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Juvenile Marbled Murrelet Nurseries and the Productivity Index PDF

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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 LITERATURE CITED Marbled Murrelets in California from observa- tions ofyoung at sea. USDA For. Serv. Gen. Tech. Rep. PSW-GTR-152:371-380. Agler, B. a., S. J. Kendall, and D. B. Irons. 1998. Abundance and distribution of Marbled and Kitt- Sealy, S. G. 1975. Aspects of the breeding biology of the Marbled Murrelet in British Columbia. litz’s murrelets in southcentral and southeast Alas- Bird-Banding 46:141-154. ka. Condor 100:254-265. Strachan, G., M. McAllister, and C. J. Ralph. Beissinger, S. R. 1995. Population trends of the Mar- 1995. Marbled Murrelet at-sea and foraging be- bysleesd. MUurSrDelAetFporr.ojeScetrevd. fGreonm. dTeemcohg.raRpehpi.cPaSnaWl-- GhaTvRi-or1.52U:S24D7A-2F5o3r.. Serv. Gen. Tech. Rep. PSW- GTR-152:385-394. Strong, C. S. 1995. Distribution of Marbled Murre- Carter, H. R. and J. L. Stein. 1995. Molts and plum- lets along the Oregon coast in 1992. Northwest. ages in the annual cycle of the Marbled Murrelet. Nat. 76:99-105. USDA For. Serv. Gen. Tech. Rep. PSW-GTR-152: Strong, C. S., B. S. Keitt, W. R. McIver, C. J. Palm- 99-112. er, AND I. Gaffney. 1995. Distribution and pop- Kuletz, K. J., S. Kendall, and D. Nigro. 1997. Rel- ulation estimates of Marbled Murrelets at sea in ative abundance of adult and juvenile Marbled Oregon during the summers of 1992 and 1993. Murrelets in Prince William Sound, Alaska: de- U.S. For. Serv. Gen. Tech. Rep., PSW-GTR-152: veloping a productivity index. Exxon Valdez Oil 339-352. Spill Restoration Proj. Final Rep. 95031. U.S. Fish Trasky, L. L., L. B. Flagg, and D.C. Burbank. 1977. and Wildl. Serv., Anchorage, Alaska. Environmental studies of Kachemak Bay and Kuletz, K. J. and D. K. Marks. 1997. Post-fledging Lower Cook Inlet. Vol. 1. Impact of oil on the behavior of a radio-tagged juvenile Marbled Mur- Kachemak Bay environment. Alaska Dept, ofFish relet. J. Field Ornithol. 68:421-425. and Game, Marine Coastal Habitat Management, Kuletz, K. J. and S. J. Kendall. 1998. A productiv- Anchorage, Alaska.

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