McGregor A.M.,University of Alberta |
McGregor A.M.,Environment Canada |
Davis C.L.,Ontario Ministry of Natural Resources |
Walters C.J.,Fisheries Center |
Foote L.,University of Alberta
Ecology and Society | Year: 2015
Increased population sizes of Double-crested Cormorants (Phalacrocorax auritus) and small-bodied (<15 cm total length) yellow perch (Perca flavescens) have occurred at Lac la Biche, Alberta, Canada, since fisheries collapsed the walleye (Sander vitreus) population. A walleye restoration program was introduced in 2005, but uncertainty around the ecosystem’s response to management made it difficult to evaluate program success. This study used 40 variations of Ecopath with Ecosim models representing ecosystem conditions over 200 years to test the potential for multiple attractors, i.e., possible ecosytem states, in a large lake ecosystem. Results suggest that alternate stable states, defined by walleye-dominated and cormorant-dominated equilibriums, existed in historical models (1800, 1900), whereas contemporary models (1965, 2005) had a single cormorant-dominated attractor. Alternate stable states were triggered by smaller perturbations in 1900 than in 1800, and model responses were more intense in 1900, suggesting a decline in system resilience between model periods. Total prey biomass consumed by walleye was up to four times greater than the biomass consumed by cormorants in historical models, but dropped to 10% of cormorant consumption in 2005 models. Differential size-selection pressures of cormorants and walleye on yellow perch provided strong feedback that stabilized each state. These results provide important theoretical support for alternate stable states as well as practical insights for restoration of large lake ecosystems affected by human induced overharvest of top-level fish predators. © 2015 by the author(s).
Ward H.G.M.,University of Calgary |
Askey P.J.,British Columbia Ministry of forests |
Post J.R.,University of Calgary |
Varkey D.A.,Fisheries Center |
McAllister M.K.,University of British Columbia
Fisheries Research | Year: 2012
Fisheries management often requires efficient methods for assessing populations across a variety of sampling units. We develop a model to assess the status of rainbow trout (Oncorhynchus mykiss) in lakes using a fixed length of multimesh gillnets. We use mark-recapture data to examine how gillnet capture efficiency varies with lake-basin characteristics. Once we accounted for variation in lake-size (net-effort density), we found that capture efficiency was best explained by surface water temperature at the time of gillnetting and lake-basin characteristics (proportion of littoral area). We use Bayesian techniques to fit our model to the data and explore how uncertainty in the estimated parameters leads to uncertainty in population estimates. Our analysis suggests that lake size, temperature and the proportion of littoral area can be used to predict population size using this index netting method. In addition to providing density estimates, our results help to better understand how fish ecology and behavior influences gillnet catches. © 2012 Elsevier B.V.
Heymans J.J.,Scottish Association for Marine Science |
Mackinson S.,Cefas |
Sumaila U.R.,Fisheries Center |
Dyck A.,Fisheries Center |
And 2 more authors.
PLoS ONE | Year: 2011
Background: This study examines the impact of subsidies on the profitability and ecological stability of the North Sea fisheries over the past 20 years. It shows the negative impact that subsidies can have on both the biomass of important fish species and the possible profit from fisheries. The study includes subsidies in an ecosystem model of the North Sea and examines the possible effects of eliminating fishery subsidies. Methodology/Principal Findings: Hindcast analysis between 1991 and 2003 indicates that subsidies reduced the profitability of the fishery even though gross revenue might have been high for specific fisheries sectors. Simulations seeking to maximise the total revenue between 2004 and 2010 suggest that this can be achieved by increasing the effort of Nephrops trawlers, beam trawlers, and the pelagic trawl-and-seine fleet, while reducing the effort of demersal trawlers. Simulations show that ecological stability can be realised by reducing the effort of the beam trawlers, Nephrops trawlers, pelagic- and demersal trawl-and-seine fleets. This analysis also shows that when subsidies are included, effort will always be higher for all fleets, because it effectively reduces the cost of fishing. Conclusions/Significance: The study found that while removing subsidies might reduce the total catch and revenue, it increases the overall profitability of the fishery and the total biomass of commercially important species. For example, cod, haddock, herring and plaice biomass increased over the simulation when optimising for profit, and when optimising for ecological stability, the biomass for cod, plaice and sole also increased. When subsidies are eliminated, the study shows that rather than forcing those involved in the fishery into the red, fisheries become more profitable, despite a decrease in total revenue due to a loss of subsidies from the government. © 2011 Heymans et al.
Kerby T.K.,University of East Anglia |
Kerby T.K.,CEFAS - Center for Environment, Fisheries and Aquaculture Science |
Cheung W.W.L.,University of East Anglia |
Cheung W.W.L.,CEFAS - Center for Environment, Fisheries and Aquaculture Science |
And 2 more authors.
