Search

Krill (Euphausia superba), a small pelagic crustacean. is the largest food resource serving many predators in the Antarctic ecosystem. Given the recent slow expansion of the krill fishery, interest is increasing on how best to harvest krill without unduly impacting its natural predators. The Mori–Butterworth Antarctic ecosystem model attempted to explain the dynamics of the "major" predators through predator–prey interactions alone. That model considered blue, fin, humpback, and minke whales, and crabeater and Antarctic fur seals. Here, this model is expanded to include "minor" krill-predators, such as mackerel icefish. It focuses on a smaller scale, roughly corresponding to International Whaling Commission Management Area II. Results suggest a meaningful difference (historical abundance trajectories differing by more than 5% on average over time) when including "minor" predators. Hence, at an area-specific level, "minor" predators should be considered for further models of at least certain sectors of the Antarctic, as they may meaningfully influence the dynamics of krill and its "major" predators. This in turn could impact management decisions for the krill fishery, as regards optimal krill harvesting. [ABSTRACT FROM AUTHOR]

John attended his first meeting of the International Whaling Commission's Scientific Committee (SC) meeting in July 1963 in London, where he served as a member of the UK delegation (Best & Bannister, 1963; Bannister & Gambell, 1965). In April 1964, John took on the responsibility for this project and other whale studies, replacing Graham Chittleborough, who left whale research to start work on rock lobsters (Bannister 1964, 1974). While working for the CSIRO, John also focused on advancing sperm whale biology, based on the whales landed at the last Australian land station in Albany, which operated until 1978 (Bannister, 1969). John went on to study live whales, mainly southern right whales, humpbacks and, more recently, blue whales (Bannister 1968, 1985, 1986, 1990, 2001). [Extracted from the article]

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Management strategy evaluation ( MSE) involves using simulation to compare the relative effectiveness for achieving management objectives of different combinations of data collection schemes, methods of analysis and subsequent processes leading to management actions. MSE can be used to identify a 'best' management strategy among a set of candidate strategies, or to determine how well an existing strategy performs. The ability of MSE to facilitate fisheries management achieving its aims depends on how well uncertainty is represented, and how effectively the results of simulations are summarized and presented to the decision-makers. Key challenges for effective use of MSE therefore include characterizing objectives and uncertainty, assigning plausibility ranks to the trials considered, and working with decision-makers to interpret and implement the results of the MSE. This paper explores how MSEs are conducted and characterizes current 'best practice' guidelines, while also indicating whether and how these best practices were applied to two case-studies: the Bering- Chukchi- Beaufort Seas bowhead whales ( Balaena mysticetus; Balaenidae) and the northern subpopulation of Pacific sardine ( Sardinops sagax caerulea; Clupeidae). [ABSTRACT FROM AUTHOR]

There is considerable international concern and scientific debate about the current state and future of tuna stocks worldwide and the capacity of Regional Fisheries Management Organisations to manage the associated fisheries effectively. In some cases, this concern has extended to predictions of imminent collapse with minimal chances of recovery, even under a commercial catch moratorium. As a viable alternative to a full fishery closure, the Commission for the Conservation of Southern Bluefin Tuna ( CCSBT) has adopted a scientifically tested, adaptive rebuilding strategy for the depleted southern bluefin tuna ( Thunnus maccoyii) stock. The management procedure ( MP) adopted involves a harvest control rule that fully specifies the total allowable catch as a function of key indicators of stock status, adjusting future harvest levels every three years so as to meet the rebuilding targets agreed by CCSBT. It was chosen from a subset of candidate MPs selected following extensive simulation testing. This involved first selecting a wide range of plausible scenarios for stock status and input data, ranging from pessimistic to optimistic, against which the alternative candidate MPs were tested to ensure that they were robust to important uncertainties. This is the first time that a comprehensively evaluated MP has been adopted for an internationally managed tuna stock. Both the process and the outcomes have broad applicability to other internationally managed stocks. [ABSTRACT FROM AUTHOR]

The article offers information on impact of fishing on predators and spatial multispecies operating model of krill-predator fishery dynamics in Scotia Sea. It states that Krill (Euphausia superba) is a species in the Antarctic, serving as a forge source for predators and subject to fishing. It mentions that it is possible to discriminate the ecosystem impacts if different spatial fishing allocations.At moderate harvesting rates, results indicated the possibility of high relative impacts on fish.

Edwards, C. T. T., Rademeyer, R. A., Butterworth, D. S., and Plagányi, É. E. 2009. Investigating the consequences of Marine Protected Areas for the South African deep-water hake (Merluccius paradoxus) resource. – ICES Journal of Marine Science, 66: 72–81. Protected areas are often touted as important management tools to mitigate the uncertainty inherent in marine ecosystems, and thereby improve the long-term prospects for sustainable resource use. However, although they certainly play an important role in conservation, their usefulness in improving fishery yields is contentious. We present a simulation model that explores spatial closure options, and apply it to the demersal hake trawl fishery off South Africa. The model is based on the age-structured approach used for current assessments, representing the dynamics of the deep-water hake Merluccius paradoxus within a zonally disaggregated spatial system. Fitting the model to two zones, which demarcate a potential closed area from the remaining fished area, we investigate the consequences that such a protected area could have for the fishery. Our model suggests that area closures would have a negligible benefit for the fishery, regardless of the level of hake movement between areas. This is likely the result of the model's simplicity, and we suggest additional factors that should be considered to quantify the impact of Marine Protected Areas on the fishery more reliably. [ABSTRACT FROM PUBLISHER]

