There are 21 and 15 species of seabirds that breed in the Humboldt and Benguela upwelling systems... more There are 21 and 15 species of seabirds that breed in the Humboldt and Benguela upwelling systems respectively. Only two species of gull are common to both systems, one as an endemic subspecies to the Benguela system. Eleven species and two subspecies are endemic (or nearly so) to the Humboldt system; seven species and one subspecies to the Benguela system. Each system has an endemic penguin, sulid, cormorant and tern that feed mainly on anchovy Engraulis spp., sardine Sardinops sagax or both these fish. The Peruvian pelican Pelecanus thagus also feeds primarily on these prey items. A plentiful availability of food has resulted in many of these seabirds attaining high levels of abundance. For the four pairs of species that feed on anchovy and sardine, those in the Humboldt system all have a biology that enables them to increase more rapidly than their Benguela counter-parts. This reflects the higher frequency of environmental perturbations that depress seabird populations in the Humboldt system. In addition, both systems have a small endemic cormorant that feeds near the coast and a small endemic tern that breeds in the adjacent mainland desert and feeds at the sea surface. Several seabirds endemic to a system have no obvious ecological equivalent in the other system: the pelican, a diving-petrel, four storm-petrels and a gull in the Humboldt system; a cormorant and a gull in the Benguela system. Some species with tropical or subantarctic affinities breed at the boundaries of the systems. Others breed also in freshwater systems. The grey gull Larus modestus, which feeds in the Humboldt system, breeds in montane deserts.
Exploitation of marine resources has been occurring in the northern Benguela ecosystem for centur... more Exploitation of marine resources has been occurring in the northern Benguela ecosystem for centuries. Understanding the cumulative long-term effects of this exploitation is important toward effective management of the modern system. Retrospective mass-balanced models of the ecosystem have been constructed, using Ecopath with Ecosim, for each of the aboriginal (1600), pre-industrial (1900), industrial (1967) and post-industrial (1990s) eras of exploitation in order to ascertain the nature of changes that may have occurred in ecosystem structure and functioning. Biomass of most exploited groups, specifically sardine, hake and seabirds, declined considerably over time. The dominant small pelagic fish, characteristic of upwelling systems, were replaced by a wider range of species, and biomass of gelatinous zooplankton appears to have increased dramatically in recent decades. Catches declined, and mean trophic level of the catch increased from 3.18 in 1967 to 3.68 in 1990, as did the weighted trophic level of the community (excluding plankton), after the collapse of small pelagic stocks in the 1970s. Environmental anomalies experienced in the 1990s had a greater influence over already depleted stocks than previous events, both directly and indirectly affecting a number of stocks negatively. This compounded any effects of fishing and prevented mitigation of declining stocks by management measures implemented after Namibian independence in 1990. Changes in ecosystem structure prior to the 1990s, as a result of heavy fishing, may have altered the trophic control mechanism operating in the system, allowing environmental effects to exert a greater influence. Although fishing certainly influenced ecosystem structure and functioning in the northern Benguela, environmental events have had a considerable, and possibly even greater, impact.
Data corresponding to Saraux et al. 2020 Seabird-induced natural mortality of forage fish varies ... more Data corresponding to Saraux et al. 2020 Seabird-induced natural mortality of forage fish varies with fish abundance: evidence from 5 ecosystems. in Fish and Fisheries. This dataset regroups information on seabird diet, numbers and fish consumption, as well as fish stock biomass in five ecosystems: the Benguela, the Humboldt, the Norwegian Sea, the Baltic Sea and around the Shetland islands. Fish considered are sardine, anchovy, herring, sprat and sandeel. Seabird species are cape gannet, peruvian booby, peruvian pelican, guanay cormorant, Atlantic puffin, common murre, and 12 other seabird species off Shetland.
Defining the trophic relationships of marine predators and their dietary preferences is essential... more Defining the trophic relationships of marine predators and their dietary preferences is essential in understanding their role and importance in ecosystems. Here we used stable isotope analysis of skin samples (δ15N values reflecting trophic level and δ13C values reflecting foraging habitat) to investigate resource partitioning and spatial differences of the feeding ecology of dusky dolphins Lagenorhynchus obscurus and Heaviside’s dolphins Cephalorhynchus heavisidii from 2 coastal study sites separated by 400 km along the coast of central (Walvis Bay) and southern (Lüderitz) Namibia in the Benguela upwelling ecosystem. Overall, isotopic niches of both predators were significantly different, indicating partitioning of resources and foraging habitats. Despite their smaller body size, Heaviside’s dolphins fed at a significantly higher trophic level than dusky dolphins. Stable isotope mixing models revealed that both species fed on high trophic level prey (i.e. large Merluccius spp., lar...
1 exert top-down control on their prey species and bottom-up control on 2 their predators and, in... more 1 exert top-down control on their prey species and bottom-up control on 2 their predators and, in this way, appear to induce unsuspected 3 ecosystem dynamics. Largely based on model results, this chapter 4 explores these effects and associated dynamics, not only ...
