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Natural Productivity in Steelhead Populations of Natural and Hatchery Origin: Assessing Hatchery Spawner Influence
Author(s) -
Lister D. Brent
Publication year - 2014
Publication title -
transactions of the american fisheries society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.696
H-Index - 86
eISSN - 1548-8659
pISSN - 0002-8487
DOI - 10.1080/00028487.2013.824919
Subject(s) - hatchery , fishery , productivity , population , biology , ecology , rainbow trout , natural population growth , fish <actinopterygii> , demography , macroeconomics , sociology , economics
Natural productivity, the number of natural‐origin adult recruits per parent, is an important parameter for assessing population status of steelhead Oncorhynchus mykiss (anadromous Rainbow Trout) and Pacific salmon Oncorhynchus spp. listed under the U.S. Endangered Species Act. Hatchery‐origin adults comprise a majority of many salmon and steelhead spawning populations. In such cases, the utility of natural productivity estimates is affected by uncertain reproductive fitness of hatchery spawners and by possible ecological or genetic interactions among hatchery and natural fish. This study examined options for analyzing population census data to assess hatchery spawner effects on natural productivity of mixed steelhead populations including spawners of hatchery and natural origin. It compared productivity in three mixed and reference (natural) population pairs, and estimated productivity as natural recruits per total spawners of natural and hatchery origin ( R nat / S tot ) or as natural recruits per natural spawner ( R nat / S nat ). Natural productivity estimated as R nat / S tot reflected hatchery program scale, not productive capacity of natal streams. This analytical approach masked natural production dynamics in populations with a major hatchery spawner proportion, and was therefore of limited use for determining hatchery spawner influence. Productivity estimated as R nat / S nat indicated similar productivity of reference and mixed populations, and an absence of hatchery spawner effect, in the case of (1) a large hatchery stray component, and (2) a hatchery supplementation program. In the third pairing, R nat / S nat productivity of the mixed population significantly exceeded that of the reference population, suggesting natural spawner abundance is below carrying capacity. Hatchery spawners contributed to natural productivity in that case, but in the presence of reduced natural spawner density. These findings suggest that hatchery spawners are unlikely to affect natural production of a mixed steelhead population unless natural spawner abundance is below carrying capacity.