CCAMLR

Pronounced environmental trends across fronts suggest that the otolith chemistry of oceanic fish can resolve zones on either side, promoting application to population questions at similar spatial scales. Trace and minor elements laid down immediately prior to capture – along the edges of otoliths from Patagonian toothfish Dissostichus eleginoides – discriminated frontal zones in the Antarctic Circumpolar Current in the Southwestern Atlantic Ocean. Mean values differentiated sampling areas by up to 2.6 standard deviations, suggesting: 1) otolith Mg/Ca enrichment related to fish activity around the Burdwood Bank; 2) Mn/Ca enrichment associated with South America; 3) Sr/Ca linked to the presence of Circumpolar Deep Water; and 4) Ba/Ca to nutrient production and mixing. In the Polar Frontal Zone, meanders or eddies may account for affinities with neighbouring sampling areas, bringing water from the Subantarctic and Antarctic Zones onto the North Scotia Ridge. Moreover, fish age showed a significant relationship with depth and improved cross-validation by 14%, giving 85% classification rates to South American and Antarctic regions, and 57 to 83% to areas along the Patagonian Shelf. These results indicate that otolith chemistry reflects hydrography, detecting oceanic gradients across the slope of continental shelves and between zones separated by strong trends like fronts.

Strong contrasts in ambient isotope ratios and in diet suggest stable isotopes in the otoliths of oceanic fish can resolve water masses and geographic areas, promising a powerful multivariate approach for examining population structure and provenance. To test this, whole otoliths were taken from Patagonian toothfish (Dissostichus eleginoides) sampled off the Patagonian Shelf and South Georgia, on either side of a population boundary, and otolith δ18O and δ13C values were measured to see if they could distinguish South American-caught fish from those taken in the Antarctic. Values of δ18O and δ13C predicted capture area with 100% success, validating their use for distinguishing provenance and corroborating the prior evidence of population isolation. Values of δ18O in the otoliths reflected ambient values as well as seawater temperature: low values in Patagonian Shelf fish were consistent with exposure to Antarctic Intermediate Water (AAIW), and high values in South Georgia fish were consistent with exposure to Circumpolar Deep Water (CDW). In contrast, differences in otolith δ13C appeared to reflect diet: relative depletion of δ13C at South Georgia compared to the Patagonian Shelf were most likely linked to differences in sources of metabolic carbon, as well as δ13C in dissolved inorganic carbon (DIC) of seawater. These contrasting properties strongly suggest that stable isotopes can resolve the provenance of toothfish from Antarctic sampling areas that hitherto have been difficult to separate. These results show that, by using the chemistry recorded in otoliths, researchers can exploit biogeochemical variation in fully marine environments to examine the spatial ecology of oceanic fish.

Recruitment variability in juvenile Patagonian toothfish (Dissostichus eleginoides), a commercially important, deepwater nototheniid fish, was examined at the sub-Antarctic island of South Georgia, South Atlantic. Data from 13 demersal trawl surveys conducted over a 20-year period were analysed. Abundance of the 1+ juvenile fish cohort (13 to 15 month old dependent on survey date) was found to vary inter-annually and was found to be inversely correlated with the sea surface temperature (SST) conditions experienced by adults prior to spawning. Environmental temperatures experienced by toothfish eggs and larvae were not significantly correlated with juvenile density. The mean length of 1+ fish attained after 13-15 months was higher in years of high juvenile abundance and was significantly inversely correlated with SST in the summer prior to adult spawning. Trends in toothfish recruitment variability mirrored those previously observed in a range of krill-dependent land-based predators at South Georgia for whom non-seasonal, large-scale climatic events such as El Niño Southern Oscillation (ENSO) are considered the most likely underlying drivers of variability in breeding success. The drivers of recruitment variability in toothfish are not fully understood but a range of possible mechanisms are considered. A better understanding of recruitment variability holds great interest for fisheries managers and could be used refine forecasts of years of good or poor recruitment for the toothfish fishery at South Georgia

The Antarctic toothfish (Dissostichus mawsoni) exhibits a circumpolar distribution in coastal waters south of the Antarctic Polar Front. For a preliminary evaluation of global population structure in this species, we examined four mitochondrial regions and 13 nuclear gene fragments in samples from four CCAMLR Subareas in the Southern Ocean (Australian Antarctic Territory (Subarea 58.4.2), Ross Dependency (Subareas 88.1 and 88.2) and the South Shetland Islands (Subarea 48.1). Significant genetic differentiation within and among locations was observed for both mitochondrial and nuclear loci. The single nucleotide polymorphism (SNP) markers developed here will be useful for more extensive analyses of population structure in this species.

This paper reports on the one-day workshop held at the CCAMLR Headquarters, Hobart, Australia on 10th October 2008 to review the future of the ad hoc WG-IMAF. The workshop briefly reviewed the history of ad hoc WG-IMAF and considered the current work programme of CCAMLR with respect to the current and future role of ad hoc WG-IMAF. The workshop briefly considered future scenarios under which it might operate and the implications for its work. The workshop agreed that in future ad hoc WG-IMAF should continue to focus on the direct impacts of fishing and marine debris on seabirds and marine mammals as well as developing, an effective relationship between CCAMLR and ACAP. The workshop noted that this scope was a part of the broader contribution of CCAMLR to the conservation of these taxa. The key recommendations from the workshop to be considered by WG-IMAF are: o revised terms of reference for WG-IMAF to reflect a purpose and revised scope of the group; o in the short-medium term WG-IMAF should place a particular focus on a reduction in incidental mortality of seabirds associated with fishing in those areas of the Convention Area where this still occurs; o that the current timing and duration of meetings are appropriate but should be kept under annual review; and o medium term functions for WG-IMAF to address as possible.

