[MARMAM] new publications on Guiana dolphins, Sotalia guianensis
sotalia at gmail.com
Tue Mar 16 11:09:26 PDT 2010
Two new publications on ecological aspects of Guiana dolphins (Sotalia
guianensis) in Brazilian waters are available through the following e-mail:
sotalia at gmail.com.
Below you can find complete references and abstracts.
Dr. Marcos Santos
Projeto Atlantis, Laboratorio de Biologia da Conservacao de Cetaceos
PROGRAMA JOVEM PESQUISADOR EM CENTROS EMERGENTES- FAPESP
Programa de Pos-Graduação em Zoologia, Departamento de Zoologia, Instituto
Universidade Estadual Paulista "Julio de Mesquita Filho" (UNESP), Campus Rio
Av 24-A, 1515, Bela Vista, Rio Claro, SP, Brasil, 13506-900.
MANUSCRIPT #1: Santos, M. C. de O., Oshima, J. E. F., Pacífico, E. S. & da
Silva, E. 2010. Feeding associations between Guiana dolphins, *Sotalia
guianensis * (Van Bénèden, 1864) and seabirds in the Lagamar estuary,
Brazil. *Brazilian Journal of Biology*, 70(1): 9-17.
ABSTRACT: The main objective of the present study was to describe the
characteristics regarding interactions between Guiana dolphins, *Sotalia
guianensis *and seabirds in feeding associations in two distinct areas of
the Lagamar estuary, Brazil. Boat-based surveys directed towards
photo-identification studies of *S. guianensis *were conducted in the
Cananéia Estuary (CE) (25° 01’ S and 47° 55’ W) from July 2004 to March
2008, as well as in the Paranaguá Estuarine Complex (PEC) (25° 24’ S and 48°
24’ W) from April 2006 to February 2008. On all occasions when seabirds were
observed engaging in multi-species feeding associations with *S. guianensis*,
data on species involved and their numbers were gathered. From 435 observed
groups of *S. guianensis *in the CE, 38 (8.7%) involved interactions with
seabirds. In the PEC, from the 286 observed groups, 32 (11.2%) involved the
mentioned interactions. The following seabirds were observed in feeding
associations with *S. guianensis*: *Fregata magnificens*, *Sula leucogaster*,
*Phalacrocorax brasilianus, *and *Sterna *sp. In the CE, *S. leucogaster *was
more commonly observed in feeding associations with Guiana dolphins (χ² =
22.84; d.f. = 3, p < 0.05), while in the PEC no differences were reported
when comparing seabird species (χ² = 5.78; d.f.=3, p = 0.1223). In the CE,
feeding associations were significantly more frequent in inner waters
(subset A0; χ² = 9.52; d.f. = 2, p < 0.05), and in winter (χ² = 12.46; d.f.
= 1, p < 0.05). Within these events, 44.7% of the association groups were
composed by more than one seabird species. Seasonality in feeding
associations was also observed in the PEC (χ² = 4.76; d.f. = 1, p < 0.05),
with same patterns observed in the CE. Interactions were more frequent in
inner waters of the Laranjeiras bay, PEC (χ² = 11.65; d.f. = 2, p < 0.05).
Within these events, 74.2% of the association groups were composed by more
than one seabird species. Water transparency, prey and seabird abundance and
distribution, cetacean group size, and the life cycle of prey and seabirds
are listed as the main factors addressing multi-species feeding associations
in the Lagamar estuary.
MANUSCRIPT #2: Santos, M. C. de O., Oshima, J. E. F., Pacífico, E. S. & da
Silva, E. 2010. Group size and composition of Guiana dolphins, *Sotalia
guianensis * (Van Bénèden, 1864) in the Paranagua Estuarine Complex, Brazil.
*Brazilian Journal of Biology*, 70(1): 111-120.
ABSTRACT: The aim of the present study was to describe the characteristics
of Guiana dolphins (*S. guianensis*) group size and composition in the
Paranaguá Estuarine Complex (25° 15’ -25° 36’ S and 48° 02’-48° 45’ W),
Paraná State, as well as to verify the existence of relationships between a
given environmental variable (water depth, salinity, transparency and
temperature) and group size. An area of around 124 km2 was surveyed by boat
from April 2006 to February 2008 in the following subsets of the estuary:
Canal do Superagui (~28 km2), Pinheiros bay (~34 km2), part of Laranjeiras
bay, which included the Guaraqueçaba sub-estuary (~38 km2), and part of the
Mixture Section of the Paranaguá Estuarine Complex (~24 km2). In 45 survey
days, a total of 147 hours were spent observing 286 groups of *S. guianensis
*. Groups varied from two individuals to aggregations of up to 90
individuals (mean ± SD: 11.5 ± 14.4 individuals). Solitary individuals were
seen only on five occasions (1.7% of all observations). Groups with calves
(n = 247) represented 86.4% overall and were more common in all sub-areas
when compared to groups without calves. Groups without calves were found in
all sub-areas and were usually smaller and composed of up to 12 individuals.
A usual group composition of 70% of adults and 30% of calves was observed
considering all sub-areas and seasons. No correlations were found between
group size and water temperature (Spearman’s rank test, r = 0.0059, p =
0.9338), transparency (Spearman’s rank test, r = 0.0597, p = 0.9333), depth
(Spearman’s rank test, r = 0.1421, p = 0.4698), and salinity (Spearman’s
rank test, r = –0.1938, p = 0.0665). While Guiana dolphin groups were seen
in the entire surveyed area, group size varied significantly among the three
main surveyed sub-areas (Kruskal Wallis, H2,196 = 29.85, p = 0.0000). Groups
were larger in Laranjeiras bay and smaller in Canal do Superagui. The
physical environment, risk of predation, seasonal distribution and
abundance of prey are the main possible factors driving larger groups in
inner and protected waters.
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