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Research project
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| Population dynamics of decapods: effects of climate and trophic interactions on snow crab |
| | The extent to which recruitment influences population dynamics of benthic marine invertebrates has been the subject of a large number of studies. Because most marine organisms have complex life cycles that include a planktonic larval phase capable of dispersal and a benthic phase, not all larvae that disperse will settle and not all settlers will survive to adulthood. For demographically open populations, recruitment is defined as the addition of new individuals to local benthic populations, after larval metamorphosis and settlement. Recruitment is therefore complex and involves a chain of processes from egg production, embryo hatching, larval advection and dispersal, settlement and early post-settlement events that may interact and operate at different temporal and spatial scales and vary according to the biotic and abiotic conditions prevailing locally or regionally. Also, early life stages (egg, larva and benthic juvenile) of marine organisms may represent the weakest link in the life cycle because of their high mortality rates. In fact, early benthic stages of marine invertebrates are known to be the most sensitive to environmental changes. Uneven production and/or survival of early life stages across years result in variable recruitment that affects subsequent adult population size.
Commercial landings and population abundances of various crab species can fluctuate greatly on decadal scales due to highly variable recruitment. One such species is the snow crab (Chionoecetes opilio), a major fisheries resource in the north Pacific and northwest Atlantic, especially in eastern Canada since the decline in groundfish abundance. Since the beginning of the fishery in the 1960s, however, snow crab landings and catch rates fluctuated greatly with periods of low availability severely impacting the snow crab industry and economy of crab-dependent communities. Settlement intensity (i.e. egg and larval production) and/or survival of early life stages may be crucial in population dynamics of snow crab. I examine the effects of climate variability and trophic interactions on the earliest life stages of the snow crab to identify the possible abiotic and biotic factors affecting snow crab populations. The abundance indices of snow crab come from a time series of snow crab population demographics and female reproductive output in a small bay located in northwest Gulf of St. Lawrence. The snow crab population in this bay has been extensively monitored since 1989 by quantitative trawl surveys that sample all body sizes including early benthic stages. Also, I develop a population model to assess the importance of several mechanisms controlling the abundance of commercially exploited snow crab populations. This will eventually allow us to predict the abundance of snow crab populations according to different scenarios of temperature and commercial exploitation, and therefore evaluate the effectiveness of fisheries management.
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