Search

Redd surveys are a commonly used technique for indexing the abundance of sexually mature fish in streams; however, substantial effort is often required to link redd counts to actual spawner abundance. In this study, we describe how genetic pedigree reconstruction can be used to estimate effective spawner abundance in a stream reach, using Pacific lamprey (Entosphenus tridentatus) as an example. Lamprey embryos were sampled from redds within a 2.5 km reach of the Luckiamute River, Oregon, USA. Embryos were found in only 20 of the 48 redds sampled (suggesting 58% false redds); however, multiple sets of parents were detected in 44% of the true redds. Estimates from pedigree reconstruction suggested that there were 0.48 (95% CI: 0.29-0.88) effective spawners per redd and revealed that individual lamprey contributed gametes to a minimum of between one and six redds, and in one case, spawned in patches that were separated by over 800 m. Our findings demonstrate the utility of pedigree reconstruction techniques for both inferring spawning-ground behaviors and providing useful information for refining lamprey redd survey methodologies. Le recensement de nids de frai est une technique couramment utilisee pour determiner l'abondance des poissons ayant atteint la maturite sexuelle dans les cours d'eau; un effort considerable est toutefois souvent necessaire pour relier le nombre de nids de frai a l'abondance reelle de geniteurs. Nous decrivons comment la reconstitution du pedigree genetique peut etre utilisee pour estimer l'abondance de geniteurs effectifs dans un troncon de cours d'eau, en utilisant la lamproie du Pacifique (Entosphenus tridentatus) comme exemple. Des embryons de lamproies ont ete preleves de nids de frai dans un troncon de 2,5 km de la riviere Luckiamute (Oregon, Etats-Unis). Si des embryons ont ete trouves dans seulement 20 des 48 nids de frai echantillonnes (ce qui indiquerait 58% de faux nids), plus d'une paire de parents ont toutefois ete detectees dans 44% des vrais nids de frai. Les estimations decoulant de reconstitutions de pedigree donnent a penser qu'il y avait 0,48 (IC a 95% de 0,29-0,88) de geniteurs effectifs par nid et revelent que des lamproies individuelles contribuent des gametes a un minimum d'un a six nids et, dans un cas, ont fraye dans des parcelles distantes de plus de 800 m. Nos observations demontrent l'utilite des techniques de reconstitution du pedigree pour mieux comprendre les comportements dans les lieux de frai et pour obtenir des renseignements permettant de peaufiner les methodes de recensement des nids de frai de lamproies. [Traduit par la Redaction], Introduction Redd surveys are a monitoring tool that is used to index the abundance of sexually mature fish in a stream, and involve counting the number of depressions that are [...]

White sturgeon were sampled after harvest from various locations in the Columbia River, including the free-flowing lower portion and several reservoirs. Low reproductive productivity in sturgeon from the reservoirs led us to investigate if this low productivity was due to endocrine disruption. There were no differences between Columbia River locations for the reproductive hormone profiles. Steroid levels indicated that most of the fish sampled were immature, although some individuals had reached a size at which cultured sturgeon may undergo maturation. Males had significantly higher levels of testosterone and 11-ketotestosterone than females; however, estradiol was similar between the sexes and the levels were much lower than those reported from females undergoing vitellogenesis. Vitellogenin was detected in plasma from a few males; however, these levels were far below those found in white sturgeon females undergoing vitellogenesis and below levels found in male rainbow trout or in carp that had been exposed to sewage treatment plant effluent. In white sturgeon collected from two reservoirs, hepatic ethoxyresorufin-O-deethylase (EROD) activity indicated induction by exposure to contaminants, but the low levels of steroids found in general in sturgeon from the Columbia make it difficult to conclude any disruptive effect on the endocrine system or reproduction.