CCAMLR Science, Volume 11 (2004)
The former fishing ground off Joinville–D’Urville Islands was revisited in the course of the Antarctic Expedition ANT XIX/3 by RV Polarstern in February 2002. Five hauls were conducted north of the two islands at depths of 149 to 282 m on 21 February 2002. Published and unpublished reports from fishing operations in the 1970s and 1980s by the Fischkombinat in Rostock (former GDR), Sea Fisheries Institute in Gdynia (Poland) and material available from YugNIRO, Kerch (Ukraine) of what is known of fishing activities in the area were analysed. These data were previously unavailable to CCAMLR. Fishing and the extent of fishing was primarily dependant on whether and to what extent the target species of the fishery, the spiny icefish (Chaenodraco wilsoni), formed concentrations. Information on these fishing operations was, however, sparse, being restricted to the two seasons (1978/79 and 1979/80) when Polish and GDR vessels fished in the area. Length compositions from several fishing nations revealed that the fishery targeted primarily fish 25–35 cm long. The fish fauna at the tip of the Antarctic Peninsula represents a combination of low- and high-Antarctic elements. The available information on the biology of C. wilsoni was reviewed. Some new information was available on the reproduction and feeding of some of the species. Krill (Euphausia superba) formed a major element in the diet of icefish. |
Molecular markers were used to investigate the stock structure of Patagonian toothfish (Dissostichus eleginoides) in the West Indian Ocean sector of the Southern Ocean. Four collections of D. eleginoides from Kerguelen (n = 1), Crozet (n = 1) and Prince Edward and Marion (n = 2) Islands were typed using two fragments of mitochondrial DNA (mtDNA) and seven nuclear microsatellite loci. MtDNA haplotype diversity ranged from 0.331 to 0.351. Observed heterozygosities per locus per collection ranged from 0.000 to 0.900 and allele counts from 1 to 21. There was no evidence of significant mtDNA heterogeneity among the four collections and only weak and inconsistent heterogeneity (based on minor allele frequency differences) at three microsatellite loci among the four collections. Neither mtDNA nor microsatellite FST values indicated population sub-structuring among collections. Genetic variance estimates of both mtDNA (FST = –0.016) and microsatellites (FST = –0.005) indicated all variation was seen within collections. Comparisons with previously collected genetic data from Heard and McDonald Island collections (n = 4) were not significant among the geographic groups (mtDNA ФCT = –0.003; microsatellite ФCT = 0.004), indicating a lack of genetic differentiation among these West Indian Ocean sector fishing locations. |
The problem of acoustically identifying and estimating the sizes of two euphausiid species is considered. A euphausiid aggregation is represented by a three-dimensional probabilistic vector whose components are the mean ratios of the volume backscattering coefficients, measured at two different frequencies. The decisions on the species and the relative misclassification errors are calculated individually for each component of a vector, using classical Bayesian techniques. Classification probabilities are derived by integrating the individual decisions. The size structure of the classified aggregation is derived from a fluid-sphere model. The effectiveness of the method is demonstrated by comparing the acoustic estimates of species and sizes to net samples collected during three surveys conducted in the Ross Sea under various environmental conditions. |
The current standard method for modelling catch and effort data for Patagonian toothfish (Dissostichus eleginoides) for CCAMLR areas is to model the haul-by-haul ratios of catch to effort as the response variable in a generalised linear model (GLM) with a square-root link function and a unit variance function. A time series of standardised CPUE estimates and their precision can be obtained from the ‘fishing year’ parameter estimates together with ‘baseline’ parameter estimates, their variance–covariance matrix, and the inverse-link function. An alternative GLM with a more rigorous theoretical basis is introduced here. Catch is modelled as the response variable using a GLM with a power variance function, with the power parameter (λ) estimated using a profile extended quasi-likelihood, and a log link function with log of effort as an offset. For 1 < λ < 2 this model is equivalent to assuming a compound Poisson-gamma distribution (i.e. Tweedie distribution) for catch that, unlike lognormal or gamma distributions, admits zero values. In addition, random vessel effects are introduced into the GLM, as specified by a generalised linear mixed model (GLMM), in order to provide more efficient estimates of the standardised CPUE time series and more realistic estimates of their precision. Extra efficiency is gained by recovery of inter-vessel information as a result of the imbalance in the number of hauls in the year-by-vessel cross-classification. Further, the inclusion of an area stratum by fishing