Du rural à l'urbain : les besoins et les motivations des personnes âgées pour vivre en milieu rural ou s'installer en milieu urbain

Après l’exode des jeunes des milieux ruraux, il semble que l’on assiste maintenant à l’exode des personnes âgées qui quittent les territoires ruraux pour s’en aller vivre vers les villes avoisinantes. Ce constat a déjà été fait dans d’autres régions du Québec et l’intérêt de faire une recherche sur ce sujet était de mieux connaître la situation régionale quant à l’exode des aînés des territoires ruraux dans la région du Saguenay–Lac-Saint-Jean. Il s’agissait aussi de mieux cerner les motivations et les besoins des personnes âgées à demeurer ou non dans le milieu rural où ils ont vécu et vivent encore pour certains. Ce rapport de recherche présente les résultats d’une recherche qui a été réalisée dans deux territoires ruraux du Saguenay–Lac-Saint-Jean, soit ceux du Bas-Saguenay Sud dans la MRC du-Fjord-du-Saguenay et de la MRC Domaine-du-Roy au Lac-Saint-Jean

Modeling the depuration potential of blue mussels (Mytilus spp.) in response to thermal shock

When contaminated, most molluscs destined for human consumption require a depuration regime lasting 48 h at a minimum temperature of 5 °C to ensure elimination of coliforms. However, this regime is unsatisfactory in northern temperate regions, where temperatures are frequently below 5 °C. A series of tests were undertaken to determine the filtration activity of mussels (Mytilus spp.) under cold temperatures. We used physiological measures rather than the more traditional method of bacterial analysis to evaluate mussel acclimation to cold temperatures. Mussels were acclimated for 4 weeks at three different temperatures (8, 4, and − 1 °C) and their scope for growth was evaluated each week to determine the level of acclimation. Mussels were then exposed to a thermal shock and clearance rates were measured after 2 h and 72 h. We observed a clearance rate of 2.45 l h− 1 g− 1 (g DW) for the 8 °C control group. Thus, within a 48-h depuration period, Mytilus spp. could filter a standard volume of 117.47 l. We used a von Bertalanffy exponential model to estimate the time required for an individual from each thermal shock treatment to filter that standard volume. We found that thermal shock had an important effect on the volume filtered by a mussel in 48 h. For example, mussels acclimated at 8 °C were able to filter the standard volume of 117.47 l in an average of 75 h at 4 °C, whereas those acclimated at 4 °C and transferred to 8 °C required only 23 h on average

Physiological differences between wild and cultured bivalves in Prince Edward Island, Canada

Bivalve culture in Canada increased by 25% from 2000 to 2016. In Prince Edward Island (PEI), bivalves are cultivated in bays and estuaries and there is limited space for further aquaculture expansion. Thus, there is merit in developing a numerical model determining the abundance of bivalve populations in relation to their food availability in order to assess the carrying capacity of shellfish growing areas. This modelling will take into account the different bivalve species present in the bay, as the cultivated Mytilus edulis and Crassostrea virginica and wild, M. edulis, C. virginica, Mya arenaria and Mercenaria mercenaria. As a first step toward a modelling goal, this study compared the physiological differences of the 6 bivalve groups. Three physiological parameters were measured: clearance rate, oxygen consumption and assimilation to determine the energy budget or scope for growth (SFG). These measurements were carried out on individuals contained in metabolic chamber at summer and autumn temperatures (20 and 8 °C, respectively). Our results show that M. edulis is best adapted to these temperature in PEI as it maintains high SFG at both temperatures. For C. virginica and M. arenaria, high physiological parameters under summer conditions were observed, followed by a decrease in autumn. For M. mercenaria rates were low at both temperatures indicating a persistently low growth potential. These results demonstrate the adaptive physiological capacity of each species and provide insight into the underlying reasons some species such as C. virginica and M. mercenaria are at their northern distribution limit in the Gulf of St. Lawrence. Finally, no differences in the SFG between cultivated and wild bivalves have been observed. These results are discussed within the context of estimating the impact of each bivalve group in bays environment from PEI and particularly on food availability

Interacting environmental stressors modulate reproductive output and larval performance in a tropical intertidal barnacle

Tropical intertidal filter-feeding invertebrates often face thermal stress and oligotrophic nearshore conditions, which may modulate reproductive responses. In order to investigate how these stressors affect resource allocation for reproduction, we first acclimated experimental populations of the higher shore barnacle Chthamalus bisinuatus to different levels of food supplies, to obtain baseline reproductive parameters, and then submitted them to consecutive stress events, by transferring populations to chambers where temperature was either unchanged (25°C) or increased to critical levels (45°C). Thermal stress decreased overall adult survival by 15% and overall larval release by 53%, while no significant effects of food shortage were detected. Experimental populations after moderate short-term stress events (transfer to control chambers) showed anticipatory fitness effects by increasing both the quantity and the quality of larvae, which survived longer without an exogenous food supply. After severe stress, parents first decreased larval release rate (thermal stress) and then produced lower-quality larvae (thermal stress plus food shortage), compatible with a selfish strategy. Lipid analyses showed that adults are very efficient in retaining essential fatty acids (EFAs) and capable of fast accumulation of reserve lipids shortly after stress, which however decreased over the experiment. Chronic stress led to decreased transfer of reserve lipids to larvae, and increased transfer of EFAs, suggesting a compensatory effect on larval quality. Populations exposed to both stressors lacked these temporal trends and produced low-quality nauplii. Unexpectedly, parental manipulation seems to involve the allocation of EFAs, not reserve lipids, as usually reported for lecithotrophic larvae

Temporal variation of secondary migrations potential: concept of temporal windows in four commercial bivalve species

