20 July 2011

THE MEMORIES OF OLD FISHERS

There's an interesting paper just out in PLoS ONE assessing whether or not the memories of old fishers could be useful to science. Specifically, whether their recollections correlate with other fisheries data from recent decades.

The authors write:

Population declines and the extinction of marine organisms may be largely underestimated due to the difficulties involved in making scientific observations. However, data sources other than scientific time-series have proven useful in providing relevant information to marine scientists in cases that are normally considered "data-poor." Some studies have used traditional (or local) ecological knowledge to reconstruct temporal population trends and discover near-extinctions of marine fauna, while studies that compare the results from scientific research with evidence based on fishers' experience have shown that both sources of knowledge give similar results and can be used to detect the essential trends.

(Photo above by Steve Evans via Wikimedia Commons.)

(Monk seal. Via.)

To investigate, the researchers delved into the memories of 106 retired trawl fishers in Italy, Spain and Greece, seeking their impressions of the abundance of long-lived marine species—dolphins, whales, monk seals, marine turtles, and sharks—in the Mediterranean.

During the interviews, the old dudes (pretty sure they were all dudes) were asked to rank abundance of these animals group during three 20-year periods between 1940 and 1999.
 
Their perceptions were based on two indicators:

  • Frequency of sightings
  • Frequency of catches (incidental or intentional) 

    (Via.)

    Specifically, they were asked about:

    • Intentional catches of dolphins 
    • Intentional catches of turtles
    • Sightings of dolphins, whales, seals, or turtles
    • Relative catches of sharks/cartilaginous fishes

    Their answers could be: "never," "occasional," "frequent," or "very frequent."
























    (Trends in catches and sightings of large marine fauna, all areas combined. Credit: Francesc Maynou, et al. PLoS ONE. DOI:10.1371/journal.pone.0021818.t001. Larger view here.)

    The results were interesting. And sad.

    • The frequency of encounters between large marine fauna and fishers declined throughout the latter half of the 20th century.
    • The decline continues at the beginning of the 21st century (except in Greece, where some dolphins are experiencing population increases).  
    • The commercial catches of sharks and other cartilaginous fishes decreased significantly.  

    The authors note that the abundance of monk seal and whales was already so low in the 20th century that the interview data were insufficient for a quantitative analysis.
      
    (Angelshark. Photo by Philippe Guillaume via Wikimedia Commons.)

    Here's what the fishers' memories revealed about recent extinctions:

    [S]moothhounds Mustelus mustelus [a kind of shark] are likely to have disappeared in the Catalan Sea before 1979, and angelsharks Squatina squatina before 1959. In western Italy, angelsharks would have disappeared by the early 1980s near the mainland and the mid-1980s in Sardinia. Smoothhounds became functionally extinct in 1990 in Italy and Greece, with only sporadic records thereafter. The sturgeon Acipenser acipenser had become extinct in the North Adriatic by 1966.


    (Photo by catrien via Flickr.)

    Bottom line is that fishers are good observers and a largely untapped treasure trove of fish tales about the health of marine ecosystems.

    If we accept that commercial trawl fishers are independent observers of the marine system, [our] results suggest that the abundance of large marine fauna has decreased considerably during the 20th century in the Mediterranean Sea (in agreement with the results of other studies), and therefore fishers' observations during a lifetime of professional activity can provide a qualitative measure of this decline.

    (Photo via.)

    Fish tails welcome too.

    ResearchBlogging.org

    Maynou, F., Sbrana, M., Sartor, P., Maravelias, C., Kavadas, S., Damalas, D., Cartes, J., & Osio, G. (2011). Estimating Trends of Population Decline in Long-Lived Marine Species in the Mediterranean Sea Based on Fishers' Perceptions PLoS ONE, 6 (7) DOI: 10.1371/journal.pone.0021818
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