CCAMLR

The aim of this paper is to review the management of the Ross Sea toothfish fishery and to identify key research objectives for the fishery over the next 3–5 years in relation to Article II of the Convention. The paper focuses primarily on Antarctic toothfish, as catches of Patagonian toothfish are negligible, and covers Subarea 88.1 and Subarea 88.2 SSRUs 88.2A and B. We begin by briefly summarising the management and operation of the fishery up to and including the 2012/13 fishing year. This includes the 3-year experiment from 2005/06 to 2007/08, the further development of the CCAMLR tagging programme and associated requirements, and other changes to the management of the fishery. We then identify uncertainties in our current knowledge that need to be addressed to fulfil the requirements of Article II. These include, for example, uncertainty in the biological parameters and stock assessment of Antarctic toothfish, uncertainty in its ecological relationships with predators and prey, and uncertainty over other ecosystem effects of fishing which can be addressed over the short to medium term. However, the need to further develop Management Strategy Evaluation and Management Procedures for the toothfish fishery in the medium-long term is also recognised. The purpose of this paper is to begin the discussion on medium-term research objectives for the Ross Sea fishery and the development of a medium-term research plan which could be adopted by the Scientific Committee.
 

We propose a multi-year and multi-member research plan using standardised longline gear to sample the toothfish populations in the northern areas (61° - 66° S) of SSRUs 88.2A–B. The purpose of the research as requested by the Scientific Committee (SC-CAMLR XXXII, paragraph 3.76) is to characterise the local toothfish populations found there to better understand stock structure, movement patterns and improve estimation of population characteristics by Ross Sea spatial population models. Additional outcomes of the research relate to mapping the bathymetry of the fishable area, documenting relative abundance of Patagonian and Antarctic toothfish, tagging toothfish for biomass estimation and for stock linkage studies, and collecting information on distribution, relative abundance, and life history of bycatch species.

This paper presents an analysis of data gained from an eight-year tagging programme of Patagonian toothfish (Dissostichus eleginoides) in Subarea 48.4. It describes the tagging procedure, the information gained about biology, growth and movement of Patagonian toothfish, and looks at the potential link between statistical subareas 48.3 and 48.4. The characterisation of tag recapture data from Subarea 48.4 shows that the tagging programme is successful in providing substantial information for the stock assessment.

Grenadiers (Macrourus spp.) are the main bycatch species in the exploratory longline fishery for toothfish in the Ross Sea. Previous studies concluded that acoustics methods could be used to index the relative abundance of grenadiers and be useful for exploring spatial distribution. Automated acoustic methods were developed to estimate grenadier distribution and abundance based on echo counting. These methods can be applied to large volumes of relatively low quality, opportunistically collected acoustic data. Trials using data from SSRU 88.1I showed positive correlations between acoustic targets and longline catches of grenadiers and toothfish. Single targets were most abundant within 250 m of the bottom at seabed depths of 700–1000 m, and revealed consistent spatial patterns, with higher numbers of targets on the eastern side of the Iselin Bank. The acoustic target strength distribution of single targets was similar to that predicted based on the expected size range of grenadiers. Variability in spatial coverage between years meant that it was not possible to obtain a consistent time-series of relative abundance estimates for grenadiers from acoustic data collected opportunistically by New Zealand vessels in SSRU 88.1I. The next step will be to apply to these methods to a wider set of data across the Ross Sea region.

Recommendation:
We recommend that other nations routinely collect acoustic data in the Ross Sea fishery and make this available for analysis. Collection of acoustic data from a larger pool of vessels would increase the available information, so that more consistent spatial coverage of grenadier distribution might be achieved.

