The Dolphins That Protection Did Not Save

ANo group of large mammals has been protected on paper for longer, or with less to show for it, than the dolphins of the great rivers. The baiji of the Yangtze was declared functionally extinct in 2006, after a six-week search of the entire navigable channel produced not one animal, and the populations that remain, in the Ganges and the Indus, in the Amazon and its tributaries, and in a scatter of Southeast Asian rivers, are all listed and all falling. India made the Ganges dolphin its national aquatic animal in 2009, and Brazil had placed the boto under federal protection long before that. The length of river carrying some form of legal protection more than doubled between 2000 and 2020, and every basin-wide count published across those years returned a lower figure than the one before it. Animals are lost to propeller injuries too, in channels that carry more traffic each season. What the protection has never settled is which of two explanations accounts for the decline: the engineering of the rivers themselves, or the gear of the people who fish them.

BVikram Quintero, a freshwater ecologist at the Gangetic Basin Hydrology Centre in Patna, holds that the second explanation cannot be tested until the first has been dealt with. Between 2004 and 2018 her group ran boat surveys along 1,150 kilometres of the Ganges main stem, dividing it into 26 reaches and setting each year's encounter rate against gauge records from the driest month. The pattern she reports is abrupt rather than gradual: below a mean February depth of about 2.1 metres, dolphins were effectively absent, and above it their numbers climbed steeply with every additional half metre. Forty-three per cent of the reaches dropped under that threshold in at least one year of the study. The relationship, she is careful to add, held only where the channel ran as a single thread; in braided reaches, where the flow divides among shifting sandbars, the reading at the gauge told her almost nothing. Withdrawal for irrigation, rather than any shortfall of rain, accounted for most of the missing water.

CThe account carries a prediction, and Quintero has tested it. If depth sets the limit, a reach that is given its water back should refill with animals even when nothing whatever changes about the fishing. From 2015 the authority managing the barrages was obliged to release a minimum flow through the dry months, and at nine reaches lying below those structures the encounter rate rose from 1.3 to 3.4 animals per ten kilometres by 2021. The gain, however, was confined to reaches separated from a surviving population by no more than one barrage; where two or more stood in between, the extra water produced a deeper channel and no dolphins at all. Quintero presents the restoration of flow as a condition to be met before anything else is attempted rather than as a substitute for the rest, and she concedes that where the dry-season channel is already deep enough, her data predict nothing about whether the animals will still be there in a decade.

DEmilio Cardoso, who studies fisheries governance at the Lower Amazon Freshwater Institute in Santarem, replies that a river losing dolphins from water deep enough to hold them is telling you about gear and incentives, not about hydrology. His survey covered 41 fishing communities on reaches that stay above three metres deep even in the driest month, and it recorded entanglement in gillnets at 0.7 incidents per boat-year where the community held a legally recognised fishing agreement over the stretch, against 2.6 where the water belonged to nobody in particular. Demand has mattered as well: dolphin flesh was widely used as bait for the scavenging catfish piracatinga until Brazil suspended that fishery in 2014, and the suspension has been renewed twice since. Cardoso concedes two weaknesses. All 41 communities lie within a single basin, and mortality was inferred from what fishers themselves chose to report, since no register of carcasses exists anywhere on the river.

EThe argument stopped being academic in 2019, when the national plans covering both basins began requiring managers to report encounter rates for the animals instead of the number of river kilometres declared protected, with the next cycle of funding tied to the return. Quintero points out, awkwardly for her own case, that a dry-season release is authorised by the ministry that allocates water and appears in no conservation budget at all, so the measure with the best evidence behind it is the one no dolphin programme is able to pay for. Cardoso answers that a fishing agreement suffers from the same disability, since it draws no boundary that anyone can shade on a map and therefore counts as nothing when protected area is totted up. Both dislike one habit more than they dislike each other's theories: the field still reports what has been designated instead of what has been seen.

FWhat is emerging is not a winner but an order of operations. Where the dry-season channel falls below the depth at which the animals can feed and surface, no arrangement with the people on the bank will hold a population in place, and the reach should never have been entered in the accounts as habitat; where the water is deep enough, everything turns instead on whose nets are set and who bears the cost of lifting them. One question resists both accounts. The animals now appearing in restored reaches may represent genuine growth, or they may have shifted in from stretches nearby that nobody has surveyed since, and no programme of individual identification has yet run long enough to tell the two apart. What both researchers reject is the assumption that produced the targets in the first place, namely that a river can be repaired by drawing lines along it.