SUFB 129: Trends in Marine Mammal Distribution in Southwestern Atlantic

Speak Up For Blue Podcast

Over the past six months, and with the help of yours truly, you may have noticed what appears to be an increasing amount of marine mammal strandings. Personally, it seems like I run across one of these stories every couple of weeks, and after a while I wonder if strandings have always been this frequent or if I’m just paying more attention now than I used to.

Well, a team of researchers published a study in PLOS One this past January titled “Long-Term Seasonal and Interannual Patterns of Marine Mammal Strandings in Subtropical Western South Atlantic,” or “LTSIPMMSSWSA” for short. The data showed that in this region, the most frequent marine mammal strandings involved Fransiscanas, South American fur seals, SA sea lions, bottlenose dolphins, and subantarctic fur seals. Basically all the really cute animals. This is going to be a rough study

What the authors found, perhaps not surprisingly, is that the seasonal variations of marine mammal strandings typically coincided with either periods of increased fishing effort, post-reproductive dispersal, or a combination of both. This would suggest that increased levels of human activity or increased abundances of juvenilles in these populations tend to mean we’re more likely to see mammal strandings. Interannual variation was linked to increased fishing effort and population growth, and over the last couple of decades we’ve seen an increased stranding rate in Fransiscanas and the SA fur seal. For bottlenose dolphins, the rate has remained steady since the 1970s, while the stranding rate for subantarctic fur seals has actually declined slightly. The SA sea lion didn’t provide enough data for any determinations to be made regarding variations in its stranding rate, so we award them no points.

The authors conclude by emphasizing the importance of marine mammal monitoring efforts. We know very little about the movements and migrations of these charismatic megafauna. Despite what TV says, very few marine biologists actually study dolphins, whales, seals, and sea lions. Therefore, it’s vital to the future of these animals that we continue to fund research examining their behavioral ecology, their movement patterns, and how increased human influence in the ocean is impacting their survival.

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