Monitoring in Kahekili Herbivore Fisheries Management Area Indicates an Increase in Fish Biomass and Improved Conditions for Corals

Five years after the Kahekili Herbivore Fisheries Management Area was established in West Maui, in the main Hawaiian Islands, monitoring indicates an increase of herbivorous fish biomass there and early signs of improved conditions for corals.

The Kahekili Herbivore Fishery Management Area (KHFMA) in Kaʻanapali, West Maui, was established by the state of Hawaii in July 2009. It involves a form of management unique within the state, namely protection of coral reef herbivores (i.e., surgeonfishes, parrotfishes, chubs, and sea urchins), which may not be killed, injured, or harvested within the boundaries of this fisheries management area. The goal of the KHFMA is to restore natural grazing processes and thereby increase the local reef's ability to resist and recover from excessive algal growth that had occurred repeatedly on local reefs through the 1990s and early part of the 2000s.

Since 2009, the PIFSC Coral Reef Ecosystem Division (CRED) has partnered with the Division of Aquatic Resources (DAR) of the Hawaii Department of Land and Natural Resources to conduct twice-annual surveys of fishes and benthos within the KHFMA.

Algal blooms occurred at Kahekili in 2001 (left) and 2005 (right).

Thus far, the KHFMA has restricted harvesting of reef herbivores for 5 years, a period that is considerably shorter than the lifespan of many of the herbivorous fish species that are protected inside the KHFMA. Therefore, full effects of protection on those fish species and on slow-growing corals will not be clear for several more years. Here are some highlights from the survey results to date (the most recent surveys were March 31–April 3, 2014):

Surgeonfish biomass has increased by 40% since establishment of the KHFMA (comparing average of 2013–2014 estimates with average of 2008–2009 estimates).
Over the same time period, parrotfish biomass has increased by 135%. Additionally, the number of large individuals (>30 cm in total length) of the dominant parrotfish species, the Bullethead Parrot (Chlorurus spilurus), has greatly increased since closure, consistent with increased survivorship of medium-to-large individuals.
Since closure, mean cover of crustose coralline algae (CCA), which is a benign algal form favorable to coral recruitment and growth, has increased from 2% to 9% (comparing 2008-2009 to 2013–2014). A strong positive correlation between parrotfish biomass and CCA cover suggests that recovery of those key herbivores inside the KHFMA is leading to improved conditions for corals.
Following recent relative stability over recent years at a level of ~32%, mean coral cover marginally increased to 34.6% over the last year.

CRED staff and DAR partners planned to conduct the next round of monitoring in late September 2014.

Semi-annual surveys indicate that mean biomass densities of surgeonfishes at the Kahekili Herbivore Fishery
Management Area have increased since the conservation area was created. Error bar shows 1 standard error of the mean.

Semi-annual surveys indicate that mean biomass densities of parrotfishes at the Kahekili Herbivore Fishery
Management Area have increased since the conservation area was created. Error bar shows 1 standard error of the mean.

Semi-annual surveys indicate that mean biomass densities of surgeonfishes and parrotfishes at the Kahekili Herbivore Fishery Management Area have increased since the conservation area was created. Error bar shows 1 standard error of the mean.