Bulletin of the Sea Fisheries Institute 2 (153) 2001 - CEEMaR

16
JONATHAN A. HARE et al.
Species Identification
Larval fish from MOCNESS, bongo and BN-1 collections were removed, identified,
enumerated and measured by staff of the Polish Plankton Sorting and Identification Center.
Larval fish from neuston collections were removed, identified, enumerated and measured by
employees of the NOAA Beaufort Laboratory. All scombrid and scombrolabracid identifications
were verified by two of the authors (JAH and ABP) using published sources, primarily Potthoff
(1974), Richards (1989) and Richards et al. (1990).
Most Thunnus larvae were identified as T. atlanticus. All larvae identified to Thunnus
atlanticus had one to several very small melanophores on the ventral margin. The most common
location was ventral to the hypural, but most specimens also had one to three very small
melanophores on the posterior half of the ventral margin. In many of the specimens these
melanophores were not evident at first, but careful examination revealed pigment. A subset of
specimens with this pigment pattern were cleared and stained (n = 41) and all had vertebral
counts of 19 + 20, identifying these larvae as T. atlanticus. This pigment pattern was then used
to identify other larvae as T. atlanticus. Thunnus larvae with no ventral pigment were not
identified below genus.
Data Analysis
Seasonal abundances of scombrid and scombrolabracid larvae were compared between cruises.
Only data from the two stations that were sampled during both cruises were analyzed
(igure 1). Total number of larvae of each taxa collected at a station were divided by total water
filtered at each station and concentrations expressed in 100 m -3 .
Vertical distributions of scombrid and scombrolabracid larvae were examined from
the May, 1984 MOCNESS collections. Concentration of larvae within a given depth strata
at a given sampling time were expressed in 100 m -3 . Weighted mean depth (and standard deviation)
of larvae were also calculated using larval concentrations (Brodeur and Rugen 1994).
BN-1 collections were not analyzed in this manner owing to the limited number of larvae
collected.
Horizontal distributions of larvae were examined from the broad-scale, November-December
1988 bongo collections. Neuston collections were not analyzed because of a strong
day/night bias (see below). Stations were divided into three regions (igure 1) and non-parametric
statistics were used to determine if larval concentrations and larval lengths differed
among regions.
RESULTS
Seasonal Abundance
Larval abundance and length distributions indicated that scombrids and scombrolabracids
spawned in both spring and winter in the Puerto Rico/St. Croix region (Table 1, igure 2).
Katsuwonus pelamis and Scombrolabrax heterolepis larvae were collected in both May and
November/December, and during both sampling times, most larvae were