Association between growth and Pan I genotype within Atlantic cod (Gadus morhua) full sib families

Studies of the pantophysin (Pan I*) locus in Atlantic cod Gadus morhua and other marine gadoids indicate that the locus is under positive selection; in Atlantic cod, genotypic variation at this locus has been linked to differences in growth. Here, we present preliminary data comparing the growth and condition of different Atlantic cod Pan I* genotypes within families held under seminatural mesocosm conditions. Larvae from three full-sibling families carrying Pan I*bb or Pan I*ab genotypes were reared for 10 weeks in two mesocosms. Multivariate analysis of variance indicated that larvae carrying the Pan I*ab genotype exhibited significantly higher standard length, dry weight, and RNA: DNA ratio (condition factor) than did larvae that carried the Pan I*bb genotype, potentially indicating selection. The influence of linked loci cannot be excluded; indeed, the absence of a significant correlation between genotype and growth in one family may substantiate this. The lack of differences in survival among genotypes indicates that moderate selective effects are acting primarily through size-specific mortality and fecundity. The proposed putative fitness effects, together with documented marked geographic differentiation in the wild, have implications for Atlantic cod population structure, effective migration rates, recruitment, and local adaptation, which are of particular relevance in a species threatened by continuing exploitation and rising sea temperatures

Can fisheries-induced evolution shift reference points for fisheries management?

Biological reference points are important tools for fisheries management. Reference points are not static, butmay change when a population's environment or the population itself changes. Fisheries-induced evolution is one mechanism that can alter population characteristics, leading to "shifting" reference points by modifying the underlying biological processes or by changing the perception of a fishery system. The former causes changes in "true" reference points, whereas the latter is caused by changes in the yardsticks used to quantify a system's status. Unaccounted shifts of either kind imply that reference points gradually lose their intended meaning. This can lead to increased precaution, which is safe, but potentially costly. Shifts can also occur in more perilous directions, such that actual risks are greater than anticipated. Our qualitative analysis suggests that all commonly used reference points are susceptible to shifting through fisheries-induced evolution, including the limit and "precautionary" reference points for spawning-stock biomass, B-lim and B-pa, and the target reference point for fishing mortality, F-0.1. Our findings call for increased awareness of fisheries-induced changes and highlight the value of always basing reference points on adequately updated information, to capture all changes in the biological processes that drive fish population dynamics

Retention of Coastal Cod Eggs in a Fjord Caused by Interactions between Egg Buoyancy and Circulation Pattern

Norwegian coastal cod form a stationary population of Atlantic cod Gadus morhua consisting of several genetically separated subpopulations. A small-scale differentiation in marine populations with pelagic eggs and larvae is made possible by local retention of early life stages in coastal environments. A numerical model was used to simulate the circulation in a fjord system in northern Norway over 2 years with different river runoff patterns. The dispersal of cod eggs was calculated with a particle-tracking model that used three-dimensional currents. The observed thickness of the low-salinity surface layer was well reproduced by the model, but the surface salinity was generally lower in the model than in the observations. The cod eggs attained a subsurface vertical distribution, avoiding the surface and causing retention. Interannual variations in river runoff can cause small changes in the vertical distribution of cod eggs and larger changes in the vertical current structure. Retention in the fjord system was strong in both years, but some eggs were subjected to offshore transport over a limited time period. The timing of offshore transport depended on the precipitation and temperatures in adjacent drainage areas. A possible match between maximized spawning and offshore transport may have a negative effect on local recruitment