The Gulf of Mexico is a subtropical marginal sea of the western North Atlantic Ocean with a diverse cetacean community. Ship‐based, line‐transect abundance surveys were conducted in oceanic waters (>200 m deep) of the northern Gulf within U. S. waters (380,432 km2) during spring from 1996 to 1997 and from 1999 to 2001. Data from these five surveys were pooled and minimum abundance estimates were based on 12,162 km of effort and 512 sightings of at least 19 species. The most commonly sighted species (number of groups) were pantropical spotted dolphin, Stenella attenuata (164); sperm whale, Physeter macrocephalus (67); dwarf/pygmy sperm whale, Kogia simalbreviceps (58); Risso's dolphin, Grampus griseus (38); and bottlenose dolphin, Tursiops truncatus (24). The most abundant species (number of individuals; coefficient of variation) were S. attenuata (91,321; 0.16); Clymene dolphin, S. clymene (17,355; 0.65); spinner dolphin, S. longirostris (11,971; 0.71); and striped dolphin, S. coeruleoalba (6,505; 0.43). The only large whales sighted were P. macrocephalus (1,349; 0.23) and Bryde's whale, Balaenopteraedeni (40; 0.61). Abundances for other species or genera ranged from 95 to 2,388 animals. Cetaceans were sighted throughout the oceanic northern Gulf and, whereas many species were widely distributed, some had more regional distributions.

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Cycleptus meridionalis is a new species recently distinguished from blue sucker C. elongatus. It occurs in large rivers draining to the northern Gulf of Mexico chiefly through Alabama and Mississippi. Collections over a 12‐month period from the Pearl and Pascagoula rivers, Mississippi, were taken to document the new species' life history characteristics. Female C. meridionalis had significantly greater wet weight (WW, kg) per given total length (TL, mm) (WW = 4.228−13 TL4.588) than males (WW = 2.000−9 TL3.237). Aged opercular bones indicated that one annulus formed during September–October at the beginning of the reproductive season. Fish ages in the sample ranged from 6 to 31 years for females and from 4 to 33 years for males. Longevity of C. meridionalis is markedly greater than previous scale aging of C. elongatus had suggested. Male C. meridionalis as small as 327 mm TL (age 4) and females as small as 444 mm TL (age 11) had visibly developed gonads; mean gonadosomatic index was elevated in both sexes between October and March and declined by early April. Spawning began in February to early March when the temperature exceeded 13–14°C. The sex ratio was not different from 1:1 (P > 0.05). Cycleptus meridionalis foraged on aquatic insect larval stages; trichopteran larvae and pupae, chironomid larvae and pupae, and coleopteran larvae were the most common prey items regardless of sex, size, or river. These life history characteristics and food habits are similar to those reported for C. elongatus in the Mississippi River drainage. Our observations indicate that C. meridionalis is viable in both rivers sampled but may be influenced by future river modification as has happened with C. elongatus, which is threatened or endangered over much of its range.

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