CCAMLR Science, Volume 20 (2013)
Managing the fishery for Antarctic krill was the driving force behind the establishment of CCAMLR. Changes in the global market for krill and the technology used to catch it have raised the prominence of the krill fishery and, although current catches are small in comparison to the catch limits in place, lessons from fisheries around the world suggest that the response times of management actions means that waiting until problems are detected sets a course for failure. The precautionary approach to managing fisheries that is embodied by CCAMLR can be likened to progressing forward at a pace that is dictated by our understanding of the effects of the fishery, rather than charging towards a cliff and hoping you will be able to stop right at the edge! At the core of the range of measures used to manage this fishery is the Krill Yield Model that was developed in the 1990s. As the paper by Kinzey et al. shows, this model is not broken, but it may be put under strain in the future, and there is a need for management models that can use a wider range of ecosystem-based inputs in determining catch limits in the krill fishery. Using ecosystem indicators to manage the krill fishery is central to CCAMLR and, while the journey from the theoretical to the operational is likely to be challenging, the two Hill papers (Hill and Cannon; Hill and Matthews) provide plenty of food for thought and some tangible pathways to take this subject forward.
Doing research in the Antarctic is always exciting, often exhilarating, sometimes a little dangerous, but always expensive. The cost of doing research means that CCAMLR relies heavily on data from fisheries as inputs into its decision-making processes. The CCAMLR tagging program, that provides tag and recapture data on both Patagonian and Antarctic toothfish, is a central component of stock assessments, including for the Ross Sea toothfish fishery. As with any scientific results, there are a range of assumptions underlying their interpretation and the importance of the tagging data to CCAMLR means that it is regularly scrutinised, as in the papers by Welsford and Ziegler and by Mormede and Dunn. This process of review is critical to ensuring management approaches are ‘robust to our uncertainties’ which basically means even if our assumptions are wrong, the management decisions that are taken will still achieve the required results.
As well as the details of managing individual fisheries, the issue of large-scale spatial conservation has been high on CCAMLR’s agenda for the last few years and the papers by Grant et al. and Trathan et al. both examine issues of conservation planning and, in particular, how taking a proactive approach to spatial conservation is preferable to waiting until a problem arises. We know the Antarctic ‘landscape’ is changing and can make predictions about the future, but there are large uncertainties. Taking a proactive approach means we need to put safety nets in place now in order to ensure the long-term sustainability of an ecosystem in which fisheries are both a provider and user of the best available scientific data.
Keith Reid
Editor
Systematic conservation planning for developing marine spatial protection includes analysis of the spatial distribution of fishing activities, existing management and ecological characteristics. This paper assesses the overlap between habitat (bioregion), existing spatial management and Antarctic krill catch in the Southern Ocean. The analysis required standardised information on the location and extent of spatial fisheries management measures, which was delivered through a Geographic Information System (GIS). During the 2010/11 season, 64% of the CAMLR Convention Area was open to fishing for at least one species. There were important differences between pelagic bioregions in terms of the fraction that was open to fishing, and the distribution of catch within the open fraction. For example, only 26% of the total area open to krill fishing has ever been fished, and this fishing is concentrated in three of the seven bioregions found in the open area. Information on the distribution of catches and catch limits among different bioregions could be used to prioritise protection for bioregions that are currently under-represented in marine protected areas (MPAs). However, conservation planning should take account of uncertainties that result from the different spatial resolution of datasets and the use of long-term averages to identify spatial boundaries. |
To infer important prey resources for Antarctic toothfish (Dissostichus mawsoni) in the southern Ross Sea, their lipid composition was determined and compared to lipid profiles of fish and invertebrate species taken as by-catch in the fishery or collected from the stomachs of toothfish. Stable carbon and nitrogen isotope ratios were also determined to further identify feeding relationships between these species. The aim of this study was to establish the feasibility of tracking the main dietary items of Antarctic toothfish by comparing results of biomarker analysis and conventional diet analysis. Samples were collected during a longline survey of pre-recruit toothfish in February 2012. Results of fatty acid (FA) and stable isotope analyses from this study provide evidence that a combination of these two techniques can delineate the main prey items of Antarctic toothfish and trophic structure of the toothfish-related fish