year interaction as an additional random effect in the GLMM is investigated. Fitting the stratum-by-year interaction as a fixed effect is problematic since it requires weighting of the individual stratum estimates by the areal extent of the stratum in order to obtain overall yearly standardised catch-per-unit-effort (CPUE) estimates. Without stratified random sampling, the determination of stratum areas that will give unbiased standardised CPUE estimates may be difficult. Fitting the stratum-by-year interaction as a random effect avoids this difficulty, and diagnostic methods to evaluate the validity of considering this interaction as random are described. The methods are demonstrated using catch and effort data from two commercial D. eleginoides fisheries: the longline fishery around South Georgia (Subarea 48.3) and the trawl fishery around Heard Island and MacDonald Islands (Division 58.5.2). |
Following an assessment of Antarctic krill (Euphausia superba) in the Scotia Sea, CCAMLR established a precautionary catch limit of 4 million tonnes and further adopted 15 small-scale management units (SSMUs). The intent was to subdivide the precautionary catch limit for krill among the SSMUs so as to preclude the inadvertent concentration of catches in a small portion of the surveyed area. Five options for allocating the catch limit among the SSMUs in the Scotia Sea are presented in this paper. The first four are static allocations where the allotment of catch to an SSMU is proportional to: (i) the historical catch within the SSMU; (ii) estimated predator demand in the SSMU; (iii) estimated standing stock of krill in the SSMU; and (iv) standing stock less predator demand in the SSMU. The fifth option is a dynamic allocation based on land-based predator monitoring conducted just prior to, or early in, the fishing season. For the purposes of illustration and comparison between the options, parameter estimates are made using available data, although it is recognised that considerable refinement of these estimates is possible. Qualitative conclusions are that: under the fi rst two options a substantial portion (>65%) of the catch limit would be allocated to three or less of the SSMUs adjacent to large concentrations of land-breeding predators; under options (iii) and (iv) a similar portion of the catch limit would be directed to pelagic SSMUs beyond the foraging range of these predators but into areas where krill fi shing has not regularly occurred; and under option (v), an example of an adjustable catch limit dependent on the results of ecosystem monitoring, the fishery would be restricted in some of its traditional fishing grounds during years of low krill availability. Under all five options there would be little effect on the existing fishery. However, as catches increase, a trade-off may be drawn between options that displace the fishery from its current operating area, but reduce the potential for contravening the terms of the Convention, and options that do not displace the fishery, but are likely to contravene the terms of the CCAMLR Convention. |
The breeding biology of the Adélie penguin (Pygoscelis adeliae) was studied at Edmonson Point, Victoria Land, during the 1999, 2001 and 2003 breeding seasons. Weather and sea-ice regimes varied notably, especially in 2003, which was characterised by extensive and persistent sea-ice and strong winds with snowfalls in December. First incubation trips by females were significantly longer than in 1999 and 2001, which in turn delayed the mean departure date of males on the second incubation trip. A high number of chicks died during the post-hatching stage and the breeding success was low with 0.3 chicks crèched per nest with eggs. The mean crèching date was also delayed compared to dates recorded in 1999 and 2001. The average weight of adults rearing chicks was lower in 2003. It is suggested in this paper that the ability of penguins to cope with severe short-term weather events could be reduced when longer-term events, such as anomalies in the persistence of sea-ice, have affected body condition. |
Killer whale (Orcinus orca) and sperm whale (Physeter macrocephalus) interactions with longline fishing operations were recorded by CCAMLR observers between 2000 and 2002 at South Georgia (Subarea 48.3). Demersal longlines, targeting Patagonian toothfish (Dissostichus eleginoides), were deployed in depths of 169 to 2 150 m. Most effort was concentrated along the 1 000 m depth contour. Sperm whales were the most abundant marine mammal observed in the vicinity of vessels when lines were being hauled, being present during 24% of hauling observations. Killer whales, the second most frequently sighted cetacean, were present during 5% of haul observations. A high inter-vessel variation was noted for interactions with both species. A comparison of geographic plots of cetacean sightings during hauls to fi shing positions showed that interactions occurred over a wide geographic range. These were mostly correlated to the fishing effort on the different grounds, although some ‘hotspots’ for interactions were noted. Killer whale pods were generally