scholarly journals Direct and indirect community effects of rebuilding plans

2010 ◽  
Vol 67 (9) ◽  
pp. 1980-1988 ◽  
Author(s):  
Ken H. Andersen ◽  
Jake C. Rice
Keyword(s):  
Indirect Effects ◽  
Management Development ◽  
Single Species ◽  
Ecosystem Approach ◽  
Trophic Levels ◽  
Fishing Mortality ◽  
Community Effects ◽  
Target Species ◽  
Expected Increase ◽  
Single Species Model

Abstract Andersen, K. H., and Rice, J. C. 2010. Direct and indirect community effects of rebuilding plans. – ICES Journal of Marine Science, 67: 1980–1988. Many fish communities are heavily exploited and rebuilding plans need to be implemented for depleted species. Within an ecosystem approach to management, development of rebuilding plans should include consideration of the expected consequences of the rebuilding of the target species on the rest of the marine community. Using size- and trait-based single-species and community models, a general assessment is made of the direct and indirect ecological consequences of a rebuilding plan based on a reduction in fishing mortality. If fishing mortality is sufficiently reduced, the time-scale of rebuilding is in the order of the time to reach maturation of an individual, and the expected trajectory can be reliably predicted by a single-species model. Indirect effects of increased abundance are a decrease in individuals in the trophic levels above and below the target species. The decrease in biomass of the neighbouring trophic levels is expected to be much smaller than the increase in the target species and to be largest in species on the trophic level above. We discuss which effects could be responsible when a rebuilding plan does not result in the expected increase and how our results could be applied in a practical management situation.

Ecosystem Considerations in Fisheries Management: Theory and Practice

2005 ◽  
Vol 20 (3) ◽  
pp. 381-422 ◽  
Author(s):  
Scott Parsons
Keyword(s):  
Fisheries Management ◽  
Single Species ◽  
Ecosystem Approach ◽  
Theory And Practice ◽  
Target Species ◽  
Management Measures ◽  
Species Analysis ◽  
Recent Developments ◽  
Fishing Fleets ◽  
Management Approaches

AbstractThis article examines recent developments with respect to the development and application of an ecosystem approach in marine fisheries management. A number of international fisheries legal instruments now include explicit references to ecosystem considerations. While there has been general agreement on the need to take ecosystem considerations into account, there is no clarity or consensus on how this can best be done. Various definitions of an ecosystem approach emphasise that the focus must be on managing the human activities, which are part of, and impact on, marine ecosystems. An ecosystem approach is neither inconsistent with, nor a replacement for, existing fisheries management approaches—it is not a panacea for the problems confronting world fisheries. Realistically, we can only move to an ecosystem approach incrementally, starting with more rigorous/cautious application and extension of single species methods. A key element of any ecosystem approach will likely be to set harvest rates for target species at even lower conservative levels than might be suggested by single species analysis. Fisheries management measures should also ensure the protection not only of target species, but also of non-target, associated or dependent species. Reducing the killing power of the world's fishing fleets is an essential component of ecosystem-based fisheries management.

Bycatch of chondrichthyans in a coastal trawl fishery on Chubut province coast and adjacent waters, Argentina

2016 ◽  
Vol 98 (3) ◽  
pp. 605-616 ◽  
Author(s):  
J. Ruibal Núñez ◽  
N. D. Bovcon ◽  
P. D. Cochia ◽  
M. E. Góngora
Keyword(s):  
Single Species ◽  
Ecosystem Approach ◽  
Squalus Acanthias ◽  
Fishing Gear ◽  
Target Species ◽  
Trawl Fishery ◽  
Merluccius Hubbsi ◽  
By Products ◽  
Discopyge Tschudii ◽  
Mustelus Schmitti

