124 research outputs found
Can fisheries-induced evolution shift reference points for fisheries management?
Biological reference points are important tools for fisheries management. Reference points are not static, butmay change when a population's environment or the population itself changes. Fisheries-induced evolution is one mechanism that can alter population characteristics, leading to "shifting" reference points by modifying the underlying biological processes or by changing the perception of a fishery system. The former causes changes in "true" reference points, whereas the latter is caused by changes in the yardsticks used to quantify a system's status. Unaccounted shifts of either kind imply that reference points gradually lose their intended meaning. This can lead to increased precaution, which is safe, but potentially costly. Shifts can also occur in more perilous directions, such that actual risks are greater than anticipated. Our qualitative analysis suggests that all commonly used reference points are susceptible to shifting through fisheries-induced evolution, including the limit and "precautionary" reference points for spawning-stock biomass, B-lim and B-pa, and the target reference point for fishing mortality, F-0.1. Our findings call for increased awareness of fisheries-induced changes and highlight the value of always basing reference points on adequately updated information, to capture all changes in the biological processes that drive fish population dynamics
The SOLAS air-sea gas exchange experiment (SAGE) 2004
Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 58 (2011): 753-763, doi:10.1016/j.dsr2.2010.10.015.The SOLAS air-sea gas exchange experiment (SAGE) was a multiple-objective study investigating
gas-transfer processes and the influence of iron fertilisation on biologically driven gas exchange in
high-nitrate low-silicic acid low-chlorophyll (HNLSiLC) Sub-Antarctic waters characteristic of the
expansive Subpolar Zone of the southern oceans. This paper provides a general introduction and
summary of the main experimental findings. The release site was selected from a pre-voyage desktop
study of environmental parameters to be in the south-west Bounty Trough (46.5°S 172.5°E) to the
south-east of New Zealand and the experiment conducted between mid-March and mid-April 2004. In
common with other mesoscale iron addition experiments (FeAX’s), SAGE was designed as a
Lagrangian study quantifying key biological and physical drivers influencing the air-sea gas exchange
processes of CO2, DMS and other biogenic gases associated with an iron-induced phytoplankton
bloom. A dual tracer SF6/3He release enabled quantification of both the lateral evolution of a labelled
volume (patch) of ocean and the air-sea tracer exchange at the 10’s of km’s scale, in conjunction with
the iron fertilisation. Estimates from the dual-tracer experiment found a quadratic dependency of the
gas exchange coefficient on windspeed that is widely applicable and describes air-sea gas exchange in strong wind regimes. Within the patch, local and micrometeorological gas exchange process studies (100 m scale) and physical variables such as near-surface turbulence, temperature microstructure at the interface, wave properties, and wind speed were quantified to further assist the development of gas exchange models for high-wind environments.
There was a significant increase in the photosynthetic competence (Fv/Fm) of resident phytoplankton
within the first day following iron addition, but in contrast to other FeAX’s, rates of net primary
production and column-integrated chlorophyll a concentrations had only doubled relative to the
unfertilised surrounding waters by the end of the experiment. After 15 days and four iron additions
totalling 1.1 tonne Fe2+, this was a very modest response compared to the other mesoscale iron
enrichment experiments. An investigation of the factors limiting bloom development considered co-
limitation by light and other nutrients, the phytoplankton seed-stock and grazing regulation. Whilst
incident light levels and the initial Si:N ratio were the lowest recorded in all FeAX’s to date, there was
only a small seed-stock of diatoms (less than 1% of biomass) and the main response to iron addition
was by the picophytoplankton. A high rate of dilution of the fertilised patch relative to phytoplankton
growth rate, the greater than expected depth of the surface mixed layer and microzooplankton grazing
were all considered as factors that prevented significant biomass accumulation. In line with the limited
response, the enhanced biological draw-down of pCO2 was small and masked by a general increase in pCO2 due to mixing with higher pCO2 waters. The DMS precursor DMSP was kept in check through grazing activity and in contrast to most FeAX’s dissolved dimethylsulfide (DMS) concentration declined through the experiment. SAGE is an important low-end member in the range of responses to iron addition in FeAX’s. In the context of iron fertilisation as a geoengineering tool for atmospheric CO2 removal, SAGE has clearly demonstrated that a significant proportion of the low iron ocean may not produce a phytoplankton bloom in response to iron addition.SAGE was jointly funded through
the New Zealand Foundation for Research, Science and Technology (FRST) programs
(C01X0204) "Drivers and Mitigation of Global Change" and (C01X0223) "Ocean
Ecosystems: Their Contribution to NZ Marine Productivity." Funding was also provided for
specific collaborations by the US National Science Foundation from grants OCE-0326814
(Ward), OCE-0327779 (Ho), and OCE 0327188 OCE-0326814 (Minnett) and the UK Natural
Environment Research Council NER/B/S/2003/00282 (Archer). The New Zealand
International Science and Technology (ISAT) linkages fund provided additional funding
(Archer and Ziolkowski), and the many collaborator institutions also provided valuable
support
Ecological and evolutionary consequences of alternative sex-change pathways in fish
Sequentially hermaphroditic fish change sex from male to female (protandry) or vice versa (protogyny), increasing their fitness by becoming highly fecund females or large dominant males, respectively. These life-history strategies present different social organizations and reproductive modes, from near-random mating in protandry, to aggregate- and harem-spawning in protogyny. Using a combination of theoretical and molecular approaches, we compared variance in reproductive success (V k*) and effective population sizes (N e) in several species of sex-changing fish. We observed that, regardless of the direction of sex change, individuals conform to the same overall strategy, producing more offspring and exhibiting greater V k* in the second sex. However, protogynous species show greater V k*, especially pronounced in haremic species, resulting in an overall reduction of N e compared to protandrous species. Collectively and independently, our results demonstrate that the direction of sex change is a pivotal variable in predicting demographic changes and resilience in sex-changing fish, many of which sustain highly valued and vulnerable fisheries worldwide
Long-distance seed dispersal by wind: disentangling the effects of species traits, vegetation types, vertical turbulence and wind speed
Ground seed density patterns under conditions of strongly overlapping seed shadows in Abies alba Mill. stands
The predictability of ecological stability in a noisy world
Random environmental variation, or stochasticity, is a key determinant of ecological dynamics. While we have some appreciation of how environmental stochasticity can moderate the variability and persistence of communities, we know little about its implications for the nature and predictability of ecological responses to large perturbations. Here, we show that shifts in the temporal autocorrelation (colour) of environmental noise provoke trade-offs in ecological stability across a wide range of different food-web structures by stabilizing dynamics in some dimensions, while simultaneously destabilizing them in others. Specifically, increasingly positive autocorrelation (reddening) of environmental noise increases resilience by hastening the recovery of food webs following a large perturbation, but reduces their resistance to perturbation and increases their temporal variability (reduces biomass stability). In contrast, all stability dimensions become less predictable, showing increased variability around the mean response, as environmental noise reddens. Moreover, we found environmental reddening to be a considerably more important determinant of stability than intrinsic food-web characteristics. These findings reveal the fundamental and dominant role played by environmental stochasticity in determining the dynamics and stability of ecosystems, and extend our understanding of how the multiple dimensions of stability relate to each other beyond simple white noise environments
Influence of tides and winds on fishing techniques and strategies in the Mamanguape River Estuary, Paraíba State, NE Brazil
Towards more efficient longline fisheries: fish feeding behaviour, bait characteristics and development of alternative baits
Coexistence of genetically modified (GM) and non-GM crops in the European Union. A review
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