to 5-6 pairs during 19681973 (Nelson & Myres 1976). Their numbers have since
remained roughly constant (Nelson 1990). On Langara,
the dominant prey species in the diet of nesting Peregrine Falcons is the Ancient Murrelet (Green 1916;
Beebe 1960; Nelson 1977, cited in Gaston 1992). Nelson
and Myers (1976) and Nelson (1990) have argued that a
decline in Ancient Murrelets during the 1950s and 1960s
was the immediate cause of the falcon decline on Langara. Gaston (1992) has suggested, however, that this reduction may have been at least in part related to chlorinated hydrocarbon contamination.
In 1981, the Canadian Wildlife Service (CWS) conducted a census of the Ancient Murrelet population of
Langara. They estimated 22,500 breeding pairs, located
primarily on the northeastern corner of the island (Rodway et al. 1983). I report the results of a 1988 survey,
compare the findings with those made in 1981, and discuss several possible factors that may have contributed
to the long-term decline of seabirds on Langara.
Methods
Langara Island (54 ° 12'N, 133o1 , W at Iphigenia Point) is
approximately 3270 ha in size and 9.5 km across at its
broadest point. The island's flora and the nesting habitat
of Ancient Murrelets have been described by Sealy
(1976) and Vermeer et al. (1984). Gaston (1992) provides a comprehensive account of Ancient Murrelet biology. A team of six researchers visited Langara from May
Bertram
6 to June 7, 1988. The results of that survey are reported
in full by Bertram (1989).
In areas where birds were still nesting, transects that
had been conducted in 1981 were resurveyed. The
transects ran along the same bearing and c o m m e n c e d at
locations specified by Rodway et al. (1983). Survey coverage within the colony was increased by running additional transects between the ones conducted in 1981.
The n e w transects were perpendicular to the shore and
were spaced 300-500 meters apart. At 40-meter intervals along each transect, the number of Ancient Murrelet burrows in 5-by-5 meter plots was counted.
Burrows were distinguished from holes in the ground
by signs of Ancient Murrelet nesting activity: egg membranes, eggshell fragments, feathers, nest cups, faecal
material, or worn, flattened earth that had been trampled underfoot. The proportion of burrows that contained an active nesting pair was estimated by inspecting the entire content of all burrows in every other plot
along a transect. Later in the season, we attempted to
make complete inspections of all burrows in every plot.
Burrows subject to complete inspection were classified
as occupied (if they contained an incubating adult, egg,
chicks, or eggshell membrane and shell remains from
freshly hatched eggs), unoccupied, or u n k n o w n (if the
ends of all tunnels could not be reached). Between plots
along each transect, evidence of murrelet activity such
as burrowing, broken eggs, and feather piles left by
avian predators, were noted to facilitate delineation of
the colony boundaries. W h e n no active burrows or
other signs of activity could be found within a plot or in
the area halfway toward adjacent plots along a transect,
the area was not considered part of the colony. Areas
classified as part of the colony in 1981 by Rodway et al.
(1983) were not surveyed in 1988 if no signs of active
burrowing could be found. Abandoned areas were explored on foot, however, to determine if small pockets
of breeding Ancient Murrelets still remained. If such areas were discovered, the number of active burrows was
conservatively estimated by counting.
The n u m b e r of breeding pairs was estimated as follows. Following Rodway et al, (1983), the area covered
by the colony was calculated by multiplying the length
of the burrowing area (determined by following the 30meter contour line on a l:50,O00-scale topographical
map of the island) by its width (determined by averaging
the extent of burrowing obtained from transects). The
n u m b e r of burrows in the colony ___ S.E. was estimated
by multiplying the colony area by the average burrow
density ___ S.E. Multiplying that figure by the proportion
of occupied burrows provided an estimate of the number of occupied burrows, or pairs of birds that consituted the nesting population in the area transected. Estimates of the number of birds breeding in pocket that
were not transected were added to obtain the estimate
of the total breeding population. To facilitate compari-
Ancient Murrelet Decline on Langara Island
867
sons of the 1981 and 1988 surveys, the raw data from
1981 (in Rodway et al. 1983) were used to recalculate
the population estimate and error term in the manner
outlined above.
