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by David Zeimann, Ph.D.

 

The Fisheries & Environmental Sciences Department conducts research on coastal marine resource issues. Among other programs, we are currently conducting research to determine the movement patterns and habitat use of Hawaiian deep-water snappers.

The Hawaiian bottom fish fishery is comprised of 12 species, the most important of which are seven deep-water snappers in the family Lutjanidae. In 1998, the Division of Aquatic Resources in the State of Hawai‘i Department of Land and Natural Resources (DLNR) developed a management plan that included the creation of 19 restricted fishing areas (RFAs) where bottom fishing is prohibited. The Kahoolawe Island Reserve (KIR) is another area where bottom fishing is prohibited.

The objective of our research was to examine whether movement of bottom fish occurred from the KIR to adjacent open fishing areas. Live opakapaka (Pristipomoides filamentosus) were caught and implanted with acoustic tags, and then released. We tracked them over the course of two months with an array of passive acoustic receivers.

Five arrays were installed on the sea floor just outside the western boundary of Kaho‘olawe at depths of 117-165 m. Each consisted of a bottom weight, an offshore acoustic release, a passive acoustic receiver, and a subsurface float and flag. The receivers were deployed in June 2004.
The five receiver arrays were recovered August 26, 2004. Data from each receiver were downloaded to a computer and data for each acoustic tag were compiled into individual files and then analyzed to generate estimates of hourly position.

Eighteen opakapaka were collected, implanted with acoustic tags, and released. Of these, signals were recorded for 12 fish for lengths of time from 0.1 to 1,485 hours. Signals were not recorded for six of the fish released.

Results showed that opakapaka typically undertake diurnal movements from the deeper area of the shelf during the day to the shallower shelf slope at night. Patterns suggest that opakapaka are feeding most actively at night.

There was also strong evidence of movement out of or into the KIR from the adjacent open shelf. Most of the tagged fish showed frequent movement in a generally east—west direction. This movement often originated within the KIR, to the east of the receiver array, took the fish across the area covered by the receiver array, and showed evidence of residence to the west of the array, well outside the KIR, for periods of hours to days until the fish returned across the array area back into the KIR.

 

 

 

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