Havukainen Liisa, Monteiro Emygdio Leite de Araujo Fiho, Filla Gislaine de Fatima
Instituto de Pesquisas Cananéia, IPeC, R. Tristão Lobo 199, CEP 11990-000, Cananéia, São Paulo, Brazil.
Rev Biol Trop. 2011 Sep;59(3):1275-84.
Population density in cetaceans can be estimated through photo-identification, mark-recapture, land-based observations and visual estimative. We the aim to contribute with conservation strategies, we used line transects (distance method) to estimate the population density of the river dolphin, S. guianensis, in the estuarine region of Cananéia, Southeastern Brazil. The study, developed from May 2003 until April 2004, during dry and rainy seasons and different times of the day, included a sampling area divided into three sectors according to their proximity to the open sea: Sector I (the closest to the open sea); Sector II (with a large flow of fresh water and a salient declivity); and Sector III (with a large flow of fresh water and non salient declivity). Onboard random sampling was carried out in all three sectors, and dolphins seen from the bow to 90 degrees on both port and starboard sides, were registered along with their position and distance from the boat. The total density found was 12.41 ind/km2 (CV = 25.53%) with an average of 2.2 individuals per group for both periods of the day, morning and afternoon. Densities also varied between dry and rainy seasons, being lower in the first with 5.77 ind/km2 (CV = 27.87%) than in the second 20.28 ind/km2 (CV = 31.95%), respectively. Regarding the three sectors, a non-causal heterogeneous distribution was found: Sector I was the most populated (D = 33.10 ind/km2, CV = 13.34%), followed by Sector II (D = 7.8 ind/km2, CV = 21.07%) and Sector III (D = 3.04 ind/km2, CV = 34.04%). The aforementioned area, due to its proximity to the open sea, has the highest salinity level and therefore has the greatest chance of holding most of the marine fish schools which can be cornered by dolphins on high declivity areas during fishing activities. This suggests that food availability may be the most important factor on the river dolphin's distribution in the estuary. Similar studies will contribute to a better understanding of these populations and are essential for future conservation strategies.
鲸类动物的种群密度可通过照片识别、标记重捕法、陆地观测和视觉估计来估算。为了对保护策略有所贡献，我们采用截线法（距离法）来估算巴西东南部卡纳内阿河口地区圭亚那河海豚（S. guianensis）的种群密度。该研究于2003年5月至2004年4月期间开展，涵盖旱季和雨季以及一天中的不同时段，抽样区域根据其与公海的距离分为三个区域：区域I（最靠近公海）；区域II（淡水流量大且有明显坡度）；区域III（淡水流量大且无明显坡度）。在所有三个区域进行船上随机抽样，记录从船头到左舷和右舷90度范围内看到的海豚，以及它们的位置和与船的距离。全天两个时段（上午和下午）的总体密度为12.41头/平方公里（变异系数=25.53%），每组平均有2.2头个体。密度在旱季和雨季也有所不同，旱季较低，为5.77头/平方公里（变异系数=27.87%），雨季较高，为20.28头/平方公里（变异系数=31.95%）。关于这三个区域，发现了一种非因果性的不均匀分布：区域I的种群数量最多（密度=33.10头/平方公里，变异系数=13.34%），其次是区域II（密度=7.8头/平方公里，变异系数=21.07%）和区域III（密度=3.04头/平方公里，变异系数=34.04%）。上述区域由于靠近公海，盐度水平最高，因此最有可能容纳大部分海洋鱼群，而海豚在捕鱼活动中可在高坡度区域将其围捕。这表明食物可获得性可能是河口地区河海豚分布的最重要因素。类似的研究将有助于更好地了解这些种群，对未来的保护策略至关重要。
