Caribbean sperm whales 817
TABLE 1 Number of groups and individuals of sperm whales Physeter macrocephalus recorded during the daytime and night-time during 2011 and 2013–2016 in the Colombian Caribbean (Fig. 1), with hours of survey effort and area surveyed. Number of individuals by age was only recorded during the daytime.
Effort (h) Year
2011 573.0 2013 1,739.2 2014 333.3 2015 2,757.1 2016 2,547.7 Total
872.9 0.0
7,950.3
2,330.3 1,916.3 5,119.5
Area (km2) 2,876.0
22,980.7 3,097.0 4,410.0
0.0 0.0
10,878.6 9,105.4 8,878.7
6,678.3 50,024.0 18,880.7 Number of groups 5
16 6 3 5
35
(Zurell et al., 2020). The functions partition the data into k folds (k = 15), determine the model algorithm, update the model for the new training data, and make predictions for the hold-out data. The values of the area under the curve (AUC) and the true skill statistic were used as indicators of the predictive ability of the models. The best model is that with an AUC value closest to 1 (Phillips et al., 2006). For the true skill statistic, a value.0.5 indicates a good pre- diction (Tobeña et al., 2016). Two types of model output are commonly used to describe the potential distribution of a species: continuous results in which sites are assigned a probability of being part of a species’ distribution, and bi- nary results in which sites are classified as either part of the distribution of the species or outside their distribution (Liu et al., 2009). For the former, the final output maps de- rived from the cross-validation predictions for each type of model were exported in raster format with values in the range 0–1, and were interpreted as an estimate of occurrence probability. For the latter, binary maps were constructed to indicate where sperm whales could be present. To do this, the maps of occurrence probability were transformed by calculating an optimal threshold (a value that maximizes the sum of model sensitivity plus specificity) using the PresenceAbsence package (Freeman & Moisen, 2008)in R, implemented in the script of Zurell et al. (2020). As we used several record types of sperm whale occurrence (pub- lished and opportunistic acoustic and sighting data), data were first cleaned, removing duplicate records and retaining only one occurrence record per grid cell.
Results Monitoring
During 2011 and 2013–2016 we surveyed for a total of 13,069.8hin 703 days over an area of 68,904.7 km2 (Table 1). We covered 52.1% of the offshore areas of the Colombian Caribbean Sea (Supplementary Fig. 1). We re- corded a total of 98 individual sperm whales in 50 groups,
0 9 0 5 1
Number of individuals
15 37 13 4 8
0
15 0 5 1
15 77 21
Number of individuals by age
Daytime Night-time Daytime Night-time Daytime Night-time Daytime Night-time Adults Juveniles 0.0
15 36 12 3 7
73
0 1 1 1 1 4
of which 77 individuals (73 adults and four juveniles) in 35 groups were during daytime in 7,950.3 h of surveys over 50,024 km2, and 21 individuals in 15 groups were during night-time in 5,119.5 h of acoustic surveys over 18,880.7 km2. Group sizes were 1–10 (mean 2.0 ± SD 1.5) and each group was recorded for a mean of 18.9 ± SD 22.1 minutes. All observations of sperm whales were during seismic sur- veys and were outside the mitigation zone (a radius of 500m around the sound source; JNCC, 2017); 62 and 38% of these observations were when the seismic airgun was ac- tive and inactive, respectively. Sperm whales exhibited slow and fast swimming, exposure of pectoral and caudal fins, resting, spyhopping (putting head out of water and looking around) and breaching behaviours (Plate 1). Mean encounter rate was 0.8 individuals and 0.4 groups
per 100 h, with 0.7 individuals and 0.5 groups per 100 hours during daytime, and 0.8 individuals and 0.3 groups per 100 h during night-time. The estimated density of sperm whales was 1.42 individuals and 0.7 groups per 1,000 km2, with 1.6 individuals and 0.7 groups per 1,000 km2 during daytime and 1.1 individuals and 0.8 groups per 1,000 km2 during night-time.
Distribution models
Data for a total of 66 groups of sperm whales and at least 124 individuals were recorded in our surveys and opportunistic sightings, and published data, combined, during 1988–2020, of which eight records were juveniles (0.8 per year). Sperm whales were recorded at a mean distance of 72.5 km from the coast (6–237 km), in a mean water depth of 1,700m (244–4,191 m; Table 2, Fig. 2). The PCA indicated environmental heterogeneity across
the water column, with the surface the most differentiated compared to the five water depth levels (Supplementary Fig. 3). The generalized linear models, ranked by Akaike’s information criterion, indicated the most important vari- ables that explain sperm whale distribution were distance to shore, and range and standard deviation of ocean mixed layer thickness (Supplementary Table 4).
Oryx, 2022, 56(6), 814–824 © The Author(s), 2022. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605321001113
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148 |
Page 149 |
Page 150 |
Page 151 |
Page 152 |
Page 153 |
Page 154 |
Page 155 |
Page 156 |
Page 157 |
Page 158 |
Page 159 |
Page 160 |
Page 161 |
Page 162 |
Page 163 |
Page 164
