Exploring the Influence of Food and Temperature on North Sea Sandeels Using a New Dynamic Energy Budget Model

Abstract

The zooplanktivorous schooling fish sandeels A. marinus comprise a quarter of North Sea fish biomass and are essential food for a number of marine mammals and birds. However, in recent decades there has been a decline in the abundance of older sandeels, with increased overwinter mortality proposed as a contributor. To survive winter animals require a minimum energy reserve which is determined by temperature, prey abundance, and possibly prey size. Here a new dynamic energy budget model is created to determine the influence of food and temperature on sandeel energy dynamics. The model hindcasts changes in energy and survival between 2000 and 2008, a period of pronounced stock decline in the northwestern North Sea. Overwinter starvation mortality was a large contributor toward a recent decline in sandeels in northern UK waters. Highest overwinter mortality rates were recorded for juveniles and not individuals aged 1 or over due to the effect of weight-specific metabolism. However, a sensitivity analysis of the model suggests that mortality rates are more sensitive to changes in copepod abundance in the build up to overwintering rather than temperature during overwintering. Further, projections show that temperature rises are negated by increases in large, but not small copepods. The conclusion is that food-driven size-selective starvation mortality contributed to the northwestern North Sea stock decline and that indirect food web effects of climate change are greater than direct physiological effects on sandeels.

Interannual decrease in condition factor of the western sand lance Ammodytes japonicus in Japan in the last decade: Evidence for food‐limited decline of the catch

“…They evaluated the minimum threshold of condition factor for successful reproduction as 4.5. MacDonald, Speirs, Greenstreet, and Heath () showed using a dynamic energy budget model that copepod biomass affected the growth and mortality of the North Sea sandeel Ammodytes marinus . Kuzuhara et al () revealed that food availability before estivation strongly affects various reproductive factors such as maturity rate and fecundity.…”

Trends in Sandeel Growth and Abundance off the East Coast of Scotland

“…Recruitment has been maintained while the number of older sandeels has declined (Heath et al, 2012). Two main factors have been proposed as responsible for the decline in sandeel abundance, increases in overwinter and predation mortality of 0-group individuals (MacDonald et al, 2018). Starvation risk decreases with increasing size (van Deurs et al, 2011); therefore, 0-group length prior to overwintering may correlate with overwinter mortality.…”

Temperature and body size affect recruitment and survival of sandeel across the North Sea

“…A significant positive effect of fish length on abundance of age-0 sandeel was found. Different mortality pathways have been proposed for first-feeding larvae (Wright and Bailey, 1996;Henriksen et al, 2018), the larval drift phase (Gurkan et al, 2012(Gurkan et al, , 2013, and overwintering of post-settled juveniles (van Deurs et al, 2011b;MacDonald et al, 2018). The size of age-0 was measured only in winter, which makes it difficult to favour any particular mechanism, but theory about early life and recruitment in fish provide insights to the processes that might be involved.…”

“…Bigger is also better for avoiding starvation of settled juveniles, since mass-specific metabolism during overwintering decrease with increasing size (van Deurs et al, 2011b). Thus, important factors affecting survival of sandeel during the first year of life are likely to be associated with changes in food condition and predation mortality (Eliasen et al, 2011;MacDonald et al, 2018MacDonald et al, , 2019. A potential close relationship with Calanus copepods has been investigated on several occasions (van Deurs et al, 2009(van Deurs et al, , 2015, where in particular "match-mismatch" (Cushing, 1990) relationships between the production of Calanus eggs and larval hatching have been highlighted (van Deurs et al, 2009;Régnier et al, 2017).…”