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Resumen del producto

Ortega-Ortiz, C.D., R.M., Mata-Cruz, T., Gerrodette & D., Gendron (2022). A photogrametic method to estimate total length of the largest mammal, the blue whale (Balaenoptera musculus). L., Karczmarski, S.C.Y., Chan, D.I., Rubenstein, S.Y.S., Chui & E.Z., Cameron (Eds.), Mammalian Biology. 102: 629–643. DOI: 10.1007/s42991-022-00307-6.

A photogrametic method to estimate total length of the largest mammal, the blue whale (Balaenoptera musculus)

Christian Daniel Ortega-Ortiz 1, Ricardo Mirsha Mata-Cruz 2, Tim Gerrodette 3 y Diane Gendron 4

1 Universidad de Colima,Facultad de Ciencias Marinas,km 20 Carr. Manzanillo-Barra de Navidad, C.P. 28860 Manzanillo, Col., Mexico
2 Instituto Politécnico Nacional, Centro Interdisciplinario de Ciencias Marinas, Pesquerias y Bilologia Marina
3 Southwest Fisheries Science Center, NOAA Fish
4 Instituto Politécnico Nacional, Centro Interdisciplinario de Ciencias Marinas
Length measurement of individuals provides useful information for biological and ecological studies and is instructive inestimating and parameterization of population dynamics and to identify changes in population structure. This study presentsa photogrammetric method to estimate the total length of blue whales from a boat, using sequential images taken to measurethe exposed body flank of the whale, from the blowhole to the dorsal fin, while simultaneously measuring the perpendiculardistance between the whale and the camera to determine the scale of the image. The photo sequences were joined and measuredwith specialized software. Total length was predicted from blowhole–dorsal fin length using body proportion, mainlyfrom whaling data. A Bayesian model calculated uncertainty in predicted total length due to errors in the photo-sequenceprocess and variability in body proportion. Nearly all the uncertainty in total length was due to variability in the photosequencemeasurements of blowhole–dorsal fin length rather than in body proportion. The precision of estimates of totallength depended on the number of replicate photo-sequences and size of whale but generally were in the range of 2–3%. Acomparison of the total lengths of four individuals simultaneously measured by replicated photo-sequences and aerial photogrammetryshowed that the photo-sequence method was unbiased. The photo-sequence method applied to 169 individualssighted during 2006–2015 in the Gulf of California revealed an average length of 20.49 m and a range of 7.45–29.01 m,which falls within the known length range for Northeast Pacific blue whales. The photo-sequence method can be carriedout in conjunction with other field studies of the species as it does not modify sampling logistics, nor add to the cost of thestudy. It also has the advantage of being adaptable to other cetaceans that show natural flank marking.

Palabras clave: Bayesian model; Blue whale; Gulf of California; Photogrammetry; Photo-sequences; Photographic field; techniques; Total length

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