South-American dolphins

Conservation of small cetaceans

High human-induced mortality levels, especially because of direct and incidental catch in coastal waters, threaten many cetacean populations that might represent evolutionary distinct lineages or incipient species. Obviously, one major challenge in the analysis of genetic variation is to work out the relative contributions of distinct processes such as genetic drift, population divergence, gene flow, and selection (all likely to be variable both in time and space). For several reasons, this task is particularly complex in cetaceans. First, many cetacean species show high dispersal abilities and are distributed across habitats where movements are difficult to record and barriers to migration are seldom understood. Second, strongly biased sex-specific dispersal can result in incongruent population histories for males and females. Third, complex behaviours such as philopatry and social organization into kinship groups can cause, even in sympatry or on a small geographical scale, significant population subdivision. Finally, detailed information on past and recent effective population sizes is lacking in many species. This often makes data interpretation difficult as fluctuations in population size lead to varying rates of drift, hence, to a nonlinear variation of genetic differentiation through time.

The molecular genetics approach: a multidisciplinary, long-term, collaborative endeavor

Molecular genetics is, especially for cetaceans, a powerful approach for deciphering the processes shaping geographical and historical patterns of diversity. However, collection of samples is a long, tedious process and laboratory work is meaningless if it is not put into perspective with field and natural history data. Below, we shortly describe our analyses of the dusky dolphin and Burmeister Porpoise populations. This work is the result of a 10 year collaboration between Michel Milinkovitch and two fine ecologists / field biologists dedicated to the conservation biology of marine mammals: Koen Van Waerebeek (Peruvian Centre for Cetacean Research; CEPEC; Museo de Delfines, Pucusana, Lima, Peru) & Julio Reyes (Areas Costeras y Recursos Marinos; ACOREMA; Pisco, Peru). Check the left column of this web page for additional information on Koen and Julio’s activities. Note that multiple other people provided samples and expertise throughout this work. A large proportion of the molecular work was performed by Insa Cassens and Athanasia C. Tzika in Michel Milinkovitch’s lab. Patrick Mardulyn played an important role in designing a new method (UMP) for genealogical network estimation. 

Clockwise from top: Joanna Alfaro, Julio Reyes, Michel & Koen working during an electricity breakdown, the harbor. All pictures were taken in Pucusana, Peru.

The Dusky Dolphin (Lagenorhynchus obscurus)

The dusky dolphin is distributed in cool temperate waters of the Southern Hemisphere. Its occurrence is well documented along the coasts off Southwest Africa, Argentina, Chile, Peru, New Zealand and, recently, Australia. Although the species has been positively recorded from the vicinity of many oceanic island groups, its pelagic occurrence in the southern oceans remains unconfirmed. Distributional information and morphological studies, which have revealed significant differentiation in cranial characteristics and body size among geographical regions suggest a disjunct distribution with discrete dusky dolphin stocks confined to continental shelves and islands. However, more data are needed in order to precisely describe population boundaries. Moreover, a better understanding of dusky dolphin population structure is of major importance with respect to species conservation. Especially in Peruvian fisheries dusky dolphins are, along with other small cetacean species, subjected to high mortality levels from by-catches and direct take (see links to Van Waerebeek & Reyes publications in the left column of this web page). Although takes of cetaceans have been banned since 1990, the species continue to be exploited for human consumption and increasingly for bait in shark fisheries. Extensive monitoring of fish landing sites over the past two decades revealed a decrease in the proportional representation of dusky dolphins in cetacean catches off central Peru, which could reflect a severe decline in abundance due to fishery activities. However, for assessing objectively the impact of this exploitation on the species, stock identity needs to be determined.

