Reproductive Behavior and Success of Captive‐Reared Chinook Salmon Spawning under Natural Conditions

Abstract

In response to declining returns of Pacific salmon Oncorhynchus spp., captive‐rearing programs have emerged as one approach to maintain natural‐origin stocks while mechanisms responsible for their decline are addressed. However, it remains unclear if observed differences in reproductive behavior between captive‐origin (captive) and natural‐origin (natural) Chinook Salmon O. tshawytscha in laboratory experiments accurately predict reproductive success of captive salmon in the natural environment. Over a 4‐year period, 859 natural Chinook Salmon juveniles were collected for full‐term rearing in captivity. From these, we returned 247 maturing adults to their natal stream over 2 years, assessed trends in habitat use, monitored their courtship and spawning behaviors, and sampled their redds to determine if fertilized eggs were present. Habitat use followed a logical trend toward spawning areas as the season progressed. Captive fish were smaller and spawned later than did natural fish, but their size did not prevent females from constructing redds or prevent males from courting and fertilizing eggs. Captive fish were observed participating in 16 spawning events over two seasons. Captive and natural males displayed the same courtship behaviors, but natural males were more aggressive. Captive females selected redd sites similar to those of natural females and displayed digging behavior consistent with published observations. Eggs were collected from 22 of the 26 redds sampled, and survival to organogenesis was 68.3% in 2001 and 34.6% in 2002. The decline in 2002 was at least partially due to an apparent failure of females from brood year 1997 to produce viable eggs. We estimated captive fish contributed 19,000 eyed eggs to the population. If the 859 juveniles reared in captivity had been left in the stream, fewer than one adult would be expected to have returned. Growth, timing of spawning, and egg survival issues remain in captive fish, which illustrates a need to focus future research on improved culture techniques.Received July 21, 2011; accepted October 26, 2012

Egg Viability and Egg‐to‐Fry Survival of Captive‐Reared Chinook Salmon Released to Spawn Naturally

“…Captive‐origin adults were produced from spawning wild fish; therefore, physiological or behavioral traits that may have reduced spawning success of captive‐origin adults were presumably imparted by the rearing environment at the hatchery (Venditti et al. ; Stark et al. ), not through genetic change.…”

“…Venditti et al. () evaluated the spawning behavior of captive‐origin adults from the captive‐rearing program; however, during egg collections to source annual rearing groups they did estimate egg viability. Although their study did not specifically compare viability they did find egg viability was lower for released captive‐reared adults than for wild adults in the West Fork of the Yankee Fork Salmon River, Idaho.…”

“…Venditti et al. () suggested the breakdown of some combination of physical and physiological processes likely occurred during maturation of captive‐reared adults, which extended through spawning. Size of spawning females (length) and their subsequent egg size were not measured during this study.…”

“…In Idaho, Venditti et al. () found adult captive‐reared Snake River Spring Chinook Salmon released to spawn exhibited similar prespawn habitat selection, male courtship (quivers and crossovers), and female spawning behavior (digging frequency) as their wild counterparts and were documented to produce redds. These estimates of egg viability and ETF survival of captive‐reared adults provides another step towards complete evaluation of captive rearing as a conservation measure to boost threatened and endangered salmonid populations (Hard ; Goodman ).…”

Simulated Effects of YY‐Male Stocking and Manual Suppression for Eradicating Nonnative Brook Trout Populations

“…Even if survival of stocked YY males is similar to that of wild males, the stocked males might not be as reproductively fit. For example, although stocked and wild male salmonids may display similar courtship behavior, wild males may be more aggressive and hence more likely to produce progeny (e.g., Venditti et al 2013). Either reduced survival or poor reproductive fitness would extend the time to eradication of nonnative populations when a TYC strategy is used (Senior et al 2013).…”