Chondrichthyans are usually caught incidentally in fisheries for species of high commercial value and then discarded on board or landed as by-products. On the coast of Chubut province and adjacent waters (43°00′S–44°56′S) a bottom trawl fishery has developed targeted at the Patagonian shrimp (Pleoticus muelleri) and common hake (Merluccius hubbsi). Since 2005, this fishery has been monitored by the On-board Observers Program of Chubut province (POBCh). With the aim of advancing towards an ecosystem approach, POBCh not only collects information about target species but also about all the species caught by the trawl nets of the province fisheries. From the information collected by this programme it was possible to identify and record the chondrichthyan species vulnerable to the fishing gear used by the coastal fleet that operates from Puerto Rawson. The composition of the fleet catch was characterized according to the target species during the 2005–2014 period. In the analysis of 3786 hauls, 23 species of chondrichthyans (seven species of sharks, 15 species of batoids and a single species of Holocephali) were identified. Seven species showed a frequency of occurrence greater than 10% (Callorhinchus callorynchus, Discopyge tschudii, Mustelus schmitti, Sympterygia bonapartii, Psammobatis normani, Squalus acanthias and Zearaja chilensis). Species spatial distribution was evaluated and five areas of species assemblages were established. Besides the aspects related to bycatch, these analyses have contributed to the knowledge of the chondrichthyan biodiversity in the provincial coast where the fleet operates, a region with incomplete and mostly dispersed and outdated information.

Trophic Cascades in Grasslands

2018 ◽  
Author(s):  
Brian J. Wilsey
Keyword(s):  
Indirect Effects ◽  
Prey Species ◽  
Trophic Levels ◽  
Herbaceous Plant ◽  
Direct Effects ◽  
Temperate Grasslands ◽  
Cascading Effect ◽  
Top Predators ◽  
Invertebrate Predators ◽  
Ecology Of Fear

Top predators have effects that can ‘cascade down’ on lower trophic levels. Because of this cascading effect, it matters how many trophic levels are present. Predators are either ‘sit and wait’ or ‘active’. Wolves are top predators in temperate grasslands and can alter species composition of smaller-sized predators, prey, and woody and herbaceous plant species, either through direct effects or indirect effects (‘Ecology of Fear’). In human derived grasslands, invertebrate predators fill a similar ecological role as wolves. Migrating populations of herbivores tend to be more limited by food than non-migratory populations. The phenology and synchrony of births vary among prey species in a way that is consistent with an adaptation to predation. Precocious species have highly synchronous birth dates to satiate predators. Non-precocious species (‘hiders’) have asynchronous births. Results from studies that manipulate both predators and food support the hypothesis that bottom-up and top-down effects interact.

scholarly journals Crying wolf to a predator: deceptive vocal mimicry by a bird protecting young

2015 ◽  
Vol 282 (1809) ◽  
pp. 20150798 ◽  
Author(s):  
Branislav Igic ◽  
Jessica McLachlan ◽  
Inkeri Lehtinen ◽  
Robert D. Magrath
Keyword(s):  
Indirect Effects ◽  
Trophic Levels ◽  
Alarm Calls ◽  
Toxic Species ◽  
Vocal Mimicry ◽  
Primary Nest ◽  
Defence Strategy ◽  
Multiple Species ◽  
Defensive Mimicry ◽  
As If

Animals often mimic dangerous or toxic species to deter predators; however, mimicry of such species may not always be possible and mimicry of benign species seems unlikely to confer anti-predator benefits. We reveal a system in which a bird mimics the alarm calls of harmless species to fool a predator 40 times its size and protect its offspring against attack. Our experiments revealed that brown thornbills ( Acanthiza pusilla ) mimic a chorus of other species' aerial alarm calls, a cue of an Accipiter hawk in flight, when predators attack their nest. The absence of any flying predators in this context implies that these alarms convey deceptive information about the type of danger present. Experiments on the primary nest predators of thornbills, pied currawongs ( Strepera graculina ), revealed that the predators treat these alarms as if they themselves are threatened by flying hawks, either by scanning the sky for danger or fleeing, confirming a deceptive function. In turn, these distractions delay attack and provide thornbill nestlings with an opportunity to escape. This sophisticated defence strategy exploits the complex web of interactions among multiple species across several trophic levels, and in particular exploits a predator's ability to eavesdrop on and respond appropriately to heterospecific alarm calls. Our findings demonstrate that prey can fool predators by deceptively mimicking alarm calls of harmless species, suggesting that defensive mimicry could be more widespread because of indirect effects on predators within a web of eavesdropping.

