Human knowledge can supplement vital marine studies

Guest post by Brooke Bessesen

Humans who spend a lot of time in nature know things. And their familiarity could help scientists to assess habitat change and species loss in at-risk environments and places where frequent fieldwork is unfeasible.

Around the world marine life is in decline and ongoing biodiversity assessments are needed to inform conservation policy. Biomonitoring, as it’s called, is often accomplished through traditional sighting surveys, which unfortunately, can be too costly and time-consuming for regular repetition. As the demand for data increases, more investigators are considering the potential of local ecological knowledge to supplement biomonitoring.

We define local ecological knowledge as “the cumulative knowledge of long-term residents regarding ecological relationships within their environment, shaped through personal observations and experiences as well as communications and beliefs shared within their community.” And LEK can be a valuable resource, especially when other sources of data are limited.

But an obvious question arises. Can LEK be trusted to provide accurate information? In an article recently published in People and Nature, The value and limitations of local ecological knowledge: longitudinal and retrospective assessment of flagship species in Golfo Dulce, Costa Rica, Manuela González-Suárez and I found an answer both complex and fascinating. (Version del artículo en espanol aqui).

The results of two interview surveys, which we conducted through questionnaires a decade apart, revealed both strengths and weaknesses in human perception. While people tended to accurately recognize what was happening in their environment in the moment, they often fell victim to poor recall when reflecting back over time.

In 2010, and again in 2020, fishermen and tour-boat guides working in the bio-rich waters of Golfo Dulce, Costa Rica, were asked how frequently they saw whales, dolphins, sea turtles, whale sharks, and sea snakes—never, rarely, occasionally, frequently, or always. During the same two time periods, our research team undertook boat-based biomonitoring to assess the occurrence of those animals first-hand.

The graph marked FIGURE 2 shows all the interview responses for both years with asterisks representing our biomonitoring results. Participants largely reported whale-sighting frequencies as occasionally in 2010, but their reports dropped closer to rarely in 2020. Sightings of sea turtles and whale sharks also dropped, while sea snakes increased. Only dolphins stayed the same.

In both years, the sighting frequencies provided by interviewees generally matched our own sighting frequencies, and likewise, when we compared interviewee responses from 2010 against those from 2020, the changes were consistent with what we empirically documented on the water.

The problem came when we asked interviewees what changes they perceived. In 2020, in addition to our original question, we asked a small panel of respondents who had participated both years to give us their opinion as to whether there was more, less, or about the same number of whales, dolphins, sea turtles, whale sharks, and sea snakes as ten years previous. Not only did their perceptions fail to sync with our biomonitoring, but they actually failed to sync with their own reporting.

As a simple example, one anonymized participant identified only as the number 12 (line 4 of the panelist data) reported seeing whales frequently (F) in 2010 but rarely (R) in 2020. That participant essentially reported a decrease in whales. However, a plus sign (in column I) indicates they perceived an increase! How is that possible?

It was likely a glitch in human perception called retrospective bias. Hindsight is not always 20/20. Memories can be distorted, including inaccurate perception of historic declines. Manuela and I had hypothesized that interviews between 2010 and 2020, when systematically analysed, might reveal changes in faunal abundance not directly perceived by the participants themselves. Yet even we were surprised by how optimistically respondents viewed the situation in comparison with their reports.

So, perceptions of historical change cannot be relied upon for accuracy. But that doesn’t mean LEK has no place in science.

When it comes to estimating current species abundance, LEK appears quite good and could certainly complement biomonitoring in areas where fieldwork is inescapably infrequent. LEK might even be useful for basic assessments of change—so long as interviewees report frequencies in the moment and change is determined by comparing their reports over time. Collected between boat-based surveys, LEK might even serve as an early warning system for negative trends.

Golfo Dulce is the perfect location for this interdisciplinary approach since its remote location makes regular sighting surveys difficult. Plus, it’s been identified as a ‘biodiversity hotspot’ and was recently declared a Hope Spot by oceanographer Dr. Sylvia Earle.

Recognizing changes in species abundance, especially those that suggest declining populations, is not only significant ecologically, but also economically. Most families in the region fish for food, and 60–80% of the economy is based in ecotourism. Disappearing marine life could therefore have devastating impacts on both the wildlife and human communities.

We hope our assessment data, informed by residents who know the environment well, spurs policymakers in Costa Rica to increase protections in Golfo Dulce. And because effective conservation also requires the motivated involvement of local citizens, we offer a heartfelt thanks to our research assistant, Jorge Largaespada, and all the fishermen and tour boat guides who supported this work by sharing their knowledge through interviews.

Bessesen, BL; González-Suárez, M (2021) The value and limitations of local ecological knowledge: longitudinal and retrospective assessment of flagship species in Golfo Dulce, Costa Rica. People and Nature 3(3): 627– 638. DOI: 10.1002/pan3.10219

(Version del artículo en espanol aqui).

Dataset publicly available at Figshare

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