Balaenoptera ricei Rosel & Wilcox & Yamada & Mullin 2021, sp. nov.

Balaenoptera ricei sp. nov.

Rice's whale

Figures 3, 7, 8; Table 1; Figures S8 – S 10

4.5.1 | Holotype and Type Locality

USNM 594665, an adult male, 1,126 cm, stranded on January 29, 2019, near Flamingo, Florida Bay, Gulf of Mexico, at the outer edge of Everglades National Park, Florida (25.0344 N, 81.0185 W). The skull (Figures 7 and S10) and complete skeleton and baleen are deposited in the U.S. National Museum of Natural History. The full mtDNA control region sequence for the holotype has been placed in GenBank with accession number MN017985.

4.5.2 | Additional Material

Lowery (1974) reported a skull found on the Chandeleur Islands, St. Bernard Parish, Louisiana, in June 1954. This specimen is housed in the Louisiana State University Museum of Natural Science (LSUMZ 17027) and was originally identified as a fin whale. We sequenced the mitochondrial DNA control region of this specimen and identified it as a Rice's whale. Unfortunately, the skull is missing a number of important bones, including the premaxillae, nasals, lacrimals, jugals, and pterygoid hamuli. Photographs of the skull are in Lowery (1974) and Figures S3 and S4.

A complete skull and skeleton of a 1,105 cm immature male whale that stranded in New Hanover County, North Carolina (34.07 N, 77.88 W) on March 13, 2003 was deposited in the U.S. National Museum of Natural History under specimen number USNM 572922. The whale was genetically confirmed to be a Rice's whale (Rosel & Wilcox, 2014). Best (2007) published photographs of the skull of this specimen and assigned it as B. edeni. Photographs of the skull are also in Figure S5.

On October 4, 2009, a 1,265 cm adult female whale stranded in Tampa Bay, Florida (27.91 N, 82.43 W) and the carcass was buried in Fort De Soto Park, Pinellas County, Florida. The whale was genetically confirmed as a Rice's whale (Rosel & Wilcox, 2014). In March 2018, the remains were excavated in the hopes of finding an intact skull to serve as a type specimen. Unfortunately, the skull had been crushed during burial and most of the specimen lay in water for the 9 years it was buried. The remains of the skull and a nearly complete vertebral column were retrieved and deposited in the Florida Museum of Natural History in Gainesville, Florida with accession number UF33536.

4.5.3 | Diagnosis

Balaenoptera ricei differs from B. e. edeni and B. e. brydei in the following morphological features: the nasals taper and curve laterally at the posterior end and have a smooth margin, meeting the medial-posterior margin of the ascending process of the maxilla; there is a broad gap between the nasal bones that does not narrow posteriorly created in part by the frontal bones which protrude anteriorly between the posterior end of the nasals (Figure 8). Rice's whale can also be differentiated from all other species of rorqual baleen whales based on molecular genetic characters, as shown in the phylogenic analyses of the mtDNA control region (Table 3, Figure 2). Within the 305 base pair alignment of the 5 0 end of the mtDNA control region, ten diagnostic sites differentiate B. ricei from both B. e. brydei and B. e. edeni (Table 2).

4.5.4 | Description

The Rice's whale is a medium-sized rorqual whale. They appear to be larger than Omura's whales and smaller than Bryde's whales, B. e. brydei, but, based on limited samples, about the same size as Eden's whales. To date, the largest verified Rice's whale was 1,265 cm in length (a lactating female) and the largest male was 1,126 cm. Rice's whales have a falcate dorsal fin (Figure S6). In the holotype specimen, the dorsal fin was located approximately 2/3 of the way back from the snout. The flippers are uniformly dark. Although sample sizes are small, the ventral grooves/pleats reach to or just past the umbilicus; in the holotype specimen 1 pleat extended 36 cm past the umbilicus and two additional pleats extended past the umbilicus but were not measured (Table S4). The number of pleats counted on the holotype specimen at the flipper insertion was 27 to the central midline making a total of 54 pleats. These whales exhibit no external asymmetrical pigmentation on the lower jaws, thereby differentiating them from the asymmetrical jaw coloration seen in fin whales and Omura's whales. Body color is uniformly dark charcoal gray above, including both the upper and lower jaws, and light to pinkish countershading ventrally. Some whales exhibit diffuse white washes on the body around the base of the dorsal fin and/or along the sides but to date no consistency in the pattern across individuals has been seen (Figure S7). The fringe of the baleen plates is uniformly cream colored throughout the entire rack, the anterior baleen plates are cream colored on both sides, with a distinct posterior transition to black plates (Figure 3). Plate count for the holotype specimen was 264 on the left side. A total of 224 plates were counted on the right side but approximately 60 cm of the baleen rack of the right side was not accessible making this is an incomplete count. Mead (1977) and Kato and Perrin (2018) indicated that the baleen bristles of members of the Bryde's whale complex are coarser than those of sei whales, and we can confirm, based on a sample size of three, that the baleen bristles of Rice's whales from the GOMx are coarser than that of a sei whale that stranded in the GOMx in 1994. However, no comprehensive analysis of bristle diameter across all the Bryde's whale taxa has yet been performed.

The vertebral formula of the holotype is cervical (7) + thoracic (13) + lumbar (13) + caudal (20) = 53. There were 13 ribs on either side and the head of each first rib is bifurcated.

