Relating juvenile migration timing and survival to adulthood in two species of threatened Pacific salmon (Oncorhynchus spp.)

Abstract

Summary1. Migration timing in animals has important effects on life-history transitions. Human activities can alter migration timing of animals, and understanding the effects of such disruptions remains an important goal for applied ecology. Anadromous Pacific salmon (Oncorhynchus spp.) inhabit fresh water as juveniles before migrating to the ocean where they gain >90% of their biomass before returning to fresh water as adults to reproduce. Although construction of dams has delayed juvenile migration for many populations, we currently lack a synthesis of patterns in migration timing and how they relate to subsequent survival to adulthood for Pacific salmon, especially for at-risk populations. 2. We studied two groups of Pacific salmon from the Columbia River basin in the northwestern United States currently listed under the U.S. Endangered Species Act. We examined how the proportion of juveniles surviving to return as adults varied with year of migration, date of arrival in the estuary, water temperature and coastal ocean upwelling using data from over 40 000 individually tagged Chinook salmon Oncorhynchus tshawytscha and steelhead Oncorhynchus mykiss. 3. In general, models with year, day and day 2 had much better support from the data than those with temperature and upwelling. For Chinook salmon, we also found a residual effect of temperature after controlling for day, but the effect was small for steelhead. 4. For both species, juveniles migrating from early to mid-May survived 4-50 times greater than those migrating in mid-June. As expected, however, the estimated peak in survival varied among years, presumably reflecting interannual variation in the nearshore physical environment and trophic dynamics that affect salmon during the critical juvenile life stage. 5. Synthesis and applications. Our results indicate a possible management objective would be to speed arrival to the estuary by increasing springtime river flows. These findings also provide some insight into the mechanisms underlying seasonal differences in survival patterns, but additional studies are needed to better resolve the issue. Future changes to river flow and water temperature associated with climate change and human activities may further alter migration timing, and thus this phenomenon deserves further attention.

A collective navigation hypothesis for homeward migration in anadromous salmonids

“…Entering the ocean at an appropriate time is critical for successful foraging and survival (e.g. Scheuerell et al 2009). Synchro nization in downstream movement of juveniles could facilitate effective collective temporal deci sion making (Conradt and Roper 2005) as to the timing of marine entry, possibly even combining independent cues from separate tributaries for more robust decisions.…”

Stock‐Specific Size and Timing at Ocean Entry of Columbia River Juvenile Chinook Salmon and Steelhead: Implications for Early Ocean Growth

“…For example, stock-specific variation in the consumption of juvenile salmon by avian predators in the Columbia River estuary has been attributed to stock differences in size, timing, and behavior (Collis et al 2001;Ryan et al 2003;Sebring et al 2013). While there may be conditions under which early timing results in beneficial growth opportunities or survival (Scheuerell et al 2009;Satterthwaite et al 2014), other conditions may select against early timing, leading to survival advantages for later timing (Ryan et al 2003;Beamish et al 2013). Similar advantages and disadvantages also likely occur for variation in fish size (e.g., Willette et al .…”

“…The size at and timing of ocean entry have been identified as important factors during this period. Minor variation in timing can have major consequences for survival (Holtby et al 1990;Scheuerell et al 2009;Chittenden et al 2010;Beamish et al 2013), while size affects growth and survival via vulnerability to predators and the availability of appropriately sized prey (Ivlev 1961;Mittelbach and Persson 1998). Several recent studies of Pacific salmon Oncorhynchus spp.…”

Estimating behavior in a black box: how coastal oceanographic dynamics influence yearling Chinook salmon marine growth and migration behaviors

“…Ample evidence supports the concept that timing of the juvenile migration plays a large role in determining marine survival (Scheuerell et al 2009, Chittenden et al 2010, McMichael et al 2013, and our results provide insight into the underlying mechanisms of this concept. Juvenile fish that migrate early tend to be larger, which may by itself result in higher rates of survival due to size-selective mortality (Zabel and Williams 2002, Duffy and Beauchamp 2011, Woodson et al 2013.…”