Ocean Futures for the World’s Largest Yellowfin Tuna Population Under the Combined Effects of Ocean Warming and Acidification

The impacts of climate change are expected to have profound effects on the fisheries of the Pacific Ocean, including its tuna fisheries, the largest globally. This study examined the combined effects of climate change on the yellowfin tuna population using the ecosystem model SEAPODYM. Yellowfin tuna fisheries in the Pacific contribute significantly to the economies and food security of Pacific Island Countries and Territories and Oceania. We use an ensemble of earth climate models to project yellowfin populations under a high greenhouse gas emissions (IPCC RCP8.5) scenario, which includes, the combined effects of a warming ocean, increasing acidification and changing ocean chemistry. Our results suggest that the acidification impact will be smaller in comparison to the ocean warming impact, even in the most extreme ensemble member scenario explored, but will have additional influences on yellowfin tuna population dynamics. An eastward shift in the distribution of yellowfin tuna was observed in the projections in the model ensemble in the absence of explicitly accounting for changes in acidification. The extent of this shift did not substantially differ when the three-acidification induced larval mortality scenarios were included in the ensemble; however, acidification was projected to weaken the magnitude of the increase in abundance in the eastern Pacific. Together with intensive fishing, these potential changes are likely to challenge the global fishing industry as well as the economies and food systems of many small Pacific Island Countries and Territories. The modelling framework applied in this study provides a tool for evaluating such effects and informing policy development

STRIPED MARLIN FISHERY INTERACTIONS

Analysis of interactions between longline and recreational gamefish fisheries taking or tagging striped marlin off NS

WCPFC-SC5-2005/SA-IP-05

Factors influencing the size of albacore tuna sampled from the South Pacific albacore longline fisherie

A critique of the ecosystem impacts of drifting and anchored FADs use by purse-seine tuna fisheries in the Western and Central Pacific Ocean

In the Western and Central Pacific Ocean (WCPO), which accounts for over half of world tuna production, purse seine effort and catch on floating objects have increased significantly due to a rapid increase in the use of fixed and free-floating fish aggregation devices (FADs). FAD fishing has had an impact on the current status of the stocks of the three main target tunas in the equatorial WCPO, skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares) and bigeye (T. obesus). FADs have been shown to influence the behaviour and movement patterns of the three tuna species with the juveniles of each species occupying shallower habitats when associated with FADs. Aggregation of tunas around drifting objects increases their vulnerability to purse seine gear, particularly for juvenile and small size classes. Further to the impacts on the target stocks, the use of FADs has increased the vulnerability of other fishes to the purse seine method, including some shark and billfish species. Given the concern over FAD-related fishing effort on target and bycatch species, there is a need to understand how FAD use affects target and bycatch stocks. Science needs to better support management decisions are highlighted including the need to identify the magnitude of broader community-level affects

Ocean acidification has lethal and sub-lethal effects on larval development of yellowfin tuna, Thunnus albacares

Ocean acidification (OA), the process by which increasing atmospheric CO₂ is absorbed by the ocean, lowering the pH of surface waters, has been shown to affect many marine organisms negatively. It has been suggested that organisms from regions with naturally low pH waters, such as upwelling areas, could serve as models for future effects of OA and may be adapted to increased pCO₂ levels. In this study, we examined the effects of OA on yellowfin tuna, a highly pelagic species that spawns in the eastern tropical Pacific, an area that includes regions of strong upwelling events. Larvae reared at decreasing pH levels (pH 8.1, 7.6, 7.3 and 6.9) showed increasing organ damage in the kidney, liver, pancreas, eye and muscle, which correlated with decreased growth and survival. These findings complement earlier studies on organ damage in Atlantic cod and herring larvae and demonstrate that OA may have detrimental effects on fish larvae, regardless of their pre-exposure to low pH waters.7 page(s

The Potential impact of ocean acidification upon eggs and larvae of yellowfin tuna (Thunnus albacares)

Anthropogenic carbon dioxide (CO₂) emissions are resulting in increasing absorption of CO₂ by the earth׳s oceans, which has led to a decline in ocean pH, a process known as ocean acidification (OA). Evidence suggests that OA may have the potential to affect the distribution and population dynamics of many marine organisms. Early life history processes (e.g. fertilization) and stages (eggs, larvae, juveniles) may be relatively more vulnerable to potential OA impacts, with implications for recruitment in marine populations. The potential impact of OA upon tuna populations has not been investigated, although tuna are key components of pelagic ecosystems and, in the Pacific Ocean, form the basis of one of the largest and most valuable fisheries in the world. This paper reviews current knowledge of potential OA impacts on fish and presents results from a pilot study investigating how OA may affect eggs and larvae of yellowfin tuna, Thunnus albacares. Two separate trials were conducted to test the impact of pCO₂ on yellowfin egg stage duration, larval growth and survival. The pCO₂ levels tested ranged from present day (~400 μatm) to levels predicted to occur in some areas of the spawning habitat within the next 100 years (<2500 μatm) to 300 years (~<5000 μatm) to much more extreme levels (~10,000 μatm). In trial 1, there was evidence for significantly reduced larval survival (at mean pCO₂ levels≥4730 μatm) and growth (at mean pCO₂ levels≥2108 μatm), while egg hatch time was increased at extreme pCO₂ levels≥10,000 μatm (⁎intermediate levels were not tested). In trial 2, egg hatch times were increased at mean pCO₂ levels≥1573 μatm, but growth was only impacted at higher pCO₂ (≥8800 μatm) and there was no relationship with survival. Unstable ambient conditions during trial 2 are likely to have contributed to the difference in results between trials. Despite the technical challenges with these experiments, there is a need for future empirical work which can in turn support modeling-based approaches to assess how OA will affect the ecologically and economically important tropical tuna resources.12 page(s

