Migratory destinations and spatial structuring of humpback whales (Megaptera novaeangliae) wintering off Nicaragua

Abstract

Understanding the migratory patterns of large whales is of conservation importance, especially in identifying threats to specific populations. Migration ecology, including migratory destinations, movements and site fidelity for humpback whales (Megaptera novaeangliae) remain poorly studied in parts of the range of the Central America population, considered endangered under the United States Endangered Species Act. This study aimed to investigate the migratory destinations of humpback whales sighted at two study sites in Nicaragua, which are part of the Central America population. A ten-year photographic database of humpback whales observed off Nicaragua was combined with citizen science contributions and sightings from dedicated research programs. The resulting image collection was compared with available historical photo identifications and databases using an automated image recognition algorithm. This approach yielded 36 years of photographic identification totaling 431 recaptures in Nicaragua (2006-2008 and 2016-2021) and 2539 recaptures (1986-2020) in both feeding and breeding grounds of 176 unique individuals sighted in Nicaragua. Our results showed that photo-identified whales were recaptured between October and April in breeding grounds and year-round in feeding grounds between British Columbia and California, with peak recaptures between June and October. Our study provided first-time evidence on fine-scale site affinity of individual humpback whales within Nicaraguan waters and to other breeding and feeding grounds.

Figure 1

Migratory destinations of humpback whales observed off (a) northern Nicaragua (N-NI) (unique individuals n = 62), (b) southern Nicaragua (S-NI) (unique individuals n = 101), (c) individuals observed in both sites with equal recapture ratios (unique individuals n = 13) and (d) both the northern and southern sites combined. Numbers in brackets represent the number of individuals observed per feeding sites defined in the feeding ground (FG). Note that one individual could be observed in multiple feeding sites. Feeding sites: BC, British Columbia; WA, Washington; OR, Oregon; NCA, northern California; CCA, central California; SCA, southern California. The background map was created with the QGIS 3.22.5 software (www.qgis.org), using country administrative boundaries provided by Diva-GIS (http://www.diva-gis.org/).

Figure 2

Migratory timing of humpback whales observed off the Pacific coast of Nicaragua with all recaptures pooled for (a) feeding grounds (n = 2073) and (b) breeding grounds (n = 897). NI, Nicaragua; Other, other breeding sites including Baja California; mainland Mexico; southern Mexico; Guatemala; El Salvador; northern Nicaragua; southern Nicaragua; northern Costa Rica; southern Costa Rica; Panama.

Figure 3

Spatio-temporal distribution of humpback whales observed off the Pacific coast of Nicaragua recaptured in feeding grounds (n = 2073) and in breeding grounds (n = 897). The background map was created with the QGIS 3.22.5 software (www.qgis.org), using country administrative boundaries provided by Diva-GIS (http://www.diva-gis.org/).

Figure 4

Site affinity and spatial structuring of humpback whale individual recaptures with a Nicaraguan site of origin. (a) Cluster analysis with the SIMPROF test based on similarity of individual recaptures. Identified clusters are indicated with a different letter with colored lines indicating a higher affinity between sites. The cluster was generated with PRIMER v. 7 software. (b) Representation of spatial structuring within the Nicaraguan whales based on individual photographic recaptures. Line thickness represents the level of similarity of each cluster based on the cluster analysis. BC, British Columbia; WA, Washington; OR, Oregon; NCA, northern California; CCA, central California; SCA, southern California, BAC, Baja California; ML, mainland Mexico; SM, southern Mexico; GUA, Guatemala; ES, El Salvador; N-NI = northern Nicaragua; S-NI, southern Nicaragua; N-CR, northern Costa Rica; S-CR, southern Costa Rica; PA, Panama. The background map was created with the QGIS 3.22.5 software (www.qgis.org), using country administrative boundaries provided by Diva-GIS (http://www.diva-gis.org/). The photograph was made available by Joëlle De Weerdt.