CCAMLR

Form used with protocol for observing warp strikes in trawl fisheries

We provide an update of the Bayesian sex and age structured population stock assessment model for Antarctic toothfish (Dissostichus mawsoni) in the Ross Sea (Subareas 88.1 and SSRUs 88.2A–B), using revised catch, CPUE, catch-at-age and tag-recapture data from New Zealand vessels. The updated reference case resulted in a much higher estimate of initial biomass, though this appeared to be almost entirely due to the impact of the catch-at-age data from the shelf fishery. Parameterising the model to better explain these data resulted in estimates of initial and current biomass that were very similar to those presented in 2005. The inclusion of the 2005 tag-release and the 2006 tag-recapture data had a small effect that slightly modified estimates from the models, suggesting that the new data had a similar pattern to that of previous years.
Preliminary models using tag-recapture data from all vessels are also presented. Inclusion of all vessels tagging data resulted in a more optimistic assessment, and was due to the increased numbers scanned but smaller increase in the reported numbers recaptured. The reason for this is unclear, however, a number of the recaptured tags were not able to be linked to a release due to non-availability of some release data from non-New Zealand vessels. Further investigation is recommended.
Overall, model fits to the data were adequate, with the tag-release and recapture data providing the most information on stock size. Monte-Carlo Markov Chain (MCMC) diagnostics suggested little evidence of non-convergence. MCMC estimates of initial (equilibrium) spawning stock abundance (B0) for the preferred model were 80 510 t (95% C.I.s 59 920–119 920 t), and current (B2006) biomass was estimated as 87% B0. Estimated yields, using the CCAMLR decision rules, were estimated to be 3046 t.

The ASPM is an integrated modeling technique used in stock assessment of different D. eleginoides fisheries (Prince Edward Islands and Patagonian Shelf) and allows fitting to many different information sources, such as catch and age and size data from fishing fleet, surveys and others abundance indexes. Last results obtained from ASPM model used to assess the D. eleginoides biomass at CCAMLR Subarea 48.3 shows an acceptable fit to CPUE series and catch-length-proportions (WG-FSA-SAM 05/5 and WG-FSA-05/73). In this paper the methodology and assumptions for the 2006 TOP assessment at CCAMLR Subarea 48.3 using ASPM are presented.

The ASPM assessment of the Prince Edward Islands toothfish resource by Brandão and Butterworth (2005) that permitted annual fluctuations about a deterministic stock-recruitment relationship is updated to take account of further catch, GLM standardised CPUE and catch-at-length information that has become available for the years 2005 and 2006. The assessment allows for a second fleet to accommodate data from a pot fishery that operated in 2004 and 2005. Updated biological parameter values for Subarea 48.3 are incorporated and lead to less optimistic results. The resource is estimated to be at about 40% of its average pre-exploitation level in terms of spawning biomass. It is suggested that it would be prudent to restrict annual legal catches to 500 tonnes or less, unless a large proportion of the catch is to be taken by pots (which avoid the cetacean predation associated with longlining). Specific issues raised at WG-FSA-SAM 2006 about this assessment are addressed.

In this paper we analyse data on the distribution of catches, the size of krill and bycatch of larval fish taken by the Saga Sea fishing with continuous trawls in 2006, and the Atlantic Navigator which fished in 2005 using both continuous trawling and conventional trawling. The sizes of krill caught by both conventional and continuous trawling techniques appear to be very similar. Although there are few data for comparison, the bycatches of larval/juvenile fish in the continuous trawl also appear to be the same as those from conventional trawls.

Two vessels, the Argos Helena (UK) and the San Aspiring (New Zealand), fished around the South Sandwich Islands (Subarea 48.4) in 2006 following one vessel, the Argos Helena, fishing in 2005. During this time animals were tagged in order to continue a mark-recapture programme started in 2005 to assess the toothfish population. We present an analysis of the catch and tagging data and a proposal for continuing research in this area in 2007.

This paper presents new results and estimation bias analyses for a Bayesian mark-recapture model, applied to the South Georgia toothfish tagging data. The updated model incorporates the data from all the analysed cohorts in the estimation routine, and we examine the potential estimation bias, using simulated data. The results confirm earlier findings, with lower estimates of natural and fishing mortality, for the given age range, than are assumed and predicted by the current assessment, respectively. Also, we find some apparent estimation bias, which is similar, but lower than is seen in similar mark-recapture models of this type. Given the increasing number of releases and recaptures in all the current tagging programs, we suggest that this type of modelling approach can serve as both a useful tool for estimating key parameters like natural mortality, as well as a method for comparing parameter estimates of the exploitation rate predicted by the full assessment models, currently being implemented.

1. As requested by SAM-2006, we provide a reference assessment for toothfish in Subarea 48.3. We provide sensitivity runs that include revised maturity and catch weighted proportion at length data. We additionally provide a sensitivity run which examines uncertainty in IUU catches from 1995, as requested by the Joint Assessment Group.
2. Also as requested by SAM-2006, we provide a review of CPUE trends and construct a model that uses age-based observations, specifically estimates of catches at age derived from otolith examination of a random sample of the catch.
3. All the assessments suggest that the SSB is now at or close to 50% of its unexploited level. Simple MPD projections suggest that catches in the region 3300 – 3600 t would be consistent with CCAMLR decision rules.

Minimizing the time gear is available to seabirds by increasing the sink rate of longlines is one method to effectively reduce seabird catch rates. We fished normal unweighted longlines (UW) and integrated weight longlines (IW-50 g/m) with and without paired streamer lines (PS) in seabird mitigation trials targeting Pacific cod in the Bering Sea, Alaska, USA. Our objective was to evaluate IW as a practical seabird mitigation device using multiple criteria: catch rates of seabirds and fish, seabird behaviour, sink rate of the gear and breaking strength.
All mitigation technologies dramatically decreased seabird bycatch rates while having little to no effect on fish catch rates. Sink rate measurements demonstrated that IW longlines reduce risk to seabirds by minimizing the distance astern that birds have access to sinking baits (~50% reduction). This study and our data from 2000 and 2002, also clearly show that the sink rate varies dramatically by vessel.
Through independent tests, we determined that IW breaking strength is 5% less than UW for new gear and 13% less for gear fished for five months; however, this difference did not manifest itself in the context of commercial fishing as increased line separations.
We conclude that IW longlines deployed with paired streamer lines is the best mitigation practice available for autoline longline systems and make recommendations for modifications to CM 24-02 and CM 25-02.

The biennial South Georgia Groundfish Survey was undertaken in January 2006 on board the FPRV Dorada. Sixty-three random trawls were undertaken, with 12.3 tonnes of mackerel icesfish caught, which produced biomass estimates of between 91000 and 117000 tonnes. The catches were dominated by fish of 20-25 cm (putative 2+), but unusually large numbers of fish of ~ 50 cm were also caught to the N and NE of South Georgia. Fish in spawning condition (Stage IV) were found at the eastern end of the island and at Shag Rocks. Spent fish were found throughout the survey area, suggesting that spawning may occur from December. The diet of icefish was dominated by Antarctic krill (82 % by weight), with Antarctomysis sp. (A. ohlini and A. maxima) and Themisto gaudichaudii the other main prey species Toothfish catches (548 kgs) were dominated by the same single cohort that was first detected as putative 1+ fish in 2003. The toothfish diet was dominated by Patagonotothen guntheri. Acoustic observations were made in association with both demersal and pelagic data and will help discriminate icefish from other scatterers.