Waterfowl management and diet of the salt marsh harvest mouse

The salt marsh harvest mouse (Reithrodontomys raviventris) is an endangered species, endemic to the marshes of the San Francisco Bay, California, USA. This species is thought to feed primarily on pickleweed (Salicornia pacifica), although its diet is poorly understood, and a large proportion of remaining habitat for salt marsh harvest mice is managed for non-pickleweed vegetation to provide habitat for waterfowl. Using 2 sets of cafeteria trials, we tested food preferences of the salt marsh harvest mouse when offered a variety of plants and invertebrates from the Suisun Marsh, Solano County, California. In a set repeated menu, and unique seasonal menus, salt marsh harvest mice showed strong preferences for food types commonly grown for waterfowl, and also for non-native plants; in contrast, pickleweed was the most preferred during only some of the set and some of the seasonal trials. These results suggest that salt marsh harvest mice have a more flexible diet than previously thought, and will allow land managers in areas such as the Suisun Marsh to promote the growth of plants that provide foods that are preferred by both waterfowl and salt marsh harvest mice. © 2019 The Authors. The Journal of Wildlife Management published by Wiley Periodicals, Inc. on behalf of The Wildlife Society.     

Physical Evolution of Restored Breached Levee Salt Marshes in the San Francisco Bay Estuary

Since 1972 over 940 ha (2,300 ac) of leveed former salt marsh sites around San Francisco Bay have been restored to tidal action, purposely or through natural processes. The evolution of these sites can inform predictions of rates of marshplain evolution and establishment of tidal channel systems. A review of the history of 15 re‐flooded sites ranging in size from 18 to 220 ha (45 to 550 ac) and in age from 2 to 29 years indicates that marshplain vegetation with more than 50% cover was established at nine of the sites within 4 to 20 years. The remaining six sites aged 2 to approximately 20 years continue to be less than 50% vegetated. The evolution of these sites is consistent with the following simple conceptual model of the physical evolution of restored tidal marshes in subsided breached sites. Initially, deposition of estuarine sediment builds up mudflats that allow vegetation establishment once elevations are high enough for vegetation to survive. Sites that are initially lower in the tidal frame take longer to vegetate than those that are initially higher. Three factors appear to retard the time frame for vegetation establishment: limited estuarine suspended sediment supply, erosion of deposited estuarine muds by internally generated wind waves, and restricted tidal exchange. These factors affect evolution more significantly in larger sites. The comparatively short time frame for vegetation colonization and marshplain evolution experienced in earlier, smaller, and/or less subsided breached levee restorations may not necessarily be replicable by simple levee breaching on larger subsided restoration sites now being planned. Our review of the 15 sites also indicates that the formation of tidal channels within the marshes is greatly dependent on whether and how high the site was filled before breaching. Filled sites at high intertidal elevations (above approximately 0.3 m below mean higher high water) can vegetate quickly but after several decades may show little development of tidal channels.     

Avian communities in baylands and artificial salt evaporation ponds of the San Francisco Bay estuary

San Francisco Bay wetlands, seasonal and tidal marshes between the historic low and high tide lines, are now highly fragmented because of development during the past 150 years. Artificial salt pond systems in the Bay are hypersaline and typically support simple assemblages of algae and invertebrates. In order to establish the value of salt ponds for migratory waterbirds, we used datasets to conduct a meta-analysis of avian communities in the baylands and salt ponds of San Pablo Bay. Fifty-three species of waterbirds in the salt ponds represented six foraging guilds: surface feeders, shallow probers, deep probers, dabblers, diving benthivores and piscivores. The total number of species and the Shannon-Weiner diversity index was higher in baylands than in salt ponds during all four seasons. However, overall bird density (number/ha) was higher in salt ponds compared with baylands in the winter and spring, primarily because of large concentrations of benthivores. Cessation of salt production in 1993 and subsequent reduction in water depth resulted in a decline of some diving duck populations that used the salt ponds.     

Conservation genetics of the endangered San Francisco Bay endemic salt marsh harvest mouse (<Emphasis Type="Italic">Reithrodontomys raviventris</Emphasis>)

The salt marsh harvest mouse (SMHM, Reithrodontomys raviventris) is an endangered species endemic to the San Francisco Bay region of California, USA, where habitat loss and fragmentation over the past century have reduced the mouse’s distribution to <25 % of its historical range. To aid in conservation prioritization, we first investigated the possibility of hybridization with the morphologically similar western harvest mouse (WHM, R. megalotis) in areas of sympatry and developed genetic tools to differentiate the two species. We then investigated the phylogeography and genetic structure of the SMHM, including support for currently recognized SMHM subspecies designations. Lastly, we evaluated the morphological criteria currently used for the identification of species in the field. Analyses using mtDNA cytochrome b sequences and 11 microsatellites from 142 mice indicated complete and substantial separation of the SMHM and WHM, with no evidence of hybridization. These genetic markers as well as the mtDNA control region also identified a deep genetic division within the SMHM concordant with the current subspecies designations, R. r. raviventris and R. r. halicoetes. We identified the lowest genetic diversity within the southern subspecies, which inhabits a much reduced and highly fragmented portion of the species range. Morphological field identification of harvest mouse species was more successful at identifying SMHM (92 %) than WHM (44 %), with a large portion of WHM being incorrectly identified as SMHM. Field identification of harvest mouse species in the range of the southern SMHM subspecies was just above 50 %, indicating that current methods for morphological differentiation of species in that area are insufficient. Our confirmation of genetically distinct SMHM subspecies highlights the importance of determining the status and genetic composition of relict populations in the remaining patches of marshland in the central San Francisco Bay where the two subspecies may occur, as well as developing better tools for the discrimination of species, particularly in the range of the southern subspecies     

