Morus capensis 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Aves Suliformes Sulidae

Scientific Name: Morus capensis (Lichtenstein, 1823)
Common Name(s):
English Cape Gannet
French Fou du Cap
Sula capensis ssp. capensis (Lichtenstein, 1823) — Dowsett and Forbes-Watson (1993)
Taxonomic Source(s): Christidis, L. and Boles, W.E. 2008. Systematics and Taxonomy of Australian Birds. CSIRO Publishing, Collingwood, Australia.
Identification information: 84-94 cm. Sleek, mainly white seabird. Black tail, primaries and secondaries. Pale yellow head. Immature dark brown, mottled paler, and shows increasing amounts of adult plumage after first year. Similar spp. Adult Masked Booby Sula dactylatra has white head, adult Northern Gannet Morus bassanus has white tail and secondaries, adult Australasian Gannet S. serrator has only four, occasionally more, black central tail feathers. Voice Usually silent at sea. Rasping arrah arrah is most common call at colonies.

Assessment Information [top]

Red List Category & Criteria: Endangered A2acde+3cde+4acde ver 3.1
Year Published: 2017
Date Assessed: 2017-10-01
Assessor(s): BirdLife International
Reviewer(s): Symes, A.
Contributor(s): Dowsett, R.J., Kemper, J., Crawford, R., Hagen , C. & Gremillet, D.
Facilitator/Compiler(s): Anderson, O., Calvert, R., Ekstrom, J., Malpas, L., Pilgrim, J., Robertson, P., Taylor, J., Symes, A., Wheatley, H.
This species has undergone a large population reduction over the past three generations and is projected to continue to decline rapidly over the next three generations. For these reasons it is listed as Endangered.

Previously published Red List assessments:

Geographic Range [top]

Range Description:Morus capensis breeds at just six islands: Bird (Lambert's Bay), Malgas and Bird (Algoa Bay), South Africa, and Mercury, Ichaboe and Possession, Namibia. Historically it bred on four more islands (Crawford et al. 1983). Outside the breeding season, adults may disperse up to c. 1,000 km from colonies, whereas juvenile birds may move > 2,000 km (Klages 1994). Birds range east to KwaZulu-Natal and Mozambique and as vagrants to Tanzania (Crawford et al. 1983, Klages 1994). On the west coast of Africa birds formerly moved north as far as Nigeria, and as vagrants to Western Sahara (Crawford et al. 1983). However, there are few recent records of birds moving north of southern Angola, suggesting possible change in dispersal pattern (Oatley et al. 1982, Klages 1994). The species usually remains over the continental shelf, often within 100 km of land (Hockey et al. 2005). Limited exchange occurs between breeding localities (Crawford et al. 1983). There has been a recent shift in the breeding distribution of the species around the southern African coast from the northwest to the southeast, which has matched a shift in the distribution of epipelagic forage fish, the Cape Gannet’s main prey, that may have been environmentally driven (Crawford et al. 2007, 2015). The most recent population estimate is 123,080 pairs (Crawford et al. 2015 updated by R. Crawford in litt. 2016) and the population is estimated to have undergone a reduction of 50-79% over the past three generation (Crawford et al. 2007, Kemper 2015, Crawford et al. 2015, R. Sherley in litt. 2017).
Countries occurrence:
Angola; Mozambique; Namibia; South Africa
Additional data:
Estimated area of occupancy (AOO) - km2:440Continuing decline in area of occupancy (AOO):Unknown
Extreme fluctuations in area of occupancy (AOO):NoEstimated extent of occurrence (EOO) - km2:326000
Continuing decline in extent of occurrence (EOO):UnknownExtreme fluctuations in extent of occurrence (EOO):No
Number of Locations:6Continuing decline in number of locations:No
Extreme fluctuations in the number of locations:No
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:The most recent population estimate is made up of 10,500 pairs at Ichaboae Island, 2,200 pairs on Mercury Island and 380 pairs on Possession Island (all in 2010) (Kemper 2015), with 81,000 pairs at Bird Island (Algoa Bay), 21,000 pairs at Malgas Island and 8,000 pairs at Bird Island (Lambert’s Bay) (in 2015) (Crawford et al. 2015 updated by R. Crawford in litt. 2016), which gives a global total of 123,080 pairs, which equates to 246,160 mature individuals, rounded here to 246,000.

