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Evaluation of Remote Sensing Technologies for the Identification of Oceanographic Features Critical to Pelagic Fish Distributions around the Hawaiian Archipelago

Progress Reports (PDF): FY 2001, FY 2000, FY 1999, FY 1998 (see below)

Project Overview
The purpose of the proposed work is to determine how best to identify mesoscale oceanographic features, using a variety of different existing satellite image products, that may be important in moderating pelagic fisheries near Hawaii. The specific objectives are to (1) develop statistical description of mesoscale structure near Hawaii; (2) to refine these statistical descriptions in order to identify discrete events; (3) relate these events to fishery statistics and describe in a manner which will describe fish distribution.


Principal Investigator:
Dr. Gary Mitchum
as of Fall 1996:
Department of Marine Science
University of South Florida
140 7th Avenue S.
St. Petersburg, Florida 33701
email: mitchum@marine.usf.edu

Dr. Jeffrey Polovina
National Marine Fisheries Service
Honolulu Laboratory
2570 Dole Street, Room 216
Honolulu, Hawaii 96822
Phone (808) 983-5390
FAX (808) 983-2902
email: jpolovin@honlab.nmfs.hawaii.edu

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Progress Report - July 1998

The project is using two satellite sensors, TOPEX/Poseidon altimetry and SeaWifs ocean color to describe the features of the Subtropical Frontal Zone which is the fishing ground for the Hawaii-based longline fishery targeting swordfish. We have developed an analytic tool to produce maps of ocean currents every 10 days from the TOPEX/Poseidon satellite. A comparison of these maps with the longline fishing grounds show the fishing grounds lie along a front represented as an eastward meandering geostrophic current. Monthly and interannual variation in swordfish catch rates are highly correlated with changes in sea surface height measured with TOPEX in the fishing ground. When sea surface height drop (rise) catch rate increase (decrease). Changes in sea surface height reflects changes in water column heat content. A drop (rise) in sea surface height indicates a shoaling (deepening) of the isotherms. We believe the swordfish vertical foraging range has a lower temperature limit, thus a shoaling (deepening) of isotherms increases (reduces) swordfish density and hence catch rates.

We have just begun to investigate the application of SeaWifs ocean color in this frontal region. Preliminary results suggest, the swordfish fishing grounds are based on a subsurface chlorophyll maximum and hence have a limited chlorophyll surface signature. However, about 100 miles to the north of the swordfish fishing grounds there is a sharp surface chlorophyll front which appears to be the foraging habitat of loggerhead turtles which are occasionally hooked in the longline gear.

Results from this work were presented in two posters at the February 1998 AGU Ocean Sciences Meeting (San Diego), and in an oral presentation at the Lake Arrowhead Tuna Conference in May 1998. The analytic approach developed in the project was used in a paper on the simulation of the spatial dynamics of lobster larvae driven by geostrophic currents estimated with TOPEX/Poseidon data which will be published by Fishery Bulletin. A student, Cheryl Kihlstrom, has been supported by this project and is expected to complete her masters thesis in 1998 (topic: physical oceanographic explanation of swordfish catch patchiness).

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This page updated August 15, 2006