Two species of grenadier are predominatly taken as bycatch in the Ross Sea region, Macrourus whitsoni and M. caml. A total of 220 otoliths from M. whitsoni and 307 otoliths of M. caml from fish taken as bycatch in the Ross Sea on New Zealand fishing vessels in the 2011–12 fishing year were used to test whether the otoliths of the two species can be discriminated. Samples of both species of macrourid were obtained from SSRUs 88.1B, 88.1C, 88.1H, 88.1J, 88.1K and from 88.2H. Lengths of M. whitsoni in the sample were 34.5–65.1 cm total length (TL), and 12.0–24.0 cm pre-anal length (PAL); lengths of M. caml in the sample were 34.5–81.5 cm TL and 11.0–30.0 cm PAL. Both males and females were included in the sample, but females predominated. A linear function of fish total length (cm), depth of the whole otolith (Depth, mm), and maximum cross-sectional area of the otolith (Area, mm²) gave excellent discrimination between the two species:

α = 1.254 + 0.03512*TL - 0.02463*Depth - 0.7668*Area

Where α<0.5 indicates M. caml and α>0.5 indicates M. whitsoni. Based on withholding data for testing in 10 folds, the multiple linear regression coefficient, R=0.776 [F(4, 522) = 272.9, p < 0.001], the proportion correctly identified was 92% (483 / 527), and the area under the receiver-operator characteristic (ROC) was 0.968. A similar discriminant function based on PAL (cm) rather than TL performed almost as well (90% correctly identified, ROC 0.97):

α = 1.330 + 0.09022*PAL - 0.02453*Depth - 0.6915*Area

There was no significant variation in the discriminant values (α) according to sex of the fish or for Subarea of capture for M. caml (CCAMLR Subareas 88.1 versus 88.2). However, there was a small but significant difference in α for M. whitsoni between subareas 88.1 and 88.2 [t(218) = 4.20, p < 0.001 ***], which provides some evidence that they could be separate stocks in the two CCAMLR Subareas.

This paper presents an analysis of data gained from nine years of tagging of Patagonian toothfish (Dissostichus eleginoides) in Subarea 48.3. In addition to providing information on tagging procedure, Patagonian toothfish biology, growth and local movement of Patagonian toothfish in 48.3 (presented in WG-SAM-14/35), it describes the spatial movements and regional connectivity in Subarea 48.3. The characterisation of tag recapture data from Subarea 48.3 shows that the tagging programme is successful in providing substantial information for the stock assessment and that it can give a first indication of spatial areas of biological interest, such as potential spawning and nursery grounds.

Elasmobranch species, such as skates (Rajiformes), are not target species within the CCAMLR longline fisheries. However, they form a major part of the bycatch and as such it is necessary to understand the effect of each fishery on the Rajiformes population. Here we describe biological information gained from the skate tag-release programme in statistical subarea 48.3 and use the tag recaptures for a simple Petersen model estimation of the population trends. The bycaught Rajiformes in subarea 48.3 are mostly one species, Amblyraja georgiana, and the Petersen estimation indicates that the stock is currently stable and has been since at least 2010.

Data from electronic archival tags are often used to characterise movement and migration patterns in fishes. Understanding these movement patterns is one of the key information needs for the assessment and management of Antarctic toothfish. We deployed 4 pop-off satellite archival tags on large toothfish on the Ross Sea slope in January 2013 and report on the first recovery of an Antarctic toothfish tagged with an archival tag. The fish was recaptured in the fishery the following season (December 24, 2013), providing 335 days of data archived at 10 min intervals. Summaries of raw data show strong and contrasting patterns throughout the time series in several variables recorded and several periods with distinct behavioural profiles, suggesting significant activity throughout the winter period. With the lack of any daylight signal resulting from constant light or darkness, along with living below the photic zone and under ice, positioning using light-based geolocation is not possible. Current efforts focus on developing a Bayesian modelling approach to fit the most likely movements of the tagged fish during its time at liberty, based on the environmental variables recorded by the tag compared with spatial environmental data on depth, temperature and magnetic field strength.

This paper investigates factors affecting the bycatch of skates (Rajiformes) and grenadiers (Macrouridae) taken by the longline fishery in statistical subarea 48.3. Bycatch was greater for vessels using autoline system than for those using the “Spanish” system, due to differences in proximity to the sea bed and type of bait used. The areas of greatest catch rates differed by area and depth range. During the period 1996–1999 skate bycatch was higher in February-March, while that of grenadiers was lower in July-August; since the limitation to a winter longline fishery there in no longer any significant seasonal variation.