MARINE RESOURCES Commercial and recreational marine fisheries
Marine Mammal Research - Projects
Our research has been focused in three areas: (1) assessment of pinniped population status and trends; (2) description of pinniped food habits and foraging behaviors; and (3) examination of site-specific situations where locally abundant pinnipeds might have a negative impact on depleted fishery resources.
PINNIPED POPULATION STATUS AND TRENDS
Pinniped survey, Rogue Reef (offshore of Gold Beach), July 7, 2015
Nearly each spring and summer, we conduct aerial photographic surveys to document the distribution and abundance of pinnipeds in Oregon waters. Mean annual counts of non-pups (adults and sub-adults) ashore are used as an index of population size and the trend in the counts are evaluated using population growth models. The following summarizes the results of these surveys for the three most common pinnipeds in Oregon.
Pacific harbor seals.—The distribution and abundance of harbor seals in Oregon has been monitored since 1977. The statewide harbor seal population grew following protection under the Marine Mammal Protection Act of 1972 until stabilizing in the early 1990s. The estimated absolute abundance of harbor seals (all age classes) during the 2002 reproductive period was 10,087 individuals (95% confidence interval was 8,445 – 12,046 individuals).
Steller sea lions.—The distribution and abundance of Steller sea lions in Oregon has been monitored since 1976. Steller sea lion rookeries in Oregon are the largest and most important in U.S. waters south of Alaska. Counts from aerial surveys increased from about 1,500 animals in the mid-1970s to nearly 4,000 by the late 1990s. An exponential growth model fitted to these count data suggests an estimated annual rate of increase of 3.7%. Even though Oregon’s population is healthy, Steller sea lions are listed under the Endangered Species Act due to significant declines in abundance in western Alaska.
California sea lions.—The abundance of California sea lions in Oregon is difficult to assess since they do not breed here, nor is a consistent proportion of the population ashore at any predictable time. As a result reliable abundance trend surveys cannot be made in Oregon. However, during several recent winter surveys, we have counted 3,000-5,000 California sea lions in Oregon waters. During this same period a roughly equivalent number of sea lions may be to the north in the waters off Washington and British Columbia, Canada. These rough estimates would suggest that nearly 10,000 California sea lions may pass through Oregon coast waters each year from fall through spring.
PINNIPED FOOD HABITS
We have been researching the diet of pinnipeds in Oregon since 1990 through the analysis of scat (fecal) samples. Since these animals are coast wide piscivorous predators their food habits can give insight into the seasonal abundance, yearly variation and type of fishes found in coastal waters and estuaries. One example of this work is an analysis we conducted of Pacific harbor seal (Phoca vitulina) scat collected from 1997 – 2002 at the Alsea River in Waldport, Oregon. A total of 3,301 harbor seal scat samples were collected during the study period. Thirty-nine species of fish and cephalopods were identified based on comparative specimens collected from the Northeast Pacific. In cooperation with geneticists at Oregon State University, we have also employed DNA analysis to identify salmonid bones to the species and individual level. Most recently we aged Dover sole otoliths in order to examine the size and age distribution of fish that were consumed by seals.
SITE-SPECIFIC INTERACTIONS BETWEEN PINNIPEDS AND FISHERY RESOURCES
Coincident with recent increases in west coast pinniped populations has been a decline in many Pacific salmonid populations, several to the point of listing under the U.S. Endangered Species Act. While not generally believed to be the cause of the declines, pinniped predation has been identified as a potential factor that may exacerbate declines or impede recovery of depressed salmonid stocks. We have investigated the issue of pinniped predation on salmonids at several locations in Oregon, including the Alsea River (Waldport), Rogue River (Gold Beach), Willamette River (Willamette Falls, Oregon City), and the lower Columbia River (Astoria, Bonneville Dam). This work has included thousands of hours of direct observation of predation events, analysis of thousands of fecal samples, and tagging and monitoring foraging behaviors of hundreds of individual seals and sea lions.
TAGS AND MARKS
We, along with other researchers on the west coast, often tag and mark seals and sea lions for scientific study. Tags are generally small plastic cattle ear tags in a variety of colors. Seals are tagged on their hind flippers and sea lions are tagged on their fore flippers. Some seals and sea lions also carry other marks such as numbered patches, brands, and/or instruments such as acoustic, radio, or satellite transmitters. If you find (or see) a tagged or marked seal or sea lion please contact us. When doing so, please provide the following: date observed, location of the animal, tag color and number (if possible), patch color and number (if present), brand number and position on body (if present), a description of the animal and it’s condition (on beach, swimming etc), and a contact number so a researcher can get in touch with you for more information if necessary. If you are not confident in the reading of the entire brand a partial read is still useful to researchers. Photos of any brands, tags or marks are also very helpful.
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