CCAMLR adopted a new conservation measure in 2007 (CM 22-06) to ensure that significant adverse impacts of bottom fishing gear on Vulnerable Marine Ecosystems (VMEs) are avoided. Due to the high levels of uncertainty surrounding both the evidence of VME presence and the consequences of interaction with different types of gear, a risk management framework is proposed, similar to that which has been used successfully by IMAF to minimise the effects of longline fishing mortality on seabirds. The aim of this risk management is to avoid significant adverse impacts on VMEs from bottom fishing activities. The framework consists of four steps: (1). Risk analysis of current and proposed fishing activities; evidence of potential VMEs; scale of interactions between fishing activities and VMEs; impact of interactions on VMEs; and recovery potential of VMEs. (2) Risk evaluation. Combine information on likelihood and consequences of interactions of bottom fishing gear with VMEs and associated uncertainties from risk analysis to produce risk metrics. (3) Risk elimination or mitigation. Unacceptable levels of risk from bottom fishing activities to VMEs must be eliminated or reduced to acceptable levels through the use of management measures including, inter alia, closed areas around identified VMEs, open and closed management areas, bycatch limits for VME-forming organisms, gear modification or spatial distribution of fishing effort. (4). Review. All of the above steps should be reviewed regularly to ensure that all relevant or new information has been included, appropriate scientific research and data collection plans are in plan and that risk mitigation measures are successful in their implementation.

Tag recapture rates in new and exploratory Dissostichus spp. fisheries in the southern Indian Ocean sector of the CCAMLR area are examined. In particular, the potential for tagging programs in new and exploratory fisheries to yield sufficient data to be of use in determining TAC’s in the early stages of fishery development is considered. Scenarios are developed using a range of tag release rates, tag detection rates, natural mortality, fish movement out of the fishery, and IUU removals in order to estimate the expected numbers of tag returns. Even under “worst case” assumptions, tag recaptures are still expected to be considerably higher than currently observed in Divisions 58.4.1 and 58.4.2. If current tag recapture rates continue, tag-based assessments of stock status 58.4.1 and 58.4.2 are likely to remain uncertain in the short to medium term, and fishing should remain focussed in areas where tag releases have been concentrated until these uncertainties can be addressed.

New Zealand proposes to conduct a scientific research survey during the austral winter in CCAMLR SSRUs 88.1B, 88.1C and, ice permitting, 88.1G in 2008/09, as the first in a three year time series. The proposal is for a targeted longline survey designed to cover critical gaps in the knowledge of the life cycle of D. mawsoni in the Ross Sea by collecting biological samples from a broad spread of locations across the northern Ross Sea during the austral winter. The survey is designed to collect information that should assist in the understanding of the early life history and reproduction of Dissostichus mawsoni in the Ross Sea region. In addition, tag data collected will give additional information on the spawning movements of mature D. mawsoni. The results of the research will lead to improved estimates of length/age of maturity, proportion mature that spawn, and contribute to an improved understanding of the Ross Sea D. mawsoni stock structure. Data collected during the survey will provide information that is likely to directly influence future assessments of D. mawsoni. The proposed research is in accordance with Conservation Measures 24-01, 33-03, 41-01 and 41-09.

The Fouth Meeting of the ACAP’s Advisory Committee was held in Cape Town, South Africa from 22 – 25 August 2008. It was preceded by a meeting of the Seabird Bycatch Working Group (SBWG) on 17-18 August 2008. This paper provides a report on the SBWG meeting. The Working Group reviewed methods to reduce seabird bycatch in trawl fisheries, and noted that the body of work investigating and documenting mitigation measures in trawl fisheries is significantly less advanced than for longline fisheries. Consequently, new developments in this field in recent years are few. Seabird interactions with trawl vessels fell into two broad categories: those focused on the trawl warps, and those focused around trawl nets. For reducing seabird strikes on trawl warps, the use of bird-scaring lines has been proven to be the most effective mitigation device in the trawl fisheries in which comparative studies have been undertaken. However, the retention or strategic management of fish waste (offal and discards) was recommended as the most effective primary measure for bycatch reduction, and should be viewed as the best long-term solution to reducing seabird bycatch in trawl fisheries. Coincident with effective fish waste management, operational measures such as cleaning the net prior to shooting and reducing the time the net is on the surface at shooting and hauling should be viewed as best practice measures and incorporated into routine fishing activities. While a number of methods have been trialed to reduce the incidence of warp strikes, there continues to be the need for more work on effective measures for reducing seabird interactions with trawl nets. The SBWG also reviewed demersal longline mitigation methods. Two tables were developed that summarised bycatch mitigation measures for demersal longline fishing, and identified knowledge gaps and research priorities for this gear type. These tables were subsequently endorsed by the ACAP Advisory Committee as representing the current best scientific advice of the SBWG. The SBWG engaged in extensive discussion regarding the Advisory Committee’s collection of seabird bycatch data from the Parties. Dr Keith Reid from CCAMLR described the CCAMLR data submission and management system, and the fine scale analysis at the level of the fishery, by area, gear type and by vessel, that is carried out by CCAMLR on both target and bycatch species. The Working Group noted the comprehensive nature of the data collection and assessment process that has been developed by CCAMLR and agreed that it formed a useful model for ACAP, noting that an observer program with high levels of coverage had been critical to understanding bycatch problems and had been key to CCAMLR’s success in reducing bycatch in its fisheries. The model was entirely relevant to other RFMOs but could also be adopted by ACAP for assessment of summary bycatch information provided by ACAP Parties.