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Postbreeding Dispersal and Drift-Net Mortality of Endangered Japanese Murrelets

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Postbreeding Dispersal and Drift-Net Mortality of Endangered Japanese Murrelets The Auk 111(4):953-961, 1994 POSTBREEDING DISPERSAL AND DRIFT-NET MORTALITY OF ENDANGERED JAPANESE MURRELETS JOHN F. PIATTx AND PATRICKJ. GOULD2 •AlaskaFish and WildlifeResearch Center, National Biological Service; and 2MigratoryBird Management, U.S. Fish and WildlifeService, 1011E. TudorRoad, Anchorage, Alaska 99503, USA ASSTRACT.--Theincidental catch of seabirdsin high-seasdrift nets was recordedin 1990- 1991 by scientificobservers on commercialsquid and large-meshfishery vesselsoperating in the North Pacific Transitional Zone. Twenty-six Synthliboramphusmurrelet deaths were recorded in the months of August through December.All but one were from the Korean squid fishery in a small area bounded by 38ø-44øNand 142ø-157øE.Five specimensof the dead birds were collected and later identified as JapaneseMurrelets (S. wumizusume).As fishing effort was widely distributedover a large area eastof Japan,these data suggestthat postbreedingJapanese Murrelets migrate north to winter in a relatively small area southeast of Hokkaido, where persistenteddies form at the confluenceof the Oyashioand Kuroshio currents.Fronts between cold Oyashiowater and Kuroshiowarm-core eddies promote the aggregationof zooplankton and pelagic fishes,which in turn may attract murrelets during the nonbreedingseason. The estimatedtotal mortality of JapaneseMurrelets in high-seas drift-net fisheriesrepresents a significantproportion of the total world populationof this rare and endangeredspecies. Received 12 October1992, accepted 4 April 1993. TrtE J•PAN•E (CR•ST•D)MVRR•t,•T (Synthli- apparentlywere killed by introducedrats (Tak- boramphuswumizusume) is the rarest member of eishi 1987, Ono 1993). The estimated total mor- the Alcidae,and its populationsare seriously talitywas 414 birds,and few breedingmurrelets threatened (Collar and Andrew 1988, Gaston are presently found in what was once a very 1992, Oho 1993, Springer et al. 1993). Along largecolony. The frequencyof carcasseson oth- with the endangeredShort-tailed Albatross (Di- er islands (Higuchi 1979) suggeststhat preda- omedeaalbatrus), Japanese Murrelets have been tion of adults is a widespreadproblem. In the declareda National Monumentin Japan(Has- Izu islands, increasing human trash has pro- egawa1984). Little is known of their population motedgrowth in populationsof the JungleCrow status,but numbersappear to be declining(Bra- (Corvusmacrorhynchos), a common predator of zil 1991,Ono 1993).Hasegawa (1984) estimated murrelet eggs (M. Ueta pets. comm.). Human 1,650 birds from colony counts and observa- visitation and the ensuing destructionof eggs tions at sea.Higuchi (1979) and Ono (1993) re- and nest sites also appearsto be an increasing portedconfirmed records of breedingon e'•ght problem at severalcolonies (Higuchi 1979,Bra- islandsor island groups,and at least 19 breed- zil 1991, Oho 1993). ing locationsare presentlyknown or suspected Away from their colonies,Japanese Murrelets (Fig. 1). The largestcolonies were found at Biro are potentially threatenedby oil pollution and Island(2,000 in 1992),Kozu Island(600 in 1991), gill nets(Kazama 1971,DeGange and Day 1991, Mimiana Island (150-200 birds in 1979), and DeGangeet al. 1993).The adverseeffect of these Koya Island (408 birds in 1974, 282 in 1976, 30 mortality factorsmay be underestimated,how- in 1991) [see below]). It is unlikely that all ever, becauseof the difficulty in distinguishing breeding colonieshave been located;however, JapaneseMurrelets from their closely related it is alsounlikely that a large colonyremains congener, the Ancient Murrelet (S. antiquus). to be discovered(Oho 1993).A recent compi- Outside of the breeding season,when Japanese lationof availabledata (Oho 1993)suggests that Murreletspossess distinctive plumes at the back fewerthan 4,000 Japanese Murrelets exist today. of the crown, they differ from Ancient Mur- Disturbance, habitat destruction and intro- relets only in having lesswhite on the sidesof ducedpredators are seriousproblems at many the neckand a slightlylonger bill (Gaston1992). colonysites (Brazil 1991,Springer et al. 1993). JapaneseMurrelets breed only in warm-wa- In 1987, the remains of 145 individual murrelets ter areas of southern Japan (Fig. 1) and tend to were found on Koya Island, where the birds remain closeto their coloniesin the breeding 953 954 PIATT•ND GOULD [Auk,Vol. 111 season(Brazil 1991, Ono 1993). In general, the We extrapolatedthe total number of murreletskilled postbreedingdispersal of JapaneseMurrelets is from numbers observedin nets using a simple ratio poorly known. Postbreedingbirds from the Izu estimate (Cochran 1963). In extrapolating total by- Islandsmay move northward becauseJapanese catch,we used only fishing effort and observations Murrelets are regularly observed off northern in an area bounded by 36ø-45øNand 141ø-147øE(Fig. 1). This limit is based on the approximaterange of Honshu, and rarely off Hokkaido (Kuroda 1955, murrelet bycatch near Japan (Fig. 1). We excluded Brazil 1991).Vagrants have been reportedas far much of the large eastern drift-net fishing area (Fig. north as Sakhalin and the Kuril Islands (Brazil 1) to avoid overestimatingthe bycatchof murrelets. 