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Steelhead Life History on California's Central Coast: Insights from a State‐Dependent Model
Author(s) -
Satterthwaite William H.,
Beakes Michael P.,
Collins Erin M.,
Swank David R.,
Merz Joseph E.,
Titus Robert G.,
Sogard Susan M.,
Mangel Marc
Publication year - 2009
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 - 10.1577/t08-164.1
Subject(s) - rainbow trout , streams , life history , fishery , range (aeronautics) , habitat , emigration , maturity (psychological) , geography , environmental science , ecology , fish <actinopterygii> , biology , engineering , archaeology , psychology , computer network , developmental psychology , computer science , aerospace engineering
Steelhead Oncorhynchus mykiss display a dizzying array of life history variation (including the purely resident form, rainbow trout). We developed a model for female steelhead in coastal California (close to the southern boundary of their range) in small coastal streams. We combined proximate (physiological) and ultimate (expected reproductive success) considerations to generalize the notion of a threshold size for emigration or maturity through the development of a state‐dependent life history theory. The model involves strategies that depend on age, size or condition, and recent rates of change in size or condition during specific periods (decision windows) in advance of the actual smolting or spawning event. This is the first study in which such a model is fully parameterized based on data collected entirely from California steelhead populations, the majority of data coming from two watersheds the mouths of whose rivers are separated by less than 8 km along the coast of Santa Cruz County. We predicted the occurrence of resident life histories and the distribution of sizes and ages at smolting for steelhead rearing in the upstream habitats of these streams. We compared these predictions with empirical results and show that the theory can explain the observed pattern and variation.