Patagonian Toothfish Fishery Research Articles

The effect of prey abundance and fisheries on the survival, reproduction, and social structure of killer whales (Orcinus orca) at subantarctic Marion Island.

Most marine apex predators are keystone species that fundamentally influence their ecosystems through cascading top-down processes. Reductions in worldwide predator abundances, attributed to environmental- and anthropogenic-induced changes to prey availability and negative interactions with fisheries, can have far-reaching ecosystem impacts. We tested whether the survival of killer whales (Orcinus orca) observed at Marion Island in the Southern Indian Ocean correlated with social structure and prey variables (direct measures of prey abundance, Patagonian toothfish fishery effort, and environmental proxies) using multistate models of capture-recapture data spanning 12 years (2006-2018). We also tested the effect of these same variables on killer whale social structure and reproduction measured over the same period. Indices of social structure had the strongest correlation with survival, with higher sociality associated with increased survival probability. Survival was also positively correlated with Patagonian toothfish fishing effort during the previous year, suggesting that fishery-linked resource availability is an important determinant of survival. No correlation between survival and environmental proxies of prey abundance was found. At-island prey availability influenced the social structure of Marion Island killer whales, but none of the variables explained variability in reproduction. Future increases in legal fishing activity may benefit this population of killer whales through the artificial provisioning of resources they provide.

Spatially explicit food web modelling to consider fisheries impacts and ecosystem representation within Marine Protected Areas on the Kerguelen Plateau

Abstract The Kerguelen Plateau in the Indian sector of the Southern Ocean is a highly dynamic region for Southern Ocean ecosystems and an important region for the Patagonian toothfish fishery. Fished regions overlap with foraging regions for predators; however, no study has explored the spatial impacts of fishing on ecosystem dynamics. We developed two spatially explicit ecosystem models to (i) explore the spatial effects of fishing on the Patagonian toothfish and the ecosystem in scenarios with and without fishing; and (ii) use modelled distributions to compare ecosystem representation in Marine Protected Areas (MPAs) with existing studies. Consistent with other studies, we found decreases in Patagonian toothfish biomass in scenarios with fishing activity. In contrast, we found no spatial fishing impacts on ecosystem interactions. A majority of functional group distributions were positively correlated with phytoplankton and well distributed within no-take areas. This could indicate a high level of representation of species in MPAs. Our study provides valuable insights into spatial ecosystem dynamics on the Kerguelen Plateau; however, our interpretations were limited and more research is needed to disentangle the natural variation from fishing impacts and further explore spatio-temporal changes in phytoplankton on the ecosystem.

Mitigating the impact of longline fisheries on seabirds: Lessons learned from the South Georgia Patagonian toothfish fishery (CCAMLR Subarea 48.3)

Seabird mortality in fisheries is a global problem and a major driver of the continued decline of many seabird populations. Unless appropriate mitigation is in place, longline fishing can cause high levels of seabird mortality. Here we describe the development and implementation of seabird mitigation measures in the Patagonian toothfish Dissostichus eleginoides fishery around the sub-Antarctic islands of South Georgia (CCAMLR Subarea 48.3), since the fishery began in the late 1980s. The initial high bycatch mortality (>5000 birds / 0.59 birds per 1000 hooks in 1996) has been reduced to negligible levels (<0.01 per 1000 hooks) through implementation of a suite of mitigation measures and a high level of compliance. The principal species killed in the fishery were black-browed albatross and white-chinned petrels, with most of the mortality occurring in April and early May. Whilst the synchronous introduction of much of the mitigation makes it is difficult to confirm which measures have been most effective, there is compelling evidence that the restriction of the fishery to the austral winter was a major factor. Night-setting and line-weighting measures have also been important in reducing mortality and the 100% observer coverage in the fishery has encouraged high levels of compliance. We also consider how different measures may be effective for different species and how novel measures, such as the use of marked hooks, have helped encourage compliance. The mitigation measures developed in the South Georgia fishery have subsequently been adopted in other CCAMLR fisheries and have helped guide global best practice in addressing seabird bycatch.

