Modelling the transport of particles in the North Sea with reference to sandeel larvae

The transport of particles representing sandeel larvae in the North Sea is simulated with a three-dimensional circulation model for the years 1976 to 1990. A great year-to-year variability in drift patterns is demonstrated. The results may explain some of the observed differences in recruitment between the main sandeel areas in the North Sea. In the northern sandeel area it seems that strong year classes are unlikely if the retention due to unfavourable currents is poor, and that a high retention in the summer may favour a good year class. In the southern sandeel area no clear coupling between year class strength and larval drift is found, possibly because the retention always seems large enough for a potentially good year class. For more quantitative use of such models in relation to sandeel recruitment, more biological knowledge is obviously needed on larval vertical distribution and timing of sandeel hatching and settling.     

The recruitment process of the Barents Sea capelin (Mallotus villosus) stock, 2001–2003

Oceanographic and predation processes are important modulators of fish larvae survival and mortality. This study addresses the hypothesis that immature Norwegian spring‐spawning herring (Clupea harengus), when abundant in the Barents Sea, determine the capelin reproduction success through consumption of Barents Sea capelin (Mallotus villosus) larvae. Combining a hydrodynamic model and particle‐tracking individual‐based model, a realistic spatio‐temporal overlap between capelin larvae and predatory immature herring was modelled for the summer seasons of 2001–2003. Capelin larvae originating from western spawning grounds became widely dispersed during the summer season, whereas those originating from eastern spawning grounds experienced a rapid drift into the southeastern Barents Sea. Herring caused a 3% mortality of the capelin larvae population in 2001 and a 16% mortality in 2003, but the effect of predation from herring on capelin larvae was negligible in 2002. Despite a strong capelin larvae cohort and a virtual absence of predatory herring, the recruitment from the capelin 2002 year class was relatively poor from a long‐term perspective. We show that the choice of capelin spawning grounds has a major impact on the subsequent capelin larvae drift patterns, constituting an important modulator of the capelin larvae survival. Variation in drift patterns during the summer season is likely to expose the capelin larvae to a wide range of hazards, including predation from young cod, sandeel and other predators. Such alternative predators might thus have contributed to the poor capelin recruitment during 2001–2003, leading to the collapse of the capelin stock in the subsequent years.     

Effects of low‐oxygen conditions on embryo growth in the painted turtle,Chrysemys picta

Low‐oxygen conditions (hypoxia; <21% O₂) are considered unfavorable for growth; yet, embryos of many vertebrate taxa develop successfully in hypoxic subterranean environments. Although enhanced tolerance to hypoxia has been demonstrated in adult reptiles, such as in the painted turtle (Chrysemys picta), its effects on sensitive embryo life stages warrant attention. We tested the hypothesis that short‐term hypoxia negatively affects growth during day 40 of development in C. picta, when O₂ demands are highest in embryos. A brief, but severe, hypoxic event (5% O₂ for 0.5 h) moderately affected embryo growth, causing a 13% reduction in mass (relative to a normoxic control). The same condition had no effect during day 27; instead, a nearly anoxic event (1% O₂ for 72 h) caused a 5% mass reduction. All embryos survived the egg incubation period. Our study supports the assumption that reptilian embryos are resilient to intermittently low O₂ in subterranean nests. Further work is needed to ascertain responses to suboptimal O₂ levels while undergoing dynamic changes in developmental physiology.     

鱼类消化道菌群与碳水化合物代谢

碳水化合物氧化分解是鱼类能量的重要来源。由于碳水化合物来源广泛、价格相对低廉,饲料中添加适量碳水化合物,不仅可以降低饲料成本,而且可以节约蛋白原料,减少氨氮排放。然而以往研究表明,鱼类摄入超量碳水化合物时会出现抗病力受损、生长迟缓、脂肪肝、死亡率升高等问题。鱼类消化道微生物参与宿主的糖、脂类和蛋白质等代谢过程,对动物营养代谢有重要的调控作用。提高鱼类对饲料的利用率,对鱼类增产、渔民增收具有重要的现实意义。本研究综述了鱼类对碳水化合物的代谢,以鱼类消化道微生物为出发点,阐述了鱼类消化道微生物调控碳水化合物代谢的方式与可能机制,旨在为鱼类高效利用碳水化合物以及节约饲料中蛋白质提供新视角。