Trend Justification:  The total breeding population was previously estimated to have declined by 1.14% per year over the 49 years between 1956-1957 and 2005-2006 (Kemper et al. 2007). Recent data, however, shows that the species may in fact be declining at a faster rate than this. Historically the global population numbered c.254,000 breeding pairs in 1956, which has subsequently decreased to c.249,000 pairs in 1968, c.179,000 in 1989 and c.145,000 pairs in 2005 (Crawford et al. 2007). The most recent population estimate is made up of 10,500 pairs at Ichaboae Island, 2,200 pairs on Mercury Island and 380 pairs on Possession Island (all in 2010) (Kemper 2015), with 81,000 pairs at Bird Island (Algoa Bay), 21,000 pairs at Malgas Island and 8,000 pairs at Bird Island (Lambert’s Bay) (in 2015) (Crawford et al. 2015 updated by R. Crawford in litt. 2016), which gives a global total of 123,080 pairs.  This gives an overall decline of 51.5% between 1956 and 2015, and with only minor extrapolation this would equate to a c.52.4% decline over 3 generations (60.6 years). An analysis that used a Bayesian state-space model fit to nests counts made between 1956 and 2016 at the species’ six breeding colonies indicated a decline of 51.5% (Bayesian 95% credible intervals: 39.5–62.5%) over three generations. Overall, 61.6% of model iterations fell within the 50–79% decline band and 38.3% fell within the 30–49% band (R. Sherley in litt. 2017). When comparing the most recent population estimate to the 1968, 1989 and 2005 estimates and projecting these rates of decline into the future, the rate of decline over 3 generations would be c.60%. Therefore, rates of decline over 3 generations likely fall within the range of 50-79%.
Current Population Trend:Decreasing
Additional data:
Number of mature individuals:246000Continuing decline of mature individuals:Yes
Extreme fluctuations:NoPopulation severely fragmented:No
No. of subpopulations:1Continuing decline in subpopulations:Unknown
Extreme fluctuations in subpopulations:NoAll individuals in one subpopulation:Yes
No. of individuals in largest subpopulation:100

Habitat and Ecology [top]

Habitat and Ecology:Behaviour: This species is not strictly migratory and the majority of birds remain within 500 km of their breeding site year round (del Hoyo et al. 1992, Klages 1994), some (mainly adult males) continuing to use the breeding grounds as roosting sites throughout the non-breeding season (Nelson 2005). However, some adults disperse up to 3300 km from the breeding colonies, moving along the African coast for about 3 months during the non-breeding season (Hockey et al. 2005; Nelson 2005). Juveniles used to disperse northwards in April (del Hoyo et al. 1992, Nelson 2005), travelling up to 4,000 km towards the equator (Nelson 2005), returning to breed around four years of age (Crawford 1999). Breeding occurs between September and April in large colonies of >10,000 pairs and in smaller groups (Crawford et al. 2007). Large foraging aggregations occur around trawling vessels (del Hoyo et al. 1992). Individuals can travel as much as 450 km in a day in search of food (Mullers 2009).

This species is strictly marine. Breeding It prefers to nests on flat or gently sloping open ground on offshore islands (Hockey et al. 2005), but will also use island cliffs as well as man-made structures such as guano platforms (Hockey et al. 2005). Non-breeding It most often forages within 120 km of the shore (Adams and Navarro 2005), particularly frequenting areas where purse-seine netting occurs (Nelson 2005). It occasionally wanders further offshore over the continental shelf (del Hoyo et al. 1992) where it benefits from the discards of deep-water stern trawlers (Nelson 2005).

It feeds mainly on shoaling pelagic fish (del Hoyo et al. 1992) such as anchovy Engraulis capensis, sardine Sardinops sagax or saury Scomberesox saurus, as well as offal discarded by fishing boats including demersal fish (Hockey et al. 2005). In South Africa fluctuations in the contribution of E. capensis and S. sagax in the diet match the changing abundance of the species (Crawford and Dyer 1995, Crawford et al. 2007).

Breeding site: 
The nest consists of a mound with a cup-shaped depression in its centre (Nelson 2005). It is made from guano, vegetation and other matter that can be scraped together (Hockey et al. 2005). Where no such material is available, eggs are laid on bare ground (Hockey et al. 2005). .