food web in the southern Ross Sea ecosystem. Similarities in total FA compositions and the FA profiles in muscle tissue of Antarctic toothfish, and Pleuragramma antarcticum, Pogonophryne barsukovi, Dacodraco hunteri and Trematomus loennbergii indicated a trophic connection between toothfish and these fish species. Mean δ15N values of Antarctic toothfish were higher than those of P. antarcticum, P. barsukovi and T. loennbergii, indicating a higher trophic position of the toothfish. In contrast, similar δ15N values between Antarctic toothfish and icefish (D. hunteri) suggested that they occupy the same trophic position. Overall results of this survey are consistent with the frequency and percentage occurrence of prey in Antarctic toothfish stomachs. Further sample collection and biomarker analyses for more pelagic and benthic biota are needed to better understand the entire food-web structure in the southern Ross Sea. |
Samples collected in 2008 led to the identification of a new species of Southern Ocean grenadier, Macrourus caml, which had hitherto been identified as M. whitsoni. The first comparison of the distribution and ecology of the two species of Macrourus in the Ross Sea region is presented. The number of rays in the left pelvic fin and number of rows of teeth in the lower jaw allowed the two species to be distinguished both in the laboratory and by scientific observers at sea. The species were sympatric by depth (900–1 900 m) and by spatial area within CCAMLR Subareas 88.1 and 88.2. There was a small but significant increase in the proportion of M. whitsoni caught with depth. Catches of females of both species exceeded that of males (especially for M. caml). Macrourus caml grows slower, reaches a larger size, lives longer and is heavier for a given length than M. whitsoni. Female sexual maturity is reached at shorter length in M. caml than M. whitsoni but at a similar age (50% sexual maturity at 16 y). Gonad staging suggests extended spawning periods, beginning before December and continuing after February. Stomach and intestine contents data show both species are euryphagous predators and scavengers, with evidence of piscivory and both benthic and pelagic feeding. Amphipods were one of the main crustaceans consumed. Data tentatively suggest that M. caml may feed more benthically than M. whitsoni, but the sample size was very small. Using stable isotope analysis, trophic level was estimated at 4.4–4.5 (M. caml) and 4.1–4.3 (M. whitsoni), consistent with one or both of these species being a main prey of Antarctic toothfish. |
The Lincoln-Petersen equation, the simplest form of an abundance estimator using tag-recapture data, was used to identify processes that may introduce bias into abundance estimates derived from tag-recapture programs. The methods that have been used in CCAMLR tag-recapture programs to mitigate such biases, or to account for their effects in stock assessments for Dissostichus spp. are also summarised. In nearly all cases, examples of at-sea or model-based approaches are available from established Dissostichus spp. tag-recapture programs to reduce these biases. Estimates of post-capture mortality, tag-detection rates and, where it occurs, post-release depredation rates are a priority for new assessments that use tag-recapture data. Due to the complexity of toothfish movements throughout their life cycle, as well as the spatial structure of release and recapture efforts by fishing and research vessels, development of spatially explicit modelling approaches is also an important next step for Dissostichus spp. assessments that use tag-recapture data. |
A reliable commercial fish tagging program is critical to the successful management of a number of toothfish fisheries in Antarctica. In particular, tag-detection rates are directly linked to stock size estimated from the tag data in an integrated stock assessment. Previous attempts to assess the relative reliability of vessels in detecting tagged fish have been inconclusive due to low numbers of recaptures after controlling for spatial and temporal confounding. This paper presents a method that utilised most of the data while also controlling for spatial and temporal variables using a case-control study design, and uses this method to develop relative indices for detection rate performance for vessels involved in the Antarctic toothfish tagging in CCAMLR Subareas 88.1 and 88.2. The index derived provides evidence of significant differences in the relative performance of vessels in the Antarctic toothfish fishery in CCAMLR Subareas 88.1 and 88.2, as well as changes in the performance of some vessels over time. Further investigations show that these indices appear robust to the assumptions made, in particular the choice of the control group and the maximum distance between fishing events compared. The results suggest that the method can be useful for assessing the relative vessel tagging performance across all CCAMLR fisheries, and may potentially be developed as a more general method for comparing relative performance of spatially and temporally heterogeneous datasets. |
