Toward Salt Marsh Harvest Mouse Recovery: Research Priorities

Author(s): Smith, Katherine R.; Riley, Melissa K.; Barthman–Thompson, Laureen; Statham, Mark J.; Estrella, Sarah; Kelt, Douglas | Abstract: [Abstracts are not presented for essays. -The SFEWS Editors.]


Potential Effects of Climate Change and Associated
Sea Level Rise. Understanding this threat and how it will affect recovery measures (e.g., tidal restoration) should be, at the least, an ancillary component underlying all research moving forward.

Priority Needs
a. When possible, research projects should be designed to explicitly investigate how the threat of climate change intersects with other threats, and how it affects SMHM biology. Climate change should be a consideration in all recommendations below.
i. Recovery Action 4.4.7 Study the effects of global climate change and resulting sea level rise on tidal marsh ecosystems (page 325).

Range-Wide Population Demographics and
Dynamics. Lack of population and demographic data for SMHM hinder efforts to identify areas of conservation concern or to understand how natural or anthropogenic changes (including habitat loss and restoration) affect population health. VOLUME 16, ISSUE 2, ARTICLE 1 Strategically allocating these in key habitats (e.g., managed, tidal, and restored wetlands) would facilitate prioritizing habitat for acquisition and enhancement. Researchers should collaborate to determine densities, carrying capacities, and population viabilities for various habitat types over both short (ca. 5 years) and longer (ca. 50 years) time-periods (USFWS 2010). Such data are essential for population-viability analyses (suggested by USFWS 2013), and crucial for conservation planning in the light of the large shifts in habitat anticipated to be a result of climate change and sea-level rise (Takekawa et al. 2013;Thorne et al. 2018).
Understanding metapopulation dynamics should help to identify characteristics of habitats that serve as demographic sources and sinks, allowing managers to prioritize the former in regional planning. Data on dispersal and colonization are important criteria in site selection for enhancement activities, and in predicting if populations can populate uninhabited patches (e.g., newly created wetlands) or whether assisted colonization will be necessary.

Priority Needs
a. Determine the realized geographic range of the species (and both sub-species) through comprehensive censuses. 3. Range-Wide Genetics. Further characterize the genetic structure of SMHM throughout the estuary, but in particular in the south San Francisco Bay where populations are smallest and habitat is most at risk. Losing even very small populations could mean losing unique and rare genetic lineages permanently.
Understanding SMHM population genetics is critical to both long-term management and prioritization of areas for conservation action (Goals Project 1999;USFWS 2013). Trapping and genetic sampling throughout the potential range of the species would allow validation of species occurrence, especially in isolated and peripheral habitat patches. Such work is essential to delineate the geographic extent of the sub-species, identify distinct populations, and improve understanding of how genetic diversity may influence the effectiveness of conservation measures such as tidal restoration.

Priority Needs
a. Genetic delineation of sub-species boundaries.
i. Recovery Action 4.3.4 Conduct research to resolve taxonomic uncertainties regarding SMHM (page 323).
b. Genetic characterization of relationships among populations, effectively using genetic markers to document demographic parameters such as extent of dispersal, barriers to dispersal, source-sink dynamics, and metapopulation structure (Peery et al. 2008 4. Response to Habitat Restoration. Virtually no data exist on the effects of restoration activities (e.g., levee removal and subsequent flooding) or the secondary effects of habitat alteration (e.g., development of tidal wetlands). A better understanding of SMMH habitat requirements and dispersal dynamics is vital to acquiring and enhancing suitable habitat in the future.
We suggest managers thoroughly investigate SMHM habitat preference and use in restored wetlands, even if pre-restoration data are lacking.

Priority Needs
a. Characterize the direct effects (e.g., altered survival or reproductive success) of restoration activities such as use of heavy equipment in currently occupied habitat, to minimize negative effects on SMHM during active restoration.
b. Characterize the secondary effects of largescale shifts in habitat after restoration activities (e.g., changes in SMHM population densities).
i. Recovery Action 4.4.1 Conduct studies on the efficacy of various habitat restoration techniques for SMHM (page 324).
c. Determine factors that may influence the colonization of newly-created, potentiallyisolated, habitat patches (e.g., typical dispersal distance, minimum viable patch size).
i. Recovery Action 4.4.5 Study the time lag between habitat restoration and recolonization by SMHM (page 325).
5. Environmental Contamination. The risk of SMHM population failure from chemical contaminationeither chronic (e.g., methylmercury) or acute (e.g., oil spill)-calls for a comprehensive assessment (USFWS 2013 Lacking baseline knowledge of predation pressure on SMHM, it will be difficult to interpret and respond to changes in predation through processes such as sea-level rise and tidal restoration (e.g., altering the availability and configuration of habitat) or urban encroachment (influencing the composition of predator fauna). The application of "molecular scatology" (see Symondson and Harwood 2014) would be optimal, but this assumes molecular barcodes are available for the forage species of interest. As an alternative, we suggest that researchers who perform routine monitoring include standardized observations of predators and predator sign in relation to habitat type and configuration. These data may be most useful to managers designing tidal restorations, especially near urban environments where human-associated predators, such as cats (Felis catus), are common.
We recommend that researchers be vigilant for indications of harmful disease outbreak, and identify and implement research needs should they arise, especially near urban areas where SMHM are more exposed to sources of disease, such as domestic pets and sewage. ii. Recovery Action 4.2.7.3 Study the impact of Spartina alterniflora and its hybrids, and Lepidium latifolium on SMHM (page 322).

Improved Collaboration and Meta-Analyses.
Collaboration and integration of parallel data sets across multiple sites-with the ultimate objective of strengthening quantitative estimates of key parameters while better understanding how local context influences SMHM biology-is essential.
The pursuit of meta-analyses across replicate sites is a critical need (e.g., Beston 2011;Koricheva et al. 2013). Current regulations mandate similar sampling efforts at a number of sites throughout the estuary, and the 2013 Recovery Plan recommends a research coordinator position to maximize the effect of potential collaborations (USFWS 2013). Non-standardized field methods have limited earlier efforts by members of the ad-hoc inter-agency SMHM Working Group to pursue integrative analyses, so standardized field methods are needed. Such coordinated efforts would support all the recovery actions listed above, as well as the following: The SMHM continues to need protection from both historic and contemporary threats. Management and conservation of SMHM in the face of emerging threats (e.g., climate change and associated sea-level rise, which "likely imperils [SMHM] and the resources necessary for its survival," USFWS 2010:27), will require continued investment in basic and applied research to help managers detect responses to largescale restoration and climate change-and implement necessary management actions. We encourage researchers to consider climate change when they design field efforts, thereby providing further insight on how SMHM may be affected.
Though coordination has been improved recently through the SMHM Working Group, we believe the greatest impediments to conservation of the SMHM are the lack of dedicated personnel and funding.
To this end, we propose creation of an independent program coordinator position to prioritize and facilitate centralized and sustained research funding toward commonly agreed-upon objectives among researchers and management agencies. This position would support complementary and managementdriven research, standardization of methods, and integration of collaborative efforts. This position, likely funded jointly by key regulatory agencies, would require programmatic autonomy and should interface closely with the SMHM Working Group. The research needs highlighted in Smith et al. (this issue) and the recommendations herein provide a foundation from which such efforts can be developed.
Our intent has been to identify key threats and associated research and management needs that will improve the chances of SMHM recovery throughout its range. We encourage researchers and managers to revisit such an effort regularly, with 5-to 10-year updates to ensure applied research remains appropriately targeted at priority research needs.