Big Fish With a Bigger Problem: The Yellowtail Tuna Faces Difficulty in More Acidic Oceans

by Max Breitbarth

Anthropogenic emissions of carbon dioxide (CO2) have resulted in increased concentrations of CO2 in ocean waters that subsequently result in ocean acidification. Bromhead et al. (2015) explored the effects of elevated CO2 levels on the development of yellowfin tuna, Thunnus albacares in their March 2015 Deep-Sea Research article. Tuna represent some of the largest predators in the ocean, and cover vast expanses across several of the earth’s oceans—meaning the effects of ocean acidification could have ramifications for the species and their ecosystems around the world. The researchers found that ocean acidification levels have a strong negative effect on growth, hatch time, and larval survival in the experimental trials. These findings show that future ocean conditions may reduce the survivability of this fish in the future and lead to drastic marine ecosystem changes—as well as affect fishing practices by humans around the world that currently depend on yellowtail as a main source of food. Continue reading

Calculating Overfishing for Tuna and Billfish

 

by Hannah Tannenbaum

Threatened fish stocks have generally only been identified as being overfished and potentially reaching extinction once they have already been exploited and are in population decline. This makes remediation efforts for overfished stocks much more difficult, because much of the damage has already been done. Burgess et al .(2013) defined the “eventual threat index” (T), taking into consideration primary effects on overfishing potential. The variables they used to understand exploitation potential include: vulnerability, population size, average catch-per-unit effort, maximum per-capita growth rate, as well as profitability. In particular, this study examined multispecies fisheries, referring to fisheries in which there is a target species, but often the fishery affects many other species as well. Therefore they identified the “key” species as the most commercially valued, or most environmentally sensitive, and therefore the most likely to be exploited. The authors then applied the eventual threat index for historical information on four Pacific tuna and billfish populations, and were successfully able to Continue reading