Record of the Kamchatka Flounder, Atheresthes evermanni, in California waters.
The Kamchatka Flounder was originally described by Jordan and Starks (1904) from a single specimen collected in Matsushima Bay, off northern Japan. Hubbs (1915) later reported on 11 additional specimens collected by the US Fish Commission Steamer Albatross between Matsushima Bay and Sakhalin Island, and discussed variation within the species. Norman (1934) stated, "I have been unable to compare these specimens [A. evermanni] with examples of A. stomias of similar size, but the two species may eventually prove to be identical." Until the mid-1980s, the validity of the 2 species of Atheresthes was uncertain, but Ranck and others (1986) provided genetic confirmation for the distinction of the 2 taxa, and Yang (1988) elaborated on morphological differences between the species, providing reliable field identification characters. There is little question now regarding the validity of these taxa; they are sibling species in the sense of Mayr (1963), and critical examination of specimens is necessary for accurate determination.
The currently recognized geographic range of A. evermanni is given as the Sea of Okhotsk and northern Sea of Japan to the Gulf of Anadyr, western and eastern Bering Sea, Aleutian Islands, and southwestern Gulf of Alaska (Love and others 2005). Allen and Smith (1988) listed A. evermanni as a "middle shelf-mesobenthal" species of the northern boreal Pacific, with a depth range of 25 to 1100 m. Wilimovsky and others (1967) examined specimens of Atheresthes from British Columbia but did not find A. evermanni from this area, and more recent studies (Ranck and others 1986; Yang 1988; Zimmermann and Goddard 1996) have not revealed the species south of Alaska. There are 3 recent collections of Kamchatka Flounder from the Gulf of Alaska in the University of Washington Fish Collection (UW 111528, 410 mm SL, off the Sanak Islands; UW 119477, 280 mm SL, near the Shumagin Islands; and UW 112900, 560 mm SL, off the Alexander Archipelago). The specimen reported here from off central California is the 1st record of A. evermanni south of the Alexander Archipelago and represents a range extension of approximately 2317 km (straight line; distance following contour of the land mass would be considerably greater) or 19 latitudinal degrees.
The characters that Yang (1988) found to be most reliable for separating A. stomias from A. evermanni are: (1) the upper eye position relative to dorsal profile of head (upper eye not noticeably extending beyond dorsal profile of head in A. evermanni [Fig. 1] versus upper eye extending beyond dorsal profile of head and visible from blind side in A. stomias); and (2) number of gill rakers on the 1st and 2nd branchial arches (A. evermanni: 1st gill arch 2-3+9-11, 2nd gill arch 1+6-9; A. stomias: 1st gill arch 3-5+9-11, 2nd gill arch 1-3+9-11). Counts, measurements, and diagnostic characters for the specimen of A. evermanni taken off California are as follows: 540 mm total length, 518 mm fork length, 455 mm standard length, 128.7 mm head length, 25.7 mm upper orbit width, 28.8 mm lower orbit width, 7.3 mm interorbital width, 73.2 mm maxilla length, dorsal-fin rays 112, and-fin rays 87, pectoral-fin rays (eyed side) 14, gill rakers (developed, eyed side) 1st arch 2+10, 2nd arch 1+8; and upper eye not noticeably visible from blind side. Due to the size of the California specimen, only the head and pectoral girdle were preserved and deposited in the Marine Vertebrate Collection of the Scripps Institution of Oceanography, SIO 96-72 (Fig. 1).
The addition of Atheresthes evermanni to the California marine ichthyofauna brings the number of pleuronectid flatfishes known from the state to 21 (Miller and Lea 1972; Lea and others 1989; Orr and Matarese 2000). The Davenport specimen represents a significant range extension of the Kamchatka Flounder south of the Gulf of Alaska. From a zoogeographic perspective, the likelihood that an unrecognized population of Kamchatka Flounder occurs off the west coast of North America south of the Gulf of Alaska would be remote. Oceanographic conditions in the eastern North Pacific including and prior to 1995 were normal or warm (since the E1 Nino of 1982-1984) with the exception of a cold-water La Nina event during 1991-1993 (Murphree and Reynolds 1995). The possibility exists that Kamchatka Flounder and other Western Boreal Pacific-Aleutian-Gulf of Alaska species (for example, Walleye Pollock, Gadus chalcogrammus; Skilfish, Erilepis zonifer; Bigmouth Sculpin, Hemitripterus bolini; and Roughscale Sole, Clidoderma asperrimum) have moved outside their normal range into more southerly latitudes under these cold-water conditions. An alternative and perhaps more plausible explanation is that Kamchatka Flounder occasionally occur off British Columbia and the west coast of the United States as expatriates and have been misidentified as the morphologically similar Arrowtooth Flounder.
Key words: Atheresthes evermanni, California flatfish record, Kamchatka Flounder
Acknowledgments.--I would like to thank S Melton who brought the Davenport flounder to my attention. MJ Allen, MS Busby, AC Matarese, and RH Rosenblatt provided comments relating to the manuscript. K Maslenikov discussed various aspects of the species including Alaskan records. D Kline aided with Figures. DE Stevenson provided editorial comments that substantially enhanced the manuscript.
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California Academy of Sciences, Department of Ichthyology, Golden Gate Park, 55 Music Concourse Drive, San Francisco, CA 94118 USA; rnlea@ comcast.net. Submitted 20 February 2013, accepted 28 April 2013. Corresponding Editor: James W Orr.
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|Author:||Lea, Robert N.|
|Publication:||Northwestern Naturalist: A Journal of Vertebrate Biology|
|Date:||Dec 22, 2013|
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