CCAMLR

The CCSBT Ecologically Related Species Working Group held its 5th meeting in Wellington in February 2004. This report provides a summary of the discussion and outcomes of that meeting from the IMAF nominated observer at the meeting.

Two molecular methods, mitochondrial DNA and introns, were used to determine genetic relationships among Antarctic toothfish, Dissostichus mawsoni, samples from three CCAMLR areas 48.1, 88.1, and 58.4.2. D. mawsoni appeared to be characterized 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 out of seven introns digested with the restriction enzymes, but there was no population differentiation among the three sea areas. While direct sequencing of cytochrome b (665 base pair) showed virtually no variation, sequences for ~600 bp of the left domain of the control region showed nucleotide variation with some haplotypes restricted to sea areas. The weak genetic differentiation is supported by oceanic gyres, which may act as juvenile retention systems, and by limited movement of adult tagged fish. It is recommended that the Ross Sea D. mawsoni be treated as a separate stock unit.

The stomach contents of 496 Antarctic toothfish (Dissostichus mawsoni) captured by bottom longline in the western Ross Sea during the 2003 summer fishing (from Dec 2002 to Jun 2003) season were analysed. Fish sampled were caught in 770-1890 m depths and ranged between 72–212 cm in total length. D. mawsoni feeds on a wide range of prey but is primarily piscivorous. The most important prey species was Whitson’s grenadier (Macrourus whitsoni), which dominated the overall diet. In continental slope waters, M. whitsoni, the icefish Chionobathyscus dewitti, eel cods (Muraenolepis spp.) and cephalopods predominated in the diet, while on oceanic seamounts M. whitsoni, violet cod (Antimora rostrata) and cephalopods were important.

Icthyoplankton sampling was carried out by the New Zealand bottom longliner Avro Chieftain in the Ross Sea Sub Area 88.1 in the 2002-03 fishing year. Four direct haul samples were taken with a UNESCO WP2 net to a maximum depth of 1620 m in areas where mature D. mawsoni had been observed. No Dissostichus eggs or larvae were observed. Larvae of Kreffichthys anderssoni and Electrona antarctica, and two unidentified egg types were found.

X-rays of vertebral half-centra, and X-rays and transmitted white light examination of caudal thorns, were used to estimate the ages of 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 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. Von Bertalanffy growth curves are provided for females, males, and both sexes combined. There was no obvious difference between the sexes, so the 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. Applying this growth curve to the estimated lengths at maturity for males and females (64 cm 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.

A number of morphological and reproductive measurements made on Antarctic toothfish Dissostichus mawsoni over the four summer seasons from 2000-01 to 2003-04 aboard the autoliner San Aotea II have been analysed. Summer seasons are defined here as the period from mid December to the beginning of April. Results of this study indicate measurable differences in a number of indices from toothfish found on the Ross shelf proper, as distinct from those sampled on the more isolated seamounts and features to the north.. These differences are fish body condition factor, reproductive development, sex ratio, and length modal distribution. D. mawsoni samples from the northern region showed that this section of the population was more advanced in reproductive development, were in poorer condition, showed a consistent and significant higher ratio of males to females, and showed a unimodal length distribution at a consistent peak over all seasons in comparison with the southern group in which the distribution was multimodal.

Two regions of the mitochondrial DNA, part of the cytochrome b gene and the control region, were sequenced in specimens of Antarctic skates from the Ross Sea (Pacific Ocean sector), the Australian Antarctic Territory (Indian Ocean sector), and around Elephant Island and the South Shetland Islands (Atlantic Ocean sector). Based on the DNA results, the species of Bathyraja referred to as B. eatonii in the Ross Sea appears to be a discrete sister species to B. eatonii from the Atlantic sector. In contrast, the DNA results for the undescribed species Bathyraja n. sp. would suggest that this species is common to the Atlantic and Pacific (Ross Sea) Ocean sectors. Two specimens of B. maccaini from the Atlantic sector and Indian Ocean sector appeared similar.

