Cape cormorants decrease, move east and adapt foraging strategies following eastward displacement of their main prey

Crawford, R. J. M.; Randall, R. M.; Cook, TR; Ryan, P G; Dyer, Bruce M.; Fox, Rebecca J.; Geldenhuys, Deon; Huisamen, Johan; McGeorge, Cuan; Smith, Mk S; Upfold, Leshia; Visagie, J; Waller, LJ; Whittington, Philip A.; Wilke, CG; Makhado, AB

doi:10.2989/1814232x.2016.1202861

Cited by 20 publications

(11 citation statements)

References 37 publications

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“…Hence, there were long-term increases in guano yields in northern Namibia and southern South Africa but decreases in the four intervening regions. The trends after the 1920s accord with the provision of nesting habitat for cormorants in the north, and with decreases of Cape Cormorants in central and southern Namibia after the 1970s and in western South Africa after the 1980s [15,22]. They also match decreases of Cape Gannets at colonies in Namibia after the 1950s and in western South Africa after the 1990s, but an increase in the Cape Gannet colony at Bird Island, Algoa Bay in southern South Africa [23].…”

Section: Guanosupporting

confidence: 63%

“…Average numbers of the BCLME's three 'guano-producing' seabirds that bred in each of the selected regions were determined for seven decades from the 1950s to the 2010s. Information was collated from [25,26] for African Penguins, [23] for Cape Gannets and [15,22,27,28] for Cape Cormorants. Unpublished data held by the Benguela Current Convention (BCC) were also utilized.…”

Section: 'Guano-producing' Seabirdsmentioning

confidence: 99%

“…Construction of platforms in northern Namibia facilitated a northern expansion of Cape Cormorants and the species also colonized Ilha dos Tigres in southern Angola [28]. Cape Cormorants likewise established several new colonies in the south, both at islands and mainland localities [22]. Cape Gannets were unsuccessful in attempts to form new colonies, but greatly enlarged their southernmost colony at Bird Island in Algoa Bay [23].…”

Section: 'Guano-producing' Seabirdsmentioning

confidence: 99%

“…In 2018, c.70% of the Cape Gannet population was at Bird Island, Algoa Bay at the eastern boundary of the BCLME [23]. In the 2010s, 54% of South Africa's Cape Cormorants bred at Dyer Island [22]. Such congregations of large proportions of a species at a single locality may offset Allee effects but render the species highly susceptible to local catastrophic events such as oil spills [64].…”

Section: Conservation Challengesmentioning

confidence: 99%

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Seabirds of the Benguela Ecosystem: Utilisation, Long-Term Changes and Challenges

Makhado¹,

Braby²,

Dyer³

et al. 2021

Birds - Challenges and Opportunities for Business, Conservation and Research

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The Benguela Current is used by c. 82 seabird species, of which seven are endemic to it. Eggs and guano of formerly abundant seabirds were heavily harvested in the 19th and 20th centuries but decreases in seabird populations led to cessation of these industries at islands. Guano is still scraped from platforms. Seabird ecotourism has grown. There were large recent decreases in numbers of African Penguins Spheniscus demersus, Cape Gannets Morus capensis and Cape Phalacrocorax capensis and Bank P. neglectus Cormorants and redistributions of these other species away from the centre of the Benguela ecosystem towards its northern or eastern boundaries. In 2020, seabirds endemic to the Benguela ecosystem and albatrosses and petrels migrating into it had high proportions of globally Near Threatened or Threatened species. The primary threat to four Endangered endemic birds was scarcity of forage resources. A Vulnerable endemic damara tern was susceptible to habitat degradation and disturbance. The principal threat to visiting albatrosses and petrels was by-catch mortality. Identification and effective protection of Important Bird Area breeding and marine foraging and aggregation sites, and a suite of complementary measures, are needed to conserve the seabirds and ensure continuation of their economic and ecosystem benefits into the future.