small (2–8 animals), while solitary animals and larger pods (>15 animals) occurred less frequently. Sperm whales were most often solitary when interacting with fishing vessels, although smaller groups (2–3 animals) were also relatively common. Interactions with killer whales were most often observed in the day, generally in the afternoon, while night-time interactions were relatively few and usually occurred before midnight. Interactions with sperm whales followed a similar pattern, occurring most often in the afternoon, while very few interactions were observed at night. Catch rates were significantly lower when killer whales were present when compared to hauls during which no cetaceans were present. Catch rates were slightly higher in the presence of sperm whales and it is possible that sperm whales were attracted to some areas because of abundant prey (toothfish). However, in areas with lower catch rates, indications are that depredation by sperm whales can lead to a decrease in catches. Some mitigation measures have been tried by vessels to reduce interactions with cetaceans, although no quantitative studies have been carried out to measure their effectiveness. Apart from the obvious economic implications of fish loss due to depredation, ecological implications such as the effect of unrecorded fish removals on stock assessment models, modifications in the behaviour of marine mammals and entanglements with fishing gear are also important considerations. Further investigations are needed to determine the extent and effects of longline–cetacean interactions, to enable observer protocols to be standardised so as to ensure the collection of valuable data, and to assess and implement mitigation strategies under controlled experimental conditions. |
Interactions of sperm whales (Physeter macrocephalus) and killer whales (Orcinus orca) with Patagonian toothfish (Dissostichus eleginoides) fishery operations were assessed in southern Chile during surveys with observers on board industrial fishing vessels between April 2002 and March 2003. For the 180 hauls monitored, the evidence of damaged catch when cetaceans were present included toothfish lips (n = 121), heads (n = 16) and trunks (n = 3). The mean rate of depredation was 3% (±2% CI 95%; n = 180 sets) and ranged between 0 and 100%. Considering that no interactions were recorded in 153 (84%) of the effectively monitored sets, and that the mode and median of the depredation rate was 0, the global impact of cetaceans on the fishing yield is considered to be low. When mixed sightings of killer and sperm whales were encountered (n = 12), the rate of depredation decreased to 0%; this could be the result of killer whales preferring to predate on sperm whales rather than on the fish caught on the line, as suggested by the response of sperm whales to the presence of killer whales (grouping into tight parallel formations). High sperm whale densities were found to be associated with various ‘hotspots’ which had high fishing yields. This relationship tends to support the hypothesis that the richest fishing grounds are also traditional feeding grounds for sperm whales. Financial loss associated with operational interactions involving depredation was US$92 684 (CI 95% US$47 302–153 745) for the whole fleet, with a mean loss per set of US$138 (CI 95% US$74.76–249.3). |
Notothenia rossii was the first target species in Southern Ocean fisheries. The species was already heavily fished at the beginning of the 1970s. The closure of the fishery for this species in 1985 was one of the first conservation measures adopted by CCAMLR. Fish biomass within a CCAMLR subarea or part of a subarea is commonly estimated from surveys that target a number of species, including N. rossii, at the same time. These surveys are conducted under the assumption that the target fish species are more or less evenly distributed over the area at the time of the survey. This assumption is violated in the case of N. rossii, which is non-randomly distributed such that a large proportion of the population tends to aggregate in small areas, leaving most of the survey area only thinly populated. In order to provide more accurate estimates of the abundance of the species, it is suggested that an acoustic survey combined with a number of identification hauls might be the most promising approach to estimating the biomass of N. rossii. |
Post-haulage survival experiments were conducted on 95 Raja sp. anon. cut off longlines at the sea surface by the Chilean fishing vessel Isla Sofía in May and June 2003 during the toothfish fishing season in Subarea 48.3. Capture depth had a consistently significant influence on the mortality of skates. There were some suggestions (not statistically significant) that wind speed (i.e. weather conditions) and the sex of rays also had some small influence on survivorship. Discard survivorship was 75% in waters shallower than 1 300 m (i.e. 1 200–1 300 m), 46% in waters 1 300–1 500 m, and 24% in waters between 1 500 and 2 000 m. These findings support CCAMLR’s recommendation that skates and rays be cut from the line at the sea surface, so as to maximise their chances of survival. Results from this experiment can also be used to calculate the expected skate mortality within the fishery, based on depth of capture. Further survival experiments should be conducted, particularly in shallow waters, where sampling in this study was restricted. |
