Contrasting effects of food quality and quantity on a marine top predator

Abstract

Overfishing of predatory fish has contributed to an increase in forage-fish stocks. At the same time, a rising demand for forage fish to supply fishmeal markets, in combination with climate change, has put strong pressure on these stocks, and this, in turn, has had an impact on marine top predators. We examined how inter-annual variation in food quality (sprat Sprattus sprattus weight-at-age) and quantity (sprat abundance) influenced Baltic Sea common murres Uria aalge during chick-rearing. Fledging success, i.e. survival from hatching to fledging, showed a positive relationship with food quality, but we found no effect of food quantity. We found no relationship between food quality and parental behaviour or chick feeding parameters, but a negative relationship between food quantity and trip duration. Our data indicate that there was room for parental birds to increase their effort to compensate for reduced food quality, but we found no signs of such compensation. We analysed different types of fish and seabird life-history data to separate effects of food quantity and quality on a top predator. Understanding such effects can contribute to clarifying causes and consequences for observed changes in life-history parameters and population dynamics of top predators.

Seabirds maintain offspring provisioning rate despite fluctuations in prey abundance: a multi‐species functional response for guillemots in the North Sea

“…It is interesting to note the role of sprat as a key forage fish for seabird populations in another North East Atlantic system, the Baltic (Hjernquist & Hjernquist ; Kadin et al . ).…”

Feather corticosterone reveals stress associated with dietary changes in a breeding seabird

“…; Kadin et al. ; Hjernquist and Hjernquist, ). Others clearly demonstrate that low‐quality prey, such as fisheries offal (Grémillet et al.…”

Increased use of intertidal resources benefits breeding success in a generalist gull species

“…66 The profitability of a food resource will be determined by its abundance, the quality 67 of the resource to meet the consumers' energetic and structural needs and the cost to 68 obtain that resource (Stephens & Krebs 1986). Within a generalist's diet resources will 69 differ in their quality, in terms of energy content and /or nutrients (Wanless et al 2005, 70 Österblom et al 2006, Kadin et al 2012). If the alternative food a consumer switches to 71 returns less energy or fewer nutrients per foraging expenditure, either because of higher 72 acquisition costs or poorer food quality, this can adversely affect the forager's demographic 73 traits (junk-food hypothesis: Alverson 1992, Grémillet et al 2008Grémillet et al , Österblom et al 2008.…”