Recruits Finding a Home

By Kevin Lino

As a fish nerd (and biologist), I was excited to hear about unusual events occurring along Hawaii’s reefs this summer. While away on another research mission, reports came in from various sources and agencies about what was being referred to as a “biblical” fish recruitment event. Across many Hawaiian reefs, there were multiple reports from researchers, fishermen, and the public of juvenile reef fishes seen in extraordinary numbers. Not just one or two species either, but a wide variety of species. Species were also appearing in locations where they had previously been very rarely encountered. After seeing the pictures and reading comments about the amazing and unprecedented numbers, our team of scientists was eager to get in the water to conduct dive surveys.

Several juvenile Bluefin Trevally (Caranx melampygus) investigate research divers.

Several juvenile Bluefin Trevally (Caranx melampygus) investigate research divers.

This September, during the fifth year of a research partnership between the Coral Reef Ecosystem Division (CRED), of the NOAA Pacific Islands Fisheries Science Center, and the Division of Aquatic Resources (DAR) of the Hawai‘i Department of Land and Natural Resources (DLNR), we got our chance. We conducted the most recent round of biannual fish and benthic dive surveys focusing on the near-shore (<18m) reef habitats of the Kahekili Herbivore Fishery Management Area (KHFMA) on the coastline of West Maui.

A large school of juvenile parrotfish and surgeonfish cruise over the reefs in the KHFMA looking for suitable grazing spots.

A large school of juvenile parrotfish and surgeonfish cruise over the reefs in the Kahekili Herbivore Fishery Management Area (KHFMA) looking for suitable grazing spots.

Knowing that these surveys were occurring late in the summer, and that the recruitment may be more site-specific, we were surprised by the numbers. Nothing I would refer to as “epic” or “biblical” but definitely impressive. During four days of surveys, there was certainly an increase in recruited (the number of new young fish that enter a population in a given year) butterflyfishes, surgeonfishes, tangs, parrotfishes, and other near-shore fishes as compared to previous years. The variety was remarkable as numbers of protected herbivorous juvenile Yellow Tang (Zebrasoma flavescens), Kole Tang (Ctenochaetus strigosus), and Lavender Tang (Acanthurus nigrofuscus) were rather abundant. Since 2009, herbivorous fishes within the KHFMA have been protected, but other groups of fish can still be harvested. This unusual management approach has proven much more acceptable to the public as compared to full closure measures. Therefore, if proven effective as a means of restoring herbivorous fish populations, and preventing coral-to-algal phase shifts, then this management approach has great potential to be more widely adopted in Hawai‘i and beyond. Observations seem to be trending in this direction with further analysis forthcoming from this data set and potentially continued research.

One of the many Hawaiian Fantail Filefish (Pervagor spilosoma) recruits seen on the reef in the Kahekili Herbivore Fishery Management Area (KHFMA).

One of the many Hawaiian Fantail Filefish (Pervagor spilosoma) recruits seen on the reef in the  KHFMA.

Our dive teams spent many hours underwater each day identifying, sizing, and counting these fish, as well as sea urchins, and collecting benthic imagery for more detailed analysis later. Divers also paid close attention to potential impacts to corals and the benthic community with much warmer waters being brought in by the current El Niño event. At least for now, little impact was noted during the time of our visit. El Niño is typically associated with a band of warm ocean water temperatures that periodically develop off the Pacific coast of South America and affect other areas in the Pacific. Since the mechanisms and impacts of this warmer water are still under study, the data collected this year will be especially valuable.

 A little White Tip Reef Shark (Triaenodon obesus) emerges from its resting spot within the shallows of the KHFMA.

A little White Tip Reef Shark (Triaenodon obesus) emerges from its resting spot within the shallows of the KHFMA.

There were other species sighted, likely enjoying the bounty, including the smallest white tip reef shark (Triaenodon obesus) that I’ve ever seen—at barely two feet long, pretty adorable. A large number of juvenile predators like Bluefin Trevally (Caranx melampygus) and various goatfish species were also fairly common. One colorful omnivore was sighted throughout all reef habitats on nearly every survey. The Hawaiian Fantail Filefish (Pervagor spilosoma) is an endemic species (only found in Hawaiian waters) that is uncommon on most dives. But as recorded in both Hawaiian culture and historical surveys, this species will have a “bloom” or “boom” year that we were fortunate enough to witness. It will be interesting to see how all of this year’s recruits will affect things in years to come.

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