Operationalising access to oceanic fisheries resources by small-scale fishers to improve food security in the Pacific Islands

Maintaining the level of fish consumption in Pacific Island countries recommended for good nutrition as the populations of coastal communities grow, and as coral reefs are degraded by global warming and ocean acidification, will depend on small-scale fishers catching more tuna and other large pelagic fish. Concerted research and development by regional agencies shows that nearshore fish aggregating devices (FADs) provide one way for small-scale fishers to make this transition. Although the full potential of FADs remains to be assessed, several investments to optimise their use have been identified. These investments include pinpointing the locations where FADs are likely to make the greatest contributions to nutrition of coastal communities, integrating use of FADs with other livelihood activities, and improving the designs of FADs. Where Pacific Island countries have committed to developing nearshore FAD programmes, additional investments are needed to operationalise the use of FADs, particularly in cyclone-prone countries. These investments include: 1) training in safe and effective FAD-fishing methods; 2) developing reliable ways for forecasting when tuna, and other large pelagic fish (e.g., mahi mahi and wahoo), are likely to associate with FADs and delivering this information to fishers effectively; and 3) storing spare FAD materials, boats and fishing gear in cyclone-proof containers so that FADs lost during cyclones can be replaced quickly. When combined with measures to sustain catches of coastal demersal fish, operationalising the use of nearshore FADs is expected to help several Pacific Island countries attain the food security goals of regional policy frameworks

Operationalising access to oceanic fisheries resources by small-scale fishers to improve food security in the Pacific Islands

Maintaining the level of fish consumption in Pacific Island countries recommended for good nutrition as the populations of coastal communities grow, and as coral reefs are degraded by global warming and ocean acidification, will depend on small-scale fishers catching more tuna and other large pelagic fish. Concerted research and development by regional agencies shows that nearshore fish aggregating devices (FADs) provide one way for small-scale fishers to make this transition. Although the full potential of FADs remains to be assessed, several investments to optimise their use have been identified. These investments include pinpointing the locations where FADs are likely to make the greatest contributions to nutrition of coastal communities, integrating use of FADs with other livelihood activities, and improving the designs of FADs. Where Pacific Island countries have committed to developing nearshore FAD programmes, additional investments are needed to operationalise the use of FADs, particularly in cyclone-prone countries. These investments include: 1) training in safe and effective FAD-fishing methods; 2) developing reliable ways for forecasting when tuna, and other large pelagic fish (e.g., mahi mahi and wahoo), are likely to associate with FADs and delivering this information to fishers effectively; and 3) storing spare FAD materials, boats and fishing gear in cyclone-proof containers so that FADs lost during cyclones can be replaced quickly. When combined with measures to sustain catches of coastal demersal fish, operationalising the use of nearshore FADs is expected to help several Pacific Island countries attain the food security goals of regional policy frameworks

Defining the stock structures of key commercial tunas in the Pacific Ocean II: Sampling considerations and future directions

Delineating the stock structure of highly-mobile, wide-ranging fishes subject to exploitation is a challenging task, yet one that is fundamental to optimal fisheries management. A case in point are stocks of skipjack tuna (Katsuwonus pelamis), yellowfin tuna (Thunnus albacares), bigeye tuna (Thunnus obesus) and albacore tuna (Thunnus alalunga) in the Pacific Ocean, which support important commercial, artisanal, subsistence, and recreational fisheries, and contribute roughly 70 % of global commercial tuna catches. Although some spatial and temporal structuring is recognised within these stocks, growing evidence from a range of approaches suggests that the stock structure of each tuna species is more complex than is currently assumed in both stock assessment and climate change models, and in management regimes. In a move towards improving understanding of the stock structure of skipjack, yellowfin, bigeye and South Pacific albacore tunas in the Pacific Ocean, an international workshop was held in Nouméa, New Caledonia, in October 2018 to review knowledge about their movement and stock structure in the region, define and discuss the main knowledge gaps and uncertainties concerning their stock structure, and develop biological sampling approaches to support the provision of this information. Here, we synthesise the discussions of this latter component. For each tuna species, we identify several general sampling considerations needed to reduce uncertainty, including i) the need for broadscale sampling in space, ideally covering each species’ distribution, targeting adults in spawning condition and adopting a phased approach; ii) the need for temporally-repeated sampling of the same geographical areas to assess stability in observed patterns over time; iii) the need to resolve patterns in spatial dynamics, such as those resulting from movements associated with the seasonal extensions of poleward flowing currents, from underlying stock structure, iv) the importance of adopting a multidisciplinary approach to stock identification, and v) the need for careful planning of logistics and coordination of sampling efforts across agencies. Finally, we present potential sampling designs that could be adopted to help overcome uncertainties around the initial identification of stocks and the provenance, mixing and proportional contributions of individuals in harvested assemblages, as well as how these uncertainties could be accounted for in fisheries management via the use of management strategy evaluation