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

Alan MacDonald,Michael R. Heath,Douglas C. Speirs,Simon P. R. Greenstreet,Philip Boulcott

doi:10.3389/fmars.2019.00201

Alan MacDonald, Michael R. Heath + Show 3 more

Open Access

https://doi.org/10.3389/fmars.2019.00201

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Abstract

Sandeels Ammodytes marinus are a crucial forage fish species in the North Sea, transferring zooplankton energy to higher trophic levels. However, there has been a sustained decline in sandeel abundance in the northwestern North Sea since 2000. Here we use field data to analyze year-to-year changes in A. marinus growth rate between 1997 and 2009 and assess whether variation in growth rate corresponded with variation in abundance. The signature of the reduction in abundance between 2000 and 2009 was a decline in age 1 sandeels, while no other age class declined. Analysis of age-length data showed that the decline in abundance coincided with a period of low growth. Growth performance indexes were correlated with zooplankton and phytoplankton biomass but not temperature. Further, we observed a significant correlation between larval growth rate and 0-group sandeel length during a period when hatch dates were relatively fixed; suggesting recent changes in length were influenced by food availability.

Highlights

Ammodytes marinus are lipid rich shoaling fish that form a vital part of the link between zooplankton production and higher trophic levels in the North Sea
Length is an indicator of energetic content (Hislop et al, 1991; Wanless et al, 2005), which is influenced by short-term variation in sandeel growth rate (0–2 years) since fish
In the present study we investigate year-to-year changes in sandeel abundance-at-age and lengthat age to (1) estimate changes in abundance-at-age in the early 2000s to determine years the stock decreased and what age classes were affected, (2) analyse year-to-year changes in growth rates between 1997 and 2006, (3) assess whether there was a correlation between larval growth rate and 0-group length in June, and (4) assess relationships between growth rates and zooplankton abundances, chlorophyll densities and Sea surface temperature (SST)

Summary

Introduction

No time series on sandeel growth rate exists, there is evidence of a decline in size; with long-term decreases in the mean lengths of age groups 0, 1, and 2 in the North Sea (Wanless et al, 2004; van Deurs et al, 2014; Howells et al, 2017). Of particular interest to United Kingdom seabird conservationists is the long term decline in 0-group length (Wanless et al, 2004; Howells et al, 2017), as breeding success and survival of many seabird species is sensitive to variation in Trends in Sandeel Growth and Abundance length and energy content of this age class (MacDonald et al, 2015). Changes in 0-group length-at-date decline could be caused by changes in spawning and hatch days, size-dependent larval mortality or larval growth rate (Frederiksen et al, 2011)

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