There has been a noticeable drop in Pacific sardine numbers off the coast of California in recent years. The number of sardines has also dropped dramatically off the coast of Mexico as well. Many fishermen have been returning with empty boats after going out to fish for the entire day. Sardine numbers frequently rise and fall, sometimes sharply, but this decline appears to be worse than usual. It appears that the population of sardines has dropped 72% from assessed 2006 levels.
The cause of the decline is not exactly known, but climate change seems to be a primary factor. Natural cold-water oscillations circulate cold water back and forth along the California coast. These oscillations often bring in more species such as squid and anchovies, but rebuff small fish species like sardines. The boom in squid has resulted in higher numbers of marine mammals, such as whales and orcas and birds such as brown pelicans in some areas.
The crash in sardines may be linked to the emaciation and stranding of over 1600 sea lion pups early in 2013. Mother sea lions depend on fatty fish like sardines to provide rich milk for their pups. When sardines aren’t available, the mother has to “make-do” with other sources of food with less nutrition. As a result, many pups didn’t get the nutrition or gain the weight that they needed when they were ready to live on their own.
The severe drop in sardines will affect many facets of the ecosystem off of California. Many sea birds and other animals depend on sardines to stay healthy. For example, even though brown pelicans live well on anchovies, they depend on sardines during the breeding season to raise healthy chicks. If the sardine numbers aren’t sufficient in their breeding areas, then their chicks are likely to suffer. Other marine animals depend on them during certain parts of the year as well and the effects of the severe drop may be seen during the next breeding season.