Broken eggs, c h e w e d spruce cones (assumed to have
been left by introduced rats), and bones or dead birds in
burrows were recorded along transects. Ancient Murrelet skulls found in burrows were identified as intact or as
chewed if the cranial case appeared to have been
opened in a way other than by deterioration. No other
mammals that might be responsible for the c h e w e d
spruce cones or skulls are k n o w n from Langara (Cowan
& Guiguet 1965).
In order to investigate the presence of rats within and
around the colony, 10 snap and three live traps were
placed at locations close to McPherson Point that appeared to be used by rats (evidence included w o r n paths
under logs or w o r n areas where c h e w e d spruce cones,
rat dung, or both were found). Most traps were placed
within 30 meters (range 10-80 m) of the edge of the
vegetation and the rocky shoreline. Some traps were
placed in the colony, mostly about 50 meters from shore
and approximately 30 meters above sea level. Other
traps were placed on the colony periphery where abandoned burrows and signs of rat activity were found.
Results
We found 160 burrows in 108 plots along 16 transects
on the northeast side of Langara. We searched the entire
contents of 56 burrows. The proportions of active burrows in plots along individual transects ranged from 0 in
areas that had been abandoned to 67% in active areas of
the colony. Within the active portions of the colony,
burrow occupancy averaged 38%.
The population estimates for the 1981 and 1988 surveys were similar: 22,000 _+ 3700 and 24,200 ___ 4000,
respectively (Table 1). Burrow density was significantly
higher in 1988 (t = - 2 . 6 2 , df = 5 1 . 4 , p = 0.049). Estimates of burrow occupancy were 26% in 1981 and 38%
in 1988, but they were statistically indistinguishable (Table 1).
The area of the Ancient Murrelet colony declined from
100.8 ha in 1981 to 46.3 ha in 1988 (Fig. 1). In 1988, the
colony was confined primarily to the north end of the island in a 3-kin zone extending west from McPherson
Point. A small pocket of nesting birds was also located
on Cohoe Point. No signs of active nesting were found
on Iphigenia Point. The area west of Fury Bay was not inspected in 1988. A dead chick was discovered in that
area, however, suggesting breeding activity in the vicinity (R. W. Nelson, personal communication).
In 1988, all regions of the colony, as well as the area
previously occupied by Ancient Muta~lets in 1981,
showed signs of rat activity. Chewed spruce cones were
ConservationBiology
Volume9, No. 4, August1995
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Ancient Murrelet Decline on Langara Island
Bertram
Table 1. Survey results for Ancient Murrelets on langara Island in 1981 (Rodway et al. 1983) and 1988 (this study).
B u r r o w D e n s i t y ( m 2) -1
Population
Estimate a
Burrow Estimate
Year
Colony Area (ha)
Mean
S.E.
no
Total Number
S.E.
O c c (%)c
Pairs
S.E.
1981
1988
100.8
46.3
0.082 a
0.136 a
0.014
0.023
39
31
82,650
63,000
14,100
10,500
26e
38e
22,000
24,200
3700
4000
aEstimate includes p a i r s f r o m areas that were n o t transected.
b n = n u m b e r o f plots within the colony.
COcc = occupancy.
at = -2.62; d f = 51.4;p = 0.049.
eNo significant difference based on a chi-square test o f the n u m b e r o f occupied a n d unoccupied b u r r o w s in each year.
found on 11 of the 16 transects, suggesting that rats
w e r e p r e s e n t throughout the northeast coast of the islands. Survey of the area south of Dibrell Bay to Cohoe
Point and the a b a n d o n e d c o l o n y at Iphigenia Point occasionally turned up c h e w e d spruce cones and a b a n d o n e d
burrows containing murrelet b o n e s (one b u r r o w had rat
dung at the entrance and c h e w e d spruce cones inside).
An active rat d e n was also found at the former site.
Ancient Murrelet bones w e r e found in 17% of the 160
burrows discovered. This figure is likely to be an underestimate, however, because many of those burrows
(65%) w e r e not completely searched. Among the 56 burrows that w e r e searched completely, 29% contained
bones. Skeletal remains w e r e most frequently discovered in a b a n d o n e d areas of the colony and w e r e least
c o m m o n in areas w h e r e b u r r o w o c c u p a n c y was high.
Sixteen skulls w e r e found in total, but seven of these
w e r e badly deteriorated. Three of the nine recent skulls
had holes in the cranium that a p p e a r e d to have b e e n inflicted by chewing.
