By Breyanna Waldsmith, Coastal Watershed Institute
Beavers are well known “ecosystem engineers”, meaning they alter their environment disproportionately to other organisms. These ecosystem modifications include the building of resident lodges, pool-forming dam systems, and foraging channels. While most think of the small mammalian rodent as a riverine or lacustrine (lake) critter, it is well known, but little understood that the North American beaver Castor canadensis resides in saline coastal ecosystems as well. To understand the beavers’ potentially critical interactions within coastal environments, we must look no further than our local Elwha nearshore.
A Bit of Background
Human interactions with beaver in coastal North America date back for centuries at a minimum.
Native tribes in the northern US and Canada utilized the beaver for meat, fashioned their teeth into tools such as chisels, and used fur as material for clothing. Eurasian citizens sought beavers for their prized furs, used principally in hat making—and ate both the flesh and the tail, which was considered a delicacy.
Castoreum was also highly prized by both cultures. Utilized for its medicinal use and as an additive in foods and perfumes (creating a ‘leathery’ or ‘vanilla’ smell), castoreum is what the beaver uses to scent-mark its territory. It is an oily substance excreted from their castor sacs, which are located near the anal gland. It is often secreted along with the animal’s urine. (Rue 2002) Today, you can even buy whiskey that is made with these secretions. (Tamworth Distilling) Yum!
By the end of the 15th century, the Eurasian beaver Castor fiber had been hunted and trapped to near extinction, and as a consequence, the quest for beaver products shifted to North America at that time. By the early 17th century, the North American beaver Castor canadensis fur trade was booming for the Eurasian settlers and ‘entrepreneurs’. Over the next two hundred plus years, C. canadensis followed the same fortune as the Eurasian beaver; trapped and hunted to near extinction.
It is guestimated that there were up to 400 million beavers before the American fur trade boom (Goldfarb 2018). Currently, the North American population has risen again to around 10-15 million, due to help of protections placed on them in the late 19th/early 20th centuries (NWF). However, the North American beaver still faces some degree of risk today, as their presence and behaviors are often considered pest-like to many humans.
Castor canadensis are herbivorous, foraging on leafy greens and the cambium of trees or shrubs. Their teeth grow continuously and are tinged a bit reddish as they contain iron minerals for strength. (PBS 2014)
Overview of Beavers in the Nearshore
C. canadensis are a keystone species in the nearshore estuarine environment, meaning that they have effects on both the community structure and the environmental function of local habitat. Without their presence, a broad array of other animal and plant populations depending on their services would suffer direly.
As “ecosystem engineers” beaver construct dams that serve to increase or create productive marshland habitat. This marshland not only amplifies the beavers’ area for their foraging activities, but also increases the amount and diversity of resident organisms. In the nearshore environment, this function is accompanied by a shift in the saltwater-freshwater balance of an area. The beaver dams entrap tidal waters from being released as a low tide exits the coastline, creating a valuable niche estuarine habitat. Beaver ponds are also heavily utilized by the resident fish species of an area, which in the Elwha nearshore include salmon species, but also fish such as three-spined stickleback (Gasterosteus aculeatus), prickly sculpin (Cottus asper), and Western river lamprey (Lampetra ayresii).
The captured water and reduced flow rates of beaver ponds also acts to retain sediment and organic matter within the marsh. Subsequent decomposition creates a nutrient rich environment, facilitating an increase in riparian vegetation and surrounding shrubbery. This vegetation may overhang the habitat, decreasing evaporative water losses and regulates water temperatures against warming in the sun. Oncorhynchus (salmon) species require cooler water temperatures, which hold more oxygen, to survive. Resident fish also rely on these shrubs as cover to safeguard themselves against predator species in the area such as great blue herons.
Another ecosystem benefit offered by beavers is the excavation of foraging channels throughout their ponds. This movement of sediment acts as a dredging mechanism to increase water depth within their ponds. The area and perimeters of the estuary and side-channel habitat are also significantly expanded: in a study by Hood and Larson on an inland ecosystem in south-central Alberta, it was found that the digging of foraging trails by C. canadensis increased wetland perimeters by over 575%, and the volume-to-surface area ratio (adding depth) by 50%, in comparison to similar areas where beavers were not present (2014). Additional area and depth protects the estuarine environment from drying up during summertime droughts, and offers the landscape increased heterogeneity, further facilitating the rise in biological diversity.
Foraging channels dug by C. canadensis can extend up to hundreds of meters, and when dug into surrounding upland forests, will increase connectivity between coastal and upland systems. This connectivity allows for greater mobility and therefore habitat availability to organisms.
