Fig 1.
North Carolina Division of Marine Fisheries gillnet and longline survey stations within Pamlico Sound from 2007–2014.
Gillnet sets are marked with red triangles and longline sets are marked with blue circles.
Table 1.
Total number captured (number of sets occurring for principal species in parentheses) and mean ± standard deviation total length (TL) and environmental factor measurements (minimum and maximum in parentheses) for each shark species captured during North Carolina Division of Marine Fisheries gillnet and longline surveys within Pamlico Sound.
Species denoted with an asterisk were designated principal species.
Fig 2.
Total numbers of sharks of each principal species captured in Pamlico Sound by year, season, and month.
A.) Smooth and Spiny Dogfish and B.) Atlantic Sharpnose, Blacktip, Bull, and Sandbar Sharks captured in Pamlico Sound from 2007–2014 survey years. Smooth and Spiny Dogfish are graphed separately due to being captured in much greater numbers than the other species.
Fig 3.
Linear discriminant function analysis canonical correspondence plot showing classification of principal shark species by environmental factors.
Correlations between canonicals and environmental factors are shown in the biplot rays and ellipses represent 95% confidence intervals. Ellipses are color-coded by species (Atlantic Sharpnose Shark (green), Blacktip Shark (black), Bull Shark (Red), Sandbar Shark (gold), Smooth Dogfish (blue), Spiny Dogfish (purple)).
Table 2.
Canonical eigenvalues, cumulative percent of variation explained, and canonical structure from linear discriminant function analysis classifying principal shark species by environmental factors.
Table 3.
Percent of individuals of principal shark species classified as each species based on environmental factors by linear discriminant function analysis.
Correct classifications are in bold.
Fig 4.
Environmental grids for Pamlico Sound representing habitat factors assumed to be static.
Depth data are from USGS bathymetry surveys and inlet distance and SAV distance are interpolated from 2007–2014 NCDMF fishery-independent surveys and spatial locations of inlets and SAV habitat. SAV habitat locations are from Kenworthy et al. [34].
Fig 5.
Environmental grids for Pamlico Sound representing environmental factors assumed to vary by season.
Seasons are those in which the greatest seasonal abundance of at least one principal shark species was recorded and fall represents early and late fall combined. Data are interpolated from North Carolina Division of Marine Fisheries 2007–2014 fishery-independent surveys.
Table 4.
Linear correlations between environmental factors recorded during 2007–2014 North Carolina Division of Marine Fisheries gillnet and longline surveys in Pamlico Sound.
Table 5.
Parameters (cross-validation score (CV), learning rate (lf), bag fraction(bf)) and contribution (% of tree splits) for binary BRT models predicting capture likelihood of six principal shark species in Pamlico Sound.
Bold text denotes the three environmental factors contributing the most tree splits for each species.
Fig 6.
Marginal effects of environmental factors contributing to predicting shark species capture likelihood.
Marginal effects are of the three environmental factors that contributed the three highest proportions of tree splits to the binary BRT model predicting capture likelihood of each of the six principal shark species within Pamlico Sound. Percentages in parentheses represent the proportion of tree splits contributed by the variable.
Fig 7.
Predicted capture likelihood maps for the six principal shark species within Pamlico Sound.
Predicted capture likelihood is based on binary presence/absence BRT results.
Table 6.
Kruskal-Wallis test results comparing predicted CPUE at the locations of sets from 2015 NCDMF gillnet and longline surveys where each species was present or absent (df = 1 for all tests).