Juvenile Marbled Murrelet Nurseries and the Productivity Index

5 Pages·1999·2.2 MB·English

by  Katherine J Kuletz

1
Short Communications
Wilson Bull.. 111(2). 1999, pp. 257-261
Juvenile Marbled Murrelet Nurseries and the Productivity Index
Katherine J. Kuletz'-^ and John F. Piatt-
—
ABSTRACT. Late summer counts of juveniles at status from British Columbia to California
sea are used as an index of Marbled Murrelet (Bra- (Ralph et al. 1995), considerable effort has
chyramplius mannoratu.s) reproductive success, but lit- been devoted to finding alternate means of es-
tle is known about juvenile dispersal or habitat use. timating murrelet reproductive success. The
Further, it is not known whether these counts accu-
rately rellect absolute breeding success. To address most practical approach is to use a productiv-
these questions we conducted five boat surveys for ity index based on surveys at sea, which uses
Marbled Murrelets and Pigeon Guillemots (Cepphus the ratio ofjuveniles to adults orjuvenile den-
coliimba) in Kachemak Bay, Alaska between 7-24 Au- sities during the fledging period as indices of
gust 1996. Juvenile murrelet distribution in the bay production (Ralph and Long 1995, Strong
was patchy, and we identified ajuvenile Marbled Mur-
1995, Kuletz and Kendall 1998). To be ac-
relet ‘nursery’ area in the outer bay. Fifty-three of 61
juvenile murrelets were in this area, whereas after- curate, surveys require some knowledge of
hatch-year (AHY) murrelets were dispersed throughout fledgling dispersal at sea, but little is known
the bay, as werejuvenile and AHY Pigeon Guillemots. about juvenile movements or habitat use.
The murrelet nursery was characterized by water in- Anecdotal evidence suggests that juvenile
m
side of or at the edge of a 20 deep contour, semi- Marbled Murrelets sometimes congregate in
protected seas, productive waters, and a large bed of
“nursery areas”, often near shore or in exten-
Nereocystis kelp. Juveniles comprised 16.1% of all
sive kelp beds (Sealy 1975, Beissinger 1995,
murrelets and 24.8% of all guillemots observed at sea.
These data suggest a maximum reproductive success Strachan et al. 1995, Strong et al. 1995). If
of0.32 chicks/pair if all AHY murrelets were breeding juveniles gather in specific habitats after
and 0.46 chicks/pair if only 70% of AHY murrelets fledging, productivity surveys could be im-
were breeding. For guillemots, maximum productivity proved by identifying their location and time
estimated from at-sea counts was 0.50 chicks/pair if of use. Here, we report on a juvenile murrelet
AHY
all were breeding and 0.71 chicks/pair if only
nursery and describe associated habitat fea-
70% were breeding. The guillemot estimate was sim-
ilar to that obtained by concurrent studies at nine guil- tures. We estimate muixelet productivity from
lemot colonies in the bay (0.56 chicks/pair). These re- the ratio ofjuveniles to adults at sea, and com-
sults suggest that at sea surveys in late summer provide pare this with Pigeon Guillemot {Cepphus col-
a reasonable index of local productivity for nearshore umba) productivity estimates obtained by both
alcids. Further, if murrelet nursery areas can be found, counts at sea and local colony studies.
at sea counts may provide a valid measure of absolute
productivity. Received Jl June 1998, accepted 7 Jan. STUDY AREA AND METHODS
1999.
We conducted surveys in Kachemak Bay. southcen-
tral Alaska on five days between 7-24 August 1996
(Eig. 1). We surveyed the south side of Kachemak Bay
Nests of the Marbled Murrelet (Brachyram- because Marbled Munelet densities are highest on the
phus marmoratus) are difficult to find or south side, which has deep water, many side bays, and
study, and reproductive success is known only a predominantly rocky, convoluted shoreline (Agler et
from widely scattered nests studied over many al. 1998).
