OpenUCT :: Browsing by Subject "African penguin"

Browsing by Subject "African penguin"

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Breeding success of African penguins Spheniscus demersus at Dassen Island, especially after oiling following the Apollo Sea spill
(2008) Wolfaardt, A C; Underhill, L G; Nel, D C; Williams, A J; Visagie, J
The reproductive success of African penguins Spheniscus demersus at Dassen Island from 1994 to 2000 was variable, but much higher than previously reported figures for the species. Breeding success was positively related to the abundance of anchovy Engraulis encrasicolus and sardine Sardinops sagax, and the high reproductive output during the study was attributed to the large biomass and high availability of these two species for much of the study period. De-oiled penguins from the Apollo Sea spill had a slightly lower hatching success but a significantly lower overall breeding success than that of un-oiled birds, driven mainly by the reduced number of chicks which fledged. Nests with two de-oiled Apollo Sea parents were less successful than nests with one de-oiled bird. There was increased mortality of chicks 40 days and older in nests with de-oiled birds. Chicks from nests with one de-oiled Apollo Sea parent grew at a similar rate to chicks from nests with no de-oiled parents. However, chicks from nests that comprised two de-oiled Apollo Sea birds had significantly slower growth rates than these other two groups. Breeding success and chick growth at nests with de-oiled birds were more negatively impacted when feeding conditions were less favourable. These results suggest that one of the main reasons for lower breeding success in de-oiled birds was their reduced ability to provision chicks, especially during the period in which the energy demands of the chicks is greatest. The rate of mate fidelity was lower in de-oiled birds than un-oiled birds, and there was a positive association between mate fidelity and breeding success.
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Data inputs for the African Penguin Spheniscus demersus model to be coupled to the pelagic OMP
(2008) Plagányi, Éva E; Robinson, William
This document serves as an updated compilation of all data currently available as inputs to the African penguin spatial model which is to be coupled to the pelagic OMP. The data are presented here together with some comments as to how they are to be used in the model and notes on their derivation and potential reliability. The model presented thus far is spatial in that different populations of penguins are represented, and different levels of movement between these populations are modelled. The main focus of the model is on Dassen and Robben Islands, which were originally combined for reasons of simplicity and because of their close proximity to each other, suggesting that the effects of external factors such as food availability would be highly correlated between the two. However, data that have recently become available indicate differences between these two colonies which suggest that it may no longer be appropriate to pool the two; hence they are split in the model. The third population is Dyer Island because it has the next largest numbers of penguins, recent declines in the population there are of concern and it is considered an important breeding site for penguins given the eastward shift of sardines. The fourth population is Boulders. Although relatively small, this colony was considered important to include because of its position, its role as the focus of several other studies and because penguins are known to have moved from Dyer Island to Boulders, Robben and Dassen, and hence it is useful to quantify to what extent movement of birds away from Dyer Island could account for observed declines at Dyer and increases at these other colonies. A summary of all the breeding colonies of penguins in so-called area i) is provided in Fig. 1 which also shows the relative abundance of breeding pairs in the different sub-areas, computed from data in Underhill et al. (2006). The regional penguin population is dominated (in terms of numbers) by two large colonies, namely Robben Island and Dassen Island; thus the model here has focused on these two colonies, with the next most important colony being Dyer Island. Fig. 2 maps the extent of strata corresponding to pelagic fish biomass estimates used to link to penguin breeding success in the model. Initially relationships were investigated with the west of Cape Agulhas pelagic spawner biomass and the west of Cape Infanta recruit abundances rather than the total South African pelagic fish abundance. More recently, this has been refined further still to use the Cape Columbine to Cape Point spawner biomass component only since this more accurately depicts the biomass available to penguins in the west coast model area. The west of Cape Infanta recruit estimates are retained because the anchovy and sardine recruits move down the West Coast. The model time step is one year and hence average trends are modelled. Penguins in each subarea are modelled starting from 1986.
Open Access
Diving behaviour of African penguins: do they differ from other Spheniscus penguins?
(National Inquiry Services Centre, 2007) Ryan, P G; Petersen, S L; Simeone, A; Grémillet, D
African penguins Spheniscus demersus closely resemble Magellanic S. magellanicus and Humboldt S. humboldti penguins and have similar breeding and feeding ecologies. Adults feed on pelagic schooling fish in continental shelf waters, but African penguins have been reported to have shallower dive angles and remain submerged longer for dives to a given depth than their congeners. The few data for African penguins were gathered using relatively large time-depth recorders. We measured diving behaviour of 36 African penguins provisioning small chicks at three colonies near Cape Town, South Africa. Maximum and mean dive depths were 69m and 14m respectively. Diving took place mainly during the day. Although dive depths differed between colonies, there were no significant differences in dive duration or maximum, median or mean depth. Total dive duration, descent time, bottom time, ascent time and dive angle all were strongly correlated with the maximum depth attained. The diving behaviour of African penguins is similar to that of its congeners. Diving performance probably was compromised by the data-logger used in the previous study. Comparative data from Humboldt penguins also indicate potential biases in an earlier study of this species. Care is needed when comparing the diving performance of penguins measured using different loggers.
