CCAMLR

Mortality in longline fisheries is a critical global threat to some seabird species. Identifying
andmainstreaming seabird avoidance methods that not only have the capacity to minimize bird interactions, but
are also practical and convenient, providing crew with incentives to employ them consistently and effectively,
will help resolve this global problem. Cooperative research and a commercial demonstration were conducted to
assess three methods’ effectiveness at avoiding incidental seabird capture, commercial viability, and practicality
in the Hawaii pelagic longline fisheries. A seabird avoidance method called side setting, which entails setting
gear from the side of the vessel, with other gear design the same as conventional approaches when setting from
the stern, had the lowest mean seabird contact and capture rates of treatments tested. Because side setting
promises to provide a large operational benefit for longline vessels, the incentive for broad industry uptake and
voluntary compliance is realistic. After making the initial conversion to side setting, there is no additional
effort required to employ the method. A seabird avoidance method called an underwater setting chute also
holds high promise, but requires additional research and evaluation to correct design problems, after which it
can be considered being made commercially available. Two chutes, one 9m long and one 6.5m long, which
deployed baited hooks 5.4m and 2.9m underwater, respectively, were used in this trial. The 9m chute had the
second lowest mean seabird interaction rates when used with swordfish gear, and the 6.5m chute had the second
lowest mean seabird interaction rates when used with tuna gear. A third seabird avoidance method, which
entails thawing and dying bait dark blue to attempt to reduce seabirds’ ability to see the baits by reducing the
bait’s contrast with the sea surface, was found to be less effective than the other two methods and was found to
be relatively impractical and inconvenient. If pre-dyed bait were commercially available, use of blue-dyed bait
in combination with other methods, such as side setting and adequate line weighting, has high promise.

A set of procedures for modelling catch and effort data using generalized linear mixed models (GLMMs) including data analytic methods for examining the appropriateness of model structure and parameter values was presented in WG-FSA-SAM 03-12 using Dissostichus eleginoides in Subarea 48.3 of the CAMLR area as an example dataset. The application of these procedures to trawl catches of Champsocephalus gunnari in Subarea 58.5.2 is described. For the trawl catch and effort data it was found the precision of the standardised CPUE estimates was considerably poorer than that of the longline data for Subarea 48.3. It is concluded that CPUE was relatively stable from the start of the fishery until 2000, after which time there was a sharp increase in 2001 with a steady decline thereafter. The sharp increase in 2001 is most likely the result of the large abundance of 3 and 4 year-old fish in that year, which has since diminished through a combination of

A set of procedures for modelling catch and effort data using generalized linear mixed models (GLMMs) including data analytic methods for examining the appropriateness of model structure and parameter values was presented in WG-FSA-SAM 03-12 using Dissostichus eleginoides in Subarea 48.3 of the CAMLR area as an example dataset. Further development of these procedures is presented in this report using trawl catches for Dissostichus eleginoides in Subarea 58.5.2. The extension described here deals with calculating an overall standardised CPUE series when the Subarea has been divided into sampling strata by incorporating ‘Stratum’ as a fixed effect term and the Stratum-by-Year interaction (S x Y) as a random effect term in the GLMM.
Statistical methods are presented for examining the validity of considering the S x Y term as random. A random S x Y term avoids the difficulty in calculating an overall standardised time series of CPUE estimates of weighting by the areal extent of each stratum which is necessary when the S x Y term is included in the GLMM as a fixed effect. Defining an areal extent of each stratum that is valid for use in calculating a weighted mean over all strata using the formula based on stratified random sampling is problematic given that hauls are not a spatially random sample within each stratum. Including the stratum term as fixed simply results in uniform scaling of the CPUE series as is the case with other additive fixed terms in the GLMM.
It was concluded that there was an increase in CPUE in the second year of the fishery with a sharp decline in the following year followed by a relatively stable series of CPUEs. It was also shown that the influence on the series of the random effects estimates for Stratum-by-Year is small.
For the trawl catch and effort data it was found that considering the S x Y term as random was valid. The precision of the standardised CPUE estimates was considerably poorer than that of the longline data for Subarea 48.3. A weak trend of decreasing CPUE values with entry into the winter months was detected using a cubic smoothing spline.