From a 10 m vessel we counted all Marbled Mur-
years. Because of the murrelet’s threatened m
relets and Pigeon Guillemots within 100 either side
of the boat. Two observers used 8 X 42 and 10 X 50
U.S. Fish and Wildlife Service, 1011 E. Tudor Rd., binoculars to identify species and plumages. Juvenile
'
Anchorage, AK 99503. murrelets, which resemble adults in basic plumage,
-Alaska Biological Sciences Center, U.S.G.S., 101 were identified using characteristics described in Cart-
E. Tudor Rd., Anchorage, AK 99503. er and Stein (1995) and Kuletz and Kendall (1998). A
^ Corresponding author; third person entered observations into a laptop com-
E-mail; [email protected] puter using DLOG (Ecological Consulting Inc., Port-
257
258 THE WILSON BULLETIN • Vol. Ill, No. 2, June 1999
FIG. 1. Survey routes (a-j) in Kachemak Bay, Alaska, surveyed by boat on five days on 7-24 August 1996.
land, Oregon). The DLOG data entry program was ferent survey routes over five days for a total area sur-
linked with a Global Positioning System and every veyed of 36.6 km- (Table 1). We refer to the area from
observation had an associated latitude and longitude. the head of Kachemak Bay to China Foot Bay as the
Survey routes followed a path parallel to shore. For inner bay and the area west of China Foot to Seldovia
most of the survey we used radar to maintain a dis- Bay as the outer bay. Our main objective was to de-
tance of 100 m from shore. In rocky or shallow sec- scribe the spatial distribution of murrelets during the
tions we surveyed outside the 20 m depth contour. fledging period, but we obtained some temporal cov-
From the head of the bay to Glacier Spit, and from erage. Portions of the survey routes overlapped on dif-
Kasitsna Bay to Seldovia Bay, we also surveyed 0.5- ferent days and all regions of the bay were surveyed
1.0 km offshore (Fig. 1). The vessel traveled at speeds both early and late in the fledging period (Table 1).
of about 7 km/hr, but because this was a reconnais- Survey dates (7-24 August) encompassed the main
sance survey, we temporarily paused or left our path and peak fledging period for mumelets, based on five
to observe potential juvenile murrelets or guillemots replicate surveys conducted independently between 7
(birds in black and white plumages). August and 4 September 1996 near Kasitsna Bay by
We surveyed a linear distance of 214 km on 10 dif- KJK and J. Figurski. These dates correspond to the
TABLE 1. Numbers of adult (after-hatch-year) and juvenile Marbled Murrelets and Pigeon Guillemots ob-
served on survey routes in Kachemak Bay, Alaska, in August 1996. Area (km-) was calculated from the survey
route length X width.
No. Marbled Murrelets No. Pigeon Guillemots
Survey Area
Bay area route Date (kni2) Adults Juveniles Adults Juveniles
Inner a 8-13 2.86 72 0 8 4
Inner h 8-24 3.44 83 1 5 16
Inner c 8-13 3.64 19 0 25 3
Inner cl 8-24 1.52 12 1 10 1
Total 1 1.46 186 2 48 24
Outer e 8-13 2.89 37 I 21 1
Outer f 8-07 5.25 43 2 12
1
Outer 8-07 1.26 7 3 94 3
Outer h 8-12 1.54 3 0 0 1
Outer 8-12 4.66 7 23 0 0
i
Outer j 8-23 9.57 34 30 12 32
Total 25.17 131 59 139 38
SHORT COMMUNICATIONS 259
FIG. 2. Distribution of adult (after-hatch-year) and juvenile Marbled Murrelets on surveys conducted in
Kachemak Bay, Alaska, on 7-24 August 1996.
fledging period in nearby Prince William Sound, Alas- Juveniles represented 16.1% of all Marbled
ka (Kuletz and Kendall 1998). Pigeon Guillemot fledg- Murrelets and 24.8% of all Pigeon Guillemots
ing dates were similar and were verified from local counted. If all of the AHY Marbled Murrelets
colony studies (Piatt et al. 1997). were breeding, our counts suggest a maximum
Because we wanted to describe the general distri- A
bution of murrelets and our survey routes varied, we reproductive success of 0.32 chicks/pair.
pooled all bird counts for a single tally. For both Mar- more conservative estimate is that only 70%
AHY
bled Murrelets and Pigeon Guillemots we determined of birds were breeding (Piatt and Ford
the ratio at sea of juveniles to adults and subadults 1993), and therefore maximum productivity is
(after-hatching-year birds; AHY). We also calculated calculated as 0.46 chicks/pair. For Pigeon
an index ofjuveniles/pair based on counts ofjuveniles Guillemots, the maximum productivity would
and half the number of adults counted on the same AHY
be 0.50 chicks/pair if all birds were
surveys. Piatt and coworkers (1997) obtained detailed
observations of Pigeon Guillemots on 60 nests in 9 breeding, and 0.71 chick/pair if only 70%
colonies distributed along the south shore of Kache- were breeding adults.
mak Bay from Glacier Spit to Seldovia Bay.
