Assessment of High Rates of Precocious Male Maturation in a Spring Chinook Salmon Supplementation Hatchery Program

Abstract

The Yakima River Spring Chinook Salmon Supplementation Project in Washington State is one of the most ambitious efforts to enhance a natural salmon population currently under way in the United States. Over the past 5 years we have conducted research to characterize the developmental physiology of natural and hatchery‐reared wild progeny spring Chinook salmon Oncorhynchus tshawytscha in the Yakima River basin. Fish were sampled at the main hatchery in Cle Elum, at remote acclimation sites, and, during smolt migration, at downstream dams. Throughout these studies, we characterized the maturational state of all fish using combinations of visual and histological analyses of testes, computation of gonadosomatic indices, and measurement of plasma 11‐ketotestosterone (11‐KT). We established that a plasma 11‐KT threshold of 0.8 ng/mL can be used to designate male fish as either immature or precociously maturing approximately 8 months prior to final maturation (1–2 months prior to release as “smolts”). Our analyses revealed that 37–49% of the hatchery‐reared males from this program undergo precocious maturation at 2 years of age and that a portion of these fish appear to residualize in the upper Yakima River basin throughout the summer. An unnaturally high incidence of precocious male maturation may result in the loss of returning anadromous adults, the skewing of female : male sex ratios, and ecological and genetic impacts on wild populations and other native species. As precocious male maturation is significantly influenced by the growth rate at specific times of year, in future studies we will alter maturation rates through seasonal growth rate manipulations.

"Research to Improve the Efficacy of Captive Broodstock Programs and Advance Hatchery Reform Throughout the Columbia River Basin." [from the Abstract], 2008-2009 Progress Report.

“…In the next funding period, plasma levels of a variety of metabolic hormones (Shimizu et al 2000) and body fat levels will be analyzed to assess growth and metabolic status to discern any effects of rearing regimes on other aspects of smolt quality. Plasma 11-ketotestosterone (11-KT) will be measured to determine treatment effects on the timing of onset of maturation (Cuisset et al 1994, Larsen et al 2004. At the end of the experiment, maturing males were readily identified by gonadosomatic indices (GSIs), however plasma 11-ketotestosterone levels in the immature males will aid in determining whether some males are maturing in the subsequent year (age 3).…”

“…In females, plasma estradiol-17ß (E 2 ) will be measured with a commercially available radioimmunoassay kit (ICN Diagnostic Products, Irvine, CA). Plasma levels 11-KT levels in males will be measured as described in Larsen et al 2004. Histological processing and developmental staging of gonadal tissues was conducted in [2008][2009].…”

“…The focus of our efforts has been to understand how hatchery rearing practices alter smoltification and age of male maturity because high rates of maturation of male spring Chinook salmon at age 2 have been documented for a variety of hatcheries in the Columbia River Basin (Larsen et al 2004;Pearsons et al, 2004;Beckman and Larsen 2005). In this study the effects of two environmental factors, photoperiod (at emergence) and food availability (growth during early rearing), on seasonal timing of smolting, smolt quality, and age of male maturity are being examined in spring Chinook salmon.…”

"Research to Improve the Efficacy of Captive Broodstock Programs and Advance Hatchery Reform Throughout the Columbia River Basin." [from the Abstract], 2007-2008 Annual Progress Report.

“…Indeed, exceptionally high rates of early (precocious) male maturation have been observed in fish reared in hatcheries or captive broodstock programs (e.g. Larsen et al 2004), in part due to the high early growth afforded by the captive environment. To address this problem and develop rearing regimes to reduce early male maturation, a series of studies were conducted during previous funding periods to; a) evaluate the relative effects of growth rate and body fat levels on rates of age-2 male maturation, b) determine critical periods when high growth influenced maturation in males and c) determine effects of growth on ovarian growth.…”

“…At the same time, maturation at age 2 increased in this hatchery population. Current estimates suggest that production releases contain 20 -50 % early maturing males (age 2, Larsen et al 2004), which have very poor reproductive success on the spawning grounds (Pearsons et al 2004). The net result could be elimination of a specific component of the juvenile population (i.e.…”