ACS Research Committee Report

MALE FRANCISCANA REPRODUCTIVE BIOLOGY
Source: Danilewicz, D., Claver, J.A., Carrera, A.L.P., Secchi, E.R., and Fontoura, N.F. 2004. Reproductive biology of male franciscanas (Pontoporia blainvillei) (Mammalia: Cetacea) from Rio Grande do Sul, southern Brazil. Fish. Bull. 102: 581-592.

The franciscana is a small coastal dolphin native to the southwestern Atlantic Ocean. It ranges from southeastern Brazil south to Golfo Nuevo, Argentina. This study was conducted on 121 individual franciscanas that were incidentally killed in fishing activities off the coast of Rio Grande do Sul State in southeastern Brazil. The reproductive activity of males was determined through measurement of testis size, as well as age, size, and maturity of individuals. Sexual maturity was estimated to be attained at 3.6 years. Average length at sexual maturity was 128.3 cm and average weight was 26.4 kg. There was not a significant seasonal change in testis size, indicating that at least some mature males remain reproductively active throughout the year. Overall, the testes of franciscana are small, indicating that sperm competition is not present in this species. However, there were also no secondary sexual characteristics that would be used by males to attract females and males rarely had scars from aggressive interactions with other males. These findings indicate that male franciscanas most likely do not combat each other for mating access to females. It is hypothesized that males and females form temporary pairs and that they mate with only that one partner during the reproductive period.    

DIEL VARIATION IN BLUE WHALE CALLS IN THE PACIFIC
Source: Stafford, K.M., Moore, S.E., and Fox, C.G. 2005. Diel variation in blue whale calls recorded in the eastern tropical Pacific. Anim. Beh. 69(4): 951-958.

Blue whales in the northeast Pacific Ocean often produce two-part calls. The first part ("A") is amplitude-modulated and lasts about 17 seconds. The second part ("B") is frequency-modulated and lasts about 19 seconds. Type B calls are more easily detected in recordings and are often used in long-term monitoring of blue whales. A hydrophone moored in the eastern tropical Pacific recorded sounds in the water from May 1996 to May 1997 and showed seasonal variability in blue whale calls. Calls were detected from February to June. Blue whales are hypothesized to use the eastern tropical Pacific as a wintering ground, but they most likely feed in the area, as well. The primary prey of blue whales is krill, shrimp-like plankton, that migrate vertically from several hundred meters depth during the day to near the surface at night. The hourly rate of blue whale B calls showed a diel (daily) pattern, with more calls during dark and twilight hours than during the day. These call patterns correlate well with prey distribution, with the highest call rates occurring when prey is close to the surface.    

PREDICTORS OF CALF MORTALITY IN INDIAN OCEAN BOTTLENOSE DOLPHINS
Source: Mann, J. and Watson-Capps, J.J. 2005. Surviving at sea: ecological and behavioural predictors of calf mortality in Indian Ocean bottlenose dolphins, Tursiops sp. Anim. Beh. 69(4): 899-909.

In this study, the behavioural ecology of bottlenose dolphin mothers and calves during their first year of life was analyzed to determine if any variables predicted calf mortality. Seventy-five percent of calves that died showed visible signs of poor health compared to only 4.7 percent of the survivors that showed similar signs. Calves that spent more time swimming in the infant position (in contact with the mother) in the first year of life were more likely to die by the age of three than calves that spent less time in this position. No other behavioural or ecological factors were significantly correlated with calf mortality. The authors hypothesize that mothers or calves may compensate for poor calf health by increasing the time spent in contact with each other. Frequent separations between the mother and calf, as well as high rates of calf socializing and foraging may be a good indicator of calf health.    

VOCAL BEHAVIOUR OF TRANSIENT KILLER WHALES
Source: Deecke, V.B., Ford, J.K.B., and Slater, P.J.B. 2005. The vocal behaviour of mammal-eating killer whales: communicating with costly calls. Anim. Beh. 69(2): 395-405.

Animals may pay a cost of for vocal behavior if predators or potential prey eavesdrop on their vocal communication. In the northeastern Pacific, there are two ecotypes of killer whales. "Resident" killer whales feed on fish, a prey with poor hearing abilities. However, "transient" killer whales feed primarily on marine mammals, which have excellent underwater hearing. This study investigates how the superior hearing of marine mammal prey may shape the vocal habits of transient killer whales. Transient killer whales produced pulsed calls significantly less often than residents. Transients only showed significant vocal behavior after a marine mammal kill or when they were demonstrating surface-active behavior. The reduced vocal activity of transients is most likely due to the greater cost for calling because of eavesdropping by potential prey. The increase in vocalizations after a kill may represent calling to inform other animals about the presence of food, or more likely an increase in social interaction during feeding and reduced cost of calling during this time.    

