Summary Mid‐winter limnological surveys of L ake E rie captured extremes in ice extent ranging from expansive ice cover in 2010 and 2011 to nearly ice‐free waters in 2012. Consistent with a warming climate, ice cover on the G reat L akes is in decline, thus the ice‐free condition encountered may foreshadow the lakes future winter state. Here, we show that pronounced changes in annual ice cover are accompanied by equally import...

Recent discoveries have altered prevailing paradigms concerning the conditions under which nitrification takes place and the organisms responsible for nitrification in aquatic ecosystems. In Lake Superior, nitrate () concentrations have increased fivefold in the past century. Although previous evidence indicated that most is generated by nitrification within the lake, important questions remain concerning the magnitude and con...

The effect of the presence of stone blocks in the spawning habitat on the reproductive success of mature male parr of Atlantic salmon Salmo salar of various sizes and ages was tested in an artificial channel. Shelters allowed smaller individuals to contribute to egg fertilization as much as large parr, suggesting that the size‐based dominance observed in a shelterless habitat was not maintained in a more complex habitat.

Hybridization between sympatric species is not uncommon in the wild. Wild allotriploids (individuals with two chromosome sets from a species + one chromosome set from another species) are generally the result of a backcross between interspecific hybrids that produce unreduced gametes and one of the parental species. In animals, allotriploids are commonly sterile, except for some vertebrate species complexes in which allotriplo...

Genetic variation at 24 enzymatic loci was investigated in eight south European Atlantic salmon populations from the rivers Nivelle, Cares, Sella, Narcea, Esva, Navia, Porcia and Eo. In these rivers, management based on supplementation of native populations with foreign stocks was carried out for more than one decade. Population genetic patterns expressed in terms of allele frequencies, mean heterozygosity and conformity to Ha...

Six males and five females anadromous Atlantic salmon were released in two sections of the Lapitxuri experimental stream (Southwest France), where they could reproduce naturally. Females had all the same size and age, contrary to males. We focussed our attention on the variation with time of spawning tactics and success of males. Two factors affected male spawning behaviour in the short term. An increase of the OSR increased t...

Both sexes of Atlantic salmon Salmo salar were very sensitive to the absence of their mate on the spawning ground, particularly females during the last hour before oviposition. The improvement of behavioural chaining just before viposition might elicit the accurate timing of synchronized gamete release for successful fertilization. While the reproductive behaviour of the opposite sex could largely affect breeding activity, rel...

Genetic analyses were performed on the progeny of Atlantic salmon ( Salmo salar L.) sampled in natural redds of three rivers flowing into the Bay of Biscay, the Nivelle, the Mandeo and the Sella. These rivers are at the southern limit of the European distribution of the species and their populations are small and endangered by human activities. Nine variable number of tandem repeat (VNTR) loci (five minisatellites and four mic...

A new nuclear DNA marker is described to identify Atlantic salmon, brown trout, and their hybrids. Species‐specific banding patterns are obtained by digestion of genomic DNA with the restriction endonuclease Sac I and hybridization with a histone DNA probe. FISH analyses in hybrid metaphases illustrate the potential of interspecific hybrids for evolutionary studies.

The influence of overripening on salmonid egg quality has often been described in artificial breeding. However, no information exists on the impact of this factor on fish reproducing naturally, although it is likely to be critical, especially in disturbed environments. Pairs of Atlantic salmon in which the size of the male and the female was evenly matched were released in a spawning channel from 1 to 12 days after ovulation....