Male competition and breeding success in captively reared and wild coho salmon (Oncorhynchus kisutch)

In the Pacific Northwest, releasing captively reared adult salmon (Oncorhynchus spp.) for natural spawning is an evolving strategy for the recovery of imperiled populations. However, the ability of captively reared fish to spawn naturally may be compromised by their artificial rearing environments. In this study, wild coho salmon (O. kisutch) males outcompeted captively reared males and controlled access to spawning females in 11 of 14 paired trials in laboratory stream channels. In two cases where satellite males were observed participating in spawning, DNA genotyping results determined that they did not sire any of the progeny. When spawning occurred at night and was not observed, DNA results confirmed behavior-based determinations of dominance made before dark. Dominance was established soon after the males were introduced into a common arena containing a sexually active female. We hypothesize that decisions by subordinate males to avoid direct competition may have minimized conflict. The competitive inferiority of captively reared coho salmon in this and a previous study probably reflects deficiencies in rearing environments, which fail to produce appropriate body coloration and body shape and perhaps alter natural behavioral development.

SWIMMING RESPONSE TO WATER CURRENT IN PARATYA AUSTRALIENSIS KEMP, 1917 (DECAPODA, ATYIDAE) UNDER LABORATORY CONDITIONS

The swimming response to flow of the freshwater shrimp Paratya australiensis Kemp, 1917, was examined in a small recirculating laboratory stream. On three occasions during 1993 larvae, juveniles, small and large adults, and ovigerous females were collected from headwater populations and tested in the laboratory at current speeds of 10 and 30 cm s-1. Juvenile and adult shrimps showed the same strong positive rheotactic response at velocities of 10 and 30 cm s-1. However, large adults moved upstream more rapidly than juveniles and small adults. This response was not influenced by the time of year of collection or time of day tested (day/night). Ovigerous females showed a weak response to flow and tended to maintain position rather than move into the current. Early stage larvae (stages III and IV) were not able to maintain position at the lowest velocities. The positive rheotactic response of shrimps, particularly large adults, is seen as an adaptation to compensate for downstream movement of larvae by drift and juvenile and adult displacement during high discharge events. La nage en reponse au courant chez la crevette d'eau douce Paratya australiensis Kemp, 1917, a ete examinee en laboratoire dans un petit courant continu d'eau. A trois reprises durant l'annee 1993, des larves, des juveniles, de petits et grands adultes, ainsi que des femelles ovigeres ont ete collectes dans populations situees en amont et testes au laboratoire a des vitesses de courant de 10 a 30 cm s-1. Les crevettes juveniles et adultes ont repondu par une forte rheotaxie positive aux vitesses de 10 a 30 cm s-1. Cependant, les adultes de grande taille se sont deplaces vers l'amont plus rapidement que les juveniles et les petits adultes. Cette reponse n'a pas ete influencee par le moment du prelevement, que ce soit au cours de l'annee ou de la journee (jour/nuit). Les femelles ovigeres ont donne une faible reponse au courant et tendaient a maintenir leur position plutot qu'a se deplacer dans le courant. Les jeunes larves (stades III et IV) n'etaient pas capables de maintenir leur position aux vitesses les plus basses. La rheotaxie positive des crevettes, en particulier des grands adultes, est consideree comme une adaptation pour compenser le mouvement des larves entrainees vers l'aval par le courant et le deplacement des jeunes et des adultes au moment des hautes eaux.