Reviews in Fish Biology and Fisheries | Year: 2012
This study compiles 100 years of North Sea demersal landings, focusing on the UK, and relating them to historical events and political, technological and economical drivers that influenced demersal fisheries. In the early twentieth century, aided by technological advances, the UK, and in particular England, had unchallenged dominance in North Sea demersal fisheries. Since then, the two World Wars and other political developments have had a great impact on British fisheries. Between the 1920s and 1960s, English ports shifted their interests away from the North Sea towards highly profitable distant waters, whereas the Scottish fleet relied less on these fishing grounds. Meanwhile, especially in the 1960s, other European countries expanded their fisheries, undermining Britain's lead. In the 1970s and 1980s, Scotland benefitted from mainly fishing in the North Sea. Firstly, the assertion of 200 nautical miles Exclusive Economic Zones made the distant waters inaccessible to English fleets at a time when England's fisheries were highly dependent on them. Secondly, the relatively minor activity in the North Sea by the English compared to the Scottish fleets coincided with the establishment of the Common Fisheries Policy. This had implications when total allowable catches were first implemented because quota allocations to countries were based on their recent catches from the North Sea. Thus, after the loss of fishing opportunities in distant waters, the North Sea once more became an important fishing ground for Britain, just as in the early twentieth century, however, the emphasis of fisheries had shifted from England to Scotland. © 2012 Her Majesty the Queen in Rights of the United Kingdom.
Ban N.C.,Fisheries Center |
Ban N.C.,James Cook University |
Alidina H.M.,WWF Canada |
Ardron J.A.,Pacific Marine Analysis and Research Association
Marine Policy | Year: 2010
Analysis of cumulative human impacts in the marine environment is still in its infancy but developing rapidly. In this study, existing approaches were expanded upon, aiming for a realistic consideration of cumulative impacts at a regional scale. Thirty-eight human activities were considered, with each broken down according to stressor types and a range of spatial influences. To add to the policy relevance, existing stressors within and outside of conservation areas were compared. Results indicate the entire continental shelf of Canada's Pacific marine waters is affected by multiple human activities at some level. Commercial fishing, land-based activities and marine transportation accounted for 57.0%, 19.1%, and 17.7% of total cumulative impacts, respectively. Surprisingly, most areas with conservation designations contained higher impact scores than the mean values of their corresponding ecoregions. Despite recent advances in mapping cumulative impacts, many limitations remain. Nonetheless, preliminary analyses such as these can provide information relevant to precautionary management and conservation efforts. © 2010 Elsevier Ltd.
Zang A.R.,VISGRAF Laboratory |
Felinto D.,Fisheries Center |
Velho L.,VISGRAF Laboratory
SIGGRAPH Asia 2012 Posters, SA 2012 | Year: 2012
Ask for a programmer and an artist what is the Holy Grail of computer graphics and you may hear completely different answers. It is part of the competence of computers to strive for reproducing reality, to mimic it bit by bit, photon by photon. It is in the core of graphics to go beyond and expand our experience of the reality with the creative input of the artist. In this project we are trying to combine both views of the field of computer graphics expanding the possibilities of photo-realistic rendering of synthetic elements combined with a captured environment. Our work is focused on (but not exclusive to) full panorama renders. The novelty of our method is the use of light-depth maps to increase the accuracy in the rendering process, as presented in our previous work [Felinto et al. 2012]. Panorama images have been extensively used in the past. As a final representation of a set, a background plate, as reflection maps, as environment light maps or even to support the modeling of the environment geometry. However, panoramas with the light field representation when combined with the scene geometry can achieve rendering calculations not yet explored. Those particular sets of panoramas are here called light-depth maps. The intent of this project is to show how they can produce more accurate photorealistic rendering of shadows, light and reflections for synthetic elements inserted in a captured scene than its current alternatives. The relevance of this project is reinforced by the growing demand for panorama content production. This is in part due to the modernization of old planetariums into digital fulldome projection systems, the existence of panorama capturing devices such as Gigapan and LadyBug and new gyroscope friendly consumer devices and applications such as Google Street View, and the soon to be released Nintendo Wii U Panorama View. Additionally, panoramas can be used for traditional film-making aimed at conventional displays. light-depth maps can be built in affordable ways and increase the quality of the augmented reality rendering productions. Copyright is held by the author / owner(s).
Haggarty D.R.,University of British Columbia |
Martell S.J.D.,Fisheries Center |
Martell S.J.D.,International Pacific Halibut Commission |
Shurin J.B.,University of California at San Diego
Canadian Journal of Fisheries and Aquatic Sciences | Year: 2016
Compliance with spatial fishing regulations (e.g., marine protected areas, fishing closures) is one of the most important, yet rarely measured, determinants of ecological recovery. We used aerial observations of recreational fishing events from creel surveys before, during, and after 77 Rockfish Conservation Areas (RCAs) were established in British Columbia, Canada. There was no evidence of a change in fishing effort in 83% of the RCAs, and effort in five RCAs increased after establishment. Fishing effort in open areas adjacent to the RCAs declined with time and was higher than effort in the RCAs in all 3 years. Next, we used compliance data for 105 RCAs around Vancouver Island to model the drivers of compliance. Compliance was related to the level of fishing effort around the RCA, the size and perimeter-to-area ratio of RCAs, proximity to fishing lodges, and the level of enforcement. Noncompliance in RCAs may be hampering their effectiveness and impeding rockfish recovery. Education and enforcement efforts to reduce fishing effort inside protected areas are critical to the recovery of depleted fish stocks. © 2016, Canadian Science Publishing. All rights reserved.
