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The Role of Oceanography on Bigeye Tuna Aggregation and Vulnerability in the Hawaii Longline Fishery from Satellite, Moored, and Shipboard Time Series

Progress Reports (PDF): FY 2005, FY 2003, FY 2002, FY 2001, FY 2000

Project Overview
Bigeye tuna (Thunnus obesus) is the principal deepwater target species of the longline fishery in the Pacific Ocean yielding total annual catches exceeding 150,000 tons (Hampton et al., 19961; Hampton et al., 19982). Stock assessment models require the use of longline fishery catch-per-unit-effort (CPUE) as an index of bigeye abundance. Fishery-dependent CPUE does not necessarily represent the abundance of stock, but rather the "catchability" of the stock. Catchability, in turn, is dependent to a considerable extent upon variable oceanographic conditions. Oceanographic variability can significantly affect the depth of the thermocline and the most likely depth of occurence of bigeye tunas as well since the preferred foraging habitat of bigeye tunas is the 8-15° C water at or near the base of the thermocline (Hanamoto, 19873; Holland et al., 19904; Boggs, 19925; Brill, 19946; Boggs et al., 19987; Musyl and Brill, 19988).

The goals of this research are to:

  1. examine closely the relationships between bigeye tuna CPUE from the Hawaii-based longline fishery and oceanographic features observed using moored, shipboard, and satellite time series of the vertical and spatial structure of the upper ocean;
  2. utilize those relationships to develop methods to improve stock assessment estimates based on standardized logbook CPUE using remotely-sensed observations of sea surface height (altimeter), sea surface temperature (AVHRR), ocean color (SeaWiFS), and surface winds (scatterometer).
  3. Proposed activities include:

    1. Moored Observations
    While there are currently three oceanographic moorings collecting vertical thermal structure data in the upper ocean which are in general proximity to the bigeye fishing grounds of the central Pacific there are some limitations. These moorings are either located outside of the main fishing grounds, not adequately equipped to sample the vertical thermal structure, and/or not equipped to measure velocity or shear of the upper 500 m. Because of the lack of adequate time series information in a region of high bigeye tuna CPUE, project researchers propose to establish a mooring to measure the vertical structure of temperature and current velocity in the bigeye tuna fishing grounds located south and west of the main Hawaiian Islands. Optimization based on CPUE, variability of CPUE, proximity to TOPEX/JASON satellites crossover paths, variability of oceanographic structure, and linkages to other components of the Pelagic Fisheries Research Program was used to determine a preferred mooring location about 185 km southwest of the island of Niihau at 20°36.0'N, 161°34.2'W. The mooring will be designed to focus on describing the habitat of bigeye tuna by providing continuous vertical profiles of temperature and velocity in the upper 500-600 m. Time-depth recorders will be deployed on longlines during research cruises and commercial longline trips to provide longline depth information concurrent with mooring data.

    2. Shipboard Sampling
    This will be conducted to: 1) identify and further characterize the area spatially represented by the mooring and provide three-dimensional ground-truthing to remotely-sensed surface measurements through hydrographic surveys in the region around the mooring; 2) conduct experiments to ascertain the influence of prevailing oceanographic conditions on longline gear performance; 3) obtain information on the biological community that constitutes the bigeye forage base. Shipboard sampling will include closely spaced (10 km) CTD casts along 200 km transect lines centered on the mooring location. The biological community will be sampled with a large dual-warp midwater trawl (140m2 fishing area at the mouth) targeting the depth strata identified as bigeye habitat from hydrographic surveys.

    3. Satellite Data
    Comparisons between both mooring and cruise data and the altimetric anomalies will be used to develop an algorithm to map estimates of the vertical thermal structure over the fishing grounds every month. Project researchers hypothesize that when the vertical thermal structure shoals the bigeye habitat contracts toward the surface and the bigeye density increases. Conversely, when the vertical structure deepens then bigeye habitat expands and bigeye density decreases. Researchers propose to use estimates of the change in vertical thermal structure (estimated from altimetry) to correct or standardize commercial longline CPUE for changes in vertical habitat following the approach of Hinton and Nakano (1996)9 so that changes in CPUE reflect changes in bigeye abundance and not changes in the vertical extent of habitat.

Funding for this project awarded in October 1999.

(1) Hampton, J., A. Lewis, and P. Williams, 1996: Estimates of western central Pacific Ocean bigeye tuna catch and population parameters. Working paper presented to the World Meeting on Bigeye Tuna, La Jolla, California, 11-15 Nov. 1996.
(2) Hampton, J., K. Bigelowe, and M. Labelle, 1998: Effect of longline fishing depth, water temperature and dissolved oxygen on bigeye tuna (Thunnus obesus) abundance indices. Standing Committee Tuna and Billfish Working Group Report.
(3) Hanamoto, E., 1987: Effect of oceanographic environment on bigeye tuna distribution. Bull. Jap. Soc. Fish. Oceanogr., 51:203-216.
(4) Holland, K.N., R.W. Brill, and R.K.C. Chang, 1990: Horizontal and vertical movements of yellowfin and bigeye tuna associated with fish aggregating devices. Fish. Bull., 88, 493-507.
(5) Boggs, C., 1992: Depth, capture time, and hooked longetivity of longline-caught pelagic fish: Timing bites of fish with chips. Fish. Bull., 90, 642-658.
(6) Brill, R.W., 1994: A review of temperature and oxygen tolerance studies of tunas pertinent to fisheries oceanography, movement models and stock assessments. Fish. Oceanogr., 3, 204-216.
(7) Boggs, C.H., M. Musyl, R. Brill, D. Curran, M. Laurs, and J. Gunn, 1998: Bigeye tuna crepuscular diving data from an archival tag indicates geoposition and lunar influences. (MS in prep.)
(8) Musyl, M. and C. Boggs, 1998: Integration of temperature-depth recorders (TDRs) with catch to assess environmental and gear factors important in the commercial landing of eight pelagic fish species, representing three families (Carcharhinidae, Istiophoridae, Scombridae), in the Hawaiian Longline Fishery with notes on their ecology: "How deep is deep?" To be submitted to J. of Fish Biol.
(9) Hinton, M.G. and H. Nakano, 1996: Standardizing catch and effort statistics using physiological, ecological, or behavioral constraints and environmental data, with an application to blue marlin (Makaira nigricans) catch and effort data from Japanese fisheries in the Pacific. Bull. Int. Am. Trop. Tuna Comm., 21(4): 171-200.


Principal Investigators:

Dr. Russell Brainard
National Marine Fisheries Service
Honolulu Laboratory
2570 Dole Street
Honolulu, Hawaii 96822
Phone (808) 983-5392
FAX (808) 983-2902
email: Rusty.Brainard@noaa.gov

Dr. Bo Qiu
Department of Oceanography
University of Hawaii at Manoa
1000 Pope Road, MSB 408
Honolulu, Hawaii 96822
Phone (808) 956-9502
FAX (808) 956-9222
email: bo@soest.hawaii.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: Jeffrey.Polovina@noaa.gov

Dr. Pierre Flament
Department of Oceanography
University of Hawaii at Manoa
1000 Pope Road, MSB 503
Honolulu, Hawaii 96822
Phone (808) 956-6663
FAX (808) 956-9225/9165
email: pierre@soest.hawaii.edu

Michael Seki
National Marine Fisheries Service
Honolulu Laboratory
2570 Dole Street
Honolulu, Hawaii 96822
Phone (808) 983-5393
FAX (808) 983-2902
email: mseki@honlab.nmfs.hawaii.edu


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This page updated August 15, 2006