Bathymetric map of [inland] beaver-created marshlands, illustrating extensive foraging channels surrounding perimeters. This study was conducted in Miquelon Lake Provincial Park, Alberta, Canada (Image adopted from Hood and Larsen, 2015).
Because of their creation of this habitat, beavers support our threatened salmon species such as coho (Oncorhynchus kisutch), Chinook (O. tshawytscha), cutthroat trout (O. clarkii), steelhead (O. mykiss) and others in the Elwha nearshore. A study conducted by Gregory Hood (2012) on Skagit River found that beaver dam-created tidal pools supported over three times as many juvenile Chinook at low tide as did the surrounding shallow areas. Furthermore, those residence rates of juvenile Chinook are eight times higher once standardized by the surface area of the pools, as is commonly considered.
In Hood’s study, beaver created habitat also supported other animal species such as shorebirds and amphibians. Based upon camera footage, there is further evidence to suggest that beaver burrows and lodges also encounter cohabitation by other small mammals such as muskrats and mice, with whom the beavers don’t seem to mind sharing their cover nor their food stores. (BBC)
Anthropogenic Interactions and Local Considerations
Beavers are still under threat from humans. Though hunting pressure on our coastal beavers has greatly decreased, people bringing along their dogs into the coastal environment has arisen as a new stress for the critters to navigate. Beavers can be chased, injured or even killed by unconfined dogs, and diseases are transferable between the animals as well.
Beavers mate for life, and typically live around 10 years-in rare cases 15 years. They reside in a small colony, which consists of two adult parents, a couple “yearlings” (teenager equivalents) who learn building techniques from the parents, and the “kits” or baby beavers.
In our own Place Road habitat near the western Elwha delta, the frequency of domestic dogs to the nearshore ecosystem has also dramatically increased. Unfortunately and not coincidentally, one of the beavers was recently found freshly dead in the middle of the main walkway to the Elwha west delta-with clear and sad signs of drag and struggle around it. The death of one beaver may not seem like a catastrophic event, but because of their colony structure, this death tears the whole working familial unit apart.
Based upon dramatic regrowth of vegetation along the shoreline, and rapid filling of the west estuary side channels, and lack of new activity, indications are that the recent beaver death has caused the colony to vacate the area directly adjacent to the Place Road dike. If beavers do not return to the area, the ecosystem will alter over time; connectivity will be reduced, dredging of the side channel will not be maintained, and sediment may infill the most critical west side channel of the Elwha delta.
(The landowners that provide access to the west side of the Elwha delta are clear: dog leashes are now REQUIRED the Place Road dike AND beach. Please use them and remain in control of your pets. A split second mistake can be costly to the entire ecosystem balance. Also, please pick up dog waste, which can spread disease to wildlife, and alter water quality. If this conservation directive isn’t adhered to, dogs will be banned from the site.)
Two resident beavers caught on camera in the Elwha nearshore environment. (Photo by Coastal Watershed Institute)
Another major issue beavers face is that of human development. Human development can halt or fragment the ability of C. canadensis to maintain and create the environments they and other animals depend on for survival. Human-built structures, such as dikes or shoreline armoring, generally fragment habitats, by creating a barrier between the upland and aquatic environments. Our local beavers remind us, teach us, and “dam near” force us to retain that connectivity.
Specifically in the Elwha nearshore environment, C. canadensis has maintained the area surrounding the Place Road dike near the Elwha River mouth. By digging out the sediment surrounding the dike, the beavers have helped to maintain water storage on both sides of the barrier, and offer beneficial habitat to waterfowl, amphibians, vegetation, macroinvertebrates and fish.
Though the beaver-created habitat on the east side of the Place Road dike has historically been sampled (by Coastal Watershed Institute) as the most heavily utilized rearing habitat for Oncorhynchus species, the west side of the dike is unreachable to these fish.. Salmon could potentially utilize this western side channel if the man-made earthen dike structure were modified to reconnect with historic estuary habitat.
The western portion of the Elwha River estuary, including the beaver lodge and pond (center), the Place road dike (left), the Elwha River main channel (far left) and the Strait of Juan de Fuca (right). Photo view is from the north, looking toward the south. (Photo by Coastal Watershed Institute, 2018)
What Else Should We Know?