Post-settlement dispersal potential of four commercial bivalve species (Mytilus edulis, Pecten maximus, Venus verrucosa and Ruditapes philippinarum) were studied through the assessment of recruits' sinking velocities by using a sinking velocity tube of five meters height. In parallel, dynamics of shear stress were monitored for five months on a tidal habitat characterized by the presence and the dispersal of the four species. By coupling both datasets we propose first theoretical estimates of temporal windows of secondary migrations. These experiments revealed interspecific differences in migration potential relate to shell shapes and behaviour, especially to secretion of byssal threads. The sensitivity to passive and active post-settlement migrations seems to rely on the synchronisation between the arrival on the sediment, the tidal regime (spring tide, neap tide), but also the rate of growth of the recruits. The present study confirms that patterns of secondary migrations of bivalve recruits result from a close physical-biological coupling involving benthic boundary layer (BBL) hydrodynamics and shell morphology as well as eco-ethological responses to environmental conditions but clearly modulated by the growth dynamics until a threshold size when drifting is no longer possible

Novel Feed from Invasive Species is Beneficial to Walleye Aquaculture

Carnivorous fishes, such as the Walleye Sander vitreus, are nutritionally demanding for fish meal. A promising alternative to marine-origin fish meal, the supply of which has been stagnant in recent decades, is fish meal derived from undesirable freshwater species, such as the White Sucker Catostomus commersonii. To evaluate the relative value of such ingredients, we examined the growth performance of Walleye juveniles. Two dietary treatments were tested: an experimental (EXP) diet that was manufactured using White Sucker as fish meal in comparison with a commercial (COM) diet, EWOS Micro (EWOS Canada, Ltd.). Dietary lipid content was 15.1% and 16.8% for EXP and COM diets, respectively. The protein content was 50.4% and 57.6% for EXP and COM diets, respectively. The energy content was 5,098.76 ± 9.23 cal/g (mean ± SD) for the EXP diet and 5,134.47 ± 10.95 cal/g for the COM diet. Starting at 27 d posthatch, Walleye juveniles (initial weight [mean ± SD] = 0.03 ± 0.008 g; initial length = 15.7 ± 1.5 mm) were reared for 6 weeks in three replicate tanks for each treatment. Condition factor (0.83), final weight (1.12 ± 0.3 g), and weight gain (1.09 ± 0.06 g) were higher in fish that were fed the EXP diet. Similarly, the energetic lipid content of fish in the EXP treatment group (mean ± SD = 5.01 ± 0.45 g/kg) was also higher than that of fish fed the COM diet (3.30 ± 0.53 g/kg). Although the polar lipid content (membrane lipids) was similar in fish from the two treatments, the nutritional ratio for COM juveniles was over 1.5 for arachidonic acid and docosahexaenoic acid, indicating selective incorporation by juveniles and suggesting a potential dietary imbalance of these fatty acids. Furthermore, the higher observed selective incorporation of oleic acid in juveniles fed the EXP diet suggested that a higher value of this fatty acid in the EXP feed could have increased Walleye growth performance. Threonine was the main essential amino acid (AA; >18.5% of total AAs), while serine and glycine contributed the highest percentages of the nonessential AAs (>31% and 8.5% of total AAs, respectively). All three AAs, often considered limiting ingredients, are important to support growth and are involved in metabolic processes in some fish species. Our results demonstrate that feed pellets made with White Sucker fish meal improved growth in Walleye juveniles and can serve as a suitable and probably lower-cost regional alternative to marine fish meal in feeds for carnivorous fishes

Trophic cues as possible triggers of mussel larval settlement in southeastern Brazil

Oligotrophic conditions may impose a nutritional challenge for the larval and early post-larval development of bivalves during the search for a suitable benthic habitat. Here we investigated what settlement cues might be important for mytilid populations in southeastern Brazil. Our results point to a trophic trigger mediating larval settlement that may include an effect of saturated fatty acids, probably linked to organic detritus and bacterial production deriving from terrestrial inputs. The prevalence of drifting in this population suggests it may be a strategy for individuals to delay final settlement until encountering favorable trophic environmental conditions

Tracking larvae with molecular markers reveals high relatedness and early seasonal recruitment success in a partially spawning marine bivalve

The partial synchronized spawning strategy\ud adopted by some marine invertebrate broadcast-spawners\ud can lead to the production of many distinct pools of larvae\ud within a single reproductive cycle. Following the fate of\ud these larval groups from birth to settlement with molecular\ud markers might shed light on mechanisms regulating their\ud population recruitment. Larvae and recruits of Mya arenaria,\ud a partially spawning marine bivalve, were monitored\ud and collected over 13 consecutive weeks during an entire\ud reproductive cycle. Each sampled individual (n = 218)\ud was sorted according to size (early veligers, late veligers,\ud post-larval recruits) and genotyped at seven microsatellite\ud loci for comparisons among samples and with adult reference\ud samples (n = 270). While traditional differentiation\ud statistics (e.g., pairwise ϴST, allelic richness) suggested\ud the absence of sweepstakes reproductive success, the level of relatedness found within and among larvae and recruit\ud samples suggested otherwise. Four samples out of ten were\ud observed to have higher within-sample relatedness values\ud than randomly expected, including the very first group\ud of early veligers produced in the season (E1) and the last\ud group of post-larvae who survived recruitment (P10). E1\ud individuals were also found to be more related than randomly\ud expected to individuals of more than 80 % of all\ud other samples including the last surviving recruits (P8 and\ud P10). These results suggest that the first larvae produced\ud in the season were the most successful to survive recruitment.\ud Results also show direct evidence for larval retention\ud and demonstrate for the first time larval and post-larval kin\ud aggregation in a marine bivalve