The influence of sediment type on the distribution of the lesser sandeel, Ammodytes marinus

The lesser sandeel Ammodytes marinus is a key species in the North Sea ecosystem, transferring energy from planktonic producers to top predators. Previous studies have shown a longterm decline in the size of 0-group sandeels in the western North Sea, but they were unable to pinpoint the mechanism (later hatching, slower growth or changes in size-dependent mortality) or cause. To investigate the first 2 possibilities we combined 2 independent time series of sandeel size, namely data from chick-feeding Atlantic puffins Fratercula arctica and from the Continuous Plankton Recorder (CPR), in a novel statistical model implemented using Markov Chain Monte Carlo (MCMC). The model estimated annual mean length on 1 July, as well as hatching date and growth rate for sandeels from 1973 to 2006. Mean length-at-date declined by 22% over this period, corresponding to a 60% decrease in energy content, with a sharper decline since 2002. Up to the mid-1990s, the decline was associated with a trend towards later hatching. Subsequently, hatching became earlier again, and the continued trend towards smaller size appears to have been driven by lower growth rates, particularly in the most recent years, although we could not rule out changes in size-dependent mortality. Our findings point to major changes in key aspects of sandeel life history, which we consider are most likely due to direct and indirect temperature-related changes over a range of biotic factors, including the seasonal distribution of copepods and intra-and inter-specific competition with planktivorous fish. The results have implications both for the many predators of sandeels and for age and size of maturation in this aggregation of North Sea sandeels. KEY WORDS: Ammodytes marinus · Growth model · MCMC · North Sea · Phenology · SandeelResale or republication not permitted without written consent of the publisher Mar Ecol Prog Ser 432: 137-147, 2011 138 dynamics and to impact higher trophic levels, and indeed have already been linked with fluctuations in both commercially exploited fish stocks , Castonguay et al. 2008 and reproductive performance of land-based predators (Frederiksen et al. 2006, Sydeman et al. 2006.The lesser sandeel Ammodytes marinus (hereinafter sandeel) is a key species in the ecology of the North Sea and other parts of the NE Atlantic (Daan et al. 1990). It is generally the most abundant small planktivorous fish, and provides a critical trophic link between secondary producers (zooplankton, particularly calanoid copepods) and a wide variety of top predators, including larger fish, marine mammals and seabirds. Several studies have highlighted the critical importance of the availability and quality of sandeels for successful reproduction of North Sea seabirds (Monaghan 1992, Rindorf et al. 2000, Wanless et al. 2005. Sandeels are also the target of a major industrial fishery for fishmeal and fish oil (Furness 2002). However, evidence from several sources has indicated that conditions for sandeels in the North Sea are less favourable than...

Section: Discussionmentioning

confidence: 87%

mentioning

confidence: 87%

Mechanisms of long-term decline in size of lesser sandeels in the North Sea explored using a growth and phenology model

Frederiksen¹,

Elston²,

Edwards³

et al. 2011

“…Even within the North Sea, kittiwakes from some estuarine colonies feed mainly on clupeids rather than sandeels (Bull et al 2004). Sandeels are closely associated with specific types of sandy sediment to which they settle as juveniles; they subsequently spend most of their life buried, except when feeding in the water column or spawning (Wright et al 2000). Thus, they are found close to areas of suitable sediment throughout the year.…”

Section: Introductionmentioning

confidence: 99%

Regional patterns of kittiwake Rissa tridactyla breeding success are related to variability in sandeel recruitment

Frederiksen¹,

Wright²,

Harris³

et al. 2005

The population dynamics of marine top predators such as seabirds may be self-regulating through local prey depletion, or they may reflect environmentally induced fluctuations in prey availability. Both mechanisms are not mutually exclusive. We examined spatio-temporal variation in breeding success of black-legged kittiwakes Rissa tridactyla, a seabird widely monitored in the British Isles. Kittiwakes here feed mostly on lesser sandeels Ammodytes marinus, a species that is strongly tied to specific sediment types and therefore shows a strong regional population structure. Neither kittiwake colony growth rate nor breeding success correlated negatively with colony size as expected under local prey depletion in the absence of regional variation in carrying capacity. We used multivariate analyses of breeding success data for 42 kittiwake colonies to identify clusters showing synchronised variation in success, and compared these with known sandeel aggregations identified from fish and fishery surveys. A number of geographically distinct clusters of kittiwakes were identified, and these were largely congruent with sandeel aggregations. Major sandeel aggregations with clear associated clusters of kittiwake colonies occurred off of east England and east Scotland, while western coasts of Britain were characterised by smaller aggregations and less obvious kittiwake clusters. There was considerable regional variability in sandeel recruitment, and this was reflected in mostly uncorrelated time series of kittiwake breeding success between different regions. These results indicate that regional variation in prey availability had a stronger effect on kittiwake dynamics than local prey depletion. An appreciation of the appropriate spatial scale of prey dynamics thus improves understanding of the dynamics of marine predator -prey systems.

“…Thereafter, the juveniles settle onto seabed areas with course, sandy substrata (Wright et al 2000). In the summer months, they form large schools in the water column during the daytime, feed on zooplankton and bury themselves within the substratum at night.…”

Section: Introductionmentioning

confidence: 99%

Sandeel recruitment in the North Sea: demographic, climatic and trophic effects

Arnott¹,

Ruxton²

2002

132

142

The lesser sandeel Ammodytes marinus, which is one of the most abundant fish in the North Sea, has highly variable recruitment dynamics. We evaluate potential associations between their recruitment and some key biological and physical factors. Population data were analysed at the North Sea scale (years 1983 to 1999) and at the regional scale (southwestern section and northeastern section; years 1984 to 1996/7). Relationships between recruitment and spawning stock biomass were weak, but Age-1 sandeels (non-spawners) were related negatively with recruitment, implying that demographic effects are important. A negative relationship was detected between recruitment and the winter index of the North Atlantic Oscillation, which affects sea temperatures during the egg and larval period. Warmer sea temperatures correlated with poorer than average recruitment. This effect was most pronounced in the southwestern part of the North Sea, which is near the southern limit of the species' distribution. There was a positive association between recruitment and Calanus copepod (Stages V and VI) abundance around the time of larval hatching, suggesting that the availability of this prey species is important for young sandeel survival. Our findings suggest that climate change may impact upon sandeel populations in the North Sea.