Implications for seabirds off South Africa of a long-term change in the distribution of sardine

Crawford, R. J. M.; Sabarros, PS; Fairweather, Tracey P.; Underhill, Les G.; Wolfaardt, A. C.

doi:10.2989/ajms.2008.30.1.18.468

Cited by 68 publications

(57 citation statements)

References 59 publications

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“…In western Greenland, great cormorants showed a high foraging efficiency in an environment with low prey abundance (Gremillet et al 2004). GPS-tracked cape gannets from the South African Atlantic coast appeared restricted to an area of the Benguela current system that no longer supports high anchovies and sardines, due to a recent regime shift, which resulted in poor foraging success and a marked decline in population (Crawford et al 2008a). This was attributed to the inability of seabirds with a limited foraging range to track the large scale movement of their prey (Gremillet et al 2008).…”

Section: Discussionmentioning

confidence: 99%

Pros and cons of using seabirds as ecological indicators

Durant¹,

Hjermann²,

Frederiksen³

et al. 2009

Clim. Res.

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108

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Climate change and overfishing are increasingly causing unanticipated changes in marine ecosystems (e.g. shifts in species dominance). In order to understand and anticipate these changes, there is a crucial need for indicators that summarise large quantities of information into a few relevant and accessible signals. Seabirds have been suggested as good candidates for ecological indicators of the marine environment; however, few studies have critically evaluated their value as such. We review the role of seabirds as ecological indicators, and discuss their limitations and drawbacks, as compared to other types of indicators. In addition, we highlight the statistical consequences of inverse inference when using seabird data as indicators. We discuss the use of integrated indices and the use of seabirds as autonomous samplers of the marine environment. Finally, we highlight the necessary steps preceding the use of seabirds as indicators. We conclude that, in order to use seabird time series properly, the use of recent advances both in statistics and in remote sensing is a way to move forward. This, along with the assessment of their usefulness, should enable us to use seabird indicators appropriately for managing urgent conservation problems.

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Section: Discussionmentioning

confidence: 99%

Pros and cons of using seabirds as ecological indicators

Durant¹,

Hjermann²,

Frederiksen³

et al. 2009

Clim. Res.

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108

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“…A change in prey availability may influence the decision to breed and can play a major role in breeding success, can affect survival and can influence inter-colony movements (Crawford & Dyer 1995, Crawford et al 2008a. Consequently, the change in the distribution of sardine and anchovy is thought to be largely responsible for the changes observed in the gannet colonies.…”

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confidence: 99%

“…The combination of these 2 factors can have severe consequences on seabird populations, yet it is often difficult to disentangle their effects (Frederiksen et al 2004, Rolland et al 2008, Gremillet & Boulinier 2009, Rolland et al 2010. It is believed that the spatial shift in the distribution of sardine and anchovy in the southern Benguela system was caused by such a combination of factors (Gremillet et al 2008a, Gremillet & Boulinier 2009 and could indicate an ecological regime shift that is likely to have significant consequences for the local marine ecosystem (Gremillet et al 2008a).The change in the abundance of prey can have a substantial, rapid effect on predators like the Cape gannet, whose mobility is limited while rearing young and who display strong site fidelity tendencies (Crawford 2007, Crawford et al 2008a, Durant et al 2009. A change in prey availability may influence the decision to breed and can play a major role in breeding success, can affect survival and can influence inter-colony movements (Crawford & Dyer 1995, Crawford et al 2008a.…”

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confidence: 99%

Factors affecting adult survival and inter-colony movement at the three South African colonies of Cape gannet

Distiller¹,

Altwegg²,

Crawford³

et al. 2012

Mar. Ecol. Prog. Ser.

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Marine systems are under pressure from both climate change and exploitation. While many of these ecosystems are inherently variable and hard to monitor, seabirds can be used as ecological indicators that provide early warning signals of deeper environmental change. The Agulhas-Benguela marine ecosystem around southern Africa has exhibited long-term changes in sea surface temperature, and the distribution of pelagic fish in this system has shifted. The Cape gannet Morus capensis is a seabird endemic as a breeding species to the Agulhas-Benguela ecosystem. Cape gannets breed at just 6 locations and are listed by the IUCN as Vulnerable. Knowledge of the survival and movements of a species is important for understanding of factors influencing its conservation. A random effects multistate capture−recapture model was used to estimate the annual survival probabilities and movement between colonies for adult birds at the 3 South African colonies of the species. The effects on survival of environmental and fisheries-related covariates were explored. Survival over the 20 yr period did not exhibit any long-term trend at the 2 southern colonies (Malgas and Bird Islands) but decreased at Lambert's Bay between 1996 and 2007. At all 3 colonies, adult birds showed a high degree of site fidelity. It may be that for Cape gannets, the primary effects of climate and fishing are on recruitment rather than on survival. The continued use of sub-optimal conditions by the west coast colonies has been referred to as an 'ecological trap' and necessitates the introduction of spatial considerations into fisheries management. KEY WORDS: Cape gannets · Multistate capture−recapture models · Fisheries management · Ecological indicator · Seabirds · Survival Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 461: [245][246][247][248][249][250][251][252][253][254][255] 2012 The Benguela upwelling ecosystem off south-western Africa is 1 of 4 major eastern boundary currents in the world's oceans and is a highly productive ecosystem which supports both sardine Sardinops sagax and anchovy Engraulis encrasicolus as the main forage fish species for several predators (Crawford 2007, Gremillet et al. 2008a). The Agulhas Current flows from the Mozambique Channel around the eastern and southern part of South Africa (Fig. 1). Both the Agulhas Current ecosystem and the southern Benguela ecosystem have exhibited long-term changes in sea surface temperature, with a cooling in the southern Benguela and a warming of the Agulhas Current over the past 2 decades (Roy et al. 2007, Rouault et al. 2009.Seabirds and other predators at the top of the food chain are especially vulnerable to ecosystem perturbations and are often used as indicators for the state of oceanic ecosystems (Piatt et al. 2007, Durant et al. 2009, Rolland et al. 2010. In particular, predators that forage on a small number of key fish species should be better indicators for the state of the system than more generalist predators that can adapt...

