FIRST RECORDS OF HUMPBACK WHALES INCLUDING CALVES AT GOLFO DULCE AND ISLA DEL COCO, COSTA RICA, SUGGESTING GEOGRAPHICAL OVERLAP OF NORTHERN AND SOUTHERN HEMISPHERE POPULATIONS

We present the first documented records of humpback whales (Megaptera novaeangliae), including mothers with calves, in Golfo Dulce and at Isla del Coco, Costa Rica. These sightings suggest a possible overlap in the spatial distribution of southern and northern hemisphere humpback whales near Costa Rica. Results of biopsy studies indicate that transoceanic genetic exchange has occurred among North Pacific and Southern Ocean populations of humpback whales. This is based on similarities in mitochondrial DNA sequence (Baker et al. 1993, 1994). Baker et al. (1993) hypothesized that equatorial waters of the eastern Pacific Ocean are a likely route for such interbreeding of northern and southern hemisphere humpbacks. However, direct observational evidence of spatial or temporal overlap of northern and southern hemisphere humpbacks has not been available. Northern hemisphere humpbacks of the North Pacific population winter primarily in low latitudes near 20”N in Mexican, Hawaiian, and Japanese waters from December to April, with most calves born between December and February; they migrate north to feeding grounds near Alaska during the summer and fall (Townsend 1935, Nishiwaki 1966, Tomilin 1967, Rice 1978, Baker et al. 1986). The previous southernmost confirmed record of northern hemisphere humpbacks in the Pacific Ocean were two whales photographed near Isla de1 Cano off Costa Rica on 16 February 1988 at 8”40’N (Fig. 1); these individuals were subsequently matched to sightings off central California (Steiger et al. 199 1). Southern hemisphere humpbacks of the eastern Pacific population winter primarily in low latitudes near the equator off Colombia, Ecuador, and in the Gulf of Panama from June to October, with a calving peak in July and August; they migrate south to antarctic feeding grounds during the austral summer and fall (Townsend 1935; Mackintosh 1942; Chittleborough 1958, 1965; Nishiwaki 1966; Rice 1978; Stone et al. 1990) (Fig. 1). The previous northernmost confirmed record of a southern hemisphere humpback was at 2”57’N, 78”12’W, near Colombia on 28 August 1986; this whale was previously sighted in