Sardines are small, oily forage fish that swim in massive schools across the world’s oceans. The term “sardine” is a common name used for many different species, such as the European Pilchard or the Pacific Sardine. Occupying a low trophic level, they are a primary food source for larger marine life, contributing to their fast-paced life cycle. Their lifespan in the wild is highly variable and relatively short compared to many other fish.
The Typical Lifespan of Sardines
The average lifespan for most sardine populations is brief, typically falling within a range of three to five years. These fish reach sexual maturity quickly, often within their first or second year of life, allowing them to reproduce early and frequently. The maximum age a sardine can reach is considerably higher than its average life expectancy. For example, the European Pilchard (Sardina pilchardus) has been recorded to live up to 13 years in oceanic environments. The Pacific Sardine (Sardinops sagax) has a reported maximum longevity of up to 25 years, though individuals reaching this age are rare in modern populations.
Geographic and Species Variation in Longevity
The term “sardine” encompasses several genera, and lifespan varies significantly across these distinct species and habitats, such as the Atlantic-dwelling Sardina and the Indo-Pacific Sardinops. This variation is often correlated with the temperature of the water they inhabit. Populations living in colder, more stable environments tend to exhibit slower growth rates and longer overall lifespans. Conversely, populations in warmer waters, such as the Mediterranean Sea, often display faster growth but shorter maximum lifespans. For instance, the Mediterranean subspecies of the European Pilchard rarely lives past four to five years, shorter than their Atlantic counterparts.
How Scientists Determine Sardine Age
Scientists determine the age of a sardine primarily by examining its otoliths, which are small, calcium carbonate structures found in the inner ear. These otoliths grow continuously throughout the fish’s life, creating distinct growth rings, a process analogous to counting the rings on a tree trunk. The otoliths are analyzed under a microscope to count the annual rings, known as annuli. Each year, the sardine deposits alternating opaque and translucent zones, with the opaque zone representing faster growth during warmer months. By counting these pairs of zones, researchers can accurately determine the age of the fish in years.
Factors Influencing Sardine Survival
Few sardines survive long enough to reach their maximum biological age due to external pressures. Predation is a significant factor, as sardines are a fundamental food source for large fish, marine mammals, and seabirds, resulting in a high natural mortality rate. Commercial fishing also targets these schooling fish, removing large numbers of individuals, especially from the younger, most abundant age classes. Environmental conditions play a substantial role in survival, particularly during the vulnerable early life stages. Fluctuations in sea surface temperature and the availability of plankton, their food source, directly impact the survival rate of eggs and larvae, reducing the number of fish that survive to adulthood.