1991). Ancient Murrelets are abundant and We assumedthat the five murrelets caught between widespread throughout boreal and subarctic 152ø-157øEwere Ancient Murrelets (see Results). Five waters of the North Pacific (Gaston 1992, different drift-net fisheries were monitored during Springer et al. 1993). A few hundred Ancient 1990and 1991,mostly in an area (Fig. 1) bounded by Murrelets may breed around Hokkaido (Brazil 31ø-46øN and 151øW-141øE. 1991, Gaston 1992), and perhaps a thousand 1. Japanesesquid fishery.--The Japanesehigh-seas squid drift-net fishery generally operatesbetween breed along the coastsof mainland China and 170øE-145øWand 35ø-46øNwith designatedtime and Korea (Gaston 1992). Ancient Murrelets are area closuresnorth of 40øN and excluding the U.S. common winter visitors to coastal and offshore 200-mile (320-km) fishery conservationzones. The watersof Japan,particularly in the Seaof Japan fishing seasonlasts from Junethrough December.Ca- (Brazil 1991). nadian, Japanese,and U.S. scientificobservers mon- Concern about the incidental catch of marine itored 114,095km of Japanesesquid drift nets in 1990 organismsin high-seasdrift nets led to an in- and 103,198 km in 1991. ternationaleffort to monitor five major fisheries 2. Japaneselarge-mesh fishery.--Most Japanese large- in the North Pacific:Japanese squid and large- mesh drift-net fishing occursbetween 175øE-145øW mesh drift-net fisheries;Korean squid drift-net and 24ø-41øN, and between 141ø-175øE and 24ø-43øN. fishery; and Taiwanese squid and large-mesh As in the squid fishery,there are designatedtime and area closures.This fishery operatesthroughout the drift-net fisheries (Canadian Department of year but peaks in the winter. Japaneseand U.S. ob- Fisheries and Oceans 1991, International North serversmonitored 25,668 km of Japaneselarge-mesh Pacific Fisheries Commission [INPFC] 1992a). drift-nets set in the North Pacific from September We report here on the bycatch of Synthlibor- 1990 through May 1991. amphusmurrelets in these five drift-net fisher- 3. Taiwanesesquid fishery.--The major Taiwanese ies, and documentthe first confirmedbycatch squid fishing groundsare between 155øE-165øWand of JapaneseMurrelets in drift nets. We assess 38'-44øN.Some fishing, however, occurs south to 33øN, the potential impact of this bycatch on popu- north to 45øN, west to 143øE and east to 146øW. West lations, and considerthe geographicdistribu- of 170øE,fishing is prohibited north of 39øN. Time and area restrictions, and closed areas are similar to tion of bycatchrecords as it relatesto postbreed- those for the Japanesefleet. Squid fishing extends ing dispersalbehavior and regional oceanog- from May through December. Taiwanese and U.S. raphy. observersmonitored 8,521 km of squid drift nets in 1990 and 8,036 km in 1991. METHODS AND STUDY AREAS 4. Taiwaneselarge-mesh fishery.--The Taiwanese large-mesh fishery operatesmostly in the area be- Scientific observerswere placed aboard high-seas tween 144*E-154øWand 30ø-440N.Fishing occursfrom fishingvessels from Japan,the Republicof Korea,and May through December. Time and area restrictions Taiwan (the Republicof China). Observersrecorded are similar to thosefor the Japanesefleet. Taiwanese the incidental catch of marine birds in drift nets and and U.S. observersmonitored 9,748 km of large-mesh retrieved voucherspecimens for assessingthe impact drift nets in 1990 and 11,876 km in 1991. of these fisherieson marine bird populations(Anon- 5. Republicof Koreasquid fishery.--The Korean squid ymous199 la, b, 1992a,b, Fitzgeraldet al. 1992,INPFC fishing grounds are between 1410E-150owand 30ø- 1991, 1992a, b, c). 46øN.The seasonextends from April'throughDecem- Five specimensof unidentifiedmurrelets were sal- ber. In April and May, fishing is mostlyin the south- vaged in 1990 and 1991 and sent to the Burke Mu- easternpart of this area and moves to the northeast seum,University of Washington,Seattle. Subsequent- in early summer(June-July). In Augustsome fishing ly, they were identified as JapaneseMurrelets. The shifts to western areasand, from Septemberthrough specimenswere preparedfor the museumcollection, December,all fishing occurswest of 170øE.Korean stomachcontents were preserved,and condition of and U.S. observers monitored 33,483 km of Korean the gonads,bursa, and body fat were recorded. squid drift nets in 1990 and 21,126 km in 1991. October1994]
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