Several dead adult Ancient Murrelets w e r e found in
the colony. On one occasion a recently killed pair was
found in a burrow, within 15 cm of each other. Both
birds had gaping w o u n d s to the nape region. Neither
had b r o o d patches. Bones w e r e also discovered in the
same burrow. A fresh, dead Ancient Murrelet was found
in the mouth of another burrow; it had an o p e n w o u n d
from the nape to the pectoral girdle. Another kill, w i t h a
similar w o u n d was located 2 meters away. One of the
latter t w o birds had b r o o d patches. Two more kills app e a r e d to have b e e n dead for longer; in one the skull
had b e e n c h e w e d o p e n and the u p p e r a b d o m e n eaten.
Eleven b r o k e n eggs w e r e found in the 108 plots surveyed; rats w e r e likely responsible for some of those
losses. Two eggs w e r e notable in that they w e r e found
in the o p e n within 1 m e t e r of a b u r r o w entrance and
w e r e largely intact e x c e p t for 3-by-2 cm holes that app e a r e d to have resulted from chewing. Neither egg
s h o w e d signs of incubation, and b o t h still contained half
of their contents.
Rat dens w e r e found near the shore among old piles of
driftwood that had b e c o m e part of the vegetation edge.
ConservationBiology
Volume9, No. 4, August1995
Rat trails w e r e c o m m o n in the forest near the shore
around our c a m p at McPherson Point. Rats w e r e rarely
seen, but one live rat was observed in the late evening
by flashlight as it m o v e d up a forested slope t o w a r d the
Ancient Murrelet colony. Two adult female Norway rats
( R a t t u s n o r v e g i c u s ; 299 and 352 g) and three young-ofthe-year w e r e t r a p p e d (90, 115, 122 g).
Discussion
The progressive decline in colony e x t e n t for Ancient
Murrelet on Langara is among the best-documented declines of a seabird p o p u l a t i o n threatened by i n t r o d u c e d
predators. It is striking that the Ancient Murrelet colony,
once r e p o r t e d to be "one continuous colony" around
the p e r i m e t e r of most of Langara (Beebe 1960) e x t e n d e d
for only 3 km on the north coast in 1988. Furthermore,
systematic surveys indicated that the colony e x t e n t in
1988 had b e e n r e d u c e d to less than half that r e p o r t e d in
1981. Despite the significant change in colony area, the
p o p u l a t i o n estimates from 1981 and 1988 w e r e similar.
But small sample sizes and large S.E. estimates contribute to inaccuracy in those p o p u l a t i o n estimates (see also
Bertram 1989). The decline in colony extent may therefore be the most instructive gauge of population size. I
evaluated three factors that could have contributed to
the decline of the Ancient Murrelet p o p u l a t i o n and
o t h e r seabirds on Langara.
Predation by Introduced Rats
Rats ( R a t t u s spp.) have r e a c h e d 82% of the worlds major oceanic islands and major island groups (Atkinson
1985). Moreover, there are many accounts of R a t t u s
spp. preying on seabird eggs, chicks, and adults (Fisher
& Baldwin 1946; Austin 1948; Kepler 1967; Harris 1970;
Imber 1975, 1978, 1984; Taylor 1979; Pye & Bonner
1980; MoUer 1983; W o o d b y 1988). The effect of introd u c e d rats on seabird populations varies from little longterm effect on productivity (Norman 1970; Fall et al.
1971) to significant declines in breeding populations
Bertram
AncientMurreletDeclineon LangaraIsland
869
N
5S=
DIXON
~ 0 8 ; a ~tand
"X~
Queen
Cludotte
I$
ENTRANCE
'~.
BRITISH COLUMBIA
~,
50=
1300
PARRY PAS|AGE
mO
it
!
2
3
4
Skm
I
I
i
I
I
SCALE
Figure 1. A reconstruction o f the extent o f the historical colony o f A n c i e n t Murrelets on Langara Island since the
1950s (adapted f r o m Gaston 1992).
(Grant et al. 1981; Tomkins 1985). Factors that influence
the servility of predation by introduced rats include
physical features of the habitat, availability of alternate
foods for the predator, and the relative size and behavior
of the predator and prey species (Moors & Atkinson
1984). Imber (1975) concluded that petrels would be
endangered by a species of rat whose maximum weight
approaches or exceeds that of the seabird.