A preliminary assessment of yield of Patagonian Toothfish, Dissostichus eleginoides, for Heard Island Plateau (Division 58.5.2) was done, using the standard CCAMLR methods, based on the result of a randomly stratified trawl survey completed between 16 April and 10 May 2003. The 2003 estimate of abundance of recruits indicates a continuation of a period relatively low recruitment since 1999. A minor revision to the recruitment series resulted in a relatively small reduction in the preliminary estimate of sustainable long-term yield assessed using the standard method. The preliminary estimate for 2004 was 2,680 t. Initial tests of length at age assumptions indicated that using a specified length at age vector that did not include growth beyond 15 years had only small effects on projected long term yields. Further work is required to evaluate the implications of current uncertainty in the rate of growth beyond this age at 58.5.2. Preliminary examinations of the effect of refinements to the design of the annual survey indicated some variability in survey catchability between years and suggest that it may be appropriate to adjust estimates of cohort strength for catchability where possible. The 2003 season saw the operation of the first commercial long line vessel in 58.5.2. An initial comparison of the length distribution of the catches suggest that the two gears sample a similar range of sizes. This initial comparison was somewhat confounded by the depth of the grounds fished by the trawl and long-line operations. Very few large (>1200 mm) fish were observed in the long-line catch. Further structured work is planned in conjunction with the commercial operators for the 2004 season to provide data for a more comprehensive comparison, and to sample greater depths that fished by the long line operator in the 2003 season.

A preliminary assessment of yield of Champsocephalus gunnari for Heard Island Plateau (Division 58.5.2) was undertaken using the standard CCAMLR methods, based on the result of a randomly stratified trawl survey completed between 16 April and 10 May 2003. The 2003 estimate of abundance was approximately 20% of the 2002 estimate. This decline in abundance is consistent with the passage of the strong 1997 cohort through the population and relatively weak recruitment in 1999 and 2000. The 1+ fish evident in the survey were not fully sampled and as such are not included in the assessment. Estimates of the strength of this cohort will not be possible until the May 2004 survey is complete. The estimates of short-term yield for 2004 and 2005 using the Mathcad implementation were 259 tonnes and 196 tonnes, respectively. Consideration is given to the potential use of alternative technical measures to control harvest of un-assessed cohorts and provide for more stable catches between fishing years, while meeting the objectives of Article II. Comparison of yield estimates between Mathcad and Generalised Yield Model (GYM) implementations indicated that the GYM version provided slightly higher estimates of short-term yield. These differences will need to be considered by the working group. The implications of the interannual variability in recruitment, natural mortality and growth of these fish, combined with the need to maintain a steady yield if possible need to be explored further in the development of a management procedure that fulfills the objectives of Article II and is robust against the uncertainties inherent in the stock dynamics of this species.

This note describes the activities of an alliance of New Zealand government, fishing industry and environmental groups that has formed to promote fishing practices that avoid seabird capture by fishing fleets in the southern hemisphere.

Following a finding that a small sample of aged Dissostichus mawsoni from McMurdo Sound (76° S) fell consistently below the von Bertalanffy curves calculated predominantly from data collected between 67 and 74° S, an investigation to test for latitudinal differences in growth rates was conducted. Length-at-age of Dissostichus mawsoni was compared across five zones in a 15.5° latitudinal range (62.5°–78.0° S). Between-zone comparisons were confounded by marked differences in the age structure of catches from the northern and southern sections of the range, and by the relatively high level of variance in the length-at-age data. There is no statistically significant difference in mean growth rates of D. mawsoni between 62.5° and 75° S. However, fish between the ages of 6 and 15 years in the southernmost zone (75–78° S) are, on average, significantly smaller at age than those in the more northern zones. There were insufficient older fish in the southernmost zone to enable a comparison with other areas. Any real latitudinal differences in growth rates for relatively sedentary fish are likely to be blurred by migration between latitudes.

This paper provides a review of the boundaries of the small scale research units (SSRUs) used to manage the exploratory fishery for D.mawsoni in Subarea 88.1. In determining appropriate SSRU boundaries we considered the physical and geographical features of the Subarea including the impact of sea ice on fishing practices, as well as the distribution and abundance of the target and bycatch species (rattails and skates). We recommend that the northern SSRU boundary (at 65°S) remain in place but that the other boundaries of the other four SSRUs are changed to reflect the underlying bathymetry, species distributions and ice conditions.

