Cetacean Society International
Whales Alive! - Vol. X No. 4 - October 2001
Franciscana Dolphin: A Threatened Species?
The biggest problem about human impacts on marine life and habitat is that we do not know enough about what we are doing. As fisheries and reefs collapse around the world the necessary solutions conflict with economic needs, and issues become political. Managers are powerless without facts, politicians will not act without facts, and people may not care even with facts. The facts come from science.
An excellent example is a report provided by Eduardo Secchi of Brazil, a Ph.D. candidate at the University of Otago, New Zealand, http://www.otago.ac.nz/marinescience/mammals/. CSI and many others have watched "Edu's" career blossom. We know that he exemplifies the best among the brilliant cadre of young scientists we have come to know, respect and depend upon during our two decades of helping scientists around the world. What follows is a summary of Eduardo's paper by CSI President William Rossiter. The full and powerful paper is available on request from CSI.
The franciscana, or De La Plata river dolphin, Pontoporia blainvillei, is a superb example of why we need to understand what human impacts are doing to marine life, and what science can do to help solve problems. Because no comprehensive study has been undertaken to assess the impact of fisheries on the species, franciscana is listed as "Data Deficient" in the IUCN Red Data Book. No useful management decisions can be made without facts.
Only 1.3 to 1.7 meters long, not even six feet, the franciscana lives in the coastal waters of the Southwest Atlantic Ocean, from Espírito Santo State, southeastern Brazil, to Chubut Province, Argentina. This tiny dolphin has limited range, low reproductive potential, and is particularly vulnerable to incidental captures in nets. Although considered one of the river dolphins, franciscanas are found mainly in coastal marine waters with occasional occurrences in estuaries. There are at least two populations. Each needs separate management help. Franciscana can live to be just over 20, but most live only 12 years. Females can produce four to eight calves in their lifetimes, beginning at three or four. Calves are weaned eight to nine months after birth. The important fact is that potential population growth is only about two percent per year, which makes the species very vulnerable to human impacts.
Modern gillnetting began over sixty years ago, with constant trends towards larger, more efficient catches. For a period up to 90 percent of the franciscana bycatch was from nets designed to catch sharks. Thousands of franciscana were killed before sharks became so depleted that fishermen turned to smaller mesh sizes in nets designed to catch bony fish, or trawled for shellfish. Today the franciscana is caught from all main fishing villages within its range in gillnets set for bottom-dwelling fish. As Brazil's fishers used larger and faster boats from the 1980's, the industry has expanded its range and scope. Even with smaller mesh, shallow water gillnets from 120 m to 11,000 m long are known to catch between 577 and 1879 franciscana all year long in Brazil alone. But most of the bycatch is still unreported.
No one seems to catch the franciscana dolphin on purpose. Instead they are "bycatch", caught in gillnets by mistake, one or two at a time. Nine were reported in one net in northern Brazil, but many if not most deaths are not reported at all. This is the dilemma, the same dilemma found around the world: do the available statistics show enough to estimate the number of franciscana truly killed as bycatch, and is that number a threat to the population or species? If it is a threat can the problem be managed?
As might be expected, more than half of the recorded catches are less experienced dolphins less than three years old. Most of the dead dolphins are discarded offshore. But some are used in many regional ways. Blubber becomes long-line shark bait, oil is used to waterproof boats and even horsehair, and the meat may be used as dog food. Human consumption seems rare, except for some use of sun dried and salted meat known as "mushame" in some Turkish, Jewish and Arab communities of Argentina.