Decadal changes in plastic litter regurgitated by albatrosses and giant petrels at sub-Antarctic Marion Island

Plastic ingestion by seabirds is an efficient way to monitor marine plastics. We report temporal variation in the characteristics of marine litter regurgitated by albatrosses and giant petrels on sub-Antarctic Marion Island between 1996 and 2018. Both fishery and other litter peaked during the height of the Patagonian toothfish fishery around the island (1997–1999). Comparing the two subsequent decades of reduced fishing effort (1999–2008 and 2009–2018), fishing litter decreased while other litter increased across all species. Litter increased most in grey-headed albatrosses, followed by giant petrels and wandering albatrosses. Similar ranked responses were found in the same species at South Georgia, but non-fishery-related litter has increased faster in the Indian Ocean than the southwest Atlantic, indicating regional changes in litter growth rates. These seabirds' regurgitations provide an easy, non-invasive way to track changes in oceanic litter in a remote area that is otherwise difficult to monitor.

The role of uncertainty in the design of sustainable and precautionary management strategies for fisheries

AbstractEnvironmental variability has a strong influence on marine fish stocks. Thus, management and harvest policies based on deterministic indicators, such as maximum sustainable yield (MSY), may be inappropriate facing such uncertainties. In this study, we investigate the long‐term behavior of a single‐species fishery, whose stock is harvested by several fleets and affected by variability in the recruitment. The dynamics of this population is modeled by a discrete‐time stochastic age‐structured model. In this context, we introduce the concepts of maximum expected, log expected, and harmonic expected sustainable yield, as biological reference points. We illustrate these concepts with a case study of the Patagonian toothfish fishery in Chile and Argentina. Via Monte‐Carlo simulations, we verify that high levels of variability have a negative effect on all these maximum expected reference points, which suggests the need to be more cautious when large levels of variability on recruitment impact the fishery. Our simulations show that the deterministic MSY may not be attained in the presence of environmental noise, and therefore its use may lead to a failure of management strategies or rebuilding plans.Recommendations for Resource Managers For sustainable harvest, proper accounting of stochasticity in recruitment dynamics is necessary. For high levels of volatility, the use of deterministic reference points to develop regulations, such as maximum sustainable yield (MSY), may lead to overexploitation and even a possible extinction of the fishery. We extend the MSY to the stochastic age‐structured framework by means of maximum expected stationary yield, maximum expected log‐sustainable yield, and maximum expected harmonic sustainable yield, which can be used as precautionary reference points. These three maximum expected yields and their respective optimal fishing mortalities decrease when the variability of fish recruitment increases. This stresses the need to be more cautious in presence of volatility.

Passive acoustic monitoring to assess depredation of killer whales on demersal longlines during soaking

Toothed whales feeding on fish caught on longlines is a growing issue worldwide. This issue named depredation has a serious socio-economic impact and raise conservation questions. In the French Patagonian toothfish fishery (Southern Ocean), a good understanding of the depredation behavior by killer whales is urgently needed to find adequate mitigation solutions. However, depredation on demersal longlines has been historically assessed from surface observation during hauling phases, thus the underwater dimension of depredation is not understood. Here, we used passive acoustic monitoring to record echolocation activity of killer whales and fishing vessels’ acoustic signatures during the fishing activity. Fixed hydrophone deployed on soaking longlines without any fishing activity nearby has recorded echolocation sounds. These recordings suggest that killer whales were feeding within the vicinity of longlines and thus very likely depredating on soaking longlines. Additionally, we also investigated fishing vessels’ acoustic signatures. We observed differences of acoustic cues emitted by the vessels between the setting and hauling phases. This suggests that killer whales may be able to recognize the boat activity and therefore localize longline positions to depredate.

How do seabirds modify their search behaviour when encountering fishing boats?

Seabirds are well known to be attracted by fishing boats to forage on offal and baits. We used recently developed loggers that record accurate GPS position and detect the presence of boats through their radar emissions to examine how albatrosses use Area Restricted Search (ARS) and if so, have specific ARS behaviours, when attending boats. As much as 78.5% of locations with a radar detection (contact with boat) during a trip occurred within ARS: 36.8% of all large-scale ARS (n = 212) and 14.7% of all small-scale ARS (n = 1476) were associated with the presence of a boat. During small-scale ARS, birds spent more time and had greater sinuosity during boat-associated ARS compared with other ARS that we considered natural. For, small-scale ARS associated with boats, those performed over shelves were longer in duration, had greater sinuosity, and birds spent more time sitting on water compared with oceanic ARS associated with boats. We also found that the proportion of small-scale ARS tend to be more frequently nested in larger-scale ARS was higher for birds associated with boats and that ARS behaviour differed between oceanic (tuna fisheries) and shelf-edge (mainly Patagonian toothfish fisheries) habitats. We suggest that, in seabird species attracted by boats, a significant amount of ARS behaviours are associated with boats, and that it is important to be able to separate ARS behaviours associated to boats from natural searching behaviours. Our study suggest that studying ARS characteristics should help attribute specific behaviours associated to the presence of boats and understand associated risks between fisheries.