The evidence from this study (particularly dead adults
found underground with rat-inflicted wounds), coupled
with other historical information, indicates that mortality caused by introduced rats is likely to be the primary
cause of the decline of Ancient Murrelets on Langara. It
is noteworthy that other studies (Austin 1948; Twigg
1975; Moiler 1983) have reported that rats commonly
kill seabirds by attacking the neck region. Descriptions
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Volume 9, No. 4, August 1995
870
Ancient MurreletDeclineon LangaraIsland
o f adult A n c i e n t Murrelets, f o u n d d e a d in b u r r o w s w i t h
similar w o u n d s , h a v e also b e e n r e p o r t e d b y p r e v i o u s visitors to Langara (Sealy 1976; V e r m e e r et al. 1984; Royal
British C o l u m b i a M u s e u m 1977, u n p u b l i s h e d data). Furt h e r m o r e , t h e adult rats t r a p p e d o n Langara in 1988 w e r e
r o u g h l y 1.5 t i m e s h e a v i e r t h a n adult A n c i e n t Murrelets.
This size difference b e t w e e n p r e d a t o r a n d p r e y suggests
that rats o n Langara c a n easily kill adult A n c i e n t Murrelets.
The high proportion of burrows containing bones,
p a r t i c u l a r l y in t h e a b a n d o n e d p a r t o f t h e colony, supp o r t s t h e i n f e r e n c e that rats are causing a d e c l i n e o f Anc i e n t Murrelets o n Langara. D e s p i t e surveys o f 31 Anc i e n t Murrelet c o l o n i e s t h r o u g h o u t t h e Q u e e n C h a r l o t t e
Islands ( G a s t o n 1992), r e p o r t s o f b o n e s in b u r r o w s are
t m k n o w n (G. W. Kaiser, p e r s o n a l c o m m u n i c a t i o n ) exc e p t f r o m o n e o t h e r c~iony, Lyell Island, w h e r e rats
(R. r a t t u s ) have also b e e n o b s e r v e d ( R o d w a y et al. 1988;
A.J. Gaston, p e r s o n a l c o m m u n i c a t i o n ) . A 1992 s u r v e y o f
Lyell Island i n d i c a t e d that t h e n u m b e r o f b r e e d i n g pairs
o f A n c i e n t Murrelets a n d t h e i r c o l o n y e x t e n t h a v e b o t h
d e c l i n e d since 1982 ( L e m o n 1993). Bones w e r e f o u n d in
15% o f t h e b u r r o w s that w e r e c o m p l e t e l y s e a r c h e d .
Moreover, 20 to 40 o c c u p i e d b u r r o w s s h o w e d signs o f
rat p r e d a t i o n - - f i v e d e a d adults a n d 15 b r o k e n eggs. T h e
d e a d adults h a d b e e n c h e w e d a b o u t t h e neck, shoulder,
a n d breast.
Black rats (R. r a t t u s ) w e r e f a s t c o l l e c t e d o n Langara in
1946 (Royal British C o l u m b i a M u s e u m s p e c i m e n s , Bert r a m & Nagorsen, u n p u b l i s h e d m a n u s c r i p t ) . T h e y w e r e
later i m p l i c a t e d as p r e d a t o r s o n A n c i e n t Murrelet eggs
( C a m p b e l l 1968; Sealy 1976; R o d w a y et al. 1983), adults
( B e e b e 1960; Sealy 1976; Royal British C o l u m b i a Mus e u m 1977, u n p u b l i s h e d data; R o d w a y et al. 1983; Verm e e r et al. 1984), a n d c h i c k s (Sealy 1976) b u t w e r e
n e v e r c o n s i d e r e d a t h r e a t to t h e p o p u l a t i o n . It is striking
that t w o o f t h e areas w h e r e rats w e r e p r e v i o u s l y rep o r t e d to p r e y o n m u r r e l e t s w e r e later a b a n d o n e d (Egeria Bay in 1981; I p h i g e n i a Point in 1988). During a visit
to Langara in J u n e 1993, n o e v i d e n c e o f b l a c k rats ( d r o p p i n g s o r tree nests) w a s found, b u t N o r w a y rats w e r e
again c a p t u r e d at M c P h e r s o n Point a n d also o n n e a r b y
Lucy Island (Fig. 1; C. W. S., u n p u b l i s h e d data). N o r w a y
rats, first r e p o r t e d in t h e Q u e e n C h a r l o t t e Islands in
1981, m a y h a v e r e p l a c e d b l a c k rats o n Langara ( B e r t r a m
& Nagorsen, u n p u b l i s h e d m a n u s c r i p t ) . If true, rat p r e d a tion i n t e n s i t y o n A n c i e n t Murrelets m a y have i n c r e a s e d
b e c a u s e R. n o r v e g i c u s is larger t h a n R. rattus, a n d it is
t h e r e f o r e likely to r e p r e s e n t a g r e a t e r t h r e a t to seabirds.
