Lamu Offshore IMMA

Globally blue whales (Balaenoptera musculus) are listed by IUCN as ‘Endangered’ (Reilly et al. 2008). At least three of the five recognized subspecies of blue whale (Thomas et al. 2015), are found in the western Indian Ocean: the Antarctic blue whale (B. m. intermedia), the pygmy blue whale (B. m. brevicauda), and the northern Indian Ocean blue whale (B. m. indica; Branch et al. 2007; Anderson et al. 2012). The Antarctic blue whale is red-listed as ‘Critically Endangered’ and the pygmy blue whale as ‘Data Deficient’ (Thomas et al. 2015). An absence of abundance data has precluded assessment of the northern Indian Ocean subspecies (Thomas et al. 2015). Blue whales found in this region represent one of, or a mixture of, the three subspecies known to occur. Additionally, Cerchio et al. (2018) suggested the likelihood of an additional, distinct, population of blue whales, based on the detection of a previously undetected blue whale call type that differs from other subspecies of blue whales that occur in the western Indian Ocean. Thirty confirmed sightings of 38 individual blue whales were made during seismic surveys off the northern Kenyan coast during September and October 2014. The surveys continued until January 2015, but no further blue whale sightings were recorded after October, suggesting that they are seasonally present in the area. Most sightings were of individuals, although groups of up to three were recorded (Barber et al. 2016). September and October mark the end of the South-East Monsoon period, a period of major upwelling and associated productivity, particularly off the Somalia coast (McClanahan 1988; Isaac and Isaac 1968). Whales sighted during the seismic surveys were not identified to subspecies. These sightings suggest that the offshore waters of northern Kenya (and likely southern Somalia) form an important habitat for blue whales in the Indian Ocean, at least during the end of the South-East Monsoon period. Redfern et al. (2017) used habitat models to predict blue whale distribution in the Northern Indian Ocean. It is not known whether these waters represent a feeding ground, a breeding region or part of a migratory route. These observations are broadly consistent with other blue whale sightings recorded within the wider western Indian Ocean, specifically off Somalia and in the Gulf of Aden. These include nineteenth century whaling records made in the Gulf of Aden in September and November (Anderson et al. 2012), Japanese records in March 1982 (Kasuya and Wada 1991), and 18 sightings of blue whales in 1985 off Somalia (October, November and December; Small and Small, 1991).