Page 22 - Islands Business May-June 2022

Oceans

BLEACHING DISTRESS SIGNAL

Turtle and bleached coral on Heron Island. Photo: File

By Rowena Singh sensitive to the ambient water temperature and its changes,”
says Dr Simon Nicol, SPC Principal Fisheries Scientist.
Recently we heard that widespread coral bleaching has “Each species has evolved toward an optimal range of
occurred on the Great Barrier Reef off Queensland for the temperature that can be different for larvae and adults.
fourth time in seven years. Scientists say the frequency of Fish like tuna living in the open ocean can move to find
these bleaching events mean there’s less and less chance for their preferred temperature ranges. For species that are
corals to recover. associated to a coastal habitat, it may be more difficult if
Meanwhile, rising ocean temperatures caused by climate there is no connectivity with other similar habitats offering
change is severely impacting tuna and other marine life in more appropriate water temperature. Therefore, under the
Pacific Islands waters. influence of ocean warming, the species composition and
The reliance of Pacific communities on tuna fisheries for distribution is changing. Some species move, some disappear
food and employment means the rise in ocean temperature and some other appear.”
also has a devastating impact on many Pacific people and Dr Nicol says that the changing dynamic of the Pacific’s
their families. oceanography is likely to see some latitudinal shifts in species
The rich tuna resources of the Western and Central Pacific ranges but also longitudinal shifts as habitats become more
Ocean (WCPO) also supply 60% of the world’s tuna. About half preferable on the eastern side of the Pacific and opposed to
of the catch is extracted from the waters of the 22 Pacific the western side for example.
Island countries and territories (PICTs) that span much of Ocean warming increases the stratification of surface
this large oceanic region. Four species of tuna dominate the water and thus limits the exchange and the input of nutrients
catch; skipjack, yellowfin, bigeye tuna and albacore. coming from the deeper layer, thus reducing productivity by
Environmental and fisheries agencies have projected that the phytoplankton at the basis of the food chain.
climate change could reduce the annual tuna catch from the Dr Nicol says that the combined effects of fishing, natural
combined waters of the 10 Pacific SIDS where most purse variability, long-term trends of climate change and delayed
seine fishing occurs by approximately 10% (140,000 tonnes) effects in long-living tuna species make the analyses very
by 2050, causing annual losses of 2-15% in total government complex. However, we know that tuna abundance and
revenue for many of these Pacific SIDS, and affecting the distribution are impacted by natural interannual climate
contributions of tuna fisheries to GDP. variability like the well-known El Nino / La Nina Oscillation
“The first obvious impact of climate change that is already (ENSO). Skipjack, the most tropical tuna species, follows the
well observed is ocean warming. Unlike marine mammals, eastward extension of the Pacific warm pool during an El Nino
fish are ectotherm (i.e., cold blood) animals and thus very event. Climate change is expected to cause further expansion

22 Islands Business, May-June 2022