Quantitative Detection of Species-Specific DNA in Feedstuffs and Fish Meals

2005 ◽  
Vol 68 (6) ◽  
pp. 1217-1221 ◽  
Author(s):  
PAVEL KRCMAR ◽  
EVA RENCOVA
Keyword(s):  
Mitochondrial Dna ◽  
Real Time ◽  
Dna Sequences ◽  
Real Time Pcr ◽  
Single Species ◽  
Absolute Quantification ◽  
Quantitative Detection ◽  
Vertebrate Species ◽  
Target Species ◽  
Species Specific

A sensitive and rapid method for the quantitative detection of bovine-, ovine-, swine-, and chicken-specific mitochondrial DNA sequences based on real-time PCR has been developed. The specificity of the primers and probes for real-time PCR has been tested using DNA samples of other vertebrate species that may also be present in rendered products. The quantitative detection was performed with dual-labeled probes (TaqMan) using absolute quantification with external standards of single species meat-and-bone meals. This method facilitates the detection of 0.01% of the target species–derived material in concentrate feed mixtures and fish meals.

scholarly journals The risk to fishery performance associated with spatially resolved management of Antarctic krill (Euphausia superba) harvesting

2009 ◽  
Vol 66 (10) ◽  
pp. 2148-2154 ◽  
Author(s):  
Simeon L. Hill ◽  
Philip N. Trathan ◽  
David J. Agnew
Keyword(s):  
Antarctic Krill ◽  
Euphausia Superba ◽  
Ecosystem Approach ◽  
Fishing Effort ◽  
Target Species ◽  
Ecosystem Models ◽  
Spatially Resolved ◽  
Management Actions ◽  
Antarctic Krill Euphausia Superba

Abstract Hill, S. L., Trathan, P. N., and Agnew, D. J. 2009. The risk to fishery performance associated with spatially resolved management of Antarctic krill (Euphausia superba) harvesting. – ICES Journal of Marine Science, 66: 2148–2154. The ecosystem approach to fisheries attempts to define objectives for target species, the wider ecosystem, and critically, the fishery itself. Proposals for implementing the approach often include spatial restrictions on harvesting, so it is important to understand how these will affect fishery performance. One metric of potential performance is the probability of encountering exploitable densities of a target species at the scale of fishing operations. The probability of encountering exploitable densities of Antarctic krill, Euphausia superba, at the scale of 1 nautical mile during an acoustic survey was predicted by bathymetry and the mean krill density at the larger scale at which the fishery is managed. This suggests that the risk to fishery performance will increase if management actions relocate the fishery into deeper water. The results also suggest that ecosystem models resolved to the spatial scale of management units could usefully predict effects at the scale of fishing operations. However, correct parameterization of these models will require better characterization of threshold densities for efficient exploitation. Finally, the distribution of catch and fishing effort over an entire fishing season reflected the distribution of krill density observed during the survey.

scholarly journals Balanced harvesting is the bioeconomic equilibrium of a size-structured Beverton-Holt model

2016 ◽  
Vol 74 (1) ◽  
pp. 112-120 ◽  
Author(s):  
Michael J. Plank
Keyword(s):  
Single Species ◽  
Size Spectrum ◽  
Ecosystem Structure ◽  
Fishing Mortality ◽  
Biomass Transfer ◽  
Body Sizes ◽  
Relative Production ◽  
Ecosystem Structure And Functioning ◽  
Classical Size ◽  
Spectrum Model

Balanced harvesting (BH) was introduced as an alternative strategy to size-at-entry fishing with the aim of maintaining ecosystem structure and functioning. BH has been criticized on a number of grounds, including that it would require an infeasible level of micromanagement and enforcement. Recent results from a size-spectrum model show that the distribution of fishing mortality across body sizes that emerges from the behaviour of a large number of fishing agents corresponds to BH in a single species. Size-spectrum models differ from classical size-structured models used in fisheries as they are based on a bookkeeping of biomass transfer from prey to predator rather than a von Bertalanffy growth model. Here we investigate a classical Beverton-Holt model coupled with the Gordon-Schaefer harvesting model extended to allow for differential fishing pressure at different body sizes. This models an open-access fishery in which individual fishing agents act to maximize their own economic return. We show that the equilibrium of the harvesting model produces an aggregate fishing mortality that is closely matched to the production at different body sizes, in other words BH of a single species. These results have significant implications because they show that the robustness of BH does not depend on arguments about the relative production levels of small versus large fish.

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