CCAMLR

Depredation is a human-wildlife conflict over resource which often includes a combination of socio-economical, ecological and conservation issues. However, estimating the amount of depredated resource can be especially challenging when depredation occurs on fish in the marine environment. This is the case for killer whales (Orcinus orca) and sperm whales (Physeter macrocephalus) depredation on the demersal Patagonian toothfish (Dissostichus eleginoides) longline fishery operating within the Crozet Islands EEZ (southern Indian Ocean). As the two species remove the entire fish from the hooks whether they depredate longline hooks separately or simultaneously, this study aimed at providing two indirect methods of assessment of depredated biomass over a 11-year period (from 2003 to 2013), both accounting for spatial variations of depredation levels. In the first method, we used fishing data from 6 525 longline sets to calculate the difference between Catch Per Unit Effort (CPUE) of non-depredated and depredated hooks. From this difference and using the fishing effort (number of hooks), we estimated that 575 ± 35 t and 739 ± 87 t of Patagonian toothfish were respectively depredated by killer whales and sperm whales when the two species occurred separately, and 1 679 ± 74 t were depredated from 2003 to 2013 when the two species co-occurred around vessels. The second method was new in a way that we used the differences of proportion of by-catch species (i.e. grenadiers – Macrourus sp.) between non-depredated and depredated longline sets to estimate the number of depredated Patagonian toothfish. This approach, which can only be implemented when a sufficient level of bycatch species occurs,  provides strong support to the CPUE method. From these two methods, depredation rates were estimated to range from 27,3% to 29.1% % of the total capture (landed + depredated), that is one of the highest among all similar depredation situations reported elsewhere in the world. In addition to providing methodology insights that could be used in other areas with such depredation issues, these findings emphasize the critical importance for fishery managers and researcher to account for depredation when assessing fish stocks, fishery economy and/or conservation of odontocetes.

Closed mostly within the Weddell Sea Subarea 48.5 is one of the closed data-poor CCAMLR subareas, where stock assessment should be carried out. In spite of hard ice conditions at most part of the Weddell Sea during most time of the year, this large water area is very similar with the Ross Sea. This similarity, which could be found in geographical location, bathymetric profile, currents system and follows from results of the first and the second stage of this program, highlight the Weddell Sea as one of the most promising area for exploratory fishery of Dissostichus sp. However, fishery in Subarea 48.5 is closed on the basis data on stock assessment absence. The main objective of the present program is collecting data for reliable stock assessment and following estimation of precautionary limits in accordance with CCAMLR decision rules. The program contains schedule and research program of the third stage of the Russian Federation multi-year research program in the Weddell Sea that are prospected for 5 years. Detailed plan of fishing operations, collecting and analysis of data will be provided for the Scientific Committee and Commission consideration.

In 2011/2012, the Saint André conducted its first exploratory fishery for Dissostichus spp. in division 58.4.3a. France notified its wish to continue this exploratory fishery over the coming years in order to achieve a robust stock assessment that would provide advice on a catch limit according to CCAMLR decision rules. This paper aims to present a research plan for 2014/2015 that takes into account the remarks made during the WG-SAM 2014. The objective is to progress on modelling tools and to improve the estimation of current biomass. The stock size in division 58.4.3a was estimated during WG-FSA 2013 using the Petersen estimator, CASAL model and the CPUE x seabed analogy method. The estimates of biomass are highly biased, because catch data used in the calculation derived from a small location at which catch rates were high, but these are extrapolated over the entire area, including to areas in which catch rates are known to be much lower. Given these results and the concentration of fishing effort, it is suggested to define a new survey design and to maintain the total catch limit of 32 tons agreed in 2012 in order to result in sufficient tag recaptures and to substantially refine the stock assessment next year. It is suggested also to define a catch limit with an appropriate local exploitation rate (4%) equivalent to 4 tons inside a research block where catches were high.

Regarding the low levels of stocks of Dissostichus spp. and the high levels of IUU fishing, CCAMLR decided to close the fishery in 2002 in division 58.4.4. Since 2008 only one vessel, Shinsei maru No. 3, has conducted research fishing in accordance with a research plan submitted under CM 24-01. France notifies its wish to collaborate in this research fishery over the coming years in order to participate in the tagging program and achieve a robust stock assessment. The aim is to provide advice on a catch limit according to CCAMLR decision rules and allow an earlier decision to reopen this area. This paper presents a research plan for 2014/2015. The stock assessments are still in development and the estimates of abundance are not sufficiently reliable to define a new catch limit. France suggests continuing with the same survey design and with the total research catch limits agreed in 2013: 25 tons for SSRU C and for 35 tons for SSRU D. It is likely to result in sufficient tag recaptures to substantially refine the stock assessment.

Regarding the low levels of stocks of Dissostichus spp. and the high levels of IUU fishing, CCAMLR decided to close the fishery in 2002 in division 58.4.4. Since 2008 only one vessel, Shinsei maru No. 3, has conducted research fishing in accordance with a research plan submitted under CM 24-01. France notifies its wish to collaborate in this research fishery over the coming years in order to participate in the tagging program and achieve a robust stock assessment. A preliminary assessment of stock status of D. eleginoides in SSRU C was made by Japan using a CASAL catch-at-length model in 2013. During the WG-SAM-2014, two developments of CASAL assessment were presented one by France and the other by Japan. The Working Group recommended that further development of the assessment should be considered. The model has not been updated with 2014 data but six new sensitive runs have been tested to highlight the contribution of IUU catch and selectivity, data weighting methods and catch-at-age or catch-at-length data. The median MPD estimates of the initial B₀ are around 500 and 900 tons and SSB₂₀₁₃ around 400 and 900 tons depending on the sensitivity run. However, MCMC estimates were significantly higher than MPD ones for each model. There was still some evidence of lack of convergence in MCMC posterior trace. The results seem to be not yet reliable and model not yet robust to use it as a management tool this year.

