Large‐scale distribution of tuna species in a warming ocean

Abstract

Tuna are globally distributed species of major commercial importance and some tuna species are a major source of protein in many countries. Tuna are characterized by dynamic distribution patterns that respond to climate variability and long‐term change. Here, we investigated the effect of environmental conditions on the worldwide distribution and relative abundance of six tuna species between 1958 and 2004 and estimated the expected end‐of‐the‐century changes based on a high‐greenhouse gas concentration scenario (RCP8.5). We created species distribution models using a long‐term Japanese longline fishery dataset and two‐step generalized additive models. Over the historical period, suitable habitats shifted poleward for 20 out of 22 tuna stocks, based on their gravity centre (GC) and/or one of their distribution limits. On average, tuna habitat distribution limits have shifted poleward 6.5 km per decade in the northern hemisphere and 5.5 km per decade in the southern hemisphere. Larger tuna distribution shifts and changes in abundance are expected in the future, especially by the end‐of‐the‐century (2080–2099). Temperate tunas (albacore, Atlantic bluefin, and southern bluefin) and the tropical bigeye tuna are expected to decline in the tropics and shift poleward. In contrast, skipjack and yellowfin tunas are projected to become more abundant in tropical areas as well as in most coastal countries' exclusive economic zones (EEZ). These results provide global information on the potential effects of climate change in tuna populations and can assist countries seeking to minimize these effects via adaptive management.

Southward re‐distribution of tropical tuna fisheries activity can be explained by technological and management change

“…However, we did not see a clear northward trend from the equator, suggesting other factors are involved. Indeed, the scale of the habitat spatial shift observed by Erauskin‐Extramiana et al () is smaller than the one of the fleet during the study period, reaffirming that other variables (e.g. management or technological variables) are also playing a role in the distribution of the fishery.…”

“…In addition to temperature, other environmental conditions might be influencing the spatial distribution of the fleet, for example upwelling systems in the study area that are expected to decline with climate change with unknown consequences to fishing communities (Sylla, Mignot, Capet, & Gaye, ). If we link the response of the fleet to what is being observed on tropical tuna species, according to Erauskin‐Extramiana et al (), tuna habitat distribution limits are already shifting poleward (on average, 6.5 km per decade in the northern hemisphere and 5.5 km per decade in the southern hemisphere). It is thus consistent to see a southward movement of the fleet over time partially explained by climate change as a response of an ecological shift.…”

“…Some models predict a biomass increase of Skipjack and YFTs in tropical areas as well as in most coastal countries’ EEZs in the long term, a decrease of BET (Dueri, Bopp, & Maury, ; Erauskin‐Extramiana et al, ) and a re‐distribution in both depth and horizontal distribution of tropical tunas (Deary et al, ; Dell et al, ; Erauskin‐Extramiana et al, ; Evans et al, ). Here, we did not take into account changes in the depth of fishing effort, but PS fishing may be more affected than other methods such as longline fisheries that can set hooks at greater depths (Marsac, ).…”

Adaptation of North Atlantic Albacore Fishery to Climate Change: Yet Another Potential Benefit of Harvest Control Rules

“…Predicted changes in ocean productivity have been used to estimate proportional changes of fish catch under CC (Lehodey et al, 2006;Cheung et al, 2010Cheung et al, , 2012Blanchard et al, 2012;Arrizabalaga et al, 2015;Errauskin-Extramiana et al, 2019; FIGURE 6 | Performance of the North Atlantic albacore fishery represented with median values of indicators of sustainability (pGreen = probability of being in the green quadrant of the Kobe plot), safety (probability of biomass staying above Blim), catch and stability (Mean Annual Proportional change of TAC). A single probabilistic estimate (median) is used to illustrate fisheries performance of sustainability, safety, catch and variability across OMs.…”

“…How CC will affect tunas in general, and North Atlantic albacore in particular, is being investigated (Dufour et al, 2010;Dueri et al, 2014;Arrizabalaga et al, 2015;Lehodey et al, 2015;Chust et al, 2019;Errauskin-Extramiana et al, 2019) and given the long life-span of albacore (compared to other tuna stocks) it is crucial to evaluate the combined influences of fishing, environmental variability and CC on this species (Dragon et al, 2015). Here, we build a series of exploratory scenarios to characterize climate impacts on North Atlantic albacore to evaluate if the HCR adopted for this stock would still be an adequate tool for achieving sustainability goals and for maintaining fisheries performance under CC.…”