Fish assessment cruises in the main Hawaiian Islands: preliminary results from latest visual surveys

Coral Reef Ecosystem Division (CRED) staff members Danny Merritt, John Rooney, and Jacob Asher are participating in the PIFSC cruise SE-12-08 aboard the NOAA Ship Oscar Elton Sette, which left Honolulu on Sept. 22 for operations in the main Hawaiian Islands to compare fishery-independent methods for assessment of bottomfish stocks. This cruise is expected to end on Oct. 4. Merritt and Asher are conducting deployments of two different baited underwater camera systems: BotCam and baited remote underwater video stations (BRUVS). Rooney is conducting surveys with the towed optical assessment device (TOAD), the video from which will be used to validate acoustic data collected during this cruise with an echo sounder. Find out more about this cruise here.

Earlier this month on Sept. 1–13, CRED led a PIFSC cruise (SE-12-07) also aboard the Oscar Elton Sette in the main Hawaiian Islands, with some activities performed from the chartered M/V Huki Pono. Investigators conducted surveys of coral reef fish assemblages at O`ahu, Maui, Lāna`i, and Moloka`i with two different methods at two different depth ranges. These operations were stationary-point-count surveys conducted by scuba divers at depths of 0–30 m and deployments of BRUVS (baited and unbaited) done at depths of 1–100 m.

Participants included staff from CRED, the PIFSC Fish Biology and Stock Assessment Branch, Joint Institute for Marine and Ecosystem Research of the University of Hawai`i at Mānoa, Hawai`i Division of Land and Natural Resources, and University of Western Australia.

Visual survey data gathered on this expedition supplements the data collected by CRED and partners for the Pacific Reef Assessment and Monitoring Program (Pacific RAMP). A similar coordinated effort of visual surveys and use of remote video technology was conducted around the island of Tutuila in American Samoa in April 2012.

Preliminary results from the visual surveys conducted during the PIFSC cruise SE-12-07 are provided in the monitoring brief below.

Pacific Reef Assessment and Monitoring Program
Fish monitoring brief: main Hawaiian Islands 2012

By Adel Heenan, Paula Ayotte, Kevin Lino, Kaylyn McCoy, Marc Nadon, Ivor Williams, and Jill Zamzow

Purpose of monitoring

Throughout the Pacific, reef fishes contribute to the biodiversity and resilience of coral reef ecosystems. They also make substantial contributions to food security, livelihoods, and generation of economic revenue through tourism and other activities. Assessment of the status and patterns of change in reef fish populations and their associated habitats is necessary to understand ecological processes and their most significant effects. Information on these resources can be used to assess and inform management interventions and policy.

Sampling effort

  • The latest reef fish monitoring took place in the central main Hawaiian Islands from 09-01-2012 to 09-13-2012.
  • Data were collected at 163 sites, which were randomly selected but balanced by the amount of coral reef habitat per depth zone per island. Surveys were conducted at Lāna`i (n=29), Maui (n=49), Moloka`i (n=50), O`ahu (n=35).
  • At each site, the fish assemblage was surveyed by underwater visual census and the benthic community of the reef was assessed.

Major findings

Around the island of O`ahu, lower fish biomass was observed across all consumer groups and size classes, compared to results from the other islands surveyed in the central main Hawaiian Islands during this cruise (Figs. 1–4). Primary consumers include herbivores (which eat plants) and detritivores (which bottom feed on detritus), and secondary consumers are largely omnivores (which eat plants and animals) and invertivores (which eat invertebrates).

Figure 1. Mean total fish biomass at sites surveyed.

Figure 2. Mean hard coral cover at sites surveyed.

Figure 3. Mean fish biomass per consumer group and island surveyed (± standard error). Primary consumers are herbivores and detritivores, and secondary consumers are omnivores and invertivores.

Figure 4. Mean fish biomass per size class and island surveyed      (± standard error). Fishes were measured by total length (TL) in centimeters (cm). Size classes shown here are 0–20, 20–60, and >50 cm TL.

Sampling method

A pair of divers surveys the fish assemblage at each site using a stationary-point-count method (Fig. 5). Each diver identifies, enumerates, and sizes all fishes within a visually estimated 15-m-diameter cylinder in which they are stationed in the center. These data are used to calculate fish biomass per unit area (g m-2) for each species. Each diver conducts a rapid visual assessment of reef composition, by estimating the percentage cover of major benthic functional groups in a cylinder. Divers also estimate the complexity of the surface of the reef structure and the abundance of sea urchins, and they take photos along a transect at each site; these photos are archived to allow for future analysis.

Figure 5. Diagram of survey method used to monitor fish assemblages and benthic communities at Rapid Ecological Assessment (REA) sites.

About the Pacific Reef Assessment and Monitoring Program

The Coral Reef Ecosystem Division (CRED) runs a long-term monitoring program, known as the Pacific Reef Assessment and Monitoring Program (Pacific RAMP). Pacific RAMP forms a key part of the National Coral Reef Monitoring Program of NOAA’s Coral Reef Conservation Program (CRCP), providing integrated, consistent, and comparable data across U.S. Pacific islands and atolls. CRCP monitoring efforts have these aims:

  • Document the status of reef species of ecological and economic importance
  • Track and assess changes in reef communities in response to environmental stressors or human activities
  • Evaluate the effectiveness of specific management strategies and identify actions for future and adaptive responses

For more information

Coral Reef Conservation Program:  http://coralreef.noaa.gov
NMFS Pacific Islands Fisheries Science Center:  http://www.pifsc.noaa.gov
CRED publications:  http://www.pifsc.noaa.gov/pubs/credpub.php
CRED fish team:  http://www.pifsc.noaa.gov/cred/fish.php
Fish team lead:  ivor.williams@noaa.gov

Follow this link for a PDF version of this main Hawaiian Islands 2012 fish monitoring brief.

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