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“…Among many examples are sandeels (or sandlance; Ammodytes spp.) in the North Sea (Monaghan et al 1989;Frederiksen et al 2008;Cook et al 2014) and Gulf of Alaska Suryan et al 2006); capelin (Mallotus villosus) around Newfoundland and Labrador (Montevecchi and Myers 1996;Regehr and Montevecchi 1997), the Barents Sea (Barrett and Furness 1990), and Gulf of Alaska ; anchovy and sardines in the Benguela Current (Crawford et al 2008; Green et al 2015), the Humboldt Current (Duffy 1983), and California Current (Mills et al 2007;Sydeman et al 2009; Thompson et al 2012); and Atlantic herring in Iceland, Norway (Anker-Nilssen 1987), and the Gulf of Maine (Diamond and Devlin 2003;Breton and Diamond 2014).…”

Section: Introductionmentioning

confidence: 99%

Seabird diets as bioindicators of Atlantic herring recruitment and stock size: a new tool for ecosystem-based fisheries management

Scopel

Diamond

Kress

et al. 2018

Can. J. Fish. Aquat. Sci.

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Ecosystem-based fishery management requires understanding of relationships between exploited fish and their predators, such as seabirds. We used exploratory regression analyses to model relationships between Atlantic herring (Clupea harengus) in the diet of seabird chicks at nine nesting colonies in the Gulf of Maine and four types of fishery-and survey-derived herring data. We found several strong relationships, which suggests spatial structuring in herring stocks and likely patterns of herring movements before they recruit into the fishery. Some types of herring data seldom used in stock assessments -notably acoustic surveys, fixed-gear landings, and mass-at-age (i.e., weight-at-age) -correlated as strongly with seabird data as more commonly used series, such as mobile-gear landings and modeled spawning stock biomass. Seabird chick diets collected at specific locations thus offer a promising means to assess the size, distribution, and abundance of juvenile herring across a broad area prior to recruitment, which is a major source of uncertainty in fisheries. Common terns (Sterna hirundo) showed the most potential as a bioindicator, correlating well and showing consistent spatial patterns with 11 of 13 fishery data series.Résumé : La gestion écosystémique des pêches nécessite une compréhension des liens entre les poissons exploités et leurs prédateurs, tels que les oiseaux marins. Nous avons utilisé des analyses de régression exploratoires pour modéliser les relations entre le hareng de l'Atlantique (Clupea harengus) dans l'alimentation de jeunes oiseaux de mer dans neuf colonies de nidification dans le golfe du Maine, et quatre types de données sur les harengs issues de la pêche et de campagnes d'évaluation. Nous avons relevé plusieurs relations marquées qui indiqueraient la présence d'une structure spatiale dans les stocks de harengs et de probables motifs de déplacement des harengs avant leur recrutement dans la pêche. Certains types de données sur les harengs rarement utilisés dans les évaluations des stocks, dont des données de relevés acoustiques, de débarquements de navires à engins fixes et de poids selon l'âge, présentent une corrélation tout aussi forte avec les données sur les oiseaux de mer que des séries plus couramment utilisées, comme les débarquements de navires à engins mobiles et la biomasse modélisée du stock reproducteur. Les régimes alimentaires des jeunes oiseaux de mer prélevés en des sites précis constituent donc une approche prometteuse pour évaluer la taille, la répartition et l'abondance des harengs juvéniles avant leur recrutement à l'échelle d'une grande région, des facteurs qui constituent une importante source d'incertitude dans les pêches. Les sternes pierregarins (Sterna hirundo) montrent le meilleur potentiel comme bioindicateur, puisqu'elles présentent une bonne corrélation et des motifs spatiaux concordants avec 11 des 13 séries de données issues de la pêche. [Traduit par la Rédaction]

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Implications for seabirds off South Africa of a long-term change in the distribution of sardine

Cited by 68 publications

References 59 publications

Pros and cons of using seabirds as ecological indicators

Pros and cons of using seabirds as ecological indicators

Factors affecting adult survival and inter-colony movement at the three South African colonies of Cape gannet

Seabird diets as bioindicators of Atlantic herring recruitment and stock size: a new tool for ecosystem-based fisheries management

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