A 17-year before and after experiment in Puget Sound that used a hatchery conservation program to aid a distressed stock of wild steelhead resulted in more redds (nests) even after supplementation ended and provided the naturally produced stock with stable or increasing measurements of genetic diversity, according to a recent study.
The Hamma Hamma River that flows down the eastern slopes of the Olympic Mountains and into the Hood Canal has just 3.6 kilometers (2.2 miles) of habitat that can be reached by anadromous fish. Before supplementation or captive breeding had begun the stream supported a mean of 10 steelhead redds. After supplementation the number had risen to a mean of 26 redds, the study says.
The study also drew on four control streams with steelhead in the same area, showing that the rise in the number of redds in the Hamma Hamma was solely due to careful supplementation.
Even after supplementation ended, the number of redds remained high, according to study author Barry Berejikian, supervisory research fisheries biologist at NOAA Fisheries’ Northwest Fisheries Science Center, Manchester Research Station.
“The number of redds (compilation of nests) constructed by natural-origin female steelhead in the supplemented population (Hamma Hamma) was 2.6 times greater in the generation after the supplemented program was terminated than it was before the program,” Berejikian said. “Samples from juveniles collected in the supplemented population indicated an increase in the effective number of breeders from 24.4 in the generation before supplementation to 38.9 after supplementation. Other measures of genetic diversity remained stable or increased.”
The four non-supplemented control populations monitored over the same 17 year period exhibited stable or decreasing trends in redd abundance, he said. Control streams were the Little Quilcene (10 before the supplementation period, 14 after), North Fork Skokomish (30 before, 29 after), Tahuya 123 before, 37 after) and Union 31 before, 9 after).
Declines in abundance of Puget Sound steelhead began in the late 1980s, followed by a listing as threatened under the federal Endangered Species Act in 2007.
The methods used in the Hamma Hamma supplementation program were non-conventional, Berejikian said. The program was designed specifically to benefit the natural population, and avoid some of the known and perceived shortcomings of typical supplementation programs.
“Supplementation programs have the greatest opportunity to benefit natural populations if they are well-conceived by having very clearly defined biological objectives, consider the properties and limiting factors of the natural population, take into consideration recent findings about promising broodstock, rearing and release strategies, and have some level of monitoring and accountability,” he said.
“Increased natural reproduction and genetic diversity one generation after cessation of a steelhead trout (Oncorhynchus mykiss) conservation hatchery program” was published online Jan. 19, 2018 in the journal PLOS/One, http://journals.plos.org/plosone/article/comments?id=10.1371/journal.pone.0190799. Berejikian’s co-author is Donald Van Doornik, research fisheries biologist, also at NOAA’s Manchester Research Station.
According to the study, “captive propagation programs have contributed to successful maintenance or amplification of some endangered populations, however, the genetic risks associated with captive propagation, and challenges associated with reintroduction raise the critical question of whether populations would fare better if left alone. Captive propagation efforts initially intended as temporary measures may become long-term endeavors if the factors causing declines are not adequately addressed.”
Some programs have prevented extinction and still maintain genetic diversity through carefully planned breeding protocols and are trending toward self-sustaining populations, the study says.
“How a supplementation program impacts the viability of natural populations (positively or negatively) will likely depend on important details of specifically how the program is operated,” Berejikian said. “The best approaches may not be the most convenient. Clearly defined rationale and goals are perhaps the most important components in establishing and evaluating supplementation programs.”
In the Hamma Hamma program, the duration of supplementation was always intended to be finite, and it was concluded as planned, he said
“Additional studies of this type are needed to determine when and how supplementation can provide some benefit to natural populations,” Berejikian said. “For example, populations that are below capacity (under-escaped) because of poor marine survival conditions may be more positively influenced by supplementation, but we have very few cases where programs have been terminated and monitored post-supplementation. The results of this study are encouraging, but habitat improvements are obviously still needed to recover natural steelhead populations.”
A recently published long-term study of Idaho supplementation programs had mixed results. It found that after 22 years supplementation in two Idaho drainages increased chinook salmon abundance at some life stages, but the effects did not persist after supplementation of hatchery stock ceased and had no apparent influence on productivity.
See CBB, January 12, 2018, “Long-Term Idaho Salmon Supplementation Study Delivers Mixed Results; Not A Stand-Alone Recovery Tool,” http://www.cbbulletin.com/440072.aspx, and “Effects of hatchery supplementation on abundance and productivity of natural-origin Chinook salmon: two decades of evaluation and implications for conservation programs,” Dec. 4, 2017, Canadian Journal of Fisheries and Aquatic Sciences (http://www.nrcresearchpress.com/doi/abs/10.1139/cjfas-2016-0344#.WlecN6inHIU).
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