Open Access
Impact of flipper-banding on breeding success of African penguins Spheniscus demersus at Robben Island: comparisons among silicone rubber bands, stainless-steel bands and no bands
(2008) Barham, P J; Underhill, L G; Crawford, R J M; Leshoro, T M; Bolton, D A
From 2001 to 2006, two new designs of flipper bands made from silicone rubbers were tested on African penguins Spheniscus demersus at 365 nests on Robben Island, South Africa. We compared, over six years, the breeding success, from hatching to fledging, of three different groups of penguins: those with rubber bands (117 nests), with conventional stainless-steel bands (103 nests) and without bands (145 nests). There were no significant differences in breeding success between the three groups, suggesting that neither the currently used steel bands, nor either of the new rubber-band designs, were harmful during the seasons investigated. The rubber bands caused less wear of feathers and less drag on a model penguin than the steel bands. In captivity, the behaviours of African penguins fitted with rubber bands were not noticeably different to those of unbanded birds.
Open Access
Leslie matrix based estimates of maximum growth rate for the African penguin population
(2007) Butterworth, Doug S; Plagányi, Éva E
Log linear regressions of breeder numbers of African penguins over 1996-2005 for Robben Island and the Western Cape as a whole (ASWS/JUL07/PENG/DAT/1, Table 1) reflect annual increase rates of 11.4% and 9.6% respectively. How consistent are these values with separate estimates of demographic parameters for the species?
Open Access
Proposed performance statistics for evaluating the effects of pelagic fishing on African Penguin populations
(2008) Plagányi, Éva E; Robinson, William
Given the move towards adopting an ecosystem approach to fisheries in the pelagic sector, the new pelagic OMP needs to be tested in the light of not only the risk parameters as considered previously, along with catch statistics for the anchovy and sardine populations, but also parameters denoting risk to the African penguin population(s) Spheniscus demersus. Penguins have been chosen as a key predator species to consider because of their conservation status, and because of their potential sensitivity to changes in pelagic fish abundance and distribution as a consequence of their land-based breeding sites. A model of penguin dynamics has been developed for use as a penguin Operating Model to be coupled to the pelagic fish OMP. This paper summarises the proposed implementation and suggests performance statistics for use in evaluating the impact on penguins of predicted future pelagic fish trajectories under alternative harvest strategies (OMPs).
Open Access
Restoration of oiled African penguins Spheniscus demersus a decade after the Apollo Sea spill
(2008) Wolfaardt, A C; Underhill, L G; Altwegg, R; Visagie, J
The bulk ore carrier Apollo Sea sank south-west of Dassen Island off western South Africa in June 1994, oiling approximately 10 000 African penguins Spheniscus demersus, most of which were collected from Dassen Island. A total of 4 076 de-oiled penguins was released with flipper bands. From 1994 to 2005, follow-up research using re-sighting and capture-mark-recapture methods indicated that about 73% of the de-oiled penguins observed back at Dassen Island attempted to breed, and were thus successfully restored into the breeding population. For de-oiled breeders, the median interval between their first recorded sighting and first recorded breeding attempt was 11 months, indicating a short-term delay in restoration. At least 45% of the de-oiled breeders were still being re-sighted five years after their release, and a minimum of 4% survived into their ninth year. These results represent the most successful restoration estimates anywhere in the world. The proportion of de-oiled juvenile penguins re-sighted back at Dassen Island and recorded breeding was lower than that of birds in adult plumage. De-oiled non-breeders spent significantly more time along the shore and less time within breeding colonies than de-oiled breeders. The mean proportion of de-oiled breeders that abstained from breeding each year during the study period was greater than expected. There was a negative relationship between breeding and subsequent survival and breeding, suggesting a cost of reproduction for de-oiled birds.
Open Access
Revised spatial Age-Structured model of African penguin Spheniscus demersus populations
(2007) Plagányi, Éva E; Butterworth, Doug S
A revised form of an earlier model is summarised in this document, with preliminary results to be presented in a separate document. The three main changes to the model are as follows: 1) the delay difference equations have been converted to fully age-structured equations instead so as to be able to model changes in the age at first maturity as requested by the task group; 2) rather than using aggregated factors to model various processes, these factors have been split into individual components so as to be more easily distinguished between and understandable; and 3) a preliminary Algoa Bay model has been added so that movement from Algoa Bay to the west can be modelled. Some suggested alternatives for modelling various processes within the model are given as a starting point for discussions by the task group.
Open Access
Spatial Age-Structured model of African penguin colonies at Robben, Dassen and Dyer Islands, and at Boulders
(2007) Plagányi, Éva E; Butterworth, Doug S
A revised form of an earlier model is summarised in this document, with preliminary results to be presented in a separate document. The three main changes to the model are as follows: 1) the delay difference equations have been converted to fully age-structured equations instead so as to be able to model changes in the age at first maturity as requested by the task group; 2) rather than using aggregated factors to model various processes, these factors have been split into individual components so as to be more easily distinguished between and understandable; and 3) a preliminary Algoa Bay model has been added so that movement from Algoa Bay to the west can be modelled. Some suggested alternatives for modelling various processes within the model are given as a starting point for discussions by the task group.