Commercial
Fishing Operations
C o m m e r c i a l fishing o p e r a t i o n s in t h e c o l o n y vicinity
d u r i n g t h e 1950s a n d 1960s w e r e a p o s s i b l e c o n t r i b u t o r
to t h e d e c l i n e o f t h e A n c i e n t Murrelet p o p u l a t i o n o n
Langara. Mortality r e s u l t e d f r o m light a t t r a c t i o n a n d
CortscrvationBiology
Volume9, No. 4, August1995
Bertram
d r o w n i n g in gill nets. Like m a n y o t h e r n o c t u r n a l s e a b i r d
species, A n c i e n t Murrelets are a t t r a c t e d to light at n i g h t
a n d o f t e n d i e w h e n t h e y c o l l i d e w i t h a n c h o r e d o r moving vessels. T h e s e p o t e n t i a l l y large s o u r c e s o f m o r t a l i t y
have r e c e i v e d little a t t e n t i o n w i t h r e s p e c t to Langara
seabirds. V e r m e e r et al. (1984) w r o t e , " . . . local fisherm e n r e p o r t e d to Sealy in 1970 a n d 1971 that an unquantiffed n u m b e r o f A n c i e n t Murrelets a n d R h i n o c e r o s
Auklets d r o w n e d in gill n e t s o n t h e east side o f Langara
Island." T h e r e p o r t o f A n c i e n t Murrelet d e a t h s is supp o r t e d b y a d e t a i l e d l e t t e r to t h e c o m m i s s i o n e r o f a Pereg r i n e F a l c o n Inquiry in British C o l u m b i a (Shelford 1988)
f r o m Charles Bellis (Masset, B. C., VOT 1M0), w h o f i s h e d
c o m m e r c i a l l y for s a l m o n a r o u n d Langara Island d u t ~ g
t h e 1950s a n d 1960s:
• . . in Cloak Bay in the 50s and 60s we used to shovel
over fifty Murrelets overboard in the mornings after they
had struck guywires of our fishing boat. We were not
the only boat anchored in the bay, and if one multiples
the number of boats anchored per night over a breeding
season, say ten per night for twenty nights, killing fifty
birds per night we would lose ten thousand birds per
season. I believe this is a conservative estimate, and
points to the seriousness of the problem.
and
• . . numbers of Murrelets... were caught in gillnets during the fishing season off Langara Island . . . . I, myself,
have not had more than fifty birds at a time, however,
one of my companions told me he had "a bird in every
mesh" one morning at Langara. This would have b e e n
over five hundred murrelets. . . . during the seabird
breeding season . . . no night fishery [should be] allowed.
Fishing activity a r o u n d Langara i n c r e a s e d significantly
d u r i n g t h e 1950s a n d r e m a i n e d i n t e n s e until t h e m i d
1960s (Fig. 2). At t h e p e a k in 1963 t h e r e w e r e 452 trolling a n d gill-netting vessels a r o u n d Langara. This large
fishing fleet h a d t h e p o t e n t i a l to c a u s e m a s s m o r t a l i t y o f
s e a b i r d s a n d m a y h a v e c o n t r i b u t e d significantly to t h e
d e c l i n e o f A n c i e n t Murrelets o n Langara p r i o r to t h e
1970s.
