**The title, authors, and abstract for this completion report are provided below. For a copy of the completion report, please contact the GLFC via e-mail or via telephone at 734-662-3209**
Genetic structure of the American eel with emphasis on the St. Lawrence River basin
Louis Bernatchez2, Caroline Côté2, Martin Castonguay3
2Département de Biologie, IBIS (Institut de Biologie Intégrative et des Systèmes), Université Laval,
Québec, Qc, G1V 0A6, Canada.
3Institut Maurice-Lamontagne (IML), Ministère des Pêches et des Océans (DFO/MPO),
850 Route de la Mer, Mont-Joli, Qc, G5H 3ZH, Canada
The American eel (Anguilla rostrata) is an economically important species but the efficiency of its management has been compromised by incomplete knowledge of the factors influencing its distribution and abundance in the various habitats it occupies. Yet, recruitment in the upper part of the St. Lawrence River and Lake Ontario has declined by 99% over the last 30 years while in more coastal waters of the Gulf of St. Lawrence, abundance indices have tripled during the same time period. This still unexplained paradox is puzzling to provincial and federal agencies responsible for the conservation of American eel. In this context, the proposed research aimed two main research objectives: i) Document the geographic pattern of genetic population structure of the American eel by means of molecular makers to rigorously test the null hypothesis of no genetic difference between eel from the upper St. Lawrence River and Lake Ontario versus other parts of the species range; ii) Test the null hypothesis of no genetically-based differences in growth and sex ratio under controlled conditions between eels from two different locations: the St. Lawrence R. system and the Maritimes where elvers used for stocking come from. For the first objective, and based on the genotyping of 18 microsatellites loci on a total of 2242 eels sampled from 32 locations from Florida to Lake Ontario, including 12 yellow eel cohorts from Canadian waters, results provided very strong and definitive support favouring the panmixia hypothesis, meaning that American eel is composed of a single randomly mating gene pool over this entire geographic range of distribution. Thus, no significant evidence of genetic differentiation was detected neither between life history stages (glass vs. yellow eels), between geographic origin within each life stages, not among age classes within yellow eels, nor between two temporal cohorts of glass eels. For this second objective, we first compared growth between glass eels collected from two different regions that were reared in fresh and brackish water during 9 months. We found that young eels from Cape Breton (Nova Scotia, Canada), grew faster, than those from Grande-Rivière-Blanche (GRB) that drains into the St. Lawrence Estuary. Eels from both origins also grew faster in brackish water, although there was a trend for origin*salinity interactions whereby this effect was more pronounced for eels from Cape Breton. Thus, these results supported the hypothesis that both salinity and quantitative genetic differences between glass eels from distinct origins influenced growth patterns in this study. Secondly, eels from these two origins were also reared until 34 months under similar, freshwater conditions. We found that the differential growth pattern observed during the first 9 months was maintained throughout the whole experiment, and that asymptotic length reached by eels from the GRB was predicted to be larger, based on the van Von Bertalanffy growth function. We did not observe any significant differences in sex ratio between origins. However, while male size distribution was clearly unimodal and characterized by relatively small variance, size distribution for females was bimodal and females from the GRB were characterized by a higher proportion of eels from the lower (slow growing) mode. Overall, the results of this study strongly suggests that there are quantitative genetics differences between glass eels colonizing different parts of the distribution range despite the fact that they all belong to a single panmictic population. Plausible explanations for this pertain to either non random dispersal based or selective mortality based on individual genetic differences. The relevance of these findings is two-folds. On the one hand, evidence for panmixia justifies the need for global coordinated actions towards improved management and conservation of eel. On the other hand, evidence for local, genetically based, phenotypic differences also justifies the needs for local actions. In particular, these results suggest that unique phenotypic attributes of eels colonizing the upper parts of the St. Lawrence River basin may be genetically distinct (from a functional standpoint) from those colonizing the Maritimes region, and as such could be irreplaceable. This also means that stocking the upper St. Lawrence River and Lake Ontario with glass eels from the Maritimes will likely not produce eels with same phenotypic attributes than those naturally colonizing these waters, as already suggested by the observations confirming that such stocked glass eels migrate as young and small silver eels with a proportion of males, a phenomenon never reported in the past.