Showing posts with label fishing. Show all posts
Showing posts with label fishing. Show all posts
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linda
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Infographic by the Pew Environment Group on the fate of Atlantic bluefin tuna—why the decline and what's needed for the species to recover. Living proof that really good-looking informative graphics will spontaneously broadcast spawn. For a metric version, click here.
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Posted by
linda
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| Puffinus shearwater. Credit: Jofre Ferrer via Flickr. |
The Balearic shearwaters (Puffinus mauretanicus) who breed on the Spanish Balearic Islands don't go far when they migrate... out the Strait of Gibraltar then north to summering grounds off the Atlantic coasts of Portugal and France.
Yet, curiously, only the females go to France.
Perhaps because of these longer migrations, they also spend longer away from their breeding grounds than the males:
- Median duration of time away for females: 91 days
- Median duration of time away for males: 83 days
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| Credit: Tim Guilford et al. PLoS ONE. DOI:10.1371/journal.pone.0033753. |
You can see in the maps above the routes of the individual birds, each with its own color track:
- Inset map shows where all the birds occurred statistically half the time throughout the year.
- Larger maps shows where all the birds occurred statistically half the time on migration to and from their breeding islands.
- The colored circles mark where four birds made trips back into eh Atlantic after their migrations.
- The red symbol is the position of the breeding colony at Sa Cella cave on Mallorca.
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| Longline hooks. Credit: Isaac Wedin via Flickr. |
The gender-specific migrations are more than a curiosity. They're vitally important knowledge since Balearic shearwaters are Europe's only critically endangered seabird. From the IUCN Red List:
This species has a tiny breeding range and a small population [known breeding population: ~3,200 pairs] which is undergoing an extremely rapid population decline owing to a number of threats, in particular predation at breeding colonies by introduced mammals [cats, genets, rats, rabbits] and at-sea mortality as a result of interactions with commercial fisheries [hooked and drowned on longlines]. Population models predict an extremely rapid decline over three generations (54 years), qualifying the species as Critically Endangered.
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| Balearic shearwater. Credit: Roger Montserrat via Flickr. |
Obviously if you have a large proportion of the females flocking and feeding in one location then the entire species becomes susceptible to mass mortality fishing events like the one that killed ~50 birds off Spain in 1999-2000. As the authors note:
[F]or approximately ¼ of the year, a large percentage of the world's population of breeding birds will be vulnerable to [fisheries] by-catch in these two core areas within the territorial waters of Portugal and France.
The paper:
- Guilford T , Wynn R , McMinn M , Rodríguez A , Fayet A , et al. (2012) Geolocators Reveal Migration and Pre-Breeding Behaviour of the Critically Endangered Balearic Shearwater Puffinus mauretanicus. PLoS ONE 7(3): e33753. doi:10.1371/journal.pone.0033753
Posted by
linda
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| Beach at Tutuala, East Timor. Credit: doug.deep Doug Anderson via Flickr. |
A new paper in Science reports on 42,000-year-old fish bones found in Jerimalai cave on the island of East Timor, just north of Australia.
This is the oldest evidence yet of human fishing activity. Even more interesting, about half the 38,000 bones were of fast-swimming pelagic species—tuna and shark—implying the ancient fishers worked offshore from vessels.
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| Credit: Froschmann : かえるおとこ H Aoki via Flickr. |
We know that people were seafaring 50,000 years ago. And seafaring and fishing are inextricably linked. But until now hard evidence of pelagic fishing was lacking. From Science Now:
Although modern humans were exploiting near-shore resources, such as mussels and abalone, by 165,000 years ago, only a few controversial sites suggest that our early ancestors fished deep waters by 45,000 years ago. The earliest sure sites are only about 12,000 years old.
What's not known is exactly how these first fishers in East Timor caught open-water species. The researchers speculate they went to sea on boats or rafts equipped with nets or hooks-and-lines.
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| A broken shell fishhook found in East Timor. Scale is in millimeters. Credit: Sue O’Connor, et al. Science. DOI: 10.1126/science.1207703. |
At Jerimalai the archaeologists also found the earliest known fish hooks—including one from a mollusk shell dating to 23,000 years ago. These hooks were too small to catch the pelagic species, so were likely used inshore.
Prior to these findings, the oldest fish hooks dated to the beginning of agriculture, or about 5,500 years ago in Southeast Asia.
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| Fisher, East Timor. Credit: United Nations Photo via Flickr. |
The paper:
- Sue O’Connor, Rintaro Ono, Chris Clarkson. Pelagic Fishing at 42,000 Years Before the Present and the Maritime Skills of Modern Humans. Science. 2011. DOI: 10.1126/science.1207703
