Fishes on Fellowship: Snapper Spawning

When I initially made arrangements to work with PICRC, I had signed on to help out with a variety of research projects, but focus on fieldwork like monitoring protected areas. By the time I arrived, my coordinator had left the island and her replacement informed me that they had finished diving for the season. I’ll be able to join visiting researchers with their work in the upcoming months, and the typhoon damage might require additional assessments, but for now I’m working on socioeconomic surveys, data entry, and writing up reports, and I’m scouting out my own opportunities for research diving (and some fun diving, of course).

There’s a pair of researchers operating out of one of the dive shops (Sam’s) studying fish aggregations and spawning. At certain points in the lunar cycle, particular species of fish come together for mass spawning events, and Palau is one of the few places where there are enough remaining large fish for spectacular spawning sightings. Studying when and where these aggregations occur is important for designing conservation policies because when fish densely pack together, the entire population could be scooped up by a single fishing trip (this is how we obliterated orange roughy). This raises possibilities for looking at temporal rather than spatial protection: perhaps limiting fishing of species just for the days around their spawning events, and allowing it for the rest of the month.

Last week, the days preceding the full moon meant snapper aggregation, so Johanna, Katherine and I joined a spawning expedition. Richard, the researcher leading the dive, picked us up at 4:30am, and we headed out to the aggregation site. As the sun began to peek over the horizon, we jumped in and immediately dropped to 100 feet. The snapper spawn at the height of outgoing tide so the gametes will disperse in the open ocean, so we had to swim hard to avoid being swept out by the current. We followed droves of snapper that were pouring from what seemed like all directions to the aggregation: a swirling mass of thousands and thousands of huge fish. I had never seen anything remotely like this before—it was absolutely crazy. Abruptly, a female lit up with red streaks and darted upward away from the group, trailed by a swarm of males; the chase ended in a cloud of gametes. This happened several more times as we gazed, awestruck, kicking against the current, while the occasional shark cut below us (unfortunately I missed the rare bull shark sighting). All too soon we had to return to the surface, everyone on the boat yelping with excitement.

Snappers begin to aggregate

SO MANY FISH

Males streak toward a spawning female; the cloud of gametes is visible to the left of the clump.

The current was getting too strong and the seas too rough to jump in again at the aggregation, so we did another dive at a site called Sandbar to check out the resident leaf fish and a huge school of bigeyes. Back at Sam’s, Johanna, Katherine, and I, reluctant to return to the office and noting that it was early yet, grabbed tanks and explored the wall off the docks. Definitely a day I’ll remember forever! I’m hoping I’ll get to tag along for bumphead parrotfish spawning near the new moon, and maybe see a bull shark for the next round of snapper.