Parameter estimates for the top models of contemporary winter abundance of Double-crested Cormorants (Phalacrocorax auritus), Great Blue Herons (Ardea herodias), and Great Egrets (A. alba) at catfish (Ictalurus spp.) aquaculture clusters in the Mississippi Delta. Abundance was modeled for each species as a function of temporal variables, characteristics within the cluster, and the surface area (ha) of aquaculture and naturally occurring waterbodies within a 4-km or 14-km buffer surrounding the cluster. Counts were recorded during aerial surveys generally twice monthly (October−April) for 3 winters (2015−2016, 2016−2017, and 2017−2018). The month of October and winter 2015−2016 (year 2015) were set as reference levels. Beta (β) estimates, standard errors (SE), and associated P-values are shown.
| . | Cormorant . | Heron . | Egret . | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Parameter . | β . | SE . | P . | β . | SE . | P . | β . | SE . | P . |
| Intercept | 1.66 | 1.25 | 2.81 | ||||||
| November | 0.01 | 0.13 | 0.93 | 0.76 | 0.25 | 0.002 | –0.60 | 0.27 | 0.03 |
| December | –0.33 | 0.13 | 0.01 | 0.35 | 0.25 | 0.17 | –0.73 | 0.27 | 0.007 |
| January | –0.42 | 0.14 | 0.003 | 1.31 | 0.27 | <0.001 | –0.53 | 0.29 | 0.07 |
| February | 1.30 | 0.13 | <0.001 | –0.51 | 0.29 | 0.08 | –1.92 | 0.31 | <0.001 |
| March | 1.98 | 0.13 | <0.001 | –2.05 | 0.27 | <0.001 | –2.60 | 0.28 | <0.001 |
| April | 1.18 | 0.13 | <0.001 | –1.50 | 0.31 | <0.001 | –2.34 | 0.32 | <0.001 |
| Year (2016) | –0.04 | 0.27 | 0.87 | 0.10 | 0.24 | 0.67 | 0.13 | 0.32 | 0.68 |
| Year (2017) | –0.60 | 0.27 | 0.03 | 0.45 | 0.26 | 0.08 | 0.05 | 0.33 | 0.88 |
| Fish type a | 0.30 | 0.15 | 0.046 | –0.02 | 0.13 | 0.82 | –0.25 | 0.18 | 0.16 |
| Aq in buffer b | 0.29 | 0.10 | 0.008 | –0.50 | 0.10 | <0.001 | 0.38 | 0.13 | 0.003 |
| Nat in buffer c | –0.19 | 0.11 | 0.08 | –0.09 | 0.10 | 0.33 | 0.21 | 0.13 | 0.11 |
| Aq hectare d | 0.47 | 0.11 | <0.001 | 0.59 | 0.10 | <0.001 | 0.40 | 0.13 | 0.002 |
| RST-VAR e | 0.18 | 0.04 | <0.001 | ||||||
| . | Cormorant . | Heron . | Egret . | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Parameter . | β . | SE . | P . | β . | SE . | P . | β . | SE . | P . |
| Intercept | 1.66 | 1.25 | 2.81 | ||||||
| November | 0.01 | 0.13 | 0.93 | 0.76 | 0.25 | 0.002 | –0.60 | 0.27 | 0.03 |
| December | –0.33 | 0.13 | 0.01 | 0.35 | 0.25 | 0.17 | –0.73 | 0.27 | 0.007 |
| January | –0.42 | 0.14 | 0.003 | 1.31 | 0.27 | <0.001 | –0.53 | 0.29 | 0.07 |
| February | 1.30 | 0.13 | <0.001 | –0.51 | 0.29 | 0.08 | –1.92 | 0.31 | <0.001 |
| March | 1.98 | 0.13 | <0.001 | –2.05 | 0.27 | <0.001 | –2.60 | 0.28 | <0.001 |
| April | 1.18 | 0.13 | <0.001 | –1.50 | 0.31 | <0.001 | –2.34 | 0.32 | <0.001 |
| Year (2016) | –0.04 | 0.27 | 0.87 | 0.10 | 0.24 | 0.67 | 0.13 | 0.32 | 0.68 |
| Year (2017) | –0.60 | 0.27 | 0.03 | 0.45 | 0.26 | 0.08 | 0.05 | 0.33 | 0.88 |
| Fish type a | 0.30 | 0.15 | 0.046 | –0.02 | 0.13 | 0.82 | –0.25 | 0.18 | 0.16 |
| Aq in buffer b | 0.29 | 0.10 | 0.008 | –0.50 | 0.10 | <0.001 | 0.38 | 0.13 | 0.003 |
| Nat in buffer c | –0.19 | 0.11 | 0.08 | –0.09 | 0.10 | 0.33 | 0.21 | 0.13 | 0.11 |
| Aq hectare d | 0.47 | 0.11 | <0.001 | 0.59 | 0.10 | <0.001 | 0.40 | 0.13 | 0.002 |
| RST-VAR e | 0.18 | 0.04 | <0.001 | ||||||
a Fish-type index (−1 to +1) represents proportion of surface area within the aquaculture cluster for raising food fish (≥20 cm) minus the area for fingerlings (<20 cm).
b Surface area of aquaculture within 4-km (herons) or 14-km (cormorants and egrets) buffer around aquaculture clusters based on top models (see Table 2).
c Surface area of naturally occurring waterbodies within 4-km (herons) or 14-km (cormorants and egrets) buffer around aquaculture clusters based on top models (see Table 2).
d Surface area (ha) of aquaculture within cluster.
e Index of the number of cormorants from surrounding roost sites likely to forage at each aquaculture cluster (see Methods).