Odontocete depredation on longlines involves socio-economic and conservation issues with significant losses for fisheries and potential impacts on wild populations of depredating species. As technical solutions to this conflict are limited and difficult to implement, this study aimed to identify fishing practices that could reduce odontocete depredation, with a focus on killer whales (Orcinus orca) interacting with Patagonian toothfish (Dissostichus eleginoides) longliners off the Crozet islands. Data collected by fishery observers from 6,013 longline sets between 2003-2013, paired with extensive monitoring of the killer whale population allowed us to model interactions with whales, CPUE and time it takes for whales to reach vessels. The significant influence of five operational variables was detected statistically using generalized linear mixed models. The probability of interactions between vessels and killer whales was decreased by, i) the number of vessels operating simultaneously in the area: the limited number of depredating killer whales (n = 78 in 2012) may induce a dilution effect with increased fleet size, and ii) depth of longline sets: vessels operating in shallow waters (500 – 700 m) may be more accessible to whales that are initially distributed on peri-insular shelves. The CPUE was negatively influenced by, iii) length of longlines: longer sets may provide killer whales access to a greater proportion of hooked fish per set, and positively influenced by, iv) hauling speed: increased speed (> 50 hooks.min^-1) may shorten the time during which toothfish are accessible to whales due to their limited diving abilities. The time it takes for killer whales to reach vessels was positively correlated to, v) the distance travelled between longline sets with an estimated threshold of 100 km beyond which whales seem to temporarily lose track of vessels. These findings provide insightful guidelines about what fishing strategy to adopt given these variables to reduce killer whale depredation here and in similar situations elsewhere. To a greater extent, this study is illustrative of how collaborative work with fishermen in a fully controlled fishery framework, paired with extensive knowledge on wild populations, may lead to the definition of cost-limited and easy-to-implement mitigation solutions when facing such human-wildlife conflict.
 

Acoustic harassment devices (AHDs) have been increasingly implemented in various fisheries that suffer significant losses caused by odontocete depredation. However, the efficacy of AHDs to deter odontocetes from fishing gear remains poorly investigated. To determine the effectiveness of AHDs in deterring depredation we experimentally tested a high amplitude device (195 dB re 1 μPa 6.5 kHz 1 m from the source) from a Patagonian toothfish longliner operating off the Crozet Islands while it was subjected to heavy depredation by killer whales. This species usually depredates longlines within a 10 - 300 m range from the vessel, as they only have access to fishing gear during hauling. We expected this distance to increase in response to the acoustic disturbance created by the AHD. The distances of 29 killer whales from the vessel (n = 1,812 records) were collected during 45 phases of AHD activation and 30 phases during which the AHD was turned off. Two multi-exposed killer whale social units fled over 700 m away from the vessel when first exposed to the AHD. However, they remained within a 10 - 300 m range and depredated longlines again past the 1st and 7th exposures respectively showing insignificant behavioural response to further activations of the AHD. When tested through Generalized Linear Mixed Models (GLMMs), the effect of AHD activation was only significant when killer whales were first exposed to the device. However, the effect disappeared after successive exposures suggesting that killer whales became habituated to the AHD and may sustain potentially harmful hearing disturbance to access the resource made available by longliners. In addition to raising significant conservation concerns, this rapid return of initial depredation behaviour strongly suggests that AHDs are ineffective at deterring depredating killer whales and that fisheries should favour the use of other mitigation techniques when facing repeated depredation by this species.
 

Three fish biomass surveys have been recently undertaken in the northern part of the Kerguelen Plateau (POKER 1, 2006; POKER 2, 2010; POKER 3, 2013) with the chartered trawler FV “Austral” repeating the same random and stratified sampling stations in the bathymetric range 100 – 1000 m. Data on the bathymetric and geographical fish distribution are available for 19 bottom-dwelling species (13 neritic and 6 deep-sea for their upper bathymetric range).  The high number of stations (up to 200 each time) allows to be confident with the estimation of fish biomass ranging from 247 000 to 268 000 tons for a ground area of about 183 000 km². Patagonian toothfish (Dissostichus eleginoides), with up to 40% of the total biomass on the shelf and surrounding deep-sea, is the dominant species in terms of biomass but other species (Notothenia rossii, Channichthys rhinoceratus, Zanclorhynchus spinifer, Lepidonotothen squamifrons, Champsocephalus gunnari, Bathyraja eatonii) including never exploited fish form the bulk of the biomass. Local densities are often specific to some species. Previously overexploited species by the trawl fishery show clear and recent strong recovery. It is the case for mackerel icefish Champsocephalus gunnari and marbled notothen Notothenia rossii. Evolution of biomass of other unexploited species (i.e. Channichthys rhinoceratus), unrelated to fishery impact seems still unclear. Such study is the first ones taking into account all the fish components of a surveyed area in the Southern Ocean.