U.S. Pacific Marine Mammal Stock Assessments

Under the 1994 amendments to the Marine Mammal Protection Act, the National Marine Fisheries Service (NMFS) and the U.S. Fish and Wildlife Service (USFWS) were required to produce stock assessment reports for all marine mammal stocks in waters within the U.S. Exclusive Economic Zone. This document contains the stock assessment reports for the U.S. Pacific marine mammal stocks under NMFS jurisdiction. Marine mammal species which are under the management jurisdiction of the USFWS are not included in this report. A separate report containing background, guidelines for preparation, and .a summary of all stock assessment reports is available from the NMFS Office of Protected Resources. This report was prepared by staff of the Southwest Fisheries Science Center, NMFS and the Alaska Fisheries Science Center, NMFS. The information presented here was compiled primarily from published sources, but additional unpublished information was included where it contributed to the assessments. The authors wish to thanks the members of the Pacific Scientific Review Group for their valuable contributions and constructive criticism: Hannah Bernard, Robin Brown, Mark Fraker, Doyle Hanan, John Heyning, Steve Jeffries, Katherine Ralls, Michael Scott, and Terry Wright. Their comments greatly improved the quality of these reports, We also thanks the Marine Mammal Commission, The Humane Society of the United States, The Marine Mammal Center, The Center for Marine Conservation, and Friends of the Sea Otter for their careful reviews and thoughtful comments. Special thanks to Paul Wade of the Office of Protected Resources for his exhaustive review and comments, which greatly enhanced the consistency and technical quality of the reports. Any ommissions or errors are the sole responsibility of the authors. This is a working document and individual stock assessment reports will be updated as new information becomes available and as changes to marine mammal stocks and fisheries occur; therefore, each stock assessment report is intended to be a stand alone document. The authors solicit any new information or comments which would improve future stock assessment reports. This is Southwest Fisheries Science Center Technical Memorandum NOAA-TM-NMFS-SWFSC- 219, July 1995. 111

The Chromosomal Complement of the Yellow-Cheeked Vole

The karyotype of Microtus xanthognathus (Leach) is described, based on material from one female and one male vole. The diploid chromosomal number was found to be 54, and the fundamental number 62. The metacentric X-chromosome was of medium size and averaged 6.6% of the haploid complement. The designated Y-chromosome was near acrocentric. The specific distinction of M. xanthognathus and Microtus chrotorrhinus (Miller) was confirmed by the recognition of major differences in karyotype and differences in fundamental number. The distributional history of M. xanthognathus is briefly discussed.

Observations on Chromosomes of Dicrostonyx torquatus stevensoni Nelson and Chromosomal Diversity in Varying Lemmings = Untersuchungen an den Chromosomen von Dicrostonyx torquatus stevensoni Nelson und chromosomale Unterschiede bei Halsbandlemmingen

English abstract: The cytogenetic characteristics of the varying lemming, Dicrostonyx torquatus stevensoni, (2n = 34), were investigated, and diploid chromosomal numbers were reported for four other nominal subspecies (exsul, nelsoni, richardsoni, and rubricatus) of the torquatus-group in North America. The diploid complements ranged from 30 to 44 chromosomes, and the fundamental number from 50 to 55. Chromosomal polymorphism was observed in all forms. In cross-breeding experiments, the mating of F1 progeny was not productive. The findings support the zoogeographic concept that populations of Dicrostonyx became fragmented or displaced southward during Würm time, with relict stocks persisting in unglaciated refugia or periglacial tundra. Speciation in the isolates led to chromosomal evolution, with the result that populations spreading from refugia in post-glacial time are reproductively isolated. The torquatus-group in North America appears to be a superspecies. German title: Untersuchungen an den Chromosomen von Dicrostonyx torquatus stevensoni Nelson und chromosomale Unterschiede bei Halsbandlemmingen German abstract: Die cytogenetischen Merkmale des Halsbandlemmings, Dicrostonyx torquatus stevensoni, (2n = 34) wurden eingehend untersucht, und für vier andere nordamerikanische Unterarten der torquatus-Gruppe wurden die somatischen Chromosomensätze festgestellt. Die Chromosomenzahl der untersuchten Populationen schwankte zwischen 30 und 44, der NF (Nombre Fondamental) zwischen 50 und 55. Zuchttiere der verschiedenen Populationen wurden erfolgreich gekreuzt, aber Sterilität der F1 Unterartbastarde war typisch. Die Halsbandlemminge wiesen Karyotypenverschiedenheiten auf, die sich durch Variationen des Robertsonschen Typus, Deletionen oder möglicherweise durch perizentrische Inversionen erklären. Die Ergebnisse sprechen dafür, daß das ursprüngliche Verbreitungsgebiet von Dicrostonyx in Nordamerika durch die letzte (Würm) Vereisung getrennt wurde, und daß die Reliktpopulationen die letzte Glazial-Phase in eisfreien Refugien oder in periglazialer Tundra überlebten, wo Karyotypevolution durch lokale Anpassungsbedürfnisse gefördert wurde. Die in der Postglazialzeit aus den Refugien sich verbreitenden Populationen von Dicrostonyx scheinen reproduktiv isoliert zu sein. Die torquatus-Gruppe in Nordamerika gilt also als Superspecies.

Heligmosomoides johnsoni sp. nov. (Nematoda: Heligmosomatidae) from the Heather Vole, Phenacomys intermedius Merriam

Heligmosomoides johnsoni sp. noy. is described from the cecum of the heather vole, Phenacomys intermedius Merriam, from the Olympic Mountains, Washington. The absence of longitudinal cuticular ridges dorsally separates H. johnsoni from species of Heligmosomoides other than H. hudsoni (Cameron, 1937), which occurs in varying lemmings, Dicrostonyx spp., and from which H. johnsoni is distinguished by its longer spicules, form of the dorsal ray, and other characters. Both Phenacomys and Dicrostonyx have a specialized cecum, with long villi around which the nematodes are found tightly coiled. The zoogeography of heligmosomid nematodes in Phenacomys is briefly discussed. French abstract: On décrit Heligmosomoides johnsoni sp. nov. parasite du caecum du rongeur néarctique, Phenacomys intermedius Merriam, des Montagnes Olympiques de Washington. L'absence de crêtes cuticulaires sur la face dorsaIe sépare H. johnsoni des autres Heligmosomoides à I'exception d'H. hudsoni (Cameron, 1937) qui se trouve chez Dicrostonyx spp., et duquel H. johnsoni se distingue par ses spicules plus longs, par la forme différente de la côte dorsale et par d'autres caractères. Phenacomys et Dicrostonyx ont un caecum spécialisé, muni de villosités allongées, autour desquelles les nématodes s'enroulent étroitement. La zoogéographie des nematodes héligmosomes chez Phenacomys est discutée.