DISCUSSION
RESULTS Juvenile Marbled Munelets in Kachemak
Fifty-nine of 61 juvenile Marbled Murrelets Bay showed a clear preference for the kelp
were found in outer Kachemak Bay and two beds approximately 4 km on either side of the
were found in the inner bay (Table 1). Most mouth of Seldovia Bay. This distribution con-
of the juveniles in the outer bay were concen- trasts shaiply with the distribution of adult
trated 0.5-1.0 km offshore, near the mouth of mun-elets found throughout the bay. Adult
Seldovia Bay (Fig. 2). This area has an exten- munelets forage on Pacific sand lance (Am-
sive kelp bed {Nereocystis sp.) and covers an modytes hexaptenis) in the inner bay (J. Piatt,
m
underwater shelf less than 20 deep. Adult unpubl. data), suggesting that the distribution
Marbled Murrelets (n = 317; 5 in basic plum- of forage fish was not limiting the distribution
age) were distributed throughout Kachemak of juvenile munelets.
Bay, with highest densities in the inner bay Why were juvenile munelets concentrated
between Glacier Spit and the bay head (Fig. along the shore in outer Kachemak Bay and
2). We found Pigeon Guillemots, both adults in extensive, dense beds of Nereocystis kelp?
(n = 249) and juveniles (n = 62), disti'ibuted Although exposed relative to the inner bay,
throughout Kachemak Bay (Table 1 ). the orientation of the shoreline in this area
260 THE WILSON BULLETIN • Vol. Ill, No. 2, June 1999
provided protection from prevailing south- from counts at sea. The estimate ofproduction
westerly winds. The southwest portion of Ka- we obtained for Marbled Murrelets also ap-
chemak Bay receives upwelled waters from proximates that found for Marbled Murrelets
the Alaska Coastal Current entering Cook In- throughout their range (0.28 chicks/pair),
let from the southeast, and gyres in the outer based on 32 nests followed to completion
bay retain nutrients and promote high local (Nelson and Hamer 1995). It is noteworthy
productivity (Trasky et al. 1977). The pres- that our estimate of murrelet production in
ence of Nereocystis, which attach to rocky Kachemak Bay is much higher than those cal-
m
substrate and grow in water 20-40 deep culated from surveys at sea in areas south of
where fast currents or upwelling occurs, is of- Alaska (e.g., 0.001-0.1 1 chicks/pair), even af-
ten associated with productive waters (Lalli ter adjustments (0.01-0.17 chicks/pair) for the
and Parsons 1993). Thus, shallow water, semi- timing of surveys (Beissinger 1995). This is
protected seas, the presence of kelp, and lo- undoubtedly because we located the nursery
cally productive waters appear to combine area near Seldovia Bay, which accounted for
here to create a favorable nursery area for 53 of 61 juveniles we observed on surveys.
newly-fledged murrelets. In addition, the kelp While the possibility of juvenile murrelet
made it difficult to see the juveniles, and so nurseries has been suggested in some areas
may provide protection from avian predators (Sealy 1975, Strachan et al. 1995), they have
such as gulls and Bald Eagles {Haliaeetus leii- never been documented, and munelet distri-
cocephalus), which are common in this area. bution may not always be as patchy as it ap-
Large Nereocystis kelp beds are not common pears to be in Kachemak Bay. In southeast
elsewhere in Kachemak Bay so this feature Alaska, VanVliet (pers. comm.) observed ju-
may be the primary defining characteristic of venile murrelets clustered near or in kelp beds
the nursery. in late August in discrete areas of Port Al-
Juvenile murrelets may use the inner bay thorp, whereas adults were distributed from
temporarily after fledging, and if fledging Inian Pass to Icy Strait. In Prince William
peaked early in August 1996, it is possible Sound, Alaska, however, juvenile murrelets
that we missed seeing them before they emi- were evenly dispersed in nearshore waters
grated to the outer bay. It is also possible that (relative to local murrelet abundance), with
juveniles were absent from the inner bay be- the exception of highly exposed shoreline
cause few murrelets may breed there now as where they were absent (Kuletz et al. 1997).