In this paper we describe in situ observations on nesting by the Scotia Sea (or blackfin) icefish Chaenocephalus aceratus that constitute the first substantive evidence of egg brooding and parental care by species of the family Channichthyidae. These novel observations are enriched by descriptions of the seafloor community that is impacted by fish nesting. Given the vulnerability of spawning grounds and their associated megafauna to damage by bottom trawling and the associated impact on recruitment to adult fish populations, we argue that appropriate management of icefish fisheries must exclude or severely restrict fishing techniques that damage the seabed.

A toothfish fishery has operated during the Antarctic summer (December - May) from 1997 to 2004, in Subareas 88.1 and 88.2. A preliminary standardised analysis of toothfish CPUE (catch (kg) per baited hook per set) carried out in 2003 compared two alternative toothfish CPUE analyses for the 1998 to 2003 seasons for Subarea 88.1.
This report revises and updates the previous analysis with the addition of data from the 2004 season using data sets based on all vessels and the two main New Zealand vessels that have been in the fishery over the entire time period. However, the fishing grounds were changed to reflect the new SSRUs used to manage the fishery, and the larger regions used to assess the fishery (Dunn et al. 2005). It also examines alternative approaches to modelling catch and effort data by using mixed-effect models following Candy (2003).
The variables entering each of the three models were similar and all explained a reasonable amount (35-46%) of the variation. The variables included in the analysis are plausible, but the models may be influenced by extreme values of soaktime and depth that reflect the exploratory nature of the fishery. Model diagnostics show a reasonable pattern in the residuals for all models, but the quantile-quantile plots indicate a deviation from the normal distribution of the residuals at either end for the lognormal GLM models, and at the lower end for the fixed effects of the mixed model. This suggests that extreme values of catch rate were not modelled well and there may be violations of model assumptions.
The CPUE indices showed consistent trends in all three models. The indices were essentially flat apart from a slight decline in 2001 and a large decline in 2004. The reason for the large decline is unclear, but may reflect the bad ice conditions in 2004 as well as increasing competition between the large number of vessels operating in the fishery.
The relationship between these indices and relative abundance is unknown, and fishery independent data are unavailable to validate this relationship. Continued monitoring of CPUE for the main grounds and main vessels is recommended. Also further research on other possible CPUE models, and inclusion of first order interactions in the analysis is suggested. Research into suitable methods for validating the relationship between CPUE seasonal indices and the relative abundance of toothfish is also recommended.

The National Marine Fisheries Service (NMFS) contracted with the International Pacific Halibut Commission (IPHC) for a project examining the feasibility of electronic monitoring systems (EMS) in the Pacific halibut longline fleet operating off the state of Alaska. The project was conducted on two of the IPHC stock assessment survey vessels fishing in Alaska during 2002. The objectives of the project were to: 1) examine the ability of an electronic monitoring system to provide images that would allow an analyst to monitor seabird avoidance devices for regulatory compliance; 2) determine the feasibility of using video images for detecting and identifying incidentally-caught seabirds; and 3) discuss options for the future use of electronic monitoring as a fishery management tool.
To determine if EMS could be used to assist in compliance determination, an EMS system was installed on two halibut longline vessels chartered by the IPHC. Cameras were placed on the stern and recorded images of halibut gear being set and the performance of seabird avoidance devices, or streamer lines, during the setting. Vessel and video observations were compared on 106 setting events. The video observations determined that the EMS was successful in detecting streamer line deployment and relative position on 100% of the daytime sets when two setting cameras were operating together. The results of the streamer line performance evaluations suggest that accurate performance recognition was positively related to the increase in image recording speed and the video analysts’ ability to distinguish measured interval markings that were attached to the streamer lines.
The ability of a video analyst to recognize and identify the species of retrieved seabirds was examined by intentionally setting previously-caught frozen seabirds on the fishing gear. No birds were caught incidentally during this study. The results indicated that correct seabird identification is related both to the analyst’s knowledge of distinguishing species characteristics, and to the size of the seabird.
In conclusion, this study indicates that an EMS monitoring program would produce accurate data and enable compliance evaluations for seabird avoidance devices. In addition, an EMS program would be able to detect a high proportion of incidentally caught seabirds. However, additional work is needed on seabird image identification and verification methods and testing the effects of soak time on the physical characteristics of seabirds.