Parameter estimates for the top models of contemporary winter abundance of Double-crested Cormorants (Phalacrocorax auritus), Great Blue Herons (Ardea herodias), and Great Egrets (A. alba) at catfish (Ictalurus spp.) aquaculture clusters in the Mississippi Delta. Abundance was modeled for each species as a function of temporal variables, characteristics within the cluster, and the surface area (ha) of aquaculture and naturally occurring waterbodies within a 4-km or 14-km buffer surrounding the cluster. Counts were recorded during aerial surveys generally twice monthly (October−April) for 3 winters (2015−2016, 2016−2017, and 2017−2018). The month of October and winter 2015−2016 (year 2015) were set as reference levels. Beta (β) estimates, standard errors (SE), and associated P-values are shown.
| . | Cormorant . | Heron . | Egret . | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Parameter . | β . | SE . | P . | β . | SE . | P . | β . | SE . | P . |
| Intercept | 1.66 | 1.25 | 2.81 | ||||||
| November | 0.01 | 0.13 | 0.93 | 0.76 | 0.25 | 0.002 | –0.60 | 0.27 | 0.03 |
| December | –0.33 | 0.13 | 0.01 | 0.35 | 0.25 | 0.17 | –0.73 | 0.27 | 0.007 |
| January | –0.42 | 0.14 | 0.003 | 1.31 | 0.27 | <0.001 | –0.53 | 0.29 | 0.07 |
| February | 1.30 | 0.13 | <0.001 | –0.51 | 0.29 | 0.08 | –1.92 | 0.31 | <0.001 |
| March | 1.98 | 0.13 | <0.001 | –2.05 | 0.27 | <0.001 | –2.60 | 0.28 | <0.001 |
| April | 1.18 | 0.13 | <0.001 | –1.50 | 0.31 | <0.001 | –2.34 | 0.32 | <0.001 |
| Year (2016) | –0.04 | 0.27 | 0.87 | 0.10 | 0.24 | 0.67 | 0.13 | 0.32 | 0.68 |
| Year (2017) | –0.60 | 0.27 | 0.03 | 0.45 | 0.26 | 0.08 | 0.05 | 0.33 | 0.88 |
| Fish type a | 0.30 | 0.15 | 0.046 | –0.02 | 0.13 | 0.82 | –0.25 | 0.18 | 0.16 |
| Aq in buffer b | 0.29 | 0.10 | 0.008 | –0.50 | 0.10 | <0.001 | 0.38 | 0.13 | 0.003 |
| Nat in buffer c | –0.19 | 0.11 | 0.08 | –0.09 | 0.10 | 0.33 | 0.21 | 0.13 | 0.11 |
| Aq hectare d | 0.47 | 0.11 | <0.001 | 0.59 | 0.10 | <0.001 | 0.40 | 0.13 | 0.002 |
| RST-VAR e | 0.18 | 0.04 | <0.001 | ||||||
| . | Cormorant . | Heron . | Egret . | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Parameter . | β . | SE . | P . | β . | SE . | P . | β . | SE . | P . |
| Intercept | 1.66 | 1.25 | 2.81 | ||||||
| November | 0.01 | 0.13 | 0.93 | 0.76 | 0.25 | 0.002 | –0.60 | 0.27 | 0.03 |
| December | –0.33 | 0.13 | 0.01 | 0.35 | 0.25 | 0.17 | –0.73 | 0.27 | 0.007 |
| January | –0.42 | 0.14 | 0.003 | 1.31 | 0.27 | <0.001 | –0.53 | 0.29 | 0.07 |
| February | 1.30 | 0.13 | <0.001 | –0.51 | 0.29 | 0.08 | –1.92 | 0.31 | <0.001 |
| March | 1.98 | 0.13 | <0.001 | –2.05 | 0.27 | <0.001 | –2.60 | 0.28 | <0.001 |
| April | 1.18 | 0.13 | <0.001 | –1.50 | 0.31 | <0.001 | –2.34 | 0.32 | <0.001 |
| Year (2016) | –0.04 | 0.27 | 0.87 | 0.10 | 0.24 | 0.67 | 0.13 | 0.32 | 0.68 |
| Year (2017) | –0.60 | 0.27 | 0.03 | 0.45 | 0.26 | 0.08 | 0.05 | 0.33 | 0.88 |
| Fish type a | 0.30 | 0.15 | 0.046 | –0.02 | 0.13 | 0.82 | –0.25 | 0.18 | 0.16 |
| Aq in buffer b | 0.29 | 0.10 | 0.008 | –0.50 | 0.10 | <0.001 | 0.38 | 0.13 | 0.003 |
| Nat in buffer c | –0.19 | 0.11 | 0.08 | –0.09 | 0.10 | 0.33 | 0.21 | 0.13 | 0.11 |
| Aq hectare d | 0.47 | 0.11 | <0.001 | 0.59 | 0.10 | <0.001 | 0.40 | 0.13 | 0.002 |
| RST-VAR e | 0.18 | 0.04 | <0.001 | ||||||
a Fish-type index (−1 to +1) represents proportion of surface area within the aquaculture cluster for raising food fish (≥20 cm) minus the area for fingerlings (<20 cm).
b Surface area of aquaculture within 4-km (herons) or 14-km (cormorants and egrets) buffer around aquaculture clusters based on top models (see Table 2).
c Surface area of naturally occurring waterbodies within 4-km (herons) or 14-km (cormorants and egrets) buffer around aquaculture clusters based on top models (see Table 2).
d Surface area (ha) of aquaculture within cluster.
e Index of the number of cormorants from surrounding roost sites likely to forage at each aquaculture cluster (see Methods).
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