ACS Research Committee Report

MORTALITY OF COMMON DOLPHINS IN PORTUGAL
Source: Silva, M.A. and M. Seguera. Patterns in the mortality of common dolphins (Delphinus delphis) on the Portuguese coast, using stranding records, 1975-1998. Aquatic Mammals, 2003. 29 (1): 77-83

Spatial and temporal patterns of distribution of common dolphins (Delphinus delphis) off the Portuguese coast were examined using stranding and by-catch data from 1975 to 1998. There were 294 stranded animals and 124 confirmed by-catches during the study. The number of observed strandings increased throughout the study, most likely due to higher observer effort. Previous stranding records suggested that common dolphins are present along the entire Portuguese coast and are seen in all seasons. However, they found larger numbers of strandings recorded in the northern and central areas of the country. This may be due to: differences in distribution and/or abundance of the species, oceanographic conditions, and/or topographic features of each area. Significant differences were found in the number of strandings per season, with 37% occurring in the spring and 33% in the winter, which may be a consequence of severe weather conditions. Information on sex and size composition was also examined. There was a significant bias in the stranding and by-catch data towards males in all geographic areas and seasons. Younger, immature animals were also found in a significantly higher proportion. These results could suggest either the existence of differential mortality by sex and maturity, or the occurrence of age and sex segregation in the population. Stranding data also suggest that fishery interactions could be responsible for up to 44% of mortalities for this population.    

CETACEANS IN THE AZORES
Silva, M.A., R. Prieto, S. Magalhaes, R. Cabecinhas, A. Cruz, J.M. Concalves, and R.S. Santos. Occurrence and distribution of cetaceans in the waters around the Azores (Portugal), Summer and Autumn 1999-2000. Aquatic Mammals. 2003. 29 (1): 88-98

To determine occurrence, relative abundance, and distribution of cetaceans around the islands of the Archipelago of the Azores, boat-based surveys were conducted during the summers of 1999 and 2000. 222 cetacean schools, of 11 different were sighted throughout the area, however the central islands recorded the highest relative abundance. Within each group of islands, cetaceans were more abundant in the coastal area (to 9 km from shore) than in the offshore area (9 to 28 km). Atlantic spotted dolphins (Stenella frontalis), short-beaked common dolphins (Delphinus delphis), and bottlenose dolphins (Tursiops truncatus) were the most frequently sighted and were found in all the islands surveyed. While there was considerable overlap in spatial distribution between these species, common and bottlenose dolphins were more common in the coastal waters, while the Atlantic spotted dolphins were more common in offshore waters.    

HUMPBACK MIGRATION IN THE ATLANTIC
Source: Stevick, P.T., J. Allen, M. Berube, P.J. Clapham, S.K. Katona, F. Larsen, J. Lien, D.K. Mattila, P.J. Palsboll, J. Robbins, J. Sigurjonsson, T.D. Smith, N. Oien, and P.S. Hammond. Segregation of migration by feeding ground origin in North Atlantic humpback whales (Megaptera novaeangliae). J. Zool. Lond. 2003. 259: 231-237

Results from YoNAH, a large scale, capture-recapture study of humpback whales (Megaptera novaeangliae) in the North Atlantic, show that feeding ground origin influences migration timing. Sampling was conducted during 1992 and 1993 in all of the major feeding areas and the West Indies breeding area. There were no significant differences observed in the number of individuals from any feeding area that were re-sighted in the common breeding area in the West Indies. However, there was a relationship between the proportion of West Indies sightings and longitude. West Indies sighting dates for individuals in the Gulf of Maine and eastern Canada were significantly earlier than dates for animals identified in Greenland, Iceland and Norway (about 10 days). Evidence for sexual segregation in migration was also found; males were seen earlier on the breeding ground than females and this pattern was consistent for animals from all feeding grounds. The temporal difference in occupancy of the West Indies between individuals from different feeding areas, along with sexual differences in migratory patterns, indicates the possibility that there are reduced mating opportunities between individuals from different high latitude areas and that there may not be as much genetic variation as we'd previously suspected.    

HUMPBACKS IN THE GULF OF MAINE VS. THE SCOTIAN SHELF
Source: Clapham, P., J. Barlow, M. Bessinger, T. Cole, D. Mattila, R. Pace, D. Palka, J. Robbins, and R. Seton. Abundance and demographic parameters of humpback whales from the Gulf of Maine, and stock definition relative to the Scotian Shelf. J. Cetacean Res. Manage. 2003. 5(1): 13-22.

The humpback feeding areas of the Gulf of Maine and Newfoundland have been well studied. However, the area of the Scotian shelf, which lies between the two, is less well known. Surveys on the shelf in the summers of 1998 and 1999 produced the first substantial dataset of identified individual humpbacks observed in this region. The results from these surveys along with results from YoNAH (Years of the Northern Atlantic Humpback) were used to assess stock boundaries, abundance, and demographic parameters between the two areas. A match rate of 27% of whales seen in both areas provides evidence that many of the matched whales were transient in the Gulf of Maine. There were no matches found to any other location in the North Atlantic. The data suggests that the range of most whales from the Gulf of Maine usually does not extend as far east as the Scotian Shelf or Newfoundland. There was a low inter-annual match rate that suggests that the abundance of humpbacks on the shelf is larger than previously recognized. The population of the Gulf of Maine population had three separate, overlapping estimates. Mark-recapture data from 1992/1993 gave an estimate of 652 whales and photo-id data from 1997 provided a minimum of 497 whales known to be alive. Both of these estimates are likely to be negatively biased due to heterogeneity in sampling and animal distribution. Line-transect surveys in 1999 yielded an estimate of 819 to 902 whales, which is more consistent with the number of humpbacks in the current photo-id catalog for the Gulf of Maine. Projected growth rate of the population has varied between 0 and 6.5%, with the maximum sustainable rate projected as 7.2%, and a decline in recent years. Most of the decline appears to be the result of a reduction in calf survival rate between 1992 and 1995, however, reduced adult female survival and increased interbirth intervals may also have contributed to the apparent decline. Another factor is the known high mortality rate of young humpbacks off the mid-Atlantic coast states; a high percentage (81.2%) of which were estimated to be first-year whales and 32% were matched to Gulf of Maine whales with no matches to any other regions. However, calf survival rates have appeared to increase since 1996.