The conservation status and population decline of the African penguin deconstructed in space and time

Abstract Understanding changes in abundance is crucial for conservation, but population growth rates often vary over space and time. We use 40 years of count data (1979–2019) and Bayesian state‐space models to assess the African penguin Spheniscus demersus population under IUCN Red List Criterion A. We deconstruct the overall decline in time and space to identify where urgent conservation action is needed. The global African penguin population met the threshold for Endangered with a high probability (97%), having declined by almost 65% since 1989. An historical low of ~17,700 pairs bred in 2019. Annual changes were faster in the South African population (−4.2%, highest posterior density interval, HPDI: −7.8 to −0.6%) than the Namibian one (−0.3%, HPDI: −3.3 to +2.6%), and since 1999 were almost −10% at South African colonies north of Cape Town. Over the 40‐year period, the Eastern Cape colonies went from holding ~25% of the total penguin population to ~40% as numbers decreased more rapidly elsewhere. These changes coincided with an altered abundance and availability of the main prey of African penguins. Our results underline the dynamic nature of population declines in space as well as time and highlight which penguin colonies require urgent conservation attention.


Introduction 50
Seabirds are considered to be the most threatened group of birds in the world [1] and globally 51 their populations may have declined by > 70% since 1950 [2]. Seabirds face a number of

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The African penguin breeds, or has bred, at 32 island and mainland colonies between central

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The methods used to count the numbers of occupied nest sites of African penguins have been 96 outlined in detail by [4,14]. Briefly, counts were undertaken by teams of people walking through 97 a penguin colony and counting occupied nest sites. Larger colonies were broken down into 98 predefined census areas, each of which was counted separately. Counts were predominately 99 made between February and September each year [4]. At some small and difficult to access 100 localities counts made outside the main breeding season were used if no other count was 101 available for that year. Where more than one count was made at a locality in a year, the highest 102 count was taken to represent the number of pairs breeding there in that year [4]. An occupied 103 site was considered active if it contained fresh eggs or chicks, or was defended by a non-104 moulting adult penguin, and considered potential if it was not active but showed recent signs 105 of use, e.g. the presence of substantial quantities of fresh guano or nesting material, the recent 106 excavation of sand from a burrow nest, the presence of many penguin footprints in its vicinity, 107 or a combination of these factors. Breeding by African penguins is not always synchronous 108 [16], so potential nests are counted as they may be occupied by pairs that have recently        Robben Island ( Figure S1). Again, in part because of that period of growth and recovery, the 226 rate decline over the last 2G (20 years) has been substantial, at −9.7% (−15.5 to −3.7%, Figure   227 4b). However, unlike elsewhere, this rapid decline has persisted in recent years; the rate of 228 change at the colonies in the West Coast region over the last 10 years (1G) was at −9.5% 229 (−16.7 to −2.1%, Figure 4b). Overall, this regional population has declined by 70.2%

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A2 were applied at a regional level, this sub-population would qualify for an EN status with 233 99.9% probability ( Figure S2).

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The trend at the South-West Coast region colonies was initially dominated by the continual 236 decline at Dyer Island, from ~23,000 pairs in 1979 to ~2,300 pairs in 1999 and ~1,050 pairs 237 in 2019 ( Figure S1); thus the median rate of change since 1979 was −2.2% (−6.3 to +2.3%) 238 overall and 1.0% (−5.6 to +3.5%) since 1989 (3G, Figure 4d). More recently, these decreases     Our results show that its classification as Endangered as per the IUCN Red List is 326 warranted going forward. This is clear cause for concern for this species. However, 327 African penguins have not declined at the same rate across their range, which is 328 disjunct between Namibia and the Western and Eastern Cape provinces of South 329 Africa. This is for various reasons, including differences in the nature and severity of 330 threats and local population dynamics. It follows, then, that there are different 331 conservation management priorities for each subpopulation. 332

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The Namibian population has declined slightly over the last three generations, but the 334 rate of decline is insufficient to warrant any Red List classification under the A criterion 335 other than Least Concern. However, the Namibian penguin population had already 336 declined by ~70% prior to the start of our dataset in 1986, coincident with the collapse 337 of the sardine stocks there in the 1970s [9]. This broad scale assessment also masks 338 a worrying decline to 3,600 pairs in 2007 before the subsequent recovery. The low 339 numbers of penguins in Namibia is likely maintained by a scarcity of small pelagic fish 340