Population Genetics, Life History, and Ecology of Arctic Marine Fishes

Résumé

... My research uses a comparative approach to reveal genetic, ecological, and life-history adaptations of Arctic fish species to the unique challenges of their environment at the northern extreme of their ranges. This paper highlights recent developments in my doctoral research, which can be separated into two general areas. The first is directed towards advancing knowledge of the evolutionary ecology and biodiversity of noncommercial Arctic marine fishes. The second concerns landlocked populations of Atlantic cod (Gadus morhua) persisting as marine relicts in saline coastal lakes on Baffin Island, at the northern extreme of the species' range in Canada. ... Noncommercial fishes were sampled from bycatch taken during Fisheries and Oceans Canada's turbot surveys in Baffin Bay and Davis Strait in September and October 2004. Trawling occurred at randomized stations in depth strata ranging from 400 to 1500 m in depth in Baffin Bay and Davis Strait .... My goal was to obtain approximately 100 specimens of species for which we had already obtained large samples of conspecifics or closely related taxa from temperate Atlantic waters. ... As conspecific samples are obtained, we will collect basic biological data, such as distribution, length, weight, sex, age, growth rate, fecundity, and age and size at maturity, to compare these features between high Arctic and temperate Atlantic populations. The most notable trend in the bycatch obtained during the fall of 2004 surveys ... was the paucity of species occurring to the north of Lancaster Sound. ... Species diversity was slightly higher ... off northeastern Baffin Island .... Our fieldwork in 2003 confirmed that the large cod in these lakes [Qasigialiminiq and Tariujarusiq Lakes, southwestern end of Cumberland Sound] were Gadus morhua, and not the more frequently landlocked Greenland cod, Gadus ogac, and that the lakes were saline meromictic lakes akin to Ogac Lake. ... The objectives of this part of my research include (i) basic physical, chemical, and biotic characterization of Arctic lakes in which Atlantic cod occur, and (ii) the study of aspects of their population biology, life history, and genetics. ... we have collected data on the length, weight, sex, maturity, liver weight, gonad weight, and stomach contents from 100 subadult and adult cod from each lake, and from a further 100 juvenile cod from Ogac Lake. Tissue samples and otoliths were also collected, for genetic and age/growth analysis, respectively. Underwater video was used to qualify benthic macrofauna and to observe cod behaviour in all three lakes. Plankton tows were made ... to compare micro-invertebrate populations among lakes .... Bathymetric measurements were taken using sonar across a number of transects in both Qasigialiminiq and Tariujarusiq to compare them to Ogac Lake.... Salinity, temperature, and dissolved oxygen strata were measured in each basin of each lake, again to compare abiotic limnology across lakes and over time at Ogac Lake. ... Temperature data loggers were deployed near the outflow of each lake to record the timing and frequency of tidal inflows. ... During the series of high spring tides that entered Ogac Lake in early July 2004, we collected samples of marine biota flowing into the lake, .... These samples consisted primarily of marine fish larvae and amphipods, although a high biomass of jelly-plankton ... was also observed entering the lake. ... Although Qasigialiminiq and Tariujarusiq are salt meromictic lakes, similar to Ogac Lake, both are warmer at all depths, and surface salinity is higher at Tariujarusiq (7 per mil) than at the other two lakes <1 per mil). ... Cannibalism appears to be less frequent among adult and subadult cod in the Cumberland Sound lakes (~14%) compared to Ogac Lake (~35%). ... Remarkably, our most conservative estimate of fish and amphipod biomass entering the lake during a 55-minute tidal inflow is 238 kg. .. Our calculations from tide predictions suggest that between 35 and 45 tides enter the lake during the open-water season each year. ... tidal inflows are crucial not only to replenish lake salinity, but also as a vital source of nutritive biomass to support these populations. The results of our genetic studies revealed remarkably low allelic variation at seven polymorphic microsatellite loci, providing evidence that these are small, inbred, and isolated marine relict populations. ... The fact that all three cod lakes occur in areas that were glaciated during the last ice age, and that the contemporary range of Atlantic cod in Canadian waters is constrained to the northern tip of Labrador, suggests that Atlantic cod probably extended their range northward during a postglacial period of ameliorated Arctic Ocean conditions, and colonized these coastal lakes, which would have been in the process of formation by glacioisostatic rebound during that period. ...