Evidence of deep-sea interactions between toothed whales and longlines.

Toothed whales (odontocetes) feeding on fish caught on hooks in longline fisheries is a growing issue worldwide. The substantial impacts that this behaviour, called depredation, can have on the fishing economy, fish stocks and odontocetes populations, raise a critical need for mitigation solutions to be developed. However, information on when, where and how odontocete depredation occurs underwater is still limited, especially in demersal longline fisheries (fishing gear set on the seafloor). In the present study, we investigated depredation by killer whales (Orcinus orca) and sperm whales (Physeter macrocephalus) on demersal longlines in the French Patagonian toothfish fishery (Southern Ocean). Using a combination of animal-borne behavioural and longline-attached data loggers, we demonstrated that both species are able to depredate longlines on the seafloor. This study, therefore, suggests that odontocetes whales-longline interaction events at depth may be unrecorded when assessing depredation rates from surface observations during hauling phases only. This result has implications for the management of fisheries facing similar depredation issues as underestimated depredation rates may result in unaccounted fish mortality in fish-stock assessments. Therefore, while further research should be conducted to assess the extent of deep-sea whale-longline interaction events during soaking, the evidence that depredation can occur at any time during the whole fishing process as brought out by this study should be considered in future developments of mitigation solutions to the issue.

Shaping sustainability of seafood from capture fisheries integrating the perspectives of supply chain stakeholders through combining systems analysis tools

Abstract Seafood from capture fisheries can be assessed in many ways and for different purposes, with sometimes divergent views on what characterizes “sustainable use”. Here we use two systems analysis tools—Ecological Risk Assessment for Effects of Fishing (ERAEF) and Life Cycle Assessment (LCA)—over the historical development of the Australian Patagonian toothfish fishery at Heard and McDonald Islands since the start in 1997. We find that ecological risks have been systematically identified in the management process using ERAEF, and with time have been mitigated, resulting in a lower risk fishery from an ecological impact perspective. LCA inventory data from the industry shows that fuel use per kilo has increased over the history of the fishery. Our results suggest that LCA and ERAEF may provide contrasting and complementary perspectives on sustainability and reveal trade-offs when used in combination. Incorporation of LCA perspectives in assessing impacts of fishing may facilitate refinement of ecosystem-based fisheries management, such as improved integration of the different perspectives of supply chain stakeholders.

Interactions between ageing error and selectivity in statistical catch-at-age models: simulations and implications for assessment of the Chilean Patagonian toothfish fishery

Abstract In age-structured fisheries stock assessments, ageing errors within age composition data can lead to biased mortality rate and year-class strength estimates. These errors may be further compounded where fishery-dependent age composition data are influenced by temporal changes in fishery selectivity and selectivity misspecification. In this study, we investigated how ageing error within age composition data interacts with time-varying fishery selectivity and selectivity misspecification to affect estimates derived from a statistical catch-at-age (SCA) model that used fishery-dependent data. We tested three key model parameters: average unfished recruitment (R0), spawning stock depletion (Dfinal), and fishing mortality in the terminal year (Fterminal). The Patagonian toothfish (Dissostichus eleginoides) fishery in southern Chile was used as a case study. Age composition data used to assess this fishery were split into two sets based on scale (1989–2006) and otolith (2007–2012) readings, where the scale readings show clear age-truncation effects. We used a simulation-estimation approach to examine the bias and precision of parameter estimates under various combinations of ageing error, selectivity type (asymptotic or dome-shaped), selectivity misspecification, and variation in selectivity over time. Generally, ageing error led to overly optimistic perceptions of current fishery status relative to historical reference points. Ageing error generated imprecise and positively biased estimates of R0 (range 10 to &amp;gt;200%), Dfinal (range −20 to &amp;gt;100%), and Fterminal (range −15 to &amp;gt;150%). The bias in Dfinal and R0 was more severe when selectivity was dome-shaped. Time-varying selectivity (both asymptotic and dome-shaped) increased the bias in Dfinal and Fterminal, but decreased the bias in R0. The effect of ageing error was more severe, or was masked, with selectivity misspecification. Correcting the ageing error inside the SCA reduced bias and improved precision of estimated parameters .

