Sutherland and Richards: Aging Lophius americanus based on length-mode progression of a strong cohort 15 
2015 year class. Normal parameters were estimated by 
using NORMSEP software, a program for analyzing a mix- 
ture of normal distributions (Pauly et al., 1986; Gayanilo 
et al., 2005). The size estimates of the length mode for each 
month were later used to select samples from within the 
mode for the validation study. 
Sample collection 
Samples of the 2015 year class (with determination of year 
class based on fish length, as described here previously) 
were obtained from the Atlantic coast of the United States 
from Virginia to Georges Bank (Fig. 1). Sampling occurred 
during the NEFSC bottom trawl surveys in 2016-2018 
(spring survey) and 2015-2016 (autumn survey) and during 
the NEFSC and Virginia Institute of Marine Sciences 
scallop dredge survey in June 2016. To obtain samples in 
months when no surveys occurred, additional samples 
were obtained through the NEFSC Study Fleet program 
(Palmer et al., 2007) and the NEFSC Fisheries Monitor- 
ing Operations Branch (NEFSC”). The overall sampling 
effort spanned from September 2015 through April 2018, 
although monthly sampling was limited to the period from 
May 2016 through July 2017. 
All fish were frozen whole and shipped to the laboratory 
for dissection. Each fish was measured (in total length 
[TL] in centimeters), weighed (in grams), and examined 
macroscopically to determine sex. The illicium and a seg- 
ment of the vertebral column were removed. 
Hatch date 
In order to verify year-class membership of fish in the 
strong length mode, we additionally removed the lapil- 
lar otoliths from 2 presumed young-of-the-year goosefish 
from within this length mode by using methods described 
in Landa et al.*® These fish were fortuitously collected on 
4 September 2015, before our dedicated sampling began. 
The lapillar otoliths were prepared for daily aging fol- 
lowing methods described in Secor et al. (1991) and Wright 
et al. (2002). Each otolith was mounted in epoxy, sectioned 
along the sagittal plane, manually ground (240- and 600- 
grit sandpaper) to reveal the primordium, and polished. 
Images of the lapillar otolith sections were taken at 
125x magnification with an Olympus* BX60 microscope, 
Olympus DP70 camera, and imaging software cellSens, 
vers. 1.11 (Olympus Corp., Tokyo, Japan). One age 
reader used the images to count the rings (Fig. 2) from 
? NEFSC (Northeast Fisheries Science Center). 2016. Observer 
operations manual, 163 p. Northeast Fish. Sci. Cent., Natl. Mar. 
Fish. Serv., Woods Hole, MA. [Available from website.] 
3 Landa, J., A. Antolinez, J. Barrado, J. Fontenla, C. Hernandez, 
B. Villamor, C. Duefias, and M. R. Navarro. 2014. Age deter- 
mination procedures for benthic fish in Spanish Institute of 
Oceanography (IEO), 34 p. Int. Doc., Inst. Esp. Oceanogr., 
Santander, Spain. [Available from website.] 
4 Mention of trade names or commercial companies is for identi- 
fication purposes only and does not imply endorsement by the 
National Marine Fisheries Service, NOAA. 
Figure 2 
Photograph of a sectioned and ground lapillar otolith of a 
14-cm-TL goosefish (Lophius americanus) captured on the 
outer shelf off the coast of Virginia on 4 September 2015. 
The estimated hatch date is 4 June 2015. The white dots 
indicate every tenth ring. 
the primordium to the outer edge, with replicate counts on 
3 successive days (this reader trained with D. Secor, of the 
University of Maryland Center for Environmental Science, 
Solomons, MD, to learn methods for processing and reading 
samples for daily aging). It was assumed that the first ring 
was formed at hatching and that each ring represented 1 d 
of growth (Hislop et al., 2001; Hernandez et al., 2015). Pro- 
vided that the 3 readings were within 10% of each other, 
the average of the 3 counts was used to calculate hatch date 
(the collection date minus the number of rings). 
Age estimation 
Illicia were prepared according to methods described in 
Duarte et al.’ Each illictum was skinned and cleaned, 
marked 0.5 cm above the top of the basal bulb, and allowed 
to dry. The illicia were then mounted in polyester resin, with 
10-15 samples per row, and sectioned at the mark on a high- 
speed saw with a diamond-impregnated blade (LabCut 250, 
Benetec Ltd., Rugby, UK) to a thickness of 0.5 mm. 
Vertebrae were processed according to methods estab- 
lished by Armstrong et al. (1992) but were not sectioned. 
The eighth vertebra was excised from the spinal column, 
cleaned of tissue, and baked at 230°C in an oven until 
dried and darkened (20-60 min). 