Systems:Terrestrial; Marine
Continuing decline in area, extent and/or quality of habitat:Yes
Generation Length (years):20.2
Movement patterns:Not a Migrant
Congregatory:Congregatory (and dispersive)

Threats [top]

Major Threat(s): Food shortage, following the collapse of the Namibian sardine fishery and an eastward displacement of epipelagic fish off South Africa, has been the main cause of declines (Crawford et al. 2007, 2014, 2015). In Namibia anchovies only temporarily and partially replace sardines in the diet when the latter becomes scarce (Crawford et al. 2007). In both Namibia and South Africa, the numbers of Cape Gannets breeding were significantly related to the biomass of epipelagic fish prey (Crawford et al. 2007). Competition with purse-seine fisheries targeting small pelagic fish has been demonstrated in South Africa, with a negative impact on foraging success, adult body condition and chick growth rates (Okes et al. 2009; Cohen et al. 2014; Grémillet et al. 2016). Faced with the scarcity of their natural prey, Cape gannets also exploit fishery waste from trawlers (Tew-Kai et al. 2013), but this low-quality resource leads to reduced adult body condition and reproductive performance (Grémillet et al. 2008). Oil-spills are also a serious threat: c.5,000 individuals were oiled during an incident in 1993. Oiling by fish oil from vessels processing fish or on-shore factories poses a chronic threat in Namibia (du Toit and Bartlett 2001). Guano collection may decrease breeding success, as it inhibits some birds from laying (through human disturbance and lack of quality nesting habitat through excessive removal of guano) and reduces the effective breeding season (Kemper et al. 2007). The Cape Fur Seal Arctocephalus pusillus displaced M. capensis from Hollam's Bird Island and killed 27,000 fledglings over the course of three breeding seasons on Malgas Island, equating to a 25% reduction in the size of the colony and threatening the sustainability of the population (Makhado et al. 2006). They also caused the abandonment of a colony at Lambert's bay in 2005/2006 (Crawford et al. 2007), although historically a programme to displace seals from Mercury Island was largely effective (Crawford et al. 1989). Other threats include predation by Great White Pelicans Pelecanus onocrotalus which are a significant threat to chicks at Malgas Island (Mullers 2009), by-catch during longline fishing (Petersen et al. 2008), exploitation for food in southern Angola, nesting habitat degradation by excessive guano removal and flooding of nests during storms (Kemper et al. 2007).

Conservation Actions [top]

Conservation Actions: Conservation Actions Underway
In South Africa, Lambert's Bay and Bird Island are nature reserves and Malgas Island is within West Coast National Park. In Namibia, the three breeding islands are administered by the Ministry of Fisheries and Marine Resources and are part of the Namibian Islands’ Marine Protected Area. All six islands have been identified as Important Bird Areas (IBAs) (Barnes 1998). Oiled birds are rehabilitated with success in South Africa, and the species is protected by law in both countries. Bycatch in trawl fisheries, through collisions with warp cables is being addressed through the use of bird scaring lines in South Africa and more recently in Namibia, although bycatch in the trawl net is more difficult to mitigate due to the birds’ plunge-diving behaviour (Maree et al. 2014).

Conservation Actions Proposed

Carry out surveys to obtain an up-to-date population estimate. Conduct regular surveys to monitor population trends. Identify key foraging hotspots of both breeding and non-breeding gannets from all colonies, in order to protect these in future. Continue research/monitoring the impact of fisheries and predation. Develop and implement a sustainable, coordinated fisheries plan for the region. Develop measures to prevent oil spills from illegal cleaning of ship tanks tanks, and minimise fish oil entering the sea during processing. Consider the potential culling of individual seals that are inflicting excessive mortality on, or causing extensive disturbance to, threatened colonies (Crawford et al. 2007). Reduce competition with purse-seine fishing activities targeting small pelagic fish in South Africa through the implementation of revised fishing quotas and/or no-take zones (Okes et al. 2009; Pichegru et al. 2009; Pichegru et al. 2010; Cohen et al. 2014; Grémillet et al. 2016).

Citation: BirdLife International. 2017. Morus capensis. The IUCN Red List of Threatened Species 2017: e.T22696668A119364110. . Downloaded on 17 January 2018.
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