Gurney L.J.,Ocean and Atmospheric science |
Pakhomov E.A.,Ocean and Atmospheric science |
Christensen V.,Fisheries Center
Ecological Modelling | Year: 2014
A model of an ecosystem provides a useful tool for the exploration of management options to achieve desired objectives. With the move to a more holistic approach to marine resource management, ecosystem models and the indicators that can be derived using them, are providing a means to move away from single species management and allow for the ecosystem effects of population dynamics to be explored. This work describes the construction of an ecosystem model of the Prince Edward archipelago. The archipelago consists of two islands, Marion and Prince Edward, which are situated southeast of the southern tip of Africa at 46°46'S, 37°51'E. The islands are host to millions of seabirds and seals that use the islands as a refuge for breeding and moulting. Using the Ecopath software, the ecosystem is described across three separate decades (1960s, 1980s, 2000s). All trophic links are described based on the rich published literature that exists for the islands. Local survey data for population estimates and trophic linkages were sourced for defining and quantifying the food web. The system is summarised into 37 functional groups which include 4 primary producer groups at the lower trophic spectrum, and 14 land based top predator groups (seals and seabirds) representing the majority of the higher trophic levels. Two detrital groups are included. The food web is compared across the three time periods with transfer efficiencies declining for the higher trophic levels through time, suggesting a decline in energetic coupling between groups. Comparison of the PEI ecosystem with eight other modeled sub Antarctic/Antarctic systems showed the ecosystem size (as measured in total biomass throughput per year, year-1) to be lower than all other systems and was found to be most similar to the Kerguelen Islands for the ecological metrics assessed. Future research priorities are highlighted based on an assessment of data availability, data gaps and sensitivity testing. The construction of this model provides a much needed tool for the advancement of management for the archipelago, which have both fisheries and conservation concerns. © 2014 Elsevier B.V.
Hawkshaw R.S.,University of British Columbia |
Hawkshaw S.,Fisheries Center |
Sumaila U.R.,Fisheries Center
Sustainability | Year: 2012
A deep reading of Hardin (1968) reveals that he had a lot more to say about the use and regulation of resources such as fisheries than he is given credit for in the literature. It appears that he is typically cited just so that authors can use the phrase "tragedy of the commons" to invoke the specter of looming catastrophe and then tie that to whatever solution they have proposed. We argue in this contribution that there is a lot more in Hardin's essay that either contradicts or greatly complicates the arguments he is cited as an authority for. © 2012 by the authors.
News Article | February 27, 2017
CORVALLIS, Ore. - Reducing human pressure on exploited predators and prey at the same time is the best way to help their populations recover, a new study indicates. The findings about synchronous recovery are important because historically about half the attempts at species restoration have amounted to a sequential, one-species-at-a-time tactic - usually the prey species first, then the predator. This study suggests that a synchronous approach almost always produces a recovery that is more rapid and more direct - faster than predator-first recovery and less prone to volatile population fluctuations than prey-first recovery. Just as crucial, synchronous is also better for the humans who earn a living harvesting the two species. Findings of the research were published today in Nature Ecology and Evolution. "You might think the loss of income associated with reducing harvest on both species at the same time would be greater than reducing harvest on one species after another, but our work suggests that synchronous recovery is ultimately better for recovering the ecosystem, and better from an economic perspective as well," said Mark Novak of the Oregon State University College of Science. Because of overharvest, declines of multiple animal populations - including at least one species that consumes other harvested species - characterize many ecosystems, Novak notes. Examples of paired population collapses wholly or partially attributable to trophy hunting, industrial fisheries or the fur trade are lions and wildebeest; Steller sea lions and Pacific herring; and mink and muskrat. Novak, assistant professor of integrative biology, notes that in both terrestrial and marine resources management, population restoration and the setting of harvest quotas has long been a single-species endeavor. Even in the more holistic ecosystem-based rebuilding of food webs - the interconnected chains of who eats whom - the dominant strategy has been to release pressure at the bottom, letting prey populations return to the point where they ought to sustain the top predators more readily, Novak said. Collaborators at the National Marine Fisheries Center, including Shannon Hennessey, now a graduate student at OSU, led the study, which points out the limitations of both of these philosophies. It also highlights the room for improvement in policy tools that synchronous recovery management could fill.