Earlier this year, Octavio Aburto, my colleague from the Gulf of California Marine Program and a research scientist at Scripps Institution of Oceanography, UC San Diego, travelled to Cabo Pulmo National Park, Mexico, to participate in the making of a film on this incredible marine reserve whose fish community rapidly recovered following protection in 1995. During that trip, he took this stunning photo of a huge aggregation of bigeye jacks swirling like a tornado in front of our friend David Castro, a local divemaster and naturalist whose family is responsible for the establishment of the reserve and the rich abundance of fishes that now reside within its borders.
The picture has gone viral over the past few weeks since he posted it on his website and Vimeo account, and submitted it to the 2012 National Geographic Photo Contest. While many viewers have marveled at the beauty of the photo itself, much of the attention surrounding it has focused on a discussion of whether it’s authentic or a doctored photo created from Octavio’s imagination.
As Octavio said in a recent interview published in National Geographic, this photo is 100-percent real and has captured one of the most amazing spectacles of the marine realm – a massive fish spawning aggregation. Spawning aggregations are gatherings of fish that occur at specific sites and during predictable times for the sole purpose of reproduction. For certain species of fish such as the bigeye jacks, these aggregations can be huge and include thousands to even millions of fish engaging in complex courtship and mating rituals. We have been conducting research on fish spawning aggregations in the Gulf of California for more than fifteen years, as many species of fish in the region are known to engage in this marvelous behavior, and coastal communities depend on the harvest of aggregating species for their livelihoods.
We are studying aspects of the biology and fisheries of spawning aggregations throughout the Gulf that can be used to protect spawning aggregation sites and species, increase public awareness on the importance of spawning aggregations to the economy and ecology of the region, and create management policies that promote sustainable fisheries for aggregating species.
Bigeye jacks are medium-sized predatory fishes that reach 85 centimeters in length and form schools of hundreds to thousands of fish on tropical and subtropical reefs and coastal areas throughout the Indian and Pacific Oceans, from the Red Sea to Central America. However, very little is known about their spawning behavior or the dynamics of their spawning aggregations.
Many divers have captured images or observed a peculiar component of the bigeye jack’s spawning repertoire, in which pairs of individuals break off from the main aggregation and proceed to chase, spiral, and whorl around each other over open water. During this time, the male changes from its normal silver color to completely black, presses the flank of his body over the top portion of the silvery female, and leads her around in a courtship dance (PHOTO).
Based on this very noticeable behavior, many believe that spawning only occurs within these pairs. This assumption makes sense, since the very same type of behavior has been reported in several species of jacks that spawn in the Caribbean, the tropical Pacific and elsewhere around the world. In fact, Octavio and his colleagues even observed this pairing-up behavior in the bigeye jack more than a decade ago while studying spawning aggregations in the southern Gulf of California.
However, our perception of how spawning occurs in these fish changed completely in 2008, when a group of us visited Cabo Pulmo to conduct our annual monitoring surveys of the fishes in the reserve. We were ascending from the reef after nearly an hour of diving when we were encircled by a school of several thousand jacks. Then, all of a sudden, several hundred fish from the school formed a vertical funnel of circling fish from the surface of the water to the near the bottom (PHOTO). A minute or so later, we noticed this same group swimming rapidly in a huge circle on the sand like a conveyor belt (PHOTO). Fortunately, we had a professional videographer on board, our friend Alfredo Barroso, who had enough air left in his tank to capture the whole thing in HD video.
That video blew us away. While we’d all seen schools of bigeye jacks before while diving in Costa Rica or the Revillagigedos, we’d never seen anything that amazing.
Our first thought was that this peculiar behavior must be related to spawning, but since we all presumed that spawning occurred in pairs, we soon dismissed the idea. However, a few months later during a workshop on spawning aggregations that we organized in Baja, we found out that our original ideas were likely true. We showed the video to our colleague Will Heyman from Texas A&M University, a leading expert on spawning aggregations, and he said “indeed, that’s spawning for sure…I’ve seen similar behaviors in jacks in Belize.” He reassured us that while you do see those paired fish all the time, the real spawning action involves huge groups of fish separating from the main school, racing to the surface, releasing their gametes, and then racing back down to rejoin the school.
We’ve been mesmerized by the bigeye jack aggregations at Cabo Pulmo for several years now, and this school has emerged as the icon of this wonderful marine reserve that actually houses and protects spawning aggregations of several types of fishes, including groupers, snappers, parrotfishes, mobula rays, and even pufferfishes! We visit the reserve on a regular basis to observe and investigate the amazing spawning behaviors of all these fishes. For the jacks, we want to understand the details of all these complex mating and courtship behaviors. How does the paired courtship behavior relate to these huge whirling tornados of fish? Does spawning occurring in both, and if so why? What types of conditions control or determine the types of mating behaviors we observe in these amazing fish? Is it tides? The moon?
Right now, we have more questions than answers, but we are working hard over the next few years to unravel the mystery of all the wonderful behaviors we are seeing in this humongous spawning aggregation of jacks as well as other aggregating fishes of the reserve. In 2013, we will begin a tagging project at Cabo Pulmo to understand how these fish utilize the reserve throughout the year, including the spawning season. Ultimately, we hope to understand how different these jacks and other fishes use the reserve for spawning, and how the protection of spawning provided by the reserve helps to replenish fish populations in the area and contribute to local fisheries that depend on this production for their livelihoods (i.e. the spillover effect).
To learn more about fish spawning aggregations, please visit the website of the Society for the Conservation of Reef Fish Aggregations (SCRFA), a international non-profit agency dedicated to scientific research and responsible stewardship of fish spawning aggregations on a global scale. The website contains a comprehensive set of information on aggregating species, which includes a database showing where spawning aggregations have been documented all over the world and a library of resources on monitoring, managing, and conserving aggregations.
– Brad Erisman is a research scientist in the Marine Biology Research Division
Related research papers:
- “Spawning aggregations and reproductive behavior of reef fishes in the Gulf of California”
- “Spawning patterns in the leopard grouper, Mycteroperca rosacea, in comparison with other aggregating groupers”
- “Commercially Important Serranid Fishes from the Gulf of California: Ecology, Fisheries, and Conservation”
- “Spatio-temporal dynamics of a fish spawning aggregation and its fishery in the Gulf of California”
- “The social and economic importance of aggregating species and the biological implications of fishing on spawning aggregations”