This report presents results from a pilot study to determine the feasibility of conducting acoustic surveys for toothfish and rattails in the Ross Sea. Acoustic data were collected during the 2002–03 exploratory fishery. Data were recorded continuously from 28 December to 2 February 2003, then during line setting only from 5–22 February 2003. Analyses were carried out to assess data quality, describe different mark types, and quantify acoustic backscatter by echo integration and echo counting. These analyses focused on the subset of acoustic data collected when setting longlines so acoustic recordings could be compared with longline catches.
Data quality was generally good. Of the 84 line recordings, 68 were considered suitable for acoustic analysis. Poor data quality was associated with strong winds and/or high seas: conditions that led to bubble interference on the hull-mounted transducer. Other issues with data quality were interference from another echosounder, and the occurrence of a double bottom echo caused by too high a ping rate.
All line recordings were in water over 1000 m deep. Because of the spreading of the acoustic beam, the acoustic deadzone at these depths is relatively large, especially if the bottom is rough or sloped. Simulations indicated that at 1500 m depth, the acoustic deadzone would be over 50 m high for a sea-bed with a slope of 20º. The problem of the acoustic deadzone was worsened by the occurrence of side-lobe echoes, produced as longlines were set on steep slopes parallel to the depth contours. Measurements indicated that side-lobe could create a deadzone of 50–100 m on apparently flat ground. Because both toothfish and rattails are considered to be demersal species, the inability of the acoustics to ‘see’ close to the bottom is a major limitation that could only be avoided with the use of a towed acoustic system.
Two types of pelagic layers were present in most acoustic recordings: a dense shallow layer between 30 and 200 m; and a more diffuse deep scattering layer between 300 and 800 m. Pelagic schools were also present in some recordings and these tended to occur at 150–400 m depth, between the layer marks. The most common demersal mark was single targets, which were present in 84% of line recordings. Most single targets occurred in a surface-referenced band between 800 and 1100 m depth, and were up to 500 m off the bottom. There was a significant positive correlation between the number of single targets counted from the echogram and the catch of rattails in the accompanying longline set. Bottom-referenced layers were present in 18% of line recordings and were also associated with higher catches of rattails. Demersal schools were present in 16% of recordings and were associated with higher catches of toothfish. Despite these associations, no acoustic marks could be reliably identified as being rattails or toothfish. It seems unlikely that the schools were toothfish or the single targets were rattails, as these were often more than 300 m off the bottom.
At this point, it is not practical to estimate toothfish or rattail abundance in the Ross Sea using hull-mounted acoustic systems. The acoustic deadzone was large, meaning it was impossible to detect demersal species close to the bottom. Echo integration was unreliable because there was a very low signal-to-noise ratio deeper than 1000 m. Echo counting showed more promise, but only relatively strong targets well separated from the bottom could be enumerated. As toothfish do not have a swimbladder, their acoustic target strength may be too weak to allow them to be counted.

Killer whale (Orcinus orca) and sperm whale (Physeter macrocephalus) interactions with longline fishing operations were recorded by CCAMLR (Commission for the Conservation of Antarctic Marine Living Resources) observers between 2000 and 2002 at South Georgia (Subarea 48.3) in the Southeast Atlantic Ocean. Demersal longlines, targeting Patagonian toothfish (Dissostichus eleginoides), were deployed in depths of 300 to 2000m, concentrated along the 1000m contour. Sperm whales were the most abundant marine mammals observed in the vicinity of vessels when lines were being hauled, occurring during 24% of hauling observations. Killer whales, the second most sighted, occurred at 5% of haul observations. A high inter-vessel variation was noted for interactions with both species. Geographic plots of cetacean sightings during hauls were compared to fishing positions. Both killer whale and sperm whale interactions occurred over a wide geographic range and were mostly dependent on the extent of fishing effort on the different grounds, although some ‘hotspots’ for interactions seem to occur. Killer whale pods were generally small, (2 – 8 animals, 57% of observations), while solitary animals (13%) and larger pods (>15 animals, 8%) occurred less frequent. Sperm whales were most often solitary (43% of observations) when interacting with fishing vessels, although smaller groups (2 – 3) were also relatively common. Larger groups were not often sighted. Interactions with killer whales were most often observed in the day, mostly 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 (P > 0.05) when killer whales were present (0.15 kg/hook; 21.5 fish/1000 hooks), when compared to hauls with no cetacean present (0.29 kg/hook; 48.5 fish/1000 hooks). The same trend was, however, not observed for catch rates when sperm whales were present during hauling (0.32 kg/hook; 51.9 fish/1000 hooks). Catch rates were in fact slightly higher in the presence of sperm whales when compared to lines with no cetacean presence. It is likely that sperm whales were attracted to areas with high catch rates, but in areas with lower catch rates indications are that depredation by sperm whales can lead to a drop-off in catches. During hook-line observations on a longliner in the 2001 season it was noted that toothfish lips on hooks were more prevalent when sperm whales were in the vicinity of the vessel, suggesting that whole fish might be ‘stripped’ off the line, leaving only the lips. This would further complicate the quantification of levels of depredation. In contrast depredation by killer whales was often characterized by the occurrence of damaged fish, with often only the heads on returning hooks, although lips were also sometimes observed when killer whales were in the vicinity. Some mitigation measures have been tried by vessels to reduce interactions with cetaceans, although no quantitative studies were done to measure their effectiveness. Further investigations are needed to determine the extent of longline-cetacean interactions, to address the problems of longlinecetacean depredation, to standardise observer protocols to ensure the collection of valuable data, and to assess and implement mitigation strategies under controlled experimental conditions.