Long-term studies of Crozet Island killer whales are fundamental to understanding the economic and demographic consequences of their depredation behaviour on the Patagonian toothfish fishery

AbstractThis paper provides a synthesis of results obtained as part of a long-term collaborative study involving biologists, fishers, and resource managers—centring on the occurrence of killer whales in the Crozet Archipelago before and after the implementation of a demersal longline fishery for Patagonian toothfish. Depredation behaviour was reported as soon as the fishery was initiated, with dramatic effects on both the demographic trajectories of the killer whales and on the amount of fish lost by the fishers. Killer whales interacting with the fishery exhibited very high mortality rates when illegal fishing took place, while killer whales not interacting were unaffected. However, after illegal fishing ended, killer whales interacting with the fishery exhibited both higher fecundity and survival rates compared with killer whales not interacting. Since whales typically removed fish entirely from the hooks, an adapted methodology that did not rely on determining the number of damaged fish was developed to estimate depredation rates. In the Crozet EEZ over a 10-year period, 33.9% of the total amount of Patagonian toothfish caught, representing a total of 28 million €, was estimated to be lost due to the combined effects of killer whale and sperm whale depredation. In an effort to reduce depredation losses, modifications to fishing methods, such as changing the fishing season, changing fishing areas when exposed to depredation and changing longline length and hauling speed were successfully tested. Acoustic deterrent devices were ineffective in deterring killer whales from depredating longlines. Alternative fishing gears, such as fish pots, were also tested. However, while providing encouraging results regarding the suppression of depredation and seabird bycatch, fish pots were not efficient enough to sustain an economically viable fishery. In conclusion, we discuss how the findings of this comprehensive study can be used elsewhere in fisheries confronted with depredation.

Influence of artificial food provisioning from fisheries on killer whale reproductive output

AbstractPrey availability is a critical factor influencing demographic trajectories of long‐lived, top predators, which may therefore be strongly affected by artificial food provisioning. In the Crozet archipelago, killer whales feed on a wide range of species including birds, marine mammals and fish. Following the development of the Patagonian toothfish fisheries in 1996, killer whales began to also depredate longlines. Social groups, hereafter referred to as matrilines, exhibited different levels of interaction; some were involved in most of the depredation events, while others were never observed interacting with fisheries. These differences in interaction levels influenced reproduction. An extensive photo‐identification effort from 2003 to 2012 allowed us to estimate the probability of calving for 21 reproductive females. Using multi‐model inference, we found a positive effect of depredation on female calving rate. These results suggest an effect of artificial food provisioning on female reproductive output with potentially far‐reaching consequences on the demography of the Crozet killer whale population. Our findings evidence the need to account for both intra‐population heterogeneity and level of interaction with fisheries when assessing conservation strategies of long‐lived marine predators involved in similar depredation worldwide.

Economically Optimal Management Strategies for the South Georgia Patagonian Toothfish Fishery

Abstract The fishery for Patagonian toothfish around the island of South Georgia in the Southern Ocean is a profitable operation targeting a high-value, slow-growing species. We substituted the complex Bayesian age-structured model currently used for assessments with a Schaefer production model, which performs equally well as an operating model for management strategy evaluation. Our analysis demonstrated that optimum long-term profitability using a discount rate of 2% would be achieved at a biomass of 59% of initial biomass, which is higher than the target biomass of 50% incorporated into the current management strategy, and at a reduction in effort of approximately 19%. A number of potential effort reduction strategies are investigated, several of which would achieve better conservation objectives and higher future profits from the fishery than those predicted using the current management strategy. JEL Classification Codes: Q22, Q28

남동대서양 파타고니아이빨고기(Dissostichus eleginoides)의 분포

Patagonian toothfish(Dissostichus eleginoides) was investigated in the southeastern Atlantic Ocean during the period of 19 March to 7 July 2007 by commercial bottom longliners. The number of 116 hauls were carried out individually in this study area by two bottom longliners during 111 days. The total catches were 89,559kg(9.91kg/100hooks) and 66,758kg(7.38kg/100hooks), respectively. Most Patagonian toothfishes were caught on the <TEX>$46-48^{\circ}S$</TEX>, <TEX>$6-11^{\circ}E$</TEX> of southeastern Atlantic Ocean. Patagonian toothfish comprised 67.01-92.49%(by weight) of the catches in the southeastern Atlantic Ocean. No Antarctic toothfish (Dissostichus mawsoni) was caught during the surveys. Patagonian toothfish was found throughout the experimental area, but the density was considerably greater in the layer of 1,300-1,900m, where 49.88% of the fishes were caught. Smaller fishes were generally distributed to the shallow waters and larger fish were more frequently caught with the depth. Mean size of Patagonian toothfish increased with depth of capture. Accordingly economically profitable fishing activities for the Patagonian toothfish fishery requires an understanding of the size distribution of the Patagonian toothfish by depth.

