McElroy et al.: Comparison of length distributions from a longline survey and a trawl survey for 2 groundfish species 237 
Table 2 
Percentage of the stratified mean abundance indices by size group, season, and year, for the Atlantic cod (Gadus morhua) and white 
hake (Urophycis tenuis) sampled in the Gulf of Maine in 2014-2018 during the NOAA Northeast Fisheries Science Center bottom 
longline survey (LLS) and bottom trawl survey (BTS). Data were selected from strata with rough bottom for the LLS and from 
strata used in the stock assessments for these species for the BTS (for strata used in the assessments, see NEFSC, 2013a, 2013b). 
TL=total length. 
LLS 
<80 cm 80-89 cm 
Species Season 
Atlantic cod Spring 
White hake Spring 
spring with occasional higher proportions of cod >70 cm TL 
in the catches of the BTS. The biggest differences between 
the surveys were observed in catches of cod with sizes 
of 15-38 cm TL. Atlantic cod <35 cm TL were regularly 
represented in BTS catches but were very limited in LLS 
catches. This difference was particularly evident in the 
fall, when cod at sizes of 25-38 cm TL were common in 
catches of the BTS (Fig. 3). Cod >80 cm TL were uncom- 
mon (<10% of the sampled fish; Table 2, Fig. 3) in both 
surveys (except for the LLS in fall 2018 and for the BTS 
in fall 2015) but were more frequent in the fall than in the 
spring for both surveys. Cod 290 cm TL were rare (<3% of 
the sampled fish) in most surveys and occurred more often 
in the fall. Only 2 cod =>100 cm TL were captured in either 
survey during the 5 years of data examined. 
The BC, used for the comparisons of annual length dis- 
tributions of Atlantic cod (Table 3) between the BTS and 
LLS, indicates variable but high overlap (BC=0.77-0.91) 
in the spring in all years except 2018 (BC=0.50). The BC 
indicates that overlap in distributions of the 2 surveys was 
generally less in the fall than in the spring but still rela- 
tively high in most years (BC=0.62-0.87) except, again, in 
2018 (BC=0.55). The BCs for surveys in 2016 are the most 
consistent across the 2 seasons (0.90 and 0.87 for spring 
and fall, respectively) and among the highest observed. 
The BCs for distributions combined across the period 
90-99 cm 
BTS 
>100 cm <80 cm 80-89 cm 90-99cm 2100cm 
TL TL 
95.8 
99.3 
98.5 
91.6 
2014-2018 indicate that overlap was high in both spring 
(BC=0.96) and fall (BC=0.89). The distributions for com- 
bined years were more complete than the distributions for 
individual years because the former were based on data 
from a larger sample than that for each individual year. 
For white hake, length distributions aggregated across 
years were dissimilar between the LLS and BTS (Table 2, 
Fig. 3). White hake in the spring LLS were most commonly 
40-75 cm TL (Fig. 3), and in the fall LLS the peak in the 
length distribution was typically 55-80 cm TL. In con- 
trast, the peak abundance in the BTS was observed for fish 
with lengths around 32 cm TL in the spring, with a couple 
of peaks in the catches at sizes around 45 and 55 cm TL 
(Fig. 3). In catches of white hake in the fall BTS, the most 
prevalent sizes were around 35-50 cm, with secondary 
peaks of abundance for fish at 20-30 cm TL and 60-65 cm 
TL (Fig. 3). Recent recruits, at sizes around 10 cm TL, 
occurred in the fall BTS, and white hake <40 cm TL were 
rarely observed in LLS catches. White hake >80 cm TL were 
regularly observed at a low frequency in the spring LLS, but 
they were common in the catches of the fall LLS (Table 2, 
Suppl. Figs. 1 and 2 [online only]). In contrast, white hake 
280 cm TL, and particularly those >90 cm TL, were infre- 
quent in the BTS across both seasons relative to the LLS. 
White hake >90 cm TL composed 2—18% of the fish sam- 
pled in the LLS among years in the fall, and although such 
