Project: Anthropogenic and environmental influences on habitat use patterns and population dynamics of Pacific harbor seals in the San Francisco Bay, CA

Introduction:

My interests lie in the use of Geographic Information Systems (GIS) as a tool to help understand habitat selection by marine animals, in the use of telemetry in the study of marine animal behavior, and in the incorporation of data on anthropogenic impacts and animal behavior into GIS models. Use of a GIS can increase our understanding of what habitat is actually available to these animals, and help us to define “quality habitat” for a given species. I would like to incorporate behavioral and demographic data into a GIS in order to better understand how animals “select” and use their habitat. Use of a computer-based GIS can help us take into account the spatial and temporal variability that is part of any system, particularly marine, in our study and understanding of habitat use.

Purpose:

My study animals are Pacific harbor seals (Phoca vitulina richardii) in the urbanized San Francisco Bay (SFB) estuary, California, USA. There is some concern about the harbor seal population in SFB, as population numbers do not appear to be recovering (following the passage of the Marine Mammal Protection Act in 1972) as many coastal populations have. A number of possible reasons for slow rate of recovery have been suggested, including limited local food resources, habitat degradation and loss, disturbance, and negative health and reproductive impacts of pollutants present in SFB waters (Allen 1991, Kopec and Harvey 1995, Grigg et al. in press).

Methods:

The primary focus of my Ph.D. work will be:

~ gaining a better understanding of spatial and temporal habitat use patterns by seals in SFB and nearby coastal waters, taking an interdisciplinary and collaborative approach and incorporating a number of environmental datasets into a GIS, integrated with behavioral and distribution data collected by the seals survey; and

~ evaluating the role of humans in influencing seal movements and habitat use patterns in this heavily populated coastal/estuarine environment

Fig. 1. Harbor seal with dorsal mount satellite-linked tag

 

Data incorporated in the GIS and statistical analyses will include:

Location and dive-depth data from seals tagged with satellite-linked telemetry tags

Environmental data such as bathymetry, productivity and prey distribution, currents, bottom topography

Locations of haul-out (land-based) sites currently used by SFB seals, and data on intensity and timing of site use

Data on anthropogenic influences on seal habitat quality, such as primary sources of disturbance and pollutant hotspots.

Fig. 2. Harbor seals hauled out in SF Bay

As this study is in the early stages, data is still being collected and assembled. This work is an offshoot of a larger project monitoring harbor seals in SFB, under the leadership of Sarah Allen (Point Reyes National Seashore) and Hal Markowitz (San Francisco State University). We have been collecting data on distribution and behavior of SFB harbor seals since 1998, including extensive data on disturbance to seals in SFB and (since early 2001) telemetry data on seal movements and haul out site use.

 

Fig. 3. KHR* (here, use area during tag attachment) estimate for one adult male harbor seal, SFB, CA

Personnel:

Emma K. Grigg, M.A.

A. Peter Klimley, Ph.D.

Department of Wildlife, Fish, & Conservation Biology, University of California, Davis

Sarah G. Allen, Ph.D., National Park Service/Point Reyes National Seashore

Hal Markowitz, Ph.D., Department of Biology, San Francisco State University

Acknowledgements:

This work is a subset of an SFB-wide harbor seal monitoring project, the Richmond Bridge Harbor Seal Survey (RBHSS), which is fully funded by the California Department of Transportation (Caltrans). Thanks to Chuck Morton, Caltrans, for support throughout the seal monitoring work. We would like to acknowledge all the hard work of Debbie Green, project manager for RBHSS, and the RBHSS field biologists in collecting population and behavioral data on SFB harbor seals; thanks to Dr. Jim Harvey (Moss Landing Marine Labs) and his tagging team for help capturing harbor seals in SFB, and Dr. Frances Gulland and Denise Greig of The Marine Mammal Center in Sausalito, CA, for monitoring seal status during capture work. Sincere thanks also to all who have provided help and advice on tagging and data analysis questions, there are too many to list here but all their input is truly appreciated.

Literature Cited:

Allen, S.G. (1991) Harbor seal habitat restoration at Strawberry Spit, San Francisco Bay.
Report to the Marine Mammal Commission, Contract No. MM2910890-9, March 1991. 43 p.

Grigg, E.K., Allen, S.G., Green, D.E., Markowitz, H. (in press) Harbor seal (Phoca vitulina) population trends in the San Francisco Bay estuary, 1970-2002. California Fish and Game.

Kopec, A.D. and Harvey, J.T. (1995) Toxic pollutants, health indices, and population dynamics of harbor seals in San Francisco Bay, 1989-1992. Moss Landing Marine Laboratories Technical Report 96-4.
Moss Landing, CA. 168 p.