Food habits of harbor seals (Phoca vitulina richardii) as an indicator of invasive species in San Francisco Bay,California

The diet of harbor seals (Phoca vitulina richardii) in San Francisco Bay (SFB), California, was determined from July 2007 to July 2008 using prey hard parts recovered from 442 scats collected at five haul‐out sites. Twenty‐two species of fish and one species of crustacean were identified, but harbor seals primarily ate a nonnative invasive species, yellowfin goby (Acanthogobius flavimanus), which increased in dietary importance since the diet was last studied in 1991/1992. Additionally, another nonnative invasive fish species, chameleon goby (Tridentiger trigonocephalus), was found for the first time in the diet of harbor seals in SFB. Harbor seal diet was statistically different between years (1991/1992 and 2007/2008), between the pupping and nonpupping seasons, and between North SFB and South SFB haul‐out locations. The diet of harbor seals was significantly correlated with fish species caught in trawl surveys conducted by the California Department of Fish and Wildlife (CDFW) during the same time periods as this study (2007/2008). Harbor seals currently are influencing the health of the SFB ecosystem in a positive manner by consuming large quantities of nonnative invasive fish species.     

Following the rivers: historical reconstruction of California voles Microtus californicus (Rodentia: Cricetidae) in the deserts of eastern California

The California vole, Microtus californicus, restricted to habitat patches where water is available nearly year‐round, is a remnant of the mesic history of the southern Great Basin and Mojave deserts of eastern California. The history of voles in this region is a model for species‐edge population dynamics through periods of climatic change. We sampled voles from the eastern deserts of California and examined variation in the mitochondrial cytb gene, three nuclear intron regions, and across 12 nuclear microsatellite markers. Samples are allocated to two mitochondrial clades: one associated with southern California and the other with central and northern California. The limited mtDNA structure largely recovers the geographical distribution, replicated by both nuclear introns and microsatellites. The most remote population, Microtus californicus scirpensis at Tecopa near Death Valley, was the most distinct. This population shares microsatellite alleles with both mtDNA clades, and both its northern clade nuclear introns and southern clade mtDNA sequences support a hybrid origin for this endangered population. The overall patterns support two major invasions into the desert through an ancient system of riparian corridors along streams and lake margins during the latter part of the Pleistocene followed by local in situ divergence subsequent to late Pleistocene and Holocene drying events. Changes in current water resource use could easily remove California voles from parts of the desert landscape.     

Phylogeographic structure in long‐tailed voles (Rodentia: Arvicolinae) belies the complex Pleistocene history of isolation,divergence, and recolonization of Northwest North America's fauna

Quaternary climate fluctuations restructured biodiversity across North American high latitudes through repeated episodes of range contraction, population isolation and divergence, and subsequent expansion. Identifying how species responded to changing environmental conditions not only allows us to explore the mode and tempo of evolution in northern taxa, but also provides a basis for forecasting future biotic response across the highly variable topography of western North America. Using a multilocus approach under a Bayesian coalescent framework, we investigated the phylogeography of a wide‐ranging mammal, the long‐tailed vole, Microtus longicaudus. We focused on populations along the North Pacific Coast to refine our understanding of diversification by exploring the potentially compounding roles of multiple glacial refugia and more recent fragmentation of an extensive coastal archipelago. Through a combination of genetic data and species distribution models (SDMs), we found that historical climate variability influenced contemporary genetic structure, with multiple isolated locations of persistence (refugia) producing multiple divergent lineages (Beringian or northern, southeast Alaska or coastal, and southern or continental) during glacial advances. These vole lineages all occur along the North Pacific Coast where the confluence of numerous independent lineages in other species has produced overlapping zones of secondary contact, collectively a suture zone. Finally, we detected high levels of neoendemism due to complex island geography that developed in the last 10,000 years with the rising sea levels of the Holocene.     

Sixteen years later: Occurrence,group size,and habitat use of humpback dolphins (Sousa plumbea) in Algoa Bay,South Africa

Coastal dolphins are more prone to cumulative impacts of environmental and anthropogenic changes than pelagic species. However, few studies use historical comparisons to evaluate those impacts across a temporal scale. The study presented here describes the pattern of occurrence, group size, behavior, and habitat use of humpback dolphins in Algoa Bay and compares these to a similar study conducted in the early 1990s. Results indicate a considerable change in the frequency of occurrence. Furthermore, the mean group size has decreased from six to three individuals, mainly due to an increase in occurrence of solitary individuals (36.3% vs. 15.4%). Foraging, which was previously the predominant activity (64%), has now been replaced by traveling (49%). Moreover, dolphins showed a negative reaction towards a variety of watercrafts and swimmers. These observed differences could be due to a change in prey abundance, direct anthropogenic disturbance, and/or population decline. We emphasize the need for long‐term environmental and biological data series and long‐term monitoring of the demographics of this population to accurately assess any changes observed in future.