Anyone who fancies nature shows has witnessed countless documentaries showing spectacular scenes of albatross or other seabirds travelling across the vast oceans to breed in massive colonies on remote islands. It is said that successful breeding at these very unique sites, which the birds travel to year in and year out, is literally critical to their survival. Similar tales are told about gray whales that travel more than 10,000 miles round trip between their feeding grounds in the Arctic to specific sites in Baja California to breed, and as a result, these sites are recognized as critical sites for conservation. What about sea turtles? Yes, you’ve guessed it – many follow these same behaviors. For instance, leatherback turtles may travel 13,000 miles across the south Pacific Ocean along very specific migration routes to nest on certain beaches in Costa Rica, and scientists are using this information to fine-tune conservation measures that protect these areas and routes. The point I’m trying to make here is that many marine animals migrate to reproduce during specific times and at very specific locations (I could carry this discussion into the terrestrial realm with stories of butterflies and wildebeasts…). These breeding sites truly represent the most epic phenomena of the natural world, which anyone who has witnessed them can attest to, and these events are widely recognized by people well outside the conservation world as places that should be protected from exploitation and human disturbance.
Oddly enough, many marine fishes engage in breeding migrations that are equally amazing and just as critical to their survival, yet these events and sites are rarely mentioned as having the same level of importance for conservation as the animals mentioned above. I realize that fishes aren’t nearly as charismatic as albatross or cute as sea turtles, but one could argue that the successful protection of their breeding aggregation sites is even more important to us than these other amazing animals. Fish breeding aggregations, which are commonly referred to as fish spawning aggregations (FSAs) support the most profitable and productive fisheries worldwide. Fisheries for salmon, tunas, cod, sardines, groupers, orange roughy, and many of the other highly-value fisheries have long targeted known sites where these fish form spawning aggregations of thousands (or even millions) of fish. Until recently, many of these sights received almost no attention as a target for management and the results are astounding. As one example, 80% of known aggregations of tropical reef fish spawning aggregations have declined and nearly 15% of aggregations have completely disappeared due to overfishing.
In the Gulf of California, more than 50 species from 14 families of fishes are known to form spawning aggregations, and most are important components of commercial, recreational, or subsistence fisheries.
These aggregations can be truly massive and the activity of spawning fish that occurs is just as amazing to observe as any seabird colony or turtle nesting. Take for instance the Gulf corvina, a large croaker (fishes who have muscularized swim bladders that allow them to produce a croaking sound for mating) that lives only in the upper Gulf of California. During the new and full moons of March and April, the entire species migrates to the mouth of the Colorado River Delta to spawn in synchrony within the estuaries and the river. During this time, more than a million corvinas will spawn en masse within the shallow channels of the Delta. Fishers say that during the spawning period, which occurs in the evening, there are so many fish croaking that the bottoms of their boats vibrate and you can hear the fish through the boats!
Fishing represents the main source of livelihood for most coastal communities in the Gulf of California, and harvesting from spawning aggregations has always been and will always be an important and necessary component to maintaining viable fisheries and communities in the region. However, given the known vulnerability of spawning aggregations to overfishing and the importance of such events for the survival of fish populations, proper management and conservation of aggregations are urgently needed. If a balance cannot be found, the region will lose both the beauty and spectacle of these important biological events and the bountiful resources they provide.
Brad Erisman is a Postdoctoral Researcher at Scripps Institution of Oceanography (SIO). Dr. Erisman obtained his PhD at the Center of Marine Biodiversity and Conservation at SIO in 2008, and his dissertation research investigated the reproductive biology and mating behavior of groupers and seabasses. He now leads several projects on the science, management, and conservation of fish spawning aggregations in the Gulf of California. Grant’s current dissertation research focuses on the ecology and behavior of cryptic reef fishes in the Gulf of California and their interactions of such fishes with society.