A range of high value tuna species (bigeye, albacore, yellowfin, skipjack) are targeted for recreational, subsistence or commercial fishing. Globally 20 out of 22 tuna stocks have shifted poleward between the 1950s and 2000s, but a lack of baseline data for the SAOTs make it difficult to identify local trends. For example, St Helena historically has a seasonal but unpredictable catch of albacore, which prefers cooler waters; however, since 2013, St Helena has not recoded landing any albacore.
Changes to primary production associated with changes in temperature and currents have been linked to impacts on fisheries (e.g., higher catches of Illex Squid in the Falklands), though it is not possible to say if these are due to short term variability or long-term trend. Increasing temperature and loss of kelp habitat may also be affecting other important commercial species, such as Tristan rock lobster which is of high importance to the revenue of Tristan da Cunha.
The major challenge for each of the SAOTs is that the pelagic species they rely are part of wider global migratory stocks which have the capacity to be impacted by actions elsewhere.
Medium evidence, medium agreement
There is substantial global evidence of shifts in species distribution, including those of commercial value to the SAOT’s. However, a shortage or complete lack of historic baseline data for the SAOT’s limits assessment of local environmental changes and their impacts on fisheries.
There is debate over the impacts of climate change on the abundance of tuna around the SAOT’s. Some global models suggest an overall increase in abundance around Ascension, St Helena and Tristan da Cunha, whilst some using high emissions scenarios project a reduction around Ascension Island and St Helena and a slight increase for Tristan da Cunha due to changes in habitat suitability. These differences may in part be due to local effects, which would not appear in global models. For example, yellowfin tuna in St Helena show a high level of site fidelity that may increase their resilience to climate change effects.
In terms of resilience, it is necessary to consider the geomorphological features (islands, seamounts and archipelagos) of the SAOTs. These features provide ideal habitats for pelagic species to feed and could mean that species remain more tolerant to climate change, in effect providing ‘havens’ for species
If more positive scenarios are realised, the SAOTs that fish commercially could benefit from increased pelagic fisheries catches, at least in the short term. This places further importance of SOAT’s as marine protected areas/zones. There is some doubt though as to whether these small areas relative to the size of the populations would be effective in rebuilding stocks, depending on whether the stocks are resident or migratory. If less positive scenarios are realised, the reduction/loss of fisheries for all four SAOTs would be devastating as they form major parts of the territories economies (commercial and tourism), are a major source of food security and recreational/cultural traditions.
Medium evidence, low agreement
Uncertainty arises as species modelling is undertaken at a global/regional scale, data collection and studies on a more local scale may provide results of more relevance.