The Burmeister’s Porpoise (Phocoena spinipinnis)

The Burmeister’s porpoise is a small cetacean species endemic to South American waters. Along the Atlantic coast, it is commonly found from Southern Brazil to the San José Gulf, Argentina, while along the Pacific coast, it occurs from Bahia de Paita (Peru) to Chiloe Island (Chile). Although Burmeister’s porpoises are described to preferentially inhabit coastal waters, their direct observation is extremely difficult due to their small size, unobtrusive swimming habits, and to the sometimes inaccessible coastline. To date, only about a few dozens confirmed sightings exist for the Southeast Pacific. Knowledge about the species biology, and more specifically its stock structure and dispersal patterns, is therefore particularly scarce. For example, although sightings and strandings suggest that Burmeister’s porpoises may be common in portions of the Magellan Strait and the Beagle Canal, it is still unclear whether the species’ distribution is continuous between the Atlantic and Pacific Ocean. On the contrary, it has been suggested that Pacific and Atlantic Burmeister’s porpoises comprise two different stocks, a hypothesis which is consistent with size differences observed between individuals from Northern Argentina and Peru/Chile. More accurate stock designations are urgently needed given that Burmeister’s porpoises are subjected to high human-induced mortality levels throughout their range. While porpoises are incidentally caught in gill-net fisheries off Argentina and Uruguay, the situation is more severe in Peruvian and Northern Chilean waters where direct catches of small cetaceans, used for human consumption and increasingly as bait in shark fisheries, have been observed since the direct collapse of the anchovy fishery in the 1970’s. Van Waerebeek and Reyes estimated the cetacean catch off Peru to be 15–20 thousands individuals per year for the period 1991–1993; whereas the number of Burmeister’s porpoises taken annually in Peruvian waters reaches at least the high hundreds. In addition, porpoises in the Peruvian upwelling system might be particularly vulnerable to local depletion as they inhabit a very rich, but unstable environment: Recurrent El Niño events cause high mortality rates among animals and plants, with the most severe oscillations of the last century having occurred in 1982–1983 and 1997–1998.

Results

Check HERE a summary of our results on the molecular population genetics and conservation of the dusky dolphins and Burmeister’s poprpoises.

Publications
Please, consult the full publications below for references and much additional information.

1. ✓Cassens I., Van Waerebeek K., Best P. B., Crespo E.A., Reyes J. & M. C. Milinkovitch
   The phylogeography of dusky dolphins (Lagenorhynchus obscurus): a critical examination of network methods and rooting procedures
   Molecular Ecology, 12: 1781-1792 (2003)
   

2. e-mail
   

3. ✓Cassens I., Van Waerebeek K., Best P.B., Tzika A., Van Helden A.L., Crespo E.A. & M. C. Milinkovitch
   Evidence for male dispersal along the coasts but no migration in pelagic waters in dusky dolphins (Lagenorhynchus obscurus)
   Molecular Ecology, 14 : 107-121 (2005)
   

4. e-mail
   

5. ✓Cassens I., Mardulyn P. & M. C. Milinkovitch
   Evaluating Intraspecific “Network” Construction Methods Using Simulated Sequence Data: Do Existing Algorithms Outperform the Global Maximum Parsimony Approach?
   Systematic Biology 54: 363-372 (2005)
   

6. Open Access
   

7. ✓Rosa S., Milinkovitch M.C., Van Waerebeek K., Berck J., Oporto J., Alfaro-Shigueto J., Van Bressem M.F., Goodall N. & I. Cassens
   Population structure of nuclear and mitochondrial DNA variation among South American Burmeister’s porpoises (Phocoena spinipinnis)
   Conservation Genetics 6: 431–443 (2005)
   

8. e-mail
   

9. ✓Mardulyn P., Cassens I. & M. C. Milinkovitch
   A comparison of methods for constructing evolutionary networks from intraspecific DNA sequence
   Pages 104-120 (Chapter 5) in ‘Population Genetics for Animal Conservation’ (Bertorelle G, Bruford M.W.,
   Hauffe H.C., Rizzoli A., & Vernesi C., eds.),
   Cambridge University Press 2009
   

10. e-mail
    

11. ✓Tzika A.C., D’Amico E., Alfaro-Shigueto J., Mangel J.C., Van Waerebeek K. & M.C. Milinkovitch
    Molecular identification of small cetacean samples from Peruvian fish markets
    Conservation Genetics 11: 2207-2218 (2010)
    

12. e-mail: Article
    

13. e-mail: Supplementary File
    

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