CCAMLR Science, Volume 22 (2015)
The three papers in this volume of CCAMLR Science reflect three very different and important elements of the focus of CCAMLR on what are referred to in the Convention as dependent and related populations. Dependant species are those that have a food-web linkage with a target species, so understanding the diet and trophic ecology of species like Antarctic toothfish is fundamental to identifying those linkages. Other than the fishery, there is a virtual absence of other sampling approaches to collecting diet data from Antarctic toothfish, so the marriage of science and fishing is essential to achieving CCAMLR’s objectives.
Related species are those species that are potentially impacted by the action of a fishery, but may not be linked to the target species in a food-web. As knowledge of Antarctic fish taxonomy increases, including the ability to identify novel species such as Macrourus caml, it is important that CCAMLR can respond to these situations in order to contribute to the understanding of the potential impact of fisheries on those species as well as ensuring that the data collected from the fishery contributes to the developing knowledge base around those species.
In the case of killer whales interacting with longline fisheries, this might be viewed as having a food-web linkage, because the killer whales eat the fish as they come up on the line, although they might not be viewed as ‘dependent species’. However, these killer whales might also be described as a related species because those toothfish might only be (or at least are much more easily) available to them because of the actions of the fishery. The really interesting element of the paper by Gasco et al. is that the killer whales are able to preferentially select toothfish from the line, rejecting by-catch species such as macrourids.
It would be hard to write this Editorial without commenting on the fact that there are only three papers in this, the 22nd, volume of the journal. In those 22 years, CCAMLR Science has published 239 papers covering a huge range of issues that have influenced the way that CCAMLR seeks to manage fisheries and the impact of those fisheries on dependent and related species. The recent reduction in the number of papers published in the journal does not reflect a diminution of the scale, scope or importance of the delivery of that science into CCAMLR. Indeed the number of papers submitted to working groups increased year on year. However, it is clear that the overall ‘publishing landscape’ has changed markedly since 1994 when the first volume of CCAMLR Science was published and this has led CCAMLR to initiate a review of the future role and format of CCAMLR Science to ensure that it can remain a suitable vehicle to promote the science that underpins the work of CCAMLR.
Depredation is a human–wildlife interaction over access to resources, which often includes a combination of socio-economic, ecological and conservation issues. However, estimating the amount of resource depredated can be especially challenging when depredation occurs on fish in the marine environment. This is the case for killer whales (Orcinus orca) and sperm whales (Physeter macrocephalus) depredation on the demersal Patagonian toothfish (Dissostichus eleginoides) longline fishery operating within the Crozet Islands EEZ (southern Indian Ocean). This study aimed at providing two indirect methods of assessment of depredated biomass over an 11-year period (2003 to 2013), accounting for spatial variations of depredation levels. In the first method, fishing data from 6 525 longline sets were used to calculate the difference between catch-per-unit-effort (CPUE) of non-depredated and depredated lines. When killer whales and sperm whales occurred separately, 575 ± 35 tonnes and 739 ± 87 tonnes of Patagonian toothfish respectively were estimated to be depredated by the two species. When the two species co-occurred around vessels, 1 679 ± 74 tonnes were depredated. The second method used the differences in the proportion of grenadiers (Macrourus spp.) between non-depredated and depredated longline sets to estimate the number of depredated Patagonian toothfish. This approach, which can only be implemented when a sufficient level of by-catch species occurs, provides comparable results and thus strong support for the CPUE method. From these two methods, depredation rates were estimated to range from 27.3% to 29.1% of the total catch (landed and depredated), which is one of the highest among all similar situations where depredation is reported elsewhere in the world. In addition to providing a methodology that could be used in other areas with depredation issues, these findings emphasise the critical importance for fishery managers and researchers to account for depredation when assessing fish stocks, fishery economics and/or conservation of odontocetes. |
That the predominant by-catch of grenadier by the toothfish fishery in the Ross Sea region is comprised of two species, rather than being solely Macrourus whitsoni, was recognised in 2010 with the identification of a new species, M. caml. Grenadier are the main by-catch in the toothfish fishery and modelling suggests that they may be subject to predation release as the abundance of toothfish reduces. In order to improve information on the spatial distribution, age-frequency and relative importance of grenadiers as prey to toothfish, a method of distinguishing between otoliths of the two species was sought. Based on 220 M. whitsoni and 307 M. caml otoliths, a linear function of fish total length, the depth of the otolith and the otolith vertically projected area gave excellent discrimination between the two species (92% success). A method was also developed to discriminate between otoliths of M. whitsoni and M. caml using otolith parameters alone. This method correctly identified 90% of otoliths to species and could be applied to otoliths removed from toothfish stomachs to estimate the relative consumption of the two species of grenadier. Models to estimate fish length, weight and age from otolith parameters are also presented. |
To identify the major prey items for Antarctic toothfish (Dissostichus mawsoni) in the small-scale research unit (SSRU) 5841C in the east Antarctic, their stomach contents, fatty acid (FA) compositions and stable carbon and nitrogen isotope ratios were determined and compared with those of species caught as by-catch and collected from toothfish stomachs. Stomach content analyses showed that Antarctic toothfish fed primarily on fish and to a lesser extent squid. FA profiles in muscle tissues of Antarctic toothfish were very similar to those of Channichthyidae caught as by-catch and several species collected from toothfish stomachs, including unidentified icefish, Arctozenus risso, Macrourus spp., and Gymnodraco acuticeps, indicating a trophic connection between them. δ15N values of Antarctic toothfish were higher than for the other species collected, indicating a higher trophic position. This is the first study to provide information on the diet of Antarctic toothfish and the trophic relationship between the toothfish and other species in the east Antarctic using these methods. Further studies on the trophic relationship between Antarctic toothfish and other species and a regional comparison of their dietary composition by the collection and subsequent biomarker analyses of more species is needed to understand better the carbon flow through Antarctic ecosystems. |
Reid, K. (2015), Book review – Biogeographic Atlas of the Southern Ocean This is a review of De Broyer, C., P. Koubbi, H.J. Griffiths, B. Raymond, C. Udekem d’Acoz, A.P. Van de Putte, B. Danis, B. David, S. Grant, J. Gutt, C. Held, G. Hosie, F. Huettmann, A. Post and Y. Ropert-Coudert (Eds). 2014. Biogeographic Atlas of the Southern Ocean. Scientific Committee on Antarctic Research, Cambridge: XII + 498 pp. |