The generalised yield model (GYM) was used by CCAMLR to establish the precautionary catch limit for the Antarctic krill (Euphausia superba) fishery. The current precautionary catch limit was based on supplying the GYM with a natural mortality rate of 0.8 and recruitment variability generated using a Beta distribution for proportional recruitment of krill. In this study, krill sampling data for empirical size frequencies were supplied to the GYM as the ‘vector of recruitments’ input option to simulate the population dynamics of krill around the Antarctic Peninsula (Subarea 48.1) along with increasing rates of natural mortality. The annual proportions of krill less than 36 mm in length to the total captured in net samples in four sampling areas of the Peninsula were used as proxies for recruitment variability. The variability of proportional recruitment in the CCAMLR study areas was similar to the variability in other krill studies and in the annual size distributions of krill in penguin diets. Simulations with either no fishing, or with fishing at the trigger level (lowest catches), at approximately half the precautionary catch limit (intermediate), or at the precautionary catch limit (highest) were conducted. As the values for natural mortality, recruitment variability and catch were increased, fewer of the scenarios were able to meet the CCAMLR decision rules. The higher precautionary level of catch was not obtainable while meeting CCAMLR decision criteria for at least two of the four recruitment vectors based on net sampling, regardless of how the specified parameters for recruitment and mortality were combined. Any substantial future increases in krill harvests in Area 48 beyond the trigger level require verification that the krill recruitment variability, natural mortality, and other parameters specified in the scenarios used to test management criteria, adequately represent the range of plausible values encompassing krill population biology. |
There is a global need to develop strategic frameworks for assessing uncertainty in ecosystem dynamics models. Such models have been used within CCAMLR to evaluate options for managing the Antarctic krill fishery in the Scotia Sea and southern Drake Passage. The model analysed here required 2 311 input values for each of four scenarios and produced 68 output statistics. Small perturbations to input values affected output statistics indicating the status of predator groups more than they affected statistics indicating the status of the target stock or the fishery. Output statistics were most sensitive to a parameter controlling predator recruitment through pre-recruit mortality. A parameter mediating the effect of a forcing function on krill recruitment, which was used to condition the model on past dynamics, was also important, and some of the parameter estimates resulting from conditioning were unstable. This highlights the tension between the parameter stability benefits of well-constrained models and the use of model conditioning to identify plausible alternative hypotheses in data-poor situations. Apparent sensitivity is a function of both input values and output statistics. Clearer specification of ecosystem-based management objectives would help to identify the important statistics for consideration when assessing uncertainty in ecosystem dynamics models. |
CCAMLR aims to develop a feedback approach to aid ecosystem-based management (EBM) of Antarctic krill fisheries. It is important to assess whether a feedback approach is likely to achieve the multiple objectives that EBM implies in the complex and uncertain conditions typical of Antarctic marine ecosystems. This study used Model Predictive Control (MPC) to achieve objectives for a harvested species, its predators and the fishery, in a simulation model that incorporates uncertainty and spatial and trophic complexity. The approach adjusted spatially resolved annual catch limits in response to estimates of the state of the system. It suggests that feedback management is both feasible and a more effective way to achieve multiple objectives than fixed catch limits, which are currently used to manage Antarctic krill fisheries. The study demonstrates that optimisation based approaches such as MPC are computationally capable of dealing with EBM-type problems. They are also useful for assessing the feasibility of candidate management policies or objectives, and characterising the trade-offs that they imply. This study characterises the trade-off between catch levels and the risk of harvested species biomass falling to unacceptable levels. |
Recent rapid climate change is now well documented in the Antarctic, particularly in the Antarctic Peninsula region. One of the most evident signs of climate change has been ice-shelf collapse; overall, 87% of the Peninsula’s glaciers have retreated in recent decades. Further ice-shelf collapse will lead to the loss of existing marine habitats and to the creation of new habitats, with consequent changes in both ecological processes and in community structure. Habitats revealed by collapsed ice shelves therefore offer unique scientific opportunities. Given the complexity of the possible interactions, and the need to study these in the absence of any other human-induced perturbation, this paper highlights why commercial fishing activities should not be permitted in these habitats, and suggests that areas under existing ice shelves in Subareas 88.3, 48.1 and 48.5 should be preserved and protected for scientific study. The boundaries of these areas should henceforth remain fixed, even if the ice shelves recede or collapse in the future. Designation of areas under ice shelves as areas for scientific study would fulfil one of the recommendations made by the Antarctic Treaty Meeting of Experts in 2010. |