This week, Grant Galland and I travelled from San Diego to Cabo Pulmo National Park in Baja California Sur, Mexico to search for spawning aggregations of large reef fishes, particularly snappers and jacks, inside the park. Our goal was to locate and describe the specific times and habitats in which spawning occurs and to capture these amazing events on high-definition video. This expedition is part of a larger research project to understand how well marine reserves in the Gulf of California (GOC) are able to protect critical spawning habitats of fishes that are important to commercial and recreational fisheries. The importance acquiring such information cannot be understated given that fish spawning aggregations in the GOC are incredibly important to regional fisheries and many aggregate-spawning species have declined due to overfishing. If large enough and placed in the appropriate locations, marine reserves have great potential to protect spawning aggregations of reef fishes. However, targeted evaluations of the utility of current marine reserves in the Gulf to preserving spawning aggregations have notbeen completed as of yet.
As with any research expedition, we were successful in some aspects and unsuccessful in others. On the positive side, we saw clear and immediate evidence that several species of reef fishes were forming spawning aggregations inside the boundaries of the park during our trip. We found several small (c. 10-50 fish) to large (c. 500 fish) schools of bigeye jacks (Caranx sexfasciatus) exhibiting obvious signs of courtship behavior throughout the day. Interestingly, large individuals were often scattered in male-female pairs, with the male taking on a black coloration and the female exhibiting the more “traditional” silvery coloration. Conversely, smaller individuals were often clustered and courting in larger groups. Several large schools of yellow snapper (Lutjanus argentiventris) also were aggregating on the reefs, and during the evening hours several aggregations coalesced and the frequency of putative courtship behaviors increased. Loose aggregations of surgeonfish (Acanthurus xanthopterus) gathered at the surface in the afternoon, and pairs of these colorful fish were seen spiraling to the surface to spawn. In addition, numerous aggregations of porcupinefish (Diodon holocanthus) were observed in dense clusters of 40-60 individuals, hovering just over the reef, including many females with enlarged bellies full of eggs.
However, capturing spawning on video is a rather elusive endeavor that usually requires a lot of patience, some luck, and numerous instances of failure — and such was the case with this expedition. While we quickly found schools of courting jacks on the very first dive of the trip, these schools seemed to vanish from the reefs in the days that followed, and spawning was never observed. Our attempts to document spawning in yellow snapper reached a similar fate. We easily located an aggregation of c. 1000 fish on El Bajo reef, and during the afternoon the fish became much more active, with fish exhibiting all the signs that spawning was imminent. On one night, we dove on the reef in the late afternoon, quickly found the school, and then returned to the boat to wait until sunset — the perfect time to capture the spawning. Unfortunately and much to our amazement, the entire aggregation had literally disappeared upon our return to the very same spot less than 30 minutes later. Even after an hour of searching the entire reef, the school was never found again that evening (although they were there again the next morning). Apparently, all the yellow snappers had quickly mobilized and made a rather rapid emigration to an unknown site to spawn.
As many fish ecologists could attest to, our expedition was a microcosm of most research endeavours that seek to document the spawning behavior of reef fishes; full of alternating bouts of excitement, anticipation, insight, confusion, and frustration. This oscillation of highs and lows can and has convinced many researchers to seek other lines of research that hold higher certainties of success. But there are a few of us ichthyophiles (a.k.a. fish-lovers) that live for these sorts of high-risk, high-reward moments. We thrive on the trials and tribulations of behavioral research, because we understand that our patience, persistence, and perseverance will ultimately result in witnessing one of the most spectacular and amazing spectacles in nature — massive, synchronous spawning of hundreds or even thousands of fish! (check out our video links from Belize to see what I mean)
For that reason, if you visit Cabo Pulmo next August, you are likely to find Grant and I there as well: dressed in full scuba gear, with cameras in hand, ready to search out the next spawning action!
Stay tuned for more updates on our research, including a brief video summarizing what we saw and experienced during the trip.
Brad Erisman is a Postdoctoral Researcher at Scripps Institution of Oceanography (SIO), and Grant Galland is a graduate student of marine biology at 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.