The scaled sardine’s unique metabolic phenotype and its implications for the susceptibility of small tropical pelagic fishes to climate change

Small pelagic fishes (e.g., sardines, anchovies and their relatives) are preyed upon by large predatory fishes, birds and mammals, and thus, are key species in marine food webs and with respect to ecosystem health and productivity. However, we know little about their physiology, and such information will be critical to predicting how their populations may be impacted by human-induced rapid environmental change (HIREC) and in implementing effective conservation strategies. As a first step, we determined the maximum swimming speed, aerobic capacity [maximum metabolic rate (MMR) and aerobic scope (AS)] and cost of transport (COT; the energy required to swim a given distance) of scaled sardines (Harengula jaguana) collected in Eleuthera (The Bahamas). The scaled sardine's critical swimming speed (U_crit) was ~ 5-6 body length's per second, and this agrees with data collected on free-swimming schools of similar fishes in the wild. However, they had unexpectedly high values for MMR and AS (~ 25% and 70% greater than tuna, respectively), and for COT. These findings have important implications with regard to how these ecologically important fishes will potentially respond to HIREC-related challenges such as increased temperature and decreases in the biomass and size of plankton upon which they feed.