Lacroix et al.: ��Su�rf �S��co��te�rs �in �������associa�t��ion �w�i�th ��epheme������ra��lly �a��bund��a���nt �p�o�ly����cha���etes ��61 SURF SCOTERS MELANITTA PERSPICILLATA AGGREGATE IN ASSOCIATION WITH EPHEMERALLY ABUNDANT POLYCHAETES
DEBORAH LISE LACROIX1, SEAN BOYD2, DAN ESLER1, MOLLY KIRK1, TYLER LEWIS1 & SANDY LIPOVSKY3
1 Centre for Wildlife Ecology, Simon Fraser University, Burnaby, British Columbia, V5A 1S6, Canada ([email protected]) 2 Pacific Wildlife Research Centre, 5421 Robertson Road, Canadian Wildlife Service, Delta, British Columbia, V4K 3N2, Canada 3 Columbia Science, PO Box 1001, Royston, British Columbia, V0R 2V0, Canada
Received 14 December 2004, accepted 31 May 2005
Sur �coters Melanitta perspicillata ��� a �arg� �art o ��ir Baynes Sound is characterized by extensive, low gradient, intertidal annual cycle in marine waters, foraging in intertidal and shallow mud a� a� �ats (BC MSRM 2002). ��r �coters and White- subtidal areas (Savard et al. 1998). They winter in large numbers wing�� �coters Melanitta fusca are one o �� �ost abundant in coastal British Columbia, oraging �rimarily o �ivalves, marine birds in the area, where they feed mostly on intertidal clams particularly mussels in rocky habitats and clams in sandy or muddy (Bourne 1984, Dawe et al. 1998, T. Lewis unpubl. data). As part of habitats (Vermeer �981, Vermeer & Bour� �984, Bour� �984, our research protocol, we conducted bird surveys, radio-telemetry, Lacroix 2001). and behavioural observations.
As i �� ca� �i� �any other �a ��cks, �� abundance and During the week of 16–23 April 2003, we observed an unusually distribution of Surf Scoters are influenced by variation and changes large aggregation o �a ��cks and a Gray Whale Eschrichtius in prey density and distribution (Guillemette & Himmelman 1996, robustus oraging at Mapleguard Point, �ocated i �� outhern Hamilton 2000, Larsen & Guillemette 2000). ��r �coter ave portion of Baynes Sound, after which the site was abandoned. The been shown to respond to ephemerally superabundant food sources flock consi��� �rimarily o ��r �coter �i� �aller ����rs (Vermeer �981) �articular� �rring �awn (Munro & Clemens of White-wing�� �coters, Long-tailed Ducks Clangula hyemalis, 1931, Hay et al. �989, Campbell et al. �990, Haeg��� �993). In and Greater �caup Aythya marila. W� ��imated approximately British Columbia, Pacific Herring Clupea harengus pallasi spawn 5000 Surf Scoters in the dense flock within a 46 ha intertidal area. in the intertidal and shallow subtidal zones in late winter and early This was the largest number of Surf Scoters counted at this site, as spring (Grosse & Ha �988). Onc� ���osited, �rring �ggs are well as in all of Baynes Sound (intertidal area = 1500 ha) during pr��� or approxima��� ��o ���k ��or� atching (Haegele 2002/2003 (Fig. 1). & Schweigert 1985). Scoters and other marine birds feast on the eggs during this period (Vermeer 1981, Rodway et al. 2003). As The aggregative response at Mapleguard Point also was illustrated Harlequin Ducks Histrionicus histrionicus �o, coters generally by individually radio-tagg�� coters. O �� April 2003, �ven of abandon their core winter foraging locations and move to spawning 15 radio-tagged scoters still remaining in the Baynes Sound study sites to consume this abundant and energy-rich food (Rodway et al. 2003, D. Esler & S. Boyd unpubl. data). Legend Mapleguard Point 02-03 6000 Baynes Sound 02-03 In additio �o responding �o �redicta��� ���rabunda� ood Baynes Sound 03-04 sources, �a ��ck av� ��� observed congregating �o orage 5000 on a ov�� oo� ource. For �xample, �arg� �ocks o �a ��cks Number a� �iving ��ck av� �odifi�� ��ir �igration a� �istribution 4000 patter �o ��� o �� introduced and abundant Zebra Mussel Herring spawn hatching period Dreissena polymorpha in Canada (Wormington & Leac �992, 3000 Petrie & Knapto �999, Mitchell et al. 2000), Uni��� ��ates of Surf (Mitchell & Carlson 1993) and Europe (Pedroli 1981, Suter 1982, 2000 Burla & Ribi 1998). Lesser Scaup Aythya affinis in San Francisco Scoters Ba av� �odifi�� ��ir �iets a� ��avior �o consume almost 1000 exclusiv�� �� �rolific introduced Asian Clam Potamocorbula 500 amurensis (Poulton et al. 2002; J.Y. Takekawa, �.E. Wainwright- 400 Herring spawn egg deposition De La Cruz & A.K. Miles unpubl. data). Additionally, Frengen and 300 Thingstad (2002) found aggregations of Common Eiders Somateria 200 mollissima opportunistica�� oraging on a �ass aggregation of 100 sandeels (Ammodytes ��.). I �� �ring of 2003, �� observed 0 Sur �coter �xhibiting a �rong �istributional a� ���rical Oct-02 Nov-02 Dec-02 Jan-03 Feb-03 Mar-03 Apr-03 response to a novel, ephemerally superabundant food source in our Date study area. Fig. 1. ��r �coter Melanitta perspicillata abundance at Mapleguard Point and in Baynes Sound between November 2002 Fro� all 200� ��i� �ring 2004, �� conduc��� �xtensiv� ield and April 2003. The thick band represents the period during which studies investigating �� �intering �cology o coters in Baynes Pacific herring spawned, and the thin line indicates the period when Sound, o �� �ast coast of Vancouver Island, British Columbia. herring roe was present.