the result of extensive damage to mature for- The areas surveyed in Prince William Sound
ests from spruce beetle (Dendroctonus nifi- did not have large kelp beds and were char-
pennis). However, the middle portion of the acterized by convoluted, rocky shorelines with
bay (China Foot to Kasitsna Bay) still has numerous protected bays and coves. In addi-
largely intact forests, and while the inner bay tion, the juveniles in Prince William Sound
is clearly an important foraging area for may not travel fai' in the first two weeks after
adults, most juveniles were found in the outer fledging (Kuletz and Marks 1997; Kuletz, un-
bay. The use of kelp beds in the outer bay by publ. data).
juvenile murrelets appears to be a recurring These results confirm that surveys at sea
event; we have observed juvenile murrelets in provide a reasonable index of productivity for
this area in previous years. Surveys of the en- nearshore seabirds such as Pigeon Guillemots
tire bay throughout the fledging period would and Marbled Murrelets. However, it is impor-
be necessary to determine whether, and if so tant to determine the post-fledging movements
when, juveniles from throughout the bay of adults and juveniles for any given area of
move to the kelp beds. study because adultrjuvenile ratios are sensi-
Estimates of Pigeon Guillemot productivity tive to late summer movements of adults and
obtained from juvenile surveys at sea com- subadults (Kuletz and Kendall 1998). Al-
pared well to the productivity of guillemots though our temporal data were limited in this
measured from colony-based reproductive study, we did not find obvious declines in
studies. Pigeon Guillemots at nine Kachemak adult numbers in August, such as occurs in
Bay colonies in 1996 produced 0.56 chicks/ Prince William Sound. If juvenile munelet
pair, which falls within the range we estimated nurseries can be located, it would facilitate the
SHORT COMMUNICATIONS 261
use of juvenile densities to measure produc- ity index for Marbled Murrelets in Alaska based
tivity and thus avoid problems associated with on surveys at sea. J. Wildl. Manage. 62:446-460.
Lalli, C. M. and T. R. Parsons. 1993. Biological
using adult:juvenile ratios (Kuletz and Ken-
oceanography: an introduction. Pergamon Press,
dall 1998). If adults remain in an area during New York.
the main fledging period where muirelet nurs- Nelson, S. K. and T. E. Hamer. 1995. Nest success
eries exist, surveys at sea may provide a valid and the effects ofpredation on Marbled Murrelets.
measure of absolute productivity, and not just USDA For. Serv. Gen. Tech. Rep. PSW-GTR-152:
89-98.
an index of production (e.g., Beissinger 1995).
Piatt, J. F. and R. G. Ford. 1993. Distribution and
abundance of Marbled Murrelets in Alaska. Con-
ACKNOWLEDGMENTS
dor 95:662—669.
Piatt, J. F, M. Robards, S. Zador, M. Litzow, and
This work was conducted with funding from the G. Drew. 1997. Cook Inlet seabirds and forage
Exxon Valdez Oil Spill Trustee Council, the U.S. Geo- fish studies. Exxon Valdez Oil Spill Restoration
logical Survey, and the U.S. Fish and Wildlife Service. Proj. Ann. Rep. 96163M, Biol. Resour. Div., U.S.
We are grateful to the Alaska Maritime National Wild- Geological Survey, Anchorage, Alaska.
life Refuge for logistic support, to B. Keitt and J. Fi- Ralph, C. J., G. L. Hunt, Jr., M. G. Raphael, and J.
gurski for assistance with surveys, and to M. Litzow F. Piatt. 1995. Ecology and conservation of the
for use of unpublished data on Pigeon Guillemot pro- Marbled Murrelet. U.S. For. Serv. Gen. Tech.
ductivity. Rep., PSW-GTR-152:1-5.
Ralph, C. J. and L. L. Long. 1995. Productivity of
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