The human fisheries have also depleted fish that were franciscana favorites. As elsewhere, the dolphins have adapted to other species less targeted by humans, such as cutlass fish. But do the franciscana have to work harder or travel farther, and is their new prey providing equal nutritional value? These are questions for the developing science of energetics. The answers may tell us if the franciscana will survive human exploitation of their normal prey. Unfortunately this species seem to swallow a significant amount of marine debris, such as cellophane packaging, plastic fragments, and fishing gear. The evidence suggests that they start soon after weaning. Does this hurt or kill a significant number of franciscana? Evidence for mortalities to marine life from ingesting human debris is worldwide, so it seems likely. What about strandings? The numbers of stranded franciscana dolphins dropped by two thirds after 1990, and have remained stable since. Rather than good news, this suggests a drop in the overall population. How do we take all the available information about human impacts on this species to answer the big question: are humans causing franciscana numbers to decline? To help with this question four Franciscana Management Areas (FMA) were established. Estimates of annual by-catch in coastal fisheries, biological data from by-caught dolphins, and abundance for each stock were used to create population models. The mathematical models then tested worst-case, best-case, and most likely scenarios. The models predicted a population decline.
Conservation measures: is a sustainable balance possible?
Developing nations received massive assistance over the second half of the last century to improve the efficiency of their fisheries. This led to a rapid over-exploitation of many fish stocks, and the decline of several marine mammal species due to competition for the same resource, or unsustainable levels of by-catch.
Mitigating these problems is not an easy task, regardless of the economic situation of the nation where the problem occurs. In many developing countries, however, high external debt along with other socioeconomic priorities have played a major role in constraining the ability of governments to allocate resources to and properly respond to environmental concerns. Although fishing yield per individual fisher has decreased in the last decades in many areas, fast demographic growth, poor education systems and high unemployment have led to a steady increase in the number of fishers in many Latin American countries. Thus, lack of options is perhaps the major cause for the continued increase in fishing effort, and for the unsustainable level of fishery-related mortality of franciscana.
Even though franciscana is legally protected in Brazil, Uruguay and Argentina, law enforcement will not likely offer a solution to the by-catch problem because the greatest threat to the species' survival is incidental captures. Legislation to limit fishing effort in terms of maximum allowable net length and number of boats or to restrict fishing grounds (for example, time and/or area closures) could be more effective. The former could easily be inspected in port, however, resources and personnel for policing fishing grounds are extremely sparse in the three countries. Therefore, effectiveness of this measure would rely on the fishers' willingness to cooperate. Since all options could negatively affect fishers' income or even be unsafe for their lives (i.e. going fishing in deeper waters further offshore), they would hardly be implemented over a short term. Furthermore, a better understanding of the spatial and temporal patterns of the franciscana by-catches are still needed before proposing regulations on fishing areas and seasons.
Other potential alternatives are likely to be found in experiments related to fishing practices. It has been suggested, in vain, to replace gillnets with long lines, as a means to reduce by-catch off Argentina. Fishers are usually conservative regarding new fishing practices. They would hardly try other gear if they suspect it to be less profitable. As stated in the article "the tragedy of the commons", a resource user will not reduce his/her profit if other users do not reduce theirs first. Because fisheries have also affected fish stocks, a wider management strategy is needed which must also consider other marine species. Moreover, cultural and social needs of the fishing communities have to be taken into account as well to avoid adding yet another social problem to the already difficult socioeconomic situation of Latin American countries. True ecosystem management would combine and balance the needs of humans, marine mammals, fish stocks and their ecosystem, upon which they all depend. Perhaps this could be achievable in a medium to long-term with fishers' cooperation and through the implementation of educational programs for fishing communities in order to increase their awareness and participation in species and natural resource conservation. However, this could take too long to be effective before some stocks reach the brink of extinction.
New approaches are urgently needed in the meantime. Acoustic deterrents were used in the nets set off Argentina. Although the experiment reached the objective of reducing incidental by-catch, it increased the rate of attack by southern sea lions on the nets; this kind of acoustic device seems to be inappropriate as a long-term management option for the region. Nevertheless, further studies on this subject should be encouraged, particularly in areas where sea lions do not occur (e.g. many small fishing villages along FMA I and II). Further experiments on gillnet modifications as well as implementation of other alternatives to minimize franciscana mortality should be encouraged on the basis of scientific data and continued independent monitoring programs. Furthermore, the possibilities for implementing multinational conservation and management actions involving Brazil, Uruguay and Argentina within the scope of the Convention for Migratory Species, the IUCN and UNESCO should also be encouraged.