Several other unique features were noted in the skeleton of the holotype. Junge (1950), Lönnberg (1931), and Omura (1959) describe the stylohyal bones of Bryde's whales as generally longer than they are wide with some degree of curvature. The stylohyal bones of the holotype of B. ricei had little curvature to them and are very broad (Figure S9). In addition, the pelvic bones of the holotype specimen are nearly straight, with only a very small projection on one side (Figure S9).

4.5.5 | Etymology

The specific name, ricei, is in honor of renowned American cetologist Dale W. Rice (1930 – 2017). We choose this species name to commemorate Dale W. Rice who had a distinguished 60-year career in marine mammal science and wrote the seminal volume “Marine Mammals of the World” (Rice, 1998), which provided the first comprehensive worldwide review of the systematics and distribution of all marine mammal species. He was the first researcher to recognize that Bryde's whales are present in the GOMx (Rice, 1965). We propose Rice's whale as the common English name. Naming it after a person is consistent with the other members of the complex: Eden's whale (B. e. edeni) having been named after Ashley Eden, a British Commissioner (Anderson, 1878 [1879]), Bryde's whale (B. e. brydei) named after Johan Bryde, a Norwegian businessman and whaler (Olsen, 1913), and Omura's whale (B. omurai) was named after the Japanese cetologist Hideo Omura (Wada et al., 2003). We note that the common name ‘Gulf of Mexico whale’ has been used for this species.

4.5.6 | Nomenclatural Statement

A Life Science Identifier (LSID) was obtained for this publication: urn:lsid:zoobank.org:pub: ACA4D8E5-1373-4D26-931F-0A657EEDE4CC.

4.5.7 | Comparison

Externally, Rice's whale is separated from all other balaenopterid whales except those in the Bryde's whale complex by the presence of three longitudinal ridges on the rostrum; one in the center and two lateral ridges (Figure 1). Omura's whale lacks these prominent lateral ridges, instead having faint ridges visible only in certain viewing conditions (Cerchio et al., 2015).

As described in Wada et al. (2003), the vertex of the skull, including the shapes and extent of the ascending process of the maxilla (APM), the nasals, frontals, premaxillae serve as much of the defining morphological characteristics that separate members of the Bryde's whale complex (Figure 8). In this region, B. ricei is clearly differentiated from B. e. edeni by the shape and extent of the ascending process of the maxilla which broaden only slightly at the posterior end, more similar in shape to B. e. brydei than B. omurai or B. e. edeni, with B. e. edeni being distinctive in its slender ascending process of the maxilla with rounded posterior end (Figures 8 and S10). B. ricei also differs from B. e. edeni in the shape of the nasals (triangular versus rectangular), and the extent of the frontals, which are exposed as a thin strip or belt between the ascending processes of the maxilla, the posterior end of the nasals and the supraoccipital, rather than the broad exposure of the frontals seen in B. e. edeni. B. ricei is most easily differentiated from B. omurai by the posterior end of the premaxillae which reach the frontals in B. ricei but not in B. omurai (Figure 8). In addition, the alisphenoid is in contact with the squamosal (Figure S8) while it is separated from the squamosal bone in B. omurai (Wada et al., 2003). Finally, B. ricei can be distinguished from B. e. brydei by the shape of the posterior end of the nasals which curve laterally and have smooth margins, while in B. e. brydei the posterior end of the nasals remains relatively straight and the posterior margin is crenulated. In addition, the frontal bones wrap around and extend anteriorly into the space between the posterior end of the nasals, creating a significant space or gap between the nasal bones along their entire length.

Finally, B. ricei is unambiguously discriminated from all other balaenopterid whales by DNA sequence of the mitochondrial genome. Ten diagnostic sites in the 5 0 end of the mitochondrial control region (between nucleotide positions 15536 – 15818 of the B. e. brydei mtDNA genome GenBank accession number AB 201259) separate B. ricei from all members of the Bryde's whale complex (Table 2). Similarly, mitochondrial cytochrome b and cytochrome oxidase I genes exhibit multiple fixed differences between B. ricei and B. e. edeni, B. e. brydei, and B. omurai (Rosel & Wilcox, 2014).

4.5.8 | Distribution

Based on vessel and aerial survey sightings, the primary core habitat of Rice's whale is currently in the northeastern GOMx, centered over the De Soto Canyon in waters between 150 and 410 m depth (Figure 4). Recently there was a genetically confirmed sighting in the western GOMx off the central Texas coast in 225 m water depth (National Marine Fisheries Service, 2018), and preliminary analysis of acoustic recordings from the western GOMx along the shelf break south of the Flower Garden Banks National Marine Sanctuary suggest the presence of Bryde's-like whales (M. Soldevilla, personal communication, April 2019) in the same area as two balaenopterid sightings made by NMFS in the early 1990s (Figure 4). While contemporary sightings are primarily confined to the northeastern GOMx, it is possible the species historically had a broader distribution in the GOMx. Reeves et al. (2011) reviewed whaling logbooks from the GOMx and identified records of “finback” whales from the north central Gulf south of the Mississippi River delta and in the southern Gulf on the Campeche Banks. As fin whales are not part of the GOMx ecosystem, these were likely Rice's whales misidentified as fin whales (Reeves et al., 2011), suggesting the whale's distribution was broader than we see today.