Behavioral Interaction between Chinook Salmon and Brown Trout Juveniles in a Simulated Stream

Abstract

The behavioral interaction between underyearling chinook salmon Oncorhynchus tshawytscha and brown trout Salmo trutta, both exotics in an unnatural sympatry in New Zealand, was tested during spring and summer in a simulated stream containing natural food. Both species were highly territorial and actively defended preferred drift-feeding sites and resting areas in the pool. Species dominance differed with season and was influenced by prior residence. In spring, chinook salmon were larger (because of their earlier emergence) and socially dominant, but they did not dominate when brown trout had prior residence. In summer, interspecific differences in size no longer existed, and brown trout were always socially dominant, although dominance required more time to establish when chinook salmon were prior residents. Most aggressive attacks of both species were initiated and won by the dominant fish in both spring and summer. Yearling brown trout in the pool in summer did not influence the interaction between underyearlings. Tactics in maintaining territory differed between species, with brown trout using a more energy-conserving strategy (frequent resting in preferred cover areas) than did chinook salmon (primarily free-swimming). Brown trout could adversely affect juvenile chinook salmon populations; therefore, this species should not be added to streams with chinook salmon.

Prey availability and diet of juvenile brown trout (Salmo trutta) in relation to riparian willows (Salix‐spp.) in three New Zealand streams

“…Consequently, differences in the relative amounts of drifting and benthic invertebrates associated with riparian willows have important implications for both the composition and the quantity of potential prey available to trout. In a study of the behaviour of juvenile salmonids in a simulated stream, Glova & Field-Dodgson (1995) reported that during their summer experiment brown trout (50-100 mm FL) fed primarily on drifting organisms; prey were taken from near the bottom and in mid water (about 45% each of the number of observations), the benthos (10%), and at the surface (about 1%). If we assume Table 8 Prey selection indices as calculated from the numbers of invertebrates in each of the principal prey categories in the diets of juvenile Salmo trutta in relation to those found in the benthos and drift during the day in each of three streams.…”

“…However, the density of terrestrial organisms in the drift is usually greater near the surface , where juvenile brown trout rarely feed (Glova & Field-Dodgson 1995).…”

Prior residence, territory quality and life-history strategies in juvenile Atlantic salmon (Salmo salar L.)

“…Moreover, the first juvenile rainbow trout, O. mykiss (Walbaum) introduced to an artificial stream also established a permanent size gap compared with later introductions of trout (Chandler & Bjornn, 1988). Prior residence also affects interspecific interactions: a similar phenomenon was documented between Atlantic salmon and brown trout in the wild (Egglishaw & Shackley, 1973), between chinook salmon, O. tshawytscha (Walbaum) and brown trout (Glova & Field-Dodgson, 1995), and between coho salmon, brook trout, Salvelinus fontinalis (Mitchill), and brown trout (Fausch & White, 1986). However, these studies used longer time intervals between early and late fish, e.g.…”

Recapture and condition of pond-reared, and hatchery-reared 1 + European grayling stocked in addition to wild conspecifics in a small river

“…Ersbak and Haase, 1983;Arias et al, 1995;Weiss and Schmutz, 1999) who also found lower post-stocking survival of artificially-reared fish. Competitive superiority of resident salmonids over introduced fish (Brännäs, 1995;Glova and Field-Dodgson, 1995), known as the 'prior residence effect' (Huntingford and DeLeaniz, 1997; Rhodes and Quinn, 1998), was a possible reason for lower recapture rate of artificially reared fish in comparison with the wild in the Within a column, different superscripts letters indicate a significant difference (P < 0.05). present study.…”