Study of Pelagic-Stage Hawaii Bottomfish Adds to Knowledge of Life History

A Cobb mid-water trawl is deployed off the stern ramp of the NOAA Ship Oscar Elton Sette to collect samples of pelagic-stage bottomfish.
A Cobb mid-water trawl is deployed off the stern ramp of the NOAA Ship Oscar Elton Sette to collect samples of pelagic-stage bottomfish.

An important aim of PIFSC fishery scientists is to better understand the biology and ecology of bottomfish (e.g., eteline snappers) supporting important commercial and non-commercial fisheries in the main Hawaiian Islands. Among the knowledge gaps to be filled is the early life history of etelines in oceanic waters surrounding the islands. To learn more about the subject, scientists collected samples of pelagic juvenile bottomfish in August 2012.

In a research expedition of the NOAA ship Oscar Elton Sette, PIFSC biologists used a mid-water Cobb trawl at various locations around the main Hawaiian Islands to collect specimens for taxonomic and life history studies and to learn more about the spatial distribution and potential offshore transport of pelagic stages of etelines. The sampling strategy extended the range of previous collections into waters farther offshore and at more leeward locations around the main Hawaiian Islands. During the cruise, 2 nighttime Cobb trawls were conducted at selected sampling locations situated 25, 50, and 75 nm off the leeward coasts of Niihau, Oahu, Lanai, and the Kona Coast of Hawaii Island. Each Cobb trawl operation targeted fish in 3 depth layers: 170-175 m, 100-120 m, and 20-25 m, with haul durations of 1 hour in each layer.

A sample of freshly collected specimens of pelagic-stage eteline snappers. Differences in body shape and the location and coloration 
               of pigment likely indicate the presence of several different species in the sample.
A sample of freshly collected specimens of pelagic-stage eteline snappers. Differences in body shape and the location and coloration of pigment likely indicate the presence of several different species in the sample.

Trawl catches were composed predominantly of squid and mesopelagic fishes. As the catch was sorted, the most sought-after parts were pelagic stages of shore fishes. And among these specimens, there were relatively few etelines and other snappers (including Lutjanus spp., probably taape). Freshly captured specimens of pelagic stage etelines had 4-5 different appearances based on color and placement of body pigmentation in relation to the base of the dorsal, anal, and caudal fins.

Analysis of the collected specimens is underway. Counts of daily increments on otoliths of the eteline snappers reveal their growth rates, pelagic-stage durations, and birth dates. Each specimen must be identified by matching its DNA sequence with reference DNA sequences originating from adult snappers of known classification.