Key catch-per-unit-effort (CPUE) indices used in Soviet krill fishery statistics, as well as the main sources of data and primary data for their calculations, were examined. The main CPUE indices were catch per vessel-days fished (CVDF), catch per extended vessel-days fished (CEVDF) and catch per hour of trawling (CHT). A relatively high correlation between mean monthly values of CVDF and CEVDF, and CVDF and CHT was observed. However, the correlation between daily mean values was quite low as a result of significant fluctuations in haul duration due to the different fishing strategies used when targeting krill intended for different end products, i.e. human consumption, krill meal and frozen krill. Daily mean CVDF and CHT calculated for specific strategies were well correlated. Depending on the fishing strategy used, the number of hauls per day ranged from 1 to 15. The duration of hauls ranged from 0.1 to 16 hours. When a final product of higher quality was required, haul durations were shorter and, accordingly, the number of hauls per day was higher. The correlation between catch and tow time was considered to be an indicator of homogeneity in krill distribution. The utility of CPUE for direct evaluation of relative changes in quantitative parameters of krill distribution inside fishing grounds is assessed. |
Sink rates of integrated weight longlines (lines with 50 g.m–1 lead integrated into two strands of the ground line – IW-50 lines) were measured during commercial fishing operations using two methods: electronic time depth recorders (TDRs) and pieces of string of known length wrapped around empty plastic bottles (bottle method). Sink rates measured to 2 m with bottles averaged 0.23 ± 0.07 m.s–1 compared to 0.17 ± 0.03 m.s–1 recorded by TDRs. This difference was not statistically significant (t12 = –0.181, P = 0.859). When the target depth was 15 m, sink rates measured using the bottle method (0.20 ± 0.02 m.s–1) were significantly slower than those measured by TDRs (0.24 ± 0.03 m.s–1, t10 = –3.851, P = 0.003). Measuring sink rates to 15 m proved difficult with bottles because they were too far behind the vessel, i.e. out of the observer’s sight, when they reached the target depth. Bottles had a high failure rate (60%) due to string becoming entangled during line setting, or bottles vanishing from sight behind waves or in congregations of seabirds before the target depth was reached. No TDRs were lost during the trial. Bottle tests were most useful, depending on sea state and weather conditions, for measuring sink rates to shallow depths when instant readings were required. TDRs can be used to measure sink rates to depths of more than 2 m down to the seabed. A major advantage of the TDRs is the archival nature of the data collected. |
Based to a large degree on the precedent set by CCAMLR in 1991, the streamer line has become the primary, and most commonly prescribed, seabird mitigation device in world longline fisheries. This paper reviews CCAMLR streamer line requirements (Conservation Measure 25-02 (2002), formerly Conservation Measure 29/XIX) in light of a review of existing literature and available data on the effectiveness of single and paired (or multiple) streamer lines. Research to determine the optimal streamer line design and configuration is lacking and is identified as a high priority. Future streamer line research should compare the attack or dive rate of multiple southern hemisphere seabird species or foraging guilds as a function of distance astern in response to single and multiple streamer lines deployed according to specific performance and material standards. Improvements to streamer line requirements set out in Conservation Measure 25-02 are discussed and proposed relative to recent Alaskan requirements. Proposed changes include: requiring that the streamer line be deployed over the hookline within 100 m of the stern; increasing the height of the streamer line attachment point to the vessel and/or specifying the aerial extent of the streamer line; requiring that individual branched streamers extend to the water in the absence of wind and swell and be attached throughout the aerial extent of a streamer line; including ultraviolet-protected plastic tubing as a permitted streamer material; relaxing the number and placement of swivels in favour of a performance standard; requiring that streamer line attachment points to the vessels and the towed object be deployed windward of the hookline; and recommending that fishers deploy a minimum of two streamer lines on a voluntary basis according to performance and material standards. Based on the recommendations of this review and the discussions of the ad hoc Working Group on Incidental Mortality Arising from Fishing (WG-IMAF), the CCAMLR streamer line requirements were changed by the Commission in 2003. |