Pelagic Fishery Research Program (PFRP)
Joint Institute for Marine and Atmospheric Research
School of Ocean and Earth Science and Technology
University of Hawaii
June 1998
Purpose of the Project:
To improve assessments of the pelagic fish resource (especially swordfish)
exploited by Hawaii-based longline fishermen by incorporating and evaluating
environmental influences affecting the availability and catchability of
the resource. In the first phase of the project we categorized all commercial
longline fishing sets by the Hawaii-based fishery from 1991-1995 by their catch
composition, and then catch rates for sets targeting swordfish and blue shark
were standardized using models to account for time-area effects, some
operational characteristics, and sea surface temperature (SST) features.
In the second phase we are using data supplied by the Fisheries Observer
Program of the National Marine Fisheries Service (NMFS) on longline sets
deployed with time-depth-temperature recorders (TDTRs) supplied by this
project. These data are being used to test hypotheses about the correlations
among catch rates (especially for swordfish and bigeye tuna), fishing
depths, and contemporaneously acquired environmental and operational factors
(e.g. temperature at fishing depth, and aspects of fishing gear configuration
that influence fishing depth) to gain insights into the habitat and ecology of
pelagic fish species caught on longlines. These efforts improve our
abilities to use commercial fishery statistics to monitor trends in the
relative fish abundance by quantifying some of the effects of fishing
techniques and non-random fish distribution (habitat preferences).
Progress in FY 1998:
A paper on categorizing longline fishing effort was published in 1997 and another paper from the first phase of the project was submitted to Fishery Oceanography, revised, and re-submitted in February 1998 (below). In the second paper generalized additive models (GAMs) were applied to examine the influence of various factors on catch-per-unit effort (CPUE) of swordfish and blue shark in the Hawaii-based commercial swordfish fishery. Relationships were analyzed for ten factors (latitude, longitude, moon phase, wind velocity, light sticks per hook, bathymetry, SST, SST frontal energy, and temporal change in SST and SST frontal energy). Depending on the resolution of SST data used (from 18-km to 1-degree latitude by longitude square) the GAM analysis accounted for 39-42% and 44-45% of the variance in CPUE for swordfish and blue shark, respectively. For swordfish, by decreasing importance, the top 5 ranked factors were: 1) latitude, 2) light sticks per hook, 3) SST frontal energy, 4) change in frontal energy, and 5) moon phase. For comparison CPUE was also modeled using a generalized linear model GLM analysis of simple time-area effects which accounted for -2% less variance than was explained by the GAMs.
In the second phase of the project, information from TDTRs were used to ecologically characterize commercial landings of albacore tuna (n=1617), bigeye tuna (n=l 376), yellowfin tuna (n=435), blue shark (n=5589), oceanic white-tip shark (n=121), blue marlin (n=156), broadbi11 swordfish (n=1964), and striped marlin (n=504) in the Hawaii-based longline fishery from 1996 to 1997. Locations of the 319 monitored TDR longline fishing sets in this period spanned an area approximately from 15º to 45º N latitude and from 130º to 175 º W longitude. A draft manuscript on these results has been completed. Results mirror the previous GAM study in that similar key factors (e.g. SST and moon phase) plus others (fishing depth, season, set time and bait type) explained a large portion of the variability in swordfish CPUE (R² =0.81; P«.001). Factors such as season and fishing depth were important in explaining variability in bigeye tuna CPUE (R²=0.81; P«0.001). In FY 1998 TDTR data was collected (but not yet compiled or analyzed) from ~ 400 additional longline sets.
Plans for FY 1999:
Funding for the project ran out in December 1997. We are continuing the work using other sources of funds, and in FY 1999 we will: 1) publish the paper re-submitted to Fishery Oceanography, 2) complete revisions to the TDTR manuscript and submit it to the Journal of Fish Biology, 3) complete a follow-up manuscript which will characterize another 36 species of pelagic fishes caught on longlines as "incidental" catch or discards, and 4) incorporate another full year of TDTR-linked catch data into the existing database. Unfortunately, analysis of the latter will be impossible without further funding. The substantial increase in ecological data from the additional TDTR-monitored sets in 1997-1998 would allow for several important components to be evaluated such as; a) variation in catch with key environmental and operational factors between years b) associated interaction terms, c) more accurate descriptions of fish habitats, and d) gear selectivity factors affecting by-catch of non-target species.
Papers published:
He, X., C. H. Boggs, and K. A. Bigelow, 1997. Cluster analysis of longline sets and fishing strategies within the Hawaii-based Fishery. Fisheries Research 31: 147-158.
Other papers:
Bigelow, K. A., C. H. Boggs and X. He. Influence of environmental factors on swordfish and blue shark catch rates in the U.S. North Pacific longline fishery. Re-submitted to Fishery Oceanography.
Musyl and Boggs. Manuscript. Integration of time-depth-temperature recorders (TDTRs) with fisheries observer program data to characterize commercial catch depths and habitats of eight pelagic fish species in the Hawaii-based longline fishery. For submission to Journal of Fish Biology.
