Recruitment of lesser sandeel Ammodytes marinus in relation to density dependence and zooplankton composition

Abstract

Recent recruitment failure of lesser sandeel Ammodytes marinus, a key prey fish in the North Sea, followed by several years of low spawning stock biomass, prompted us to investigate factors influencing the recruitment of this species. We tested 2 hypotheses that relate to ecological mechanisms of recruitment regulation in lesser sandeel: (1) a positive spawning stock-recruitment relationship is decoupled in years associated with high abundances of age-1 sandeels and (2) the survival success of early larvae depends specifically on the abundance of Calanus finmarchicus and not C. helgolandicus. The findings of the present study supported both hypotheses and resulted in a multiple linear recruitment model with pronounced predictive capabilities. The model includes interactions between age-1 abundance and spawning stock biomass, plus the effect of C. finmarchicus abundance, and it explained around 65% of the inter-annual variation in recruitment in contrast to only 12% by a traditional Ricker curve. We argue that early egg production in C. finmarchicus supports the survival of larvae, and that climate-generated shifts in the Calanus species composition lead to a mismatch in timing between food availability and the early life history of lesser sandeels.

Towards an integrated forecasting system for fisheries on habitat-bound stocks

“…Consequently, fundamental difficulties in analyzing ecosystem behaviour arise and hypotheses are numerous and difficult to discriminate (Carpenter, 2002), further complicated by mathematical issues typical of non-linear systems like instabilities, chaos and regime shifts. These pessimistic prospects have spurred some interest in alternative routes to ecosystem forecasting, like artificial neural networks (Chen and Ware, 1999;Huse and Ottersen, 2003;Suryanarayana et al, 2008). However, ecosystems are facing regime shifts and major trophic reorganization these years (Beaugrand et al, 2009), which renders-unguided machine learning from recent history dubious; there is no safe way around improving a process-oriented representation of the marine ecosystems.…”

Effects of copepod size on fish growth: a model based on data for North Sea sandeel

“…In recent times, the abundance of C. finmarchicus has declined all over the northeastern Atlantic, whereas C. helgolandicus has increased, but only in the southern North Sea (Planque & Taylor 1998). The decline in C. finmarchicus has been linked to reduced survival of fish larvae (Beaugrand et al 2003, van Deurs et al 2009) and food consumption and growth of lesser sandeel in the North Sea (van Deurs et al 2014). The northward shift in the distribution of C. finmarchicus may have caused a northward shift in the feeding migration of North Sea herring (Corten 2000).…”

Environmental Impacts—Marine Ecosystems

“…The species is a very important prey item for the small fish favoured by seabirds . In particular, the recruitment of lesser sandeel in the North Sea is strongly positively correlated with C. finmarchicus abundance (van Deurs et al 2009).…”

“…Although Arnott and Ruxton (2002) and van Deurs et al (2009) found this species to be sensitive to changes in sea temperature, this important forage fish is very difficult to study, and little is known about how it is affected by rising sea temperatures. Studies indicate that in recent warmer years, birds have been struggling to find sufficient food for their chicks, because sandeels have been too few, too small, too lean, or have not been available at the right time.…”