Timing of hatching inAmmodytes marinus from Shetland waters and its significance to early growth and survivorship

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.

Section: Discussionmentioning

confidence: 99%

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

Frederiksen¹,

Wright²,

Harris³

et al. 2005

“…Further details about model parameters are summarized in Table 1. Energy intake was predicted for different sizes of sandeel, ranging from newly metamorphosed sandeels of 5 cm (Wright & Bailey 1996) all the way to 17 cm, which is the maximum attainable length of lesser sandeels in the central North Sea (Boulcott & Wright 2008, Jensen et al 2011). Our analysis focused on 2 distinct size groups of copepods, viz.…”

Section: Methodsmentioning

confidence: 99%

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

Deurs¹,

Jørgensen²,

Fiksen³

2015

In productive marine off-shore ecosystems, the flow of energy from zooplankton to large predators is channeled through a few species of short-lived, highly abundant schooling planktivorous fish. There are indications that these species respond to qualitative and phenological changes in the zooplankton. If so, the climate-induced alterations of the local copepod communities that we see in temperate and arctic regions may influence the energy flux in marine food chains. In order to investigate how different processes contribute to the relationship between copepod size and fish growth, we merged 2 mechanistic models from relevant data: (1) a model of the bioenergetics and stomach filling/evacuation dynamics, and (2) a Holling type II functional response model that encompasses visual range from basic principles. The model predicts that going from a situation where large Calanus copepods (2 mm) dominate the prey field of lesser sandeel Ammodytes marinus in the central North Sea to a situation where only relatively small (1 mm) and less energy-rich copepods are available roughly halves the energy intake of sandeels even if prey biomass concentration remains constant. Visual constraint on foraging was the most important factor, followed by handling time limitation and prey energy content. These limitations became stronger with increasing fish length, showing that copepod size and energy content have a strong effect on the specific growth potential of these fish.

“…Moreover, we also see rapid nestling growth for piscivorous rhinoceros auklets (this study and Bertram et al 2001) and tufted puffins (Gjerdrum et al 2003) in cool years when diets are dominated by 0+ sand lance. As sand lance themselves feed primarily on copepods (Field 1988), cool years would provide favourable feeding conditions for young fish and thus contribute to strong recruitment to local populations (see also Wright & Bailey 1996). In British Columbia, Pacific sand lance are within the southern third of their range (Hart 1973), and, based upon Myers' (1998) assertion regarding environment-recruitment relationships, we expect the proposed associations between spring SST, copepod availability and sand lance recruitment to hold in this system across years.…”

Section: H1: Recruitment Of Sand Lance Around Triangle Increases At Cmentioning

confidence: 99%

Effects of interdecadal climate variability on marine trophic interactions: rhinoceros auklets and their fish prey

Hedd

Bertram²,

Ryder³

et al. 2006

This paper presents time-series information on the diet composition and breeding performance of rhinoceros auklet Cerorhinca monocerata at Triangle Island, British Columbia, Canada, during 15 breeding seasons between 1976 and 2001. Three shifts in ocean climate occurred within British Columbia during this period (1976-77, 1989-90, 1998-99), allowing us to evaluate associations between marine environmental conditions and the reproduction of this piscivorous seabird. Lipid-rich Pacific sand lance Ammodytes hexapterus was the single most important prey delivered to chicks across years (15 yr avg. 38%; annual range 4 to 86%). Interannual variability was high, but in general breeding performance was strongest when 0+ sand lance predominated chick diets. Other annually important prey taxa included Pacific saury Cololabis saira, juvenile rockfishes Sebastes spp., Pacific herring Clupea pallasi and juvenile salmonid Oncorhynchus spp. The dietary importance of these prey also varied seasonally. Marine environmental conditions (evaluated using sea surface temperatures, SSTs) were clearly associated with reproduction of rhinoceros auklet, as both occurrence of sand lance in the diet and the growth rates of chicks diminished as spring SSTs increased (r = -0.680, p < 0.01, and r = -0.697, p < 0.01, respectively). We hypothesized that recruitment to local sand lance populations was temperature dependent. The strong negative relationship between dietary occurrence of 0+ sand lance and spring SST (r = -0.560, p < 0.05), coupled with the lack of a similar relationship for 1+ sand lance (p > 0.20), was consistent with the temperature-dependent recruitment hypothesis. Our data suggest that SSTs could interact with population age structure to affect the recruitment dynamics of Pacific sand lance. We estimated the annual dietary importance of 0+ sand lance to rhinoceros auklets using spring SST and the importance of 0+ sand lance in the diet the previous year.