Search

Populations of the macaroni penguin Eudyptes chrysolophus and the eastern rockhopper penguin E. filholi breeding at Marion Island (Prince Edward Islands) in the sub-Antarctic Indian Ocean decreased from 1994 to 2018. We examined their diets when rearing chicks during this period. There was substantial overlap in the diets of the two species, with crustaceans, dominated by the euphausiids Thysanoessa vicina and Euphausia vallentini, making up >80% of the diets by number and >60% by mass over the study period. The lanternfishes Krefftichthys anderssoni and Protomyctophum tenisoni were the most-commonly consumed fish in the diet of breeding macaroni penguins and dominated in their diet in three of the 25 years (1994, 1998 and 2014); they were also the most commonly consumed fish by eastern rockhopper penguins. Macaroni penguins consumed more of the amphipod crustacean Themisto gaudichaudii and the lanternfish Electrona carlsbergi as well as a greater diversity of and larger-sized fish than did eastern rockhopper penguins. The horsefish Zanclorhynchus spinifer was found in substantial amounts in the diet of eastern rockhopper penguins in 1996 and 1997. Despite annual variations in relative prey contributions to the diets, there were no significant long-term changes in the diet of either penguin species over the study period or when compared with an earlier assessment in 1982. We conclude that changes in the relative proportions of prey in the diets of these penguin species during breeding are unlikely to account for the recent declines in these penguin populations.

Flying fish and squid flushed by a ship’s passage are easy to count, but the value of such data is compromised by uncertainty regarding the proportion of individuals flushed. Wind direction relative to the ship’s course plays an important role in determining this proportion, with on average 6 times (range 2.5–10.8) more fish flushed on the windward side of the ship when there are moderate to strong cross winds. As a result, counts of flying fish that cover only one side of a ship’s bow should sample the windward side.Keywords: count technique, Exocoetidae, wind strengthAfrican Journal of Marine Science 2013, 35(4): 585–587

The main impact of the fishery for Tristan rock lobster Jasus tristani on seabirds at the Tristan archipelago and Gough Island is through night strikes, when petrels collide with a ship after being disorientated by its lights. Tristan fishery observers have kept records of night strikes on the MV Edinburgh since the 2010/2011 fishing season. Over the last three years, 723 seabirds from nine species were recorded coming aboard the fishing vessel, with at least 39 (5.4%) birds dying as a result. Birds killed were broad-billed prions Pachyptila vittata (41%), common diving petrels Pelecanoides urinatrix (23%), and storm petrels (Pelagodroma marina and Fregetta grallaria/tropica 36%). All these species are listed as Least Concern globally, and the numbers killed per year are

Populations of the African penguin Spheniscus demersus have decreased dramatically over the past century, due in part to competition for food with commercial fisheries, and the species is now endangered as a result. Economic arguments are used to favour fisheries over the needs of penguins, but penguins have direct value to the South African economy thanks to penguin-based tourism at several breeding colonies. We estimated the value of African penguins at the most important tourist site for African penguins: Boulders on the Cape Peninsula, South Africa. As a mainland colony close to Cape Town, Boulders is accessible to large numbers of visitors; gate revenues in 2009/2010 alone were R14.5 million (US$2 million). A zonal travel-cost analysis revealed an average consumer surplus among Cape Town residents of some R20 per visit. Penguin-based tourism thus forms an integral part of the R25 billion Western Cape tourism sector. Given that the future survival of this valuable resource is dependent, among others, on the availability of sufficient prey, competition with South Africa’s purse-seine fishing fleet should be limited through management strategies that lessen the potential effects of fishing on prey available at the local scale.Keywords: economy, investment, revenue, tourists, valuationAfrican Journal of Marine Science 2012, 34(4): 497–504

Once one of the most numerous seabirds of the Benguela upwelling system, the population of Cape cormorants Phalacrocorax capensis has decreased by 60% in the past three decades and the species is listed as Near Threatened. Declines in prey availability and/or abundance brought about by recent changes in the distribution of pelagic fish stocks and industrial purse-seine fishing are hypothesised to be a key driver of seabird population decreases in the southern Benguela. We investigated the foraging behaviour of breeding Cape cormorants by deploying GPS and temperature–depth recorders on 24 breeding adults from three islands off the coast of South Africa, two of them to the north of Cape Point and a third farther south on the western Agulhas Bank. This provided the first measures of foraging dispersal by a cormorant in the Benguela system, and enabled a comparison of foraging behaviour between birds from these islands. Foraging trips of Cape cormorants lasted between 17 min and >7 h, at a maximum distance of between 2 and 58 km away from their colony. Foraging effort was significantly greater for birds from farther north off the West Coast in terms of trip duration, distance travelled, number of dives and time spent flying compared to those from the southernmost island (Dyer), which is probably a response to low prey availability in the north. Coastal reserves that exclude pelagic fishing from inshore feeding grounds around Cape cormorant breeding colonies may result in increased local prey availability, which would benefit Cape cormorant populations.Keywords: activity budget, biotelemetry, coastal reserves, Engraulis encrasicolus, Phalacrocorax capensis, small pelagic fishAfrican Journal of Marine Science 2012, 34(2): 233–240

