Top Predator Populations Research Articles

Respective impact of climate and fisheries on the growth of an albatross population

Climate and human activities such as fisheries impact many animal species. However, the demographic processes through which the population vital rates are affected, and the sensitivity of their growth rates, are poorly understood. The Black-browed Albatross, Thalassarche melanophrys, is a long-lived threatened seabird species. Previous studies have shown that the adult survival and breeding success of the population breeding at Kerguelen are affected by sea surface temperature anomalies (SSTA) during both the breeding and the nonbreeding season, and by tuna long-lining in Tasmanian waters through bycatch mortality. Here, using long-term demographic data from a Black-browed Albatross colony monitored for 26 years at Kerguelen, we estimate all demographic parameters from early to adult stages of the life cycle in order to build a fully parameterized population model and predict population growth rates under several scenarios of climate and fishing effort. The observed population growth rate (1.003) indicates that the population was stable or slightly increasing, and our population model gives a close estimate of 1.008. Population growth rate is more sensitive to survival of experienced breeders and accordingly to a change in SSTA during incubation and to tuna long-lining effort (both affecting survival of experienced breeders) than to other demographic parameters/environmental covariates. The population stability results from multiple factors and complex relationships between demographic parameters and environmental conditions, and therefore population equilibrium is precarious. If fishing effort remains stable at its current level and positive SSTA increase, or inversely if fishing effort decreases and SSTA remain similar to present values, then the population would increase. However, if fishing effort increases by 20% (i.e., to 40 million hooks) on the wintering grounds, without any change in SSTA, then the population would decrease at 0.9% per year. If fishing effort stops, the population would increase at 3.5% per year, suggesting that bycatch mortality probably currently limits the Black-browed Albatross population at Kerguelen. Our study shows how this type of model could be useful to predict trajectories of top predator populations, and eventually lower trophic web levels, in relation to climatic projections and future human activities. We highlight the need to reinforce mitigation measures.

Dynamics of physical and biological systems of the Prince Edward Islands in a changing climate

Sub-Antarctic islands are classified as isolated, hostile, impoverished regions, in which the terrestrial and marine ecosystems are relatively simple and extremely sensitive to perturbations. They provide an ideal ecological laboratory for studying how organisms, ecological processes and ecosystems respond to a changing ocean climate in the Southern Ocean. 1hese islands are characterised by large populations of top predators and subsequently any changes in the oceanographic frontal dynamics associated with the Antarctic Circumpolar Current, either in the vicinity of these islands or further afield, may have strong implications on their foraging behaviour. The relatively easy accessibility of the Prince Edward Islands from South Africa and their location between the main frontal systems bordering the Antarctic Circumpolar Current enable high-resolution synoptic field studies to be undertaken. Such studies have provided information on the impact changes in the large-·scale ocean dynamics have on the local marine ecosystems.

Density Dependent Predator Death Prevalence Chaos in a Tri-trophic Food Chain Model

Ecological systems have all the properties to produce chaotic dynamics. To predict the chaotic behavior in an ecological system and its possible control mechanism is interesting. Aziz-Alaoui [1] considered a tri-trophic food-chain model with modified Leslie-Gower type growth rate for top-predator population and established the chaotic dynamics exhibited by the model system for a certain choice of parameter values. We have modified the said model by incorporating density dependent death rate for predator population. Our mathematical findings reveal the fact that there are two coexisting equilibrium points one of which is a source and the other one is a sink. The positive equilibrium point which is sink is actually globally asymptotically stable under certain parametric conditions. Numerical experiment analysis shows that the model system are capable to produce chaotic dynamics when the rate of intra specific completion is very low and chaotic dynamics disappears for a certain value of the rate of intra specific completion for predator species. Our results suggest that the consideration of density dependent death rate for predator species have the ability to control the chaotic dynamics.

Production and Toxicity of the Marine Biotoxin Domoic Acid and Its Effects on Wildlife: A Review

ABSTRACT Domoic acid (DA), produced by marine diatom species in the genus Pseudo-nitzschia, is a potent excitotoxin linked since the late 1990s to massive marine mammal and seabird mortalities along the California coast. These and a previous incident involving human intoxication and deaths prompted many studies, some of which have unveiled the trophic transfer of DA from benthic invertebrates and planktivorous fish to top predators, demonstrating serious health risk to marine wildlife and humans. Top predator populations that may be more adversely affected by DA include those with narrow geographical distribution or those that are already in decline as a result of other environmental stressors or natural cyclic fluctuations. However, to date no studies have attempted to assess the population effects of recurrent exposures to DA on any of the affected wildlife species. Ecological risk assessment can help to identify DA effects on wildlife, but meaningful assessments require the integration of many types of information, often not available to conduct such studies. Hence, determining short- and long-term effects on marine wildlife populations is rather challenging. The purpose of this review is to highlight recent research efforts and information gaps, and the need for interdisciplinary programs that allow collaborative wildlife population risk assessments of critical species.

A junk-food hypothesis for gannets feeding on fishery waste

Worldwide fisheries generate large volumes of fishery waste and it is often assumed that this additional food is beneficial to populations of marine top-predators. We challenge this concept via a detailed study of foraging Cape gannets Morus capensis and of their feeding environment in the Benguela upwelling zone. The natural prey of Cape gannets (pelagic fishes) is depleted and birds now feed extensively on fishery wastes. These are beneficial to non-breeding birds, which show reduced feeding effort and high survival. By contrast, breeding gannets double their diving effort in an attempt to provision their chicks predominantly with high-quality, live pelagic fishes. Owing to a scarcity of this resource, they fail and most chicks die. Our study supports the junk-food hypothesis for Cape gannets since it shows that non-breeding birds can survive when complementing their diet with fishery wastes, but that they struggle to reproduce if live prey is scarce. This is due to the negative impact of low-quality fishery wastes on the growth patterns of gannet chicks. Marine management policies should not assume that fishery waste is generally beneficial to scavenging seabirds and that an abundance of this artificial resource will automatically inflate their populations.

