swordfish PFRP Home > Statistical and Modeling Projects List

Estimation of Bycatch and Discards of Sharks and Other Species by the Hawaii Longline Fishery

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

Project Overview
The target species of the Hawaii longline fishery are broadbill swordfish (Xiphias gladius) and tuna (Thunnus spp.), but large numbers of fishers with little or no commercial value are also caught. The goals of this project are to develop procedures for estimating the amount and species composition of the bycatch, to understand the effects of fishing methods, area, and season on bycatch, and ultimately, to estimate the impact on the blue shark population.

Technical report published by Xi He and Chris Boggs:
Bycatch and discards of blue shark, Prionace glauca, by the Hawaii-based longline fishery from 1991 to 1995. 1996

See Other Publications for other articles by PFRP investigators


Principal Investigator: (formerly Dr. Xi He)
Dr. Pierre Kleiber
National Marine Fisheries Service
2570 Dole Street
Honolulu, Hawaii 96822
Phone (808) 983-5399
FAX (808) 983-2902
email: pkleiber@honlab.nmfs.hawaii.edu
Dr. Christofer Boggs
National Marine Fisheries Service
Honolulu Laboratory
2570 Dole Street, Room 212
Honolulu, Hawaii 96822
Phone (808) 983-5370
FAX (808) 983-2902
email: cboggs@honlab.nmfs.hawaii.edu

William Walsh
National Marine Fisheries Service
Honolulu Laboratory
2570 Dole Street
Honolulu, Hawaii 96822
Phone (808) 983-5346
FAX (808) 983-2902
email: William.Walsh@noaa.gov

rainbow horizontal bar

Progress Report - April 1998

William Walsh & Pierre Kleiber

The principal activities supported by this grant during the July 1997-June 1998 funding cycle have been a series of data verification and preparation procedures, followed by a statistical analysis of a seven-year set of logbook records (November 1990-October 1997) from commercial vessels operating within the Hawaii-based commercial longline fishery. Although this fishery targets swordfish and several species of tunas, the most numerous species in the catch was blue shark. This is a large, common, oceanic species, but many aspects of its biology are inadequately understood, especially those related to its abundance. The major question relevant to this fishery is whether, and if so, to what extent, the seemingly large incidental catch (approximately 100,000 blue sharks per year) has affected the population status of this species. Therefore, the objectives of this study were to describe and assess blue shark catch trends, those of other important species taken by the fishery, and fishing effort in general. The results, which were generated by an objective statistical method termed cluster analysis, demonstrated that several distinct assemblages of fishes have occurred in the catch during the seven-year study period, usually in association with specific types of fishing effort (i.e. swordfish-directed, tunas-directed, or a more generalized "mixed species" strategy). By defining the associations, determining the allocation of fishing effort, and assessing blue shark catches (i.e. monthly catch totals) and catch per unit effort (i.e. sharks caught per gear deployment) within the fish assemblages, it was possible to delineate recent trends in the population status of blue shark. These trends suggest that blue shark catch per unit effort remained approximately stable for the last 3-4 years of the study period. As such, it appears that observed fluctuations in blue shark catch totals may have been attributable to changes in allocation of fishing effort, rather than decreased blue shark abundance caused by the fishery. Additional results helped to explain the changes in catch patterns for swordfish, bigeye tuna, and albacore that were characteristic of this fishery during the seven-year study period.

Progress to Date

This project includes three major categories of activities relevant to the Hawaii-based commercial longline fishery: preparation of logbook and observer data, a series of modern statistical analyses, and presentation of results. As of this writing (April 1998), progress has been achieved in each area. The focus thus far has been on the NOAA Fisheries seven-year logbook data set derived from the records of commercial vessels.

The initial task required by the project was data processing, to make the logbook data set as complete, correct, and amenable to manipulation as possible. To this end, a series of data verification procedures were applied to the logbook data, for the period November 1990-October 1997. The objective of these procedures was to identify individual longline gear sets in the logbook data, in order to use sets as the observations in statistical analyses. This work was necessary because set identifications were done indirectly, on the basis of operational variables (e.g. set and haul dates and times), rather than from unique identifiers.

After preparing and verifying the accuracy of the seven-year logbook data set, a cluster analysis was conducted by methods similar to those used by He et al. (1997) with logbook data for 1991-1994. A draft manuscript describing the results has been completed. The intention is to submit an abridgment of this report for publication in a refereed journal.

Planned Activities

The next series of activities, expected to begin in June 1998, will include additional data preparation, followed by different types of statistical analyses. The preparatory activities are expected to include the addition of several environmental variables (e.g. sea surface temperature, lunar phase), and operational characteristics (e.g. numbers of lightsticks, numbers of hooks) to the logbook data. These variables will then be employed in statistical analyses, which are expected to include the development of generalized additive models, generalized linear models, and regression trees. These methods will be evaluated to assess their predictive capability regarding blue shark catches. Addition of environmental variables and development of statistical models represent a major project activity and deliverable, respectively.

Additional data preparation and management will be conducted on an ongoing basis. This will include cross-validation of fishery observer data with logbook records, in order to estimate the magnitude of finning and shark mortality associated with longline catches. The linked logbook and observer data will then be used in combination with the cluster analysis in a manner similar to He and Boggs (in review). Briefly, this will entail determination of the correspondence between logbook and observer data, and expansion of the observer-determined finning and mortality estimates to a fishery-wide basis.

Budget Status

There are no plans to seek additional funding for this project. At present, the budget is projected to last through November 1998. It is believed that this will allow sufficient time and money to complete the work described in the proposal.

Literature Cited

He, X. and C.H. Boggs. (In review). Bycatch and discards of blue shark, Prionace glauca, by the Hawaii-based longline fishery from 1991 to 1995. Submitted as a NOAA Technical Memorandum.

He, X., K.A. Bigelow, and C.H. Boggs. 1997. Cluster analysis of longline sets and fishing strategies within the Hawaii-based fishery. Fisheries Research 31:147-158.

rainbow horizontal bar

This page updated August 16, 2006