November 2011 saw an unprecedented irruption of buoy barnacles Dosima fascicularis in coastal waters off the Western Cape, South Africa. Buoy barnacles not uncommonly strand in the region attached to feathers, plastic litter and other small objects, but the 2011 irruption saw exceptional numbers of unusually large colonies (average 23.5 individuals; SD 18.5), most of which relied on their own floats. The largest individuals (49 mm capitulum length) were larger than previous records for the species. Buoy barnacles were first observed at sea off the Cape Peninsula on 2 November 2011. During the following three weeks they washed ashore along at least 500 km of coast from Paternoster on the West Coast to De Hoop, east of Cape Agulhas. Mass strandings attained densities of up to 42 (SD 23) colonies per metre of beach (n = 10), with a wet mass of around 10 kg m–2. They were accompanied by large numbers of bluebottles Physalia physalis and other neustonic organisms. Of 100 buoy barnacle colonies examined, only three were attached to obvious floating items (two Janthina shells and one piece of plastic). Dissection failed to reveal foreign attachment sites in 40 floats, but digesting 70 floats in potassium hydroxide revealed small plastic fragments in eight floats, one tar ball and one Velella skeleton. The 100 study colonies were comprised solely of buoy barnacles, but a Janthina shell had one buoy barnacle and 18 Lepas pectinata goose barnacles. Float size was poorly related to the number of barnacles, but was strongly correlated with the size of the largest animal. Most colonies had multiple large individuals, raising the possibility that several cyprid larvae settle together, jointly forming the communal float. Unusually persistent westerly winds prior to the strandings may have carried colonies into coastal waters from the South Atlantic gyre, but it is not evident why such events are so rare.Keywords: attachment substrata, colony size, float volume, Janthina mass stranding, Physalia, size distribution, VelellaAfrican Journal of Marine Science 2012, 34(1): 157–162

The number of African penguins Spheniscus demersus breeding in South Africa collapsed from about 56 000 pairs in 2001 to some 21 000 pairs in 2009, a loss of 35 000 pairs (>60%) in eight years. This reduced the global population to 26 000 pairs, when including Namibian breeders, and led to classification of the species as Endangered. In South Africa, penguins breed in two regions, the Western Cape and Algoa Bay (Eastern Cape), their breeding localities in these regions being separated by c. 600 km. Their main food is anchovy Engraulis encrasicolus and sardine Sardinops sagax, which are also the target of purse-seine fisheries. In Algoa Bay, numbers of African penguins halved from 21 000 pairs in 2001 to 10 000 pairs in 2003. In the Western Cape, numbers decreased from a mean of 35 000 pairs in 2001–2005 to 11 000 pairs in 2009. At Dassen Island, the annual survival rate of adult penguins decreased from 0.70 in 2002/2003 to 0.46 in 2006/2007; at Robben Island it decreased from 0.77 to 0.55 in the same period. In both the Western and Eastern Cape provinces, long-term trends in numbers of penguins breeding were significantly related to the combined biomass of anchovy and sardine off South Africa. However, recent decreases in the Western Cape were greater than expected given a continuing high abundance of anchovy. In this province, there was a south-east displacement of prey around 2000, which led to a mismatch in the distributions of prey and the western breeding localities of penguins.Keywords: African penguin, diet, numbers breeding, numbers moulting, Spheniscus, survivalAfrican Journal of Marine Science 2011, 33(1): 139–156

The incidental mortality of seabirds in tuna longline fisheries is estimated for the continental South African Exclusive Economic Zone (EEZ). Fishery observers accompanied 13 fishing trips and observed 108 sets (143 260 hooks) during the period 1998–2000. Despite most lines being set at night, seabird bycatch rates were high, with a mean of 1.6 birds killed per 1 000 hooks. Japanese vessels (1% effort observed) had a higher bycatch rate (2.6 birds per 1 000 hooks, range per trip 0.1–5.4) than South African vessels (0.8, range 0.0–4.3; 17% effort observed), possibly as a result of gear differences. Bird bycatch differed regionally in relation to the numbers of birds attending vessels. In international waters off the Northern Cape and southern Namibia, where there are few birds, only one bird was caught on 93 600 hooks (0.01 birds per 1 000 hooks). Shy Thalassarche cauta, black-browed T. melanophris and yellow-nosed T. chlororhynchos albatrosses, and white-chinned petrels Procellaria aequinoctialis were killed most frequently. Based on 1998–1999 fishing effort, simple extrapolation suggests that 19 000–30 000 seabirds are killed annually in South Africa's EEZ, of which 70% are albatrosses. Confidence in these estimates is low, given the small proportion of effort observed, but it is clear that urgent steps are needed to reduce seabird bycatch within South African waters.Keywords: longline bycatch, seabird mortality, southern AfricaAfrican Journal of Marine Science 2002, 24: 103–110