Bien que les orques soient nettement moins nombreux autour des iles Saint Paul et Amsterdam que p... more Bien que les orques soient nettement moins nombreux autour des iles Saint Paul et Amsterdam que pres des iles subantarctiques, ce sont des visiteurs reguliers. Ils presentent de nettes variations saisonnieres d'abondance, rares en juillet et aout ils sont communs en fevrier et mars
There are 21 and 15 species of seabirds that breed in the Humboldt and Benguela upwelling systems... more There are 21 and 15 species of seabirds that breed in the Humboldt and Benguela upwelling systems respectively. Only two species of gull are common to both systems, one as an endemic subspecies to the Benguela system. Eleven species and two subspecies are endemic (or nearly so) to the Humboldt system; seven species and one subspecies to the Benguela system. Each system has an endemic penguin, sulid, cormorant and tern that feed mainly on anchovy Engraulis spp., sardine Sardinops sagax or both these fish. The Peruvian pelican Pelecanus thagus also feeds primarily on these prey items. A plentiful availability of food has resulted in many of these seabirds attaining high levels of abundance. For the four pairs of species that feed on anchovy and sardine, those in the Humboldt system all have a biology that enables them to increase more rapidly than their Benguela counter-parts. This reflects the higher frequency of environmental perturbations that depress seabird populations in the Humboldt system. In addition, both systems have a small endemic cormorant that feeds near the coast and a small endemic tern that breeds in the adjacent mainland desert and feeds at the sea surface. Several seabirds endemic to a system have no obvious ecological equivalent in the other system: the pelican, a diving-petrel, four storm-petrels and a gull in the Humboldt system; a cormorant and a gull in the Benguela system. Some species with tropical or subantarctic affinities breed at the boundaries of the systems. Others breed also in freshwater systems. The grey gull Larus modestus, which feeds in the Humboldt system, breeds in montane deserts.
Exploitation of marine resources has been occurring in the northern Benguela ecosystem for centur... more Exploitation of marine resources has been occurring in the northern Benguela ecosystem for centuries. Understanding the cumulative long-term effects of this exploitation is important toward effective management of the modern system. Retrospective mass-balanced models of the ecosystem have been constructed, using Ecopath with Ecosim, for each of the aboriginal (1600), pre-industrial (1900), industrial (1967) and post-industrial (1990s) eras of exploitation in order to ascertain the nature of changes that may have occurred in ecosystem structure and functioning. Biomass of most exploited groups, specifically sardine, hake and seabirds, declined considerably over time. The dominant small pelagic fish, characteristic of upwelling systems, were replaced by a wider range of species, and biomass of gelatinous zooplankton appears to have increased dramatically in recent decades. Catches declined, and mean trophic level of the catch increased from 3.18 in 1967 to 3.68 in 1990, as did the weighted trophic level of the community (excluding plankton), after the collapse of small pelagic stocks in the 1970s. Environmental anomalies experienced in the 1990s had a greater influence over already depleted stocks than previous events, both directly and indirectly affecting a number of stocks negatively. This compounded any effects of fishing and prevented mitigation of declining stocks by management measures implemented after Namibian independence in 1990. Changes in ecosystem structure prior to the 1990s, as a result of heavy fishing, may have altered the trophic control mechanism operating in the system, allowing environmental effects to exert a greater influence. Although fishing certainly influenced ecosystem structure and functioning in the northern Benguela, environmental events have had a considerable, and possibly even greater, impact.
Data corresponding to Saraux et al. 2020 Seabird-induced natural mortality of forage fish varies ... more Data corresponding to Saraux et al. 2020 Seabird-induced natural mortality of forage fish varies with fish abundance: evidence from 5 ecosystems. in Fish and Fisheries. This dataset regroups information on seabird diet, numbers and fish consumption, as well as fish stock biomass in five ecosystems: the Benguela, the Humboldt, the Norwegian Sea, the Baltic Sea and around the Shetland islands. Fish considered are sardine, anchovy, herring, sprat and sandeel. Seabird species are cape gannet, peruvian booby, peruvian pelican, guanay cormorant, Atlantic puffin, common murre, and 12 other seabird species off Shetland.
Defining the trophic relationships of marine predators and their dietary preferences is essential... more Defining the trophic relationships of marine predators and their dietary preferences is essential in understanding their role and importance in ecosystems. Here we used stable isotope analysis of skin samples (δ15N values reflecting trophic level and δ13C values reflecting foraging habitat) to investigate resource partitioning and spatial differences of the feeding ecology of dusky dolphins Lagenorhynchus obscurus and Heaviside’s dolphins Cephalorhynchus heavisidii from 2 coastal study sites separated by 400 km along the coast of central (Walvis Bay) and southern (Lüderitz) Namibia in the Benguela upwelling ecosystem. Overall, isotopic niches of both predators were significantly different, indicating partitioning of resources and foraging habitats. Despite their smaller body size, Heaviside’s dolphins fed at a significantly higher trophic level than dusky dolphins. Stable isotope mixing models revealed that both species fed on high trophic level prey (i.e. large Merluccius spp., lar...
1 exert top-down control on their prey species and bottom-up control on 2 their predators and, in... more 1 exert top-down control on their prey species and bottom-up control on 2 their predators and, in this way, appear to induce unsuspected 3 ecosystem dynamics. Largely based on model results, this chapter 4 explores these effects and associated dynamics, not only ...
Bien que les orques soient nettement moins nombreux autour des iles Saint Paul et Amsterdam que p... more Bien que les orques soient nettement moins nombreux autour des iles Saint Paul et Amsterdam que pres des iles subantarctiques, ce sont des visiteurs reguliers. Ils presentent de nettes variations saisonnieres d'abondance, rares en juillet et aout ils sont communs en fevrier et mars
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