Résumé: As marine protected areas (MPAs) are increasingly being utilised as a tool for fishery management, their impact on the food web needs to be fully understood. However, little is known about the effect of MPAs on fish assemblages, especially in the presence of different life history and ecological traits. Modelling the observed changes in fish population structures may provide a mechanistic understanding of fish assemblage dynamics. In addition, modelling allows a quantitative estimate of MPA spill-over. To achieve this purpose, we adapted an existing ecosystem model, OSMOSE (Object-oriented simulator of marine biodiversity exploitation), to the specific case of the presence of fish with multiple life histories. The adapted model can manage 4 main categories of life history identified in an estuary MPA: fish that (1) spend their entire life cycle locally, (2) are present only as juveniles, (3) enter the area as juveniles and stay permanently except during reproduction periods, which occur outside the estuary, and (4) are present occasionally and for a short time for foraging purposes. To take into account these specific life-history traits, the OSMOSE code was modified. This modelling approach was developed in the context of the Bamboung Bolong MPA, located in a mangrove area in the Sine-Saloum Delta, Senegal. This was the ideal case to develop our approach as there has been scientific monitoring of the fish population structure inside the MPA before fishery closure, providing a reference state, and continuous monitoring since the closure. Ecologically similar species were pooled by trophic traits into 15 groups that represented 97% of the total biomass. Lower trophic levels (LTL) were represented by 6 compartments. The biomass of the model species was calibrated to reproduce the reference situation before fishery closure. Model predictions of fish assemblage changes after fishery closure corresponding to the Bamboung MPA creation scenario were compared to field observations; in most cases the model reproduces observed changes in biomass (at least in direction). We suggest the existence of a “sanctuary effect”, that was not taken into account in the model, this could explain the observed increase in biomass of top predators not reproduced by the model. Finally, the annual MPA fish spill-over was estimated at 11 tons (~33% of the fish biomass) from the model output, mainly due to diffusive effects.

Résumé: Hyperallometric reproduction, whereby large females contribute relatively more to the renewal of the population than small females, is purported to be widespread in wild populations, especially in fish species. Bioenergetic models derived from a sufficiently general metabolic theory should be able to capture such a relationship but it was recently stated that no existing models adequately capture hyperallometric reproduction. If this were true it would seriously challenge our capacity to develop robust predictions of the life history and population dynamics in changing environments for many species. Here, using the European sea bass (Dicentrarchus labrax) as a test case, we demonstrate multiple ways that hyperallometric reproduction in a population may emerge from the Dynamic Energy Budget (DEB) theory, some inherently related to the metabolism and life history and others related to plastic or genetically based intraspecific variation. In addition, we demonstrate an empirical and modelled hypoallometric scaling of reproduction in this species when environment is controlled. This work shows how complex metabolic responses may underlie apparently simple relationships between weight and reproduction in the wild and provides new and testable hypotheses regarding the factors driving reproductive scaling relationships found in the wild.

Résumé: Abstract Oxidative stress has been proposed as a central causal mechanism underlying the life?history trade?off between current and future reproduction and survival in wild animals. While mixed evidence suggests that maternal oxidative stress may act both as a constraint and a cost to reproduction, some studies have reported a lack of association between reproduction and maternal oxidative stress. The oxidative shielding hypothesis offers an alternative explanation, suggesting that mothers may pre?emptively mitigate the oxidative costs of reproduction by increasing antioxidant defences prior to reproduction. We tested the oxidative constraint, cost and shielding hypotheses using a longitudinal field study of oxidative stress levels in a species that breeds using daily energy income, the Columbian ground squirrel (Urocitellus columbianus). Elevated maternal oxidative damage prior to reproduction was associated with higher maternal investment in litter mass at birth, but not at weaning. Breeding females increased their antioxidant capacity and decreased their oxidative damage from birth to lactation, compared to non?breeding females measured at the same time periods. However, lower maternal oxidative stress during lactation was not associated with higher offspring survival or mass growth over this period. Our results provide little evidence for maternal oxidative stress acting as a constraint on, or cost to, reproduction in Columbian ground squirrels, but partially support the idea that oxidative shielding occurred to buffer potential oxidative costs of reproduction. A plain language summary is available for this article.