Butterworth, D. S., and Rademeyer, R. A. 2008. Statistical catch-at-age analysis vs. ADAPT-VPA: the case of Gulf of Maine cod. – ICES Journal of Marine Science, 65: 1717–1732.In 2003, given an estimate of a spawning-stock biomass (Bsp) of 27% of the maximum sustainable yield (MSY) level based on an adaptive framework-virtual population analysis (ADAPT-VPA) assessment using data only after 1981, the Gulf of Maine cod (Gadus morhua) stock was deemed “overfished” under the US Magnuson–Stevens Act. However, an alternative statistical catch-at-age assessment (SCAA) at the time, using survey data from 1964, indicated Bsp above . This is investigated, together with other (sometimes conflicting) suggestions made during a number of recent assessment reviews of this stock. The primary reason for the different result is that the ADAPT-VPA assessment imposed asymptotically flat selectivity-at-age when there was strong statistical evidence for dome-shaped selectivity. Once adjusted for this, either assessment method robustly estimates Bsp relatively close to rather than below the “overfished” threshold of 0.5 . SCAA allows the longer series of survey data available to be incorporated, providing a better basis to estimate MSY-related targets and doubling the related precision in some cases. As such targets are important when implementing the Magnuson–Stevens Act, SCAA seems preferable to ADAPT-VPA for assessing this stock. Some broader inferences to be drawn from this comparative process include the need for: (i) careful treatment of the plus-group, especially if selectivity may be dome-shaped; (ii) flexible parameterizations of selectivity-at-age in SCAA to avoid false perceptions of the precision of results; and (iii) care in the use of the Beverton–Holt stock–recruitment function, as it gives inappropriately low estimates of if there is an overall negative trend in the estimates of recruitment plotted against Bsp. [ABSTRACT FROM PUBLISHER]

Plagányi, É. E., Rademeyer, R. A., Butterworth, D. S., Cunningham, C. L., and Johnston, S. J. 2007. Making management procedures operational — innovations implemented in South Africa. – ICES Journal of Marine Science, 64: 626–632.Operational management procedures (OMPs) have become an indispensable fisheries management tool in South Africa in light of their ability to consider the consequences of the main sources of assessment uncertainty. An overview is provided of the MP approaches applied to the major South African fisheries for hake, sardine and anchovy, and west coast rock lobster. As these are among the first OMPs to be implemented worldwide, some for periods longer than 10 y, they provide useful examples of some of the successes and problems encountered with the approach. Particular emphasis is given to some recent innovations and adaptations. These include moves to (i) joint two-species OMPs for the hake and sardine/anchovy resources; (ii) a reference set of weighted operating models for primary testing and tuning in preference to a single model; (iii) consideration of a “research-conditional” approach for hake to allow greater catches in the short term, conditional on research being implemented to resolve a key uncertainty; and (iv) incorporation of some ecosystem considerations by developing appropriate robustness tests (which link with moves towards an ecosystem approach to fisheries). Key lessons gained from experience over the past decade of OMP implementation in South Africa are summarized. [ABSTRACT FROM PUBLISHER]

Rademeyer, R. A., Plagányi, É. E., and Butterworth, D. S. 2007. Tips and tricks in designing management procedures. – ICES Journal of Marine Science, 64: 618–625. Management procedures (MPs) are becoming widely used in fisheries management, but guidelines to assist in their construction, evaluation, and implementation are few. We provide simple guidelines by drawing on experience from developing and applying MPs in southern Africa and internationally. Suggestions are provided on how to choose between candidate MPs and on key trade-offs in selecting between data-based (empirical) and model-based formulations. Assistance is also provided in dealing with different sources of uncertainty, such as deciding which operating models should be included in a reference set used for primary simulation testing and tuning (in contrast to robustness or sensitivity tests), and on how weights for the associated alternative hypotheses are most practically assigned. Finally, some guidelines are given for presenting the results effectively, which is one of the key challenges of a successful implementation process. [ABSTRACT FROM PUBLISHER]

Butterworth, D. S. 2007. Why a management procedure approach? Some positives and negatives. – ICES Journal of Marine Science, 64: 613–617. The origin of the management procedure (MP) approach (sometimes termed management strategy evaluation), with its simulation testing of feedback-control algorithms as a necessary and structured basis for dealing with the inevitable uncertainties associated with fisheries assessments, is briefly reviewed. Also discussed are the advantages that overcome some of the difficulties of the “traditional” approach of coupling an annual “best” assessment to some harvest control rule, such as a failure to consider longer-term trade-offs properly. The MP approach does, however, also have disadvantages, such as the length of time typically required for its development and an argued inflexibility after implementation. Solutions that have been developed to overcome some of these difficulties are discussed. [ABSTRACT FROM PUBLISHER]