Reduced
Zooplankton
Production
N e l s o n a n d Myres (1976) h y p o t h e s i z e d t h a t t h e d e c l i n e
o f A n c i e n t Murrelets o n L a n g a r a m a y have r e s u l t e d f r o m
r e d u c t i o n s in t h e z o o p l a n k t o n u p o n w h i c h t h e birds
feed. T h e y r e a s o n e d t h a t "Either b i o c i d e s have a f f e c t e d
p l a n k t o n ( p r o b a b l y via t h e D a v i d s o n C u r r e n t f l o w i n g
n o r t h f r o m California), o r an a n o m a l o u s i n t r u s i o n o f
w a r m w a t e r n e a r t h e British C o l u m b i a c o a s t for m o s t o f
1957-71 has r e d u c e d t h e s u p p l y o f p l a n k t o n " ( N e l s o n &
Myres 1976; s e e also N e l s o n 1976). G a s t o n (1992) arg u e d t h a t it is u n l i k e l y that p e s t i c i d e s o r o c e a n o g r a p h i c
c h a n g e s c a u s e d a c o n s i s t e n t d e c l i n e in z o o p l a n k t o n prod u c t i o n in t h e region. G a s t o n ' s (1992) v i e w is f u r t h e r
supported by zooplankton samples collected from the
w e a t h e r s h i p at O c e a n Station P (50°N, 145°W) d u t ~ g
Bertram
Q
¢-
Ancient Murrelet Decline on Langara Island
6OO
,--j
"lO
e-
TrolkDm
5O0
.~_
m
¢I1=
.0
E
1951
Z
1953
19~:~
1957
1959
1961
1963
1965
Year
Figure 2. The mean number of flshing vessels in May
and June reported for the Langara Island region (Area
1 of the British Columbia fisheries regions) from 1951
to 1965. Data were compiled from annual area history reports by the Department of Fisheries and
Oceans Canada (unpublished).
1956-1980, the longest continuous data series of plankton density for the North Pacific (Fulton 1983). Peterm a n (1987) used this data to develop an index of the total annual zooplankton biomass for the Gulf of Alaska.
Peterman's indexes s h o w no consistent decline in plankton production b e t w e e n 1957 and 1971, or at any time
since (F = 0.036, df = 1,9;p = 0.854; Fig. 3). Moreover,
a recent reanalysis of the zooplankton biomass data from
Ocean Station P (using collections taken from June 15 to
July 31 only) shows a significant long-term increase from
1957 to 1980 (Brodeur and Ware 1992).
My study implicates introduced rats as the primary
contributor to the decline of Ancient Murrelets on Langara. In the 1980s the colony area contracted signifi-
Gooo
g
pC . C
e~
~sooo
871
cantly, leaving the remaining birds consolidated in an
area of high density. A 1993 survey of the Langara Ancient Murrelet population indicated that colony area has
decreased by 50% and the breeding population has declined by 40% since 1988 (Harfenist 1994). The Canadian Wildlife Service is presently planning a campaign to
eradicate rats and restore the seabird populations on
Langara island. The o u t c o m e of such a campaign will be
of considerable interest to Conservation Biologists because Langara will be the largest island for which rat
eradication had b e e n attempted (G. W. Kaiser, personal
communication).
Historical commercial fishing operations likely caused
significant mortality of Iangara Ancient Murrelets prior
to the 1970s, but their contribution to the long-term
population decline are unknown. Future management
plans should evaluate the impact of the timing and location of commercial and sport fishing activities in the vicinity of the island. Managers should also identify anchorage sites used by all vessels in the Langara region to
evaluate the potential for fatal light attraction and ways
to mitigate its effects on present and future populations
of seabirds.
Acknowledgments
This project was part of the Canadian Wildlife Service
Migratory Bird Conservation program. I thank K. Henderson, G. W. Kaiser, M. McKay, and especially H. Hay
and N. Holmes for assistance in the field. A. Harfenist led
the Canadian Wildlife Service survey to Langara in 1993
and kindly discussed the results. The Canadian Coast
Guard provided helicopter transportation to and from
Langara. The light keepers at Langara, K. Brunn and L.
Faurette, provided support and w a r m hospitality. I
thank the Old Massett Village Council for permission to
w o r k in Duu Guusd Tribal Park, w h i c h includes Kit's
Gwaii (Langara, Lucy, and Cox islands). K. Moore provided valuable logistical support on short notice. I am indebted to M. Lemon and M. Rodway for providing training in seabird survey techniques. B. Spilsted, of the
Department of Fisheries and Oceans, Canada, provided
information on the historical salmon fishery around Langara. S. Sealy and R. W. Nelson shared their personal observations on Langara. I thank A. J. Gaston, G. W. Kaiser,
C.J. Ralph, and an anonymous reviewer for constructive
c o m m e n t s on the manuscript.
C
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1NO
19S
19"/0
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