CCAMLR Science, Volume 12 (2005)
Haul-by-haul logbook catch and effort data from the Japanese krill fishery for the 1980/81 to 2003/04 fishing seasons were analysed. For a number of definitions of effort and catch-per-unit-effort (CPUE), variables were modelled using linear mixed models in order to obtain time series of predicted intra- and interannual trends of standardised fishery indices. The results strongly suggest that the krill fishery in the South Georgia area is operating at a critical level of krill availability which is just enough to maintain the best factory performance. In this analysis the status of fishing in Subareas 48.1 and 48.2 was not clear. A linear correlation was observed between ‘catch per searching time’ and ‘catch per day’ within their lower ranges, suggesting these may have some value as abundance indices. Standardised CPUE for the pelagic areas showed significant correlations with previously published interannual series of acoustic density estimates from scientific surveys. To refine these CPUE indices, it will be necessary to collect more detailed information from fishing vessels. It is also important to undertake the same kind of analysis for fleets from other fishing nations. |
Ages of Patagonian toothfish (Dissostichus eleginoides) caught off Kerguelen in 1999 were estimated by reading transverse-sectioned otoliths. Randomly interspersed otoliths from reference collections were used to measure precision; relative bias for the age data was estimated to be –0.6 years and residual variance 2.9. Age distributions of toothfish caught by two vessels showed discrepancies due to gear-specific catchability, or differences in the available population with depth or season. Age–length keys were constructed for use in assessing toothfish catches made by trawlers and longliners at Kerguelen, and longevity was estimated to be 36 years. Total instantaneous mortality Z was estimated to be between 0.09 and 0.12. Significant differences in age-at-length data between sexes were found, estimating von Bertalanffy parameters for males to be L∞ = 95.9, K = 0.12, t0 = –4.6 and for females L∞ = 103.5, K = 0.11, t0 = –4.7. |
Two molecular methods, mitochondrial and intron DNA markers, were used to determine genetic relationships among Antarctic toothfish (Dissostichus mawsoni) samples from three CCAMLR areas: Subareas 48.1 and 88.1 and Division 58.4.2. D. mawsoni appeared to be characterised by low diversity; no genetic variation was detected with restriction enzyme digests of nine sub-regions of the mitochondrial genome. Polymorphisms were found in four of seven introns digested with the restriction enzymes, but there was no population differentiation among the three sea areas. Direct sequencing of cytochrome b (665 bp) and the left domain of the control region (639 bp) showed very little variation and no significant genetic differentiation among sea areas. |
The legal Patagonian toothfish (Dissostichus eleginoides) longline fishery operating in the French Exclusive Economic Zones (EEZs) of Crozet and Kerguelen Islands (Subarea 58.6 and Division 58.5.1 respectively) killed 26 668 seabirds between September 2001 and August 2003. Overall, the white-chinned petrel (Procellaria aequinoctialis) was the most frequently killed species, with males being more frequently caught than females. Grey petrels (Procellaria cinerea) were caught accidentally in large numbers over this same period. Giant petrels (Macronectes spp.), black-browed albatrosses (Diomedea melanophrys) and grey-headed albatrosses (D. chrysostoma) were also caught over this period. A multivariate analysis suggests that a combination of factors (environmental and relating to fishing techniques) have an effect on the observed numbers of seabirds caught incidentally. The results of this study suggest that a significant part of the mortality of white-chinned petrels and grey petrels is explained by the time of year, geographical area and type of longliner (manual versus automatic baiting). Almost all of the incidental mortality occurred exclusively during the breeding season, except for giant petrels. The highest mortality of white-chinned petrels, grey petrels, black-browed albatrosses and grey-headed albatrosses corresponded to the chick-rearing period. In addition, the vessels using automatic baited longlines caught many more birds than those using manual baited longlines. Based on the results of this analysis, several recommendations are made with the aim of reducing the incidental mortality of the various species concerned in the French EEZs of Crozet and Kerguelen Islands (Subarea 58.6 and Division 58.5.1 respectively). |
CCAMLR has the primary competency for managing fishing south of the Antarctic Polar Front. Despite a relatively long history of scientific research and fisheries, CCAMLR’s fisheries management strategy has often had to deal with incomplete and uncertain information on affected resources. Fishery-independent studies are difficult and expensive to conduct. In addition, the size of the Convention Area, its remoteness and prevailing inclement weather further complicate matters. Therefore, in addition to the standard catch and effort data supplied by vessels, the collection of data by scientifically qualified observers on board fishing vessels has assumed prominence in the collection of essential data for fisheries management purposes. The Scheme of International Scientific Observation, adopted by CCAMLR in 1992, is designed to gather and validate fishery-related information essential for assessing the status of target species as well as the impact of fishing on dependent and related species, including seabirds and marine mammals. The scheme is limited to scientific observation only and is separate from enforcement issues which are covered by the CCAMLR System of Inspection. Under the scheme, observers are deployed under bilateral agreements between CCAMLR Members and they operate on vessels under flags other than that of their own country. This paper outlines the history of the scheme in terms of its logistics, participation, coverage, changes in research priorities, volume of data collected and data usage. The advantages and shortcomings of the scheme are explored. |
