Comparison of triploid and diploid rainbow trout (Oncorhynchus mykiss) fine-scale movement, migration and catchability in lowland lakes of western Washington.

Fisheries managers stock triploid (i.e., infertile, artificially produced) rainbow trout Oncorhynchus mykiss in North American lakes to support sport fisheries while minimizing the risk of genetic introgression between hatchery and wild trout. In Washington State, the Washington Department of Fish and Wildlife (WDFW) allocates approximately US $3 million annually to stock hatchery-origin rainbow trout in > 600 lakes, yet only about 10% of them are triploids. Many lakes in Washington State drain into waters that support wild anadromous steelhead O. mykiss that are listed as threatened under the U.S. Endangered Species Act. As a result, there is a strong interest in understanding the costs and benefits associated with stocking sterile, triploid rainbow trout as an alternative to traditional diploids. The objectives of this study were to compare triploid and diploid rainbow trout in terms of: (1) contribution to the sport fishery catch, (2) fine-scale movements within the study lakes, (3) rate of emigration from the lake, and (4) natural mortality. Our results demonstrated that triploid and diploid trout had similar day-night distribution patterns, but triploid trout exhibited a lower emigration rate from the lake and lower catch rates in some lakes. Overall, triploid rainbow trout represent a viable alternative to stocking of diploids, especially in lakes draining to rivers, because they are sterile, have comparable home ranges, and less often migrate.

Size, age, growth and site fidelity of anadromous cutthroat trout Oncorhynchus clarkii clarkii in the Salish Sea.

Pacific salmon Oncorhynchus spp. have been the focus of scientific research for over a century, but anadromous trout in this genus, in particular anadromous coastal cutthroat trout Oncorhynchus clarkii clarkii, have been neglected. Oncorhynchus clarkii clarkii occupy a diverse range of habitats including fresh water, brackish estuaries and marine water, but have a relatively small home range making them ideal for studies of behaviour and movements during ocean residency. In 2015, we sampled O. c. clarkii monthly along a small stretch of beach (47.08° N, 122.98° W) in Eld Inlet, south Puget Sound, Washington using a beach seine. We collected tissue for genetic tagging and stock identification and scales for aging from 427 O. c. clarkii, ranging in size from 118 to 478 mm fork length. Additionally, we enumerated redds in natal streams of those fish tagged to describe inter-habitat movement patterns and investigate site fidelity of juvenile and adult O. c. clarkii in the marine environment. Consistent with other anadromous salmonids, O. c. clarkii captured at our study beach exhibited rapid growth rates, particularly in spring following dispersal into the marine environment (mean ± SD = 0.61 ± 0.29 mm-d ). Genetic tag data revealed that while O. c. clarkii undergo inter-estuarine migrations, O. c. clarkii of all life stages exhibited site fidelity in the marine environment. Twenty-one percent (64/305) of sampled O. c. clarkii were recaptured at least once during the course of the study while multiple fish (n = 3) were recaptured up to five times. These results suggest that O. c. clarkii occupying south Puget Sound reside in or regularly return to a small geographic area in the nearshore environment for much of their life and therefore may be particularly vulnerable to anthropogenic disturbance (development, angling, etc.).