Marine Ornithology 33: 61–63 (2005) 62 Lacroix et al.: ��Su�rf �S��co��te�rs �in �������associa�t��ion �w�i�th ��epheme������ra��lly �a��bund��a���nt �p�o�ly����cha���etes
area (three Surf Scoters; four White-winged Scoters) were in the The presence of a feeding Gray Whale at Mapleguard Spit further foraging flock off Mapleguard Point. This was the largest number highlig� �� �iq�� ature o �i �vent. These cetaceans are of radioed scoters recorded at Mapleguard Point during the entire rarely found in the area (J. Ford pers. comm.). From 1972 to 2004, 2002/2003 field season (Fig. 2). this is the first recorded Gray Whale sighting in Baynes Sound out of a �otal o �309 recor��� ightings in all of British Columbia During the winter period (20 December 2002 – 15 February 2003), (VAMSC & FOC 2004). T�� �ales are kno� �o orage on an average of 40 radio�� coters (n = �5) ��r� ����cted i �� polychaetes (Darling et al. 1998). study area every week. Once the herring spawn commenced in the northern Strait of Georgia, the number of radioed scoters located Ophryotrocha ��cies are interstitial inhabitants of organically i �� ��� area �ro���� �o an average o ine individua� ��r enriched and anthropogenica�� �istur��� ��iments (Sella & week as the scoters moved out of the area to the largest traditional Ramella �999, Dahlgren et al. 2001, Brooks et al. 2003). ��veral spawning grounds (Hay & McCarter 2004). During the spawning species of Ophryotrocha produce a net of mucous-lined tubes where period (after 16 February 2003), an average of 19 radioed scoters �� ind conspecifics, a� �ate a� �roo� ��ir oung (Sella & were found out of the study area foraging on the most profitable Ramella 1999). They converge in areas where mucous trails meet, spawning grounds (Rusch 2003). The genera� �attern o coters generating a clumped distribution (Sella & Ramella 1999). moving out of the study area during the spawning period was also observed in the bird survey data from 2003 and 2004 (Fig. 1). Mapleguard Point is not considered a polluted or disturbed area. It has only a small marina nearby and low amounts of marine traffic. T� ��r �coters at Mapleguard Poi� ��re observ�� �imming We speculate that the relatively untouched herring spawn deposited clo� �o ore i ��� aggregations a� �iving chronously. on algae as it decomposed created an organically rich environment These foraging behaviors are not typically seen in Baynes Sound, conduciv� �o an Ophryotrocha aggregation. Teztlin et al. (1997) where scoters feed primarily on clams, a more patchily distributed discovered a ��cies of Ophryotrocha colonizing and inhabiting resource (Gillespie 2000, Gillespie et al. 2004, T. Lewi �����. aggregations of decaying kelp fronds in the White Sea. data), and do not normally dive synchronously. Our observations clear� �gg�� �a� oraging coter owed a We first suspected that the scoters were feeding on herring spawn. strong distributional and numerical response to the Ophryotrocha However, on 21 April, a cuba �iver a� �� ite observed a �arge species. The scoter flock at Mapleguard Point likely consisted of continuous gelatino� �atrix �������� �i� �illions o �all both wintering residents and migrants; a radioed Surf Scoter that polychaetes and collec��� amples. Thi ���ic �atrix �as wintered in San Francisco Bay was detected in the aggregation on surrounded by loose decaying algae. No herring roe was observed. 15 April 2003. T� �ack o �rring �ggs i �rther ���or��� � �rring �awn dive and aerial surveys conducted for Fisheries and Oceans Canada We ar� �aware of any other record o coters aggregating or 12–23 March. Those surveys found that Pacific Herring spawned foraging o �����rally abunda� �olychaetes. This observation at Mapleguard Poi� ������ �� a� �9 March 2003 (Rusch is another �xample o �� ability o ��r �coters and other �a 2003). By 11 April, the herring eggs would have hatched given the ducks to locate and capitalize on ephemeral food sources, whether average two-week period between deposition and hatch (Haegele predictable or not. & Schweigert 1985). Samples of the polychaetes were taken to a taxonomist and were identified to the genus Ophryotrocha. ACKNOWLEDGEMENTS
We thank Scott Wallace for diving and collecting the polychaete 8 samples. We also thank Jake Schweigert from Fisheries and Oceans
Number of radioed-scooters at Canada for providing 2003 herring spawn data for Baynes Sound. Both M.R. Petersen and an anonymous reviewer �a�� �veral 6 valuable comments and suggestions that improved the manuscript. Mapleguard Point
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Marine Ornithology 33: 61–63 (2005) A portion of the feeding flock of Surf Scoter Melanitta perspicillata (with scattered Greater Scaup Aythya marila) foraging on polychaetes at Mapleguard Spit, British Columbia (photo Molly Kirk)