CCAMLR is developing a management procedure for the krill fishery, including the evaluation of candidate management procedures in a simulation framework, using plausible models of the Antarctic marine ecosystem. This paper develops a framework for erecting such models. It discusses the general model requirements and presents a conceptual framework for allowing flexibility in dealing with biological, spatial and temporal scales. The body of the paper is concerned with conceptualising an element of the ecosystem to account for the varying qualities of data and knowledge and for exploring the consequences of uncertainty. |
This paper describes a new method for estimating illegal, unregulated and unreported (IUU) catches of fish and by-catch of birds. It utilises high quality, well-documented fisheries protection vessel (FPV) cruise data. The method takes explicit account of both ‘seen’ and ‘unseen’ IUU fishing by using a simulation model to arrive at statistically rigorous estimates of, and confidence intervals for, fish and bird catches by IUU vessels. In order to estimate an IUU catch there must have been at least one encounter with an FPV in a year; no encounters in a year are interpreted as zero IUU fishing. For each IUU incident detected by the FPV, a theoretical maximum time over which this IUU activity could have occurred was calculated. This was then converted to estimated actual IUU fishing time, using a model simulating IUU vessel and FPV behaviour. IUU activity was considered to have been observed when the IUU vessel and the FPV vessel were in the same place at the same time. When this occurred, the FPV was assumed to detect IUU activity according to an ‘encounter probability’. The encounter probability was estimated from the known encounters of FPVs with licensed vessels. The total annual IUU catch of toothfish and birds was calculated using a second simulation model. Subarea 48.3 was divided into six areas for the purposes of the estimation of fish and bird catch associated with IUU fishing. The mean and variance of fish catch rate was calculated for each area and each year using reported catch and effort data. The catch rate of birds was estimated separately for summer and winter by bootstrapping previously published CCAMLR observer data weighted by the number of hooks observed. These data were obtained in the early licensed fishery (1997) when few vessels used mitigation measures. Three years were analysed: 1998/99, 1999/2000 and 2000/01. Each year fully covered the period 1 October to 30 September, thus including one summer and one winter period. The estimated mean toothfish catches attributable to IUU fishing were 776, 1 019 and 198 tonnes in 1998/99, 1999/2000 and 2000/01 respectively (a total over the three years of 1 994 tonnes). The distribution of estimated total bird catch was highly skewed, with medians in the three years of 621, 2 852 and 550 birds respectively. 95% confidence limits were calculated to be 54–2 017, 468–1 779 and 22–487 tonnes respectively for fish and 162–7 752, 1 040–23 361, 140–9 023 respectively for birds. Despite continuing high levels of FPV coverage from 2001 to 2004, no further IUU activity has been detected, leading to estimates of zero fish and bird catches for the years 2001/02, 2002/03 and 2003/04. |
A new method for estimating illegal fishing effort is put forward. The results from this new method are similar to those of the Agnew and Kirkwood (2005) method, and this suggests that the current method is adequate under circumstances of low evasion and when good knowledge exists that zero observations reflect zero illegal fishing. The new method performs better in the case of zero detections and can potentially better handle the evasion of detection by illegal activity. Both the new and the current method suffer from the fact that the observation method used directly affects the system. This is the prevention/detection problem, in which the greater the number of detections for a given level of illegal fishing, the more often the illegal fishers will curtail their fishing trips. This leads to a negative correlation between the amount of fishing and the estimated amount of fishing for a given number of illegal cruises. As the number of illegal cruises increases, both the estimate and the average amount of illegal fishing increase. This gives some confidence that the method can produce results that have a degree of legitimacy. However, the range of actual fishing (in the simulation datasets) for a given estimated level of fishing is very large. This range of uncertainty increases as the evasion rate increases. This research suggests that it would be possible to calculate a precautionary assessment of illegal fishing such that the actual number of illegal fishing days is less than, or equal to, the precautionary assessment with some given level of confidence (for example 80%) |
