Freshwater life-cycle timing of Pacific salmon and steelhead (Oncorhynchus spp.) in Canada

Understanding species’ phenology and distribution is essential for mitigating anthropogenic disturbances and understanding climate change vulnerability. Pacific salmon (Oncorhynchus spp.) have complex life cycles that span freshwater and marine environments and unfold over many thousands of kilometers. Currently, there is no central repository of life-cycle timing for unique salmon and steelhead populations throughout their Canadian range. We have compiled a dataset of timing for key freshwater life-cycle events - fry migration from incubation to rearing grounds, juvenile migration from rearing grounds to the ocean, adult entry into rivers, and spawning - for salmon and steelhead trout from British Columbia and the Yukon, Canada. We summarize patterns across species and populations to improve understanding of when species are in different freshwater habitats but found significant data gaps in remote regions that may challenge environmental planning. The data and insight we provide allow for more detailed examination of how salmon and steelhead populations will be exposed to future climate changes and can be used to inform adaptive management of fisheries and mitigation during human development.

Methods
The life cycle events we estimated are:

1) fry migration- the movement of fry from the gravel to freshwater rearing grounds

2) ocean entry- juvenile migration into the marine environment - adjusted for downstream migration distance given average swim speeds where rearing locations (and points of data collection) are >~40km from the ocean.

3) adult run timing – the entrance of returning adults into freshwater.

4) spawning 

For each of these life cycle events, we have estimated the start and end of the timing window as the 2.5th and 97.5th percentiles of the cumulative timing from available data for the CU.

Fry migration and ocean entry timing were determined through a literature review and compilation of historic data. Migration data were typically collected using rotary screw traps, incline plane traps, and fyke nets. Adult run timing was determined from reports of catch (e.g., Tyee test fishery; Albion fishery) assigned to CUs based on genetic stock identification. Spawn timing (except for steelhead) was estimated for each CU using NuSEDs data on start, peak, and end spawn times for river populations within that CU. Run timing and spawn timing for steelhead trout were collated from historic reports. In these reports, timing was typically determined using radio telemetry.

Note (1) Conservation Units have been defined under Canada’s Wild Salmon Policy as ecologically and genetically unique groups of salmon that, if extirpated, are unlikely to be recolonized within an acceptable timeframe. Steelhead were not formally included in the Wild Salmon Policy or work led by DFO to define CUs for salmon. However, past work has been done to define 36 provisional CUs for steelhead in BC, which characterize the biodiversity of steelhead in BC using similar methods to those used to define salmon CUs (Tautz et al. 2011, Parkinson et al. 2005). Future work is needed to review and potentially refine these steelhead CUs based on more recent research and data to ensure they fully capture the diversity of steelhead in BC and meet the Wild Salmon Policy's definition of a CU. We have used provisional steelhead CUs from Tautz et al. (2011) for the Skeena Region and from Parkinson et al. (2005) for all other Regions when summarizing timing data."