Wednesday, April 25, 2012

Wednesday search challenge (4/25/12): World's biggest fish story?


This week I’m a volunteer at the Glover’s Reef Research Station in Belize.    I’m here with a bunch of folks to help out the researchers by counting the local numbers of lionfish and measure sea turtles (both population and sizes).  It’s pretty interesting work and leads to some tall tales in the evening.  

Or ARE they tall?

After dinner, we were sitting around swapping fish stories.  One of the old salts told about seeing a fish that was 10 meters long.  That's a big fish, but his buddy claimed HE saw one that was 12 meters long and at least 7 meters across. 

Should I believe these stories?  

This leads to today’s questions:

  1. What is the average size of the world’s largest fish?  And what is it?  (I  to see data from some original research reports, NOT fish stories and secondhand reportage.  We should get data for both length and girth.)

  2.  Given that fish are somewhat hard to tell apart, what’s the current best method for estimating the number of these fish?

  3. (Extra credit)  Can you find (or generate) a map of these fish worldwide?  How many do the researchers believe there are?


Enjoy your search while I dive!

Search on.

4 comments:

  1. google search 'largest fish' I thought it was a whale shark, but a wanted to make sure.
    http://www.environment.gov.au/biodiversity/threatened/publications/recovery/r-typus-issues/biology.html - found species name and publication of original sighting (smith 1828)

    average size is tricky because this report says that recent shark sightings have been about 6.5ft less than normal
    Decline in whale shark size and abundance at Ningaloo Reef over the past decade: The world’s largest fish is getting smaller

    http://www.sciencedirect.com/science/article/pii/S0006320708001791
    this reports on a large fish 12m (in report), standard 10.23m; girth of body 5.05m
    http://eprints.cmfri.org.in/2819/1/MFIS_66-9.pdf

    this report says length is 10-12 meters long
    Title: Threatened fishes of the world: Rhincodon typus (Smith 1828) (Rhincodontidae)
    Source: Environmental biology of fishes [0378-1909] yr:2005 vol:74 iss:2 pg:184


    method of counting - capture mark recapture (CMR) using photographs...identify spot pattern between gills and dorsal fin, individual contributors and anyone in the world- found by google web search 'estimating number rhincodon typus' and 'research report whale shark'
    http://www.usm.edu/gcrl/whaleshark/report_a_sighting.php
    http://www.ecocean.org/
    http://www.int-res.com/articles/esr2009/7/n007p039.pdf
    http://www.conservationregistry.org/assets/0000/1519/EndangeredSpeciesResearch_n007p039.pdf
    "estimating population size, structure, and residency time for whale sharks rhincodon typus through collaborative photo-identification"

    map worldwide - found by google images search "rhincodon typus map" and reading through the pages http://www.discoverlife.org/20/q?search=Rhincodon%20typus

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  2. First part is too easy. I guessed it would be a whale shark, and got immediate confirmation on the search page, mainly second-hand reports, like a BBC story that the longest on record was 13.5m.

    One site that looked promising was http://www.whale-shark.org/whale_shark_research_facts.php which claims to be a research project in Thailand. They have the map you asked for. On http://www.whale-shark.org/whale_shark_research_and_you.php they recommend a non-invasive method of photographing the spot patterns behind the gills, which they match against databases to identify specific individual sharks. http://www.whale-shark.org/whale_shark_research_method.php has more details on the method.

    "Average size" is a rather meaningless question for a fish that continues to grow over 60 years. Here is the best I could do for you:
    "The whale shark is the largest living fish. Maximum size is thought to be 20m. The smallest free-living individuals are from 55cm (21.7 inches) long. Sexual maturity in both sexes may not occur until the sharks are over 9m in length."
    http://www.whale-shark.org/whale_shark_research_facts.php

    Time to find web pages: 10 seconds. Time to read them to answer questions about 4 minutes.

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  3. This one was easy (or I assume it was, unless my answers are wrong). The problem was different sites contradicted - including generally reputable sites.

    It took me under 15 seconds to type in "largest fish is" and get the answer "whale shark". Lots of sites give information including a map of the fish distribution. These include wikipedia and http://www.whalesharkproject.org/v.asp?level2=6376&depth=2&level3=6376&level2id=6376&rootid=6371&nextlevel=6376

    Numbers are estimated by counting them at the Ningaloo reef where they migrate each year. http://www.abc.net.au/news/2007-12-26/whale-shark-numbers-increasing-study-finds/996638

    Yearly numbers of Whale Sharks in Ningaloo Marine Park is estimated to vary between 200 and 400 individuals although it's not known if this is the global population, which is unknown. http://www.environment.gov.au/cgi-bin/sprat/public/publicspecies.pl?taxon_id=66680

    The average size is 20.6 tons (18.7 tonnes) on http://animals.nationalgeographic.com/animals/fish/whale-shark/
    This differs considerably from Wikipedia which gives the average size of adult whale sharks as 9.7 metres (31.82 ft) and 9 tonnes (20,000 lb) while another site says that the average size is 25 feet (7.6 m) long http://www.enchantedlearning.com/subjects/sharks/species/Whaleshark.shtml
    The average girth was harder but seems to be about 4m (although the biggest specimen found was 7m.

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  4. I saw a whale shark while swimming in the Sea of Cortez (we took a rubber boat 100 yards away from shore). I was 14 at the time and jumped in the water and IMMEDIATELY jumped back in the boat (there is something unnerving about swimming with a GIANT fish that that has the word "shark" in it's name).

    This particular whale shark was probably 9-10 ft long. (not humongous, but the largest "fish" I've ever seen up close and in the wild). Anyhow, not that it helps to have one person say, "I've seen a whale shark!", but the maps coincide with where I saw this particular whale shark.

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