To our knowledge, there are no studies yet investigating the relationship or reliance of C. canadensis on abundance and availability of soft, fine sediments. However, it is well understood that beavers build their burrows and structures using fine sediment. Once Glines Canyon and Elwha dams were removed on the Elwha River in 2012-14, the approximately 21 million cubic meters of fine sediment locked behind the dams began a journey downriver, half of which is predicted to the nearshore ( Warrick et al 2015; Shaffer et. al 2017). Before these removals, was it a challenge for C. canadensis to live on sediment-starved beaches? It stands to reason that this sediment delivery would benefit the beavers’ habitat immensely, providing them with one of the essential materials they require to build with. Unfortunately, there has been no research yet conducted on the impacts of dam removal and sediment delivery, specific to the nearshore, for the beavers.
In the future, as we see other large man-made dams with projected removals, understanding the benefits or obstacles C. canadensis faces throughout restoration process is necessary. We know beavers reside in and have an impact on the nearshore—the entrance gate to our critical rivers. It’s time the paucity of research on beavers’ role in restoration processes be reexamined, and that the helpful role of beaver in the nearshore be quantified. It is time the “ecosystem engineer”, C. canadensis, receive it’s due protection, and consideration, in future river conservation and dam removal projects.
Thank you to Dr. Michael Pollock (NOAA), Dr. Greg Hood (Skagit System Coop), and Dr. Anne Shaffer (CWI) for input and guidance. Thanks to Malcolm Dudley and Chuck Janda provided access to beaver sites on the Elwha.
Goldfarb, B. 2018. Eager: The Surprising, Secret Life of Beavers and Why They Matter. Chelsea Green Publishing
Hood, G. A., and Larson D. G. 2014. Ecological engineering and aquatic connectivity: a new perspective from beaver-modified wetlands. John Wiley & Sons Ltd, Freshwater Biology, 60:198–208. doi:10.1111/fwb.12487
Hood W. G. 2012. Beaver in Tidal Marshes: Dam Effects on Low-Tide Channel Pools and Fish Use of Estuarine Habitat. Wetlands, 32:401–410, doi: 10.1007/s13157-012-0294-8
Leidholt·Bruner, K., Hibbs, D. E., and McComb W. C. 1992. Beaver Dam Locations and Their Effects on Distribution and Abundance of Coho Salmon Fry in Two Coastal Oregon Streams. Department of Forest Science, Oregon State University. Corvallis, OR (http://www.martinezbeavers.org/wordpress/wp-content/uploads/2018/01/Leidholt-Bruner-Beaver-Dam-Locations-and-Their-Effects-on-Distribution-and-Abundance-of-Coho-Salmon-Fry-in-two-Coastal-Oregon-Streams-Northwest-Science-1992.pdf)
Miranda, D. 2017. The Community Builder: Beaver’s Role in the Ecological Community. Wetlands Conservancy. http://wetlandsconservancy.org/wp-content/uploads/2017/03/Donette-Miranda-Beavers_Role_in_the_Ecological_Community-Final.pdf
Oregon Department of Fish and Wildlife. 2005. Final Report-The Importance of Beaver (Castor Canadensis) to Coho Habitat and Trend in Beaver Abundance in the Oregon Coast Coho ESU.
Public Broadcasting Service. 2014. Leave It to Beavers. USA. at http://naturedocumentaries.org/14851/leave-beavers-pbs-2014/
Pollock, M.M., M. Heim, and R.J. Naiman. 2003. Hydrologic and geomorphic effects of beaver dams and their influence on fishes. Pages 213-234 in S.V. Gregory, K. Boyer, and A. Gurnell, editors. The ecology and management of wood in world rivers. American Fisheries Society, Bethesda, Maryland.
Pollock, M.M., Pess, G.R., Beechie T.J., and Montgomery D.R. 2004. The Importance of Beaver Ponds to Coho Salmon Production in the Stillaguamish River Basin, Washington, USA. North American Journal of Fisheries Management, 24:749–760.
Rue, L. L. (III). 2002. Beavers. Colin Baxter Photography Ltd., Moray, Scotland.
Shaffer, J.A., E. Higgs, C. Walls, F. Juanes. 2017. Large-scale Dam Removals and Nearshore Ecological Restoration: Lessons Learned from the Elwha Dam Removals. Ecological Restoration 35(2).
Tamworth Distilling (Beaver Whiskey): http://tamworthdistilling.com/spirits/house-of-tamworth-eau-de-musc/
Warrick, J.A., Bountry, J.A., East, A.E., Magirl, C.S., Randle, T.J., Gelfenbaum, G., Ritchie, A.C., Pess, G.R., Leung, V. and Duda, J.J., 2015. Large-scale dam removal on the Elwha River, Washington, USA: Source-to-sink sediment budget and synthesis. Geomorphology, 246, pp.729-750.