The Patagonian toothfish fishery in Falkland Islands’ waters

Abstract This paper examines and provides updated information on the status of toothfish stocks within Falkland Islands conservation zones and also provides a historical perspective of the fishery. The Patagonian toothfish has been taken as a bycatch since the trawl fishery was established in the Falkland Islands. However, specialised exploitation of the Patagonian toothfish started with the opening of the Falkland Islands Outer Conservation Zone (FOCZ) in 1994 when demersal longliners started to target this species at depths of greater than 600 m. When compared to trawlers, analysis showed that longline catches were higher in weight but not numbers. Generally longline catches comprised fish of greater than their length at 50% maturity whereas this situation is rare in catches taken by trawlers. Longliner CPUE peaked in the first year of the fishery and gradually declined until 2000–2001 after which it remained relatively stable with a small increase in 2003–2004. The latter is attributed to a strong year class born in 1994. Toothfish recruitment in the Falkland Islands was found to be very variable. Strong year classes seem to occur every 4–5 years. The mean size of toothfish has decreased since the onset of the longline fishery. This decrease mainly occurred between 1994 and 1999, since then the size of toothfish in catches has remained relatively stable. Fox and Schaefer production models show a strong decline in biomass with the current stock size at about 50% of its unexploited state. It is concluded that the fishery is still just within its limits of sustainable use.

Foraging ecology and interactions with fisheries of wandering albatrosses (Diomedea exulans) breeding at South Georgia

AbstractKnowledge about the areas used by the foraging wandering albatross, Diomedea exulans, its prey and overlap with longline fisheries is important information not only for the conservation of this species but also for furthering our understanding of the ecology of its prey. We attached satellite‐tracking devices and activity recorders to wandering albatrosses between May and July of 1999 and 2000 (years of differing food availability around South Georgia) in order to assess inter‐annual variation in the main foraging areas, association with oceanographic features (i.e. fronts, bathymetry), diet and interactions with fisheries. The overall foraging patterns of the tracked birds were similar in 1999 and 2000, ranging between southern Brazil (28°S) and the Antarctic Peninsula (63°S) and between the waters off Tristan da Cunha (19°W) and the Patagonian Shelf and oceanic waters south of Cape Horn (68°W) in the South Atlantic. In 1999, wandering albatrosses spent most time in sub‐Antarctic oceanic waters, their trip durations were significantly longer and they fed on fish and cephalopods (53 and 42% by mass, respectively). In contrast, in 2000, they spent more time in Antarctic waters, foraging trips were shorter and the diet was predominantly fish (84% by mass). Wandering albatrosses were associated with the sub‐Antarctic Front (SAF; both years), Subtropical Front (STF; in 1999) and the Tropical Front (TF; in 2000) suggesting that this species exploits prey concentrated at oceanic fronts. Fisheries discards also seemed to provide a very good source of food. Several fish species that are targeted (e.g. Patagonian toothfish, Dissostichus eleginoides) or are available as offal/discards from commercial fisheries (e.g. the macrourids, Antimora rostrata and Macrourus holotrachys) were mainly associated with the South Georgia shelf and the Patagonian Shelf, respectively. Wandering albatross foraging areas overlapped with longline fisheries in three different regions: around South Georgia, at the Patagonian Shelf and in oceanic waters north of 40°S. Females commuted more frequently to the Patagonian Shelf and to oceanic areas where longline fisheries were operating. Males, on the other hand, spent more time on the shelf/shelf slope of South Georgia where they were more at risk from the local Patagonian toothfish fishery, particularly in 2000. These results emphasize that inter‐annual variation in foraging preferences could lead to increased incidental mortality of this vulnerable species. Potential evidence for this is provided by a satellite‐tracked wandering albatross (male; 1.8‐day trip), whose diet contained a Patagonian toothfish head and a longline hook, and who spent extensive time in the water (44% of the time wet; 0.3 days of the trip) where a Patagonian toothfish longline fishing vessel was operating.