Investigating the Life History and Ecology of Opah and Monchong in the North Pacific

Progress Reports (PDF): FY 2004, FY 2003, FY 2002

Project Overview
Two miscellaneous pelagic fish species incidentally caught by Hawaii longline vessels targeting bigeye tuna are the opah and monchong. Particularly valued by restaurants, these exotic, deep-water fishes are generally harvested in small, but nevertheless significant quantities. Since neither are targeted species, these fishes have historically been poorly studied and as a result available information pertaining to the biology and ecology of this resource are virtually nonexistent.

The primary objective of this project is to investigate and define some of the fundamental life history and ecological characteristics of the opah and monchong resource in the North Pacific. The focus will be on the opah (moonfish), Lampris guttatus, and on two species of monchong (pomfret): the bigscale pomfret (Taractichthys steindachneri) and the lustrous pomfret (Eumegistus illustris). Project researchers will gather biological and ecological data through:

• a comprehensive collection of shoreside data and biological sampling,
  
• analysis and merging of fishing industry (NMFS observer and logbook, North Pacific driftnet, auction), research and environmental datasets, and
  
• capturing depth information collected from vessels of opportunity.

A daily biological sampling program will be launched at the Honolulu-based fish auction United Fishing Agency (UFA), and at other local fish buyers/dealers to obtain metrics (length, weight, sex) and samples (ovaries, otoliths, and stomachs) required to conduct a comprehensive biological and ecological assessment. Special effort will be made to link the UFA collected metric data with the biological samples extracted for the corresponding fish at the dealers. For monchong, special attention will be given to species differentiation between T. steindachneri and E. illustris enabling treatment of species individually. Preliminary results from species specific sampling conducted during 1987-91 suggest considerable differences between the sizes of species landed at the auction. Data analysis will produce comprehensive seasonal and, where possible, interannual biometric summaries and relationships (e.g., length-weight, sex ratio, etc.). Obtaining gonads and the determination of reproductive parameters such as size and age at maturity, fecundity, spawning season, and gonadosomatic index will be the primary focus of biological collections. Hard parts will be collected for possible ageing though it is unlikely that a comprehensive assessment would be possible with the time frame of this study. This is particularly true for opah, whose saggital otoliths are apparently of vaterite form and not conducive for daily increment enumeration; the lapillus or vertebrae may turn out to be better for ageing. For monchong, light microscopy of sagittal otoliths should be adequate for first cut ageing efforts. Stomachs will be collected in support of the studies on trophic relationships as listed below.

The assessment of spatial distribution patterns, preferred habitat, faunal associations and trophic relationships will involve the analysis and merging of industry (NMFS observer and logbook data, North Pacific driftnet, auction), research, and environmental datasets, and capture depth information from vessels of opportunity. This project will benefit from the efforts of an ongoing PFRP-funded project being conducted by NMFS-HL researchers, William Walsh and Sam Pooley, that focuses on the development of reliable databases on the historical catch and distribution of six major non-target species including monchong and opah (see Walsh and Pooley project). Specifically, Walsh and Pooley's efforts will generate corrected logbook data, expand the dataset to include weights and prices in addition to fish numbers, and will apply a generalized additive model (GAM) to examine the effects of extrinsic (operational and environmental) factors and to generate corrected catch estimates. Using predictor variables such as the number of hooks per set, set latitude, vessel length, type of fishing trip (i.e. swordfish- or tuna- directed) exemplify the use of geographic, operational (hooks and vessel size), and biological factors to describe catch rates of opah and its importance within the Hawaii-based longline fishery.

The proposed study will further examine distribution patterns and faunal associations using the corrected logbook and observer datasets and concurrent environmental (i.e., remotely sensed or in situ oceanographic) datasets. Time-depth-temperature recorders (TDRs) will also be deployed through commercial fishing vessels known to catch opah and monchong. During 1987-91, ten TDRs deployed on commercial longline sets yielded information suggesting that monchong are taken on deeper sets that settle in water greater than 350 m, consistent with that predicted by the GAM.

Year 1 funding awarded September 2001.