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Fishery Bulletin 11 5(4) 
Similar to the analysis of acoustically tagged coho 
and Chinook salmon, analysis of coded-wire tagging 
data also revealed differences and similarities that 
shed light on the phenomenon of residency (partial mi¬ 
gration) of salmon. Residency seems much more prev¬ 
alent with Chinook salmon (O’Neill and West, 2009; 
Chamberlin et ah, 2011) than with coho salmon (Rohde 
et ah, 2014), although it is not possible to precisely 
estimate the fraction for either species that adopts this 
behavior. However, the proportions of subyearling and 
yearlings adopting resident behavior were positively 
correlated between the two species among years, as 
well correlated with environmental variables (Rohde 
et ah, 2014), suggesting common influences on behav¬ 
ior. In addition, salmon of both species that remain as 
residents in Puget Sound tend to be caught in natal 
basins more often than would happen by chance, al¬ 
though some movement certainly occurs (Chamberlin 
and Quinn, 2014; Rohde et al., 2014). Taken together, 
the combination of tagging and tracking studies for 
both species indicate that commonalities exceeded dif¬ 
ferences, and that the main difference was the greater 
prevalence of residency and somewhat more restricted 
movements within Puget Sound for Chinook salmon. 
A number of diadromous species also exhibit alter¬ 
native migratory behaviors that include resident forms 
of behavior similar to those of Puget Sound coho and 
Chinook salmon (Chapman et al., 2012a, Chapman et 
al. 2012b). Striped bass (M or one saxatilis) have both 
resident fish that do not leave the natal river or estu¬ 
ary and migratory fish that travel long distances in 
coastal waters. Clarke (1968) referred to these fish as 
contingents within populations, defined as “a group of 
fish that engage in a common pattern of seasonal mi¬ 
gration between feeding areas, wintering areas, and 
spawning areas” (p. 320). Subsequent research with 
otolith microchemistry has revealed 3 distinct contin¬ 
gents: a resident group that remains in fresh water, a 
mesohaline group that occupies estuarine waters, and 
a migratory group that uses the coastal Atlantic Ocean 
(Secor, 1999). White perch (M. americana ) displays 2 
contingents; the great majority use estuarine habitats 
and a small fraction reside in rivers (Kerr et al., 2009). 
Individual white perch adopt one pattern or the other 
and do not switch patterns, whereas striped bass can 
shift between patterns (Zlokovitz et al., 2003). 
The widespread occurrence of residency in diadro¬ 
mous species, such as salmonids, suggests advantages 
for having a portion of the population not undergo 
extensive ocean migrations. One explanation for the 
phenomenon is that resident fish, compared to ocean 
migrants, might be exposed to fewer predators (Em¬ 
mett and Schiewe, 1997). However, one consequence of 
residency is slower growth than that of members of the 
cohort feeding in the ocean, as evidenced by smaller 
size at age in coho salmon (Milne, 1950; Pressey 1 ; Ro¬ 
hde et al., 2014) and pink salmon (Pressey 1 ), and the 
smaller size of resident Chinook salmon (Pressey 1 ). 
Therefore, any hypothesis to explain residency must 
address this growth differential, as well as the greater 
prevalence of residency among Chinook than among 
coho salmon. Perhaps, because coho salmon tend to 
spend only a single winter at sea, the need to grow fast 
is greater than it is for Chinook salmon (Sandercock, 
1991; Pearcy, 1992), which delay maturation and the 
corresponding return to spawn when growth is reduced 
(Healey, 1991). 
In Puget Sound, the incidence of transients, some 
of which later return from the coast and resume resi¬ 
dency in the sound, implies behavioral patterns that 
reflect modes along a continuum rather than discrete 
variants. This variability contributes to the “portfolio 
effect” (where diversification minimizes the risk of insta¬ 
bility) for Chinook salmon and coho salmon, although 
in the face of broad regime shifts and anthropogenic 
effects across the entire region, it has not precluded 
declines in the species. The processes affecting migra¬ 
tory decisions, whether physiological (e.g., growth rate, 
lipid deposition, hormone levels) or environmental (e.g., 
water temperature, prey availability) remain unknown. 
However, the contribution of these drivers differs for 
coho salmon, because residency is less often displayed, 
compared with Chinook salmon. Regardless, although 
not likely accounting for a large portion of Salish Sea 
salmonids, partial migration and late migration strat¬ 
egies could justify adjustment to calculations of early 
marine mortality in Chinook salmon survival studies 
such as that of Neville et al. (2015), and the concept 
could be explored for other species, such as sockeye 
salmon (Oncorhynchus nerka) (Wood et al., 2012). 
In summary, Chinook salmon display a wide range 
of alternative migration patterns. These patterns in¬ 
clude those of nonanadromous males that mature as 
parr (Gebhards, 1960; Pearsons et al., 2009; Johnson et 
ah, 2012), of juveniles that migrate to sea in their first 
or second year of life (Taylor, 1990; Healey, 1991), and 
of a no dromons fish that remain as residents in pro¬ 
tected marine waters (Pressey 1 ) or that migrate to the 
coast or the open North Pacific Ocean (Healey, 1983; 
Sharma and Quine, 2012). This list should also include 
variants, such as those termed transients, fish initially 
adopting residency and then moving to the outer coast, 
and some that return to Puget Sound before matura¬ 
tion. Although the sample size and approach used in 
our study cannot precisely quantify the degree of prev¬ 
alence of late migration and partial migration strate¬ 
gies, these are behaviors clearly adopted by a portion 
of the population as a whole. 
Alternative patterns of migration, as well as the 
presence of nonmigratory and migratory animals, 
can enhance the resilience of populations (Kerr et al., 
2010) because the fish experience different regimes of 
growth and mortality. The reduced growth of resident 
salmon compared with those feeding along the coast is 
balanced against the higher survival rates of resident 
fish. Survival rates of coho salmon entering the Salish 
Sea are higher on average than coho salmon of coast¬ 
al populations but the survival rates in these regions 
have shown different trajectories over the past decades 
(Zimmerman et al., 2015). Assuming similar patterns 