Are marine protected areas useful for the recovery of the Mediterranean mussel populations?

1. Mussel beds are important intertidal communities in the Mediterranean Sea and have traditionally been exploited by humans. 2. Marine protected areas are management tools for recovering over-fished populations, normally top predator populations, which may in turn undermine prey abundance. Therefore, mussel populations might not recover inside protected areas, as they are affected by increasing fish populations. 3. To study the effects of both human and fish predation on mussels, three locations were selected: the Reserve (R), where all types of exploitation were banned and fish were abundant; the Partial Reserve (PR), where only angling was permitted, and fish abundance was low; and the Non-Reserve (NR), where no protection existed and fish were rare. 4. Data from mussel bed surveys indicate that recruitment is critical to sustain mussel populations, and similar size structures were found at all three locations. However, the overall biomass in the PR was nearly double that in both R and NR, suggesting disturbance of some sort at these latter two sites. 5. A tethering experiment showed that fish predation greatly affected mussels in R, while the analysis of harvester collections from the NR showed that the most harvested size classes were those least abundant in the mussel bed. 6. Both protected and non-protected areas are unable to increase mussel populations due to trophic cascade effects, while partial reserves, where fish populations are exploited and mussels protected, are areas where the Mediterranean mussel populations can recover.

Trophic control of mesopredators in terrestrial ecosystems: top‐down or bottom‐up?

It has been argued that widespread extinctions of top predators have changed terrestrial ecosystem structures through mesopredator release, where increased abundances of medium-sized predators have detrimental effects on prey communities. This top-down concept has received much attention within conservation biology, but few studies have demonstrated the phenomenon. The concept has been criticized since alternative explanations involving bottom-up impacts from bioclimatic effects on ecosystem productivity and from anthropogenic habitat change are rarely considered. We analyse the response of a mesopredator (the red fox) to declines in top predators (wolf and Eurasian lynx) and agricultural expansion over 90 years in Sweden, taking bioclimatic effects into account. We show a top-down mesopredator release effect, but ecosystem productivity determined its strength. The impacts of agricultural activity were mediated by their effects on top predator populations. Thus, both top-down and bottom-up processes need to be understood for effective preservation of biodiversity in anthropogenically transformed ecosystems.

Visualizing the Food-Web Effects of Fishing for Tunas in the Pacific Ocean

Hinke, J. T., I. C. Kaplan, K. Aydin, G. M. Watters, R. J. Olson and J. Kitchell 2004. Visualizing the Food-Web Effects of Fishing for Tunas in the Pacific Ocean. Ecology and Society 9(1):10. https://doi.org/10.5751/ES-00626-090110

Symbiotic nesting of birds with formidable animals: a review with applications to biodiversity conservation

Increased predation and parasitism of bird nests has become a major problem in many biological communities altered by human activities, often causing declines in bird populations. To help solve this threat to biodiversity, I propose restoring the abundance of symbiotic nest-protecting animals in habitats where birds face an increased risk from predators and parasites, so that birds there can increase their chances of reproductive success by nesting close to these protectors. The re-establishment of such protective nesting associations to increase avian reproductive success differs from other proposed solutions to this problem in that it involves point defense of bird nests themselves. Rather than diminishing the number of nest predators and brood parasites in the whole habitat or community, as proposed with other approaches, the presence, activity and success of these enemies are reduced only within the microhabitat defended by the protector. The animal protecting the nest need not be larger in size than the predators or brood parasites, and is often many times smaller. In addition, it need not be from a higher trophic position, and in many cases comes from the same or a lower trophic level. Research suggests that an informed and careful use of nest protecting animals by wildlife managers can help reverse or prevent the decline of many bird populations, especially when used in combination with other approaches such as restoration of top predator populations and habitats. Although wildlife biologists have long recognized the important role that plants play in concealing and protecting bird nests from enemies, and regularly recommend manipulation of vegetation to enhance nest survival, they have generally ignored the important role that formidable animals play in protecting bird nests, and failed to incorporate animal protectors into management strategies. Because of this neglect, a host of new studies and experiments are urgently needed to provide managers with the critical information needed to use protective nesting associations effectively in integrated strategies to preserve avian biodiversity.

Life-support value of ecosystems: a case study of the Baltic Sea Region

Ecosystems support the economy with necessary environmental goods and services. In the Baltic Sea Region the accumulated pressure from industries, agriculture and fisheries has reduced this support. Water and soil quality has decreased, forests and the quality of commercial fish species have been degraded, and marine top predator populations have diminished. Humans have through predation, pollution and competition replaced the seals as the major top consumers of the Baltic Sea food-web. Our estimates indicate that up to 85% of the total primary production of the Baltic Sea nowadays supports the fish catches. In the Baltic Sea Region the natural capital is increasingly replacing man-made capital as the limiting factor for socio-economic development. In order to attain sustainable development socio-economic activities and their feed-back flows must be adapted to the capacity of the life-supporting ecosystems. The challenge for the future of the whole region is to fit the industrial societies into ecosystem processes and functions. Input management of production systems and ecological engineering are important tools for this purpose.