Non-Breeders as a Buffer Against Environmental Stress: Declines in Numbers of Great Skuas on Foula, Shetland, and Prediction of Future Recruitment

Klomp, Nicholas I.; Furness, Robert W.

doi:10.2307/2404503

Cited by 66 publications

(46 citation statements)

References 11 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Nonbreeders may fill vacancies that arise in the breeding component, such that breeding numbers remain relatively stable even during a period of rapid decrease in total population numbers. An example of such buffering is provided by great skuas in Foula during the 1980s, when numbers of nonbreeders decreased rapidly due to adverse feeding conditions but breeding numbers changed little (Klomp and Furness, 1992). Thirdly, responses of seabird populations will tend to lag behind changes in environmental conditions because seabirds show delayed maturity.…”

Section: Reductions In Discharge Of Discards and Offal At Seamentioning

confidence: 99%

Impacts of fisheries on seabird communities

Furness¹

2003

Sci. Mar.

188

156

View full text Add to dashboard Cite

SUMMARY: Long-line by-catch of albatrosses and petrels may soon lead to species extinctions. Set-net bycatch has caused major reductions in certain seabird populations. Some fisheries may decrease numbers of seabirds by reducing abundance of prey-fish. Other fisheries may increase seabird numbers, by increasing prey-fish abundance through depletion of predatory fish stocks, or by provision of offal and discards. These latter impacts of fisheries on seabirds are often difficult to measure against a background of many and varied environmental and human influences. Depletion of stocks of small lipid-rich fish have reduced numbers of seabirds, in Peru, the Norwegian Sea, and the Barents Sea. However, reductions of predatory fish stocks in the North Sea have more than compensated for quantities of sandeels removed by the sandeel fishery. While piscivorous fish stocks remain low, sandeel fishery and seabirds appear to be able to coexist. However, if piscivorous fish stocks recover in the North Sea, reduced availability of sandeels to seabirds may affect certain species. Provision of discards and offal can stimulate large increases in scavenging seabird numbers. Desirable reductions in discard rates may have an unfortunate side-effect of forcing some scavenging seabirds to turn to killing smaller seabirds, with drastic consequences for community structure.Key words: conservation, discards, ecosystem, fisheries management, industrial fisheries, predator-prey, sandeel. RESUMEN: EL IMPACTO DE LAS PESQUERIAS EN LAS COMUNIDADES DE AVESMARINAS. -Las capturas accidentales de los albatros y petreles en palangres pueden llevar pronto a algunas especies a la extinción. La captura en redes de trasmallo ha causado también grandes reducciones en ciertas poblaciones de aves marinas. Ciertas pesquerías pueden provocar la disminución en el número de aves marinas al reducir la abundancia de los peces presa. Otras pesquerías pueden hacer crecer el número de aves marinas, al incrementar la abundancia de los peces presa mediante la disminución de las efectivos de los peces depredadores, o mediante el suministro de despojos y descartes. Estos últimos impactos de las pesquerías en las aves marinas son con frecuencia difíciles de medir por el efecto de numerosas y variadas influencias ambientales y humanas. La disminución de efectivos de pescado azul de pequeño tamaño ha reducido el número de aves marinas en Perú, el Mar de Noruega y el Mar de Barents. Sin embargo, en el Mar del Norte, la reducción del lanzón (A. marinus) como consecuencia de su pesca específica se ha visto ampliamente compensada por una reducción en los efectivos de peces predadores. Mientras los efectivos de peces piscívoros se mantengan bajos, la pesca del lanzón y las aves marinas parecen ser capaces de coexistir. No obstante, si los efectivos de peces piscívoros se recuperan en el Mar del Norte, reduciendo la disponibilidad de lanzones para las aves marinas, esto afectaría a ciertas especies. El aprovisionamiento de descartes y despojos pudiera estimular grandes increme...

show abstract

Section: Reductions In Discharge Of Discards and Offal At Seamentioning

confidence: 99%

Impacts of fisheries on seabird communities

Furness¹

2003

Sci. Mar.

188

156

View full text Add to dashboard Cite

show abstract

“…Brown skuas at the Chathams (New Zealand) and Tristan skuas at Gough and Inaccessible Islands hunt almost exclusively at night, catching petrels on the ground or in some cases excavating burrows (Furness 1987, Young et al 1988, Ryan & Moloney 1991, and herring gulls Larus argentatus in Newfoundland and slaty-backed gulls L, schistisagus in Japan catch Leach's petrels during the latter's nocturnal visits to the colony (Watanuki 1986, Pierotti & Annett 1991. Some great skuas at St Kilda might have the same feeding habits, although great skuas at other north Atlantic colonies appear to be largely inactive at night (Bayes et al 1964, Furness 1987, Klomp & Furness 1992.…”

Section: Discussionmentioning

confidence: 99%

“…Why this should be the case when there were potentially huge numbers of seabird prey available at Foula is unclear, but may be related to a high level of intra-specific competition. Klomp & Furness (1992) estimated that 2300 to 2400 pairs of great skuas were breeding on Foula in 1988 to 1990. By comparison at St Kilda, where the total number of great skuas is an order of magnitude lower, predation on other seabirds would appear to be a very effective feeding method for adults to adopt.…”

Section: Discussionmentioning

confidence: 99%

Inter-colony variation in diet and reproductive performance of great skuas Catharacta skua

Phillips¹,

Catry²,

Thompson³

et al. 1997

Mar. Ecol. Prog. Ser.

View full text Add to dashboard Cite

Sustained population growth of great skuas Catharacta skua during the current century has been attributed largely to a high abundance of sandeels, principally Ammodytes marinus, and a plentiful supply of discards from whitefish trawlers in the vicinity of breeding colonies A new colony of great skuas was establ~shed at St Kilda, Outer Hebrides, in 1963 and has since grown rapidly despite an apparent lack of sandeels in the waters surrounding the archipelago and the presence of only a small whitefish fishery. This paper presents an analysis of diet and breeding ecology of great skuas at Hirta, St Kilda, over 3 seasons, 1994 to 1996, with comparative data from Foula, Shetland, the largest and one of the oldest of the British colonies. At St Kilda, breeding adults, nonbreeders and chicks all fed extensively upon other seabirds (44 to 65'\L of pellets over the 3 yr), and to a lesser extent on goose barnacles Lepassp. (18 to 30":, of pellets) and fish (16 to 30'X of pellets), with sandeel virtually absent from the diet (0.2 to 0.3% of pellets). In contrast, at Foula only 4 to 1 2 % of pellets were of other seabirds, with sandeels and d~scarded fish together const~tuting the vast majority ( 4 to 3 6 "~ and 55 to 88% of pellets, respectively). Despite the low availability of sandeels and discards at St k l d a , egg volumes, chick body condition and annual productivity were at least as high as at Foula, and territorial attendance of breeding adults was much higher, indicating considerably lower foraging effort during chick-rearing. Great skuas at St Kilda are therefore able to make effective use of other seabirds as a food resource during the breeding season, in sharp contrast to Foula where adult mortality increased and chick growth rates and breeding success plummeted during the marked decline in sandeel abundance in the late 1980s.

show abstract

“…Usually, immature skuas gather at speciWc sites (called clubs) on the nesting islands, in the years before they start breeding (Klomp and Furness 1992). In large colonies, such clubs are often attended by hundreds of birds (Klomp and Furness 1992;Phillips et al 2004).…”

mentioning

confidence: 99%

“…In large colonies, such clubs are often attended by hundreds of birds (Klomp and Furness 1992;Phillips et al 2004). It is, therefore, most telling that we have never been able to locate any club site at New Island.…”

mentioning

confidence: 99%