Seasonal variation in the diurnal vertical migration and aggregation of Antarctic krill (Euphausia superba) associated with the daylight phase over the diurnal cycle (i.e. brightness categories) was examined for the Scotia Sea (South Shetland Islands (SS), South Orkney Islands (SO) and South Georgia (SG) areas) using Japanese fishery data. Average trawling depth usually showed a marked diurnal change during summer and winter in SS and SO. Daily average trawling depth tended to be shallower during austral summer and early autumn, deepened gradually from autumn and reached maximum depth in winter in the Scotia Sea, shifting to shallower depths again in early spring. The average catch-per-unit-effort (CPUE) was highest during the day and lowest at night in autumn and winter in each area, but lower during the day in summer in SS and SO. It is suggested that the seasonal and diurnal changes in vertical migration and aggregation of krill are closely related to its feeding and spawning ecology and avoidance of visual predators. |
The otolith microstructure of juvenile mackerel icefish (Champsocephalus gunnari) (5.5–13.3 cm in length) was analysed using samples taken during a trawl survey of juveniles in February–March 2002 on the South Georgia shelf. Juvenile fish comprised two year classes arising from spawning in the 1999/2000 and 2000/01 split-years. The mean width of daily otolith growth increments decreased from 6 μm during the first 100 days (total length (TL) 4.5 cm) to 2.8 μm at 500 days (TL 13.1 cm). The pelagic stage of egg incubation development for fish of the 2001/02 year class lasted four months. This was estimated based on a retrospective count of daily increments. TL varied from 5.5 to 10.4 cm for fish in their first year (120–250 days) to 12.5–13.3 cm in 1-year-old fish (477–533 days). The radius of the first annulus ranged from 0.7 to 1.3 mm. The relationship found between fish length and daily otolith increments could be used for age differentiation of juvenile fish between consecutive year classes. |
X-rays of vertebral half-centra, and x-rays and transmitted white light examination of caudal thorns, were used to estimate the ages of the Antarctic skate (Amblyraja georgiana) from the Ross Sea. Caudal thorns viewed with transmitted white light provided the clearest growth bands, but reading precision was low, producing uncertain age estimates. Furthermore, annual deposition of thorn bands has not been validated. The maximum estimated age was 14 years, but this should be regarded as a conservative estimate of longevity because of the possibility that thorn growth ceases in large individuals. There was no obvious difference in growth between the sexes, so the von Bertalanffy curve for both sexes provides the best available representation of growth in the species: Lt = 70.8 (1-e -0.308[t+1.10]), where Lt is the pelvic length (PL) in centimetres at age t years. Applying this growth curve to the estimated lengths at maturity for males and females (64 and 66–69 cm PL respectively) produced estimated ages at maturity of 6–7 years for males and 8–11 years for females. These estimates are near the middle to upper end of the range of ages at maturity for skates worldwide. The results of this study are preliminary and should be used with caution. Further work is needed to determine whether the thorn ageing technique presented here produces reproducible and reliable age estimates. |
At the 2004 meeting of the Working Group on Ecosystem Monitoring and Management (WG-EMM) in Siena, Italy, the UK reported on the by-catch of fur seals (Arctocephalus gazella) in the krill fishery around South Georgia, and on mitigation methods that were being developed and deployed to avoid fur seal deaths in the fishery. WG-EMM requested that the UK provide further details of the methods employed for consideration by the ad hoc Working Group on Incidental Mortality Arising from Fishing (WG-IMAF). Three CCAMLR international scientific observers recorded mitigation measures for fur seal entanglements on krill vessels fishing around South Georgia in the 2004 fishing season. The measures implemented were based on four approaches: physical barrier, barrier plus escape hatch, manufactured seal-exclusion devices and gear configuration. Those vessels initially without mitigation measures were able to introduce them without further cost and minimal disruption to fishing activity during the season. These approaches, aimed at reducing seal entanglements, are similar to the two systems implemented by Japanese vessels during the 2003 krill fishing season around South Georgia (Japan Deep Sea Trawlers Association, 2004). |
Experimental fishing for Patagonian toothfish (Dissostichus eleginoides) took place from 28 June to 27 July 2003. This experiment was carried out by a Spanish longliner, following commercial fishing procedures, in a restricted area south of Madagascar and north of Prince Edward and Marion Islands and the Crozet Islands, outside EEZs and CCAMLR waters. A total of 57 hauls was made at depths between 360 and 1 950 m. D. eleginoides was present in all hauls, with catches varying from 53 to 1 158 kg. The northward distribution of D. eleginoides is closely related to the extension of the Sub-Antarctic Front, and especially the intermediate layer of sub-Antarctic water masses, which defines the area of D. eleginoides toothfish distribution. The survey area would seem to be located at the edge of the principal area of D. eleginoides concentration, in which a residual recruitment effect persists. The total CPUE was 42.21 kg/thousand hooks. Within the study area, depth was the most important factor in the distribution of CPUE of D. eleginoides. |