Redwood Creek Coho Salmon Rescue and Captive Rearing Project

Central California Coast coho salmon are listed as an endangered species under both the state and federal Endangered Species Acts (ESA and CESA), and the conservation of endangered species is an explicit State policy under the California Endangered Species Act (CESA). The causes of coho salmon decline in California are multiple and include loss of suitable habitat and climatic factors, such as poor oceanic conditions that reduce food availability and drought conditions that reduce the quality of stream rearing. Human activities contributing to the decline of coho salmon in California include the commercial overfishing of ocean stocks and the loss and degradation of suitable freshwater and estuarine habitats through land and water developments associated with agriculture, forestry, gravel mining, urbanization, water withdrawal and altered flow conditions, and river regulation. In the early 1990’s, declining coho salmon populations prompted the closure of all commercial and recreational fisheries for coho salmon in the State, followed by the listing of California coho salmon under CESA and ESA. Despite the legal protection, coho salmon populations in many coastal watersheds are still declining and some, particularly in the central coast, are already extirpated or approaching extirpation. There is considerable risk that populations of coho salmon, and other native salmonids present in many of California’s coastal watersheds, may become extinct in the wild within this century.

Both the state and federal governments have prepared coho salmon recovery plans. These plans contain numerous recommendations which, if implemented, will help in the recovery of coho salmon. The prolonged severe drought in California is placing this coho population at increased risk of extirpation in the next few years, due to decreased freshwater survival and already extremely low abundance.

Coho salmon recovery actions fall into two broad categories: habitat-based actions and population-based actions. The protection and restoration of coho salmon habitat is an essential component of coho salmon recovery and it is unlikely that lasting recovery can be achieved without adequate amounts of functional habitat. However, habitat restoration alone will not achieve recovery if there are too few coho salmon left to maintain self-sustaining populations in the available habitat.

Populations that have been reduced in abundance to levels too low to maintain themselves through natural reproduction are candidates for captive rearing intervention. In the case of Redwood Creek (Marin County), population monitoring shows that annual abundance of adult coho salmon has fallen to single digits in recent years. The population is nearly extirpated, and captive rearing is proposed to prevent extirpation. This project would include temporary removal of juvenile coho from Redwood Creek, rearing them to maturity, and releasing them as adults back into their stream of origin. No hatchery spawning will occur. This project is a temporary measure that will help promote natural reproduction so that the population may persist in the future. The NOAA recovery target for this population based on historic carrying capacity is 272 adults per broodyear.

Captive rearing programs are a “last resort” effort to prevent local extirpation, or even complete extinction of a species within a region. In all captive rearing programs, the decision to intervene in population recovery through hatchery-based captive rearing must be weighed against the potential ecological and genetic risks of such interventions as well as the potential costs and demands on staff time and other agency resources. The decline in abundance of Redwood Creek coho salmon over the past decade, significantly exacerbated by the coast-wide crash in central California salmonid populations in 2008, as well as the current prolonged severe drought conditions in California greatly increases the possibility of a complete disappearance of coho salmon from Redwood Creek. Resource agencies have been monitoring coho salmon and implementing habitat restoration projects with the goal to recover this and other coho salmon populations in California.

Captive rearing of Redwood Creek coho salmon was first considered, and then recommended, as a coho salmon recovery action by the collaborative CDFW / NOAA Priority Action Coho Team (PACT) in 2012. The proposed captive rearing of Redwood Creek coho salmon has now reached a point of urgency, necessitated especially by the continuing drought conditions that have affected coho escapement in Redwood Creek this season and are likely to affect instream survival of any coho that were spawned last winter.

Given the current environmental conditions and the extremely low abundance of Redwood Creek coho salmon, any further delays in commencing captive rearing of Redwood Creek coho are likely to put the population at expected risk of extirpation.

Captive rearing strategies range from temporary rescue rearing of small numbers of salmon to full-scale conservation hatchery programs using artificial spawning. The proposed Redwood Creek coho salmon captive rearing project was developed as an appropriate approach balancing costs with the size of the watershed and program and the planned duration of the intervention. It benefits from the proximity of Don Clausen / Warm Springs Hatchery (WSH) and the experience and technical expertise developed in the Russian River Coho Salmon Captive Broodstock Program (RRCSCBP).

This Redwood Creek captive rearing project will commence in August, 2014. As currently proposed, it consists of collecting up to 200 juvenile coho from Redwood Creek in each of three consecutive years (2014-2016), rearing them at WSH to adulthood and releasing the mature adult coho back into Redwood Creek (2016-2018). A small number of adults from nearby watersheds (e.g., Olema Creek) that are also being reared at Warm Springs Hatchery may be released along with Redwood Creek coho to diversify the genetic makeup of the population, simulating natural straying that occurs in the wild and reducing potential inbreeding. This approach has three important advantages. First, it reduces the costs of maintaining consecutive generations of spawned fish at a hatchery facility. Second, it avoids artificial mate selection at the hatchery, instead permitting the mature coho salmon to spawn and choose mates freely in their natural environment. And third, it reduces domestication potential by subjecting the offspring to natural selection pressures in the wild from the moment of their birth.

To evaluate the success of captive rearing of Redwood Creek coho salmon, juvenile coho surveys will be conducted in each summer following the release of adult coho (2017-2019), and tissue samples will be analyzed genetically to determine how many of the released coho spawned successfully. Genetic analysis will be performed by Dr. Carlos Garza at the NMFS Southwest Fisheries Science Center (SWFSC) in Santa Cruz. The project is a collaborative effort between CDFW, NMFS, GGNRA-NPS, ACOE, CDPR, Friends of Lake Sonoma, and Golden Gate National Parks Conservancy. It is funded in part by the Redwood Creek Watershed Collaborative, a partnership of the CDPR, GGNRA-NPS, and the Golden Gate National Parks Conservancy. The project will be adaptively managed throughout its duration by CDFW, NMFS and GGNRA-NPS. 

Biologists of the collaborating agencies agree that this project as currently proposed has a good chance of a positive outcome with a low risk potential. Several factors will contribute to successfully preventing the loss of the three coho salmon brood-years in the next few years. First, the Redwood Creek watershed is mostly in public ownership by land managers that are vested in the protection and restoration of creeks and their fauna and flora, both currently and into the future. In addition, the proposed captive rearing project will benefit from the experience and expertise of the hatchery staff implementing the Russian River Coho Salmon Captive Broodstock Program and the NPS monitoring efforts already occurring in Redwood Creek. Furthermore, this captive rearing and release proposal complements extensive restoration actions in the Redwood Creek watershed. GGNRA- NPS has recently implemented several habitat restoration and management actions that have improved instream, riparian and floodplain juvenile coho salmon rearing habitat. These restoration actions are increasing the stream’s capacity to accommodate higher numbers of fish, and this capacity is only expected to increase as the restored habitat matures.