Lee and Rock: The forgotten need for spatial persistence in catch data from fixed-station surveys 
71 
Figure 2 
Map of the locations of the 29 stations (•) selected for use in the persistence 
analysis and sampled during 1979-2016 in the Pamlico Sound system in North 
Carolina as part of the Estuarine Trawl Survey of the North Carolina Division of 
Marine Fisheries. 
and by using the mk.test function in the package trend, 
vers. 1.01 (Pohlert, 2017). Trends were considered sig¬ 
nificant at a=0.05. 
Following Nicholson et al. 2 , we applied a 2-way anal¬ 
ysis of variance (ANOVA) to test the significance of the 
interaction of year and station for each target species. 
This analysis was conducted in R with the aov function 
in the stats package (R Core Team, 2017). Samples col¬ 
lected at the same station during May and June within 
the same year were considered replicates in order that 
the interaction term could be tested. The interaction 
was considered significant at a=0.05. A significant in¬ 
teraction indicates a lack of persistence. Main effects 
were also included in the ANOVA but the results are 
not presented here. 
Results 
The target species range widely in frequency of occur¬ 
rence from being present in less than 2% of tows (sum¬ 
mer flounder) to being present in over 98% of tows (for 
spot) (Table 1). 
The indices of relative abundance exhibit consid¬ 
erable interannual variability for all species (Fig. 3). 
Statistically significant decreasing trends were de¬ 
2 Nicholson, M. D., T. K. Stokes, and A. B. Thompson. 1991. 
The interaction between fish distribution, survey design and 
analysis. ICES CM 1991/D:11, 9 p. [Available from web¬ 
site.] 
Table 1 
Frequency of occurrence of 10 target species in 2204 
trawl samples from the North Carolina Division of Ma¬ 
rine Fisheries Estuarine Trawl Survey, 1979-2016, in 
the Pamlico Sound system in North Carolina. 
Species 
Number 
of tows 
Occurrence 
(%) 
Atlantic croaker 
1889 
85.7 
Atlantic menhaden 
1290 
58.5 
Southern flounder 
1339 
60.8 
Spot 
2162 
98.1 
Summer flounder 
27 
1.2 
Weakfish 
100 
4.5 
Blue crab 
1450 
65.8 
Brown shrimp 
1489 
67.6 
Pink shrimp 
100 
4.5 
White shrimp 
52 
2.4 
tected for Atlantic croaker, Atlantic menhaden, spot, 
and weakfish (Table 2). Statistically significant in¬ 
creasing trends were found for southern flounder, 
brown shrimp, and white shrimp. No statistically sig¬ 
nificant trends were present in the indices of relative 
abundance for summer flounder, blue crab, or pink 
shrimp. 
