Larval Fish Identification from Cruises at Oahu, TC-85-04, TC-85-05, TC-86-02, TC-86-04

Four cruises aboard the NOAA ship Townsend Cromwell were conducted, collectors included George Boehlert and Bruce Mundy.  Two transects, oriented in an east-west direction, were established, one each on the leeward and the windward sides of the island. Stations were located 1.8, 9.3, and 27.8 km from shore along the leeward side  and 3.7, 9.3, and 27.8 km from shore along the windward side. Larvae were sampled below the surface with a 1 m2 multiple opening-closing net and environmental sensing system (MOCNESS) and at the sea surface with a 0.49 m2 Manta net modified to take surface samples to a depth of 0.7 m. All nets were constructed of 0.333 mm Nitex mesh. Estimates of water volumes filtered by both gear types were based on mechanical flowmeter readings. Samples were taken in eight depth strata (neuston, 0-10, 10-20, 20-30, 30-40, 40-50, 50-60, and 60-80 m) at each nearshore station and in nine depth strata (neuston, 0-20, 20-40, 40-60, 60-80, 80-100, 100-120, 120-160, and 160-200 m) at the 4 offshore stations. MOCNESS hauls were 12 minutes duration for each net (stratum), fished in a stepped oblique fashion from deep to shallow with mean tow speeds of approximately 75 cm/sec; the tow speed was adjusted to maintain a net mouth angle near 45". Neuston tows were 24 minutes, taken during the mid-point of the MOCNESS tows. Replicate tows were taken at each station in both day and night, but only the first replicate sample was sorted for the December, April, and June cruises, whereas both replicates were processed for the September cruise.  

All fish larvae were identified to the lowest taxonomic level possible by Bruce C. Mundy.  Squid paralarvae were transferred to the Dr. Richard Young (Dept. of Oceanography, Univ. of Hawai'i). Other taxa were not routinely sorted, but heteropods from selected samples have been transferred to Dr. Roger Seapy (Dept. of Biological Sciences, California State Univ. Fullerton; see Seapy 1990. Patterns of vertical distribution in epipelagic heteropod molluscs off Hawaii. Mar. Eco1.-Prog. Ser., 60: 235-246.) and numbers of four species of copepods were obtained from subsamples from certain stations by Dr. R. Patrick Hassett (Dept. of Zoology, Arizona State Univ.; see Hassett and Boehlert 1995. Seasonal, vertical and horizontal distributions of four species of copepods around Oahu, Hawaii: data report. NOAA Tech. Memo. NMFS, NOAA-TM-NMFS-SWFSC-215, 21 p.).  

In 2023, Andrea Schmidt (andrea.schmidt@noaa.gov) provided:

1) RB008AA1_V_LAT_LONG_MEANS_V - Latitude and longitude from cruise reports and MOCNESS sensor data were inserted into RB008AA1_V data.

2) RB008AA1_UKUSIZES_V - A dataset with larval measurements for uku, Aprion virescens.

Methodology: We processed larval uku from a backlog of existing partially processed wet-archived ichthyoplankton samples from O'ahu that were likely to contain larval uku and enhance available record data. We identified and measured uku larvae from ichthyoplankton samples collected around the island of O'ahu on cruises TC8504 (September 6-15, 1985) and TC8604 (June 24-July 2, 1986). These cruises were part of a yearlong series of quarterly surveys described in Boehlert and Mundy (1996). Every three months a series of MOCNESS tows were conducted at 1.8, 9.3, and 27.8 km from shore during the day and the night. Two replicates were collected for each station, but not all replicates were processed. Since the entirety of these samples were archived and stored at PIFSC, we processed the second replicate for TC8604 and measure all previously identified uku from TC8504. These were the only depth integrated samples for which we could generate length data along a gradient from shore. Examination occurred under an EVOCAM2 scope (Vision Engineering Ltd, United Kingdom) and measurements of larval standard length were conducted with the ViPlus software (Vision Engineering Ltd, United Kingdom). The first replicates of the Boehlert and Mundy (1996) dataset were used to review Lutjanidae identification with a focus on uku and were examined several times. Previously unexamined samples from the second replicate were examined and the Aprion therein were removed. All identified Aprion were measured for standard length using the "line" tool in ViPlus. Flexion larvae were measured in segments, measurement points started from the caudal end of the vertebrae to the lateral line at the deepest point of the curve. The next measurement started from the same point and went to the most protruding point on the nose. Bent larvae, or those curled in on themselves which were not easily flattened without damaging the specimen, were laid vertically and measurements were taken in segments along their dorsal side from nose to tail end. In all other cases, a straight, single line measurement was taken.

Tags: archival, copepod, doc/noaa/nmfs/pifsc, frmd, ichthyoplankton, larvae, larval fish, lhp, main hawaiian islands, mocness, national marine fisheries service, net, noaa, oahu, pacific islands fisheries science center, pifsc, townsend cromwell, u.s. department of commerce
Organization: National Oceanic and Atmospheric Administration, Department of Commerce