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Section: Guanosupporting

confidence: 63%

Section: 'Guano-producing' Seabirdsmentioning

confidence: 99%

Section: 'Guano-producing' Seabirdsmentioning

confidence: 99%

Section: Conservation Challengesmentioning

confidence: 99%

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Seabirds of the Benguela Ecosystem: Utilisation, Long-Term Changes and Challenges

Makhado¹,

Braby²,

Dyer³

et al. 2021

Birds - Challenges and Opportunities for Business, Conservation and Research

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“…These include southward and eastward shifts in the distributions of several important prey species including sardine, anchovy and West Coast rock lobster. Correspondingly, there have been associated effects on the survival, abundance, distribution, feeding behaviour and diet of several top predator populations such as the African penguin (Spheniscus demersus), Cape gannet (Morus capensis) and Cape cormorant (Phalacrocorax capensis) in the southern Benguela [36][37][38][39][40]. Changes that have been documented include longer foraging trips, feeding on suboptimal food, reduced adult and chick survival, declines in abundance and eastward shifts in distribution.…”

Section: Introductionmentioning

confidence: 99%

Dive behaviour and foraging effort of female Cape fur sealsArctocephalus pusillus pusillus

et al. 2019

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While marine top predators can play a critical role in ecosystem structure and dynamics through their effects on prey populations, how the predators function in this role is often not well understood. In the Benguela region of southern Africa, the Cape fur seal (Arctocephalus pusillus pusillus) population constitutes the largest marine top predator biomass, but little is known of its foraging ecology other than its diet and some preliminary dive records. Dive information was obtained from 32 adult females instrumented with dive recorders at the Kleinsee colony (29°34.17′ S, 16°59.80′ E) in South Africa during 2006–2008. Most dives were in the depth range of epipelagic prey species (less than 50 m deep) and at night, reflecting the reliance of Cape fur seals on small, vertically migrating, schooling prey. However, most females also performed benthic dives, and benthic diving was prevalent in some individuals. Benthic diving was significantly associated with the frequency with which females exceeded their aerobic dive limit. The greater putative costs of benthic diving highlight the potential detrimental effects to Cape fur seals of well-documented changes in the availability of epipelagic prey species in the Benguela.

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A structured seabird population model reveals how alternative forage fish control rules benefit seabirds and fisheries

Koehn

Siple

Essington

2021

Ecological Applications

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Fisheries for forage fish may affect the survival and reproduction of piscivorous predators, especially seabirds. However, seabirds have evolved life history strategies to cope with natural fluctuations in prey and it is difficult to separate effects of fishing on seabirds from impacts of natural variability. To date, potential impacts of forage fisheries on seabirds have mainly been explored using ecosystem models that simplify seabird–forage‐fish dynamics. We sought to explore how different forage fish harvest policies affect seabirds, accounting for structured population dynamics, life history specifics, and variation in forage fish dependencies across life stages; and how impacts vary across seabird and forage fish life histories. To explore these impacts, we developed an age‐stage structured seabird model that incorporates seabird diet specialization, foraging behavior, and reproductive strategy, as well as different functional responses between prey availability and adult survival, juvenile survival, reproductive success, and breeder propensity. We parameterized this model for two contrasting seabird life histories: (1) a low fecundity, limited foraging range, diet specialist (“restricted”); and (2) a high fecundity, wide ranging, diet generalist (“flexible”). Each was paired with two different forage fish prey archetypes that were fished under various control rules. The restricted seabird population was expectedly less robust to constant fishing pressure than the flexible seabird, and this sensitivity was mainly due to functional response parameterization, rather than other life history parameters. Particularly, the restricted seabird was highly sensitive to the relationship between prey availability and adult survival but was not sensitive to the relationship between prey and reproductive success. An adaptive biomass‐limit harvest rule for forage fish resulted in substantially higher seabird abundance compared to constant fishing across all scenarios, with minimal trade‐offs to the fishery (depending on fishery management objectives). However, mechanisms governing the impact of the forage fish fishery on the seabird varied by forage fish type. Therefore, tailoring forage fish management strategies to forage fish life history can lead to mutually acceptable outcomes for fisheries and seabirds. If data or time are limited, an adaptive control rule is likely a safe bet for meeting seabird conservation objectives with limited impacts to fisheries.

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Cape cormorants decrease, move east and adapt foraging strategies following eastward displacement of their main prey

Cited by 20 publications

References 37 publications

Seabirds of the Benguela Ecosystem: Utilisation, Long-Term Changes and Challenges

Seabirds of the Benguela Ecosystem: Utilisation, Long-Term Changes and Challenges

Dive behaviour and foraging effort of female Cape fur sealsArctocephalus pusillus pusillus

A structured seabird population model reveals how alternative forage fish control rules benefit seabirds and fisheries

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