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A spatial model of African penguin Spheniscus demersus populations in the Western Cape
(2007) Plagányi, Éva E
A number of questions have recently been raised regarding the status and management of the African penguin Spheniscus demersus. The PWG penguin task team agreed that it would be useful to develop a dynamic model to assist in understanding the population dynamics as well as in an attempt to reconcile the various data sources. This document describes the development of such a model. Although still preliminary only, the model is of a form that can readily be linked to the pelagic OMP (Operational Management Procedure) to take account of the relationship between the breeding success of African penguins and the abundance of both anchovy Engraulis encrasicolus and/or sardine Sardinops sagax (e.g. Crawford et al. 2006). The aims of the current model are as follows: 1) To provide a dynamic representation of penguin dynamics; 2) To fit to available data to provide estimates of important demographic parameters such as survival rates, which can then be compared to other available estimates; 3) To attempt to reconcile some apparent contradictory trends in the different data series; 4) By gradually increasing the complexity of the model to represent different plausible hypotheses, the model should assist in identifying the most parsimonious hypothesis to explain the observed trends in the population; 5) To quantify and provide additional substantiation for the relationship between penguin breeding success and pelagic fish abundance; 6) To dynamically project the penguin population assuming various future scenarios to assist in providing advice regarding the management of the penguin population (and possibly pelagic fish populations as well).
Open Access
Summary of available data for modelling African penguin Spheniscus demersus populations
(2007) Plagányi, Éva E; Butterworth, Doug S
This document serves as a compilation of all data currently available as inputs to the African penguin spatial model (Plagányi and Butterworth 2007) being developed. The data are presented here together with some comments as to how they are to be used in the model and notes on their derivation and potential reliability. Note that this is a working group document only and hence should be extended and improved in future, particularly as regards critical evaluation of different data sources. The model presented thus far is spatial in that different populations of penguins are represented, and different levels of movement between these populations are modelled. The main focus of the model is on Dassen and Robben Islands, which were originally combined for reasons of simplicity and because of their close proximity to each other, suggesting that the effects of external factors such as food availability would be highly correlated between the two. However, data that have recently become available indicate differences between these two colonies which suggest that it may no longer be appropriate to pool the two; hence they are being split in an updated model. The third population is Dyer Island because it has the next largest numbers of penguins, recent declines in the population there are of concern and it is considered an important breeding site for penguins given the eastward shift of sardines. The fourth population is Boulders. Although relatively small, this colony was considered important to include because of its position, its role as the focus of several other studies and because penguins are known to have moved from Dyer Island to Boulders, Robben and Dassen, and hence it is useful to quantify to what extent movement of birds away from Dyer Island could account for observed declines at Dyer and increases at these other colonies. An Algoa Bay component can also be linked to the model if required.
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Surviving off junk: low-energy prey dominates the diet of African penguins Spheniscus demersus at Mercury Island Namibia between 1996 and 2009
(2010) Ludynia, Katrin; Roux, J-P; Jones, R; Kemper, J; Underhill, Leslie
The diet of African penguins Spheniscus demersus in Namibia consisted mainly of sardine Sardinops sagax in the 1950s. Since the collapse of pelagic fish stocks in the 1970s, birds fed mainly on bearded (pelagic) goby Sufflogobius bibarbatus, a low-energy prey species. We present diet data for African penguins breeding at Mercury Island, the largest colony for this species in Namibia, between 1996 and 2009. Bearded goby was the main prey item throughout the study period, both in terms of frequency of occurrence (67.8%; SD 31.2) and in terms of mass (59.2%; SD 31.5). Diet composition varied throughout the year as well as between years; birds occasionally fed on a variety of fish species other than bearded goby. In Namibia, poor prey abundance is considered as a major factor contributing to the decline of penguin numbers after the collapse of the sardine stocks. However, bearded goby appears to be relatively abundant along Namibia's southern coast and low prey quality rather than low abundance appears to be a key factor influencing population dynamics of African penguins and other marine top predators in southern Namibia.
Open Access
Update of available data for the African Penguin Spheniscus demersus model to be coupled to the pelagic OMP
(2008) Plagányi, Éva E; Robinson, William
This document serves as an updated compilation of all data currently available as inputs to the African penguin spatial model (MCM/2008/SWG-PEL/21b) which is to be coupled to the pelagic OMP. The data are presented here together with some comments as to how they are to be used in the model and notes on their derivation and potential reliability. Note that this is a working group document only and hence should be extended and improved in future, particularly as regards critical evaluation of different data sources.
Open Access
Update to the African Penguin population model taking account of new moult count information
(2009) Robinson, William M L; Butterworth, Doug S
Refitting the penguin model to adjusted data taking into consideration possible undercounting of moulters in recent years, we have been able to obtain a better model fit. Also, analysis indicates that the depletion of penguins (expressed as abundance in 2008 relative to 2002) is about 5% less than previously estimated at the colony assumed to be the origin of the extra moulters at Stony Point. The calculated model likelihoods suggest that these birds are more likely to come from Dassen Island.

Browsing by Subject "African penguin"

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