PREY DETECTION BY BOTTLENOSE DOLPHINS
Source: Gannon, D.P., Barros, N.B., Nowacek, D.P., Read, A.J., Waples, D.M., and Wells, R.S. 2005. Prey detection by bottlenose dolphins, Tursiops truncates: an experimental test of the passive listening hypothesis. Anim. Beh. 69(3): 709-720.

Bottlenose dolphins possess a sophisticated echolocation system, but evidence suggests that they use this system sparingly in the wild. Several authors have noted that fish that produce sound are common in the diet of bottlenose dolphins, leading to the hypothesis that these dolphins may detect prey by passive listening. In this study, playback experiments were conducted on free-ranging dolphins in Sarasota Bay, Florida. Recordings of prey fish and sounds of snapping shrimp were used as experimental and control conditions, respectively. The direction of dolphin travel and the rate of echolocation were recorded as response variables. Dolphins changed their direction of travel significantly, turning towards the sound source during playbacks of fish sounds. In addition, dolphins significantly increased their echolocation rate immediately following playbacks of fish sounds. The sounds of snapping shrimp elicited neither the directional nor the echolocation changes. The occurrence of echolocation sounds was low except after the playback of fish sounds. The results found here support the hypothesis that dolphins use passive listening to locate fish. Once the sounds of fish are detected, the dolphins use echolocation to track and capture the prey. The sparing use of echolocation suggests that it may be energetically costly.   

WINTER FEEDING OF NARWHALS
Source: Laidre, K.L. and Heide-Jorgensen, M.P. 2005. Winter feeding intensity of narwhals (Monodon monoceros). Mar. Mamm. Sci. 21(1): 45-57.

The stomach contents from 121 narwhals harvested in the eastern Canadian High Arctic and West Greenland were used to quantify seasonal changes in feeding activity and prey selection. In the summer, narwhal stomachs were mostly empty with little evidence of recent feeding. However, in the late fall and winter, their stomachs had considerable amounts of undigested prey with evidence of recent feeding. In the summer, Arctic cod, polar cod, and squid are the primary narwhal diet. In the late fall and winter, Greenland halibut and squid were primary prey items. These results indicate that narwhals have a restricted diet across all seasons.    

MOVEMENTS AND DIVE PATTERNS OF A LONGFINNED PILOT WHALE
Source: Mate, B.R., Lagerquist, B.A., Winsor, M., Geraci, J., and Prescott, J.H. 2005. Movements and dive habits of a satellite-monitored longfinned pilot whale (Globicephala melas) in the Northwest Atlantic. Mar. Mamm. Sci. 21(1): 136-144.

Longfinned pilot whales are common in the waters of the northeast United States, with a typical distribution on the shelf edge and slope waters. Pilot whales are very social and can be found in groups of up to 200; they have a high frequency of mass stranding. The animal followed in this study was part of a mass stranding of 30 pilot whales on Cape Cod, Massachusetts, in December 1986. The only survivors were three juveniles, which were taken in to the New England Aquarium for rehabilitation and released in June 1987. One of the whales was fitted with a satellite tag to monitor its post-rehabilitation behavior. The whale was released southeast of Cape Cod and was tracked for 3,144 km. It had an overall minimum speed of 1.4 km/h. Following its release, the pilot whale remained on Georges Bank for 9 d, then it moved south into deeper water beyond the continental slope where it remained for 10 d before moving back to the shelf. It spent the next 2 d traveling north across the New England shelf west of the Great South Channel. Then it entered the Gulf of Maine, where it remained for the duration of the tracking period (total tracking time was 94.5 d). Average dive duration ranged from 24-62 sec; the percentage of time the whale spent at the surface ranged from 5.6% to 47.4%. The whale had slower travel speeds during August and September in the Gulf of Maine, perhaps representing non-directional, feeding movements. Higher travel speeds occurred in the other areas prior to the whale entering the Gulf of Maine; these high speeds may indicate searching, either for prey or for other whales. The dive duration increased throughout the study period, indicating that the whale's diving ability may have increased as it matured or as it gained strength after its rehabilitation.